JP4987134B1 - Video display device - Google Patents

Abstract

When a backlight is divided into a plurality of parts and the luminance of the backlight is controlled in accordance with a video signal corresponding to each area, noise in a low luminance part is made inconspicuous.
An area active control unit 2 divides a video signal into a plurality of regions and outputs a first feature amount for each region. The LED control unit 3 determines the first luminance of each divided region of the LED backlight 5 according to the first feature amount for each region. Then, the second luminance is determined by uniformly multiplying the first luminance by a constant magnification within a range where the total value of the LED driving currents is equal to or less than a predetermined allowable current value. Further, the second luminance is compared with the threshold value, and only in the region where the second luminance is lower than the threshold value, the second luminance is decreased again to become the third luminance, and the third luminance and the second luminance are decreased. The light emission of the LED is controlled for each divided area by using the second luminance of the area that is not to be used.
[Selection] Figure 1

Description

  The present invention relates to a video display device, and more particularly to a video display device that divides a backlight into regions and controls luminance for each region.

  In video display devices, those using LED backlights are widely used for illumination of display panels. The LED backlight has an advantage that local dimming is possible. In local dimming, the backlight is divided into a plurality of areas, and the light emission of the LEDs is controlled for each area according to the video signal of each area. For example, it is possible to control such that a dark portion in the screen suppresses light emission of the LED, and a bright portion in the screen causes the LED to emit light strongly. Thereby, the power consumption of the backlight can be reduced and the contrast of the display screen can be improved.

For example, FIG. 15 shows a conventional local dimming control example. Here, the backlight is divided into eight regions, and the luminance of the LED is controlled according to the maximum gradation value of the video signal corresponding to each region. It is assumed that the maximum gradation value of the video signal in each area is in the state shown in FIG. A to H are region Nos. The number below is the maximum gradation value in each area.
For example, the luminance of the LED in each region by local deming is as shown in FIG. That is, the brightness of the LED is controlled for each area according to the video signal of each area. Here, since the video is relatively dark in the region where the maximum gradation value of the video signal is low, the brightness of the LED is lowered to reduce the black float and improve the contrast, and the power consumption of the LED is reduced. Yes. In this case, the maximum luminance in each region is limited to the luminance (for example, 450 cd / m ² ) when all LEDs of the backlight are turned on with a duty of 100%.

  For example, Patent Literature 1 discloses a peak for reducing flicker and moving image blur even when the light emission period is varied over a wide range. A brightness level control technique is disclosed. In this control method, when setting the lighting period in the display panel in which the peak luminance level is variable by controlling the total lighting period length that is the sum of the lighting periods arranged in the field period, the average luminance level of the entire screen is set. Based on this, the light emission mode is determined. Thereafter, in order to obtain a peak luminance level set in accordance with the input image data, the number of lighting periods arranged in one field period, the arrangement position, and the setting condition defined for the determined light emission mode Set the period length.

JP 2009-192753 A

As described above, in the conventional local dimming control in which the backlight is divided into a plurality of areas and the brightness of the LED is controlled according to the video signal corresponding to each area, the maximum brightness in each area is The brightness is limited to the brightness when all LEDs are turned on with a duty of 100%, and the brightness control of the LEDs according to the video signal is performed within the limit. In this case, in a low gradation region of the video signal, if the luminance of the noise component, which is a low gradation component, is enhanced by the light emission of the LED, the noise becomes conspicuous and the quality deteriorates. Since the user pays attention to the brightness of the high-luminance portion, there is a need for an image processing device that specifically brightens a bright video area and further enhances the brightness without conspicuous noise.

  The present invention has been made in view of the above-described circumstances. When the backlight is divided into a plurality of parts and the brightness of the backlight is controlled according to the video signal corresponding to each area, the noise in the low-brightness portion is determined. An object of the present invention is to provide a video display device in which the image becomes inconspicuous.

