JP3990624B2 - Liquid crystal display - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display device that displays an image using a liquid crystal display panel, and more particularly to a liquid crystal display device that prevents motion blur that occurs during moving image display.
[0002]
[Prior art]
In recent years, flat panel display devices (FPD) such as liquid crystal display devices (LCD) that can realize high definition, low power consumption, and space saving have been actively developed, and in particular, computer display devices and television display devices. The spread of LCDs for such applications is remarkable. However, in contrast to a cathode ray tube (CRT) display device that has been mainly used for such applications, the LCD has a blurred outline of the moving part when a moving image is displayed. It has been pointed out the disadvantage of the so-called “motion blur” that it is perceived.
[0003]
It has been pointed out that the motion blur in moving image display is caused not only by the delay of the optical response time of the liquid crystal but also by the LCD display method itself as described in, for example, Japanese Patent Laid-Open No. 9-325715. In a CRT display device that scans an electron beam and emits phosphors to perform display, each pixel emits light in an almost impulse-like manner although there is some afterglow of the phosphors. Yes.
[0004]
On the other hand, in the LCD display device, the charge stored by applying the electric field to the liquid crystal is held at a relatively high rate until the next electric field is applied (particularly in the TFT LCD, the pixel is configured. A TFT switch is provided for each dot to be operated, and since an auxiliary capacitor is usually provided for each pixel, the stored charge is very high in capacity), so that the liquid crystal pixel is based on the image information of the next frame. This is a so-called hold type display system in which light emission is continued until rewriting is performed by applying an electric field.
[0005]
In such a hold-type display device, since the impulse response of the image display light has a temporal spread, the temporal frequency characteristic is deteriorated, and the spatial frequency characteristic is also lowered accordingly, and the visual image is blurred. . In view of this, for example, Japanese Patent Laid-Open Nos. 4-302289 and 2001-42831 have proposed that the frame frequency of a display image is increased to suppress the reduction of the spatial frequency characteristic that causes the motion blur. Yes.
[0006]
This will be described with reference to FIG. In FIG. 7, reference numeral 1 denotes a motion vector detection unit that detects motion vector information from an input image signal, and 2 denotes an input image by generating a subframe image using the motion vector information obtained by the motion vector detection unit 1. A frame frequency conversion unit that converts the frame frequency of the signal to 2 times, for example, 3 is an electrode drive for driving the data electrodes and the scan electrodes of the liquid crystal display panel 4 based on the image signal frequency-converted by the frame frequency conversion unit 2 Reference numeral 4 denotes an active matrix type liquid crystal display panel having a liquid crystal layer and electrodes for applying scanning signals and data signals to the liquid crystal layer.
[0007]
In the above configuration, the motion vector detection unit 1 may obtain motion vector information using, for example, a matching method or a gradient method, and if the input image signal includes motion vector information in some form, You may use it as it is. For example, since image data compressed and encoded using the MPEG system includes motion vector information of a moving image calculated at the time of encoding, the motion vector information may be acquired and output.
[0008]
The frame frequency conversion unit 2 generates a frame interpolated image (subframe image) by motion interpolation using the motion vector information output from the motion vector detecting unit 1, and the generated interpolated frame signal is generated. By sequentially outputting together with the input frame signal, the frame frequency (60 Hz) of the input image signal is converted to 120 Hz, which is doubled, and the image signal converted to the double speed is supplied to the liquid crystal display panel 4 via the electrode driver 3. The liquid crystal display panel 4 is driven at double speed.
[0009]
In this way, by performing motion adaptive frame interpolation processing using motion vector information and increasing the display frame frequency, it is possible to approximate the display state of the hold-type drive to the display of the impulse-type drive such as the CRT. It is possible to improve image quality degradation due to motion blur that occurs during moving image display.
[0010]
[Patent Document 1]
JP-A-9-325715 [Patent Document 2]
JP-A-4-302289 [Patent Document 3]
Japanese Patent Laid-Open No. 2002-42831
[Problems to be solved by the invention]
In order to improve the image quality degradation due to motion blur that occurs when displaying a moving image in the hold-type display device, the above-described conventional technology has one or more in one frame period (for example, 16.7 msec in the case of 60 Hz progressive scan). The subframes are motion-compensated and supplied to the liquid crystal display panel to shorten the display frame cycle. To prevent image quality degradation due to motion blur, the display frame cycle (subframe It is desirable to make the image display period) as small as possible.
