Display device and backlight control method

Abstract

To reduce the power consumption of backlights.SOLUTION: A display device includes a backlight including a plurality of backlight blocks, a display panel for producing display by light from the backlight, and a control device. The control device acquires a video frame, determines a grayscale feature value corresponding to each of the plurality of backlight blocks from a pixel grayscale indicated by the video frame, determines the light emission amount of each of the plurality of backlight blocks from the grayscale feature value in accordance with the current conversion function, and accesses the need for change of the current conversion function on the basis of the result of comparison of the statistical value of light emission amount of the plurality of backlight blocks with one or more preliminarily set thresholds of light emission amount.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present disclosure relates to the control of the backlight of a display device.

Background Art

[0002] In order to reduce the power consumption of the backlight of a liquid crystal display device and improve the contrast ratio, local dimming technology is used, in which the light emitting surface of the backlight is divided into a plurality of blocks, and the light emission amount of each block is individually increased or decreased according to the brightness and darkness in the video frame.

[0003] For example, in the case of displaying a white window on an all-black background, local dimming technology increases the lighting amount (brightness) of the area (block) of the backlight facing the area where white is displayed and decreases the light emission amount of the area (block) of the backlight in the background (black) portion.

[0004] By this control, the power of the backlight can be reduced compared to the state where the entire area of the backlight is always lit at 100%. Furthermore, since the brightness difference between the portion with a small light emission amount and the portion with a large light emission amount of the backlight becomes large, the contrast ratio within the same plane can be increased, and the display quality can be improved.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] Local dimming technology may use a frame memory to temporarily store the gradation data of a video frame in order to grasp the brightness and darkness within the video frame. In addition, since the light emission of each block of the backlight divided into a plurality of blocks affects adjacent peripheral blocks as leakage light, it is necessary to store the luminance distribution of each block considering the leakage light and perform correction control of the backlight emission amount according to the luminance distribution and the brightness and darkness of the video frame. For this reason, when attempting to perform more faithful local dimming with respect to the brightness and darkness of a video frame, the memory capacity and the scale of the arithmetic circuit increase.

[0007] As an example of the local dimming driving technology for the backlight, only one threshold is provided, and when the gradation threshold < input gradation, luminance reduction control is performed so that the luminance of the backlight block gradually decreases according to the input gradation in the gradation range from the gradation threshold to the low gradation side, and when the gradation threshold ≤ input gradation, a method of not performing the luminance reduction control of the backlight block is conceivable. Since there is only one threshold value, the memory capacity and the arithmetic circuit can be reduced.

[0008] However, in this method, when all the gradations of the input image are equal to or higher than the gradation threshold, the light emission amount of the backlight is 100%, and the power reduction effect of the backlight cannot be obtained. If the gradation threshold is set to a high value to enhance the power reduction effect, the light emission amount of the backlight for a low gradation image becomes too low, and the image quality may be degraded.

Means for Solving the Problems

[0009] A display device according to an aspect of the present disclosure includes a backlight including a plurality of backlight blocks, a display panel that performs display by light from the backlight, and a control device, wherein the control device acquires a video frame, determines a gradation feature value corresponding to each of the plurality of backlight blocks from the pixel gradations indicated by the video frame, determines the light emission amount of each of the plurality of backlight blocks according to the current conversion function from the corresponding gradation feature value, and determines whether to change the current conversion function based on a comparison result between a light emission amount statistical value of the plurality of backlight blocks and one or more preset light emission amount threshold values. [Effect of the Invention]

[0010] According to one aspect of the present disclosure, it is possible to reduce power consumption while suppressing a decrease in display quality of a display device. [Brief Description of the Drawings]

[0011]

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[0012] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be noted that this embodiment is merely an example for realizing the present disclosure and does not limit the technical scope of the present disclosure. The same reference numerals are assigned to common configurations in each figure. For the sake of clarity in the description, the dimensions and shapes of the illustrated objects may sometimes be exaggerated.

[0013] One embodiment of the present disclosure describes local dimming (LD) control of a backlight of a display device. In local dimming control, the backlight is divided into a plurality of blocks (backlight blocks), and the light emission amount of each backlight block is controlled according to the gradation of each pixel indicated by the video data.

[0014] As an example of local dimming control, one threshold value is provided, and when the gradation threshold value > input gradation, luminance reduction control of the backlight block is performed so that the luminance of the backlight block gradually decreases in the gradation range on the lower gradation side from the gradation threshold value according to the input gradation, and when the gradation threshold value ≤ input gradation, a method of not performing luminance reduction control of the backlight block is conceivable.

[0015] However, in this method, when all gradations of the input image are equal to or higher than the gradation threshold value, the light emission amount of the backlight is 100%, and the power reduction effect of the backlight cannot be obtained. If the gradation threshold value is set to a high value to enhance the power reduction effect, the light emission amount of the backlight for a low gradation image becomes too low, and the image quality may be deteriorated.

[0016] Hereinafter, the display device according to the embodiment of the present disclosure will be specifically described. The display device according to the embodiment of the present disclosure determines the light emission amount of each backlight block using a conversion function from the gradation data of the video frame. The display device determines whether to change the conversion function used based on the determined light emission amount, and changes the conversion function under predetermined conditions. Thereby, effective power consumption reduction is realized while suppressing deterioration of display quality. <First Embodiment>

[0017] FIG. 1 shows a configuration example of a display device according to an embodiment of the present disclosure. The display device displays an image by controlling the amount of light transmitted from the backlight. FIG. 1 shows a configuration example of a liquid crystal display device 1 as an example of the display device. The liquid crystal display device 1 includes a signal processing board 10, a power supply source 13, a video signal supply source 14, a liquid crystal display panel 20, a display driving driver 21, and a scanning driver 22. The liquid crystal display device 1 further includes a backlight 30, a backlight driving board 31, and a power supply source 32 for the backlight. The signal processing board 10 includes a power generation circuit 11 and a video signal processing circuit 12. For example, the signal processing board 10, the display driving driver 21, and the scanning driver 22 are included in a control device that controls the liquid crystal display panel 20.

[0018] The liquid crystal display device 1 displays a video corresponding to video data input from the outside. The video data includes video frames (also simply referred to as frames) that are sequentially displayed. The liquid crystal display panel 20 is disposed on the front side (viewing side) of the backlight 30, and displays the sequentially input video frames (images) by controlling the amount of transmitted light of the light from the backlight 30.

[0019] The power generation circuit 11 includes, for example, a DC-DC converter, generates a power supply for other circuits to operate, and supplies power to them. The video signal processing circuit 12 performs processing related to video display, such as generation of a signal for displaying an image on the liquid crystal display panel 20 and a signal for controlling the backlight 30. The power supply source 13 supplies power to the power generation circuit 11. The video signal supply source 14 supplies a video signal to the video signal processing circuit 12 according to video data from the outside.

[0020] The power generation circuit 11 generates a power supply for driving ICs such as the video signal processing circuit 12, the display driving driver 21, and the scanning driver 22. The display driving driver 21 and the scanning driver 22 are configured to operate by the power supply supplied from the power generation circuit 11 and execute their respective processes.

[0021] The display driving driver 21 generates a data signal from the video signal transmitted from the video signal processing circuit 12 and supplies it to the liquid crystal display panel 20. The scanning driver 22 sequentially selects the scanning lines of the liquid crystal display panel 20 according to the timing signal transmitted from the video signal processing circuit 12. The video signal processing circuit 12 also transmits a timing signal to the display driving driver 21, and the display driving driver 21 generates a data signal from the received video signal according to the timing signal and supplies it to the liquid crystal display panel 20.

[0022] The video signal processing circuit 12 uses the power supply supplied from the power generation circuit 11 to perform data array conversion for transmitting the externally input video signal to the display driving driver 21, and generation and transmission of the timing signal for the display driving driver 21 and the scanning driver 22 to operate.

[0023] The video signal processing circuit 12 further generates a drive control signal for driving and controlling a plurality of backlight blocks included in the backlight 30 and transmits it to the backlight drive substrate 31. The backlight blocks may simply be called blocks. Examples of the drive control signals include a backlight ON / OFF control signal and a dimming signal. The dimming signal is a PWM (Pulse Width Modulation) signal for time-division controlling the lighting time of the light source or a signal for controlling the amount of current flowing through the light source.

[0024] The backlight 30 is a planar light source device that is arranged on the back side of the liquid crystal display panel 20 and emits the light necessary for the liquid crystal display panel 20 to display an image. The backlight driving substrate 31 includes a backlight driving circuit and controls the light emission amount (luminance) of the backlight 30 according to the driving control signal transmitted from the video signal processing circuit 12. The backlight driving substrate 31 operates with the power supply from the backlight power supply source 32.

[0025] The liquid crystal display device 1 adopts local dimming technology. In the configuration example of FIG. 1, the backlight 30 is divided into X blocks (regions) along the X-axis and into Y blocks along the Y-axis. That is, each backlight block is rectangular, and the backlight blocks are arranged in a matrix.