  In order to solve the above problems, a first technical means of the present invention includes a display panel that displays a video signal, a backlight that uses an LED as a light source that illuminates the display panel, and a light emission luminance of the backlight. A control unit that controls, the control unit divides the backlight into a plurality of regions, and controls light emission of the LED for each of the divided regions, wherein the control unit includes the division The first brightness of the LED is determined for each of the areas in accordance with the first feature amount of the video of the display area corresponding to each of the areas, and the LED is driven with respect to the first brightness of each area. In a range where the total value of currents is equal to or less than a predetermined allowable current value, a second luminance is determined for each region obtained by uniformly multiplying the first luminance by a constant magnification, and a second luminance for each region is further determined. Comparing the brightness with a predetermined threshold, Only for the region where the luminance of 2 is lower than the threshold value, the second luminance is lowered again to the third luminance, and the third luminance and the second luminance of the region where the second luminance is not lowered are changed. It is characterized by controlling the light emission of the LED for each divided region.

  The second technical means is characterized in that, in the first technical means, the third luminance for each of the regions matches the first luminance of each region.

  The third technical means is characterized in that, in the first technical means, the third luminance for each region is within a predetermined range including the first luminance of each region.

  According to a fourth technical means, in any one of the first to third technical means, the control unit sets the threshold value as a fixed value.

  According to a fifth technical means, in any one of the first to third technical means, the control unit sets the threshold value according to a second feature amount of the video.

  The sixth technical means is that in any one of the first to third technical means, the control unit reduces the second luminance and sets the number of regions to be the third luminance to a predetermined number. Further, the threshold value is set.

  According to a seventh technical means, in the fifth technical means, when the control unit lowers the second luminance by the threshold value, an image having a smaller second feature amount is set to the first luminance. The second luminance is lowered so as to approach the second luminance.

  According to an eighth technical means, in the fifth or sixth technical means, when the control unit decreases the second luminance by the threshold, the second luminance is lower than the threshold. The second luminance is lowered so that the region where the second luminance is smaller is closer to the first luminance.

  A ninth technical means is any one of the first to eighth technical means, wherein the first feature amount is a maximum gradation value of a video signal in the divided area. It is.

  According to a tenth technical means, in the fifth or seventh technical means, the second feature amount is an APL of an image.

  An eleventh technical means is the fifth or seventh technical means, wherein the second feature amount is a maximum gradation value for each frame of the video.

  According to the present invention, it was made in view of the above situation, and when the backlight is divided into a plurality of parts and the brightness of the backlight is controlled according to the video signal corresponding to each area, It is possible to provide a video display device in which the noise in the screen becomes inconspicuous.

It is a figure explaining the structural example of the principal part of the video display apparatus which concerns on this invention. It is a figure for demonstrating the example of a setting of LED brightness by the LED control part of a video display apparatus. It is a figure explaining an example of local dimming by electric power limit control. It is a figure explaining the example of control of local deming by electric power limit control. It is a figure explaining the example of a specific process of the area active control part of a video display apparatus. It is a figure which shows the state which arranged the area | region shown in FIG. 5 in order of area | region No. FIG. It is a figure which shows the state which reduced the brightness | luminance of LED of the area | region which has a maximum gradation value smaller than threshold value Th, and rearranged in order with the brightness | luminance value of LED. It is a figure which shows an example of the gradation curve which uses as input the maximum gradation value of each area | region, and outputs the brightness | luminance of LED of each area | region. It is a figure which shows the example of an image | video with APL 50% and contrast comparatively small. It is a figure which shows the example of an image | video with APL 50% and contrast comparatively large. It is a figure which shows the example of an image whose APL is 50% and the contrast of the whole image is extremely large. It is a figure explaining the process example which fixes a threshold value to a fixed value irrespective of the state of an image | video. It is a figure explaining the other process example which fixes a threshold value to a fixed value irrespective of the state of an image | video. It is a figure explaining the further example of a process which fixes a threshold value to a fixed value irrespective of the state of an image | video. It is a figure explaining the example of control of the conventional local dimming.