[0012]
By the way, as shown in FIG. 8, the response speed of the liquid crystal greatly depends on the gradation transition of the current frame data with respect to the previous frame data, and generally the followability from one halftone to another halftone is extremely poor. It is known that the response time increases. That is, in the above-described conventional technique, when the frame frequency of the display image signal is increased, depending on the gradation transition pattern of the input image signal, the next subframe image may be displayed before the liquid crystal completely responds and reaches the target luminance. As a result, there is a problem that the image quality of the display image is deteriorated, such as a more serious afterimage such as tailing.
[0013]
The present invention has been made in view of the above problems, and variably controls high-speed display driving (frame frequency conversion rate) of a liquid crystal display panel according to gradation transitions before and after one vertical period of an input image signal. The present invention provides a liquid crystal display device capable of improving the display quality of moving images.
[0014]
[Means for Solving the Problems]
The present invention relates to a liquid crystal display device including frame frequency conversion means for converting a frame frequency of an image signal supplied to a liquid crystal display panel by interpolating a predetermined subframe with respect to an input image frame, Gradation transition detection means for detecting gradation transition before and after one vertical period of the image signal, and control means for variably controlling the frame frequency conversion rate by the frame frequency conversion means based on the detected gradation transition. It is characterized by having.
[0015]
According to the liquid crystal display device of the present invention, when the display frame frequency is converted to a high frequency in order to prevent motion blur, the frame frequency conversion rate is set according to the gradation transition before and after one vertical period of the input image signal. Appropriate automatic switching makes it possible to display the next image after the liquid crystal has fully responded to reach the target brightness, realizing high-quality moving image display that suppresses the occurrence of afterimages along with motion blur. can do.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described in detail with reference to FIG. 1 to FIG. 6, but the same reference numerals are given to the same parts as the above-described conventional example, and the description thereof will be omitted. Here, FIG. 1 is a functional block diagram showing a schematic configuration of the main part of the liquid crystal display device of the present embodiment, FIG. 2 is a timing chart showing the operation of the frame frequency conversion unit in the liquid crystal display device of the present embodiment, and FIG. 4 is a schematic explanatory diagram for explaining the operation of the frame frequency conversion unit in the liquid crystal display device of the embodiment, FIG. 4 is an explanatory diagram for explaining the optical response characteristics of the liquid crystal display panel in the liquid crystal display device of the present embodiment, and FIG. Is a flowchart showing the basic operation principle of the liquid crystal display device of the present embodiment, and FIG. 6 is an explanatory diagram for explaining the basic operation principle of the liquid crystal display device of the present embodiment.
[0017]
As shown in FIG. 1, the liquid crystal display device according to the present embodiment is read from the frame memory 5 for storing the input image signal of the previous frame, in addition to the conventional example described above with reference to FIG. Control for detecting the gradation transition between the previous frame data and the current frame data and variably controlling the frame frequency conversion rate in the frame frequency conversion unit 12 based on the gradation transition before and after one frame of the input image signal And a control CPU 6 for outputting a signal.
[0018]
The frame frequency conversion unit 12 includes, for example, a frame memory, stores an image of one frame of the input image signal in the frame memory, and then stores an image at a predetermined frame frequency based on a control signal from the control CPU 6. By subtracting a time frame by reading the signal and performing motion adaptive frame interpolation using the motion vector information obtained by the motion vector detection unit 1, a subframe image (shown by hatching in FIG. 3) is obtained. Then, the frame frequency of the display image signal is converted into a high frequency.
[0019]
In the present embodiment, for example, for the input image signal shown in FIG. 2A, as shown in FIG. 2B and FIG. 3A, the image signal is converted at the same speed without converting the frame frequency as it is. 2 (c) and FIG. 3 (b), a mode for outputting an image signal in which the frame frequency is doubled, and FIGS. 2 (d) and 3 (c). As shown, a mode for outputting an image signal obtained by converting the frame frequency to three times is provided, and each mode can be switched in accordance with a control signal from the control CPU 6. That is, the frame frequency conversion rate by the frame frequency conversion unit 12 can be varied between 1 to 3 times.
