Patent Publication Number: US-2023139266-A1

Title: Display device and method of controlling backlight of display device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2021-18051 7 filed in Japan on Nov. 4, 2021 and Patent Application No. 2022-122435 filed in Japan on Aug. 1, 2022, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND 
     This disclosure relates to control of the backlight of a display device. 
     A technology called local dimming is used to reduce the power consumption of the backlight of a liquid crystal display device and improve the contrast ratio in the displayed image. Local dimming divides the light emitting plane of the backlight into a plurality of blocks and controls whether to increase or decrease the amount of light emission of each block individually depending on the brightness in the video frame. 
     For example, in displaying a white window in a full black background, the local dimming controls the backlight so that the region (blocks) opposite to the region to display the white window will emit more light (at higher luminance) and the region (blocks) opposite to the region (blocks) to display the background (in black) will emit less light. 
     Such control achieves reduction in the power for the backlight, compared to the case where the whole region of the backlight lights at 100% all the time. Furthermore, the increased difference in luminance between the region emitting more light and the region emitting less light provides a higher contrast ratio in the same plane, which improves the display quality. 
     SUMMARY 
     An aspect of this disclosure is a display device including: a backlight including a plurality of backlight blocks; a display panel configured to display an image with light from the backlight; and a controller. The controller is configured to: acquire video data; determine provisional luminance values for the plurality of backlight blocks based on the video data; determine an adjustment coefficient for a backlight block of interest selected from the plurality of backlight blocks; determine an adjusted luminance value for the backlight block of interest based on the provisional luminance value and the adjustment coefficient for the backlight block of interest; and control the backlight block of interest in accordance with the adjusted luminance value. In determining the adjustment coefficient for the backlight block of interest, the controller is configured to: calculate a statistic of provisional luminance values for a plurality of reference backlight blocks including backlight blocks adjacent to the backlight block of interest; calculate a relative value of the statistic with respect to the provisional luminance value for the backlight block of interest; and determine the adjustment coefficient for the backlight block of interest based on the relative value and a predefined function. 
     An aspect of this disclosure is a method of controlling a backlight of a display device. The backlight includes a plurality of backlight blocks. The method includes: acquiring video data; determining provisional luminance values for the plurality of backlight blocks based on the video data; determining an adjustment coefficient for a backlight block of interest selected from the plurality of backlight blocks; determining an adjusted luminance value for the backlight block of interest based on the provisional luminance value and the adjustment coefficient for the backlight block of interest; and controlling the backlight block of interest in accordance with the adjusted luminance value. The determining an adjustment coefficient for the backlight block of interest includes: calculating a statistic of provisional luminance values for a plurality of reference backlight blocks including backlight blocks adjacent to the backlight block of interest; calculating a relative value of the statistic with respect to the provisional luminance value for the backlight block of interest; and determining the adjustment coefficient for the backlight block of interest based on the relative value and a predefined function. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates a configuration example of a display device in an embodiment of this specification; 
         FIG.  2    schematically illustrates an example of the functional configuration of a video signal processing circuit; 
         FIG.  3    is a flowchart of an example of processing to determine adjusted luminance values for individual backlight blocks in response to an input video frame; 
         FIG.  4    illustrates a backlight block of interest and the reference backlight blocks therefor; 
         FIG.  5    provides examples of the function for calculating an adjustment coefficient; 
         FIG.  6 A  provides a provisional luminance value for a backlight block of interest and provisional luminance values for its reference backlight blocks; 
         FIG.  6 B  provides a provisional luminance value for a backlight block of interest and provisional luminance values for its reference backlight blocks; 
         FIG.  6 C  provides a provisional luminance value for a backlight block of interest and provisional luminance values for its reference backlight blocks; 
         FIG.  7 A  illustrates an example of real backlight blocks included in a backlight and virtual backlight blocks; 
         FIG.  7 B  illustrates a method of determining provisional luminance values for some virtual backlight blocks; 
         FIG.  7 C  illustrates a method of determining provisional luminance values for the other virtual backlight blocks; 
         FIG.  8    is a diagram for explaining a method of determining an adjustment coefficient for a backlight block of interest; 
         FIG.  9    is a diagram for explaining an example of the method of determining an adjusted luminance value for a backlight block of interest; 
         FIG.  10    illustrates another example of the disposition of reference backlight blocks; 
         FIG.  11    illustrates still another example of the disposition of reference backlight blocks; 
         FIG.  12 A  provides the luminance distribution of a video frame, and a provisional luminance value distribution, a multiplier distribution, and an adjusted luminance value distribution to the backlight blocks obtained from the luminance distribution of the video frame; 
         FIG.  12 B  provides a graph representing the frontal luminance distribution generated by the backlight blocks controlled in accordance with the adjusted luminance value distribution in  FIG.  12 A ; 
         FIG.  13 A  provides the luminance distribution of another video frame, and a provisional luminance value distribution, a multiplier distribution, and an adjusted luminance value distribution to the backlight blocks obtained from the luminance distribution of the video frame; 
         FIG.  13 B  provides a graph representing the frontal luminance distribution generated by the backlight blocks controlled in accordance with the adjusted luminance value distribution in  FIG.  13 A ; 
         FIG.  14 A  provides the luminance distribution of still another video frame, and a provisional luminance value distribution, a multiplier distribution, and an adjusted luminance value distribution to the backlight blocks obtained from the luminance distribution of the video frame; 
         FIG.  14 B  provides a graph representing the frontal luminance distribution generated by the backlight blocks controlled in accordance with the adjusted luminance value distribution in  FIG.  14 A ; 
         FIG.  15 A  provides the luminance distribution of still another video frame, and a provisional luminance value distribution, a multiplier distribution, and an adjusted luminance value distribution to the backlight blocks obtained from the luminance distribution of the video frame; 
         FIG.  15 B  provides a graph representing the frontal luminance distribution generated by the backlight blocks controlled in accordance with the adjusted luminance value distribution in  FIG.  15 A ; 
         FIG.  16 A  provides the luminance distribution of still another video frame, and a provisional luminance value distribution, a multiplier distribution, and an adjusted luminance value distribution to the backlight blocks obtained from the luminance distribution of the video frame; 
         FIG.  16 B  provides a graph representing the frontal luminance distribution generated by the backlight blocks controlled in accordance with the adjusted luminance value distribution in  FIG.  16 A ; 
         FIG.  17 A  provides the luminance distribution of still another video frame, and a provisional luminance value distribution, a multiplier distribution, and an adjusted luminance value distribution to the backlight blocks obtained from the luminance distribution of the video frame; 
         FIG.  17 B  provides a graph representing the frontal luminance distribution generated by the backlight blocks controlled in accordance with the adjusted luminance value distribution in  FIG.  17 A . 
         FIG.  18    provides the luminance distribution of still another video frame, and a provisional luminance value distribution, a multiplier distribution, and an adjusted luminance value distribution to the backlight blocks obtained from the luminance distribution of the video frame in an embodiment of this specification; 
         FIG.  19    is a flowchart of an example of the processing of an adjustment coefficient calculator; 
         FIG.  20    illustrates a configuration example of a display device in another embodiment of this specification; 
         FIG.  21    schematically illustrates a configuration of a backlight; 
         FIG.  22    illustrates an example of information on provisional luminance values communicated between video signal processing circuits; 
         FIG.  23    illustrates an example of the relation between a video frame and adjusted luminance values for the corresponding backlight blocks; 
         FIG.  24    illustrates examples of data communicated between video signal processing circuits; 
         FIG.  25    illustrates examples of waveforms of the clock signal, the data signal, and the control signal in  FIG.  24   ; 
         FIG.  26    illustrates a configuration example of a display device in still another embodiment of this specification; 
         FIG.  27    schematically illustrates a configuration of a backlight; 
         FIG.  28    illustrates an example of information on provisional luminance values communicated between video signal processing circuits; 
         FIG.  29    illustrates an example of information on provisional luminance values communicated between video signal processing circuits; 
         FIG.  30    illustrates an example of information on provisional luminance values communicated between video signal processing circuits; 
         FIG.  31    illustrates an example of information on provisional luminance values communicated between video signal processing circuits; and 
         FIG.  32    illustrates an example of the relation between a video frame and adjusted luminance values for the corresponding backlight blocks. 
     
    
    
     EMBODIMENTS 
     Hereinafter, embodiments of this disclosure will be described with reference to the accompanying drawings. It should be noted that the embodiments are merely examples to implement this disclosure and are not to limit the technical scope of this disclosure. Elements common to the drawings are denoted by the same reference signs and some elements in the drawings are exaggerated in size or shape for clear understanding of the description. 
     A display device in an embodiment of this specification disclosed herein includes a display panel and a backlight including a plurality of backlight blocks. The display device determines provisional luminance values for the individual backlight blocks based on an input video data. The display device adjusts the provisional luminance value for a backlight block of interest based on the provisional luminance value for the backlight block of interest and a statistic of the provisional luminance values for reference backlight blocks including backlight blocks adjacent to the backlight block of interest. 
     The luminance (frontal luminance) recognized or measured directly above (in front of) a backlight block of interest depends on not only the light emitted from the backlight block of interest but also the light leaking from backlight blocks neighboring the backlight block of interest. Under the condition where the luminance of light emitted from the backlight block of interest is unchanged, the frontal luminance of the backlight block of interest is low when the neighboring backlight blocks are not lit, compared to when they are lit. 
     Adjusting the provisional luminance value for the backlight block of interest based on a statistic of the provisional luminance values for the reference backlight blocks enables the display device to attain improved display quality and power consumption with a simple configuration. 
     In an embodiment of this specification, the display device compares the provisional luminance value for the backlight block of interest with a statistic of the provisional luminance values for the reference backlight blocks and determines an adjustment coefficient based on the comparison result and a predefined function. The comparison result in an embodiment of this specification is a value obtained by dividing the statistic of the provisional luminance values for the reference backlight blocks by the provisional luminance value for the backlight block of interest. 
     The reference backlight blocks can include not only real backlight blocks in the backlight but also virtual backlight blocks. For example, a backlight block of interest located at an end of the backlight does not have a backlight block adjacent thereto outside the backlight. 
     The display device in an embodiment of this specification defines virtual backlight blocks located outside the backlight as reference backlight blocks for such a backlight block of interest. The provisional luminance value for a virtual backlight block can be determined based on the provisional luminance values for one or more real backlight blocks. The virtual backlight blocks enable adjustment of the luminance value for a backlight block with a simpler configuration. 
     The display device inputs those values to a predefined function to calculate the adjustment coefficient for adjusting the provisional luminance value for a backlight block of interest. The adjustment coefficient in an embodiment of this specification is an adjustment multiplier. The display device calculates the product of the adjustment multiplier and the provisional luminance value for the backlight block of interest to determine the adjusted luminance value for the backlight block of interest. 