FIG. 1 is a diagram illustrating a configuration example of a main part of a video display device according to the present invention. The video display device is configured to display an image by performing image processing on an input video signal, and can be applied to a television device or the like.
The image processing unit 1 inputs a video signal separated from a broadcast signal or a video signal input from an external device, and performs the same video signal processing as that of the prior art. For example, IP conversion, noise reduction, scaling processing, γ adjustment, white balance adjustment, and the like are appropriately executed. Further, the contrast, color, etc. are adjusted based on the user set value and output.

  The area active control unit 2 divides the video signal into predetermined regions according to the video signal output from the image processing unit 1, and extracts the maximum gradation value of the video signal for each divided region. The maximum gradation value for each region is output to the LED control unit 3 as LED data. The area active control unit 2 outputs data indicating the gradation of each pixel of the liquid crystal to the liquid crystal control unit 6 as liquid crystal data. At this time, the liquid crystal data and the LED data are output so that synchronization is maintained between the LED backlight 5 and the liquid crystal panel 7 which are final outputs.

  The LED data is the maximum gradation value of the video signal for each divided area, but is not the maximum gradation value but other predetermined statistical values such as the average gradation value of the video signal in the divided area. There may be. As LED data, the maximum gradation value in the region is generally used, and in the following description, the maximum gradation value in the divided region is used.

  The LED control unit 3 performs power limit control on the LED data output from the area active control unit 2 and determines a control value for controlling lighting of each LED of the LED backlight 5. Power limit control is to increase the brightness of the backlight and improve the contrast for areas that require more brightness in the display screen. The total amount of drive current when the backlight LEDs are fully lit. Is set to the upper limit, and the emission luminance of the LED is increased within a range in which the total amount of drive current of the LEDs that are lit in each region does not exceed the total amount of drive current at the time of full lighting.

The brightness of the LED of the LED backlight 5 can be controlled by PWM (Pulse Width Modulation) control, current control, or a combination thereof. In either case, control is performed so that the LED emits light with a desired luminance. In the following example, PWM duty control will be described as an example. The control value output from the LED control unit 3 performs LED light emission control for each divided region of the area active control unit 2, thereby realizing local dimming. The control unit of the present invention corresponds to the area active control unit 2 and the liquid crystal control unit 6.
The LED driver 4 performs light emission control of each LED of the LED backlight 5 according to the LED data output from the LED control unit 3.

FIG. 2 is a diagram for explaining an example of setting the LED brightness by the LED control unit.
The LED control unit 3 of the video display device determines the luminance of the LED backlight 5 in the relationship as shown in FIG. The horizontal axis represents the lighting rate (window size) of the backlight. The lighting rate determines the average lighting rate of the entire backlight, and can be expressed as a ratio of the total lighting region (window region) to the extinguishing region. The lighting rate is zero when there is no lighting region, the lighting rate increases as the window of the lighting region increases, and the lighting rate becomes 100% with full lighting. The vertical axis indicates the luminance of the LED in the divided area, and indicates the luminance of the LED in an area where the maximum luminance can be obtained among the divided areas. That is, the brightness of the area including the window in the screen is shown.

By the power limit control, the power for turning on the LED (total amount of drive current value) is constant. Therefore, as the lighting rate increases, the power that can be input to one divided region decreases.
An example of the relationship between the lighting rate and the maximum brightness of the divided area is as shown in FIG. In a range where the lighting rate (window size) is small, power can be concentrated on the small window, so that each LED can be lit up to the maximum luminance with a duty of 100%. However, in a region (P1 to P2) where the lighting rate is small and all the LEDs in one divided region cannot be lit, the luminance of the entire region is low even if the lighting LED is set to 100% duty. In this case, the luminance of the region is the lowest when the lighting rate = 0 (window size = 0), and the window size in the region increases as the lighting rate increases, so the luminance of the region also increases. Therefore, it can be seen that the shape of the luminance curve from P1 to P2 also changes depending on the number of divisions of the video (the size of the divided areas).

