JP2007299001A - Liquid crystal display device - Google Patents

Liquid crystal display device Download PDF

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JP2007299001A
JP2007299001A JP2007153722A JP2007153722A JP2007299001A JP 2007299001 A JP2007299001 A JP 2007299001A JP 2007153722 A JP2007153722 A JP 2007153722A JP 2007153722 A JP2007153722 A JP 2007153722A JP 2007299001 A JP2007299001 A JP 2007299001A
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luminance
brightness
apl
light source
video signal
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Inventor
Seiji Kobashigawa
Hironari Sekiguchi
Yuichiro Yamaguchi
誠司 小橋川
祐一郎 山口
裕也 関口
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Sharp Corp
シャープ株式会社
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Abstract

An object of the present invention is to perform an optimal video expression according to a change in a feature amount of a video signal without reducing display quality, and to realize a reduction in power consumption.
A liquid crystal display device includes a liquid crystal panel that displays an image and a light source that illuminates the liquid crystal panel. When the feature amount of an input video signal is smaller than a predetermined value C1, the feature amount of the light source decreases as the feature amount decreases. The light emission luminance of the light source is variably controlled so as to reduce the light emission luminance. Here, the feature amount of the input video signal is a ratio of the average luminance level in one frame to the maximum luminance level of the input video signal. The predetermined value C1 is set such that the ratio of the average luminance level in one frame to the maximum luminance level of the input video signal is in the range of 2.0% to 12.2%.
[Selection] Figure 4

Description

  The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device in which the light emission luminance of a backlight light source is changed in accordance with an input video signal.

  In a liquid crystal display device having a liquid crystal panel that modulates light source light according to a video signal and a backlight light source for illuminating the liquid crystal panel, by controlling the emission luminance of the backlight light source according to the input video signal A technique for improving the quality of display video is known.

  For example, an average luminance level (Average Picture Level (hereinafter referred to as “APL”) in one frame is calculated as a feature amount of the input video signal, and the emission luminance of the backlight light source is adjusted according to the APL. By analyzing the luminance level histogram of the input video signal, etc., by adjusting the emission luminance of the backlight light source based on the maximum luminance level and the minimum luminance level among the luminance levels of the pixels in one frame of the backlight, Some devices adjust the light emission luminance of the light source.

For example, in Patent Document 1, in order to provide an image with optimal screen brightness to an observer, the visual contrast is improved while avoiding black floating interference, and a high-quality image with glossiness is reproduced. A liquid crystal display device is disclosed. The liquid crystal display device of Patent Document 1 detects the APL of the input video signal and controls the luminance of the backlight light source according to the detected APL. Further, the peak value of the input video signal is detected, and the control characteristic of the light emission luminance of the backlight light source is corrected according to this peak value.
JP 2004-258669 A

In recent liquid crystal display devices, improvement in display quality and reduction in power consumption of a backlight have become major issues as the size of the device increases.
For example, when displaying an image with a very small APL, which is the feature amount of the video signal, it is possible to reduce the light emission luminance of the backlight light source without impairing display quality.

  Therefore, when displaying an image with a very small APL, which is the feature amount of the video signal as described above, power consumption can be reduced by appropriately reducing the light emission luminance of the backlight light source.

  However, in the thing of the said patent document 1, paying attention to the feature-value of a video signal, the device technical idea of reducing power consumption, maintaining the quality of a display image is not made | formed at all, and display quality is not made. There is a problem that power consumption cannot be reduced without lowering.

  The present invention has been made in view of the above-described circumstances, and when controlling the light emission luminance of the backlight light source according to the feature amount of the video signal, the power consumption is also reduced without degrading the display quality. An object of the present invention is to provide a liquid crystal display device capable of realizing the above.

  In order to solve the above-described problem, the first technical means includes a liquid crystal panel for displaying an image and a light source for illuminating the liquid crystal panel, and the feature is obtained when the feature amount of the input video signal is smaller than a predetermined value. A liquid crystal display device that variably controls the light emission luminance of the light source so as to reduce the light emission luminance of the light source as the amount decreases, wherein the feature amount of the input video signal is within one frame with respect to the maximum luminance level of the input video signal. The predetermined value is set such that the ratio of the average luminance level in one frame to the maximum luminance level of the input video signal is in the range of 2.0% to 12.2%. It is characterized by being.

  According to the present invention, when controlling the light emission luminance of the backlight light source according to the feature amount of the input video signal, it is possible to realize further reduction in power consumption without degrading the display quality.

  According to the embodiment of the liquid crystal display device according to the present invention, an average picture level (APL) in one frame of the video signal is used as the feature amount of the input video signal. And the brightness | luminance control table for controlling the light emission brightness | luminance of a backlight light source according to APL is hold | maintained. In the liquid crystal display device, the APL of the video signal to be displayed is detected, and the backlight is controlled so that the light emission luminance corresponding to the detected APL is obtained using the luminance control characteristic of the luminance control table. At this time, when a video signal with a very small APL or a video signal with a very large APL is input, the display quality (luminance, contrast, sharpness, etc.) of the displayed video is maintained by appropriately controlling the light emission luminance of the backlight light source. While reducing the power consumption of the backlight.

Furthermore, the display quality of the display image (brightness, contrast, sharpness) is changed by changing the control characteristic of the light emission luminance of the backlight light source for APL according to the light control mode of the liquid crystal display device or according to the brightness around the liquid crystal display device. ), While reducing the power consumption of the backlight.
Hereinafter, embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

  FIG. 1 is a block diagram for explaining a configuration of an embodiment of a liquid crystal display device according to the present invention. The tuner 12 of the liquid crystal display device 1 selects a broadcast signal received by the antenna 11. The decoder 13 decodes and demultiplexes the broadcast signal selected by the tuner 12 and outputs a video signal for driving the liquid crystal panel 20.

