HK1149836B - Video display device - Google Patents

Description

Video display device

Technical Field

The present invention relates to a video display device for expressing a desired display video.

Background

Conventionally, various video representations such as adjustment of gain of a video signal and improvement of contrast have been attempted (for example, patent document 1).

When a video having a strong visual effect is to be displayed, a sense of brightness of a screen is required, and therefore, processing for increasing the screen brightness is performed. In this regard, patent document 2 describes the following technique: that is, conventionally, in order to obtain a bright feeling of a display video, a video display is performed by increasing the pixel gain from the low region to the middle region of the γ correction characteristic and by decreasing the pixel gain in the high region in order to prevent saturation of a bright pixel.

However, such gain control has the following problems: that is, in the case of a completely bright video, since the gain of most pixels is reduced and the luminance is reduced, it is also tried to apply different control according to the characteristics of the video without uniformly applying the gain control to all the input videos. Patent document 3 is one of the techniques. In patent document 3, after detecting an amplitude peak of an RBG signal of an input video signal, a γ circuit performs the following processing on a video signal not including a high peak component: that is, a signal having brightness in a middle region or less is linearly amplified, a signal having brightness in a high region is less amplified (γ characteristic is shown in fig. 23 b), and with respect to a video signal including a high peak component, γ operation is canceled and the video signal is output as it is (γ characteristic is shown in fig. 23 a), thereby preventing white clipping at a time of a large amplitude.

Patent documents 4 and 5 describe the following techniques: that is, the Average luminance (hereinafter, referred to as "APL" (Average Picture Level) of the input video signal is detected, and the lower the detected APL is, the greater the degree of amplification of the signal having brightness in the middle region or less is (in fig. 24, the lower the APL is, gain control is performed in the order of (b) → (c) → (d)), and on the other hand, when the APL is higher than a fixed value, the video signal is output as it is without gain control (fig. 24(a)) to prevent saturation on the white side.

In the above patent documents 3 to 5, the following operations are performed: that is, when the video feature satisfies the predetermined condition, the input signal is always amplified, and when the video feature does not satisfy the predetermined condition, the input signal is not always amplified.

That is, in patent document 3, when a condition that the amplitude peak of the RGB signal as the video feature value does not include a high peak component is satisfied, the signal is always amplified, and when the condition that the amplitude peak does not include a high peak component (when a high peak component is included) is not satisfied, the video signal is not always amplified.

Similarly, in patent documents 4 and 5, when a condition that APL as a video feature amount is equal to or less than a fixed value is satisfied, the degree of amplification (constant amplification) of a signal having brightness equal to or less than a middle region (equal to or less than a fixed brightness value) is increased in proportion to the value of APL, and when the condition that APL is equal to or less than the fixed value is not satisfied (when the APL is equal to or more than the fixed value), gain control is not performed at all times and the video signal is not amplified.

As described above, although attempts have been made to prevent white clipping and improve contrast by detecting a video feature amount such as a peak value or APL of an input video signal and controlling a gain of the input video signal based on a result of the detection, whether or not to amplify the video signal is determined by using a specific condition that the video feature amount satisfies as a limit, even when a condition that the APL is not equal to or less than a fixed value is not satisfied, it is sometimes desirable to enhance the video signal at a certain luminance value or less in order to obtain a sense of brightness when the ratio included in a dark video signal is not small.

Even when the APL is very low, if priority is given to preventing the proportion of high-luminance pixels such as saturation on the white side from being included is not small, it may be preferable not to amplify the video signal in consideration of the luminance reduction in the high-luminance portion.

In addition, for a video with a small peak value or APL, since enhancement processing is performed on a video signal with brightness below the middle region, black depth is always sacrificed.

Here, in a video display device that displays a video by irradiating light from the back surface of a display screen, such as a liquid crystal display device, since video representation is performed by adjusting the light source brightness in addition to processing a video signal, more complicated video representation can be performed if these are reasonably combined.

Patent documents 6 to 9 disclose techniques of a liquid crystal display device which combine processing of a video signal and dimming of light source luminance to enhance video expression particularly on the black side.

These documents describe the following techniques: that is, in the case of a video input that is dark as a whole, a black depth that cannot be expressed only by a normal video display is obtained by reducing the light source luminance, and the luminance of the whole video is prevented from being reduced by amplifying the video signal.

Patent document 6 discloses the following technique, as will be described in detail: that is, a histogram of an input video signal is analyzed, and when the luminance of a light source is lowered after the light source luminance that can best represent the histogram is selected, the video signal is amplified to compensate for the lowered luminance. The magnification ratio can be calculated by the following formula: magnification ratio (brightness of light source at maximum light emission/brightness of light source after reduction)^1/γThereby amplifying the video signal when the brightness of the light source is reduced.

Therefore, in the techniques as in patent documents 6 to 9, the following processing is performed: that is, when the light source is caused to emit light at the maximum luminance, the video signal is not amplified, and when the luminance of the light source is reduced, the video signal is amplified. That is, the video signal may be amplified, or the video signal may not be amplified, and the condition of the video feature amount of the video signal may not be used.

Further, patent document 10 discloses the following technique: that is, the APL and the maximum value/minimum value of the input video signal are detected, the input video signal is amplified in a dynamic range, and the luminance at the time of video display, which deviates due to the amplification of the video signal, is compensated by adjusting the light emission luminance of the light source.

The technique of patent document 10 can realize the following: that is, when the conditions that the maximum luminance and the minimum luminance, which are video feature amounts of the input video signal, match the dynamic range are satisfied, the video signal is not always amplified, and when the conditions that the maximum luminance and the minimum luminance match the dynamic range are not satisfied (when the maximum luminance and the minimum luminance do not match the dynamic range), the video signal is always amplified.

The importance ratio of the black depth, the opposite importance ratio of the white color, the importance degree of the power consumption, and the like are not the same for all the videos, but are different depending on the characteristics of the videos. In this regard, for example, patent document 11 discloses the following technique: that is, the light source luminance control characteristic of the liquid crystal display device is changed according to the image quality modes such as the motion mode, the standard mode, the movie mode, and the game mode, thereby achieving the purpose of obtaining desired display luminance and reducing power consumption.

In patent document 12, a mode is provided in which priority is given to either image quality or power saving, and the power saving rate of the backlight is changed according to the mode.

Patent document 1: japanese patent laid-open No. 6-62277

Patent document 2: japanese patent laid-open No. 2006-101363

Patent document 3: japanese patent laid-open No. 6-350874

Patent document 4: japanese patent laid-open No. 2003-167544

Patent document 5: japanese patent laid-open No. 2003-309741

Patent document 6: U.S. patent application publication No. 2006/0274026 specification

Patent document 7: japanese patent laid-open No. 2006-276677

Patent document 8: japanese patent laid-open No. 2006-267995

Patent document 9: japanese patent laid-open No. 2007-36728

Patent document 10: japanese patent laid-open No. 2001-27890

Patent document 11: japanese patent laid-open No. 2007-140436

Patent document 12: japanese patent laid-open No. 2007-219477

Disclosure of Invention

As described above, there is a demand for video representation with strong visual expression that exhibits a sense of brightness, while there is a contradictory demand for video representation with black depth when displaying a dark video as a whole, such as a movie, from a display video.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a video display device capable of expressing a bright feeling in which white clipping is avoided or suppressed to an insignificant degree, and performing video expression with improved black depth.

In order to solve the above problems, a first technical means of the present invention is a video display device for adjusting the degree of amplification of an input video signal in accordance with a video feature amount of the input video signal, wherein the input video signal is always amplified when the video feature amount satisfies a predetermined condition, and the input video signal is amplified or not amplified when the video feature amount does not satisfy the predetermined condition.

A second technical means is the video display device of the first technical means, wherein the video feature amount is an average luminance of the input video signal, and the predetermined condition is that the average luminance of the input video is equal to or less than a predetermined value.

A third technical means is the video display device of the first technical means, wherein the video feature amount is an average luminance of the input video signal, and the predetermined condition is that the average luminance of the input video signal is equal to or higher than a first value and equal to or lower than a second value.

A fourth technical means is the video display device as defined in the first technical means, wherein the video feature value is a frequency that cannot be expressed when the input video signal is stretched, and the predetermined condition is that the frequency is equal to or less than a predetermined ratio.

A fifth technical means is the video display device as defined in the first technical means, wherein the video feature value is an average luminance of the input video signal and a frequency that cannot be expressed when the input video signal is stretched, and the predetermined condition is that the average luminance is equal to or less than a predetermined value and the frequency is equal to or less than a predetermined ratio.

A sixth technical means is the video display device of the first technical means, wherein the video feature value is an average luminance of the input video signal and a frequency that cannot be expressed in the input video signal when the input video signal is stretched, and the predetermined condition is that the average luminance of the input video signal is equal to or higher than a first value and equal to or lower than a second value, and the average luminance is equal to or lower than a predetermined value and equal to or lower than a predetermined ratio.

A seventh technical means is the video display device of the first technical means, wherein the video feature amount is a maximum luminance and a minimum luminance of the input video signal, and the predetermined condition is that the minimum value of the input video signal is a first value or more and the maximum luminance of the input video signal is a second value or less.

An eighth technical means is the video display device of any one of the first to seventh technical means, wherein the display device includes a display unit and a light source, and the display unit is configured to display a video by inputting a video signal to the display unit and irradiating the display unit with light from the light source.

A ninth technical means is the video display device of the eighth technical means, wherein when the video feature amount does not satisfy the predetermined condition, the input video signal is not amplified when the light source luminance is maximum luminance, and the input video signal is amplified when the light source luminance is decreased from the maximum luminance.

A tenth technical means is the video display device of the eighth technical means, wherein the degree of amplification of the video signal depends on a light emission luminance of the light source.

An eleventh technical means is the video display device of the tenth technical means, wherein the amplification degree of the video signal is set so that when the emission luminance of the light source is maximized, the amplification degree is larger than a value of an input video signal that can appropriately display the maximum luminance.

A twelfth technical means is the video display device of the tenth technical means, wherein the degree of amplification of the video signal is determined in consideration of a target light emission luminance value of the light source.

A thirteenth technical means is the liquid crystal display device of the twelfth technical means, wherein the target light emission luminance value of the light source is set to a value greater than 100%.

A fourteenth technical means of the present invention is the image display device of the first technical means, wherein the predetermined condition is changed according to an image quality mode.

A fifteenth technical means is the video display device of the second or fifth technical means, wherein the predetermined value is changed according to the image quality mode.

A sixteenth technical means is the video display device of any one of the third, sixth and seventh technical means, wherein the first value and/or the second value is changed in accordance with an image quality mode.

A seventeenth technical means is the video display device of any one of the fourth to sixth technical means, wherein the predetermined ratio is changed according to an image quality mode.

According to the present invention, when the feature amount of the video signal satisfies the predetermined condition, the enhancement processing is always performed on the signal having a constant luminance value or less, thereby further expressing the brightness, and when the predetermined condition is not satisfied, the black depth can be expressed while considering the white slice.

Drawings

Fig. 1 is a diagram for explaining a relationship between an input video signal and a luminance value on a liquid crystal panel.

Fig. 2 is a block diagram showing an example of a system configuration according to an embodiment of the video display device according to the present invention.

Fig. 3 is a diagram for explaining a histogram of a video signal and its transition.

Fig. 4 is a block diagram showing an example of the configuration of the scene change detection unit in the video display device of fig. 2.

Fig. 5 is a diagram showing an example of the configuration of the first temporary filter in the video display apparatus of fig. 2.

Fig. 6 is a diagram for explaining an example of the light emission luminance level selection processing performed by the distortion module in the video display apparatus of fig. 2.

Fig. 7 is a diagram for explaining a specific example of the luminance modulation process in the video display device according to the present invention.

Fig. 8 is a diagram showing a video luminance range when the light emission luminance level, which is one of selection targets, is 100% in the video display device.

Fig. 9 is a diagram showing a video luminance range when the emission luminance level, which is one of selection targets, is 70% in the video display device.

Fig. 10 is a diagram showing a video luminance range when the emission luminance level, which is one of selection targets, is 50% in the video display device.

Fig. 11 is a diagram showing an example of the gain set by the RGB γ/WB adjusting unit in the video display device of fig. 2.

Fig. 12 is a diagram for explaining the adjustment processing in the RGB γ/WB adjustment unit.

Fig. 13 is a diagram for explaining an example of the operation of the normal pre-luminance modulation in which the emission luminance level for reference is set in the range of 100% or less.

Fig. 14 is a diagram for explaining an embodiment of a front luminance modulation process applicable to the video display device of the present invention.

Fig. 15 is a diagram showing an example of a histogram of a video signal.

Fig. 16 is a diagram showing another example of the histogram of the video signal.

Fig. 17 is a diagram showing an example of luminance conversion characteristics used for the pre-luminance modulation process.

Fig. 18 is a diagram showing a relationship between white clipping used in the pre-luminance modulation process and the light emission luminance level for reference.

Fig. 19 is a diagram showing a relationship between a luminance value and a frequency used in the pre-luminance modulation processing.

Fig. 20 is a diagram showing a relationship between an APL used in the pre-luminance modulation processing and a light emission luminance level for reference.

Fig. 21 is a diagram showing another example of the relationship between the APL used in the pre-luminance modulation processing and the light emission luminance level for reference.

Fig. 22 is a diagram showing another example of the relationship between the APL used in the pre-luminance modulation process and the light emission luminance level for reference.

Fig. 23 is a diagram showing a relationship between input and output of a video signal described in patent document 3.

Fig. 24 is a diagram showing a relationship between input and output of a video signal described in patent document 4.

Description of the reference symbols

1 scaling part

2Y histogram detection unit

3 APL detection part

4 histogram stretching part

5 distortion module

6 scene change detection unit

7 temporary filter

8 BL luminance level setting unit

9 temporary filter

10 variable delay

11 CPLD

12 BL adjusting part

13 arrangement design part

14 image quality correction unit

15 WB adjusting part

16 FRC part

17 video output unit

20 front brightness modulation part

61 histogram buffer

62 histogram change detection unit

Detailed Description

In the present invention, the degree of amplification of an input video signal is adjusted in accordance with the video feature quantity of the input video signal. In the embodiment of the present invention described below, in a video display device including a backlight as a light source, the degree of amplification (gain) of an input video signal is adjusted in accordance with the video feature amount of the input video signal, and at this time, a contrast (target CR) to be a target is set, and video expression is performed by controlling the emission luminance of the backlight and controlling the gain so as to approach the target CR. In this specification, the video signal and the luminance modulation process of the backlight are referred to as a front luminance modulation process.