When the lighting rate increases from a state where the lighting rate is 0 and the lighting rate is such that all the LEDs in one region can be lit (P2), the luminance in that region becomes maximum. The duty of the LED at this time is 100%. This is because power can be input to a smaller area for power limit control.
Further, as the lighting rate increases from point P2, the number of LEDs to be lit increases, so the power that can be input to each LED by power limit control decreases, and therefore the maximum brightness that the area can take gradually decreases. Go. The point P3 is a state in which the entire screen is fully lit. In this case, the duty of each LED decreases to, for example, 36.5%.

  In the power limit control, the luminance of the backlight is further increased and the contrast is improved in an area where the luminance is further required in the display screen. Here, the upper limit is the total amount of drive current when the backlight LEDs are fully lit, and the total amount of drive current of the LEDs that are lit in each region is within the range that does not exceed the total amount of drive current when all the LEDs are lit. Is increased at a constant magnification.

That is, as shown in FIG. 4, the luminance is increased by multiplying the light emission luminance of the LED determined for each region in FIG. 15B by a fixed magnification (a times). The condition at this time is the total amount of drive current values in each region <the total drive current value when all the LEDs are turned on. In this case, in one area, it is allowed to exceed the luminance at the time of full lighting (for example, 450 cd / m ² ), and more driving current is input to the LED in a range where there is a margin of power to make it brighter. It is. By performing such control, it is possible to actually express a peak luminance of 2 to 3 times.

FIG. 3 is a diagram showing a state of luminance on the liquid crystal panel when the luminance duty of the LED is changed. The horizontal axis represents the gradation of the video signal, and the vertical axis represents the luminance value on the liquid crystal panel.
For example, when the LED of the LED backlight is controlled with a duty of 36.5%, the gradation expression of the video signal becomes T1. At this time, the luminance value on the liquid crystal panel = (gradation value) is ^2.2 (that is, gamma = 2.2). Here, when the LED is controlled with a duty of 100%, the gradation expression becomes T2. That is, since the luminance of the LED is increased by about 2.7 times from 36.5% to 100%, the luminance value on the liquid crystal panel is also increased by about 2.7 times. At this time, the luminance increases by about 2.7 times not only in the region H where it is desired to increase the brightness of the high luminance but also in the low gradation region L where noise is conspicuous due to the increase in luminance. Accordingly, although the contrast of the image is improved, there are disadvantages due to the luminance increase such as black floating in the low gradation region.

  Therefore, in the embodiment according to the present invention, the light emission duty of the LED is controlled by the power limit control, and the duty of the LED in the low gradation region where it is not desired to further increase the screen brightness from the state where the duty is uniformly increased within the allowable power range. Reduce brightness.

Specific processing examples of the area active control unit 2 and the LED control unit 3 according to the present invention will be described. FIG. 5 shows an example in which the display screen is divided into eight. Each divided region No. Are A to H, and indicate the maximum gradation value of the image for each region. The maximum gradation value corresponds to the first feature amount of the present invention. As described above, the first feature amount is the maximum gradation value for each region, but other statistical values such as an average of the gradation values in the region may be used.
In this example, the maximum gradation value of the video in the eight divided areas is 64, 224, 160, 32, 128, 192, 192, 96, and the average of the maximum gradation values is 53 for 256 gradations. % Value. That is, in this case, it corresponds to a lighting rate (window size) of 53% in the graph of FIG.

In FIG. 2, it is assumed that when the lighting rate is 53% (P4), the duty of the LED corresponding to the luminance of the backlight in the region where the maximum luminance can be obtained is 55%. That is, when the lighting rate on the screen is 53%, the backlight can be raised to 55% duty by power limit control. This corresponds to about 1.5 times the duty of 38.5% when fully lit (lighting rate 100%).
In other words, when the LED duty is 38.5% when the LEDs are fully lit, when the lighting rate is 53%, power is supplied to the lighting LEDs so that the brightness is 1.5 times that of 38.5%. Can do.