[0026] The backlight 30 is composed of a plurality of backlight block rows, and each backlight block row consists of backlight blocks arranged in the X-axis direction (row direction). In one example, the number of backlight blocks in all backlight block rows is the same. Although it is the same for the sake of explanation, the number of backlight blocks does not have to be the same.

[0027] From another perspective, the backlight is composed of a plurality of backlight block columns, and each backlight block column consists of backlight blocks arranged in the Y-axis direction (column direction). The number of backlight blocks in all backlight block columns is the same. Although it is the same for the sake of explanation, the number of backlight blocks does not have to be the same. Note that the backlight blocks may be arranged in another layout different from the matrix layout.

[0028] The liquid crystal display device 1 can individually control the light emission amount of (X×Y) blocks. The liquid crystal display device 1 individually increases or decreases the light emission amount of each block according to the brightness and darkness of the pixels in the video frame in order to reduce power consumption and improve the contrast ratio.

[0029] The backlight 30 is, for example, a direct-lit backlight, and can include a light source array arranged within the backlight plane so as to face the liquid crystal display panel 20, and a diffusion plate between the light source array and the liquid crystal display panel 20. A typical example of the light source is an LED. One or more LEDs can be arranged within each block. The number of LEDs within one block is arbitrary. Based on the luminance efficiency and luminance distribution of the LEDs, an optimal number of LEDs are arranged at optimal positions.

[0030] The backlight 30 may not be a direct-lit type as described above, but an edge type including a light guide plate and a light source arranged on the side surface. The light-emitting region of the backlight 30 may be composed of, for example, blocks arranged in a matrix, or may be composed of a row of blocks in the horizontal or vertical direction.

[0031] The video signal processing circuit 12 generates a drive control signal for controlling the light emission amount of each block of the backlight 30, and transmits it to the backlight drive substrate 31. The backlight drive substrate 31 drives and controls the light sources of the backlight 30, such as LEDs, so that the blocks emit light at the light emission amount indicated by the drive control signal from the video signal processing circuit 12 for each block.

[0032] The video signal processing circuit 12 generates a timing signal for the display drive driver 21 and the scan driver 22 in accordance with the timing signal of the input video signal, and sequentially transmits the signal (frame signal) of each video frame within the video signal to the display drive driver 21. The frame signal indicates, for example, the gradation level of each pixel in the video frame. In color display, each pixel indicates a gradation level of red (R), green (G), or blue (B), and in monochrome display, it indicates a gradation level of white.

[0033] The video signal processing circuit 12 further analyzes the video frame and generates and transmits a drive control signal to the backlight 30 that illuminates the liquid crystal display panel 20 from the back based on the analysis result. The drive control signal to the backlight 30 is a drive control signal for the analyzed video frame or a video frame subsequent thereto. In the following description, it is assumed that the drive control signal to the backlight 30 is a drive control signal for a video frame subsequent to the analyzed video frame. Thereby, the memory amount for processing can be reduced.

[0034] As described above, the liquid crystal display device 1 employs local dimming technology. The video signal processing circuit 12 determines the provisional light emission amount of each block of the backlight 30 based on the analysis result of the video frame. Further, the video signal processing circuit 12 determines the corrected light emission amount of each backlight block based on the provisional light emission amount of the backlight block. The corrected light emission amount includes the maintained provisional light emission amount when not corrected. The video signal processing circuit 12 determines the corrected light emission amount of each block as the light emission amount for controlling the light emission of each backlight block.

[0035] The video signal processing circuit 12 generates a drive control signal corresponding to the corrected light emission amount and outputs it to each backlight block. For each backlight, the relationship between the corrected light emission amount and the drive control signal is preset. The drive control signal represents the actual light emission amount of each backlight block. In one example, the drive control signal indicates the duty ratio of the pulse width of PWM (Pulse Width Modulation) for power control.

[0036] Hereinafter, the details of the control of the backlight 30 by the video signal processing circuit 12 will be described. FIG. 2 schematically shows an example of the functional configuration of the video signal processing circuit 12. The video signal processing circuit 12 includes a display control drive signal generation unit 231, a block light emission amount determination unit 202, a block light emission amount arrangement unit 203, an LD threshold adjustment unit 210, and a backlight drive control signal generation unit 221. The LD threshold adjustment unit 210 includes an average value determination unit 211, a gradation threshold determination unit 212, and a block light emission amount average value calculation unit 213.

[0037] The display control drive signal generation unit 231 generates signals to be transmitted to the display drive driver 21 and the scanning driver 22 from the video signal received from the video signal source 14. The display control drive signal generation unit 231 transmits the signal of the gradation level of each pixel indicated by the video frame to the display drive driver 21 together with the timing signal, and transmits the timing signal to the scanning driver 22.

[0038] The block light emission amount determination unit 202 and the block light emission amount arrangement unit 203 determine the light emission amount of each backlight block based on the gradation of the pixels indicated by the video frame. Specifically, the block light emission amount determination unit 202 determines the light emission amount of each block of the backlight 30 based on the gradation of the pixels of the video frame.

[0039] The block light emission amount determination unit 202 determines a gradation feature value by a predetermined method from the gradation of the pixels in the portion of the display area facing the backlight block (also referred to as the display area block). The backlight blocks are respectively associated with the opposing display area blocks. The gradation feature value may be a statistical value of the gradation in the display area block, and may be, for example, a maximum value, an average value, or a frequently occurring value. From the viewpoints of image quality and circuit operation scale, a more preferable form is the maximum value.

[0040] The block light emission amount determination unit 202 holds a function that associates the gradation feature value with the backlight block light emission amount. The block light emission amount determination unit 202 calculates the light emission amount of the backlight block by inputting the gradation feature value into the function. The light emission amount of the backlight block is a normalized relative value and is assumed to be in the range from 0 to 1. The block light emission amount determination unit 202 transmits the light emission amount of each backlight block to the LD threshold adjustment unit 210.

[0041] Based on the gradation threshold obtained from the LD (Local Dimming) threshold adjustment unit 210, the block emission amount determination unit 202 determines a function (relationship) for determining the backlight block emission amount from the gradation characteristic value. In this example, the LD threshold adjustment unit 210 determines the gradation threshold for the current video frame based on the emission amount of the backlight blocks for the past video frames, and transmits it to the block emission amount determination unit 202.

[0042] The LD threshold adjustment unit 210 includes an average value determination unit 211, a gradation threshold determination unit 212, and a block emission amount average value calculation unit 213. The block emission amount average value calculation unit 213 calculates the average value of the emission amounts of all the backlight blocks for one video frame received from the block emission amount determination unit 202. The average value determination unit 211 compares the block emission amount average value calculation unit with one or a plurality of predetermined emission amount thresholds, and determines their relationship. The gradation threshold determination unit 212 determines the gradation threshold based on the determination result by the average value determination unit 211, and transmits it to the block emission amount determination unit 202. Details of the processing of the LD threshold adjustment unit 210 will be described later.

[0043] The block emission amount array unit 203 generates an array of the emission amounts of each of the backlight blocks determined by the block emission amount determination unit 202. The array associates the blocks of the backlight 30 with their emission amounts. The block emission amount array unit 203 transmits the generated array of emission amounts to the backlight drive control signal generation unit 221.

[0044] The backlight drive control signal generation unit 221 acquires the determined emission amounts of the respective backlight blocks from the block emission amount array unit 203, and generates drive control signals corresponding thereto. The backlight drive control signal generation unit 221 generates, for example, drive control signals for a specified emission amount according to the physical characteristics of the light sources included in the respective backlight blocks. The backlight drive control signal generation unit 221 transmits the drive control signals of the respective backlight blocks to the backlight drive substrate 31. Note that even if the relative values of the emission amounts of different backlight blocks are the same, the actual brightness (emission amount) of the backlight blocks may or may not be the same.

[0045] FIG. 3 shows a flowchart of an overall processing example of backlight block emission amount control by the video signal processing circuit 12. The flowchart of FIG. 3 shows the processing for one video frame.

[0046] The block emission amount determination unit 202 analyzes the gradation of the pixels of the video frame received from the video signal source 14, and determines gradation feature values for the respective backlight blocks (S11). The gradation feature value is a statistical value determined by a predetermined method from the gradations of the respective pixels of a pixel group (region composed of a plurality of pixels) associated with each block in advance. In this example, the gradation feature value is the maximum gradation in the corresponding pixel group.

[0047] Next, the block emission amount determination unit 202 determines the current function from the currently acquired gradation threshold value from the LD threshold adjustment unit 210 (S12). The function defines the relationship between the gradation feature value and the backlight block emission amount. The relationship between the gradation threshold value and the function is specified in advance. Further, the block emission amount determination unit 202 determines the emission amount of each backlight block from the gradation feature value of each backlight block and the current function (S13).

[0048] Next, the backlight drive control signal generation unit 221 drives and controls each backlight block according to the determined light emission amount of each backlight block (S14). Specifically, the determined light emission amount of each backlight block is transmitted to the block light emission amount array unit 203. The block light emission amount array unit 203 generates an array of the light emission amounts of each backlight block. The array associates each backlight block with its light emission amount. The array of light emission amounts is transmitted to the backlight drive control signal generation unit 221.