(outline of Pre-brightness modulation processing)

It is desirable that the display luminance when displaying a video faithfully reproduces the gradation of a video signal to be displayed. That is, in the case of displaying a black screen, the display luminance ideally needs to be 0. For a video display device using a liquid crystal panel and a backlight light source, there is actually some light leakage in the liquid crystal panel, and thus not black display but gray display even when a black picture is displayed.

The contrast ratio (hereinafter referred to as CR) is one of the important performances of the video display apparatus. In the video display apparatus, CR is a ratio of maximum luminance and minimum luminance on the liquid crystal panel. For a video display device using a liquid crystal panel and a backlight, the maximum luminance depends on the maximum light emission luminance of the backlight light source, and the minimum luminance depends on the amount of light leakage at the time of black display. Thus, when the emission luminance of the backlight light source is fixed, the contrast ratio of the same liquid crystal panel is fixed.

Fig. 1 is a graph showing a relationship between a pixel value of an input video signal (a luminance value of a video signal) and a luminance value on a liquid crystal panel of each of liquid crystal panels having CR of 3000 and 6000. Although the maximum luminance is all 450cd which is the same, the display luminance (minimum luminance) on the liquid crystal panel with a pixel value of 0 is 0.15cd in the case of CR3000 and 0.075cd in the case of CR6000 by a factor of two.

For example, in the case where the emission luminance of the light source is reduced to 50% when the liquid crystal panel of CR3000 is used, the relationship between the pixel value of the input video signal and the luminance value of the liquid crystal panel is shown by the broken line in fig. 1. Since the light emission luminance of the light source is 50%, a video having a pixel value larger than 128 cannot be displayed. However, the pixel values 0 to 128 can be expressed by the brightness of the liquid crystal panel close to CR 6000.

Therefore, when the maximum value of the pixel values included in the video is 128 or less, the same contrast feeling as that of the CR6000 liquid crystal panel can be obtained by setting the emission luminance of the light source to 50%, and the same luminance expression performance as that of the CR6000 liquid crystal panel can be obtained by doubling the pixel value of the video signal. This extension can be achieved by setting a gain by which the pixel value of the video signal becomes twice. In addition, since not only CR is increased but also the emission luminance of the backlight light source is reduced to 50%, power saving can be achieved. In the above example, since the maximum value of the pixel value is 128 or less, simply doubling the pixel value does not cause white clipping.

In the pre-luminance modulation process, as in this example, in order to achieve power saving and approach the target CR (target CR), the luminance of the backlight light source is suppressed, the gain of the video signal is set in conjunction with the suppression of the luminance, and the video signal is stretched by using the gain setting, so that the decrease in the luminance of the backlight light source is compensated for by the output value of the video signal to the liquid crystal panel. In addition to the above example, for example, even when white portions are extremely small in a video, the black appearance can be improved by reducing the degree of emphasis of the white portions. In this case, the white clip of the inconspicuous part may be disregarded, and even if a gain that can achieve the target CR is set, the gain of the white side region may be determined to relax the white clip.

In the front-end luminance modulation processing, in order to achieve power saving, processing for dynamically suppressing the emission luminance level of the backlight light source based on the video feature value such as APL of the video obtained from the video signal is also performed as described below.

That is, first, power saving is achieved by setting an emission luminance level, which is used as a reference for gain setting and emission luminance level setting of the backlight light source, based on histogram information such as an APL and a peak value (maximum luminance value), and a process for obtaining a contrast feeling as described above is further performed on the emission luminance level for reference (that is, the emission luminance level is set to an appropriate value equal to or lower than the emission luminance level for reference), and a gain of the video signal is set in conjunction with the process to secure visual luminance in order to improve CR and save more power.

(example of System configuration of video display apparatus for performing Pre-luminance modulation processing)

Fig. 2 is a block diagram showing an example of a system configuration of an embodiment of the video display device according to the present invention. The video display apparatus illustrated in fig. 2 includes: a scaling section 1, a Y histogram detection section 2, an APL detection section 3, a BL (backlight) luminance level setting section 8, a CPU (Central processing unit)/CPLD (Complex Programmable Logic Device) 11, a BL dimming section 12, an image quality correction section 14, an RGB γ/WB (White Balance) adjustment section 15, an FRC (Frame Rate Control) section 16, and a video output section 17.

The video display apparatus illustrated in fig. 2 includes a front luminance modulation section 20 that performs a main part of the front luminance modulation process. The front luminance modulating section 20 includes: a histogram extension unit 4, a distortion block 5, a scene change detection unit 6, a first temporary filter 7, a second temporary filter 9, a variable delay unit 10, and an arrangement design unit 13. As described above, the pre-luminance modulation process not only performs dynamic light source emission luminance control corresponding to a video feature quantity such as APL, but also performs reference emission luminance gradation BL for a light source determined by a predetermined condition of the video feature quantity_refSelecting a light-emitting luminance level BL_reducedTo further obtain a sense of contrast and also to set the gain of the video signal, is an improved brightness modulation process.

First, an outline of each block in the video display device of fig. 2 will be described.

The video output section 17 outputs and displays a video signal to be displayed. In this example, a liquid crystal panel is used as a display panel for performing video display. Thus, the video output section 17 includes: a liquid crystal panel that displays a video according to a video signal; and a liquid crystal control circuit that converts the video signal into a signal for driving the liquid crystal panel and outputs the signal to the liquid crystal panel. As will be described in detail later, the video signal is converted by the gain set by the pre-luminance modulating section 20 and then input to the video output section 17. That is, in the pre-luminance modulation process, a video signal indicating a video to be displayed on the video output unit 17 is a processing target. The gain and its setting will be explained later.

The BL adjusting section 12 includes a lamp composed of a fluorescent tube and a lamp driving circuit for driving the lamp, and constitutes a light source (backlight source, or simply referred to as a backlight) for illuminating the liquid crystal panel of the video output section 17 from the back or side. In the front-end luminance modulation processing of this example, the backlight light source is the subject of emission luminance control.

The BL adjusting section 12 is controlled by the CPU/CPLD 11. CPU/CPLD11 represents the light emission luminance level BL based on the output from the front luminance modulation unit 20_reducedIs converted into a signal for actual dimming (for example, a signal applied to driving such as pulse width modulation) in a lamp driving circuit (for example, an inverter circuit) of the BL adjusting section 12, and is output to the BL adjusting section 12. For converting the backlight dimming value into a signal for actual backlight dimming. Further, as the lamp, for example, a lamp composed of an LED (Light Emitting Diode) or a lamp composed of a combination of an LED and a fluorescent tube may be used, and a lamp driving circuit corresponding to the LED may be provided at the same time.

The parts for processing the video signal output to the video output unit 17 and controlling the BL adjusting unit 12 by the CPU/CPLD11 are the scaling unit 1, the Y histogram detecting unit 2, the APL detecting unit 3, the BL luminance level setting unit 8, the image quality correcting unit 14, the RGB γ/WB adjusting unit 15, the FRC unit 16, and the pre-luminance modulating unit 20.

First, the scaling section 1 changes the number of pixels of a video frame indicated by an input video signal (input video signal) or the aspect ratio of the video frame by calculation according to the resolution of the liquid crystal panel or the like.

Here, as the input video signal, for example, a signal obtained by demodulating a video signal received as a broadcast wave, a video signal received via a communication network, a signal read out from a video signal stored in an internal storage device, a video signal received from an external device such as various recorders, various players, or a tuner device, or the like, or a video signal obtained by subjecting these video signals to various video processing is used. Although not shown, the video display device in fig. 2 may be configured to acquire any of these video signals.

The image quality correction unit 14 changes the contrast, color tone, and the like of the video from the video signal output from the scaling unit 1 in accordance with user settings and the like.

The RGB γ/WB adjustment unit 15 adjusts γ, WB, and the like of the video image with respect to the video signal output from the image quality correction unit 14. The RGB γ/WB adjusting unit 15 changes the gain of the signal in accordance with a gain setting signal from the front-end luminance modulating unit 20 (actually, the arrangement designing unit 13). Here, the gain of the video signal output from the image quality correction unit 14 may be changed, or the gain of the video signal subjected to γ adjustment in the RGB γ/WB adjustment unit 15 may be changed. Then, the RGB γ/WB adjusting unit 15 performs conversion of the video signal based on the gain, and compensates the luminance reduction amount by the gain for control for reducing the emission luminance level in the front luminance modulating unit 20 as described below. Here, in order to suppress noise in a low gradation portion, it is preferable to perform the conversion after the γ adjustment and before the WB adjustment.

The gain setting signal from the front-end luminance modulating section 20 is a signal indicating a conversion coefficient for converting the pixel value (video signal level) of the video signal to be output to the liquid crystal panel.

As will be described later, the gain setting signal is set to one common conversion coefficient for multiplying the video signal (in this example, a video signal having a pixel value of 0 to 255), and the gain may be corrected by the RGB γ/WB adjusting unit 15 for a range based on a certain video signal level obtained by performing a range of a video signal level in which the gain reaches the maximum value, or the like, as will be described later.

The FRC unit 16 is a frame rate converter, and detects a motion vector of a video from the adjusted video signal output from the RGB γ/WB adjusting unit 15 to generate an interpolated video, thereby converting the interpolated video from a normal display frequency of 60Hz to a display frequency of 120 Hz. Needless to say, the display frequency of the processing target or the display frequency after the processing in the FRC unit 16 is not limited to this. In the example of fig. 2, the liquid crystal driving circuit of the video output section 17 converts the video signal output from the FRC section 16 into a signal for driving the liquid crystal panel, and outputs the signal to the liquid crystal panel.

The Y histogram detection unit 2 divides a video frame into pixel units, etc., and generates a histogram indicating the frequency of occurrence of luminance values of each pixel. The histogram generated by the Y histogram detection unit 2 has a frequency value for each of pixel values (Y)0 to 255, for example. The APL detecting unit 3 calculates an average luminance level of a video signal for each video frame. The value calculated by the APL detection unit 3 is a value indicating 0% when the entire screen is black, and a value indicating 100% when the entire screen is white.

The histogram extension unit 4 sets a range to be used in the front-end luminance modulation unit 20, based on the histogram generated by the Y histogram detection unit 2. For example, assume a case where the distortion module 5 is a module that performs operations from the minimum value 0 to the maximum value 255, and the input video signal is a signal (for example, a broadcast signal) whose value is initially from the minimum value 10 to the maximum value 235. In this case, the histogram extension unit 4 extends the frequency values corresponding to the minimum value 10 to the maximum value 235 to serve as the frequency values corresponding to the minimum value 0 to the maximum value 255 in accordance with the calculation of the distortion block 5.

The distortion module 5 is configured to generate a reference emission luminance level (also referred to as a backlight target value) BL based on the histogram input by the histogram extension unit 4 and the emission luminance level for reference set by a BL luminance level setting unit 8 (described later)_refThe actually set light emission luminance level (also referred to as backlight source value) BL is selected (determined)_reducedI.e. for controlling the light emission brightness level of the backlight light source. The selection is made from a plurality of preset light emission brightness levels, so that the light emission brightness level BL for reference set by the BL brightness level setting unit 8 is not exceeded_refIs carried out within the range of (1). Here, the emission luminance level BL that can realize a display video closer to the liquid crystal panel having the target CR is selected_reduced. The distortion parameter of the target CR or the like can be set by a main CPU not shown. In addition, the light emission luminance level BL is determined based on APL_reducedIn the case (embodiment 6 described later), the APL detected by the APL detecting unit 3 is input to the distortion block 5.

The scene change detection unit 6 detects whether or not there is a scene change based on the histogram of the previous frame and the degree of change in the current histogram. For example, an integrated value of frequency changes of the luminance values is calculated, and when the integrated value is larger than a specific value, it is determined that the scene has changed.

The first temporary filter 7 is arranged to prevent the above-mentioned actually set light-emission luminance level BL selected at the distortion module 5_reducedThe brightness level BL is adjusted to have a visual sense of incongruity generated when a sudden change occurs_reducedAfter the variation amount of (b) is changed slowly with time, it is taken as the actually set light emission luminance level BL_reducedAnd outputting to a later stage. In addition, when the scene is changed, a slow light-emitting brightness level BL is implemented_reducedSince the change of (2) causes a stronger sense of incongruity, the value of the first temporary filter 7 is changed by the scene change detection signal of the scene change detection unit 6, so that a relatively fast change can be made.

The BL luminance level setting unit 8 determines the maximum value of the luminance level of the backlight by referring to the APL value output from the APL detecting unit 3, the video feature amount such as the histogram information output from the Y histogram detecting unit 2, the value of OPC (Optical Picture Control, also called a brightness sensor) output from a main CPU, not shown, or a user setting value. For example, when the APL is high, the maximum value of the emission luminance level of the backlight is setThe value is set to a low value, so that a video without feeling dazzling can be obtained. The maximum value of the emission luminance levels of the backlight is the emission luminance level (backlight target value) BL for reference of the front luminance modulation performed by the front luminance modulation section 20_ref. As light-emission luminance levels BL for determining reference_refAs described above, the video feature amount of (2) can be selected according to the embodiment using the APL or the histogram information. The histogram information includes a peak value (maximum luminance value) or minimum luminance of a video, a frequency of a video that cannot be expressed when a video signal is stretched, and the like.

In addition, the distortion module 5 is selected so as not to exceed the reference light emission luminance level BL set by the BL luminance level setting unit 8_refIn the BL luminance level setting section 8, the maximum value of the emission luminance levels of the backlight is set to the emission luminance level BL for reference_ref。

In the example of fig. 2, the light emission luminance level for reference through the second temporary filter 9 is set as BL_ref。

The second temporary filter 9 is a filter having the same function as the first temporary filter 7. To briefly describe, when the APL changes abruptly and the change does not affect the selection of the distortion block 5, the light emission luminance level BL output from the first temporary filter 7_reducedThe change over time is moderated. However, the gain setting is a reference light emission luminance level BL outputted from the BL luminance level setting unit 8_refSince the calculation is performed on the basis, the display luminance on the liquid crystal panel changes rapidly when the gain changes. In order to eliminate or mitigate such a sharp change in display luminance, a second temporary filter 9 is provided.