FIG. 6 is a diagram illustrating a state in which the areas illustrated in FIG. 5 are arranged in the order of the area numbers. The horizontal axis represents the region No. The vertical axis represents the luminance value of the LED in each region. The luminance value of the LED can be represented by a gradation value (LED gradation) of 0-255, for example.
First, the luminance value of the LED for each region is determined by the same method as in the conventional local dimming control. This luminance is the first luminance. The first luminance is determined to be relatively small in the region where the maximum gradation value of the image is small, and relatively large in the region where the maximum gradation value of the image is large (similar to FIG. 15B). ). Thus, as in the prior art, low gradation black floating is avoided, the contrast is improved and the power consumption is reduced, and the brightness in the high gradation region is increased to increase the brightness. At this time, the brightness of the LEDs in each region is set so as not to exceed the screen brightness (for example, 450 cd / m ² ) when all the LEDs are turned on.

  Then, the brightness value calculated by the power limit control as described above (here, 1.5 times) is multiplied by the brightness value of the LED in each region. Here, all areas are uniformly multiplied by a value corresponding to the brightness increase. The LED duty when the LEDs are fully lit is 36.5%, but when the lighting rate is 53%, the brightness of the LEDs increases to a duty of 55%. A state in which the first luminance is multiplied by 1.5 corresponds to the vertex position of the histogram data of each region shown in FIG. This luminance value is set as the second luminance (V2).

As a feature of the embodiment according to the present invention, the second luminance (V2) of each region is compared with a predetermined threshold (LED gradation value) Th, and the second luminance (V2) is smaller than the threshold Th. For the region, the second luminance (V2) is further reduced by a predetermined amount. For example, when the threshold Th is 80 gradations, the brightness of the LEDs in the second brightness (V2) region smaller than 80 gradations is reduced. The reduction value is, for example, 1 / 1.5 = 0.68 times. That is, 1.5 times the first luminance value (first luminance) (second luminance) is again multiplied by 0.68 to obtain the third luminance (V3). As a result, the brightness value (first brightness) of the original LED is restored.
In the control of the LED backlight, the LED is controlled using the second luminance (V2) in the region where the maximum gradation value is equal to or greater than the threshold Th. In the region where the maximum gradation value is smaller than the threshold value Th, the LED is controlled using the third luminance (V3). As a result, in a low gradation image area having a maximum luminance value smaller than the threshold value Th, even when power is applied to the LED by power limit control, the luminance of the LED is not excessively increased and noise is not conspicuous. It is possible to eliminate the deterioration of black float.

  At this time, if the third luminance (V3) is made to coincide with the first luminance, the first luminance is applied to the region having the maximum gradation value smaller than the threshold even in the luminance control by the power limit. Can be returned to. This is an effective measure when, for example, the image is very noisy, or conversely, since the quality of the image is high, a slight increase in the amount of noise becomes a problem.

  In addition, as described above, the first luminance of the LED is uniformly increased to the second luminance by the power limit control, and the second luminance is compared with the threshold Th and has a maximum gradation value smaller than the threshold Th. In the case of lowering the luminance of the LED, the LED may be made closer to the first luminance without matching the first luminance. For example, the third luminance is set to fall within a predetermined range of the first luminance. Therefore, the first luminance and the third luminance do not coincide with each other and become close values.

  For example, in the above example, when the lighting rate is 53%, the increase from the first luminance to the second luminance is about 2.7 times. On the other hand, it is said that the noise in the video can be recognized by the viewer when the luminance increases by 3 dB (1.4 times), and the noise becomes conspicuous when the luminance increases by 6 dB (2 times).