     The backlight block of interest is controlled in accordance with the adjusted luminance value. The provisional luminance value and the adjusted luminance value can be relative luminance values having a relation proportional to the actual luminance value for the backlight block. For example, the relative luminance value is normalized so that the maximum value is 1 and the minimum value is 0. The actual maximum luminance values of the emitted light can be different among the backlight blocks. When different backlight blocks are assigned the same adjusted luminance value, the luminance values of the emitted light (the luminance values of the light to be recognized) of the backlight blocks can be the same or different. Hereinafter, display devices according to the embodiments of this specification will be described more specifically. 
     First Embodiment 
       FIG.  1    illustrates a configuration example of a display device in an embodiment of this specification. The display device displays an image by controlling transmission of light from the backlight.  FIG.  1    illustrates a configuration example of a liquid crystal display device  1  as an example of a display device. The liquid crystal display device  1  includes a signal processing board  10 , a power supply  13 , a video signal supply  14 , a liquid crystal display panel  20 , a display driver  21 , and a scanning driver  22 . The liquid crystal display device  1  further includes a backlight  30 , a backlight driver board  31 , and a backlight power supply  32 . The signal processing board  10  includes a power generation circuit  11  and a video signal processing circuit  12 . The signal processing board  10 , the display driver  21 , and the scanning driver  22  can be included in the controller for controlling the liquid crystal display panel  20 . 
     The liquid crystal display device  1  displays a picture in accordance with video data input from the external. The video data includes video frames to be displayed successively. The liquid crystal display panel  20  is disposed in front (on the side to be viewed by the user) of the backlight  30  and controls the amount of the light from the backlight  30  to be transmitted therethrough to display video frames (images) successively input from the external. 
     The power generation circuit  11  can include a DC-DC converter; it generates and supplies electric power for the other circuits to operate. The video signal processing circuit  12  performs processing involved in displaying a picture, such as generating a signal for displaying an image on the liquid crystal display panel  20  and a signal for controlling the backlight  30 . The power supply  13  supplies electric power to the power generation circuit  11 . The video signal supply  14  supplies a video signal to the video signal processing circuit  12  in accordance with the video data from the external. 
     The power generation circuit  11  generates electric power to drive ICs such as the video signal processing circuit  12 , the display driver  21 , and the scanning driver  22 . The display driver  21  and the scanning driver  22  are configured to operate using the power supplied from the power generation circuit  11  to perform their processing. 
     The display driver  21  generates a data signal from the video signal sent from the video signal processing circuit  12  and supplies the data signal to the liquid crystal display panel  20 . The scanning driver  22  selects scanning lines of the liquid crystal display panel  20  one by one in accordance with a timing signal sent from the video signal processing circuit  12 . The video signal processing circuit  12  also sends the timing signal to the display driver  21 . In accordance with the timing signal, the display driver  21  generates a data signal from the received video signal and supplies the data signal to the liquid crystal display panel  20 . 
     The video signal processing circuit  12  converts the data arrangement of the video signal input from the external to send it to the display driver  21  and generates and sends a timing signal for the display driver  21  and scanning driver  22  to operate, using the power supplied from the power generation circuit  11 . 
     The video signal processing circuit  12  further generates a driving control signal for controlling the driving of a plurality of backlight blocks included in the backlight  30  and sends the driving control signal to the backlight driver board  31 . A backlight block can be simply referred to as block. Examples of the driving control signal include a backlight ON/OFF control signal and a dimming control signal. The dimming control signal is a pulse width modulation (PWM) signal for controlling the lighting periods of light sources by time sharing or a signal for controlling the amounts of electric current flowing in the light sources. 
     The backlight  30  is a planar light source device disposed behind the liquid crystal display panel  20  to emit light required for the liquid crystal display panel  20  to display an image. The backlight driver board  31  includes a backlight driver circuit and controls the lighting (luminance) of the backlight  30  in accordance with the driving control signal sent from the video signal processing circuit  12 . The backlight driver board  31  operates using the power supplied from the backlight power supply  32 . 
     The liquid crystal display device  1  employs local dimming. In the configuration example of  FIG.  1   , the backlight  30  is divided into X blocks (regions) along the X-axis and Y blocks along the Y-axis. Each backlight block has a rectangular shape and the backlight blocks are disposed in a matrix. 
     The backlight  30  consists of a plurality of backlight block rows. Each backlight block row consists of backlight blocks aligned in the X-axis direction (row direction). In an example, all backlight block rows include the same number of backlight blocks. However, each backlight block row can have a different number of backlight blocks. From another point of view, the backlight  30  consists of a plurality of backlight block columns. Each backlight block column consists of backlight blocks aligned in the Y-axis direction (column direction). All backlight block columns have the same number of backlight blocks. Each backlight block column can have a different number of backlight blocks, although it is stated that all backlight block columns have the same number of backlight blocks for convenience of explanation. The backlight blocks can be disposed in another layout. 
     The liquid crystal display device  1  can individually control the luminance values (the amounts of light emission) of the (X×Y) blocks. The liquid crystal display device  1  controls whether to increase or decrease the amount of light emission of each block individually depending on the brightness of the pixels in the video frame to reduce the power consumption and improve the contrast ratio. 
     The backlight  30  can be a direct backlight, which includes a light source array disposed within the backlight plane to be opposite to the liquid crystal display panel  20  and a diffuser panel between the light source array and the liquid crystal display panel  20 . A typical example of the light source is an LED. A plurality of LEDs can be disposed in a backlight block. A desirable number of LEDs can be included in one backlight block. An optimum number of LEDs are disposed at optimum locations based on the luminance efficiency and luminance distribution of the LEDs. 
     Instead of the above-described direct type, the backlight  30  can be of an edge type, which includes a light guide panel and light sources disposed on opposite sides. The light-emitting area of the backlight  30  can be composed of backlight blocks disposed in a matrix or backlight blocks disposed in a horizontal or a vertical line. 
     The video signal processing circuit  12  generates a driving control signal for controlling the luminance of individual blocks of the backlight  30  and sends the driving control signal to the backlight driver board  31 . The backlight driver board  31  drives and controls the light sources (for example, LEDs) of the backlight  30  so that the individual blocks light at the luminance values (the amounts of light emission) specified in the driving control signal from the video signal processing circuit  12 . 
     The video signal processing circuit  12  generates a timing signal for the display driver  21  and the scanning driver  22  in accordance with the timing signal for the input video signal and also, successively sends a signal (frame signal) of each video frame in the video signal to the display driver  21 . The frame signal can specify the intensity levels of red (R), green (G), and blue (B) of each pixel in a video frame. 
     The video signal processing circuit  12  further analyzes the video frame, generates a driving control signal for the backlight  30  to illuminate the liquid crystal display panel  20  from its behind based on the analysis result, and sends the driving control signal to the backlight  30 . As described above, the liquid crystal display device  1  employs local dimming. The video signal processing circuit  12  determines provisional luminance values for individual blocks of the backlight  30  based on the analysis result on the video frame. 
     Furthermore, the video signal processing circuit  12  determines adjusted luminance values for individual backlight blocks based on the provisional luminance values for the backlight blocks. The video signal processing circuit  12  determines the adjusted luminance values to be the luminance values with which to control the light emission of the individual backlight blocks. 
     In the example described in the following, provisional luminance values are normalized to range from a minimum value of 0 to a maximum value of 1. Then, some adjusted luminance values could be calculated as a value greater than 1. In that case, the adjusted luminance values are normalized to range from a minimum value of 0 to a maximum value of 1, while the provisional luminance values are converted in advance to corresponding relative values. For example, in the case where the largest multiplier to obtain an adjusted luminance value is known as 2, the adjusted luminance value is to be 1 after the maximum provisional luminance value is multiplied by 2. Accordingly, it can be determined in advance that the maximum provisional luminance value is 0.5. 
     The video signal processing circuit  12  generates driving control signals specifying luminance values corresponding to the adjusted luminance values and outputs them to individual backlight blocks. The relation between the adjusted luminance value and the driving control signal is predetermined for each backlight block. A driving control signal specifies the actual luminance value of light to be emitted from a backlight block. In an example, the driving control signal specifies the duty ratio of the pulse width in the pulse width modulation (PWM) for power control. As described above, the actual luminance values corresponding to the same adjusted luminance value can be determined differently depending on the backlight blocks. 
     The frontal luminance of a backlight block depends on the luminance of the light emitted by the backlight block and further, the light leaking from backlight blocks neighboring the backlight block. Determining an adjusted luminance value for the backlight block based on the provisional luminance value for the backlight block and the provisional luminance values for the reference backlight blocks neighboring the backlight block leads to high display quality. 
     Hereinafter, control of the backlight  30  by the video signal processing circuit  12  is described in detail.  FIG.  2    schematically illustrates an example of the functional configuration of the video signal processing circuit  12 . The video signal processing circuit  12  includes a display control driving signal generator  231 , an RGB level-luminance converter  201 , a block provisional luminance value calculator  202 , a block provisional luminance value arranger  203 , a backlight luminance controller  210 , and a backlight driving control signal generator  221 . The backlight luminance controller  210  includes a reference block luminance determiner  211 , an adjustment coefficient calculator  213 , and an adjusted luminance value calculator  214 . 
     The display control driving signal generator  231  generates signals to be sent to the display driver  21  and the scanning driver  22  from a video signal received from the video signal supply  14 . The display control driving signal generator  231  sends the display driver  21  a signal specifying the RGB intensity levels of each pixel in a video frame together with a timing signal and sends the scanning driver  22  the timing signal. 
     The RGB level-luminance converter  201 , the block provisional luminance value calculator  202 , and the block provisional luminance value arranger  203  are circuits for determining provisional luminance values (provisional amounts of light emission) for individual blocks of the backlight  30  based on a video frame. Specifically, the RGB level-luminance converter  201  converts the RGB intensity levels of each pixel specified by the video frame into relative luminance values. The luminance value of a pixel to be used to determine the luminance for the backlight can be the highest luminance value among the values of red, blue, and green components (also referred to as subpixels) constituting the pixel. 
     The block provisional luminance value calculator  202  determines provisional luminance values for individual blocks of the backlight  30  based on the luminance values of the pixels of the video frame. The block provisional luminance value calculator  202  determines a luminance value determined from the highest luminance value among the luminance values of the pixels in a part (also referred to as display region block) of the display region opposite to a block to be the luminance value for the block. Each backlight block is associated with the display region block opposite to the backlight block. 