[0020]
Here, the input image signal is a 60 Hz progressive scan signal. Therefore, the frame frequencies output by the frame frequency conversion unit 12 in each mode are 60 Hz, 120 Hz, and 180 Hz, respectively, and the frame period is 1/60 seconds (16.7 msec). 1/120 seconds (8.3 msec) and 1/180 seconds (5.6 msec).
[0021]
In the present embodiment, for example, the liquid crystal display panel 4 having optical response characteristics (gradation transition dependency) such that the transition time from black or low gradation to intermediate gradation is particularly slow as shown in FIG. By controlling the frame frequency conversion unit 2 so as to convert the frame frequency of the input image signal to a predetermined frequency in accordance with the gradation transition before and after one frame of the input image signal, A period during which a certain liquid crystal responds (liquid crystal response time) is sufficiently secured.
[0022]
Next, the operation of the present embodiment configured as described above will be described with reference to the flowchart of FIG. First, it is determined whether or not the gradation transition of the current frame data with respect to the previous frame data is included in the area A (gradation transition pattern with a particularly slow response speed) in FIG. 4 for at least M pixels in one screen. (Step 1) When the pixel data of M or more is included in the region A, the response speed of the liquid crystal corresponding to the pixel is considered to be considerably slow. Therefore, the frame frequency conversion by the frame frequency conversion unit 12 is stopped, By setting the through output (the frame frequency conversion rate is 1), the liquid crystal display panel 4 is driven at the same speed (that is, the high-speed display drive is turned off) (step 2).
[0023]
In this case, as shown in FIG. 6A, the image display period of each frame is 16.7 msec, and the occurrence of motion blur cannot be prevented. However, the liquid crystal is completely displayed within this image display period (16.7 msec). Therefore, it is possible to expect to reach the target luminance in response to the occurrence of afterimage such as tailing due to the incomplete response of the liquid crystal, which has a greater influence on image quality degradation than motion blur.
[0024]
Further, when it is determined in step 1 that pixel data of M or more is not included in the region A, the gradation transition of the current frame data with respect to the previous frame data for at least N or more pixels in one screen is shown in FIG. It is determined whether or not it is included in region B (gradation transition pattern with a slow response speed) (step 3). When pixel data of N or more is included in the region B, the response speed of the liquid crystal corresponding to the pixel is considered to be slightly slow. Therefore, the frame frequency conversion rate by the frame frequency conversion unit 12 is doubled, and the liquid crystal display panel 4 Are driven at double speed (step 4).
[0025]
In this case, as shown in FIG. 6B, the image display period of each sub-frame is 8.3 msec, and it is possible to reduce the occurrence of motion blur, and this image display even if the response speed of the liquid crystal is somewhat slow. Since it can be expected that the liquid crystal completely reaches the target luminance within the period (8.3 msec), it is possible to reduce the occurrence of afterimage such as tailing.
[0026]
Furthermore, if it is determined in step 3 that pixel data of N or more is not included in the region B, the response speed of the liquid crystal is considered to be sufficiently fast for the entire screen, so that the frame frequency conversion by the frame frequency conversion unit 12 is performed. The liquid crystal display panel 4 is driven three times at a rate of 3 (step 5).
[0027]
In this case, as shown in FIG. 6C, the image display period of each subframe can be set to 5.6 msec, and the occurrence of motion blur can be sufficiently prevented. Further, the response speed of the liquid crystal is sufficiently high, and the liquid crystal completely responds within this image display period (5.6 msec) to reach the target luminance, so that afterimage such as tailing does not occur.
[0028]
As described above, when a gradation transition having a poor optical response characteristic of the liquid crystal display panel 4 is detected with respect to an input image signal around one frame, the frame frequency conversion rate in the frame frequency conversion unit 12 is reduced. A sufficient image scanning period (liquid crystal response period) is ensured, and after the liquid crystal completely responds and reaches the target luminance, the next image display can be performed. Therefore, it is possible to realize high-quality moving image display by appropriately suppressing the occurrence of motion blur and afterimage according to the gradation transition of the input image. Here, the variable control of the frame frequency conversion rate is performed for each input image frame.