  Therefore, in order to make the noise inconspicuous even when the luminance is increased by 2.7 times, it is conceivable to reduce the luminance to twice the original luminance (first luminance). For example, when the rate of increase from the first luminance to the second luminance is 2.7 times due to the power limit control, the second luminance is set for the region having the maximum gradation value smaller than the predetermined threshold. The third luminance is obtained by multiplying by 0.74. As a result, the third luminance is twice the value of the first luminance. When the increase rate from the first luminance to the second luminance is twice or less, the luminance is maintained as it is, and the luminance is not lowered to a lower luminance. Further, if the noise is further suppressed and the luminance increase in the low gradation region is suppressed to 3 dB, the second luminance is reduced to 0 when the increase from the first luminance to the second luminance is 2.7 times. When multiplied by .52, the third luminance is about 1.4 times (3 dB) the first luminance. Thus, by setting the third luminance within a predetermined range of the first luminance, it is possible to suppress the noise and obtain a high-quality image.

As described above, in the embodiment according to the present invention, the brightness of the low gradation LED is used to improve the contrast and reduce the power saving based on the maximum gradation value (first feature amount) of the divided area of the video. With respect to the first luminance that has been reduced, power is supplied to the LED by power limit control to increase the second luminance, and the second luminance is compared with the threshold Th, and the maximum gradation value smaller than the threshold is set. The luminance of the LED in the area is reduced to a third luminance. At this time, by increasing the third luminance to the first luminance, it is possible to eliminate an increase in noise due to the luminance increase from the first luminance to the second luminance.
Further, even if the third luminance is reduced to a predetermined range of the first luminance, for example, about twice the first luminance without reducing the third luminance to the first luminance, the effect of making the noise inconspicuous Can be obtained. Furthermore, the third luminance may be lowered to a luminance lower than the first luminance. In this case, the noise of the original video can be made less noticeable.

  Further, when the second luminance is reduced to the third luminance, the luminance of the LED is not reduced uniformly at a constant magnification among the divided regions having the maximum gradation value smaller than the threshold Th. Depending on the value of the brightness, the reduction rate (or amount of decrease) of the brightness of the LED may be varied. For example, in the region having the maximum gradation value smaller than the threshold Th, the region where the second luminance is lower increases the LED luminance reduction magnification or increases the amount of reduction. At this time, in the region where the second luminance is small, the LED luminance is made to coincide with the first luminance, or the luminance of the LED is lowered to the vicinity of the first luminance, and in the region where the second luminance is relatively large, for example, The brightness of the LED is reduced to about twice the brightness of 1. As a result, it is possible to obtain the effect of increasing the brightness due to the power limit while suppressing the occurrence of noise.

  In addition, in the region where the maximum gradation value is smaller than the threshold Th, the luminance of the LED is lowered so as to approach the first luminance as the second feature amount (APL or the maximum gradation value of the image) is smaller. May be. For example, in an image having a relatively high APL, in an area where the maximum luminance value is smaller than the threshold value, the noise of the LED is returned to a predetermined range, for example, about twice the first luminance without returning the LED luminance to the first luminance. A reduction effect can be obtained. Since the gradation value is originally low in the region where the APL is small, the noise is reduced by returning to the first luminance. Thereby, in the region where APL is high, it is possible to suppress the conspicuous noise while maintaining the video expression without excessively suppressing the LED luminance. The same applies to the case where the maximum gradation value of the video is used as the second feature amount.

  As shown in FIG. 6, the luminance of the LED in the region having the maximum gradation value smaller than the threshold value Th is reduced by adopting any of the above-described methods. Then, as shown in FIG. 7, the obtained LEDs are rearranged in ascending order of brightness. Then, a gradation curve is created in which the maximum gradation value of each region is input and the luminance of the LED of each region is output.

  FIG. 8 is a diagram illustrating an example of the obtained gradation curve, in which the horizontal axis indicates the LED gradation value (input gradation) corresponding to the second luminance, and the vertical axis indicates the LED gradation corresponding to the third luminance. The value (output gradation) is shown. Before correction means a gradation curve when the second luminance is output without being corrected to the third luminance, and after correction is when the second luminance is corrected to the third luminance according to the threshold value. The gradation curve is shown.