     In the following description, the luminance values of the pixels and the luminance values of the backlight blocks are normalized relative luminance values ranging from 0 to 1. The block provisional luminance value calculator  202  determines the highest value among the luminance values of the pixels in the opposite display region block to be the provisional luminance value for the backlight block. In the case where different backlight blocks are assigned the same provisional luminance value, their actual luminance values may be the same or different because of the individual differences of the blocks or LEDs or the disposition of the blocks, even though the signals for the backlight blocks are the same. 
     The block provisional luminance value arranger  203  generates an array (distribution) of the provisional luminance values for the backlight blocks calculated by the block provisional luminance value calculator  202 . In the array, the provisional luminance values are associated with the blocks of the backlight  30 . The block provisional luminance value arranger  203  sends the generated array of provisional luminance values to the backlight luminance controller  210 . 
     The backlight luminance controller  210  adjusts the received provisional luminance values to determine the adjusted luminance values for the backlight blocks. The backlight luminance controller  210  determines adjustment coefficients for the provisional luminance values for the backlight blocks based on the array of provisional luminance values. The details of the adjustment method will be described later. 
     The backlight driving control signal generator  221  acquires the adjusted luminance values determined for the individual backlight blocks from the backlight luminance controller  210  and generates driving control signals in accordance with the adjusted luminance values. For example, the backlight driving control signal generator  221  generates driving control signals that make the specified luminance values conform to the physical characteristics of the light sources included in individual backlight blocks. The backlight driving control signal generator  221  sends the driving control signals for the individual blocks to the backlight driver board  31 . 
     Hereinafter, an example of the method for the backlight luminance controller  210  to adjust the luminance values for individual blocks of the backlight  30  is described. The backlight luminance controller  210  determines the adjustment amounts for the provisional luminance values determined in accordance with a video frame based on the provisional luminance values. The backlight luminance controller  210  adjusts the provisional luminance values by the adjustment amounts. As a result, the display quality can be improved while saving the power by local dimming. 
     In an embodiment of this specification, the backlight luminance controller  210  determines the adjusted luminance value for a backlight block of interest based on the provisional luminance value for the backlight block of interest and the provisional luminance values for the reference backlight blocks in a predetermined disposition with respect to the backlight block of interest. 
     In the example described in the following, the backlight luminance controller  210  adjusts the provisional luminance value for a backlight block of interest, depending on the relative values (comparison values) of the provisional luminance values for the reference backlight blocks to the provisional luminance value for the backlight block of interest. When the provisional luminance values for the reference backlight blocks are smaller, the backlight luminance controller  210  increases the provisional luminance value for the backlight block of interest more. This configuration enables the frontal luminance of each backlight block to get closer to a desired value, in conformance to the distribution of provisional luminance values for the backlight blocks. 
     The disposition of the reference backlight blocks depends on the design; various patterns can be employed. The reference backlight blocks are composed of neighboring backlight blocks of the backlight block of interest. Some examples will be provided as follows. In one example, the reference backlight blocks are all backlight blocks that are adjacent to the backlight block of interest. 
     A backlight block adjacent to the backlight block of interest is a backlight block one side or one corner of which is in contact with the backlight block of interest. In the example described in this specification where rectangular backlight blocks are disposed in a matrix, adjacent backlight blocks are the backlight blocks surrounding the backlight block of interest. In the case where the backlight block of interest is located at the center of the backlight  30 , the backlight block of interest is surrounded by eight real adjacent backlight blocks. 
     In another case where the backlight block of interest is located at an end of the backlight  30 , real adjacent backlight blocks are located only inside the backlight  30 . The reference blocks for a backlight block of interest located at an end can be composed of only the real adjacent backlight blocks or include virtual adjacent backlight blocks, as will be described later. 
     In the case where the reference backlight blocks are composed of only real backlight blocks, the number of reference backlight blocks for a backlight block of interest located at an end is smaller than eight. In the case where the reference backlight blocks include virtual backlight blocks, the number of reference backlight blocks for any backlight block of interest is eight. 
     As an option, the reference backlight blocks can be composed of some of the adjacent backlight blocks. For example, the reference backlight blocks can be real backlight blocks that are in contact with the backlight block of interest on its left, right, top, and bottom. The adjacent backlight blocks on the left and right of the backlight block of interest are backlight blocks adjacent along the X-axis (horizontally) and the adjacent backlight blocks on the top and bottom of the backlight block of interest are backlight blocks adjacent along the Y-axis (vertically). 
     The reference backlight blocks of a backlight block of interest located at an end of the backlight  30  can be composed of real backlight blocks only or both real and virtual backlight blocks. In the case where the reference backlight blocks include virtual backlight blocks, the reference backlight blocks for any backlight block of interest are composed of four adjacent backlight blocks. In the case where virtual backlight blocks are not defined, the number of reference backlight blocks for a backlight block of interest located at an end is smaller than four. 
     In another example, the reference backlight blocks are composed of the adjacent backlight blocks and their adjacent backlight blocks located outer than the adjacent backlight blocks. In the case of a matrix layout, a backlight block of interest located at the center is surrounded by 24 real reference backlight blocks. The virtual backlight blocks to be referenced for a backlight block of interest located in the vicinity of an end of the backlight  30  can be treated in the same way as the foregoing examples. 
     The backlight luminance controller  210  in an embodiment of this specification compares a statistic of the provisional luminance values for the reference backlight blocks with the provisional luminance value for the backlight block of interest and adjusts the provisional luminance value for the backlight block of interest based on the comparison result (relative value). The statistic can be an average, such as a simple average or a weighted average, or a median, for example. 
     In an embodiment of this specification, the backlight luminance controller  210  can use division to compare the provisional luminance values for the reference backlight blocks with the provisional luminance value of a backlight block of interest. For example, a relative value of the provisional luminance value for the backlight block of interest can be calculated by dividing the statistic of the provisional luminance values for the reference backlight blocks by the provisional luminance value for the backlight block of interest. Instead of division, subtraction can be used. 
       FIG.  3    is a flowchart of an example of processing to determine adjusted luminance values for individual backlight blocks in response to an input video frame. The reference block luminance determiner  211  selects an unselected backlight block as a backlight block of interest from the backlight  30  (S 11 ). The reference block luminance determiner  211  determines provisional luminance values for the reference backlight blocks of the selected backlight block of interest with reference to the information on the provisional luminance values for the backlight blocks acquired from the block provisional luminance value arranger  203  (S 12 ). 
     The adjustment coefficient calculator  213  acquires the provisional luminance values for the reference backlight blocks from the reference block luminance determiner  211  and determines their statistic (S 13 ). The statistic can be a simple average, a weighted average, or a median. The adjustment coefficient calculator  213  compares the calculated statistic with the provisional luminance value for the backlight block of interest to determine a relative value of the statistic with respect to the provisional luminance value for the backlight block of interest (S 14 ). An example of the relative value is a value obtained by dividing the statistic by the provisional luminance value for the backlight block of interest. 
     The adjustment coefficient calculator  213  determines an adjustment coefficient based on the calculated relative value and a predefined function (S 15 ). The function can be expressed by an arithmetic expression or a lookup table, for example. An example of the adjustment coefficient is a multiplier for the provisional luminance value for the backlight block of interest. 
     The adjusted luminance value calculator  214  adjusts the provisional luminance value for the backlight block of interest with the calculated adjustment coefficient and determines the adjusted luminance value (S 16 ). The driving control signal in accordance with this adjusted luminance value is sent to the backlight driver board  31  to light the backlight block of interest. 
     The reference block luminance determiner  211  determines whether all backlight blocks of the backlight  30  have been selected (S 17 ). If an unselected backlight block exists (S 17 : NO), the processing returns to Step S 11 . If all backlight blocks have been selected (S 17 : YES), the processing to calculate adjusted luminance values for the backlight blocks for the current video frame ends. 
     Hereinafter, an example of a method of adjusting the provisional luminance value for a backlight block of interest is described. In the example described in the following, real backlight blocks have identical rectangular shapes and they are disposed in a matrix. Virtual backlight blocks have the same shape as the real backlight blocks. Reference backlight blocks are all real or virtual backlight blocks adjacent to the backlight block of interest. That is to say, the number of reference backlight blocks is eight. In the following description, a backlight block means a real backlight block unless stated specifically. 
     Although X and Y in  FIG.  1    can be any natural numbers, the following description will be provided assuming that X is 3 and Y is 3. First, a method of determining an adjusted luminance value for a backlight block of interest located at the center of the backlight  30  is described.  FIG.  4    illustrates a backlight block of interest and the reference backlight blocks therefor. The backlight block of interest  300  is surrounded by eight reference backlight blocks  301  to  308 . The reference backlight blocks  304  and  305  are horizontally adjacent to the backlight block of interest  300 . The reference backlight blocks  302  and  307  are vertically adjacent to the backlight block of interest  300 . The reference backlight blocks  301 ,  303 ,  306 , and  308  are diagonally adjacent to the backlight block of interest  300 . 
     The reference block luminance determiner  211  acquires information on the provisional luminance values for all backlight blocks from the block provisional luminance value arranger  203 . The reference block luminance determiner  211  determines the provisional luminance values LUMI_ 1  to LUMI_ 8  for the reference backlight blocks  301  to  308  with reference to the information. 
     The adjustment coefficient calculator  213  calculates a statistic of the provisional luminance values for the reference backlight blocks  301  to  308 . This example calculates the simple average AVE_ADJ as expressed by the following formula: 
         AVE _ ADJ =( LUMI _1+ LUMI _2+ LUMI _3+ LUMI _4+ LUMI _5+ LUMI _6+ LUMI _7+ LUMI _8)/8. 
     Next, the adjustment coefficient calculator  213  compares the statistic AVE_ADJ of the provisional luminance values for the reference backlight blocks with the provisional luminance value LUMI_SELF for the backlight block of interest  300  and calculates a relative value LUMI_COEF of the statistic AVE_ADJ with respect to the provisional luminance value LUMI_SELF for the backlight block of interest  300 . 
     In this example, the adjustment coefficient calculator  213  divides the statistic AVE_ADJ of the provisional luminance values for the reference backlight blocks by the provisional luminance value LUMI_SELF for the backlight block of interest  300  as expressed by the following formula: 
         LUMI _ COEF=AVE _ ADJ/LUMI _ SELF.    
     The maximum value for LUMI_COEF is defined as 1. In other words, if the value of AVE_ADJ/LUMI_SELF is greater than 1, the value of LUMI_COEF is determined to be 1. Further, if the value of LUMI_SELF is 0, the value of LUMI COEF is determined to be 1. 