  The video signal separated by the decoder 13 is input to an LCD controller 19 that drives and controls the liquid crystal panel 20 after various video processes are performed by the video processing unit 18. The LCD controller 19 outputs a liquid crystal drive signal to a gate driver and a source driver (not shown) of the liquid crystal panel 20 based on the input video signal, whereby an image according to the video signal is displayed on the liquid crystal panel 20.

  The video signal separated by the decoder 13 is also output to the APL measurement unit 14. The APL measurement unit 14 measures the APL for each frame of the video signal output from the decoder 13. The measured APL is sent to the filter 15. APL corresponds to one of the feature quantities of the video signal in the present invention, and will be expressed as a ratio (%) to the maximum luminance level below. In the present embodiment, light emission luminance control of the backlight unit 17 according to APL is performed based on the luminance control characteristics of the luminance control table 23.

  In the example shown in FIG. 1, the APL is measured by the video signal decoded by the decoder 13, but the APL may be measured after the video processing by the video processing unit 18. However, the video processing unit 18 may perform, for example, OSD (on-screen display) display processing, scaling processing, or letterbox display (screen area restriction by a black mask or the like) processing. Here, the APL is measured from the video signal output from the decoder 13 (that is, the video processing by the video processing unit 18 is not performed), so that the input video signal is not affected by the video processing by the video processing unit 18. It is possible to control the backlight luminance corresponding to the above. Therefore, it is more preferable to measure APL from the video signal before video processing as shown in FIG.

  For example, as shown in FIG. 2, the backlight unit 17 is configured by arranging a plurality of thin fluorescent tubes 31 at equal intervals in a housing 30 attached to the back surface of the liquid crystal panel 20. Further, the diffusing plate 32 uniformly diffuses the illumination light emitted from the fluorescent tube 31.

  In this case, for example, the backlight unit 17 performs pulse width modulation in which the signal period ratio (duty) of the high potential level and the low potential level of the rectangular wave changes according to the backlight luminance adjustment signal input from the backlight control unit 16. A dimming control circuit for outputting the output as a dimming signal, and receiving a dimming signal from the dimming control circuit, generating an alternating voltage with a period and voltage corresponding to the dimming signal, and applying this to the fluorescent tube 31 And an inverter (all not shown) that is driven to light. The inverter operates when the output of the dimming control circuit is at a high potential level, stops operating when the output is at a low potential level, and performs an intermittent operation in accordance with the output duty of the dimming control circuit. The brightness is adjusted.

  As shown in FIG. 3, the backlight unit 17 includes a plurality of LED light sources including three primary colors of red, green, and blue, that is, a red light source 41, in a housing 30 attached to the back surface of the liquid crystal panel 20. A green light source 42 and a blue light source 43 may be provided. The light emission luminance of the LED light source can be controlled by the LED current for each LED light source. Although not shown, a backlight unit 17 that uses a combination of a fluorescent tube and an LED as described above can also be applied. Furthermore, the liquid crystal panel 20 may be illuminated by a so-called side edge type configuration in which light from a light source such as a fluorescent tube or an LED is made uniform by using a light guide plate.

  The luminance control table 23 defines the relationship of the light emission luminance of the backlight light source according to the feature amount (APL in this case) of the video signal for each frame of the input video signal. A luminance control table 23 is stored in advance in a table storage memory 22 such as a ROM, and the light emission luminance of the backlight unit 17 is controlled by the luminance control table 23 according to the APL detected from the input video signal to be displayed. .

  The filter 15 regulates the follow-up of the light emission luminance of the backlight light source with respect to the APL change between frames when the backlight luminance is controlled according to the measured value of APL, and is constituted by, for example, a multistage digital filter. ing.

  The filter 15 receives the APL for each frame measured by the APL measurement unit 14, and performs a weighted average according to each weight between each frame and the APL for one or more frames in the past. An operation is performed to calculate the output APL. Here, the number of past frame steps to be reflected on the frame can be variably set, and weights are set for each of the current frame and the past frame (for the set number of steps). Then, the APL of the current frame and the APL of the delay frame corresponding to the number of used stages are weighted and averaged according to the respective weights and output. Thereby, the followability of the output APL according to the actual APL change can be set as appropriate.

  The APL output from the filter 15 is input to the backlight control unit 16. Based on the luminance control table 23 to be used, the backlight control unit 16 outputs a backlight luminance adjustment signal for adjusting the backlight luminance according to the input APL, and controls the light source emission luminance of the backlight unit 17.

The liquid crystal display device 1 also includes a remote control light receiving unit 25 for receiving a remote control signal transmitted from the remote control device 27. The remote control light receiving unit 25 is constituted by a light receiving LED for receiving a remote control operation signal using infrared rays, for example.
The remote control operation signal received by the remote control light receiving unit 25 is input to the microcomputer 21, and the microcomputer 21 performs predetermined control according to the input remote control operation signal.

  The liquid crystal display device 1 also has a dimming mode function for dimming the brightness of the display screen of the liquid crystal panel 20 in response to a user operation on a predetermined operation means such as the remote control device 27. The dimming mode function dimmes the brightness of the display screen of the liquid crystal panel 20 by changing the light source emission luminance of the backlight unit 17 in accordance with a user operation.