The variable delayer 10 is a delay section for synchronizing the video output of the video output section 17 and the backlight dimming of the BL adjustment section 12. When the dimming value is determined for the backlight dimming, the backlight luminance control is performed after a small amount of processing is performed. On the other hand, the video signal is delayed in time because the gain of the video is determined by the pre-luminance modulation, and after the luminance level of the video signal is changed, many processes such as the frame rate control of the FRC unit 16 and the conversion of the liquid crystal control circuit into the panel control signal are performed. This causes a deviation in timing of backlight dimming control and video gain control that should be performed at the same time, which results in a disruption in the balance between the backlight and the video. Therefore, the variable retarder 10 delays the backlight dimming, and the timing of the backlight dimming control and the timing of the gain control of the video are made to coincide with each other.

The arrangement design unit 13 sets the reference emission luminance level BL determined by the BL luminance level setting unit 8 according to the reference emission luminance level BL_refAnd the selected light-emitting brightness level BL of the distortion module 5_reducedAnd determining the gain of the video signal. In the example of fig. 2, each level BL_reduced、BL_refThe levels after passing through the filters 7 and 9 are used, respectively. If the reference emission luminance level (backlight target value) BL_refAnd the selected light emission luminance level (backlight value) BL_reducedSimilarly, the gain is 1 without changing the brightness level of the video signal. In addition, at the selected light-emission luminance level BL_reducedLuminance level BL lower than that for reference_refIn the case of (3), a gain is set in a direction of raising the luminance level of the video signal according to the value of (3).

(detailed description of the Main Unit for performing the Pre-luminance modulation processing)

The main units of the video display apparatus of fig. 2 will be described in the order of the BL luminance level setting unit 8, the scene change detection unit 6, the first temporary filter 7, the distortion block 5, the arrangement design unit 13, and the RGB γ/WB adjusting unit 15.

(BL luminance level setting unit 8)

The BL luminance level setting unit 8 receives the APL of the video signal detected by the APL detecting unit 3, and also receives a control signal based on detection information of a sensor (not shown) that measures the ambient brightness (ambient illuminance), and a control signal based on user setting for setting the brightness of the liquid crystal panel.

When information such as the frequency that cannot be expressed when the video signal is stretched or the minimum luminance and the maximum luminance of the video signal is used as the video feature amount, the information (as histogram information) required for the video signal on a screen-by-screen basis (on a frame-by-frame basis) is input from the histogram detection unit 2. When both APL and histogram information are used, the respective information is input to the BL luminance level setting unit 8.

Then, the BL luminance level setting section 8 outputs the reference light emission luminance level BL based on the control signal and the video feature amount_ref. Specifically, a method of dynamically adjusting the light emission luminance of the backlight light source in accordance with the input video signal that changes on a screen-by-screen basis (on a frame-by-frame basis) is applied, and the light emission luminance level obtained thereby is used as the light emission luminance level for reference (backlight target value) BL_refAnd outputting the data.

For generating reference light emission luminance levels BL_refThe luminance control table (lookup table) stored in the BL luminance level setting unit 8 is used. The luminance control table defines a relationship of luminance levels of the backlight corresponding to video feature quantities (APL, histogram information, and the like) of the input video signal, that is, a luminance control characteristic. A plurality of selectable luminance control tables are prepared in advance and stored in a table storage Memory such as a ROM (Read Only Memory) provided in the BL luminance level setting unit 8.

For example, a photodiode can be used as a brightness sensor for measuring brightness around a video display device. The brightness sensor generates a dc voltage signal corresponding to the detected ambient light and outputs the dc voltage signal to a main CPU, not shown. The main CPU outputs a control signal for selecting a luminance control table to the BL luminance level setting section 8 based on a dc voltage signal corresponding to the ambient light.

The main CPU outputs a luminance adjustment coefficient for adjusting a luminance control value of the luminance control table as a control signal based on user setting for setting the brightness of the liquid crystal panel. The brightness adjustment coefficient is used for setting the brightness of the whole screen according to the user operation. For example, a menu screen stored in the video display device is provided with an item for adjusting the screen brightness. The user can set arbitrary screen brightness by operating the setting item. The main CPU recognizes the brightness setting, and outputs the brightness adjustment coefficient to the BL brightness level setting section 8 based on the set brightness.

The BL luminance level setting section 8 specifies a table number and selects a luminance control table by using a control signal output from the main CPU based on the detection information of the luminance sensor. Or the brightness control table to be selected may be generated by an operation. Then, the luminance conversion value of the selected luminance control table is multiplied by a luminance adjustment coefficient obtained based on a control signal set by the user to change the slope of the luminance control characteristic of the luminance control table, and finally, the luminance gradation BL for generating the reference luminance is determined_refThe brightness control table of (1). Then, the BL luminance level setting unit 8 generates the reference emission luminance level BL based on the APL output from the APL detecting unit 3 or the histogram information output from the histogram detecting unit 2 by using the luminance control characteristics of the determined luminance control table_refAnd output is performed.

Thus, the reference emission luminance level BL output from the BL luminance level setting section 8_refDelayed by the action of the first temporary filter 7, is input to the arrangement design section 13 for the calculation of the video gain, and is input to the distortion block 5 for determining the emission luminance level BL corresponding to the histogram_reduced。

(scene change detector 6)

Fig. 3 is a diagram for explaining a Y histogram of a video signal and its transition, fig. 3(a) is a diagram showing an example of a Y histogram of a previous frame, fig. 3(B) is a diagram showing an example of a Y histogram of a current frame following fig. 3(a), and fig. 3(C) is a diagram showing a portion where histograms of respective frames shown in fig. 3(a) and 3(B) are merged and a frequency change portion is shown. Fig. 4 is a block diagram showing an example of the configuration of the scene change detection unit in the video display device of fig. 2.

When a scene of a video changes, the content of the video changes greatly, and thus it is considered that the luminance distribution of the video signal also changes greatly. The scene change detection unit 6 detects a scene change by using this, and specifically detects whether or not a scene change has occurred from the histogram of the previous frame of the video signal and the degree of change in the current histogram.

The scene change detection unit 6 includes a histogram buffer 61 and a histogram change detection unit 62. The histogram buffer 61 stores histogram data of the previous frame. The histogram change detection unit 62 compares the histogram data of the current frame and the histogram data of the previous frame, calculates an integrated value of the frequency changes, and determines that a scene change has occurred when the integrated value is greater than a specific value. When determining that a scene change has occurred, the histogram change detection unit 62 outputs a detection signal indicating that a scene change has occurred between the frames to the first temporary filter 7.

As a specific example, a case is considered where the video of the previous frame is a histogram as shown in fig. 3(a) and the video of the current frame is a histogram as shown in fig. 3 (B). In this case, the histogram buffer 61 stores therein the histogram data of fig. 3 (a). The histogram change detection unit 62 compares the data of the histogram buffer 61 with the histogram data of the current frame, and detects a change in frequency thereof. The hatched portion in fig. 3(C) is a frequency change portion. The histogram change detection unit 62 calculates an accumulated value, that is, an area of the frequency change portion, and determines that the scene has changed when the calculated area is larger than a predetermined value. Then, the histogram change detection unit 62 outputs a scene change detection signal only for the frame determined to have a scene change.

(first temporary Filter 7)

Fig. 5 is a diagram showing an example of the configuration of the first temporary filter in the video display apparatus of fig. 2. The first temporary filter 7 is a loop type low-pass filter, and as shown in fig. 5, includes: a multiplier for multiplying the weighting coefficient 1-a by the input value Xn of the current frame n; a multiplier for multiplying the weighting coefficient a by the output value Yn-1 of the previous frame n-1; and an adder that adds outputs of the multipliers. Here, let n be a natural number and a be a coefficient smaller than 1. The above structure of the first temporary filter 7 is expressed by the following equation (1).

Yn＝aYn-1+(1-a)Xn (1)

In the front-end luminance modulation process executed by the front-end luminance modulation section 20, although the emission luminance level of the backlight light source is dynamically changed, if the emission luminance level of the backlight is largely changed on a frame-by-frame basis, a sense of incongruity may be felt. Therefore, as the first temporary filter 7, a low-pass filter having a time constant of about one second is used, and here, the light emission luminance level BL determined by the distortion block 5 is made to be equal to or lower than the predetermined value_reducedThis eliminates the sense of incongruity of luminance variation of the backlight light source.

Further, since the video itself is largely changed at the time of scene change, no sense of incongruity is generated even if the light emission luminance level of the backlight is abruptly changed. Accordingly, the coefficient a of the first temporary filter 7 is reduced at the scene change time, so that the luminance variation of the backlight light source can be accelerated. Specifically, the coefficient a of expression (1) is sufficiently reduced only for the frame in which the scene change is detected, and the original value of the coefficient a is restored from the next frame. Thereby, the value close to the input becomes the output of the first temporary filter 7, and the emission luminance level BL of the backlight light source is accelerated_reducedA change in (c).

(distortion module 5)

The basic idea of the front luminance modulation process performed by the front luminance modulation section 20 is: the range of video luminance that can be displayed when the emission luminance level of the backlight light source is 100% is set in the liquid crystal panel used, the range of video luminance that can be displayed is set in the liquid crystal panel having a target (also referred to as ideal) CR (target CR), and the range of video luminance that can be displayed on the liquid crystal panel having the target CR as a property is brought close to by controlling the emission luminance level of the backlight light source in the liquid crystal panel used.

Here, since the emission luminance level of the backlight light source is lowered, when the video signal includes a high luminance portion, a white clip is generated in the high luminance portion in which the lowered emission luminance of the backlight cannot be fully expressed. In addition, when the low luminance is not included in the video signal, it is not necessary to decrease the light emission luminance level of the backlight.

Therefore, the distortion module 5 is configured to digitize, as a criterion for determining luminance control of the backlight light source, a degree of low luminance portions and a degree of high luminance portions, which cannot be expressed in a certain luminance level, as an evaluation value (distortion). Here, the distortion module 5 performs this digitization within a predetermined luminance control range of the backlight light source, and selects the light emission luminance level with the smallest evaluation value as the light emission luminance level BL_reduced. The luminance control range of the backlight light source is one of distortion parameters, and indicates a range allowed as the light emission luminance level of the backlight light source. For example, 10% to 100%, 20% to 100%, etc., may be determined in advance by default settings, user settings, etc.

When there are a plurality of light emission luminance levels having the smallest evaluation value, the lowest light emission luminance level is selected as the light emission luminance level BL_reduced. The reason for this is that: if the video display quality on the liquid crystal panel is the same, the power can be saved by reducing the brightness level of the backlight light source.

Fig. 6 is a diagram for explaining an example of the light emission luminance level selection processing performed by the distortion module in the video display apparatus of fig. 2. h1 represents a Y histogram of the video signal. Here, the horizontal axis represents the pixel value (video signal level) of the video signal, and the vertical axis represents the frequency of each pixel value.

In the histogram h1 of such a video, a video luminance range that can be displayed when the emission luminance level of the backlight light source on the liquid crystal panel used is 100% is defined as a. The range of video luminance that can be displayed on the liquid crystal panel of the target CR is B. Further, C is set as a video luminance range that can be displayed by a specific one of the light emission luminance levels selectable by the distortion module 5. In the histogram h1, the portions where both sides of the video luminance range C overlap with the video luminance range B are the portions to be digitalized, and the evaluation values are calculated. Among the evaluation value-calculated portions, the low-luminance portion is D1, and the high-luminance portion is D2.

The evaluation value (Distortion) is calculated by using the frequency and the weight of the selectable light emission luminance levels according to the following expression (2).

Distortion ∑ (frequency of video luminance range D1+ D2) × (distance weight) } (2)

As the weight, a distance weight that becomes larger as being distant from the video luminance range C that can be displayed by the light emission luminance level that becomes the evaluation value calculation target is used. Here, the distance weight of the low luminance portion D1 is set to E1, and the distance weight of the high luminance portion D2 is set to E2. Therefore, even with the same frequency value, the evaluation value increases as the frequency value is farther from the range where the expression can be performed. This is because the farther from the range where the video can be represented, the greater the influence on the video that cannot be represented. The values calculated by the frequency and weight are F1 (low luminance portion) and F2 (high luminance portion). The evaluation value is a total value of the areas (accumulations) of F1 and F2.

In the distortion module 5, the light emission luminance level corresponding to the video luminance range C having the lowest evaluation value among the evaluation values calculated for the respective light emission luminance levels is selected as the light emission luminance level BL to be outputted_reduced。

At this time, in the distortion block 5, the reference emission luminance level BL set by the BL luminance level setting section 8 and relaxed by the second temporary filter 9 is not exceeded_refWithin the range of (1), the selection and evaluation values are the lowestThe video luminance range C of_reduced。

For the calculation of such evaluation values, it is desirable that all selectable light emission luminance levels are calculated in the distortion module 5. However, due to restrictions on processing time and the like, the light emission luminance levels may be calculated, for example, every 10% or so, by equally dividing the luminance control range of the selectable light emission luminance levels.

That is, the evaluation value is calculated for each emission luminance gradation by sequentially using the selectable emission luminance gradations with C being the video luminance range which can be displayed by the specific emission luminance gradation of the above expression (2). Then, the light emission luminance gradation having the smallest evaluation value among the calculated evaluation values is set as the selected light emission luminance gradation BL_reducedThis value is output to the first temporary filter 7 for use in dimming control of the backlight, and is output to the arrangement designing section 13 for use in setting (calculating) the video gain. At this time, when there are a plurality of light emission luminance levels having the smallest evaluation value, the lowest light emission luminance level is selected.

Referring to fig. 7 to 10, the selection process in the distortion module 5 will be described with specific numerical values. Fig. 7 is a diagram illustrating an example of the relationship between the panel CR and the target CR in the video histogram, for explaining a specific example of the luminance modulation process in the video display device according to the present invention. Here, let CR (panel CR) of the liquid crystal panel used be 2000, target CR be 3500, luminance control range of the backlight be 20% to 100%, and maximum luminance of the liquid crystal panel at a backlight luminance of 100% be 450 cd. In fig. 7, reference numerals of the respective letters refer to fig. 6.

In this example, the luminance range a of the video image that can be displayed on the liquid crystal panel used is 450cd to 0.225 cd. The target liquid crystal panel can display a video luminance range B of 450cd to 0.128 cd. Then, frequencies corresponding to the respective video signal levels 0 to 255 are assigned so as to match the video luminance range B. In this case, the difference between the video luminance range a and the video luminance range B is about 5 bits (pixel value).