[0049] The backlight drive control signal generation unit 221 acquires the determined light emission amount of each backlight block from the block light emission amount array unit 203, and generates a drive control signal according thereto. The backlight drive control signal generation unit 221 transmits the drive control signal of each backlight block to the backlight drive substrate 31.

[0050] The light emission amount of each backlight block determined in step S13 is transmitted to the LD threshold adjustment unit 210. The block light emission amount average value calculation unit 213 calculates the average value (arithmetic mean) of the backlight block light emission amounts (S15). The average value determination unit 211 and the gradation threshold determination unit 212 determine the next gradation threshold from the relationship between the light emission amount average value and the light emission amount threshold (S16). The average value of the light emission amounts can be obtained by arithmetic mean, which can minimize the scale of the arithmetic circuit. However, calculation methods or statistical values different from the arithmetic mean may also be used.

[0051] For example, in the case of a display image where most of the display screen is bright and a part is dark, when using the arithmetic mean, the calculation result may be strongly affected by the light emission amount of the backlight blocks in the bright display area. To cope with such cases, the geometric mean may be used for the calculation of the average value. Also, considering that the light emission amount of each backlight block is based on the gradation characteristic value of the display area block, the harmonic mean may be used. Since there is a magnitude relationship of arithmetic mean ≥ geometric mean ≥ harmonic mean, if it is known in advance that there are many high-gradation display images, using the geometric mean or the harmonic mean will have a higher effect of reducing the backlight power.

[0052] Also, the root mean square may be used. Also, weighted averaging may be performed based on the frequency distribution table (histogram) of the light emission amount, or trimmed averaging that excludes extreme light emission amounts may be performed. When using the frequency distribution table (histogram), the light emission amount may be determined based on the class with a high frequency, or may be determined using the median.

[0053] FIG. 4 shows an example of a function (tone characteristic value - light emission amount conversion formula) that defines the relationship between the tone characteristic value and the light emission amount of the backlight block. As described above, the block light emission amount determination unit 202 determines a function that defines the relationship between the tone characteristic value and the light emission amount according to the tone threshold received from the LD threshold adjustment unit 210. In the example shown in FIG. 4, the block light emission amount determination unit 202 selects one from two functions according to the specified tone threshold.

[0054] In the graph of FIG. 4, the horizontal axis represents the tone characteristic value of the backlight block, that is, the maximum tone in the corresponding pixel group. In this example, the tone of the pixel takes any integer from 0 to 255. The vertical axis represents the light emission amount of the backlight block. The light emission amount is shown as a relative value, with the maximum value being 1 and the minimum value being 0.

[0055] Function 401 (first conversion function) represents the initial function, and the corresponding tone threshold A (first tone threshold) is 64. Function 402 (second conversion function) represents the function corrected from the initial function, and the corresponding tone threshold B (second tone threshold) is 80. For all tone characteristic values, the light emission amount by function 402 is less than or equal to the light emission amount by function 401, and in at least a part of the tone characteristic value region, the light emission amount by function 402 is less than the light emission amount by function 401. Note that the values of the tone threshold A and the tone threshold B are just examples and may be other values. In this example, the tone thresholds A and B are fixed values.

[0056] The function 401 is represented by a linear function with an intercept of 0 when the gradation characteristic value is between 0 and 64, and is a constant value of the maximum light emission amount 1.0 when the gradation characteristic value is in the range of 64 to 255. That is, the light emission amount of the initial function increases from 0 to 1.0 in the range of the gradation characteristic value from 0 to 64, and maintains the maximum value of 1.0 in the range of the gradation characteristic value from 64 to 255.

[0057] The function 402 is represented by a linear function with an intercept of 0 when the gradation characteristic value is between 0 and 80, and is a constant value of the maximum light emission amount 1.0 when the gradation characteristic value is in the range of 80 to 255. That is, the light emission amount of the correction function increases from 0 to 1.0 in the range of the gradation characteristic value from 0 to 80, and maintains the maximum value of 1.0 in the range of the gradation characteristic value from 80 to 255.

[0058] In the range where the gradation characteristic value is from 1 to 79, the light emission amount by the correction function 402 is smaller than the light emission amount by the initial function 401. Therefore, the power consumption can be further reduced. On the other hand, since the light emission amount by the correction function 402 is smaller than the light emission amount by the initial function in the low gradation range, the light emission amount in the low gradation image may become too low and the image visibility may deteriorate. One embodiment of the present disclosure determines a gradation threshold according to the light emission amount of the entire backlight. Thereby, the possibility that the light emission amount in the low gradation image becomes too low and the image visibility deteriorates is reduced.

[0059] FIG. 5 shows the relationship between the light emission amount threshold referred to for determining the gradation threshold and the functions 401 and 402 for determining the backlight block light emission amount. In this example, two light emission amount thresholds C and D are preset. For example, the light emission amount threshold C (the first light emission amount threshold) is 0.5, and the light emission amount threshold D (the second light emission amount threshold) is 0.8.

[0060] The LD threshold adjustment unit 210 calculates the average value of the backlight block light emission amount for one frame, and determines a gradation threshold for the next frame based on the relationship between the light emission amount average value and the light emission amount thresholds C and D. In one embodiment of the present disclosure, the LD threshold adjustment unit 210 determines a gradation threshold according to the following conditions.

[0061] Condition 1: Average emission amount ≤ Emission amount threshold C When the average value of the backlight block emission amount is less than or equal to the emission amount threshold C, the LD threshold adjustment unit 210 determines the gradation threshold as the initial gradation threshold A. If the emission amount threshold C is 0.5, when the average value of the backlight block emission amount is 0.5 or less, the gradation threshold is determined to be 64.

[0062] Condition 2: Average emission amount > Emission amount threshold D When the average value of the backlight block emission amount exceeds the emission amount threshold D over N consecutive frames (a predetermined number of consecutive times), the LD threshold adjustment unit 210 determines the gradation threshold as the corrected gradation threshold B. The corrected gradation threshold B may be a fixed value or a function of the average emission amount. Note that N is an integer of 1 or more. When N is a value greater than 1 (multiple consecutive frames), it is possible to reduce the deterioration of display quality due to frequent changes in the gradation threshold or the difficulty of backlight control.

[0063] Condition 3: Emission amount threshold C < Average emission amount ≤ Emission amount threshold D When the average value of the backlight block emission amount is greater than the emission amount threshold C and less than or equal to the emission amount threshold D, the LD threshold adjustment unit 210 maintains the gradation threshold of the previous frame. Thereby, it is possible to reduce the deterioration of display quality due to frequent changes in the gradation threshold or the difficulty of backlight control.

[0064] There may be only one specified emission amount threshold. When the average emission amount exceeds the emission amount threshold, the gradation threshold B is selected, and when the average emission amount is less than or equal to the emission amount threshold, the gradation threshold A is selected. The condition for selecting the gradation threshold B may be that the average emission amount exceeds the emission amount threshold in a plurality of consecutive frames.

[0065] FIG. 6 shows an example of the gradation characteristic value and the light emission amount of the backlight blocks for one frame. In the disclosed example of FIG. 6, the backlight consists of 15 backlight blocks divided into 5 parts in the x-axis direction and 3 parts in the y-axis direction. The video data of one frame is composed of 15 display area blocks facing the 15 backlight blocks. The gradation characteristic value is determined from the gradation data displayed on the pixels included in the display area block, and the cell matrix 411 indicates the gradation characteristic value of the backlight block. The cell matrix 412 indicates the light emission amount of the backlight block when the gradation threshold value is 64. The cell matrix 413 indicates the light emission amount of the backlight block when the gradation threshold value is 80.

[0066] The numbers in each cell of the cell matrix 411 indicate the gradation characteristic value of each backlight block. The numbers in each cell of the cell matrices 412 and 413 indicate the light emission amount of each backlight block.

[0067] As shown in FIG. 6, the light emission amount of the backlight block with a gradation characteristic value of 48 when the gradation threshold value is 64 is 48 / 64 = 0.75. On the other hand, the light emission amount of the backlight block with a gradation characteristic value of 48 when the gradation threshold value is 80 is 48 / 80 = 0.6. Thus, by increasing the gradation threshold value, the backlight power consumption can be further reduced.

[0068] On the other hand, if the corrected gradation threshold value is increased too much, the difference in the light emission amounts between the low-gradation backlight blocks and the high-gradation backlight blocks becomes large, and the display quality may be significantly degraded. Therefore, an appropriate correction value (gradation threshold value B - gradation threshold value A) with respect to the initial value is set so as to be within an appropriate range.

[0069] FIG. 7 is a flowchart showing details of the processing of the video signal processing circuit 12. The block light emission amount determination unit 202 receives one video frame (S21), and further reads the current gradation threshold value (S22). The block light emission amount determination unit 202 compares the gradation feature value with the gradation threshold value for each backlight block (S23). In the example described with reference to FIG. 5, the gradation threshold value is 64 or 80.