  Specifically, the microcomputer 21 outputs a luminance adjustment coefficient in accordance with a user operation for a predetermined operation. The brightness adjustment coefficient is used for setting the brightness of the entire screen in accordance with a user operation. For example, screen brightness adjustment items are set on a menu screen or the like held by the liquid crystal display device 1. The user can set an arbitrary screen brightness by operating the setting item. The microcomputer 21 recognizes the brightness setting and outputs a brightness adjustment coefficient to the multiplier 26 according to the set brightness. The multiplier 26 illuminates the backlight unit 17 with the brightness according to the brightness setting by multiplying the brightness control value by the brightness control table 23 currently used by the brightness adjustment coefficient.

  Alternatively, a plurality of luminance control tables 23 corresponding to the brightness setting in the dimming mode are prepared in the table storage memory 22, and the microcomputer 21 recognizes the brightness setting in the dimming mode, and You may make it select the brightness | luminance control table used for control. Further, when changing the brightness control table, a plurality of brightness control tables may be obtained between the brightness control table after the change by calculation or the like, and the brightness control table may be changed step by step.

Further, the liquid crystal display device 1 includes a brightness sensor 24 as brightness detection means for detecting the brightness around the liquid crystal display device 1 (ambient illuminance). As the brightness sensor 24, for example, a photodiode can be applied. In the brightness sensor 24, a DC voltage signal corresponding to the detected ambient light is generated and output to the microcomputer 21.
The microcomputer 21 outputs a brightness adjustment coefficient to the multiplier 26. The multiplier 26 turns on the backlight unit 17 with the brightness according to the brightness around the apparatus by multiplying the brightness control value by the brightness control table 23 currently used by the brightness adjustment coefficient.

  Alternatively, a plurality of brightness control tables 23 corresponding to the brightness around the device are prepared in the table storage memory 22, and the microcomputer 21 recognizes the brightness around the liquid crystal display device and controls the backlight unit 17. You may make it select the brightness | luminance control table to be used. Further, when changing the brightness control table, a plurality of brightness control tables may be obtained between the brightness control table after the change by calculation or the like, and the brightness control table may be changed step by step.

  FIG. 4 shows an example of the luminance control characteristic of the backlight light source using the luminance control table. In FIG. 4, the horizontal axis represents APL as a percentage. When the display image is all black on the entire screen, APL is 0%, and when it is all white, APL is 100%. The vertical axis represents the light emission luminance ratio of the backlight light source, which is 100% when the light emission luminance of the backlight light source is brightest, and 0% when the backlight light source is turned off.

  The luminance control characteristics shown in FIG. 4 are based on a signal region having a low APL indicated by A, a signal region having an intermediate level of APL indicated by B and C, and a signal region having a high APL indicated by D. This represents changing the luminance control characteristic of the light source. Here, a point at which the slope of the luminance control characteristic of the backlight light source changes with respect to the feature amount (APL in this example) of the video signal is defined as a characteristic change point. In FIG. 4, the intersections p1, p2, and p3 of the straight lines of the four regions A to D serve as characteristic change points, and the APL value of p1 is set to a first predetermined value C1 and a second predetermined value C2, and p3 Is set to a third predetermined value C3. Here, the predetermined value of the present invention corresponds to the first predetermined value C1. Note that FIG. 4 shows a luminance control characteristic that maximizes the light emission luminance of the backlight light source at one point of the APL value (= C1) at which the feature change point p1 is set. For example, the luminance control characteristic shown in FIG. When there is an APL region (C1 to C2) in which the light emission luminance of the backlight light source is constant at the maximum value, the lowest APL side APL value in the APL region is set to the first predetermined value C1. And the APL value on the highest APL side is the second predetermined value C2. That is, in the case of the luminance control characteristics of FIG. 4, CPL = C2 because the APL indicating the maximum value of the light emission luminance of the backlight light source is only one point.

  In the region (region A) where the feature amount of the video signal is extremely small, there are many videos that can maintain the display quality of the video even if the luminance of the backlight light source is lowered, as will be described later. This is because there are many images that have a low contrast on the entire screen and are not easily affected by the backlight luminance. Further, such video tends to increase as the feature amount of the video signal decreases. Therefore, the luminance of the backlight light source can be lowered as the feature amount of the video signal is smaller. In the area A, the emission luminance decreases as the APL decreases from the characteristic change point p1 of the maximum luminance of the backlight light source.

  Next, in the region (region D) where the feature amount of the video signal is extremely large, there are many videos that can maintain the display quality of the video even if the luminance of the backlight light source is lowered, as will be described later. Further, the feature amount of such a video signal tends to increase as the feature amount increases. This is because as the feature amount of the video signal increases, the brightness of the entire video increases, and sufficient video display quality can be maintained even if the luminance of the backlight light source is reduced. Therefore, the luminance of the backlight light source can be lowered as the APL increases. In region D, the emission luminance decreases as the APL increases from the luminance characteristic change point p3 of the backlight light source.

  Next, in the regions B and D, as in the conventional technique described above, the light emission luminance of the backlight light source is increased in the vicinity of the feature change point p1 to improve the contrast, and the light emission of the backlight light source in the vicinity of the feature change point p3. Reduce brightness to reduce unnecessary glare. Between the characteristic change points p1 and p3, the luminance characteristic of the backlight light source is appropriately determined according to the contrast feeling or the like.

  In determining the characteristic change points p1 and p3, a subjective experiment was conducted on the relationship between the light emission luminance of the backlight light source and the display quality of the video, and the relationship between the luminance control characteristic of the backlight light source and the power consumption was examined. . The subjective experiment quantified the relationship between the APL value of the input video signal and the influence of the light emission luminance of the backlight light source when the input video signal is displayed and output.