In the histogram h1, if a video exists in a portion of the difference between the video luminance range B and the video luminance range a, it is possible to obtain a luminance expression closer to the target CR by lowering the light emission luminance level of the backlight. However, if videos are distributed also on the high-luminance side, the reduction of the emission luminance level of the backlight causes an unexplainable portion. Therefore, as described above, the evaluation value is calculated to obtain the most appropriate light emission luminance level BL_reduced。

Fig. 8 is a diagram showing the video luminance range C when the light emission luminance level of one of the selection objects is 100%, fig. 9 is a diagram showing the video luminance range C when the light emission luminance level of one of the selection objects is about 70%, and fig. 10 is a diagram showing the video luminance range C when the light emission luminance level of one of the selection objects is 50%. The reference numerals of the letters in fig. 8 to 10 are based on fig. 6.

As shown in fig. 8, in the case where the light emission luminance level is shown as 100%, the evaluation value F1 for the low luminance portion has a certain value, and the evaluation value F2 for the high luminance portion has no value. In addition, as shown in fig. 9, when the light emission luminance level is reduced to about 70%, both the evaluation value F1 for the low luminance portion and the evaluation value F2 for the high luminance portion have low values. In addition, as shown in fig. 10, when the light emission luminance level is reduced to about 50%, the evaluation value F1 in the low luminance portion has no value, and the evaluation value F2 in the high luminance portion has a higher value. When the evaluation value calculation results of the light emission luminance levels shown in fig. 8 to 10 are compared in area (cumulative) with each other, the light emission luminance level becomes the smallest when it is 70%. Therefore, the distortion block 5 selects the light emission luminance level of 70% for output.

(arrangement design section 13)

The following expression (3) shows a basic model representing the relationship between the pixel value input to the liquid crystal panel and the display luminance on the liquid crystal panel. Here, Y is the display luminance on the liquid crystal panel, BL is the emission luminance level of the backlight (backlight DUTY: backlight DUTY ratio), and CV (Code Value: Code Value) is the pixel Value input to the liquid crystal panel. In this example, the gradation of the video signal is quantized to 0 to 255.

Y＝BL(CV/255)^γ (3)

The arrangement design part 13 uses the distortion module 5 to select the light-emitting brightness level BL_reducedWhen the brightness of the backlight source is reduced, the video gain is adjusted to improve the brightness on the picture. The pixel value after the gain is set as CV_reducedWhen the luminance level is lowered, the brightness of the screen (display brightness on the liquid crystal panel) is BL_reduced(CV_reduced/255)^γ. On the other hand, the light emission luminance level BL for reference_refWhen the backlight source is controlled, the brightness of the picture is BL_ref(CV_ref/255)^γ. By determining the pixel values so that these values are equal, it is possible to compensate for the difference in the light emission luminance level BL_reducedThe amount of decrease in the luminance of the backlight caused. That is, the arrangement design unit 13 may be set to a gain that satisfies the following expression (4).

Y＝BL_reduced(CV_reduced/255)^γ＝BL_ref(CV_ref/255)^γ (4)

Therefore, the gain (G) is expressed by the following equation (5). For example, in the reference light emission luminance level BL_refAt 100%, the following formula (6) is obtained. Furthermore, it is preferable to combine BL_refAnd BL_reducedThe relationship (2) is stored as a look-up table in a ROM or the like of the layout design section 13, so that the arithmetic processing of the following expression (5) can be executed at high speed.

G＝CV_reduced/CV_ref＝(BL_ref/BL_reduced)^1/γ (5)

G＝(1/BL_reduced)^1/γ (6)

(RGB gamma/WB adjusting part 15)

Fig. 11 is a diagram showing an example of the video signal gain set by the RGB γ/WB adjusting unit based on the gain setting signal output from the front-end luminance modulating unit in the video display device of fig. 2, and fig. 12 is a diagram for explaining an example of the adjustment processing performed by the RGB γ/WB adjusting unit in the video display device of fig. 2.

The relationship between the input gain setting value (conversion coefficient) and the gain characteristic curve obtained thereby will be described with reference to fig. 11. As shown in fig. 11(a), when the gain of the video signal output from the front luminance modulating section 20 is set to 1.0, the value is simply multiplied by the gain for all luminances, that is, linearity is maintained without any problem. However, when the gain is 1.0 or more, as shown in fig. 11(B), the high-luminance portion is uniformly set to a value of 255, that is, white clipping occurs. The basic idea of the pre-luminance modulation processing is to further darken the black color at the expense of the white clipping of a small number of white luminance portions, and in the case shown in fig. 11B, the RGB γ/WB adjusting unit 15 can perform the processing with a gain, but it is preferable to avoid directly fixing the high luminance portions to the value 255 (to the maximum value) for the sake of quality.

Therefore, it is preferable to reduce the decrease in the gradation characteristic in the high luminance portion by performing signal stretching corresponding to gain setting for low and medium luminance and making the gain characteristic curve nonlinear for high luminance. The method trades off the relationship between brightness and white clipping. When the nonlinear region is reduced, the region in which normal brightness can be expressed increases, but the gradation of high brightness decreases. Conversely, if the area is widened to be nonlinear, the area in which normal brightness can be expressed is reduced, but the gradation of high brightness can be maintained to some extent. In an actual product, the luminance that becomes nonlinear may be a portion of 90% or more, or a portion of 95% or more, for example, based on the gain setting output, and only the portion affected by the white clip may be made nonlinear. Fig. 11(C) shows a gain characteristic curve corrected so that 90% or more of the gain is nonlinear when the gain is set to 1.2. Fig. 11(D) shows a gain characteristic curve corrected so that 90% or more of the gain is nonlinear when the gain is set to 1.6.

As described above, in order to avoid reaching the maximum value when the gain setting exceeds 1.0, it is necessary to make a part of the gain characteristic curve nonlinear. However, the RGB γ/WB adjusting unit 15 performs simple proportional calculation based on the gain setting, and cannot calculate such a gain characteristic curve. Therefore, it is conceivable to provide each gain setting with a gain characteristic curve, but it is difficult to realize the gain setting due to the relation of memory capacity. Therefore, the linear portion is simply calculated based on the gain setting value, and the nonlinear portion may be calculated by interpolation or the like for 90% or more of the portions as illustrated in fig. 11(C) and (D). Further, since the gain setting is changed every frame, the gain characteristic curve is calculated every time.

Next, the adjustment processes by the RGB γ/WB adjustment unit 15 will be described with reference to fig. 12. The RGB γ/WB adjusting unit 15 performs gain acquisition processing, video γ adjustment processing, WB adjustment processing, and adjustment of CT (color temperature) and the like on the video signal output from the image quality correcting unit 14 using the gain characteristic curve described above. Note that the CT adjustment process may be executed by referring to one adjustment characteristic curve together with the WB adjustment process.

The RGB γ/WB adjusting unit 15 independently performs the processing on the video signal R, G, B. In this case, the γ adjustment processing, the gain acquisition processing, and the like are performed using the same characteristic curve for R, G, B, and the WB adjustment processing and the CT adjustment processing are performed using different characteristic curves for R, G, B. Then, as the sequence of each process executed by the RGB γ/WB adjustment unit 15, it is preferable to perform the γ adjustment process, then perform the gain acquisition process, and finally perform the WB adjustment process/CT adjustment process. Actually, as shown in fig. 12, the low gray scale region N is not enlarged much as NA → NB → NC, and the noise of the low luminance portion is not conspicuous. On the other hand, when the processing is performed in the order of gain → γ adjustment → WB/CT, the noise in the first low-luminance region is amplified. This may also be understood as a process of obtaining a gain is a conversion for compensating for a decrease in the light emission luminance level of the backlight, and is preferably performed in the vicinity of the liquid crystal panel.

(specific example of Pre-brightness modulation processing)

In the pre-luminance modulation processing, the most suitable luminance level BL of the backlight is selected based on the luminance histogram of the input video signal_reducedProviding the selected light-emitting brightness level BL_reducedThe corresponding video gain substantially maintains brightness on the screen, and achieves low power consumption by reducing the emission luminance of the backlight.

In addition, conventionally, in order to improve the visibility of a display image and reduce power consumption, there has been provided a video display device of a system in which the emission luminance of a backlight is dynamically adjusted in accordance with an input video signal that changes on a screen-by-screen basis. In this method, for example, APL or histogram is detected as a video feature amount of an input video signal, and the light emission luminance level of the backlight is changed in accordance with the detected video feature amount. Thus, for each picture, the picture brightness changes according to the video feature quantity of the picture. Thus, for example, it is possible to perform control for suppressing the backlight luminance so that the user does not feel dazzling at the time of high luminance, perform video display with optimum video quality, and realize low power consumption of the backlight.

In the present invention, the control method of the emission luminance of the backlight corresponding to the video feature amount is used, and the emission luminance level corresponding to the video feature amount is used as the reference value (BL)_ref) And is used for the calculation of the video gain (refer to the above equation (5)), and also the reference value (BL)_ref) Light emission luminance level BL for practical application to backlight control_reduced(iii) (decision corresponding to histogram and target CR).

In the embodiment according to the present invention, using the above-described pre-luminance modulation technique, it is possible to express a bright feeling in which white clipping is avoided, and to perform video expression in which black depth is improved. Hereinafter, comparative examples and examples according to the present invention using front-end luminance modulation will be described.

Comparative example

FIG. 13 is a diagram for explaining the light emission luminance levels BL to be referred to_refFig. is a diagram of an operation example of front-end luminance modulation in the case where the value is set to 100%.

The setting values set in the distortion module 5 are as follows.

a) Panel CR (contrast ratio of panel used): 2000

B) Target CR (contrast ratio of panel set as target): 3500

c) Luminance control range of backlight: 20 to 100 percent

The histogram of the input video signal is distributed over all luminance values 0 to 255 as shown in fig. 13 (B). In addition, the APL of the input video signal was set to 50%. The graph F of fig. 13(a) also shows the same histogram.

Emission luminance level BL for reference of backlight light source to APL_refAs shown in fig. 13(C), the APL of the input video signal is set to a fixed 100%. Further, a graph G of fig. 13(a) shows the luminance control characteristic.

The reference emission luminance level (target emission luminance value) BL set by the BL luminance level setting unit 8_RefThe light emission luminance level BL is always 100% regardless of the APL of the input video signal, and therefore even in the case where the APL is 50% (arrow g), for example_RefAlso set to 100%.

Due to the reference light-emitting luminance level BL_RefTo 100%, therefore loseThe true module 5 selects the luminance level of the backlight source so that the luminance observable when the panel displays is 100%. Here, the evaluation value is determined from the histogram of the input video signal, and the lowest light emission luminance level is selected from the acquired light emission luminance levels.

In this example, the histogram of the video is distributed over all 0 to 255, and the frequency of the maximum luminance 255 is small, so that the evaluation value of the light emission luminance level of 100% is the lowest. Therefore, 100% is selected as the light emission luminance level BL in the distortion block 5_reduced。

The front-end luminance modulation section 20 outputs a backlight duty of 100% based on the setting of the distortion block 5. In addition, the arrangement design unit 13 is based on the reference light emission luminance level BL_RefAnd the selected light-emission luminance level BL in the distortion module 5_reducedThe gain of the video signal is set. In this case, since the two light-emission luminance levels BL_Ref、BL_reducedThe gain is 100%, and therefore, the gain is set to 1.00 by calculation of the equation (5), and the gain is not changed. Therefore, on the panel, the level of the input signal is kept constant and display is performed regardless of the APL value.

(example 1)

Fig. 14 is a diagram for explaining an embodiment of a front luminance modulation process applicable to the video display device of the present invention. In this embodiment, a video with intermediate brightness is displayed with higher brightness and higher contrast, and a high-brightness video can be displayed clearly without white clipping, and a low-brightness video can be displayed with darker black.

In this embodiment, APL is used as a video feature quantity defining a luminance control characteristic, and in order to make a video of an intermediate luminance brighter and more highly contrasted, when the APL of a video signal is at an intermediate level, the light emission luminance gradation for reference is set to a value larger than 100% which cannot be output originally.

Various settings in this embodiment are as follows.

a) Panel CR (contrast ratio of panel used): 2000

B) Target CR (contrast ratio of panel set as target): 3500

c) The brightness control range of the backlight source; 20 to 100 percent

Then, in the present embodiment, the luminance control characteristic defining the emission luminance of the backlight light source with respect to the APL is set so as to be the characteristic shown in fig. 14B (the same as the graph G of fig. 14 a). That is, when the APL is in the range of the intermediate luminance of the first value L1 or more or the second value L2 or less, the emission luminance level BL for reference is set_RefThe value is set to 105% (as shown in fig. 14(B), a slight inclination may be provided at the boundary between 100% and 105%).

Original reference light emission luminance level BL_RefThe value should be within a range that can be practically used, but in the embodiment according to the present invention, the value is set to 105% outside the range.

When APL is lower than the first value L1 or higher than the second value L2, the light emission luminance level BL for reference is set to be the reference light emission luminance level BL_RefSet to a value of 100%.

By changing the reference light emission luminance level BL_RefThe gain is set to 105%, and when the light emission luminance of the light source is maximized, the degree of amplification of the video signal by the gain can be set to a value larger than the value of the input video signal that can appropriately exhibit the maximum luminance.

In this embodiment, since the APL of the input video signal is 50%, which corresponds to the portion of the arrow g in fig. 14(B), 105% is selected as the light emission luminance level BL for reference_Ref. Here, in the distortion block 5, though the light emission luminance level BL for reference is used_Ref105%, but since the luminance control range of the backlight is 20% to 100%, the light emission luminance level BL for control is selected therefrom_reduced. Here, and aboveIn the same manner as in fig. 13 of the comparative example, since the histograms are distributed over all 0 to 255, 100% having the lowest evaluation value is selected as the light emission luminance level BL_reduced. The front-end luminance modulating section 20 outputs a backlight duty at a luminance level of 100% based on the setting of the distortion block 5.

In addition, the arrangement design unit 13 selects the light emission luminance level (BL) based on the distortion module 5_reduced) 100%, and the emission luminance level for reference (BL)_Ref) 105%, the gain of the video signal is set. In this case, gain (105/100)^1/γ1.02 (2.2). Thus, the light emission luminance level observed on the panel display can obtain an effect of 105% instead of 100%, and a clearer video display can be performed.

As described above, the light-emission luminance levels BL for reference_RefSince the 105% region is only a predetermined range in which the APL is moderate, when the APL is high, the entire video can be made clear by eliminating the white clip, and when the APL is intermediate level, the video can be represented with higher contrast and brighter than when the emission luminance level of the backlight is 100%.

That is, when the APL is in a predetermined range of the middle level, the reference light emission luminance level BL is set_RefThe value of more than 100% is set, and a bright and high-contrast video can be displayed.