     The adjustment coefficient calculator  213  determines an adjustment coefficient for the provisional luminance value LUMI_SELF for the backlight block of interest  300  from the relative value LUMI_COEF. The adjustment coefficient calculator  213  uses information of a predefined function to calculate the adjustment coefficient from the relative value LUMI_COEF. The function can be expressed by a mathematical expression or a lookup table. For example, the adjustment coefficient MULT_COEF can be calculated by the following linear function: 
         MULT _ COEF=A− ( A− 1)* LUMI _ COEF,    
     where the constant A represents the maximum value for the adjustment coefficient. 
     As described above, the maximum value for the relative value LUMI_COEF is 1. Accordingly, the minimum value for the adjustment coefficient MULT_COEF calculated by the above formula is 1. The function to calculate the adjustment coefficient is not limited to a linear function. For example, a quadratic or higher-order function can be used. 
       FIG.  5    provides examples of the function to calculate the adjustment coefficient. In the graph, the line  401  represents an example of a linear function and the line  402  represents an example of a quadratic function. The function to calculate the adjustment coefficient can be a higher-order function than a linear function. An example of the high-order function can be expressed as follows: 
       MULT _ COEF= 1+( A− 1)*( ABS ( LUMI _ COEF− 1))^ n,    
     where ABS() represents an absolute value and n is a natural number greater than 1. In the case of a quadratic function, n is 2. 
     The line  401  represents the linear function in accordance with the above formula where the constant A is 2. In either function  401  or  402 , the maximum value for the adjustment coefficient MULT_COEF is 2 and the minimum value is 1. As indicated in  FIG.  5   , the value of the adjustment coefficient MULT_COEF in accordance with the quadratic function  402  is not larger than the value of the adjustment coefficient MULT_COEF in accordance with the linear function  401 . The quadratic function can save the power consumption more than the linear function. 
     Next, the adjusted luminance value calculator  214  adjusts the provisional luminance value LUMI_SELF for the backlight block of interest with the calculated adjustment coefficient MULT_COEF. In this example, the adjustment coefficient MULT_COEF is used as a multiplier to adjust the provisional luminance value LUMI_SELF. In other words, the adjusted luminance value calculator  214  multiplies the provisional luminance value LUMI_SELF by the adjustment coefficient MULT_COEF to calculate the adjusted luminance value for the backlight block of interest. 
     In the above-described example, when the statistic of the provisional luminance values for the reference backlight blocks is equal to or larger than the provisional luminance value for the backlight block of interest, the relative value LUMI_COEF is 1. In this case, the adjustment coefficient is 1 and the adjustment amount for the provisional luminance value for the backlight block of interest is 0. In other words, the provisional luminance value for the backlight block of interest is maintained. 
     When the statistic of the provisional luminance values for the reference backlight blocks is smaller than the provisional luminance value for the backlight block of interest, the adjustment coefficient is greater than 1. The smaller the statistic of the provisional luminance values for the reference backlight blocks, the greater the adjustment coefficient. As understood from this description, when the amount of light leaking from the reference backlight blocks is smaller, the provisional luminance value for the backlight block of interest is increased more. This configuration enables the luminance value for the backlight block of interest to be determined more appropriately depending on the amount of light leaking from the reference backlight blocks. 
     Hereinafter, specific examples of adjustment of the provisional luminance value for a backlight block of interest with the linear function  401  in  FIG.  5    are described. To be adjusted is the provisional luminance value LUMI_SELF for the backlight block of interest  300  in  FIG.  4   . 
       FIG.  6 A  provides a provisional luminance value for the backlight block of interest  300  and provisional luminance values for its reference backlight blocks  301  to  308 . In the example of  FIG.  6 A , the provisional luminance values for the backlight block of interest  300  and the reference backlight blocks  301  to  308  are all 1. 
     The simple average AVE_ADJ of the provisional luminance values for the reference backlight blocks  301  to  308  is 8/8=1. The relative value LUMI_COEF of the statistic of the provisional luminance values for the reference backlight blocks with respect to the provisional luminance value for the backlight block of interest  300  is 1/1=1. Accordingly, the adjustment coefficient (multiplier) MULT_COEF is (2−(2−1)*1)=1. 
       FIG.  6 B  provides a provisional luminance value for the backlight block of interest  300  and provisional luminance values for its reference backlight blocks  301  to  308 . In the example of  FIG.  6 B , the provisional luminance value for the backlight block of interest  300  is 1 and the provisional luminance values for the reference backlight blocks  301  to  308  are 0. 
     The simple average AVE_ADJ of the provisional luminance values for the reference backlight blocks  301  to  308  is 0/8=0. The relative value LUMI_COEF of the statistic of the reference backlight blocks with respect to the provisional luminance value for the backlight block of interest  300  is 0/1=0. Accordingly, the adjustment coefficient (multiplier) MULT_COEF is (2−(2−1)*0)=2. 
       FIG.  6 C  provides a provisional luminance value for the backlight block of interest  300  and provisional luminance values for its reference backlight blocks  301  to  308 . In the example of  FIG.  6 C , the provisional luminance value for the backlight block of interest  300  is 1 and the provisional luminance values for the reference backlight blocks  301  to  308  are as shown in  FIG.  6 C . 
     The simple average AVE_ADJ of the provisional luminance values for the reference backlight blocks  301  to  308  is 1.25/8=0.15625. The relative value LUMI_COEF of the statistic of the provisional luminance values for the reference backlight blocks with respect to the provisional luminance value for the backlight block of interest  300  is 0.15625/1=0.15625. Accordingly, the adjustment coefficient (multiplier) MULT_COEF is (2−(2−1)*0.15625)=1.84375. 
     Next, a method of adjusting the provisional luminance value for a backlight block of interest located at an end of the backlight  30  is described. The example described in the following defines virtual backlight blocks and includes real backlight blocks and virtual backlight blocks in the reference backlight blocks. Defining virtual backlight blocks enables the provisional luminance values for all real backlight blocks to be adjusted with the same calculation method. In other words, all provisional luminance values can be adjusted with a single operational circuit or operation code. 
     The reference backlight blocks are eight backlight blocks adjacent to the backlight block of interest, like those in the example described with reference to  FIG.  4   . Some of the eight backlight blocks are real backlight blocks and the remaining backlight blocks are virtual backlight blocks. The provisional luminance value for a backlight block located at an end can be adjusted based on the provisional luminance values of less than eight real backlight blocks. In that case, the calculation method of the adjustment coefficient is determined differently depending on the location of the backlight block. 
       FIG.  7 A  illustrates an example of real backlight blocks included in the backlight  30  and virtual backlight blocks. The backlight  30  consists of real backlight blocks  451  to  459 . Virtual backlight blocks  471  to  486  are defined around the real backlight blocks  451  to  459 . 
     In the configuration example of  FIG.  7 A , the provisional luminance value for the real backlight block  455  is 1.0 and the provisional luminance values of the other real backlight blocks are 0.0. The provisional luminance values for the virtual backlight blocks  471  to  486  have not been determined yet. 
     The reference block luminance determiner  211  determines provisional luminance values for the virtual backlight blocks  471  to  486  based on the provisional luminance values for the real backlight blocks  451  to  459 . In an embodiment of this specification, the provisional luminance value for a virtual backlight block is the same as the provisional luminance value for the real backlight block closest to the virtual backlight block. Hence, an appropriate provisional luminance value for a virtual backlight block is determined. 
       FIG.  7 B  illustrates a method of determining provisional luminance values for the virtual backlight blocks  476  to  481 . The reference block luminance determiner  211  determines the provisional luminance value for the virtual backlight block  476  to be the provisional luminance value for the real backlight block  451  adjacent thereto on the right. In similar, the provisional luminance values for the virtual backlight blocks  478  and  480  are determined to be the provisional luminance values for the real backlight blocks  454  and  457  adjacent thereto on the right. 
     The reference block luminance determiner  211  determines the provisional luminance value for the virtual backlight block  477  to be the provisional luminance value for the real backlight block  453  adjacent thereto on the left. In similar, the provisional luminance values for the virtual backlight blocks  479  and  481  are determined to be the provisional luminance values for the real backlight blocks  456  and  459  adjacent thereto on the left. 
       FIG.  7 C  illustrates a method of determining provisional luminance values for the virtual backlight blocks  471  to  475  and  482  to  486 . The reference block luminance determiner  211  determines the provisional luminance value for the virtual backlight block  472  to be the provisional luminance value for the real backlight block  451  adjacent to its bottom. In similar, the provisional luminance values for the virtual backlight blocks  473  and  474  are determined to be the provisional luminance values for the real backlight blocks  452  and  453  adjacent to their bottoms. 
     The provisional luminance values for the virtual backlight blocks  471  and  475  are determined to be the provisional luminance values for the virtual backlight blocks  476  and  477  adjacent to their bottoms. In other words, the provisional luminance values for the virtual backlight blocks  471  and  475  are determined to be the provisional luminance values for their closest adjacent backlight blocks  451  and  453 . 
     The reference block luminance determiner  211  determines the provisional luminance value for the virtual backlight block  483  to be the provisional luminance value for the real backlight block  457  adjacent to its top. In similar, the provisional luminance values for the virtual backlight blocks  484  and  485  are determined to be the provisional luminance values for the real backlight blocks  458  and  459  adjacent to their tops. 
     The provisional luminance values for the virtual backlight blocks  482  and  486  are determined to be the provisional luminance values for the virtual backlight blocks  480  and  481  adjacent to their tops. In other words, the provisional luminance values for the virtual backlight blocks  482  and  486  are determined to be the provisional luminance values for their closest adjacent backlight blocks  457  and  459 . 
     An example of determining the adjustment coefficient for a backlight block of interest located at an end of the backlight  30  is described.  FIG.  8    is a diagram for explaining the method of determining the adjustment coefficient for the backlight block of interest  451 . The backlight block of interest  451  is located at the upper left corner of the backlight  30 . 
     The reference backlight blocks for the backlight block of interest  451  are the virtual backlight blocks  471  to  473 ,  476 , and  478 , and the real backlight blocks  452 ,  454 , and  455 . 
     The provisional luminance value for the backlight block of interest  451  is 0.0 and the provisional luminance value for the reference backlight block  455  is 1.0. The provisional luminance values for the other reference backlight blocks are 0.0. The simple average AVE_ADJ of the provisional luminance values for the reference backlight blocks  471  to  473 ,  476 ,  452 ,  478 ,  454 , and  455  is 1/8=0.125. Since the provisional luminance value for the backlight block of interest  451  is 0.0, the relative value LUMI_COEF of the statistic of the provisional luminance values for the reference backlight blocks is 1. Accordingly, the adjustment coefficient (multiplier) MULT_COEF is (2−(2−1)*1)=1. 
     Second Embodiment 
     Hereinafter, other examples of the method of determining an adjusted luminance value for a backlight block of interest are described. In the examples described in the following, the virtual backlight blocks to be referenced for a backlight block located at an end of the backlight can be treated in the same way as described in the first embodiment. 