Specifically, multiple images of each APL value are prepared, and while displaying each image, the video display quality when the luminance of the backlight light source is switched between high and low is observed. Whether or not the light emission luminance of the light source needs to be high was determined by a five-step evaluation. The criteria for the five-level evaluation were as follows, and the experiment was performed by five subjects, and the average was taken.
5 Clearly high brightness required 4 High brightness required to some extent 3 Neither can be said 2 Very high brightness is not required 1 Clearly high brightness is not required

  The result of the experiment is shown in FIG. The X-axis is the APL value of the video, the Y-axis is the video evaluation value, and is the average value of subjective evaluation values related to video display quality. This indicates that the higher the Y-axis value is, the higher the luminance of the backlight light source must be in order to maintain the display quality of the video.

  First, in an area where APL is 2% or less and 90% or more, the video evaluation value is 1, and it was determined that high luminance is clearly unnecessary for evaluation. In other words, high brightness is unnecessary for all images belonging to this range. This is probably because APL of 2% or less is not recognized as an image, and an image having an APL of 90% or more is almost white on the entire screen, so it is determined that the necessity of high brightness is not felt.

  Next, in the region where APL is 2% to 25%, as the APL value increases, the necessity of high luminance increases almost linearly, and when the APL is around 12%, the image that requires high luminance is half. It became about. This seems to be because there are few images that require high brightness when the APL is near 12% or less, and there are many images that require high brightness when the APL is near 12% or more.

  When the APL is around 25%, almost all images need to have high brightness. This seems to be because almost all images require high brightness because contrast is required for details as images.

  Next, in the region where the APL is 30% to 90%, the necessity for high luminance gradually decreases. As with images with APL around 30%, most images need to have high brightness as well as images with APL around 25%, but when APL changes from 30% to 90%, the screen gradually becomes dazzling. When the APL is around 68%, about half of the video does not need to have high brightness, and when the APL is 90%, most of the video does not need to have high brightness. This seems to be because there is a high need to make it. In addition, it is considered that the judgment as to whether or not the image requires high luminance varies depending on whether the APL is near 68% or more.

Next, the evaluation results regarding the video display quality in the low APL region and the high APL region were approximated by a straight line or a quadratic curve. When approximating APL 25% or less with a linear line,
y = 0.20x + 0.61
Thus, the APL value when the video evaluation value is 3 is 12.2%. That is, if the first predetermined value C1 is set to 12.2% or less, it can be said that the minimum video display quality can be maintained.

Approximating APL 30% to 90% with a quadratic curve,
y = −0.0008x ^ 2 + 0.030x + 4.71
Thus, the APL value when the video evaluation value is 3 is 68.2%. That is, if the third predetermined value C3 is set to 68.2% or more, it can be said that the minimum video display quality can be maintained.

  Next, the relationship between the luminance control characteristic of the backlight light source and the power consumption will be described. Based on the distribution of APL extracted from an arbitrary video, the power reduction amount when the value of the feature change point p1 in the luminance control characteristic of the backlight light source was changed from 0 to 25 was calculated. The amount of decrease in luminance of the backlight light source on the low APL side (region A) from the feature change point p1 was 15% per 10% change in APL. This is because if the luminance change of the backlight light source per 10% change of APL exceeds 15%, the luminance change becomes abrupt, and the viewer may feel uncomfortable. The video to be measured was a movie. This is because a movie is video content that viewers care most about video quality, and the frequency of low APL is greater than other content.

  The result of the measurement is shown in FIG. The X axis is the value of C1, which is the APL value of the feature change point p1, and the Y axis is the power reduction amount based on the case where the value of C1 is 0. From FIG. 13, when C1 = 0, the reduction amount is zero, and the power reduction amount increases as C1 increases. When the value of C1 is 10%, the power reduction amount is about 1%, and the value of C1 is further increased. It can be seen that the power reduction amount increases non-linearly by setting to the high APL side, and when the value of C1 is 25%, the power reduction amount is about 7.7%.

  The above experiment and the power calculation result will be considered. In this type of product, reduction of power consumption and improvement of video display quality are important issues. Therefore, in order to reduce power consumption without degrading the display quality of the video, the video evaluation value is an area where there are many videos where the luminance of the backlight light source should not be lowered in order to maintain the display quality of the video. Is an area where the image evaluation value is 3 or less, which is an area where there is no problem in display quality of the image even if the light emission luminance of the backlight light source is reduced without reducing the light emission luminance of the backlight light source. For the above, it is sufficient to reduce the light emission luminance of the backlight light source.

  Specifically, for images with an APL of 12.2% or less and 68.2% or more, the power consumption is reduced while maintaining the display quality of the image by further reducing the light emission luminance of the backlight light source. It becomes possible to do.

  By the way, the priority between the video display quality and the power reduction amount varies depending on the situation. The video display quality may be the highest priority, and the power reduction amount may be the highest priority. Therefore, the extent to which the values of C1 and C3 can be changed will be examined.

  As described above, the optimum value of C1 that can maximize the power reduction amount while maintaining the minimum video display quality is 12.2%. On the other hand, although there are a small number in the region where the video evaluation value is 3 or less, there is a video in which the display quality of the video is lowered when the luminance of the backlight light source is lowered. Therefore, the display quality of more images can be maintained by decreasing the value of C1. Specifically, by reducing the value of C1 from 12.2%, the number of images that can maintain the display quality of the image increases. When the value of C1 is set to 2%, the display quality for all images is reduced. Can be maintained. Therefore, it is preferable to set the value of C1 within the range of 2% to 12.2%.

  As described above, the value of C1 can range from 2% to 12.2%, and the smaller the value, the better the display quality of the entire video. On the other hand, the power reduction amount increases as the value of C1 increases. That is, there is a trade-off relationship between video display quality and power reduction. Therefore, as an actual product, it is necessary to decide whether to place importance on video display quality or power saving, and to set the value of C1 accordingly.