[0070] When the gradation feature value is greater than or equal to the gradation threshold value (S23: N), the light emission amount of the backlight block is determined to be 1 (S25). When the gradation feature value is less than the gradation threshold value (S23: Y), the light emission amount of the backlight block is obtained by dividing the gradation feature value by the gradation threshold value (S24). The block light emission amount determination unit 202 determines the light emission amount calculated according to the conditions of the gradation feature value and the gradation threshold value as the light emission amount of each backlight block (S26).

[0071] The calculated backlight block light emission amount is transmitted to the LD threshold adjustment unit 210. The block light emission amount average value calculation unit 213 calculates the average value G of the light emission amounts of the backlight blocks (S31). Next, the average value determination unit 211 compares the light emission amount average value G with the light emission amount threshold value C and the light emission amount threshold value D. As shown in FIG. 5, the light emission amount threshold value C < the light emission amount threshold value D.

[0072] First, the average value determination unit 211 compares the light emission amount average value G with the light emission amount threshold value C (S32). When the light emission amount average value G is less than or equal to the light emission amount threshold value C (S32: N), the gradation threshold value determination unit 212 determines the gradation threshold value as the initial gradation threshold value A, and further resets the counter value k to 0 (S33). The determined gradation threshold value is transmitted to the block light emission amount determination unit 202.

[0073] When the average emission amount G is greater than the emission amount threshold value C (S32: Y), the average value determination unit 211 compares the average emission amount G with the emission amount threshold value D (S34). When the average emission amount G is less than or equal to the emission amount threshold value D (S34: N), the gradation threshold value determination unit 212 determines to maintain the gradation threshold value at the current value, and further resets the counter value k to 0 (S35). The determined gradation threshold value is transmitted to the block emission amount determination unit 202.

[0074] When the average emission amount G is greater than the emission amount threshold value D (S34: Y), the average value determination unit 211 compares the counter value k with a preset maximum value N (S36). When the counter value k has reached N (S36: N), the gradation threshold value determination unit 212 determines whether the current gradation threshold value is 80 of the correction value (S37).

[0075] When the current gradation threshold value is 64 (S37: N), the gradation threshold value determination unit 212 changes the gradation threshold value from 64 to 80 and maintains the counter value k (S38). The determined gradation threshold value is transmitted to the block emission amount determination unit 202. When the current gradation threshold value is 80 (S37: Y), the gradation threshold value determination unit 212 maintains the gradation threshold value at 80 of the current value and maintains the counter value k (S39). The determined gradation threshold value is transmitted to the block emission amount determination unit 202.

[0076] In step S36, when the counter value k has not reached N (S36: Y), the gradation threshold value determination unit 212 maintains the gradation threshold value at the current value and increments the counter value k (S40). The determined gradation threshold value is transmitted to the block emission amount determination unit 202.

[0077] In this embodiment, when a sufficient power reduction effect is obtained with the initial set gradation threshold value and the gradation-emission amount conversion formula (for example, when the average emission amount is less than or equal to the emission amount threshold value C), there is no need for additional power reduction, so the initial setting is maintained. When the power reduction effect cannot be obtained with the gradation threshold value and the gradation-emission amount conversion formula, the power reduction effect can be obtained by appropriately changing the gradation threshold value and the gradation-emission amount conversion formula. <Second Embodiment>

[0078] Hereinafter, a second embodiment of the present disclosure will be described. Hereinafter, the differences from the first embodiment will mainly be described. Unless otherwise specified, the description of the first embodiment can be applied to the second embodiment.

[0079] FIG. 8 shows an example of a function that defines the relationship (tone characteristic value - light emission amount conversion formula) between the tone characteristic value and the light emission amount of the backlight block in the second embodiment. The block light emission amount determination unit 202 determines a function that defines the relationship between the tone characteristic value and the light emission amount according to the tone threshold received from the LD threshold adjustment unit 210. In the example shown in FIG. 8, the block light emission amount determination unit 202 selects one from two functions according to the specified tone threshold.

[0080] In the graph of FIG. 8, the horizontal axis represents the tone characteristic value of the backlight block. The vertical axis represents the light emission amount of the backlight block. The function 401 (first conversion function) represents the initial function, and the corresponding tone threshold A is 64. The function 401 has the same configuration as described with reference to FIGS. 4 and 5. The function 403 (second conversion function) represents the function corrected from the initial function, and the corresponding tone threshold E (third tone threshold) is 70. For all tone characteristic values, the light emission amount by the function 403 is less than or equal to the light emission amount by the function 401, and in at least a part of the tone characteristic value region, the light emission amount by the conversion function 403 is less than the light emission amount by the function 401. Note that the values of the tone threshold A and the tone threshold E are merely examples and may be other values. In this example, the tone thresholds A and E are fixed values.

[0081] The function 401 is represented by a linear function (the first linear function) that monotonically increases from 0 to 1.0 when the gradation characteristic value is between 0 and 64, and is represented by a constant linear function (the second linear function) in the range where the gradation characteristic value is from 64 to 255. The function 403 is represented by a linear function (the third linear function) that monotonically increases from 0 to the light emission coefficient F when the gradation characteristic value is between 0 and 70, and is represented by a linear function (the fourth linear function) that increases from the light emission coefficient F to 1.0 in the range where the gradation characteristic value is from 70 to 255. The slope when the gradation characteristic value is from 70 to 255 is smaller than the slope when the gradation characteristic value is from 0 to 70. The light emission coefficient F is a value greater than 0 and less than 1.0, for example, 0.8. In the example shown in FIG. 8, the value of the light emission coefficient F (the value of the light emission amount) coincides with the light emission threshold D, but these may be different, and either may be larger.

[0082] In the function 403 (correction function), the part of the low gradation characteristic value range where the gradation characteristic value is from 0 to the gradation threshold E is represented by the following formula. Light emission amount = (light emission coefficient F / gradation threshold E) × gradation characteristic value (conversion formula 1)

[0083] In the function 403 (correction function), the part of the high gradation characteristic value range where the gradation characteristic value is from the gradation threshold E to the maximum gradation is represented by the following formula. Light emission amount = ((1 - light emission coefficient F) / (maximum gradation - gradation threshold E)) × (gradation characteristic value - maximum gradation) + 1 (conversion formula 2) For example, the light emission coefficient F is 0.8, the gradation threshold E is 70, and the maximum gradation is 255.

[0084] Similarly, the function 401 (initial function) can also be represented by the above conversion formula 1 and conversion formula 2. However, some coefficients are changed. Specifically, the part of the gradation characteristic value in the low gradation characteristic value range from 0 to the gradation threshold A is represented by the conversion formula 1. The part of the gradation characteristic value in the high gradation characteristic value range from the gradation threshold A to the maximum gradation is represented by the conversion formula 2. Also, the light emission amount coefficients in the conversion formula 1 and the conversion formula 2 are 1.0, and the gradation threshold A is used instead of the gradation threshold E. The gradation threshold A is, for example, 64. In this way, the two functions can be defined with the light emission amount coefficient, the gradation threshold, and the maximum gradation as coefficients.

[0085] As shown in FIG. 8, the light emission amounts by the two functions 401 and 403 are the same at the gradation characteristic values of 0 and 255, and between them (in the range of the gradation characteristic values from 1 to 254), the light emission amount by the correction function 403 is smaller than the light emission amount by the initial function 401. Therefore, the power consumption can be further reduced. Since the slope of the correction function is smaller on the high gradation side, the influence on the display quality (reduction of the display luminance) can be minimized.

[0086] As shown in FIG. 8, each function for calculating the light emission amount from the gradation characteristic value has a bending point. This bending point may be within the region 410. The region 410 is a quadrilateral with the coordinates (A, 1.0), the coordinates (0.8A, 0.8), the coordinates (64, 0.8), and the coordinates (80, 1.0) as vertices. Here, A is the gradation threshold A, 80 gradations are the tolerance limit of the bending point, and the light emission amount 0.8 is the tolerance limit of the bending point. The tolerance limit is determined in the design. Thereby, the reduction of the display quality can be suppressed.

[0087] In this embodiment, similar to the first embodiment, the gradation threshold is determined according to the light emission amount of the entire backlight. Similar to the first embodiment, two light emission amount thresholds C and D are preset. The LD threshold adjustment unit 210 calculates the average value of the backlight block light emission amount for one frame, and determines the gradation threshold for the next frame based on the relationship between the light emission amount average value and the light emission amount thresholds C and D. In this embodiment, the LD threshold adjustment unit 210 determines the gradation threshold according to the following conditions.

[0088] Condition 1: Average emission amount ≤ Emission amount threshold C When the average value of the emission amount of the backlight block is less than or equal to the emission amount threshold C, the LD threshold adjustment unit 210 determines the gradation threshold as the initial gradation threshold A. If the emission amount threshold C is 0.5, when the average value of the emission amount of the backlight block is 0.5 or less, the gradation threshold is determined to be 64.

[0089] Condition 2: Average emission amount > Emission amount threshold D When the average value of the emission amount of the backlight block exceeds the emission amount threshold D over N consecutive frames (a predetermined number of consecutive times), the LD threshold adjustment unit 210 determines the gradation threshold as the corrected gradation threshold E. The corrected gradation threshold E may be a fixed value or a function of the average emission amount. Note that N is an integer of 1 or more. When N is a value greater than 1 (multiple consecutive frames), it is possible to reduce the deterioration of display quality due to frequent changes in the gradation threshold or the difficulty of backlight control.