  As shown in FIG. 8, in the corrected gradation curve, in the case of a low gradation area smaller than a predetermined threshold, control is performed to reduce the luminance of the LED whose luminance is increased by the power limit again. In other words, only in a low gradation region smaller than the predetermined threshold, the luminance of the LED is not increased, and is maintained at the same level as the luminance of the original LED (first luminance) or in a nearby level. As a result, the luminance of the LED is not excessively increased only in a predetermined low gradation region, the expression of noise on the display can be suppressed, and a video expression with a more brilliant feeling can be obtained in the high luminance region. It becomes possible.

  In addition, the threshold value may be determined according to the number of areas in the divided area where the luminance is reduced. For example, the threshold value can be set so that the second luminance is reduced to a third luminance by a predetermined number from the region having the lowest maximum gradation value among the plurality of divided regions. For example, the third luminance is set for only two of the eight divided areas. As a result, for a certain number of low-luminance regions, it is possible to suppress an increase in the luminance of the LEDs and prevent noise from being noticeable.

The threshold value Th may be dynamically changed according to the feature amount of the video. As the feature amount, APL (Average Picture Level) of the video, maximum gradation value (peak value), or the like can be used. These feature amounts are set as a second feature amount according to the present invention.
Here, the LED data is generally the maximum gradation value of the video signal in the divided area as described above. APL is an average value of the luminance of the video signal, and is generally an average value of the entire video, not an average value of a specific area of the video. APL therefore changes dynamically from frame to frame.

For example, the threshold Th can be dynamically changed according to the APL of the video.
FIG. 9 is a diagram illustrating an example of an image with an APL of 50%. The horizontal axis is the division area number. The vertical axis indicates the luminance value of the LED in each region. The vertex position of the histogram data of each region indicates the maximum gradation value (first feature amount) of each region.
In general, there is a certain degree of correlation between the APL of the video and the maximum gradation value of the divided area, but it varies greatly depending on the video. For example, in the case where there are many locations where the difference in luminance is large in the video, the maximum gradation value may exceed the APL value in all the divided regions.

FIG. 9 shows an image with a relatively small contrast. The entire image is flat and the difference in brightness is small. For example, in a room or in a foggy image, the image is in this state. In this case, the difference between APL and the maximum gradation value of each region is small.
Since APL is an average value of the luminance of the entire image, the region where the maximum gradation value is lower than APL is a region where there are few shining portions in the region and the luminance should be lowered. Therefore, in the areas of NoA and B, control is performed such that the brightness of the LED whose brightness is increased by the power limit is lowered again. Specifically, for the region having the maximum gradation value smaller than the APL of the video, the threshold value is set so that the second luminance value of the region is smaller than the threshold value. The amount of reduction follows any of the above processing examples.

  FIG. 10 shows an example of an image having an APL of 50% and a relatively high contrast. This example is an image that often exists, and the difference between APL and the maximum gradation value of each region is larger than the example of FIG. When the threshold value is set so as to decrease the luminance of the LED in the region where the maximum gradation value is smaller than APL, region No. In A to C, control is performed such that the luminance of the LED whose luminance is increased by the power limit is decreased again.

FIG. 11 shows an example of an image in which the APL is 50% and the contrast of the entire image is extremely large. This example is a video with a large sharpness. For example, such a video is displayed when the outside is projected through a grid or when many white objects are arranged on a black background. In this case, the maximum gradation value exceeds APL in all regions.
Here, since the maximum gradation value is greater than or equal to APL in all the regions, control for reducing the luminance of the LED whose luminance has been increased by the power limit is not performed for any region. That is, for a region having a maximum gradation value larger than the APL of the video, the threshold value is set so that the second luminance value of the region is equal to or greater than the threshold value.
Thus, by setting the threshold value Th to APL and dynamically changing the threshold value according to the APL, it is possible to perform appropriate LED brightness control according to the state of the video.