  Nowadays, power saving of electronic devices is an essential matter, and when a power saving effect is claimed as a product, it is considered that an effect of at least 1% or more is necessary. % And above were set. For example, the reason why the annual factory efficiency improvement target under the Energy Conservation Law is set at 1% may be because 1% is the border. When the power reduction amount is set to 1% or more, the value of C1 is 10%. Therefore, in the present embodiment, the following description will be made assuming that the value of C1 is set to 10%.

Here, in order to clarify the above-mentioned content, FIG. 14 shows the image display quality value superimposed on FIG. The video display quality is a value obtained by inverting the video evaluation value. 5 indicates that the display quality of all videos can be maintained, and 1 indicates that the number of videos that can maintain the video display quality is the smallest. . Therefore, when the value of C1 is set to 25%, the display quality of all videos cannot be maintained.
Also, by decreasing the value of C1 from 25%, the number of images that can maintain the video display quality gradually increases, and when the value of C1 is set to 2%, the display quality of all images should be maintained. It means that can be done. In particular, the video evaluation value is 3 or more when the value of C1 is set within the range of 2% to 12.2%. On the other hand, in order to make the power reduction amount 1% or more, This indicates that the value of C1 needs to be set to 10% or more.

  C3 is also examined in the same manner as C1. The optimum value for C3 is 68.2. In addition, although there are a small number of regions where the image evaluation value is 3 or less, there are images in which the display quality of the image decreases when the light emission luminance of the backlight light source is decreased. Therefore, the display quality of more images can be maintained by increasing the value of C3.

  Specifically, by increasing the value of C3 from 68.2%, the number of images that can maintain the display quality of the image increases, and when the value of C3 is 90%, the display quality for all images is increased. Can be maintained. Therefore, it is desirable to set the value of C3 within the range of 68.2% to 90%.

  As described above, the optimum value of C3 that can maximize the power reduction amount while maintaining the minimum video display quality is 68.2%. However, for the reason that the power reduction effect is less on the high APL side than on the low APL side, in this embodiment, the video display quality is maintained to the maximum, and the value of C3 is set to 90%. Will be described below.

As described above, in the example of the present embodiment, the characteristic change point p1 existing on the lowest APL side in the luminance control characteristic is set at a position where the APL is 10%, and the characteristic change point p3 existing on the highest APL side. Is set to a position where the APL is 90%.
In addition, in order to increase the light source emission brightness with a lower APL value, improve the contrast feeling, lower the light source emission brightness with a higher APL value, and reduce unnecessary glare, as in the prior art described above, A characteristic change point p2 is set at a position of 40%, and a characteristic change point p1 having an APL of 10% is set as a characteristic change point at which the light emission luminance of the backlight light source becomes maximum.

As described above, in the present embodiment, as described above, the luminance of the backlight light source in one or both of the video with the extremely small feature amount of the video signal and the video with the extremely large size is suppressed to maintain the image quality. It is characterized by reducing power consumption.
As long as such characteristics can be satisfied, the luminance control characteristics are not limited to the above example. For example, as shown in FIG. 7, there may be a signal region q in which the light emission luminance value of the backlight light source is constant in a signal region where the APL is larger than the characteristic change point p1 on the lowest APL side. Widening the signal region q increases the region where the light emission luminance of the backlight light source is higher, and increases the region where an image with a higher contrast feeling can be obtained. Therefore, the display quality of the video can be improved. In the luminance control characteristic of FIG. 7, the APL value (10%) at which the characteristic change point p1 is set corresponds to the first predetermined value C1, and the APL value (20%) at which the characteristic change point p4 is set is The APL value (90%) at which the characteristic change point p3 is set corresponds to the second predetermined value C2, and corresponds to the third predetermined value C3. As in the example of FIG. 4, the predetermined value of the present invention corresponds to the first predetermined value C1.

Further, the luminance control characteristic may be not only the linear as described above but also a non-linear characteristic. When the luminance control characteristic is nonlinear, the nonlinear luminance control characteristic is approximated to the linear luminance control characteristic, and the characteristic change point in the approximated linear luminance control characteristic is assumed, and the same as the linear luminance control characteristic described above. The brightness control of the backlight light source can be defined.
Further, the luminance control characteristic between the first predetermined value C1 and the third predetermined value C3 of the APL is such that the light emission luminance of the backlight light source is reduced as the APL is reduced. At the same time, by increasing the amplitude of the video signal, the black float may be suppressed and the contrast improved.

Next, a control example for changing the light emission luminance characteristics of the backlight light source according to the light control mode of the liquid crystal display device and the brightness around the liquid crystal display device will be described.
As described above, the liquid crystal display device 1 has a dimming mode function for dimming the brightness of the display screen displayed on the liquid crystal panel 20 in accordance with a user operation on a predetermined operation means such as the remote control device 27, and the liquid crystal display. A function of detecting the brightness around the device 1 (ambient illuminance) is provided.

  Here, the luminance control characteristic for controlling the light emission luminance of the backlight light source is changed in accordance with the setting of the dimming mode or in accordance with the change in ambient brightness. Thus, it is possible to display an image with appropriate image quality and low power consumption according to changes in these conditions. Such a change in luminance control characteristics may be executed only in accordance with the dimming mode, or may be executed only in accordance with a change in ambient brightness. Further, it may be executed depending on both conditions of the light control mode and the brightness around the apparatus. Furthermore, different brightness control characteristics may be obtained in each condition of the light control mode and the brightness around the apparatus.