[0090] Condition 3: Emission amount threshold C < Average emission amount ≤ Emission amount threshold D When the average value of the emission amount of the backlight block is greater than the emission amount threshold C and less than or equal to the emission amount threshold D, the LD threshold adjustment unit 210 maintains the gradation threshold of the previous frame. Thereby, it is possible to reduce the deterioration of display quality due to frequent changes in the gradation threshold or the difficulty of backlight control.

[0091] There may be only one specified emission amount threshold. When the average emission amount exceeds the emission amount threshold, the gradation threshold E is selected, and when the average emission amount is less than or equal to the emission amount threshold, the gradation threshold A is selected. The condition for selecting the gradation threshold E may be that the average emission amount exceeds the emission amount threshold in a plurality of consecutive frames.

[0092] FIG. 9 is a flowchart showing details of the processing of the video signal processing circuit 12. The block light emission amount determination unit 202 receives one video frame (S51), and further reads the current gradation threshold value (S52). The block light emission amount determination unit 202 compares the gradation feature value with the gradation threshold value for each backlight block (S53). In the example described with reference to FIG. 8, the gradation threshold value is 64 or 70.

[0093] When the gradation feature value is less than the gradation threshold value (S53: Y), the light emission amount of the backlight block is calculated using conversion formula 1 on the low gradation feature value side (S54). When the gradation feature value is greater than or equal to the gradation threshold value (S53: N), the light emission amount of the backlight block is calculated using conversion formula 2 on the high gradation feature value side.

[0094] In the example shown in FIG. 8, conversion formula 1 of the initial function is the conversion formula in the range of gradation feature values from 0 to 64 in function 401, and conversion formula 2 thereof is the conversion formula in the range of gradation feature values from 64 to 255 in function 401. Similarly, conversion formula 1 of the correction function is the conversion formula in the range of gradation feature values from 0 to 70 in function 403, and conversion formula 2 thereof is the conversion formula in the range of gradation feature values from 70 to 255 in function 403.

[0095] The block light emission amount determination unit 202 determines the light emission amount calculated according to the conditions of the gradation feature value and the gradation threshold value as the light emission amount of each backlight block (S56).

[0096] The calculated backlight block light emission amount is transmitted to the LD threshold adjustment unit 210. The block light emission amount average value calculation unit 213 calculates the average value G of the light emission amounts of the backlight blocks (S61). Next, the average value determination unit 211 compares the light emission amount average value G with the light emission amount threshold values C and D.

[0097] First, the average value determination unit 211 compares the average emission amount G with the emission amount threshold C (S62). When the average emission amount G is less than or equal to the emission amount threshold C (S62: N), the gradation threshold determination unit 212 determines the gradation threshold as the initial gradation threshold A, the emission amount coefficient as 1.0, and further resets the counter value k to 0 (S63). That is, the initial function (function 401) is selected. The determined gradation threshold and emission amount coefficient are transmitted to the block emission amount determination unit 202.

[0098] When the average emission amount G is greater than the emission amount threshold C (S62: Y), the average value determination unit 211 compares the average emission amount G with the emission amount threshold D (S64). When the average emission amount G is less than or equal to the emission amount threshold D (S64: N), the gradation threshold determination unit 212 determines to maintain the gradation threshold and the emission amount coefficient at their current values, and further resets the counter value k to 0 (S65). The determined gradation threshold and emission amount coefficient are transmitted to the block emission amount determination unit 202.

[0099] When the average emission amount G is greater than the emission amount threshold D (S64: Y), the average value determination unit 211 compares the counter value k with the preset maximum value N (S66). When the counter value k has reached N (S66: N), the gradation threshold determination unit 212 determines whether the current emission amount coefficient is the correction value F (for example, 0.8) (S67).

[0100] When the current emission amount coefficient is 1.0 and not F (S67: N), the gradation threshold determination unit 212 changes the gradation threshold from 64 (gradation threshold A) to 70 (gradation threshold E) and changes the emission amount coefficient from 1.0 to F. The value of k is maintained (S68). The determined gradation threshold and emission amount coefficient are transmitted to the block emission amount determination unit 202.

[0101] When the current emission amount coefficient is F (S67: Y), the gradation threshold determination unit 212 maintains the gradation threshold at its current value and maintains the emission amount coefficient at its current value F. The value of k is maintained (S69). The determined gradation threshold and emission amount coefficient are transmitted to the block emission amount determination unit 202.

[0102] In step S66, when the counter value k has not reached N (S66: Y), the gradation threshold determination unit 212 maintains the gradation threshold and the light emission amount coefficient at the current values, and increments the counter value k (S70). The determined gradation threshold and the light emission amount coefficient are transmitted to the block light emission amount determination unit 202.

[0103] The correction function of the second embodiment can obtain a power reduction effect smaller than the initial function over the entire gradation. The power reduction effect can be obtained without significantly reducing the light emission amount of the backlight block from the initial state over the entire gradation. Furthermore, power can be reduced even in the high gradation region. <Third Embodiment>

[0104] Hereinafter, the third embodiment of the present disclosure will be described. Hereinafter, the differences from the first embodiment will be mainly described. Unless otherwise specified, the description of the first embodiment can be applied to the third embodiment. In this embodiment, when the high light emission amount of the backlight continues, the gradation threshold is gradually increased. Thereby, while reducing the power consumption due to the decrease in the light emission amount, it is possible to suppress the deterioration of the display quality due to the sudden decrease in the light emission amount.

[0105] FIG. 10 schematically shows the stepwise change of the gradation threshold. FIG. 10 shows an example of a function that defines the relationship (gradation characteristic value - light emission amount conversion formula) between the gradation characteristic value and the light emission amount of the backlight block in the third embodiment. The block light emission amount determination unit 202 determines a function that defines the relationship between the gradation characteristic value and the light emission amount according to the gradation threshold received from the LD threshold adjustment unit 210. In the example shown in FIG. 10, the block light emission amount determination unit 202 determines a function according to the specified gradation threshold.

[0106] In the graph of FIG. 10, the horizontal axis represents the gradation characteristic value of the backlight block. The vertical axis represents the light emission amount of the backlight block. The function 401 (first conversion function) represents the initial function, and the corresponding initial gradation threshold (fourth gradation threshold) is 64. The function 401 has the same configuration as described with reference to FIGS. 4 and 5.

[0107] Function 404 (the second conversion function) represents the function corrected from the initial function 401, and the corresponding gradation threshold value (the fifth gradation threshold value) is 72. Function 404 is represented by a linear function that increases from 0 to 1.0 when the gradation feature value is between 0 and 72, and shows a constant 1.0 when the gradation feature value is in the range of 72 to 255. The difference between the gradation threshold value of function 404 and the gradation threshold value of function 401 is 8.

[0108] Function 402 (the third conversion function) represents the function corrected from function 404, and the corresponding gradation threshold value (the sixth gradation threshold value) is 80. Function 402 has the configuration as described with reference to FIGS. 4 and 5. The difference between the gradation threshold value of function 402 and the gradation threshold value of function 404 is 8. Thus, in this example, the step ΔJ of the gradually increasing gradation threshold value is constant. This value does not have to be constant, and for example, it may gradually increase or decrease.

[0109] In the example shown in FIG. 10, the maximum value of the gradation threshold value is 80, but it may be other numerical values. Also, the value of the step ΔJ of the gradation threshold value is not limited to 8, and for example, it may be a smaller value.

[0110] Similar to the first embodiment, this embodiment determines the gradation threshold value according to the light emission amount of the entire backlight. Similar to the first embodiment, two light emission amount threshold values C and D are preset. The LD threshold adjustment unit 210 calculates the average value of the backlight block light emission amount for one frame, and determines the gradation threshold value for the next frame based on the relationship between the light emission amount average value and the light emission amount threshold values C and D. In this embodiment, the LD threshold adjustment unit 210 determines the gradation threshold value according to the following conditions.

[0111] First condition: light emission amount average value ≤ light emission amount threshold value C When the average value of the backlight block light emission amount is less than or equal to the light emission amount threshold value C, the LD threshold adjustment unit 210 determines the gradation threshold value as the initial gradation threshold value A. Assuming that the light emission amount threshold value C is 0.5, when the average value of the backlight block light emission amount is 0.5 or less, the gradation threshold value is determined to be 64.

[0112] Second condition: Average emission amount > Emission amount threshold D When the average value of the backlight block emission amount exceeds the emission amount threshold D over N consecutive frames (a predetermined number of consecutive times), the LD threshold adjustment unit 210 increases the gradation threshold by ΔJ. The step value (correction amount) ΔJ may be a fixed value or a function of the gradation threshold immediately before the change. Note that N is an integer of 1 or more.

[0113] Third condition: Emission amount threshold C < Average emission amount ≤ Emission amount threshold D When the average value of the backlight block emission amount is greater than the emission amount threshold C and equal to or less than the emission amount threshold D, the LD threshold adjustment unit 210 maintains the gradation threshold of the previous frame.