In the present invention, when the video feature value satisfies the predetermined condition, the input video signal is always amplified, and when the video feature value does not satisfy the predetermined condition, the input video signal may be amplified or not amplified. In the present embodiment, the video feature amount is APL, and the predetermined condition is that the APL is greater than or equal to the first value L1 and less than or equal to the second value L2. In this case, the reference light emission luminance level BL is used_RefThe value exceeds 100%, and therefore, whatever light-emitting luminance level (BL) is selected in the distortion module 5_reduced) The gain always exceeds 1Value, the input video signal is always amplified. In addition, when the APL is smaller than the first value L1 or larger than the second value L2, the light emission luminance level BL for reference is caused_RefThe value of 100% is obtained, and the light emission luminance level (BL) selected by the distortion module 5 is used_reduced) The case where the input video signal is amplified and the case where the input video signal is not amplified occur by making the gain larger than 1 or making the gain 1.

An example of the operation of performing the pre-luminance modulation according to embodiment 1 on various input video signals is shown below.

(operation example 1-1)

In the present operation example, the input video signal is a video as shown in fig. 15(a), and the high luminance value and APL of the video signal in which the histogram is distributed in the vicinity of 255 are 90% (for example, a video of a snow scene).

In this case, since the histogram of the video signal contains many high-luminance components, the distortion module 5 selects 100% as the light-emission luminance level BL of the backlight light source_reduced。

When the APL is 90%, the APL, which is a predetermined condition of the luminance control characteristic shown in fig. 14(B), is not equal to or higher than the first value L1 and equal to or lower than the second value L2, and therefore 100% is set as the reference light emission luminance level BL_Ref. Thus, the gain set by the arrangement designing section 13 becomes (100/100)^1/2.2No video is zoomed in 1. This prevents white clipping from occurring in a video signal with a high luminance. This condition is an example in which the video is not enlarged when the video feature quantity (APL) of the video signal does not satisfy a predetermined condition. In this case, the predetermined condition is not satisfied, and when the light source luminance is the maximum luminance, the amplification is not performed.

(working examples 1-2)

In the present operation example, the input video signal is a video as shown in fig. 15(B), the histogram of the video signal has a high luminance value in the vicinity of 255, and has a not-small scale distribution in the vicinity of a low luminance value, and the APL is 85% (for example, a video of a person wearing black clothes in a snowy scene).

In this case, since the histogram of the video signal contains many high-luminance components, the distortion module 5 selects 100% as the light-emission luminance level BL of the backlight light source_reduced. The reason for this is that if BL is set_reducedIf the number is set to less than 100%, the number of pixels that cannot be expressed in the high-luminance portion increases, and the evaluation value (distortion) increases.

When the APL is 85%, the APL, which is the predetermined condition of the luminance control characteristic shown in fig. 14(B), is not equal to or more than the first value L1 and equal to or less than the second value L2, and therefore 100% is set as the reference light emission luminance level BL_Ref. Thus, the gain set by the arrangement designing section 13 becomes (100/100)^1/2.2No video is zoomed in 1. This prevents white clipping from occurring in a video signal with a high luminance. This condition also shows an example in which video is not enlarged when the video feature quantity (APL) of the video signal does not satisfy a predetermined condition. In this case, when the predetermined condition is not satisfied and the light source luminance is the maximum luminance, the amplification is not performed.

(working examples 1 to 3)

In this operation example, the input video signal is a video as shown in fig. 15(C), and the histogram distribution of the video signal is slightly lower than the luminance values in the vicinity of 230 in the above operation examples 1 and 2, but there is a not small proportional distribution in the vicinity of low luminance values, and the APL is 81% (for example, a video of a bright forest).

In this case, the frequency of the histogram of the video signal in the vicinity of black is 0, and the evaluation value at this time is 0. Thus, the light emission luminance level of the backlight light source is selected so that the distortion evaluation value in the vicinity of white is also 0, for example, 80% is selected as the BL_reduced。

When the APL is 81%, the predetermined condition of the luminance control characteristic shown in fig. 14(B), that is, the APL is equal to or higher than the first value L1 and the second value L is not satisfied2 or less, and thus 100% is set as the light emission luminance level BL for reference_Ref. Thus, the gain set by the arrangement designing section 13 becomes (100/80)^1/2.2The video is amplified 1.11. In this case, although the video signal is amplified by an amount corresponding to a slight decrease in the luminance of the backlight light source, since the maximum luminance of the amplified video signal is 255 or less, white clipping does not occur. This condition shows an example of amplifying a video signal when the video feature quantity (APL) of the video signal does not satisfy a predetermined condition. In this case, the amplification is performed when the predetermined condition is not satisfied and the light source luminance is lower than the maximum luminance.

(working examples 1 to 4)

In this operation example, the input video signal is a video as shown in fig. 16(a), the histograms of the video signals are distributed at the high luminance side and the low luminance side at the same ratio with the center of the middle luminance, and the APL is 48% (for example, a video of a news studio).

In this case, since there is no video of extremely high luminance in the histogram of the video signal, the distortion module 5 selects 60% from the evaluation value of the histogram as the light emission luminance level BL of the backlight light source_reduced。

In addition, when the APL is 48%, the predetermined condition of the luminance control characteristic shown in fig. 14(B), that is, the APL is equal to or more than the first value L1 and equal to or less than the second value L2, is not satisfied, and therefore 105% is set as the emission luminance level BL for reference_Ref. Thus, the gain set by the arrangement designing section 13 becomes (105/60)^1/2.2The video is amplified 1.29. In this case, the light emission luminance level BL for reference will be referred to in addition to the compensation amount corresponding to the amount of slightly lowering the luminance of the backlight light source_RefBy setting the value to be greater than 100%, the video signal is slightly amplified, and a high-contrast video with a bright feeling can be displayed. This condition shows an example of amplifying a video signal when a video feature quantity (APL) of the video signal satisfies a predetermined condition.

(working examples 1 to 5)

In the present operation example, the input video signal is a video as shown in fig. 16(B), the histogram of the video signal is distributed at low luminance and at a small ratio at bright luminance, and the APL is 22% (for example, a video of a night sky star).

In this case, although there is an extremely high luminance of not small proportion in the histogram of the video signal, if the distortion module 5 selects 100% as the light emission luminance level BL of the backlight light source_reducedThis results in a large evaluation value (distortion), and 70% which can represent black and can be maintained as high as possible is selected as the light-emission luminance level BL_reduced。

When the APL is 22%, the predetermined condition for the luminance control characteristic shown in fig. 14(B), that is, the APL is equal to or more than the first value L1 and equal to or less than the second value L2, is not satisfied, and therefore the light emission luminance level BL for reference is set to_RefThe set is 100%. Thus, the gain set by the arrangement designing section 13 becomes (100/70)^1/2.2The video is amplified 1.18. In this case, a video in which black expression is emphasized and a very small amount of white clipping is allowed can be displayed. This condition shows an example of amplifying a video signal when the video feature quantity (APL) of the video signal does not satisfy a predetermined condition. In this case, the amplification is performed when the predetermined condition is not satisfied and the light source luminance is lower than the maximum luminance.

Further, depending on the brightness of the background or the number of stars, the light emission luminance of the selected backlight may also change, and the video may not be enlarged.

(working examples 1 to 6)

In the present operation example, a video as shown in fig. 16(C) is used as the input video signal, the histogram of the video signal is distributed at low luminance, and the APL is 25% (for example, a video of a movie). In this case, since there is almost no high luminance in the histogram of the video signal, the distortion module 5 selects a low level from the evaluation values of the histogram50% of the emission luminance level BL of the backlight light source_reduced。

When the APL is 25%, the predetermined condition for the luminance control characteristic shown in fig. 14(B), that is, the APL is equal to or more than the first value L1 and equal to or less than the second value L2, is not satisfied, and therefore the light emission luminance level BL for reference is set to_RefThe set is 100%. Thus, the gain set by the arrangement designing section 13 becomes (100/50)^1/2.2The video is amplified 1.37. In this case, by disregarding a video with little high luminance side, a black depth on the low luminance side can be exhibited. This condition shows an example of amplifying a video signal when the video feature quantity (APL) of the video signal does not satisfy a predetermined condition. In this case, the amplification is also performed when the predetermined condition is not satisfied and the light source luminance is lower than the maximum luminance.

As described above, according to embodiment 1, when the APL as the video feature amount is within the range of the intermediate luminance between the first value L1 and the second value L2, the operation is performed so that the video signal can be amplified further, and the video signal is always amplified.

On the other hand, when the APL is larger than the second value L2, the video is enlarged when compensating for a slight decrease in the light source luminance, but the video is not enlarged for an image to be displayed with the maximum light emission luminance of the light source.

When APL is smaller than the first value L1, the entire image is dark, and therefore the video signal is amplified so that the emission luminance of the light source is substantially compensated, but when a high luminance portion is present at a non-small ratio such as a star at night sky or a firework image, the light source may be displayed at the maximum emission luminance, and therefore, in such a case, the operation is performed so that the image is not amplified.

(example 2)

This embodiment makes the intermediate-luminance video and the low-luminance video brighter and more highly contrasted, and makes it possible to display the high-luminance video sharply while avoiding white clipping.

In this embodiment, in order to make the video of the intermediate luminance and the low luminance brighter and more highly contrasted, when the APL as the video feature amount is equal to or lower than the intermediate level, the reference light emission luminance level BL is set to be the reference light emission luminance level BL_RefThe value is set to a value larger than 100% which cannot be output originally.

Various settings in this example are the same as in example 1, as follows.

a) Panel CR (contrast ratio of panel used): 2000

B) Target CR (contrast ratio of panel set as target): 3500

c) The brightness control range of the backlight source; 20 to 100 percent

Then, in this embodiment, the luminance control characteristic defining the emission luminance of the backlight light source with respect to the APL is set so as to have the characteristic shown in fig. 7. That is, when the APL is in the low-medium luminance range of the predetermined value L3 or less, the emission luminance level BL for reference is set_RefThe setting was 105%.

When the APL is larger than the predetermined value L3, the light emission luminance level BL for reference is set_RefSet to a value of 100%. That is, the luminance control characteristic as shown in fig. 17 is a case where the operation is changed only when the APL is within a predetermined range of a medium level or less.

In the present embodiment, the same operation is performed also in the present embodiment for the operation when the APL of the input video signal is larger than the predetermined value L3, that is, for the video signals of operation example 1-1 to operation example 1-3 in embodiment 1. In the present embodiment, the same operation is performed for the operation when the APL is equal to or greater than the first value L1 and equal to or less than the second value L2 in the embodiment, that is, for the video signals of operation examples 1 to 4 in embodiment 1.

(working examples 2 to 5)

The operation example of the present embodiment will be described using the video signals of operation examples 1 to 5 of embodiment 1. In the present operation example, the input video signal is a video as shown in fig. 16(B), the histogram of the video signal is distributed at low luminance and at a small rate at bright luminance, and the APL is 22%.

In this case, although there is an extremely high luminance of not small proportion in the histogram of the video signal, if the distortion module 5 selects 100% as the light emission luminance level BL of the backlight light source_reducedThis results in a large evaluation value (distortion), and 70% which can represent black and can be maintained as high as possible is selected as the light-emission luminance level BL_reduced。

In addition, when the APL is 22%, the emission luminance level BL to be referred to satisfies the predetermined condition of the luminance control characteristic shown in fig. 17, that is, the APL is equal to or less than the predetermined value L3_RefThe setting was 105%. Thus, the gain set by the arrangement designing section 13 becomes (105/70)^1/2.2The video is amplified 1.20. In this case, the low-luminance portion is amplified by the luminance compensation degree or more, and the sense of brightness can be prioritized. However, the white clip on the high luminance side increases slightly. This condition shows an example of amplifying a video signal when a video feature quantity (APL) of the video signal satisfies a predetermined condition.

(working examples 2 to 6)

The operation example of the present embodiment will be described using the video signals of operation examples 1 to 6 of embodiment 1. In the present operation example, the input video signal is a video as shown in fig. 16(C), the histogram of the video signal is distributed at low luminance, and the APL is 25%. In this case, since there is almost no high luminance in the histogram of the video signal, the distortion module 5 selects, as the light emission luminance level BL of the backlight light source, 50% of the low level from the evaluation value of the histogram_reduced。

In addition, when the APL is 25%, the predetermined condition of the luminance control characteristic shown in fig. 17 is satisfiedThat is, the APL is equal to or less than the predetermined value L3, and therefore the light emission luminance level BL for reference is set_RefThe setting was 105%. Thus, the gain set by the arrangement designing section 13 becomes (105/50)^1/2.2The video is amplified 1.40. In this case, the display can be performed with the contrast feeling of brightness enhanced more than that of the black display. This condition shows an example of amplifying a video signal when a video feature quantity (APL) of the video signal satisfies a predetermined condition.

In this operation example, since almost no video signal is present in the high-luminance portion, the white clip is not conspicuous.

(example 3)

In this embodiment, the following structure is adopted: in the present invention, the video feature amount is a value obtained by multiplying the input video signal at all times when the video feature amount satisfies a predetermined condition, and the video feature amount does not satisfy the predetermined condition, and the input video signal is not multiplied or is multiplied.

In the present embodiment, the light emission luminance level BL to be referred to is estimated_RefThe frequency of occurrence of white clipping is set to a value larger than 100% which cannot be output originally, and the reference light emission luminance level BL is determined_RefWhether the value is set to 100% or more than 100%. That is, the occurrence of white clipping is suppressed to a minimum by estimating the frequency of white clipping.

Various settings in this example are the same as in example 1, as follows.

a) Panel CR (contrast ratio of panel used): 2000

B) Target CR (contrast ratio of panel set as target): 3500

c) The brightness control range of the backlight source; 20 to 100 percent

In this embodiment, as shown in fig. 18, if the estimated frequency of white clipping is less than W%, the light emission luminance level BL for reference will be referred to_RefThe content is set to 105%, and when W% or more is set to 100% or less. Next, the operation performed in this embodiment will be described using the same example as the input video signal used in embodiment 1.

(operation example 3-1)

In the present operation example, the input video signal is a video as shown in fig. 15 (a): the histogram of the video signal has a high luminance value around 255, and the APL is 90%. As described in operation example 1-1 of embodiment 1, since the video signal contains many high-luminance components, the distortion module 5 selects 100% as the light-emission luminance level BL of the backlight light source_reduced。

Here, if the reference light emission luminance level BL is set_RefWhen the gain is set to 105%, the gain at this time becomes (105/100)^1/2.2The limit luminance at which white clipping occurs is 255/1.02 to 250, 1.02.