  Further, the change of the luminance control characteristic at this time may be a configuration in which the luminance control value based on the luminance control table is corrected by the luminance adjustment coefficient as described above, and a plurality of luminance control tables 23 are prepared, You may make it select the brightness | luminance control table used according to conditions. Further, when changing the brightness control table, a plurality of brightness control tables may be obtained between the brightness control table after the change by calculation or the like, and the brightness control table may be changed step by step.

FIG. 8 is a diagram for explaining a setting example of luminance control characteristics used in accordance with setting of the light control mode or ambient brightness.
The brightness control characteristics of the plurality of brightness control tables are set as shown in FIG. In the example of FIG. 8, seven types of luminance control characteristics (I) to (VII) are set.
In this case, basically, the luminance of the backlight light source is decreased in the setting for dimming the screen brightness in conjunction with the user's operation for setting the light control mode. Alternatively, the light emission luminance of the backlight light source is decreased as the brightness around the liquid crystal display device becomes darker. Thereby, the glare of the screen and the irritation to the eyes can be reduced, the video can be displayed with appropriate luminance, and the power consumption can be reduced.

  In FIG. 8, the brightness control characteristic (IV) indicates a standard set value (initial value). The luminance control characteristic (IV) uses the luminance control characteristic shown in FIG. Therefore, the concept of the standard brightness control characteristic is as described above, and the control characteristic realizes low power consumption while maintaining the image quality.

Here, first, let us consider a case where light emission luminance control of a backlight light source according to APL is not performed. When there is no light emission luminance control according to APL, generally, the backlight light source is simply raised or lowered to a certain light emission luminance in the control by the light control mode or the control according to the brightness around the apparatus. Wherein placing the light emission brightness value (the dimming level) and d 2. Among them, the initial value (standard value) is d 0 , the maximum light emission brightness of the backlight light source is d max , and the minimum light emission brightness is d min .

It is assumed that emission luminance control according to APL is added to the above specifications. Then the light emission brightness value Motoma' from the curve of the brightness control property to d 1. In that case, the control based on the dimming mode / brightness around the apparatus is added by the following formula, and the final emission luminance D of the backlight source is obtained.

When the dimming level d 2 is larger than the initial value d 0 D = d 1 + (d 2 −d 0 ) {(d max −d 1 ) / (d max −d 0 )} (1)
When the dimming level d 2 is smaller than the initial value d 0 D = d 1 − (d 0 −d 2 ) {(d 1 −d min ) / (d 0 −d min )} (2)

  In accordance with the above formulas (1) and (2), the horizontal axis is APL, and the vertical axis is the light emission luminance of the backlight light source, whereby luminance control characteristics as shown in FIG. 8 are obtained.

  That is, the luminance control characteristic (I) is set to the maximum light-emission luminance of the backlight light source. In this case, the luminance control characteristic (I) is constant without depending on the APL that is the feature amount of the video signal. The luminance control characteristic (VII) is set to the minimum light-emission luminance of the backlight light source. Also in this case, the luminance control characteristic (VII) is constant without depending on the APL which is the feature amount of the video signal.

The distance between each characteristic change point of the standard luminance control characteristic (IV) and the luminance control characteristic (I) is divided into three equal parts, and the characteristic change points of the luminance control characteristics (II) and (III) are determined respectively. It is done. Similarly, the distance between each characteristic change point of the standard luminance control characteristic (IV) and the luminance control characteristic (VII) is divided into three equal parts, and the characteristic change points of the luminance control characteristic (V) and (VI), respectively. Is determined.
Among these brightness control characteristics (I) to (VII), the brightness control characteristic used for the light emission brightness control of the backlight light source is selected according to the setting of the dimming mode or according to the ambient brightness ( (Or calculated by calculation).

  By setting the brightness control characteristics, a slope is always formed between the characteristic change points in one brightness control characteristic, except for the brightness control characteristics (I) and (VII), which are set to the maximum / minimum light-emitting brightness. The user can feel the brightness change of the screen according to the APL change. For example, when the standard luminance control characteristic (IV) is translated in the light emission luminance direction, when the maximum light emission luminance or the minimum light emission luminance is close, the protruding portion of the luminance control characteristic is the maximum light emission luminance or the minimum light emission luminance. It hits and flat part is made.

  In this case, even if APL changes, the light emission luminance of the backlight light source does not change. At this time, in a plurality of luminance control characteristics, a portion where the light emission luminance level overlaps occurs. In such a case, in particular, when the luminance control characteristic is linked to the dimming mode, there is a case where the light emission luminance of the backlight light source does not change even if the dimming is performed.

  As described above, by changing the light emission luminance in multiple steps at equal intervals between the initial value and the maximum light emission luminance of the backlight light source, and between the initial value and the minimum light emission luminance of the backlight light source. When the user adjusts the light control level or adjusts the screen brightness according to the brightness of the surroundings of the device, it can be adjusted while feeling the change in brightness while watching any video .

FIG. 9 is a flowchart showing an example of an operation in which a plurality of luminance control tables are prepared and the table No. is changed to prevent an abrupt luminance change of the backlight light source. Here, an example of changing the brightness control table according to the brightness around the liquid crystal display device will be described.
First, when the brightness control table currently referenced is No. M (S1), when the brightness around the liquid crystal display device is changed by the brightness sensor (S2), the brightness control table based on the brightness is changed. The usage table number is determined to be “N” (S3).

  The luminance control characteristics of the current luminance control table M among the plurality of luminance control tables having intermediate luminance control characteristics between the luminance control table N determined in S3 and the current luminance control table M. The brightness control table n closest to is selected and updated as the current brightness control table n (S4).