       FIG.  9    is a diagram for explaining an example of the method of determining an adjusted luminance value for a backlight block of interest. Like in the example described with reference to  FIG.  4   , all backlight blocks adjacent to the backlight block of interest are referenced to adjust the provisional luminance value for the backlight block of interest. 
     In the example of  FIG.  9   , the statistic about the reference backlight blocks is a weighted average. The other points are the same as those in the example described with reference to  FIG.  4   . This example assigns a smaller weight to diagonally adjacent backlight blocks  301 ,  303 ,  306 , and  308  than horizontally or vertically adjacent backlight blocks  302 ,  304 ,  305 , and  307 . Assigning a smaller weight to the backlight blocks far from the backlight block of interest enables the individual amounts of light leaking from the reference backlight blocks to be referenced more appropriately. 
     The weights are determined appropriately depending on the design. The weights for the horizontally or vertically adjacent backlight blocks  302 ,  304 ,  305 , and  307  are the same and the weights for the diagonally adjacent backlight blocks  301 ,  303 ,  306 , and  308  are the same. 
     The weighted average WAVE_ADJ can be calculated by the following formula: 
         WAVE _ ADJ=B ( LUMI _1+ LUMI _3+ LUMI _6+ LUMI _8)+ C ( LUMI _2+ LUMI _4+ LUMI _5+ LUMI _7))/8, 
     where B and C are weighting coefficients determined appropriately depending on the design. 
     In the case of using the function provided in  FIG.  5   , a relation of (B+C)=2 can be satisfied. For example, B is 1.25 and C is 0.75. 
       FIG.  10    illustrates another example of the disposition of reference backlight blocks. Compared to the example in  FIG.  4   , the backlight blocks diagonally adjacent to the backlight block of interest are excluded from the reference backlight blocks. In other words, the reference backlight blocks are composed of only horizontally or vertically adjacent backlight blocks. 
     The method of calculating an adjustment coefficient from the provisional luminance values for the reference backlight blocks and the provisional luminance value for the backlight block of interest illustrated in  FIG.  10    can be the same as the method described with reference to  FIG.  4   . That is to say, the average of the provisional luminance values for the reference backlight blocks  302 ,  304 ,  305 , and  307  is calculated and the adjustment coefficient is calculated from the average and the provisional luminance value for the backlight block of interest  300  with a predefined function. 
     Calculating the adjustment coefficient from the provisional luminance values for the reference backlight blocks in  FIG.  10    is equivalent to assigning  0  to the weighting coefficient for the diagonally adjacent backlight blocks in the example described with reference to  FIG.  9   . 
       FIG.  11    illustrates still another example of the disposition of reference backlight blocks. The reference backlight blocks in this example includes outer backlight blocks  521  to  536  in addition to the backlight blocks  511  to  518  adjacent to the backlight block of interest  500 . The outer backlight blocks  521  to  536  are adjacent to the backlight blocks  511  to  518  that are adjacent to the backlight block of interest  500 . 
     Calculating the statistic about the reference backlight blocks includes the provisional luminance values for the outer backlight blocks  521  to  536  in addition to the provisional luminance values for the adjacent backlight blocks  511  to  518 . 
     In the case where the statistic is a weighted average, the weight for the outer backlight blocks  521  to  536  can be determined to be smaller than the weight for the adjacent backlight blocks  511  to  518 . This is because the outer backlight blocks  521  to  536  are located farther from the backlight block of interest  500  than the adjacent backlight blocks  511  to  518 . Hence, a statistic consistent with the amounts of light leaking from the reference backlight blocks to the backlight block of interest can be calculated. 
     The weighted average can be calculated by the following formula: 
         WAVE _ ADJ 2=( D ( LUMI _ A 1+ LUMI _ A 2+ LUMI _ A 3+ LUMI _ A 4+ LUMI _ A 5+ LUMI _ A 6+ LUMI _ A 7+ LUMI _ A 8)+ E ( LUMI _ B 1+ LUMI _ B 2+ LUMI _ B 3+ LUMI _ B 4+ LUMI _ B 5+ LUMI _ B 6+ LUMI _ B 7+ LUMI _ B 8+ LUMI _ B 9+ LUMI _ B 10+ LUMI _ B 11+ LUMI _ B 12+ LUMI _ B 13+ LUMI _ B 14+ LUMI _ B 15+ LUMI _ B 16))/24, 
     where D and E are weighing coefficients that are determined appropriately depending on the design. 
     In the case of using the function provided in  FIG.  5   , a relation of (D+E)=2 can be satisfied. 
     Like the example described with reference to  FIG.  9   , the four backlight blocks located at a corner among the adjacent backlight blocks  511  to  518  can be assigned a weight smaller than the weight for the other backlight blocks. The same applies to the outer backlight blocks  521  to  536 . The methods of calculating the relative value of the statistic of the provisional luminance values for the reference backlight blocks with respect to the provisional luminance value for the backlight block of interest and the adjustment coefficient can be the same as those in the first embodiment. 
     Examples of Calculation of Frontal Luminance 
     Hereinafter, examples of frontal luminance values of the backlight blocks acquired by the adjusted luminance values determined in accordance with the method of the first embodiment are described. As described in the following, the methods according to the embodiments of this specification attain desired frontal luminance values directly above the individual backlight blocks. 
     In the examples described in the following, reference backlight blocks are the eight backlight blocks adjacent to the backlight block of interest. The statistic of the provisional luminance values for the reference backlight blocks is a simple average and the relative value is a value obtained by dividing the simple average of the provisional luminance values for the reference backlight blocks by the provisional luminance value for the backlight block of interest. The adjustment coefficient is calculated using the linear function described with reference to  FIG.  5    and it is a multiplier for the provisional luminance value for the backlight block of interest. 
       FIG.  12 A  provides a luminance distribution  610  of a video frame, and a provisional luminance value distribution  611 , a multiplier distribution  612 , and an adjusted luminance value distribution  613  to the backlight blocks obtained from the luminance distribution  610 . The term “distribution” in “luminance distribution” or “provisional luminance value distribution” does not mean the information on luminance gradient (luminance distribution) in each backlight block when the backlight block is lit but means a set (array) of luminance values assigned to the backlight blocks. 
     The video frame  610  consists of an area where the relative luminance value is 1.0 and its surrounding area where the relative luminance value is 0.0. The area at the relative luminance value of 1.0 faces only one backlight block located at the center. Accordingly, in the backlight block set, the provisional luminance value for the central backlight block is 1.00 and the provisional luminance values for the other backlight blocks are 0.00. The multipliers as adjustment coefficients for the backlight blocks are as indicated in the multiplier distribution  612 . As a result, the adjusted luminance value distribution  613  to the backlight blocks is obtained. 
       FIG.  12 B  provides a graph representing the frontal luminance distribution generated by the backlight blocks controlled in accordance with the adjusted luminance value distribution  613 . The horizontal axis of the graph represents the position on the X-axis at the center of the Y-axis in the main face of the backlight. 
     The vertical axis represents frontal luminance. The frontal luminance value of 1.0 means the desired frontal luminance value. 
     Regarding the example of  FIG.  12 A , the desired frontal luminance value for the central backlight block is 1.0 and the desired frontal luminance values for the other backlight blocks are 0.0. The line  711  represents the frontal luminance value of the backlight controlled in accordance with the adjusted luminance values and the line  712  represents the frontal luminance value of the backlight controlled in accordance with the provisional luminance values. The backlight controlled in accordance with the adjusted luminance values attains frontal luminance values closer to the desired frontal luminance values. 
       FIG.  13 A  provides a luminance distribution  620  of a video frame, and a provisional luminance value distribution  621 , a multiplier distribution  622 , and an adjusted luminance value distribution  623  to the backlight blocks obtained from the luminance distribution  620 . 
     The video frame  620  consists of an area where the relative luminance value is 1.0 and its surrounding area where the relative luminance value is 0.0. The area at the relative luminance value of 1.0 faces four lower-right backlight blocks. Accordingly, in the backlight block set, the provisional luminance values for the four lower-right backlight blocks are 1.00 and the provisional luminance values for the other backlight blocks are 0.00. The multipliers as adjustment coefficients for the backlight blocks are as indicated in the multiplier distribution  622 . As a result, the adjusted luminance value distribution  623  to the backlight blocks is obtained. 
       FIG.  13 B  provides a graph representing the frontal luminance distribution generated by the backlight blocks controlled in accordance with the adjusted luminance value distribution  623 . The line  721  represents the frontal luminance value of the backlight controlled in accordance with the adjusted luminance values and the line  722  represents the frontal luminance value of the backlight controlled in accordance with the provisional luminance values. The backlight controlled in accordance with the adjusted luminance values attains frontal luminance values closer to the desired frontal luminance values. 
       FIG.  14 A  provides a luminance distribution  630  of a video frame, and a provisional luminance value distribution  631 , a multiplier distribution  632 , and an adjusted luminance value distribution  633  to the backlight blocks obtained from the luminance distribution  630 . 
     The video frame  630  consists of an area where the relative luminance value is 1.0 and its surrounding area where the relative luminance value is 0.0. The area at the relative luminance value of 1.0 faces six backlight blocks on the right. Accordingly, in the backlight block set, the provisional luminance values for the six backlight blocks on the right are 1.00 and the provisional luminance values for the other backlight blocks are 0.00. The multipliers as adjustment coefficients for the backlight blocks are as indicated in the multiplier distribution  632 . As a result, the adjusted luminance value distribution  633  to the backlight blocks is obtained. 
       FIG.  14 B  provides a graph representing the frontal luminance distribution generated by the backlight blocks controlled in accordance with the adjusted luminance value distribution  633 . The line  731  represents the frontal luminance value of the backlight controlled in accordance with the adjusted luminance values and the line  732  represents the frontal luminance value of the backlight controlled in accordance with the provisional luminance values. The backlight controlled in accordance with the adjusted luminance values attains frontal luminance values closer to the desired frontal luminance values. 
       FIG.  15 A  provides a luminance distribution  640  of a video frame, and a provisional luminance value distribution  641 , a multiplier distribution  642 , and an adjusted luminance value distribution  643  to the backlight blocks obtained from the luminance distribution  640 . 
     The video frame  640  consists of an area where the relative luminance value is 1.0 and its surrounding area where the relative luminance value is 0.0. The area at the relative luminance value of 1.0 faces all the nine backlight blocks. Accordingly, in the backlight block set, the provisional luminance values for all backlight blocks are 1.00. The multipliers as adjustment coefficients for the backlight blocks are as indicated in the multiplier distribution  642 . As a result, the adjusted luminance value distribution  643  to the backlight blocks is obtained. 