[0114] Note that the emission amount thresholds C and D may be fixed values (maintaining the initial values) or may be changed according to the gradation threshold.

[0115] FIG. 11 is a diagram for explaining an example of gradation threshold control in the present embodiment. For convenience of explanation, the backlight is composed of 6 backlight blocks, and the display area blocks facing them are also 6. In this example, the gradation threshold is gradually increased from the initial value of 64 to 80. The maximum value of the gradation threshold is assumed to be greater than 80. The increase step ΔJ of the gradation threshold is 8. The emission amount threshold C is 0.5, and the emission amount threshold D is 0.8. Also, the number of consecutive video frames (count number) N for increasing the gradation threshold is 3. That is, when the average emission amount exceeds the emission amount threshold D = 0.8 in three consecutive video frames, the gradation threshold is increased by ΔJ = 8 for the video frame next to the three consecutive video frames. Note that if the gradation threshold has already reached the maximum value, that value is maintained.

[0116] In state S1, the gradation threshold is the initial value of 64. The gradation characteristic value of each backlight block indicated by the input video frame is 64. Therefore, the emission amount of each backlight block is 1.0. Their average emission amount is 1.0, which is greater than the emission amount threshold D = 0.8. When state S1 continues for three consecutive video frames, the gradation threshold of the fourth video frame thereafter is set to 72.

[0117] In state S2, the gradation threshold is 72. Assuming that video frames of the same data are continuously received, the gradation characteristic value of each backlight block is 64. Since the gradation threshold is 72, the light emission amount for the gradation characteristic value of 64 is 0.89. The average light emission amount is 0.89, which is greater than the light emission amount threshold D = 0.8. When state S2 continues for three consecutive video frames, the gradation threshold for the fourth video frame thereafter is set to 80.

[0118] In state S3, the gradation threshold is 80. Assuming that video frames of the same data are continuously received, the gradation characteristic value of each backlight block is 64. Since the gradation threshold is 80, the light emission amount for the gradation characteristic value of 64 is 0.8. The average light emission amount is 0.8, which is less than or equal to the light emission amount threshold D = 0.8 and greater than the light emission amount threshold C = 0.5. Therefore, the gradation threshold is maintained at 80.

[0119] As described above, the third embodiment is effective as control when it is not desired to reduce the in-plane contrast. <Fourth Embodiment>

[0120] Hereinafter, a fourth embodiment of the present disclosure will be described. Hereinafter, the differences from the first embodiment will mainly be described. Unless otherwise specified, the description of the first embodiment can be applied to the fourth embodiment. In this embodiment, when a high light emission amount of the backlight continues, in the function that converts the gradation characteristic value into the backlight block light emission amount, the value of the light emission amount at the inflection point is gradually decreased along the initial function. That is, the gradation threshold is decreased. Thereby, while reducing the power consumption due to the decrease in the light emission amount, it is possible to suppress the deterioration of the display quality due to the sudden decrease in the light emission amount. In addition, it is possible to reduce the possibility that the light emission amount in the low gradation image becomes too low and the image visibility deteriorates.

[0121] FIG. 12 shows an example of a function that defines the relationship (tone characteristic value - light emission amount conversion formula) between the tone characteristic value and the light emission amount of a backlight block in the fourth embodiment. The block light emission amount determination unit 202 determines a function that defines the relationship between the tone characteristic value and the light emission amount according to the tone threshold received from the LD threshold adjustment unit 210. In the example shown in FIG. 12, the block light emission amount determination unit 202 determines a function according to the specified tone threshold.

[0122] In the graph of FIG. 12, the horizontal axis represents the tone characteristic value of the backlight block. The vertical axis represents the light emission amount of the backlight block. The function 431 (first conversion function) represents the initial function, and the corresponding initial tone threshold is 80. The function 431 has the same configuration as the function 402 described with reference to FIGS. 4 and 5. In the function 431, from the origin (0, 0) to the inflection point B0, it is represented by a monotonically increasing linear function, and the light emission amount from the tone characteristic value of the inflection point B0 to the maximum tone characteristic value is constant at 1.0. Note that the light emission amount from the tone characteristic value of the inflection point B0 to the maximum tone characteristic value may be represented by a monotonically increasing linear function.

[0123] The function 432 (second conversion function) represents a function obtained by correcting the initial function 431 one or more times. As described above, the correction is, for example, subtracting the light emission amount of the inflection point in a predetermined step. The inflection point B1 of the function 432 is located at the coordinate where the light emission amount is 0.9 in the initial function 431. The tone threshold (seventh tone threshold) of the inflection point B1, that is, the value of the tone threshold of the correction function 432 is 72.

[0124] The function 432 is composed of two linear functions in the same manner as the function 403 shown in FIG. 8. That is, in the function 432, the light emission amount from the tone characteristic value 0 to the inflection point B1 is represented by a monotonically increasing linear function. The light emission amount from the inflection point B1 to the maximum tone characteristic value can be represented by a monotonically increasing linear function. The slope from the origin to the inflection point B1 is greater than the slope from the inflection point B1 to the maximum tone characteristic value.

[0125] Function 433 (the third conversion function) represents a function obtained by performing one or more corrections on correction function 432. The inflection point B2 of function 433 is located at the coordinate where the light emission amount is 0.85 in the initial function 431. The gradation threshold value (the eighth gradation threshold value) of inflection point B2, that is, the value of the gradation threshold of correction function 433 is 68.

[0126] Functions 431, 432, and 433 can each be represented by conversion formula 1 and conversion formula 2 described in the second embodiment. The slopes from the gradation characteristic value 0 to the inflection point are common to all functions. Also, in each function, the slope from the gradation characteristic value 0 to the inflection point is greater than the slope from the inflection point to the maximum gradation characteristic value. The slope from the inflection point to the maximum gradation characteristic value increases from function 431 to function 433. The step (subtraction amount) of subtracting the light emission amount of the inflection point for function correction may be, for example, a constant 0.01. Also, the minimum value of the light emission amount after subtraction may be 0.8.

[0127] Similar to the first embodiment, this embodiment determines the gradation threshold according to the light emission amount of the entire backlight. Similar to the first embodiment, two light emission amount threshold values C and D are preset. The LD threshold adjustment unit 210 calculates the average value of the backlight block light emission amount for one frame, and determines the position of the inflection point, that is, the gradation threshold, for the next frame based on the relationship between the light emission amount average value and the light emission amount threshold values C and D. In this embodiment, the LD threshold adjustment unit 210 determines the gradation threshold according to the following conditions.

[0128] First condition: Light emission amount average value ≤ light emission amount threshold value C When the average value of the backlight block light emission amount is less than or equal to the light emission amount threshold value C, the LD threshold adjustment unit 210 determines the inflection point as the initial inflection point B0 (the gradation threshold as the initial gradation threshold). Assuming the light emission amount threshold value C is 0.5, when the average value of the backlight block light emission amount is 0.5 or less, the initial inflection point is determined at the coordinate (80, 1.0). That is, the gradation threshold is determined to be 80.

[0129] Second condition: Light emission amount average value > light emission amount threshold value D When the average value of the backlight block light emission amount exceeds the light emission amount threshold D over N consecutive frames (a predetermined number of consecutive times), the LD threshold adjustment unit 210 decreases the light emission amount at the inflection point by ΔL. That is, the gradation threshold is decreased by ΔR. The step value (correction amount) ΔL may be a fixed value or a function of the gradation threshold immediately before the change. If ΔL is constant, ΔR is also constant. ΔL may be, for example, 0.01. Note that N is an integer of 1 or more.

[0130] Third condition: Light emission amount threshold C < average light emission amount ≤ light emission amount threshold D When the average value of the backlight block light emission amount is greater than the light emission amount threshold C and less than or equal to the light emission amount threshold D, the LD threshold adjustment unit 210 maintains the inflection point (coordinates) of the previous frame and maintains the function. Note that the light emission amount thresholds C and D may be fixed values (maintaining the initial values) or may be changed according to the gradation threshold.

[0131] FIG. 13 is a diagram for explaining an example of the control of the inflection point (gradation threshold) in the present embodiment. This example shows an example in which the light emission amount at the inflection point is gradually decreased from 0.95 to 0.85. The initial value of the light emission amount at the inflection point is 1.0. Also, the decrease step ΔL is -0.05. The gradation threshold also changes according to the change in the light emission amount at the inflection point. In the example shown in FIG. 13, the gradation threshold gradually decreases from 76 to 68. The decrease step ΔR is 4.

[0132] The light emission amount threshold C is 0.5, and the light emission amount threshold D is 0.88. Also, the number of consecutive video frames (count number) N for decreasing the light emission amount at the inflection point is 3. That is, when the average light emission amount exceeds the light emission amount threshold D = 0.88 in three consecutive video frames, the light emission amount at the inflection point is decreased by ΔL = 0.05. Note that if the light emission amount at the inflection point has already reached the minimum value, that value is maintained.