  Then, it is determined whether or not the current luminance control table n is the same table as the target luminance control table N (S5). If they are not the same table, after waiting for a certain time (for example, 5 frames) (S6), the luminance control table n + 1 whose luminance control characteristic is closest to the luminance control table N next to the luminance control table n is selected (S7). Then, the selected n + 1 luminance control table is updated as the current table n (where n + 1 is updated) (S4).

  By the above processing, the stepwise change of the luminance control characteristic is repeated until the current luminance control table becomes the target luminance control table N. When the current luminance control table becomes N, the ambient brightness The switching control process of the luminance control table according to the change in the length ends.

  In the above example, the example of switching selection processing of the luminance control table according to the ambient brightness of the liquid crystal display device has been described. However, when the luminance control table is switched according to the user operation in the dimming mode, the above S2 Thus, it is determined whether or not the brightness of the screen has been changed due to the dimming mode, and the No. of the brightness control table to be used is determined based on these change conditions in step S3. As a result, the luminance control characteristics can be switched step by step until the target luminance control table to be used is reached.

FIG. 10 is a flowchart illustrating an operation example in which when the luminance control table No. is changed, the operation is gradually shifted to the luminance control table after the change by calculation. Here, the loop R of the selected portion of the luminance control table shown in FIG. 1 is used.
First, when the brightness control table No. currently referred to is S (S11), when the brightness around the liquid crystal display device is changed by the brightness sensor (S12), the brightness control table based on the brightness is used. The table number is determined (S13) (here, it is assumed that the use table number is determined to be "T").

  Then, the brightness (control value for controlling the light emission brightness of the backlight light source) with respect to the feature amount (here, APL) of the video signal of the input video signal of the current brightness control table S and the determined brightness control table T ) Is extracted, and it is determined whether or not the extracted difference is smaller than a predetermined threshold value m (S15). Here, with respect to the brightness control tables S and T, all control values for controlling the light emission brightness of the backlight light source are compared, and a difference is obtained for each comparison result.

  When it is determined that the difference is equal to or greater than the threshold value m, the light emission luminance characteristic of the current luminance control table S is corrected so as to be close to the light emission luminance characteristic of the target luminance control table T by a predetermined value, and S is changed to S ′. (S17). Then, after waiting for a certain time (for example, 5 frames) (S18), the process returns to S14 again to extract a difference between the corrected current table S (updated to S ′) and the target luminance control table T, The extracted difference is compared with the threshold value m.

  As described above, when the difference between the current brightness control table S and the target brightness control table becomes smaller than the threshold value m, the current brightness control table S is changed in steps of the brightness control characteristics. The luminance control table T is changed (S16), and the luminance control table switching selection process according to the change in ambient brightness is completed.

  Similarly, in the above example, when the luminance control table is switched by the dimming mode, it is determined whether or not the screen brightness has been changed by the dimming mode in S12, and based on these changing conditions in the step S13. The brightness control table number to be used is determined. As a result, the luminance control characteristics can be switched step by step until the target luminance control table to be used is reached.

FIG. 11 is a flowchart illustrating an operation of gradually changing to the brightness control characteristic of the table after the change by changing the brightness a predetermined number of times when the table No. is changed. Hereinafter, an operation for changing the luminance control characteristics over 256 frames will be described with reference to FIG.
When the table No. currently referred to is P (S21), when the brightness sensor detects that the brightness around the liquid crystal display device has changed (S22), the genre code after the change is changed accordingly. The corresponding usage table number is determined (here, it is assumed that the table number is determined to be Q). At the same time, the number of changes c is set to 1 (S23). Then, according to the following equation (3), the change luminance by weighting the current table P and the determined use table Q is calculated, and the luminance is corrected (S24).
Corrected luminance P ′ = (Q · c + P (256−c)) / 256 (3)

  Then, it is confirmed whether c = 256 (256 times as the set number of times has been corrected) (S25). When the set number has not been reached, the count value c is updated once (S27), and again. The current luminance is corrected to P ′ by the above equation 1. When the operations of S24 → S25 → S27 are repeated a predetermined number of times and the set number of times is corrected 256 times, the current table P is finally changed to the use table Q. In the above example, the luminance table is gradually corrected over 256 frames. However, the degree of change (transition time) can be adjusted by setting a predetermined number of times, not limited to 256 frames. . Thus, when the brightness around the liquid crystal display device changes, it is possible to prevent a sudden change in the light emission luminance of the light source.

  Similarly, in the above example, when the brightness control table is switched by the dimming mode, it is determined whether or not the screen brightness has been changed by the dimming mode in S22, and based on these changing conditions in the step S23. No of the brightness control table to be used is determined. As a result, the luminance control characteristics can be switched gradually until the target luminance control table to be used is reached.

In addition, when suppressing the light emission luminance of the backlight light source based on APL, it is not necessary to obtain the average value of the luminance levels of the video signals of all the frames in order to obtain APL. For example, the edge of the display video is excluded. An average value of luminance levels of the video signal near the center may be obtained and used as a feature amount of the video signal. For example, based on the genre information separated / obtained from the broadcast reception signal, the gate control is performed so as to exclude a preset screen area (which is highly likely to be superimposed with characters / symbols, etc.). You may make it measure the feature-value of the video signal of only a partial area | region.
As described above, the present invention has been illustrated with reference to the drawings. In each of the above examples, APL is used as the feature amount of the input video signal, and the light emission luminance of the backlight is controlled according to the APL. The feature amount of the video signal is not limited to APL, and for example, the state (presence or absence) of one frame of the input video signal may be used.
Similarly, as the feature quantity of the input video signal, the maximum brightness level, the minimum brightness level, and the brightness distribution state (histogram) in a predetermined region (period) in one frame are used, or the feature quantity of the video signal obtained by combining them. Based on the above, the emission luminance of the backlight may be variably controlled.