       FIG.  15 B  provides a graph representing the frontal luminance distribution generated by the backlight blocks controlled in accordance with the adjusted luminance value distribution  643 . The line  741  represents the frontal luminance value of the backlight controlled in accordance with the adjusted luminance values and the line  742  represents the frontal luminance value of the backlight controlled in accordance with the provisional luminance values. The backlight controlled in accordance with the adjusted luminance values attains desired frontal luminance values. 
       FIG.  16 A  provides a luminance distribution  650  of a video frame, and a provisional luminance value distribution  651 , a multiplier distribution  652 , and an adjusted luminance value distribution  653  to the backlight blocks obtained from the luminance distribution  650 . 
     In the video frame  650 , the relative luminance values of two straight lines crossing each other are 1.0 and the relative luminance value of their surrounding area is 0.0. The two straight lines face five backlight blocks of the backlight blocks at the four corners and the central backlight block. Accordingly, in the backlight block set, the provisional luminance values for these five backlight blocks are 1.00 and the provisional luminance values for the other backlight blocks are 0.00. The multipliers as adjustment coefficients for the backlight blocks are as indicated in the multiplier distribution  652 . As a result, the adjusted luminance value distribution  653  to the backlight blocks is obtained. 
       FIG.  16 B  provides a graph representing the frontal luminance distribution generated by the backlight blocks controlled in accordance with the adjusted luminance value distribution  653 . The line  751  represents the frontal luminance value of the backlight controlled in accordance with the adjusted luminance values and the line  752  represents the frontal luminance value of the backlight controlled in accordance with the provisional luminance values. The backlight controlled in accordance with the adjusted luminance values attains frontal luminance values closer to the desired frontal luminance values. 
       FIG.  17 A  provides a luminance distribution  660  of a video frame, and a provisional luminance value distribution  661 , a multiplier distribution  662 , and an adjusted luminance value distribution  663  to the backlight blocks obtained from the luminance distribution  660 . 
     In the video frame  660 , the relative luminance value of a rectangular frame close to the outer end is 1.0 and the relative luminance value of the other area is 0.0. The rectangular frame faces eight backlight blocks except for the central backlight block. Accordingly, in the backlight block set, the provisional luminance values for the aforementioned eight backlight blocks are 1.00 and the provisional luminance value for the central backlight block is 0.00. The multipliers as adjustment coefficients for the backlight blocks are as indicated in the multiplier distribution  662 . As a result, the adjusted luminance value distribution  663  to the backlight blocks is obtained. 
       FIG.  17 B  provides a graph representing the frontal luminance distribution generated by the backlight blocks controlled in accordance with the adjusted luminance value distribution  663 . The line  761  represents the frontal luminance value of the backlight controlled in accordance with the adjusted luminance values and the line  762  represents the frontal luminance value of the backlight controlled in accordance with the provisional luminance values. The backlight controlled in accordance with the adjusted luminance values attains frontal luminance values closer to the desired frontal luminance values. 
     Third Embodiment 
     Another embodiment of this specification is described. The following mainly describes differences from the first embodiment. The adjustment coefficient calculator  213  calculates the adjustment coefficient MULT_COEF using the following method when predetermined conditions are satisfied: 
         MULT _ COEF=K+LUMI _ SELF ×(1− K ),
 
     where K is a given coefficient (0≤K&lt;1). 
     The predetermined conditions are the following two conditions:
         Condition 1: The provisional luminance values for all adjacent blocks are 1 (AVE_ADJ=1); and   Condition 2: LUMI_SELF&lt;1.       

     If all blocks adjacent to the backlight block of interest are lit (Condition 1) and the backlight block of interest is lit at a luminance value lower than the maximum value (Condition 2), the backlight block of interest receives light leaking from the adjacent backlight blocks without exception. For this reason, the contrast ratio of the backlight block of interest to the adjacent backlight blocks becomes low. This embodiment lowers the luminance of the backlight block of interest by the amount of contribution of the light leaking from the adjacent backlight blocks. This configuration restrains degradation of image quality and further, saves the power for the backlight block of interest. 
       FIG.  18    provides a luminance distribution  800  of a video frame, and a provisional luminance value distribution  801 , a multiplier distribution  802 , and an adjusted luminance value distribution  803  to the backlight blocks obtained from the luminance distribution  800 . The video frame  800  consists of a sub-region located at the center where the relative luminance value is 0.5 and its surrounding sub-regions where the relative luminance value is 1.0. Each sub-region is opposite to a different backlight block. The provisional luminance value for the central backlight block is 0.5 and the provisional luminance values for the other backlight blocks are 1.0. The multipliers as adjustment coefficients for the backlight blocks are as indicated in the multiplier distribution  802 . As a result, the adjusted luminance value distribution  803  to the backlight blocks is obtained. 
     The multipliers (adjustment coefficients) are calculated as follows. The multiplier for the central backlight block is calculated using the following formula in this embodiment: 
         MULT _ COEF=K+LUMI _ SELF ×(1− K ),
 
     where K is a value greater than 0 and smaller than 1. In this example, the coefficient K is 0.8. 
     The multipliers for the surrounding backlight blocks are calculated using the following formula in the first embodiment: 
         MULT _ COEF=A− ( A− 1)* LUMI _ COEF,    
     where the coefficient A is 2. 
     In the example illustrated in  FIG.  18   , the central backlight block receives light leaking from its adjacent backlight blocks in the actual luminance distribution including the leakage light. Accordingly, a luminance value higher than the primary target feature value of 0.5 is attained. Using a multiplier (adjustment coefficient) smaller than 1 attains the target feature value. In determining the value for the coefficient K to calculate the multiplier (adjustment coefficient), the adjustment coefficient calculator  213  calculates the amount of light leaking from the adjacent backlight blocks in advance and determines a value for the coefficient K so that the result of adding the luminescence calculated with the multiplier and the leakage from the adjacent backlight blocks will become higher than the calculated feature value of the backlight block. The adjustment coefficient smaller than 1 can be determined by a different method. The adjustment coefficient calculator  213  determines such an adjustment coefficient based on the relation between the provisional luminance value for the backlight block of interest and the statistic of the provisional luminance values for the reference backlight blocks. 
     As described with reference to  FIG.  10   , this embodiment can also exclude the backlight blocks diagonally adjacent to the backlight block of interest from the reference backlight blocks. In other words, the reference backlight blocks can consist of horizontally adjacent backlight blocks and vertically adjacent backlight blocks. The method of calculating the adjustment coefficient can be the same as illustrated in  FIG.  18   , except that some of the reference backlight blocks are excluded. 
       FIG.  19    is a flowchart of an example of the processing of the adjustment coefficient calculator  213 . The adjustment coefficient calculator  213  calculates the statistic AVE_ADJ of the provisional luminance values for the reference backlight blocks (S 31 ) as described in the first embodiment and makes determination on the value (S 32 ). If the value of AVE_ADJ is smaller than 1 (S32: AVE_ADJ &lt;1), the adjustment coefficient calculator  213  calculates the relative value LUMI_COEF of the statistic AVE_ADJ with respect to the provisional luminance value LUMI_SELF for the backlight block of interest  300  (S 33 ) as described in the first embodiment. Further, the adjustment coefficient calculator  213  calculates the adjustment coefficient MULT_COEF (S 34 ) as described in the first embodiment. 
     If the determination at Step S 32  is that the value of AVE_ADJ is 1 (S 32 : AVE_ADJ=1), the adjustment coefficient calculator  213  determines whether the provisional luminance value LUMI_SELF for the backlight block of interest  300  is 1 (S 35 ). If the provisional luminance value LUMI_SELF for the backlight block of interest  300  is 1, the adjustment coefficient calculator  213  proceeds to Step S 33 . If the provisional luminance value LUMI_SELF for the backlight block of interest  300  is smaller than 1, the adjustment coefficient calculator  213  calculates the adjustment coefficient MULT_COEF by the method of this embodiment (S 36 ). 
     Fourth Embodiment 
       FIG.  20    illustrates a configuration example of a display device in another embodiment of this specification. The following mainly describes differences from the configuration example in  FIG.  1   . The liquid crystal display device  1  includes video signal supplies  14 A and  14 B and display drivers  21 A and  21 B. The signal processing board  10  includes video signal processing circuits  12 A and  12 B. The video signal processing circuit  12 A is a first processing circuit and the video signal processing circuit  12 B is a second processing circuit. This configuration can be employed when the display region is divided horizontally or vertically to be driven by different ICs because the display region has a resolution too high to be driven by one IC. 
     The liquid crystal display panel  20  includes a first display region  250 A and a second display region  250 B adjoining each other. The video signal processing circuit  12 A performs processing involved in displaying a picture, such as generating a signal for displaying an image in the first display region  250 A and a signal for controlling the backlight  30 . The video signal processing circuit  12 B performs processing involved in displaying a picture, such as generating a signal for displaying an image in the second display region  250 B and a signal for controlling the backlight  30 . The video signal supply  14 A supplies a video signal to the video signal processing circuit  12 A and the video signal supply  14 B supplies a video signal to the video signal processing circuit  12 B. 
     The display driver  21 A generates a data signal from the video signal sent from the video signal processing circuit  12 A and supplies the data signal to the first display region  250 A. The display driver  21  B generates a data signal from the video signal sent from the video signal processing circuit  12 B and supplies the data signal to the second display region  250 B. The video signal processing circuit  12 A also sends a timing signal to the display driver  21 A and the display driver  21 A generates a data signal from the received video signal and supplies the data signal to the first display region  250 A in accordance with the timing signal. The video signal processing circuit  12 B also sends a timing signal to the display driver  21 B. The display driver  21 B generates a data signal from the received video signal and supplies the data signal to the second display region  250 B in accordance with the timing signal. The video signal processing circuit  12 A converts the data arrangement of the video signal input from the external to send it to the display driver  21 A and generates and sends a timing signal for the display driver  21 A and the scanning driver  22  to operate using the power supplied from the power generation circuit  11 . The video signal processing circuit  12 A further generates a driving control signal for controlling the driving of the backlight  30  and sends it to the backlight driver board  31 . 
     The video signal processing circuit  12 B converts the data arrangement of the video signal input from the external to send it to the display driver  21  B and generates and sends a timing signal for the display driver  21 B and the scanning driver  22  to operate using the power supplied from the power generation circuit  11 . The video signal processing circuit  12 B further generates a driving control signal for controlling the driving of the backlight  30  and sends it to the backlight driver board  31 . 
     The backlight driver board  31  includes a backlight driver circuit and controls the lighting (luminance) of the backlight  30  in accordance with the driving control signals sent from the video signal processing circuits  12 A and  12 B. 