  The threshold value Th may be fixed to a constant value regardless of the state of the video. For example, in FIGS. 12 to 14, 33% of the luminance that can be obtained for the images of FIGS. 9 to 11 is set as a fixed value, and the luminance of the LED is decreased in an area having a maximum gradation value smaller than the fixed value. Set the threshold. That is, for a region having a maximum gradation value smaller than 33% of the luminance that the video can take, the threshold value is set so that the second luminance value of the region is smaller than the threshold value.

  As described above, when the brightness of the LED is increased by the power limit, noise becomes a problem in the low brightness area of the video signal. For example, when the entire video signal is divided into high, medium, and low luminance, approximately 33% or less is a low luminance image. By reducing the second luminance to the third luminance with respect to the region having this value as the maximum gradation value, only the region having the low gradation maximum gradation value, regardless of the state of the entire image. Then, it is possible to perform control such that the brightness of the LED whose brightness is increased by the power limit is lowered again.

  In the example of FIG. 12, since the maximum gradation value of all the regions is a fixed value of 33% or more, the control for reducing the luminance of the LED whose luminance is increased by the power limit again is performed for any region. I will not. Further, in the example of FIG. 13, control is performed to reduce again the brightness of the LEDs whose brightness has been increased due to the power limit in the areas A and B.

Further, in the example of FIG. 14, the maximum gradation value of all the areas is a fixed value of 33% or more as in FIG. 12. It is not done for regions.
In this way, the low gradation area where noise is conspicuous is determined by the fixed value of the video signal, and the brightness of the gradation area where noise is conspicuous is not increased regardless of the state of the video signal. The shine of the key part can be constantly increased.

DESCRIPTION OF SYMBOLS 1 ... Image processing part, 2 ... Area active control part, 3 ... LED control part, 4 ... LED driver, 5 ... LED backlight, 6 ... Liquid crystal control part, 7 ... Liquid crystal panel.

Claims (11)

A display panel that displays a video signal; a backlight that uses an LED as a light source that illuminates the display panel; and a control unit that controls the light emission luminance of the backlight. A video display device that divides into a plurality of regions and controls the light emission of the LED for each of the divided regions,
The control unit determines a first luminance of the LED for each region according to a first feature amount of a video of a display region corresponding to each of the divided regions,
Further, for each region obtained by multiplying the first luminance uniformly by a constant magnification within a range in which the total value of the LED driving currents is equal to or less than a predetermined allowable current value with respect to the first luminance for each region. The second brightness of
Further, the second luminance for each region is compared with a predetermined threshold, and only for the region where the second luminance is lower than the threshold, the second luminance is reduced again to the third luminance,
An image display apparatus, wherein light emission of an LED is controlled for each divided region using the third luminance and the second luminance in a region where the second luminance is not reduced. The video display device according to claim 1,
The video display device according to claim 1, wherein the third luminance for each region matches the first luminance for each region. The video display device according to claim 1,
3. The video display device according to claim 1, wherein the third luminance for each region is within a predetermined range including the first luminance of each region. The video display device according to any one of claims 1 to 3,
The video display device, wherein the control unit sets the threshold value as a fixed value. The video display device according to any one of claims 1 to 3,
The video display device, wherein the control unit sets the threshold according to a second feature amount of video. The video display device according to any one of claims 1 to 3,
The video display device, wherein the control unit sets the threshold value so that the number of regions for reducing the second luminance to obtain the third luminance is a predetermined number. The video display device according to claim 5,
When the controller reduces the second brightness by the threshold, the controller reduces the second brightness so that the video having a smaller second feature amount approaches the first brightness. A characteristic video display device. The video display device according to claim 5 or 6,
When the control unit lowers the second luminance by the threshold value, a region where the second luminance is smaller among regions where the second luminance is lower than the threshold value approaches the first luminance. As described above, the video display device is characterized in that the second luminance is lowered.   9. The video display device according to claim 1, wherein the first feature amount is a maximum gradation value of a video signal in the divided area.   8. The video display device according to claim 5, wherein the second feature amount is an APL of the video.   8. The video display device according to claim 5, wherein the second feature amount is a maximum gradation value for each frame of the video.

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