[0133] In state S101, the gradation threshold is 76, and the light emission amount at the inflection point is 0.95. That is, state S101 is the correction state next to the initial state. As described above, the gradation threshold of the initial state (initial function) is 80, and the light emission amount at the inflection point is 1.0. The gradation feature value of each backlight block indicated by the input video frame is 80.

[0134] Therefore, the light emission amount of each backlight block is calculated by conversion formula 2 described in the second embodiment of the corresponding function, and the value is 0.95. Their average light emission amount is 0.95, which is greater than the light emission amount threshold D = 0.88. When state S101 continues for three consecutive video frames, the light emission amount at the inflection point of the fourth video frame thereafter is 0.9, and the gradation threshold is set to 72 of the gradation feature value at that inflection point.

[0135] In state S102, the gradation threshold is 72, and the light emission amount at the inflection point is 0.90. Assuming that video frames of the same data are continuously received, the gradation feature value of each backlight block is 80. The light emission amount of each backlight block is calculated by conversion formula 2 of the corresponding function 432, and the value is 0.90. Their average light emission amount is 0.90, which is greater than the light emission amount threshold D = 0.88. When state S102 continues for three consecutive video frames, the light emission amount at the inflection point of the fourth video frame thereafter is 0.85, and the gradation threshold is set to 68, which is the gradation feature value at that inflection point.

[0136] In state S103, the gradation threshold is 68, and the light emission amount at the inflection point is 0.85. Assuming that video frames of the same data are continuously received, the gradation feature value of each backlight block is 80. The light emission amount of each backlight block is calculated by conversion formula 2 of the corresponding function 433, and the value is 0.86. Their average light emission amount is 0.86, which is less than or equal to the light emission amount threshold D = 0.88 and greater than the light emission amount threshold C = 0.5. Therefore, the coordinates of the inflection point are maintained, that is, the light emission amount and gradation threshold at the inflection point are maintained.

[0137] As described above, the fourth embodiment is effective as control when it is desired to suppress the image quality discomfort in an image with continuously changing gradations. <Fifth Embodiment>

[0138] Hereinafter, the fifth embodiment of the present disclosure will be described. In the fifth embodiment, after performing the control of the gradation characteristic value - light emission amount conversion characteristic (first control) according to the third embodiment, the control of the gradation characteristic value - light emission amount conversion characteristic (second control) according to the fourth embodiment is performed. Alternatively, the first control may be the control of the gradation characteristic value - light emission amount conversion characteristic according to the first embodiment, and the second control may be the control of the gradation characteristic value - light emission amount conversion characteristic according to the second embodiment. Thereby, while reducing the light emission amount of the entire backlight, it is possible to suppress a decrease in display quality due to excessive reduction of the light emission amount in the low gradation region. Hereinafter, an example of shifting from the control of the third embodiment to the control of the fourth embodiment will be described.

[0139] FIG. 14 is a diagram for explaining the control method of the gradation characteristic value - light emission amount conversion characteristic of the present embodiment. When a video frame with a high light emission amount is continuously input, in the present embodiment, after changing the gradation characteristic value - light emission amount conversion function by the first control, the gradation characteristic value - light emission amount conversion function is further changed by the second control.

[0140] The first control is the control described in the third embodiment, and the second control is the control described in the fourth embodiment. In FIG. 14, the graph of the first control is the same as the graph of FIG. 10, and the graph of the second control is the same as the graph of FIG. 12. The last function 402 in the first control and the initial function 431 in the second control are the same. Therefore, seamless transition from the first control to the second control can be achieved.

[0141] As described above, when a high light emission amount continues, the first control changes the current gradation characteristic value - light emission amount conversion function in the order of function 401, function 404 (first conversion function), and function 402 (second conversion function). The gradation threshold of function 401 is 64, the gradation threshold (ninth gradation threshold) of function 404 is 72, and the gradation threshold (tenth gradation threshold) of function 402 is 80.

[0142] As described above, the function 402 and the function 431 of the second control are the same function (second conversion function). When shifting from the first control to the second control, the second control changes the current tone characteristic value - light emission amount conversion function from the function 402, that is, the function 431 to the function 432 (third conversion function). The tone threshold value (eleventh tone threshold value) of the function 432 is 72, which is the tone characteristic value of the bending point B1.

[0143] In this embodiment, after the tone threshold value reaches the maximum value (80 in this example) by the first control, the process shifts to the second control. An example of the control of this embodiment will be described below. FIG. 15A is a diagram for explaining an example of tone threshold value control in the first control. In this example, the tone threshold value is gradually increased from the initial value of 64 to 80. The maximum value of the tone threshold value is set to 80.

[0144] The increase step ΔJ of the tone threshold value is 8. The light emission amount threshold value C is 0.5, and the light emission amount threshold value D is 0.8. Also, the number of consecutive video frames (count number) N for increasing the tone threshold value is set to 3. That is, when the average light emission amount exceeds the light emission amount threshold value D = 0.8 in three consecutive video frames, the tone threshold value is increased by ΔJ = 8.

[0145] As shown in FIG. 15A, in the state S151, the tone threshold value is the initial value of 64. The tone characteristic value of each backlight block indicated by the input video frame is 80. Therefore, the light emission amount of each backlight block is 1.0. Their average light emission amount is 1.0, which is greater than the light emission amount threshold value D = 0.8. When the state S151 continues for three consecutive video frames, the tone threshold value of the fourth video frame thereafter is set to 72.

[0146] In the state S152, the tone threshold value is 72. Assuming that the video frames of the same data are continuously received, the tone characteristic value of each backlight block is 80. Since the tone threshold value is 72, the light emission amount for the tone characteristic value 80 is 1.0. The average light emission amount is 1.0, which is greater than the light emission amount threshold value D = 0.8. When the state S152 continues for three consecutive video frames, the tone threshold value of the fourth video frame thereafter is set to 80.

[0147] In state S153, the gradation threshold is 80. Assuming that video frames of the same data are continuously received, the gradation characteristic value of each backlight block is 80. Since the gradation threshold is 80, the light emission amount corresponding to the gradation characteristic value 80 is 1.0. The average light emission amount is 1.0, which is greater than the light emission amount threshold D = 0.8. Since the gradation threshold has already reached the maximum value of 80, the control of the gradation characteristic value - light emission amount conversion characteristic shifts from the first control to the second control.

[0148] FIG. 15B shows an example in which, in the second control, the light emission amount of the inflection point is gradually decreased from 0.95 to 0.85. The initial value of the light emission amount of the inflection point is 1.0, and the initial value of the gradation threshold is 80. The decrease step ΔL is -0.05. The gradation threshold also changes in response to the change in the light emission amount of the inflection point. In the example shown in FIG. 15B, the gradation threshold gradually decreases from 76 to 68. The decrease step ΔR is 4.

[0149] The light emission amount threshold C is 0.5, and the light emission amount threshold D is 0.88. Between the first control and the second control, the values of the light emission amount thresholds C and D may be different or common. The number of consecutive video frames (count number) N for decreasing the inflection point light emission amount is set to 3. That is, when the average light emission amount exceeds the light emission amount threshold D = 0.88 in three consecutive video frames, the inflection point light emission amount is decreased by ΔL = 0.05. ΔL may be 0.01. Note that if the inflection point light emission amount has already reached the minimum value, that value is maintained. Note that between the first control and the second control, the threshold N of the number of consecutive frames may be common or different. For example, in the second control, N may be 1.

[0150] State S154 is a state that has changed from the state of state S153 by the second control. State S153 is the initial state of the second control. In state S154, the gradation threshold value is 76 and the light emission amount at the inflection point is 0.95. That is, state S154 is the next correction state after the initial state S153. The gradation threshold value of state S153 is 80 and the light emission amount at the inflection point is 1.0. The gradation feature value of each backlight block indicated by the input video frame is 80 as before.

[0151] The light emission amount of each backlight block is calculated by conversion formula 2 described in the second embodiment of the corresponding function, and the value is 0.95. Their average light emission amount is 0.95, which is greater than the light emission amount threshold D = 0.88. When state S154 continues for three consecutive video frames, the light emission amount at the inflection point of the fourth video frame thereafter is 0.9, and the gradation threshold value is set to 72 of the gradation feature value at that inflection point.

[0152] In state S155, the gradation threshold value is 72 and the light emission amount at the inflection point is 0.90. Assuming that video frames of the same data are continuously received, the gradation feature value of each backlight block is 80. The light emission amount of each backlight block is calculated by conversion formula 2 of the corresponding function 432, and the value is 0.90. Their average light emission amount is 0.90, which is greater than the light emission amount threshold D = 0.88. When state S155 continues for three consecutive video frames, the light emission amount at the inflection point of the fourth video frame thereafter is 0.85, and the gradation threshold value is set to 68, which is the gradation feature value at that inflection point.

[0153] In state S156, the gradation threshold value is 68 and the light emission amount at the inflection point is 0.85. Assuming that video frames of the same data are continuously received, the gradation feature value of each backlight block is 80. The light emission amount of each backlight block is calculated by conversion formula 2 of the corresponding function 433, and the value is 0.86. Their average light emission amount is 0.86, which is less than or equal to the light emission amount threshold D = 0.88 and greater than the light emission amount threshold C = 0.5. Therefore, the coordinates of the inflection point are maintained, that is, the light emission amount and gradation threshold value at the inflection point are maintained.