Then, since the input video signal of this example includes a luminance of 250 or more W% (here, 5%), 100% is set as the reference light emission luminance level BL_Ref. Thus, the gain set by the layout design unit 13 becomes (100/100)^1/2.2No video is zoomed in 1. This prevents white clipping from occurring in a video signal with a high luminance. This condition is an example in which the video is not enlarged when the video signal does not satisfy the predetermined condition. In this case, when the predetermined condition is not satisfied and the light source luminance is the maximum luminance, the amplification is not performed.

(operation example 3-2)

In the present operation example, the input video signal is a video as shown in fig. 15 (B): the histogram of the video signal has a high luminance value around 255, a small proportion around a low luminance value, and an APL of 85%. As described in operation example 1-2 of embodiment 1, since the video signal contains many high-luminance components, the distortion module 5 selects 100% as the light-emission luminance level BL of the backlight light source_reduced. Thus, the operation result is the same as that described above (operation example 1-2 of example 1), and 100% is set as the reference light-emission luminance level BL_RefGain becomes (100/100)^1/2.2No video is zoomed in 1. This prevents white clipping from occurring in a video signal with a high luminance. This condition is an example in which the video is not enlarged when the video signal does not satisfy the predetermined condition. In this case, when the predetermined condition is not satisfied and the light source luminance is the maximum luminance, the amplification is not performed.

(operation examples 3 to 3)

In this operation example, the input video signal is a video as shown in fig. 15(C), and the histogram of the video signal is distributed at a luminance value near 230, but there is a not small proportional distribution also near a low luminance value, and the APL is 85%. As described in operation examples 1 to 3 of embodiment 1, since there is no video with extremely high luminance although the video signal contains many high-luminance components, 80% of the distortion module 5 is selected as the light-emission luminance level BL of the backlight light source_reduced。

Here, if the reference light emission luminance level BL is set_RefWhen the gain is set to 105%, the gain at this time becomes (105/80)^1/2.2The limit luminance at which white clipping occurs is 255/1.13 to 225 at 1.13.

Then, since the input video signal of this example includes a luminance of 225 or more W% (here, 5%) or more, 100% is set as the reference light emission luminance level BL_Ref. Thus, the gain set by the layout design unit 13 becomes (100/80)^1/2.2The video is amplified 1.11. Thus, although the video signal is amplified, white clipping does not occur. This condition is an example of amplifying a video signal when the video signal does not satisfy a predetermined condition. In this case, when the predetermined condition is not satisfied and the luminance of the light source is lower than the maximum luminance, the discharging is performedIs large.

(operation examples 3 to 4)

In the present operation example, the input video signal is a video as shown in fig. 16(a), the histogram of the video signal is distributed on the high luminance side and the low luminance side at the same ratio with the middle luminance as the center, and the APL is 48%. As described in operation examples 1 to 4 of embodiment 1, since there is no video with extremely high luminance in the histogram of the video signal of this example, the distortion module 5 selects 60% from the evaluation value of the histogram as the light emission luminance level BL of the backlight light source_reduced。

Here, if the reference light emission luminance level BL is set_RefWhen the gain is set to 105%, the gain at this time becomes (105/60)^1/2.2The limit luminance at which white clipping occurs is 255/1.29 to 198.

Then, in the input video signal of this example, since the luminance of 198 or more hardly exists, that is, the luminance is less than W% (here, 5%), 105% is set as the light emission luminance level BL for reference_Ref. Thus, the gain set by the layout design unit 13 becomes (105/60)^1/2.2The video is amplified 1.29. Thereby, the sense of brightness can be exhibited better than usual, and since there are almost no pixels in the white clip region, the white clip is also inconspicuous. This condition is an example of amplifying a video signal when the video signal satisfies a predetermined condition.

(working examples 3 to 5)

In this operation example, the input video signal is a video as shown in fig. 16(B), the histogram of the video signal is distributed in the low-luminance video signal and is distributed at a not small ratio in the bright luminance, and the APL is 22%. As described in operation examples 1 to 5 of embodiment 1, the distortion module 5 selects 70% that can represent black and can be maintained as high as possible as the emission luminance level BL of the backlight light source from among the evaluation values of the histogram_reduced。

Here, if the reference light emission luminance level BL is set_RefWhen the gain is set to 105%, the gain at this time becomes (105/70)^1/2.2The limit luminance at which white clipping occurs is 255/1.20 to 213, 1.20.

Then, since the input video signal of this example includes a luminance of not less than 213% and not less than W% (here, 5%), the light-emission luminance level BL for reference is set to 100%_Ref. Thus, the gain set by the layout design unit 13 becomes (100/70)^1/2.2The video is amplified 1.18. This prevents the occurrence of white clipping more than necessary while maintaining black appearance. In this example, black rendering and white clipping prevention are prioritized over the sense of brightness. This condition is an example of amplifying a video signal when the video signal does not satisfy a predetermined condition. In this case, the amplification is performed when the predetermined condition is not satisfied and the light source luminance is lower than the maximum luminance.

(operation examples 3 to 6)

In the present operation example, the input video signal is a video as shown in fig. 16(C), and in the histogram of the video signal, the video signal is distributed in all low luminance, and the APL is 25%. As described in the above-described operation examples 1 to 6 of embodiment 1, since there is almost no high luminance in the histogram, the distortion module 5 selects 50% from the evaluation values as the light emission luminance level BL of the backlight light source_reduced。

Here, if the reference light emission luminance level BL is set_RefWhen the gain is set to 105%, the gain at this time becomes (105/50)^1/2.2The limit luminance at which white clipping occurs is 255/1.40 to 182.

Then, in the input video signal of this example, since the luminance of 182 or more is almost nonexistent, that is, less than W% (here, 5%), 105% is set as the light-emission luminance level BL for reference_Ref. Thus, the gain set by the layout design unit 13 becomes (105/50)^1/2.2The video is amplified 1.40. Thus, by disregarding a signal with a very small amount on the high luminance side, it is possible to display a video with priority given to brightness while allowing the occurrence of a white clip with little influence. The condition being that the video signal satisfies a predetermined specificationThe condition is an example of amplifying a video signal.

(example 4)

In this embodiment, the following structure is adopted: in the present invention, the video feature amount is a value that is used to amplify the input video signal at all times when the video feature amount satisfies a predetermined condition, and the video feature amount does not satisfy the predetermined condition, and the video feature amount is a value that is used to set the predetermined condition such that the APL of the input video signal is equal to or less than a predetermined value and the frequency is equal to or less than a predetermined ratio.

In this embodiment, both the APL of the video in embodiment 1 or 2 and the frequency of white clipping in embodiment 3 are detected as the video feature amount, and when the APL is within a predetermined range and the frequency of white clipping is less than W%, the light emission luminance level BL for reference is set_RefThe value of more than 100% which cannot be output originally is set.

That is, in the present embodiment, by setting the predetermined condition to the condition of "satisfying both the condition of embodiment 1 or 2 and the condition of embodiment 3", the APL exhibits a moderate brightness contrast feeling, and the influence of the white clip is sufficiently considered.

Various settings in this example are the same as in example 1, as follows.

a) Panel CR (contrast ratio of panel used): 2000

B) Target CR (contrast ratio of panel set as target): 3500

c) The brightness control range of the backlight source; 20 to 100 percent

In the present embodiment, as shown in fig. 14B, if the APL is not less than the first value L1 and not more than the second value L2 (embodiment 1), and the estimated frequency of white clipping is less than W% (for example, less than W%) as shown in fig. 185%), the reference light emission luminance level BL is set_RefThe value is set to 105%, and if these two conditions, APL and white clipping, are not satisfied, the value is set to 100%.

In the case of using the conditions of example 2, if the APL is equal to or less than the third value L3 and the frequency of white clipping is less than W%, the light emission luminance level BL for reference is set_RefThe value is set to 105%, and if these two conditions, APL and white clipping, are not satisfied, the value is set to 100%.

If the same example as the input video signal used in embodiment 1 is used, operation 1-1 to operation 1-3 in embodiment 1 do not satisfy the condition that APL is moderate as in the description of embodiment 1, and do not satisfy the condition that the white clip frequency is less than 5% as in operation 3-1 to operation 3-3 in embodiment 3, and therefore, the operation is the same as in embodiment 1 to embodiment 3.

(operation examples 4 to 4)

The operation example of the present embodiment will be described using the video signals of operation examples 1 to 4 of embodiment 1. In the present operation example, the input video signal is a video as shown in fig. 16(a), the histogram of the video signal is distributed on the high luminance side and the low luminance side at the same ratio with the middle luminance as the center, and the APL is 48%.

As described in operation examples 1 to 4 of embodiment 1, since there is no video with extremely high luminance in the histogram of the video signal of this example, the distortion module 5 selects 60% from the evaluation value of the histogram as the light emission luminance level BL of the backlight light source_reduced。

As described in operation examples 1 to 4 of example 1, when the APL is 48%, the predetermined condition of the luminance control characteristic shown in fig. 14(B) of example 1, that is, the APL is equal to or higher than the first value L1 and equal to or lower than the second value L2 is satisfied. In addition, when the conditions of fig. 17 of example 2 are used, the conditions that the APL is the third to L3 or less are also satisfied.

In addition, if the light for reference is brightDegree class BL_RefWhen the gain is set to 105%, the gain at this time becomes (105/60)^1/2.2The limit luminance at which white clipping occurs is 255/1.29 to 198. Then, since the input video signal of this example has almost no luminance above 198, that is, less than W% (here, 5%), a condition is satisfied that the frequency of the video in which white clipping occurs is equal to or less than a predetermined ratio.

Thus, since the predetermined conditions of APL and the frequency of occurrence of white clipping are satisfied at the same time, 105% is set as the reference light emission luminance level BL_Ref. Thus, the gain set by the layout design unit 13 becomes (105/60)^1/2.2The video is amplified 1.29. This makes it possible to exhibit a more bright feeling than usual, and since there are almost no pixels in the white clip region, the white clip is not conspicuous. This condition is an example of amplifying a video signal when the video signal satisfies a predetermined condition.

(working examples 4 to 5)

The operation example of the present embodiment will be described using the video signals of operation examples 1 to 5 of embodiment 1. In this operation example, the input video signal is a video as shown in fig. 16(B), the histogram of the video signal is distributed in the low-luminance video signal and is distributed at a not small ratio in the bright luminance, and the APL is 22%.

As described in operation examples 1 to 5 of embodiment 1, although the histogram of the video signal of this example has extremely high luminance with a not small ratio, the distortion module 5 selects 100% as the light-emission luminance level BL of the backlight light source_reducedThis results in a large evaluation value (distortion), and therefore 70% which can represent black and can be maintained as high as possible is selected as the light-emission luminance level BL_reduced。

As described in operation examples 1 to 5 of embodiment 1, when the APL is 22%, the predetermined condition of the luminance control characteristic shown in fig. 14(B), that is, the APL is equal to or higher than the first value L1 and equal to or lower than the second value L2, is not satisfied. On the other hand, as in example 2, when the luminance control characteristic shown in fig. 17 is used, a predetermined condition that the APL is equal to or less than the predetermined value L3 is satisfied.

If the reference light emission luminance level BL is set_RefWhen the gain is set to 105%, the gain at this time becomes (105/70)^1/2.2The limit luminance at which white clipping occurs is 255/1.29 to 213 at 1.20. Then, since the luminance of the input video signal of this example is not less than 213% and not less than W% (here, 5%), the condition that the frequency of the video in which the white clip occurs is not more than the predetermined ratio is not satisfied.

In this example, since the predetermined conditions of APL and the frequency of occurrence of white clipping are not satisfied, 100% is set as the reference light emission luminance level BL_Ref. Thus, the gain set by the layout design unit 13 becomes (100/70)^1/2.2The video is amplified 1.18. This makes it possible to maintain black appearance without causing white clipping more than necessary. This condition is an example of amplifying a video signal when the video signal does not satisfy a predetermined condition. In this case, the amplification is performed when the predetermined condition is not satisfied and the light source luminance is lower than the maximum luminance.

(working examples 4 to 6)

The operation example of the present embodiment will be described using the video signals of operation examples 1 to 6 of embodiment 1. In the present operation example, the input video signal is a video as shown in fig. 16(C), the histogram of the video signal is distributed at low luminance, and the APL is 25%.

As described in operation examples 1 to 6 of embodiment 1, since there is almost no video with extremely high luminance in the histogram of the video signal of this example, the distortion module 5 selects 50% from the evaluation value of the histogram as the light emission luminance level BL of the backlight light source_reduced。

As described in operation examples 1 to 6 of example 1, when the APL is 25%, the predetermined condition of the luminance control characteristic shown in fig. 14(B), that is, the APL is equal to or higher than the first value L1 and equal to or lower than the second value L2, is not satisfied. On the other hand, as in example 2, when the luminance control characteristic shown in fig. 17 is used, a predetermined condition that the APL is equal to or less than the predetermined value L3 is satisfied.

If the reference light emission luminance level BL is set_RefWhen the gain is set to 105%, the gain at this time becomes (105/50)^1/2.2The limit luminance at which white clipping occurs is 255/1.40 to 182. Then, since the luminance of the input video signal in this example is less than W% at 182 or more (here, 5%), a condition is satisfied that the frequency of the video in which white clipping occurs is equal to or less than a predetermined ratio.

In this example, when determining the APL using the conditions of example 1, since the predetermined condition of the APL is not satisfied, 100% is set as the light emission luminance level BL for reference_Ref. Thus, the gain set by the layout design unit 13 becomes (100/50)^1/2.2The video is amplified 1.37.

On the other hand, when APL is determined using the conditions of example 2, the predetermined condition for APL is satisfied, and the predetermined condition for the frequency of occurrence of white clipping is also satisfied. Thus, 105% is set as the light emission luminance level BL for reference_RefThe gain set by the arrangement design unit 13 is (105/50)^1/2.2The video is amplified 1.40.

Thus, whether (the predetermined condition of) APL is satisfied and the predetermined condition of the frequency of occurrence of white clipping may differ depending on the setting of APL determination. Depending on the setting of the APL, importance is attached to the black depth (corresponding to example 1) or importance is attached to the appearance of the sense of brightness (corresponding to example 2).

(example 5)

In this embodiment, the following structure is adopted: in the present invention, the predetermined condition is set such that the minimum luminance of the input video signal is equal to or higher than a first value and the maximum luminance of the input video signal is equal to or lower than a second value, using the maximum luminance and the minimum luminance of the input video signal as the video feature amount.