     Each of the video signal processing circuits  12 A and  12 B generates a driving control signal for controlling the luminance of individual blocks of the backlight  30  and sends the driving control signal to the backlight driver board  31 . The backlight driver board  31  drives and controls the light sources of the backlight  30  so that the individual blocks light at the luminance values specified in the driving control signals from the video signal processing circuits  12 A and  12 B. 
     The video signal processing circuit  12 A generates a timing signal for the display driver  21 A and the scanning driver  22  in accordance with the input timing signal for the video signal and also, successively sends a signal (frame signal) of each video frame in the video signal to the display driver  21 A. The video signal processing circuit  12 B generates a timing signal for the display driver  21 B and the scanning driver  22  in accordance with the input timing signal for the video signal and also, successively sends a signal (frame signal) of each video frame in the video signal to the display driver  21 B. The video signal processing circuit  12 A analyzes the video frame, generates a driving control signal for the backlight  30  to illuminate the first display region  250 A from its behind based on the analysis result, and sends the driving control signal to the backlight  30 . The video signal processing circuit  12 B analyzes the video frame, generates a driving control signal for the backlight  30  to illuminate the second display region  250 B from its behind based on the analysis result, and sends the driving control signal to the backlight  30 . 
       FIG.  21    schematically illustrates the configuration of the backlight  30 . The backlight  30  consists of a first backlight region  350 A on the left and a second backlight region  350 B on the right. The first backlight region  350 A is directly beneath the first display region  250 A. The first backlight region  350 A is located behind and opposite to the first display region  250 A to illuminate the first display region  250 A. The second backlight region  350 B is directly beneath the second display region  250 B. The second backlight region  350 B is located behind and opposite to the second display region  250 B to illuminate the second display region  250 B. 
     The first backlight region  350 A consists of twelve backlight blocks B 1 L to B 12 L (the first backlight block group). Although a case of twelve backlight blocks is described here, the number of backlight blocks is not limited to twelve; the first backlight region  350 A can consist of N×M blocks (N and M are natural numbers). The second backlight region  350 B consists of twelve backlight blocks B 1 R to B 12 R (the second backlight block group). The backlight blocks B 3 L, B 6 L, B 9 L, and B 12 L adjoin the second backlight region  350 B. The backlight blocks B 1 R, B 4 R, B 7 R, and B 10 R adjoin the first backlight region  350 A. 
     The video signal processing circuit  12 A sends the video signal processing circuit  12 B information on provisional luminance values for the first backlight region  350 A. The video signal processing circuit  12 B determines adjustment coefficients for the second backlight region  350 B based on the provisional luminance values for the second backlight region  350 B and the provisional luminance values for the first backlight region  350 A received from the video signal processing circuit  12 A. The video signal processing circuit  12 B sends the video signal processing circuit  12 A information on provisional luminance values for the second backlight region  350 B. The video signal processing circuit  12 A determines adjustment coefficients for the first backlight region  350 A based on the provisional luminance values for the first backlight region  350 A and the provisional luminance values for the second backlight region  350 B received from the video signal processing circuit  12 B. 
       FIG.  22    illustrates an example of the information on provisional luminance values communicated between the video signal processing circuits  12 A and  12 B. The video signal processing circuit  12 A sends the video signal processing circuit  12 B information on the provisional luminance values for the backlight block set  351 A in the first backlight region  350 A that is adjoining the second backlight region  350 B. The backlight block set  351 A consists of the backlight blocks B 3 L, B 6 L, B 9 L, and B 12 L. 
     The video signal processing circuit  12 B sends the video signal processing circuit  12 A information on the provisional luminance values for the backlight block set  351  B in the second backlight region  350 B that is adjoining the first backlight region  350 A. The backlight block set  351 B consists of the backlight blocks B 1 R, B 4 R, B 7 R, and B 10 R. 
     The video signal processing circuit  12 A refers to the information on the provisional luminance values for the backlight block set  351 B received from the video signal processing circuit  12 B in calculating the adjustment coefficients for the backlight block set  351 A. In similar, the video signal processing circuit  12 B refers to the information on the provisional luminance values for the backlight block set  351 A received from the video signal processing circuit  12 A in calculating the adjustment coefficients for the backlight block set  351 B. The method of determining each adjustment coefficient can be the same as described in the first embodiment. 
     Each of the video signal processing circuits  12 A and  12 B sends the other video signal processing circuit the provisional luminance values for the backlight blocks that are assigned to itself and adjacent to the backlight blocks controlled by the other video signal processing circuit, so that the backlight blocks located in the border between backlight regions can be provided with more appropriate adjustment coefficients. 
       FIG.  23    illustrates an example of the relation between a video frame and adjusted luminance values for the corresponding backlight blocks. In the video frame  821 , only the region opposite to one backlight block is white and the other regions are black. The video signal processing circuit  12 A controls only the first backlight region  350 A and the video signal processing circuit  12 B controls only the second backlight region  350 B. 
     As described above, in the case where a backlight block of interest is adjoining the segmentation boundary of the backlight  30 , each video signal processing circuit sends information on the provisional luminance values for the backlight blocks adjoining the boundary to the other video processing circuit to complement necessary information. 
     In  FIG.  23   , only the region of the video frame corresponding to the backlight block B 4 R is white and the other regions are black. The video signal processing circuit  12 B refers to not only the provisional luminance values for the backlight blocks B 1 R, B 2 R, B 5 R, and B 7 R in the second backlight region  350 B but also the provisional luminance values for the backlight blocks B 3 L, B 6 L, and B 9 L in the first backlight region  350 A to determine the adjustment coefficient for the backlight block B 4 R. The calculation method of the adjustment coefficient can be the same as described in the first embodiment. As a result, the backlight block B 4 R can be provided with an appropriate adjusted luminance value of 2.0. 
       FIG.  24    illustrates examples of data communicated between the video signal processing circuits  12 A and  12 B. The video signal processing circuit  12 A sends the video signal processing circuit  12 B a data signal SDA 1  specifying provisional luminance values using a clock signal SCK 1  and a control signal CS 1 . The video signal processing circuit  12 B sends the video signal processing circuit  12 A a data signal SDA 2  specifying provisional luminance values using a clock signal SCK 2  and a control signal CS 2 . The signal transmission lines can be reduced by sharing one or more of the signal lines between the video signal processing circuits  12 A and  12 B. 
       FIG.  25    illustrates examples of waveforms of the clock signal SCK 1 , the data signal SDA 1 , and the control signal CS 1  in  FIG.  24   . The data signal SDA 1  is an example of the data signal for the signal processing circuit  12 A to send data on four border backlight blocks to the signal processing circuit  12 B. In the example of  FIG.  25   , each of the provisional luminance values for the four backlight blocks are transmitted in 16 bits and a provisional luminance value is expressed in 12-bit resolution. 
     In the foregoing example, each of the display region and the backlight region is divided into two regions and the divided regions are controlled by two video signal processing circuits. In another example, the number of regions divided from the display region and the backlight region and the number of video signal processing circuits can be three or more. Information on provisional luminance values is communicated between the video signal processing circuits controlling adjoining display regions and the backlight regions therefor. 
     Fifth Embodiment 
       FIG.  26    illustrates a configuration example of a display device in still another embodiment of this specification. The following mainly describes differences from the configuration example in  FIG.  1   . The liquid crystal display device  1  includes video signal supplies  14 A to  14 D and display drivers  21 A to  21 D. The signal processing board  10  includes video signal processing circuits  12 A to  12 D. The video signal processing circuits  12 A to  12 D are a first processing circuit to a fourth processing circuit. The liquid crystal display panel  20  is divided into four display regions  250 A to  250 D. The video signal processing circuit  12 A performs processing involved in displaying a picture in the first display region  250 A; the video signal processing circuit  12 B performs processing involved in displaying a picture in the second display region  250 B; the video signal processing circuit  12 C performs processing involved in displaying a picture in the third display region  2500 ; and the video signal processing circuit  12 D performs processing involved in displaying a picture in the fourth display region  250 D. 
     The video signal supply  14 A supplies a video signal to the video signal processing circuit  12 A; the video signal supply  14 B supplies a video signal to the video signal processing circuit  12 B; the video signal supply  14 C supplies a video signal to the video signal processing circuit  120 ; and the video signal supply  14 D supplies a video signal to the video signal processing circuit  12 D. 
     The display driver  21 A generates a data signal from the video signal sent from the video signal processing circuit  12 A and supplies the data signal to the first display region  250 A. The display driver  21  B generates a data signal from the video signal sent from the video signal processing circuit  12 B and supplies the data signal to the second display region  250 B. The display driver  21 C generates a data signal from the video signal sent from the video signal processing circuit  12 C and supplies the data signal to the third display region  250 C. The display driver  21 D generates a data signal from the video signal sent from the video signal processing circuit  12 D and supplies the data signal to the fourth display region  250 D. 
     The video signal processing circuit  12 A converts the data arrangement of the video signal input from the external to send it to the display driver  21 A and generates and sends a timing signal for the display driver  21 A and the scanning driver  22  to operate, using the power supplied from the power generation circuit  11 . The video signal processing circuit  12 A further generates a driving control signal for controlling the driving of the backlight  30  and sends the driving control signal to the backlight driver board  31 . The video signal processing circuit  12 B converts the data arrangement of the video signal input from the external to send it to the display driver  21  B and generates and sends a timing signal for the display driver  21 B and the scanning driver  22  to operate, using the power supplied from the power generation circuit  11 . The video signal processing circuit  12 B further generates a driving control signal for controlling the driving of the backlight  30  and sends the driving control signal to the backlight driver board  31 . 
     The video signal processing circuit  12 C converts the data arrangement of the video signal input from the external to send it to the display driver  21 C and generates and sends a timing signal for the display driver  21 C and the scanning driver  22  to operate, using the power supplied from the power generation circuit  11 . The video signal processing circuit  12 C further generates a driving control signal for controlling the driving of the backlight  30  and sends the driving control signal to the backlight driver board  31 . 
     The video signal processing circuit  12 D converts the data arrangement of the video signal input from the external to send it to the display driver  21 D and generates and sends a timing signal for the display driver  21 D and the scanning driver  22  to operate, using the power supplied from the power generation circuit  11 . The video signal processing circuit  12 D further generates a driving control signal for controlling the driving of the backlight  30  and sends the driving control signal to the backlight driver board  31 . 
     The backlight driver board  31  includes a backlight driver circuit and controls the lighting (luminance) of the backlight  30  in accordance with the driving control signals sent from the video signal processing circuits  12 A to  12 D. Each of the video signal processing circuits  12 A to  12 D generates a driving control signal for controlling the luminance of individual blocks of the backlight  30  and sends the driving control signal to the backlight driver board  31 . The backlight driver board  31  drives and controls the light sources of the backlight  30  so that the individual blocks light at the luminance values specified in the driving control signals from the video signal processing circuits  12 A to  12 D. 