[0029]
In the case of the above-described embodiment, for example, when a gradation transition having poor response characteristics of the liquid crystal display panel 4 is detected for a predetermined number of pixels in one frame, the liquid crystal display panel 4 is supplied. Although the control is performed so that the frame frequency of the image signal is switched to a low frequency, the present invention is not limited to this. When even one pixel detects a gradation transition with poor response characteristics of the liquid crystal display panel 1 in one frame. The frame frequency conversion rate of the image signal may be determined based on the gradation transition region having the highest detection frequency in one frame by switching the frame frequency of the image signal to a low frequency.
[0030]
Further, in the present embodiment, the description has been given of the case where the frame frequency of the display image signal is switched by 1 to 3 times according to the gradation transition of the input frame image, but the present invention is not limited to this and the present invention is not limited to this. Obviously, the frame conversion may be performed at any frame frequency. This may be designed as appropriate according to the optical response characteristics of the liquid crystal display panel. Furthermore, the perception of motion blur varies depending on the image content and image content, and there are large individual differences. Therefore, a configuration in which the user can select and instruct an arbitrary frame frequency conversion rate may be added.
[0031]
Further, as is clear from FIG. 7, the response speed of the liquid crystal greatly varies depending on the environmental temperature, and particularly the followability with respect to the input signal at a low temperature is extremely deteriorated, and the response time is increased. The conversion frame frequency may be determined in consideration of the temperature inside the apparatus in addition to the gradation transition pattern. Thereby, it is possible to realize an appropriate moving image display according to the optical response characteristics of the liquid crystal.
[0032]
As described above, in the liquid crystal display device according to the present embodiment, a predetermined number of subframes are interpolated with respect to the input image frame, and the liquid crystal display panel is driven at high speed, thereby bringing the display state close to the impulse-type display state. Since the display drive speed (frame frequency conversion rate) is controlled in accordance with the gradation transition of the input image signal before and after one frame when the motion blur is prevented by the above, the occurrence of motion blur is prevented and the tailing, etc. It is possible to prevent the occurrence of afterimages and improve the image quality of the display image.
[0033]
【The invention's effect】
Since the liquid crystal display device of the present invention is configured as described above, the liquid crystal is completely switched by appropriately automatically switching the frame frequency conversion rate in accordance with the gradation transition before and after one vertical period of the input image signal. After reaching the target luminance in response, it is possible to perform the next image display, and it is possible to realize a high-quality moving image display that suppresses the occurrence of afterimage as well as motion blur according to the image content.
[Brief description of the drawings]
FIG. 1 is a functional block diagram showing a schematic configuration of a main part in an embodiment of a liquid crystal display device of the present invention.
FIG. 2 is a timing chart showing an operation of a frame frequency conversion unit in an embodiment of the liquid crystal display device of the present invention.
FIG. 3 is a schematic explanatory diagram for explaining an operation of a frame frequency conversion unit in an embodiment of the liquid crystal display device of the present invention.
FIG. 4 is an explanatory diagram showing optical response characteristics of a liquid crystal display panel used in an embodiment of the liquid crystal display device of the present invention.
FIG. 5 is a flowchart showing a basic operation principle in an embodiment of the liquid crystal display device of the present invention.
FIG. 6 is an explanatory diagram for explaining a basic operation principle in one embodiment of the liquid crystal display device of the present invention.
FIG. 7 is a functional block diagram showing a schematic configuration of a main part in a conventional liquid crystal display device (high-speed drive type).
FIG. 8 is an explanatory diagram illustrating an example of optical response characteristics of a liquid crystal display panel.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Motion vector detection part 3 Electrode drive part 4 Liquid crystal display panel 5 Frame memory (FM)
6 Control CPU
12 Frame frequency converter

Claims (1)

A liquid crystal display device comprising frame frequency conversion means for converting a frame frequency of an image signal supplied to a liquid crystal display panel by interpolating a predetermined number of subframes with respect to an input image frame,
Gradation transition detecting means for detecting gradation transition before and after one vertical period of an input image signal;
A liquid crystal display device comprising: control means for variably controlling a frame frequency conversion rate by the frame frequency conversion means based on the detected gradation transition.

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