In this embodiment, the maximum luminance value (hereinafter referred to as "MAX value") and the minimum luminance value (hereinafter referred to as "MIN value") of a video are detected as video feature values for each image, and when the MIN value is equal to or greater than the first value M1 and the MAX value is equal to or less than the second value M2, the reference light emission luminance level BL is set to be the reference light emission luminance level BL_RefThe value of more than 100% which cannot be output originally is set. That is, in the present embodiment, the brightness contrast feeling is exhibited only when the APL is moderate, and the influence of the white clip and the black expression are considered in other cases.

Various settings in this example are the same as in example 1, as follows.

a) Panel CR (contrast ratio of panel used): 2000

B) Target CR (contrast ratio of panel set as target): 3500

c) The brightness control range of the backlight source; 20 to 100 percent

In this embodiment, as shown in fig. 19, when the MIN value of the input video signal is equal to or more than the first value M1 and the MAX value is equal to or less than the second value M2, the emission luminance level BL for reference is used_RefSet to 105%, the reference light emission luminance level BL is set when the MIN value is less than the first value M1 or the MAX value is greater than the second value M2_RefThe set is 100%.

The first value M1 is, for example, a luminance value 51 (20%) that can exhibit a darkening effect. The second value M2 is the luminance value 204 (80%) which is originally high luminance and is more desirable for preventing white clipping than the sense of brightness.

If the same example as the video signal used in embodiment 1 is used, the MAX value has a luminance value exceeding 204 for the video signals of operation example 1-1 to operation example 1-3 of embodiment 1, and the predetermined conditions in this embodiment are not satisfied (MIN value is equal to or greater than luminance value 51 and MAX value is equal to or greater than luminance value 51)Value 204 or less), and hence the light emission luminance level BL for reference_RefThe set is 100%.

In addition, in the video signals of the operation examples 1 to 5 and 1 to 6 of example 1, since the MIN value has a luminance value of 51 or less and the predetermined condition of this example is not satisfied (the MIN value is 51 or more and the MAX value is 204 or less), the reference light emission luminance level BL is set to be the reference light emission luminance level BL_RefThe set is 100%.

Next, an operation example of the present embodiment will be described with reference to the input video signals of the remaining operation examples 1 to 4 of embodiment 1.

(operation examples 5 to 4)

The input video signal in this operation example is a video as shown in fig. 16(a), and the histogram of the video signal is distributed on the high luminance side and the low luminance side at the same ratio with the middle luminance as the center, and the APL is 48%.

As described in operation examples 1 to 4 of embodiment 1, since there is no video with extremely high luminance in the histogram of the video signal of this example, the distortion module 5 selects 60% from the evaluation value of the histogram as the light emission luminance level BL of the backlight light source_reduced。

Then, since the input video signal of this example satisfies the predetermined conditions that the MIN value is equal to or more than the luminance value 51 and the MAX value is equal to or less than the luminance value 240, 105% of the emission luminance level BL for reference is set_Ref. Thus, the gain set by the layout design unit 13 becomes (105/60)^1/2.2The video is amplified 1.29. This makes it possible to exhibit a more bright feeling than usual, and since there are almost no pixels in the white clip region, the white clip is not conspicuous. This condition is an example of amplifying a video signal when the video signal satisfies a predetermined condition.

(example 6)

In this embodiment, the following structure is adopted: in the present invention, the APL of the input video signal is used as the video feature amount, and the predetermined condition is set such that the APL of the input video signal is equal to or greater than a first value and equal to or less than a second value.

In addition, in the present embodiment, the selection of the light emission luminance level BL of the backlight light source is not based on the distortion calculation_reducedInstead, the brightness level BL of the backlight source is adjusted according to the APL_reducedSelection of (2).

In the present embodiment, the light emission luminance level BL for the backlight light source_reducedWhen the overall dark video is large, a low value is selected, and when the overall bright video is large, a high value is selected.

In the present embodiment, as shown in fig. 20, the light emission luminance level BL of the backlight light source_reducedIs varied according to the APL, 20% when the APL is, for example, less than 51, 100% when the APL is, for example, greater than 204, and a value between 20% and 100% is proportionally selected according to the size of the APL when the APL is more than or equal to 51 and less than 204.

Then, the reference light emission luminance level BL_RefSimilarly to embodiment 1, when the APL is a medium level (the first value L1 or more and the second value L2 or less), it is set to a value larger than 100% which cannot be output originally. Next, the operation of the present embodiment will be described using the same example of video signals as in embodiment 1.

(operation example 6-1)

In the present operation example, the input video signal is a video as shown in fig. 15(a), the histogram of the video signal has a high luminance value around 255, and the APL is 90%. In this example, since the APL of the input video signal is 90%, the distortion module 5 selects 100% as the light-emission luminance level BL of the backlight light source_reduced. In addition, in the present embodiment, the distortion module 5 does not calculate the evaluation value (loss) by calculatingTrue) to select the luminance level BL of the backlight light source_reducedHowever, the distortion module 5 is used to replace the light emitting brightness level BL of the backlight source in the above embodiments_reducedThe selection block of (2) is explained. In this case, the APL detected by the APL detecting unit 3 is input to the distortion module 5, and the emission luminance level BL is selected based on the APL_reduced。

On the other hand, when the APL is 90%, the above-mentioned predetermined condition that the APL is moderate is not satisfied, and therefore 100% is set as the reference light emission luminance level BL_Ref。

Thus, the gain set by the layout design unit 13 becomes (100/100)^1/2.2No video is zoomed in 1. This prevents white clipping from occurring in a video signal with a high luminance. This condition is an example in which the video is not enlarged when the video feature quantity (APL) of the video signal does not satisfy a predetermined condition. In this case, when the predetermined condition is not satisfied and the light source luminance is the maximum luminance, the amplification is not performed.

(operation example 6-2)

In this operation example, the input video signal is a video as shown in fig. 15(B), and the histogram of the video signal has a high luminance value in the vicinity of 255, but has a not small proportional distribution in the vicinity of a low luminance value, and the APL is 85%.

In this example, since the APL of the input video signal is 85%, the distortion module 5 selects 100% as the light-emission luminance level BL of the backlight light source_reduced。

In the case where the APL is 85%, the above-described predetermined condition that the APL is medium is not satisfied, and therefore 100% is set as the reference light emission luminance level BL_Ref。

Thus, the gain set by the layout design unit 13 becomes (100/100)^1/2.2No video is zoomed in 1. This prevents white clipping from occurring in a video signal with a high luminance. This condition is a video feature quantity of the video signal (APL) does not satisfy the predetermined condition. In this case, when the predetermined condition is not satisfied and the light source luminance is the maximum luminance, the amplification is not performed.

(operation examples 6-3)

In this operation example, the input video signal is a video as shown in fig. 15(C), and the histogram of the video signal is distributed at a luminance value near 230, but there is a not small proportional distribution also near a low luminance value, and the APL is 81%.

In this example, since the APL of the input video signal is 81%, the distortion module 5 selects 100% as the light-emission luminance level BL of the backlight light source_reduced。

In the case where the APL is 85%, the above-described predetermined condition that the APL is medium is not satisfied, and therefore 100% is set as the reference light emission luminance level BL_Ref。

Thus, the gain set by the layout design unit 13 becomes (100/100)^1/2.2No video is zoomed in 1. Due to the brightness level BL of the backlight light source_reducedDoes not start to decrease from 100%, and therefore cannot attempt to decrease power consumption, but at the light emission luminance level BL_reducedAt 100%, all the input video signals can be represented, and no white clipping occurs, so there is no problem with video representation. This condition is an example in which, unlike operation examples 1 to 3 of embodiment 1, a video is not enlarged when the video feature quantity (APL) of the video signal does not satisfy a predetermined condition. In this case, when the predetermined condition is not satisfied and the light source luminance is the maximum luminance, the amplification is not performed.

(operation examples 6 to 4)

In the present operation example, the input video signal is a video as shown in fig. 16(a), the histogram of the video signal is distributed on the high luminance side and the low luminance side at the same ratio with the middle luminance as the center, and the APL is 48%.

In this example, since the APL of the input video signal is 48%,therefore, the distortion module 5 selects, for example, 50% as the light-emitting brightness level BL of the backlight light source_reduced。

In addition, when the APL is 48%, 105% is set as the reference light emission luminance level BL since the above-described predetermined condition that the APL is moderate is satisfied_Ref。

Thus, the gain set by the layout design unit 13 becomes (105/50)^1/2.2The video is amplified 1.40. Here, except for slightly reducing the light-emitting brightness level BL of the backlight light source_reducedThe reference light emission luminance level BL is set in addition to the compensation amount corresponding to the amount of_RefBy setting the value to be larger than 100%, the video signal is slightly amplified, and thus a high-contrast video with a bright feeling can be displayed. This condition is an example of amplifying a video when a video feature quantity (APL) of a video signal satisfies a predetermined condition.

(operation examples 6 to 5)

In this operation example, the input video signal is a video as shown in fig. 16(B), the histogram of the video signal is distributed at low luminance and at a small rate at bright luminance, and the APL is 22%.

In this example, since the APL of the input video signal is 22%, the distortion module 5 selects, for example, 25% as the light-emission luminance level BL of the backlight light source_reduced。

In the case where the APL is 22%, the above-described predetermined condition that the APL is moderate is not satisfied, and therefore 100% is set as the reference light emission luminance level BL_Ref。

Thus, the gain set by the layout design unit 13 becomes (100/25)^1/2.2The video is amplified 1.88. Here, by changing the emission luminance level BL of the backlight light source_reducedThe black color can be enhanced by setting the value to be low, but the amplification of the video signal is large and the noise increases as compared with operation examples 1 to 5 of embodiment 1. The condition being in the video signalAn example is not to enlarge a video when the video feature quantity (APL) does not satisfy a predetermined condition. In this case, the amplification is performed when the predetermined condition is not satisfied and the light source luminance is lower than the maximum luminance.

(operation examples 6 to 6)

In the present operation example, the input video signal is a video as shown in fig. 16(C), the histogram of the video signal is distributed at low luminance, and the APL is 25%.

In this example, since the APL of the input video signal is 25%, the distortion module 5 selects, for example, 30% as the light-emission luminance level BL of the backlight light source_reduced。

In the case where the APL is 25%, the above-described predetermined condition that the APL is moderate is not satisfied, and therefore 100% is set as the reference light emission luminance level BL_Ref。

Thus, the gain set by the layout design unit 13 becomes (100/30)^1/2.2The video is amplified 1.73. This enables the black depth on the low luminance side to be exhibited. This condition is an example of amplifying a video when a video feature quantity (APL) of a video signal does not satisfy a predetermined condition. In this case, the amplification is performed when the predetermined condition is not satisfied and the light source luminance is lower than the maximum luminance.

In the present embodiment described above, as an algorithm, the light emission luminance level BL of the backlight light source is selected in accordance with the APL_reducedIt is easy to perform gain setting by gain calculation, and it is needless to say that the gain may be calculated first by using the light emission luminance level calculated by the APL, and then the gain may be set, and then the luminance of the backlight light source may be adjusted.

(example 7)

In this embodiment, the following structure is adopted: amplifying the input video signal all the time when the video characteristic quantity satisfies a predetermined condition, and amplifying the input video signal and not amplifying the video signal when the video characteristic quantity does not satisfy the predetermined conditionIn the case of line enlargement, in the configuration of the present invention, the APL of the input video signal is used as the video feature amount, and the predetermined condition is that the APL of the input video signal is equal to or more than a first value and equal to or less than a second value. Here, in embodiment 1 described above, when the APL is smaller than the first value L1 or larger than the second value L2, the light emission luminance level BL for reference is used_RefAlthough 100% is set, in this embodiment, power saving is also taken into consideration, and therefore, the reference light emission luminance level BL may be set for a video image with a low APL and a low possibility of including a bright image_RefSet to a value less than 100%.

In this embodiment, as shown in fig. 21, when the APL is equal to or more than the first value L1 and equal to or less than the second value L2, the light emission luminance level BL for reference will be used_RefThe APL is set to 105%, and when the APL is smaller than the first value L1, the reference light emission luminance level BL is set_RefThe setting was 70%. When APL is larger than the second value L2, the reference light emission luminance level BL_RefThe same as in example 1 was found to be 100%.

Various settings in this example are the same as in example 1, as follows.

a) Panel CR (contrast ratio of panel used): 2000

B) Target CR (contrast ratio of panel set as target): 3500

c) The brightness control range of the backlight source; 20 to 100 percent

Next, the operation of the present embodiment will be described using the same input signal as that used in embodiment 1.

First, the same operation is performed for the video signals of operation example 1-1 to operation example 1-4 of embodiment 1 in which the APL is equal to or higher than the first value L1 in this embodiment. Next, an operation example of the present embodiment using the video signals used in operation examples 1-5 to 1-6 of embodiment 1 will be described.

(operation examples 7 to 5)

In this operation example, the input video signal is a video as shown in fig. 16(B), the histogram of the video signal is distributed at low luminance and at a small rate at bright luminance, and the APL is 22%. In this case, although there is an extremely high luminance of not small proportion in the histogram of the video signal, if the distortion module 5 selects 100% as the light emission luminance level BL of the backlight light source_reducedThis results in a large evaluation value, and 70% which can represent black and can be maintained as high as possible is selected as the light emission luminance level BL_reduced。

In addition, when the APL is 22%, the predetermined condition of the luminance control characteristic shown in fig. 21(B), that is, the APL is not less than the first value L1 and not more than the second value L2, is not satisfied, and therefore the light emission luminance level BL for reference will be used_RefThe setting was 70%. Thus, the gain set by the layout design unit 13 becomes (70/70)^1/2.2No video is zoomed in 1. In this case, power saving can be prioritized. This condition shows an example in which the video signal is not amplified when the video feature quantity (APL) of the video signal does not satisfy the predetermined condition.

(operation examples 7 to 6)

In the present operation example, the input video signal is a video as shown in fig. 16(C), the histogram of the video signal is distributed at low luminance, and the APL is 25%. In this case, since there is almost no high luminance in the histogram of the video signal, the distortion module 5 selects, as the light emission luminance level BL of the backlight light source, 50% of the low level from the evaluation value of the histogram_reduced。

In the case where the APL is 25%, the predetermined condition of the luminance control characteristic shown in fig. 21, that is, the APL is equal to or more than the first value L1 and equal to or less than the second value L2, and the APL is smaller than the first value L1, is not satisfied, and therefore the light emission luminance level BL for reference will be used_RefThe setting was 70%. Thus, the gain set by the layout design unit 13 becomes (70/50)^1/2.2The video is amplified 1.17. In this case, since the video signal is hardly present in the white clip region, it is possible toAvoiding white clipping while performing both black rendering and power saving is achieved. This condition shows an example of amplifying a video signal when the video feature quantity (APL) of the video signal does not satisfy a predetermined condition.