     The video signal processing circuit  12 A generates a timing signal for the display driver  21 A and the scanning driver  22  in accordance with the input timing signal for the video signal and also, successively sends a signal (frame signal) of each video frame in the video signal to the display driver  21 A. The video signal processing circuit  12 B generates a timing signal for the display driver  21 B and the scanning driver  22  in accordance with the input timing signal for the video signal and also, successively sends a signal (frame signal) of each video frame in the video signal to the display driver  21 B. 
     The video signal processing circuit  12 C generates a timing signal for the display driver  21 C and the scanning driver  22  in accordance with the input timing signal for the video signal and also, successively sends a signal (frame signal) of each video frame in the video signal to the display driver  21 C. The video signal processing circuit  12 D generates a timing signal for the display driver  21 D and the scanning driver  22  in accordance with the input timing signal for the video signal and also, successively sends a signal (frame signal) of each video frame in the video signal to the display driver  21 D. 
     The video signal processing circuit  12 A analyzes the video frame, generates a driving control signal for the backlight  30  to illuminate the first display region  250 A from its behind based on the analysis result, and sends the driving control signal to the backlight  30 . The video signal processing circuit  12 B analyzes the video frame, generates a driving control signal for the backlight  30  to illuminate the second display region  250 B from its behind based on the analysis result, and sends the driving control signal to the backlight  30 . The video signal processing circuit  12 C analyzes the video frame, generates a driving control signal for the backlight  30  to illuminate the third display region  250 C from its behind based on the analysis result, and sends the driving control signal to the backlight  30 . The video signal processing circuit  12 D analyzes the video frame, generates a driving control signal for the backlight  30  to illuminate the fourth display region  250 D from its behind based on the analysis result, and sends the driving control signal to the backlight  30 . 
       FIG.  27    schematically illustrates the configuration of the backlight  30 . The backlight  30  consists of an upper left first backlight region  350 A, an upper right second backlight region  350 B, a lower left third backlight region  350 C, and a lower right fourth backlight region  350 D. 
     The first backlight region  350 A is directly beneath the first display region  250 A. The first backlight region  350 A is located behind and opposite to the first display region  250 A to illuminate the first display region  250 A. The second backlight region  350 B is directly beneath the second display region  250 B. The second backlight region  350 B is located behind and opposite to the second display region  250 B to illuminate the second display region  250 B. 
     The third backlight region  350 C is directly beneath the third display region  250 C. The third backlight region  350 C is located behind and opposite to the third display region  250 C to illuminate the third display region  250 C. The fourth backlight region  350 D is directly beneath the fourth display region  250 D. The fourth backlight region  350 D is located behind and opposite to the fourth display region  250 D to illuminate the fourth display region  250 D. 
     The first backlight region  350 A, the second backlight region  350 B, the third backlight region  350 C, and the fourth backlight region  350 D are controlled by the video signal processing circuit  12 A, the video signal processing circuit  12 B, the video signal processing circuit  12 C, and the video signal processing circuit  12 D, respectively. 
     The first backlight region  350 A consists of twelve backlight blocks B 1 UL to B 12 UL. The second backlight region  350 B consists of twelve backlight blocks B 1 UR to B 12 UR. The third backlight region  350 C consists of twelve backlight blocks B 1 DL to B 12 DL. The fourth backlight region  350 D consists of twelve backlight blocks B 1 DR to B 12 DR. Although a case of twelve backlight blocks is described here, the number of backlight blocks is not limited to twelve; each backlight region can consist of N×M blocks (N and M are natural numbers). The number of blocks can be different among the backlight regions. 
     Hereinafter, communication of information on luminance values among video signal processing circuits is described. In the example described in the following, information on provisional luminance values for the border area between horizontally adjacent backlight regions is communicated first between the video signal processing circuits to complement necessary information. Next, information on provisional luminance values for the border area between vertically adjacent backlight regions is communicated between the video signal processing circuits to complement necessary information. The information about the border area between vertically adjacent backlight regions can be communicated first between video signal processing circuits and the information about the border area between horizontally adjacent backlight regions can be communicated thereafter. 
       FIGS.  28  to  31    illustrate examples of information communicated between video signal processing circuits. In the example described in the following, the provisional luminance value for the backlight block B 10 UR is 1.0 and the provisional luminance values for the other backlight blocks are 0.0. 
       FIG.  28    illustrates an example of information on the provisional luminance values communicated between the video signal processing circuits  12 A and  12 B. The video signal processing circuit  12 A sends the video signal processing circuit  12 B information on the provisional luminance values for the backlight block set  351 A that is included in the first backlight region  350 A and adjoining the second backlight region  350 B. The backlight block set  351 A consists of the backlight blocks B 3 UL, B 6 UL, B 9 UL, and B 12 UL. 
     The video signal processing circuit  12 B sends the video signal processing circuit  12 A information on the provisional luminance values for the backlight block set  351  B that is included in the second backlight region  350 B and adjoining the first backlight region  350 A. The backlight block set  351 B consists of the backlight blocks B 1 UR, B 4 UR, B 7 UR, and B 10 UR. 
       FIG.  29    illustrates an example of information on the provisional luminance values communicated between the video signal processing circuits  12 C and  12 D. The video signal processing circuit  12 C sends the video signal processing circuit  12 D information on the provisional luminance values for the backlight block set  351 C that is included in the third backlight region  350 C and adjoining the fourth backlight region  350 D. The backlight block set  351 C consists of the backlight blocks B 3 DL, B 6 DL, B 9 DL, and B 12 DL. 
     The video signal processing circuit  12 D sends the video signal processing circuit  12 C information on the provisional luminance values for the backlight block set  351 D that is included in the fourth backlight region  350 D and adjoining the third backlight region  350 C. The backlight block set  351 D consists of the backlight blocks B 1 DR, B 4 DR, B 7 DR, and B 10 DR. 
       FIG.  30    illustrates an example of information on the provisional luminance values communicated between the video signal processing circuits  12 A and  12 C. The video signal processing circuit  12 A sends the video signal processing circuit  12 C information on the provisional luminance values for the backlight block set  352 A that is included in the first backlight region  350 A or the backlight block set  351 B and adjoining the third backlight region  350 C or the backlight block set  351 D. The backlight block set  352 A consists of the backlight blocks B 10 UL, B 11 UL, B 12 UL, and B 10 UR. 
     The video signal processing circuit  12 C sends the video signal processing circuit  12 A information on the provisional luminance values for the backlight block set  352 C that is included in the third backlight region  350 C or the backlight block set  351 D and adjoining the first backlight region  350 A or the backlight block set  351 B. The backlight block set  352 C consists of the backlight blocks B 1 DL, B 2 DL, B 3 DL, and B 1 DR. 
       FIG.  31    illustrates an example of information on the provisional luminance values communicated between the video signal processing circuits  12 B and  12 D. The video signal processing circuit  12 B sends the video signal processing circuit  12 D information on the provisional luminance values for the backlight block set  352 B that is included in the second backlight region  350 B or the backlight block set  351 A and adjoining the fourth backlight region  350 D or the backlight block set  351 C. The backlight block set  352 B consists of the backlight blocks B 10 UR, B 11 UR, B 12 UR, and B 12 UL. The video signal processing circuit  12 D sends the video signal processing circuit  12 B information on the provisional luminance values for the backlight block set  352 D that is included in the fourth backlight region  350 D or the backlight block set  351 C and adjoining the second backlight region  350 B or the backlight block set  351 A. The backlight block set  352 D consists of the backlight blocks B 1 DR, B 2 DR, B 3 DR, and B 3 DL. 
     Through the foregoing processing, the video signal processing circuit  12 A acquires the provisional luminance values for the backlight blocks B 1 UR, B 4 UR, B 7 UR, B 10 UR, B 1 DL, B 2 DL, B 3 DL, and B 1 DR that are adjacent to the first backlight region  350 A. The video signal processing circuit  12 B acquires the provisional luminance values for the backlight blocks B 3 UL, B 6 UL, B 9 UL, B 12 UL, B 3 DL, B 1 DR, B 2 DR, and B 3 DR that are adjacent to the second backlight region  350 B. 
     The video signal processing circuit  12 C acquires the provisional luminance values for the backlight blocks B 1 DR, B 4 DR, B 7 DR, B 10 DR, B 10 UL, B 11  UL, B 12 UL, and B 10 UR that are adjacent to the third backlight region  350 C. The video signal processing circuit  12 D acquires the provisional luminance values for the backlight blocks B 3 DL, B 6 DL, B 9 DL, B 12 DL, B 12 UL, B 10 UR, B 11 UR, and B 12 UR that are adjacent to the fourth backlight region  350 D. 
     Each video signal processing circuit refers to provisional luminance values for other backlight regions received from other video signal processing circuits in calculating the adjustment coefficients for a backlight block set that is included in the backlight region assigned thereto and adjacent to other backlight regions. The method of determining each adjustment coefficient can be the same as described in the first embodiment. 
       FIG.  32    illustrates an example of the relation between a video frame and adjusted luminance values for the corresponding backlight blocks. In a video frame  851 , only the region opposite to one backlight block is white and the other regions are black. 
     As described above, in the case where a backlight block of interest is adjoining a segmentation boundary in the backlight  30 , each video signal processing circuit sends information on the provisional luminance values for the backlight blocks adjoining the boundary to another video signal processing circuits to complement necessary information. 
     In  FIG.  32   , only the region in the video frame corresponding to the backlight block B 10 UR is white and the other regions are black. The video signal processing circuit  12 B refers to not only the provisional luminance values for the backlight blocks B 7 UR, B 8 UR, and B 11 UR in the second backlight region  350 B but also the provisional luminance values for the backlight blocks B 9 UL and B 12 UL in the first backlight region  350 A, the provisional luminance value for the backlight block B 3 DL in the third backlight region  350 C, and the provisional luminance values for the backlight blocks B 1 DR and B 2 DR in the fourth backlight region (see  FIG.  27   ) to determine the adjustment coefficient for the backlight block B 10 UR. The calculation method of the adjustment coefficient can be the one described in the first embodiment. As a result, the backlight block B 10 UR can be provided with an appropriate adjusted luminance value of 2.0. 
     As set forth above, embodiments of this disclosure have been described; however, this disclosure is not limited to the foregoing embodiments. Those skilled in the art can easily modify, add, or convert each element in the foregoing embodiments within the scope of this disclosure. A part of the configuration of one embodiment can be replaced with a configuration of another embodiment or a configuration of an embodiment can be incorporated into a configuration of another embodiment.