  Note that the luminance control as described above is applied not only to a direct-view type liquid crystal display device having a backlight unit 17 as shown in FIG. 2 or FIG. 3, but also to a projection type display device such as a liquid crystal projector. it can. Also in this case, image display is performed by irradiating light source light from the back side of the liquid crystal panel, and the light emission luminance of the light source light may be controlled in accordance with the luminance control characteristics.

It is a block diagram for demonstrating the structure of one Embodiment of the liquid crystal display device by this invention. It is a figure which shows the structural example of the backlight unit applicable to the liquid crystal display device of this invention. It is a figure which shows the other structural example of the backlight unit applicable to the liquid crystal display device of invention. It is a figure which shows an example of the luminance control characteristic of the backlight light source using a luminance control table. It is a histogram which shows the example of distribution of APL extracted from the broadcast program. It is a histogram which shows the example of distribution of APL extracted from the broadcast program of a movie genre. It is another figure which shows an example of the brightness control characteristic of the backlight light source using a brightness control table. It is a figure for demonstrating the example of a setting of the luminance control characteristic used according to the light control mode or the brightness around a liquid crystal display device. It is a flowchart which shows the operation example which prevents the rapid brightness change of a backlight light source by preparing two or more brightness | luminance control tables and changing the table number. It is a flowchart which shows the operation example which transfers to the brightness | luminance control table after a change gradually by a calculation, when a brightness | luminance control table No. is changed. It is a flowchart which shows the operation | movement which transfers to the brightness | luminance control characteristic of the table after a change gradually by changing a certain number of times of brightness | luminance when table No. is changed. It is explanatory drawing for demonstrating the relationship between the light emission luminance of a backlight light source, and the display quality of an image | video. It is explanatory drawing for demonstrating the relationship between the luminance control characteristic of a backlight light source, and power consumption reduction amount. It is explanatory drawing for demonstrating the relationship between the display quality of an image | video, and the power reduction amount.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display device, 10 ... APL, 11 ... Antenna, 12 ... Tuner, 13 ... Decoder, 14 ... APL measurement part, 15 ... Filter, 16 ... Backlight control part, 17 ... Backlight unit, 18 ... Video processing part , 19 ... LCD controller, 20 ... Liquid crystal panel, 21 ... Microcomputer, 22 ... Table storage memory, 23 ... Brightness control table, 24 ... Brightness sensor, 25 ... Remote control light receiving unit, 26 ... Multiplier, 27 ... Remote control device, 30 ... Case, 31 ... Fluorescent tube, 32 ... Diffusion plate, 41 ... Red light source, 42 ... Green light source, 43 ... Blue light source.

Claims (1)

  1. A liquid crystal panel for displaying an image; and a light source for illuminating the liquid crystal panel. When the feature amount of the input video signal is smaller than a predetermined value, the light emission luminance of the light source is decreased as the feature amount is decreased. A liquid crystal display device that variably controls the light emission luminance of a light source,
    The feature amount of the input video signal is a ratio of the average luminance level in one frame to the maximum luminance level of the input video signal,
    The predetermined value is set such that a ratio of an average luminance level in one frame to a maximum luminance level of the input video signal is set in a range of 2.0% to 12.2%. .
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US7961199B2 (en) 2004-12-02 2011-06-14 Sharp Laboratories Of America, Inc. Methods and systems for image-specific tone scale adjustment and light-source control
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US9083969B2 (en) 2005-08-12 2015-07-14 Sharp Laboratories Of America, Inc. Methods and systems for independent view adjustment in multiple-view displays
US7839406B2 (en) 2006-03-08 2010-11-23 Sharp Laboratories Of America, Inc. Methods and systems for enhancing display characteristics with ambient illumination input
US7826681B2 (en) 2007-02-28 2010-11-02 Sharp Laboratories Of America, Inc. Methods and systems for surround-specific display modeling
US8345038B2 (en) 2007-10-30 2013-01-01 Sharp Laboratories Of America, Inc. Methods and systems for backlight modulation and brightness preservation
US8155434B2 (en) 2007-10-30 2012-04-10 Sharp Laboratories Of America, Inc. Methods and systems for image enhancement
US9177509B2 (en) 2007-11-30 2015-11-03 Sharp Laboratories Of America, Inc. Methods and systems for backlight modulation with scene-cut detection
US8378956B2 (en) 2007-11-30 2013-02-19 Sharp Laboratories Of America, Inc. Methods and systems for weighted-error-vector-based source light selection
US8169431B2 (en) 2007-12-26 2012-05-01 Sharp Laboratories Of America, Inc. Methods and systems for image tonescale design
US8203579B2 (en) 2007-12-26 2012-06-19 Sharp Laboratories Of America, Inc. Methods and systems for backlight modulation with image characteristic mapping
US8207932B2 (en) 2007-12-26 2012-06-26 Sharp Laboratories Of America, Inc. Methods and systems for display source light illumination level selection
US8223113B2 (en) 2007-12-26 2012-07-17 Sharp Laboratories Of America, Inc. Methods and systems for display source light management with variable delay
US8179363B2 (en) 2007-12-26 2012-05-15 Sharp Laboratories Of America, Inc. Methods and systems for display source light management with histogram manipulation
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US8531379B2 (en) 2008-04-28 2013-09-10 Sharp Laboratories Of America, Inc. Methods and systems for image compensation for ambient conditions
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US8416179B2 (en) 2008-07-10 2013-04-09 Sharp Laboratories Of America, Inc. Methods and systems for color preservation with a color-modulated backlight
US9330630B2 (en) 2008-08-30 2016-05-03 Sharp Laboratories Of America, Inc. Methods and systems for display source light management with rate change control
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