As described above, the present embodiment is particularly effective in the case where no video signal is present in the high luminance region.

(example 8)

In the above embodiments, the degree of amplification of the video signal is determined based on the relationship with the luminance of the backlight light source, but in the present embodiment, there is shown an effect that the video signal is amplified in order to obtain a sense of brightness contrast even if the luminance of the backlight light source is constant.

In this embodiment, when the light emission luminance of the backlight light source is made constant, the light emission luminance gradation BL for reference of embodiment 1 is set to be constant_RefAnd the light emission luminance level BL for reference of embodiment 2_RefThe setting of (2) is changed according to the condition of the respective video characteristic quantities.

Specifically, the emission luminance level of the backlight is fixed at 100%. Then, as shown in fig. 22, when the APL is smaller than the first value L1, if the peak value as the video feature amount is equal to or larger than a predetermined value (for example, 204 (80%)), the light-emission luminance level BL for reference will be referred to_RefSet to 105% (m in FIG. 22), and if the peak value is smaller than a predetermined value, the light emission luminance level BL for reference is set_RefSet to 100% (n of fig. 22).

In the present embodiment, the predetermined condition is set such that the reference light emission luminance level BL is set when "the APL of the input video signal is equal to or less than a medium level and has a peak value equal to or greater than a predetermined value when the APL is low"_RefSet to a value exceeding 100 (here 105%).

Various settings in this embodiment are as follows.

a) Panel CR (contrast ratio of panel used): 2000

B) Target CR (contrast ratio of panel set as target): 3500

c) The brightness control range of the backlight source; 100 percent

Next, the operation of the present embodiment will be described using the same input signal as that used in embodiment 1. In act 1-1 and act 1-2 of example 1, the selected light emission luminance level BL_reduced100% of the reference light emission luminance level BL_RefSince the setting of (2) is also in the high APL region, the same operation as in example 1 is also performed in this example. The following describes an operation example of the present embodiment with reference to the video signals of operation examples 1-3 to 1-6 of embodiment 1.

(operation examples 8 to 3)

In this operation example, the input video signal is a video as shown in fig. 15(C), and the histogram of the video signal is distributed at a luminance value near 230, and is distributed at a not-small ratio even near a low luminance value, and the APL is 81%.

In this example, the APL of the input video signal is 81%, and therefore the condition that the peak value is equal to or greater than the predetermined value (80%) is satisfied. However, the condition that the APL is smaller than the first value L1 is not satisfied, and therefore the predetermined condition according to the present embodiment is not satisfied (the APL of the input video signal is equal to or smaller than a moderate level, and has a peak value equal to or larger than a predetermined value when the APL is low). Thus, 100% is set as the light-emission luminance level BL for reference_Ref。

Thus, the gain set by the layout design unit 13 becomes (100/100)^1/2.2No video is zoomed in 1. In this operation example, unlike operation examples 1 to 3 of embodiment 1, an operation for lowering the luminance of the backlight light source is not performed, but there is no disadvantage except that the power consumption is slightly increased. This condition is an example in which the video signal is not amplified when the video feature amount of the video signal does not satisfy the predetermined condition. In this case, when the predetermined condition is not satisfied and the light source luminance is the maximum luminance, the amplification is not performed.

(operation examples 8 to 4)

In the present operation example, the input video signal is a video as shown in fig. 16(a), the histogram of the video signal is distributed on the high luminance side and the low luminance side at the same ratio with the middle luminance as the center, and the APL is 48%.

In this example, the predetermined condition according to the present example is satisfied (the APL of the input video signal is equal to or less than the moderate level, and has a peak value equal to or more than the predetermined value when the APL is low) because the condition that the peak value of the input video signal is equal to or more than the predetermined value (80%) is satisfied and the condition that the APL is lower than the first value L1 is satisfied. Thus, 105% is set as the light emission luminance level BL for reference_Ref。

Thus, the gain set by the layout design unit 13 becomes (105/100)^1/2.2The video is amplified 1.02. In this operation example, unlike operation examples 1 to 3 of embodiment 1, an operation for lowering the luminance of the backlight light source is not performed, but there is no disadvantage other than a slight increase in power consumption in order to enhance the contrast feeling of brightness. This condition is an example of amplifying a video signal when a video feature amount of the video signal satisfies a predetermined condition.

(operation examples 8 to 5)

In this operation example, the input video signal is a video as shown in fig. 16(B), the histogram of the video signal is distributed at low luminance and at a small rate at bright luminance, and the APL is 22%.

In this example, the predetermined condition according to the present example is satisfied (the APL of the input video signal is equal to or less than the moderate level, and has a peak value equal to or more than the predetermined value when the APL is low) because the condition that the peak value of the input video signal is equal to or more than the predetermined value (80%) is satisfied and the condition that the APL is lower than the first value L1 is satisfied. Thus, 105% was set as the light emission luminance level for reference_BLRef。

Thus, the gain set by the arrangement designing section 13 becomes (105/100)^1/2.2The video is amplified 1.02. In this operation example, although the power consumption is increased, a video representation in which the peak value is emphasized can be performed, and a sense of contrast of brightness can be provided. This condition is an example of amplifying a video signal when a video feature amount of the video signal satisfies a predetermined condition.

(operation examples 8 to 6)

In the present operation example, the input video signal is a video as shown in fig. 16(C), the histogram of the video signal is distributed at low luminance, and the APL is 25%.

In this example, the condition that the APL is lower than the first value L1 is satisfied, but the condition that the peak value of the input video signal is equal to or higher than the predetermined value (80%) is not satisfied. Therefore, the predetermined condition according to the present embodiment is not satisfied (the APL of the input video signal is equal to or less than a medium level, and when the APL is low, the APL has a peak value equal to or more than a predetermined value). Thus, 100% is set as the light-emission luminance level BL for reference_Ref。

Thus, the gain set by the layout design unit 13 becomes (100/100)^1/2.2No video is zoomed in 1. In this operation example, the effects of darkening and reducing power consumption cannot be obtained by making the emission luminance level of the backlight constant. Further, since there is no peak, a normal video display is performed without providing a brightness contrast. This condition is an example in which the video signal is not amplified when the video feature amount of the video signal does not satisfy the predetermined condition. In this case, when the predetermined condition is not satisfied and the light source luminance is the maximum luminance, the amplification is not performed.

In addition, the present invention can be applied to other display devices that do not include a light source such as a liquid crystal display device by performing gain calculation based on the light emission luminance level of the backlight in the gain setting example as in the above-described embodiment.

(example 9)

In this embodiment, the various parameters and settings described in embodiments 1 to 8 are changed according to the image quality mode.

The video display apparatus can set the image quality mode as a video display mode that can be set by a user. The image quality mode is a mode for optimizing the brightness or contrast of a screen so as to have a quality suitable for the content viewed by the user. The image quality modes include: a "dynamic mode" in which a sense of contrast of brightness is fully exhibited, a "standard mode" set at home or the like, a "movie mode" in which the image quality of movies is particularly expressed perfectly, a "game mode" in which the image quality can be given less priority because of a large amount of monotonous expression, and a "power saving mode" in which power consumption is emphasized more than the image quality. In the present embodiment, the panel CR is assumed to be 2000.

(dynamic mode)

In the dynamic mode, emphasis is placed on displaying a video brighter and sharper than the standard and performing a video expression with a darker color. Therefore, the target CR is set to a value greater than the panel CR, for example, 3500. If the target CR is large, black that cannot be expressed (appears) when the emission luminance of the backlight is 100% can be expressed as black closer to 0, and thus the degree of deepening of black can be enhanced.

Then, in order to make the entire image with intermediate brightness appear bright and clear, the reference light emission luminance level BL is set under the condition that the APL is moderate (corresponding to the above-described example 1)_RefThe value of more than 100%, for example, 102%, which cannot be normally output, is set. In this case, the first value L1 and the second value L2 in example 1 may be changed as compared with other image quality modes.

As described above, a bright video can be displayed more brightly, and a dark portion can be displayed more darkly. For example, it is effective to be able to dynamically display a video when displayed in a shop or the like.

(Standard mode)

The standard mode is a mode that is mainly used at home, and the adjustment frequency of the backlight and the gain is reduced, and natural video expression is focused on.

Further, the frequency of use is assumed to be high, and the setting is such that power saving can be achieved to some extent. Thus, in the standard mode, reducing the target CR to 2100, for example, represents a natural video, and also allows for low power consumption. In the standard mode, the reference light emission luminance level BL is minimized_RefSet to a value greater than 100%. Here, as in the above-described example 7, the light emission luminance level BL for reference may be set_RefTo a value of less than 100%.

(Power saving mode)

In the present embodiment, the target CR is set to be large, for example, 3500, and the light emission luminance level BL for reference is set_RefIt is also fixed at 70% or the like to place importance on power saving.

(movie mode)

The movie mode is a mode in which a more realistic black representation is achieved with importance placed on faithful reproduction of video. Therefore, in the movie mode, the target CR is set to be large, for example, 3500. This makes it possible to realize power saving while paying attention to true black. However, some white clipping may be allowed.

(Game mode)

In the game mode, since the requirement for the reproducibility of the image quality is not high, power saving is more important than the image quality. For example, in the above-described embodiment 8, the light emission luminance levels BL for reference_RefFixed at a value less than 100% or varied according to APL.

As described above, in the present embodiment, various parameter settings are changed according to the image quality mode. As the changed parameter, there is a target CR corresponding to the image quality mode.

In addition, the predetermined condition for always amplifying the input video signal is changed according to the image quality mode.

For example, the following conditions can be changed according to the image quality mode: that is, (1) a condition that the APL of the input video is equal to or less than a predetermined value; (2) a condition that an APL of an input video is equal to or higher than a first value and equal to or lower than a second value; (3) setting a frequency that cannot be expressed by stretching to a predetermined ratio or less; (4) a condition that an average luminance of an input video signal is equal to or less than a predetermined value and a frequency that cannot be expressed by stretching of the input signal is equal to or less than a predetermined ratio; (5) a condition that an average luminance of an input video is equal to or higher than a first value and equal to or lower than a second value, and a frequency that cannot be expressed by stretching an input signal is equal to or lower than a predetermined ratio; and (6) a condition that the minimum luminance of the input video signal is equal to or more than a first value and the maximum luminance of the input video signal is equal to or less than a second value.

Specifically, when the operation example 3 of each example is used, the predetermined condition relating to the video characteristic amount may be changed according to the image quality mode, and the operation example may be used, for example, in the dynamic mode (example 3), or may be used, for example, in the power saving mode, to use the light emission luminance level BL to be referred to_RefFixed at 70% (example 8), etc.

Alternatively, the predetermined value in the condition (1) or the predetermined value in the condition (4) may be changed according to the image quality mode. Alternatively, the first value and/or the second value in the above conditions (2), (5), or (6) may be changed according to the image quality mode. Alternatively, the predetermined ratio of the above (3) to (5) may be changed according to the image quality mode.

In addition, only one parameter may be changed according to the image quality mode, or a combination of parameters may be changed.

In the case where the light source is used in the present invention described above, a fluorescent tube, an LED, an organic EL lighting, or the like may be used.

Then, the extraction of the video feature amount, the setting of the predetermined condition, the application, and the video expression based on these may be performed in each area by dividing the display screen into a plurality of areas.

Industrial applicability of the invention

The present invention can be applied to a display device such as a broadcast receiver.

Claims (15)

1. A video display device includes a display section to which a video signal is input and a light source that irradiates light emitted from the light source to the display section to display a video,

adjusting a degree of amplification of an input video signal based on a video feature amount of the input video signal,

always amplifying the input video signal in a case where the video feature amount satisfies a predetermined condition,

in a case where the video feature amount does not satisfy a predetermined condition, there are a case where the input video signal is amplified and a case where the amplification is not performed, wherein the degree of amplification of the input video signal depends on the light emission luminance of the light source.

2. The video display apparatus of claim 1,

the video feature quantity is an average luminance of an input video signal,

the predetermined condition is that an average brightness of the input video is below a predetermined value.

3. The video display apparatus of claim 1,

the video feature quantity is an average luminance of an input video signal,

the predetermined condition is that the average brightness of the input video is above a first value and below a second value.

4. The video display apparatus of claim 1,

the video feature amount is a frequency that cannot be expressed in the input video signal once the input video signal is stretched,

the predetermined condition is that the frequency is below a predetermined ratio.

5. The video display apparatus of claim 1,

the video feature value is an average luminance of the input video signal and a frequency at which the input video signal cannot be expressed when stretched,

the predetermined condition is that the average brightness is below a predetermined value and the frequency is below a predetermined ratio.

6. The video display apparatus of claim 1,

the video feature value is an average luminance of the input video signal and a frequency at which the input video signal cannot be expressed when stretched,

the predetermined condition is that the average brightness of the input video is equal to or greater than a first value and equal to or less than a second value, and the average brightness is equal to or less than a predetermined value and the frequency is equal to or less than a predetermined ratio.

7. The video display apparatus of claim 1,

the video feature quantities are the maximum luminance and the minimum luminance of the input video signal,

the predetermined condition is that a minimum luminance of the input video signal is above a first value and a maximum luminance of the input video signal is below a second value.

8. The video display apparatus of claim 1,

and under the condition that the video characteristic quantity does not meet a preset condition, when the light source brightness is the maximum brightness, the input video signal is not amplified, and when the light source brightness is reduced from the maximum brightness, the input video signal is amplified.

9. The video display apparatus of claim 1,

the degree of amplification of the video signal is set to the following value: so that when the light source luminance is maximum, it is larger than a value of an input video signal capable of properly displaying the maximum luminance.

10. The video display apparatus of claim 1,

the degree of amplification of the video signal is also determined in consideration of the target light emission luminance of the light source.

11. The video display apparatus of claim 10,

the target light emission luminance value of the light source is set to a value greater than 100%.

12. The video display apparatus according to claim 1, wherein the control unit controls the display unit to display the video signal

The predetermined condition is changed according to the picture quality mode.

13. A video display apparatus as claimed in claim 2 or 5, characterized in that

The predetermined value is changed according to the image quality mode.

14. A video display apparatus according to any one of claims 3, 6 and 7, characterized in that

The first value and/or the second value is/are changed according to the picture quality mode.

15. Video display apparatus according to any one of claims 4 to 6, characterized in that

The predetermined ratio is changed according to the picture quality mode.