[0154] FIG. 16 shows the results of the control according to the present embodiment for the gradation characteristic values by several video frames. Specifically, it shows the light emission amount from the gradation characteristic value of each backlight block shown by the input video frame and the average value of the light emission amounts. The light emission amount threshold D is set to 0.88.

[0155] Case C1 shows the control results for continuous video frames including gradation characteristic values slightly exceeding the initial gradation threshold (= 64). The light emission amount of all backlight blocks by the initial function with the gradation threshold = 64 is 1.0, and their average value is 1.0. After the gradation threshold increases by the first control, the light emission amount of the backlight blocks decreases, and their average value decreases to 0.87. This value is smaller than the light emission amount threshold D 0.88, and the transition to the second control is not necessary.

[0156] Case C2 shows the control results for continuous video frames showing gradation characteristic values in which low gradation (= 48) and relatively high gradation (= 160) are mixed. The average value of the light emission amount by the initial function with the gradation threshold = 64 is 0.97. After the gradation threshold increases by the first control, the light emission amount of the backlight blocks decreases, and their average value decreases to 0.95. This value is larger than the light emission amount threshold D 0.88, and the control shifts from the first control to the second control. After the gradation threshold decreases by the second control, the light emission amount of the backlight blocks decreases, and their average value decreases to 0.85. This value is smaller than the light emission amount threshold D 0.88.

[0157] Case C3 shows the control results for continuous video frames showing gradation characteristic values in which low gradation (= 48) and high gradation (= 200) are mixed. The average value of the light emission amount by the initial function with the gradation threshold = 64 is 0.95. After the gradation threshold increases by the first control, the light emission amount of the backlight blocks decreases, and their average value decreases to 0.92. This value is larger than the light emission amount threshold D 0.88, and the control shifts from the first control to the second control. After the gradation threshold decreases by the second control, the light emission amount of the backlight blocks decreases, and their average value decreases to 0.87. This value is smaller than the light emission amount threshold D 0.88.

[0158] This embodiment increases the possibility of ensuring that the light emission amount of the backlight block is 80% or more of the initial value. In particular, it is possible to control the backlight so that the light emission amount in the low gray scale region does not decrease too much. <Sixth Embodiment>

[0159] Hereinafter, the sixth embodiment of the present disclosure will be described. The sixth embodiment describes various characteristics of the gray scale characteristic value from 0 to the gray scale threshold value after changing the gray scale threshold value from the initial value, that is, various conversion formulas from the gray scale characteristic value to the light emission amount. All functions (conversion formulas) described below are monotonically increasing functions.

[0160] Figures 17A to 17F show examples of functions where the gray scale characteristic value ranges from 0 to the gray scale threshold value. Figure 17A shows a function consisting of a convex upward curve. As a comparative example, a monotonically increasing linear function is also shown. The linear function can achieve a small circuit scale, and since the change rate of the function is constant, the portion that causes image quality discomfort can be minimized as much as possible. The convex upward curve requires a relatively large circuit scale, but since the decrease in the light emission amount near the inflection point is small, it is effective when prioritizing the image quality near the threshold value.

[0161] Figure 17B shows a function consisting of a convex downward curve. As a comparative example, a monotonically increasing linear function is also shown. The convex downward curve requires a relatively large circuit scale, but it is effective when prioritizing the power reduction effect over the light emission amount near the inflection point.

[0162] Figure 17C shows a function that is convex upward and continuously connects two types of linear functions with different slopes. As a comparative example, a monotonically increasing linear function is also shown. Such a function can be realized with a relatively small-scale circuit, and since the decrease in the light emission amount near the inflection point is small, it is effective when prioritizing the image quality near the threshold value.

[0163] FIG. 17D shows a function that is convex downward and continuously connects two linear functions with different slopes. As a comparative example, a monotonically increasing linear function is also shown. Such a function can be realized in a relatively small-scale circuit and is effective when prioritizing the power reduction effect over the light emission amount near the inflection point.

[0164] FIG. 17E shows a function that continuously connects an upward convex curve and a downward convex curve. As a comparative example, a monotonically increasing linear function is also shown. Such a function requires a relatively large circuit scale but is effective for control that minimizes the reduction of the light emission amount in the low-tone region.

[0165] FIG. 17F shows a function that continuously connects a downward convex curve and an upward convex curve. As a comparative example, a monotonically increasing linear function is also shown. Such a function is effective when prioritizing the luminance near the inflection point over the low-tone region. <Seventh Embodiment>

[0166] Hereinafter, the seventh embodiment of the present disclosure will be described. The seventh embodiment changes the tone characteristic value - light emission amount conversion function in the opposite direction to the change of the tone characteristic value - light emission amount conversion function described in the first to fourth embodiments.

[0167] As described with reference to FIG. 5 in the first embodiment, the tone characteristic value - light emission amount conversion function is changed from the initial function 401 to the correction function 402. In this embodiment, with the threshold B as the initial tone threshold and the function 402 as the initial function, the function to be used is selected from the initial function 402 and the function 401 based on the relationship between the average light emission amount and the light emission amount threshold. The conditions for determining the tone threshold in the first embodiment can be rewritten as follows.

[0168] First condition: Average light emission amount ≤ light emission amount threshold C When the average value of the backlight block light emission amount is less than or equal to the light emission amount threshold C (the first light emission amount threshold) over N consecutive frames (a predetermined number of consecutive times), the LD threshold adjustment unit 210 determines the tone threshold as the corrected tone threshold A. N is an integer of 1 or more. The corrected tone threshold A may be a fixed value or a function of the average light emission amount.

[0169] Second condition: average light emission value > light emission threshold D When the average value of the backlight block light emission amount exceeds the light emission threshold D, the LD threshold adjustment unit 210 determines the gradation threshold as the initial gradation threshold B.

[0170] Third condition: light emission threshold C < average light emission value ≤ light emission threshold D When the average value of the backlight block light emission amount is greater than the light emission threshold C and equal to or less than the light emission threshold D, the LD threshold adjustment unit 210 maintains the gradation threshold of the previous frame.

[0171] As described with reference to FIG. 8, in the second embodiment, the gradation characteristic value - light emission amount conversion function is changed from the initial function 401 to the correction function 403. In this embodiment, with the threshold E as the initial gradation threshold and the function 403 as the initial function, the function to be used is selected from the initial function 403 and the function 401 based on the relationship between the average light emission value and the light emission threshold. The conditions for determining the gradation threshold in the second embodiment can be rewritten as follows.

[0172] First condition: average light emission value ≤ light emission threshold C When the average value of the backlight block light emission amount is equal to or less than the light emission threshold C for N consecutive frames (a predetermined number of consecutive times), the LD threshold adjustment unit 210 determines the gradation threshold as the gradation threshold A. The gradation threshold A may be a fixed value or a function of the average light emission value. N is an integer of 1 or more.

[0173] Second condition: average light emission value > light emission threshold D When the average value of the backlight block light emission amount exceeds the light emission threshold D, the LD threshold adjustment unit 210 determines the gradation threshold as the initial gradation threshold E.

[0174] Third condition: light emission threshold C < average light emission value ≤ light emission threshold D When the average value of the backlight block light emission amount is greater than the light emission threshold C and equal to or less than the light emission threshold D, the LD threshold adjustment unit 210 maintains the gradation threshold of the previous frame.

[0175] As described with reference to FIG. 10, the third embodiment increases the gradation threshold value step by step from the initial value. As shown in FIG. 18, in this embodiment, the gradation threshold value is decreased step by step from the initial value. In this embodiment, the initial value which is the maximum value of the gradation threshold value, the minimum value, and the amount of decrease of the gradation threshold value at each step are set. The conditions for determining the gradation threshold value in the third embodiment can be rewritten as follows.

[0176] Condition 1: Average emission amount ≤ Emission amount threshold C When the average value of the backlight block emission amount is less than or equal to the emission amount threshold C over N consecutive frames (a predetermined number of consecutive times), the LD threshold adjustment unit 210 decreases the gradation threshold value by ΔJ. ΔJ may be a fixed value or a function of the gradation threshold value immediately before the change. N is an integer of 1 or more.

[0177] Condition 2: Average emission amount > Emission amount threshold D When the average value of the backlight block emission amount exceeds the emission amount threshold D, the LD threshold adjustment unit 210 determines the gradation threshold value as the initial gradation threshold value (maximum value).

[0178] Condition 3: Emission amount threshold C < Average emission amount ≤ Emission amount threshold D When the average value of the backlight block emission amount is greater than the emission amount threshold C and less than or equal to the emission amount threshold D, the LD threshold adjustment unit 210 maintains the gradation threshold value of the previous frame. Note that the emission amount thresholds C and D may be fixed values (maintaining the initial values) or may be changed according to the gradation threshold value.

[0179] As described with reference to FIG. 12, in the fourth embodiment, the light emission amount at the inflection point is gradually decreased from the initial value. That is, the gradation threshold value, which is the gradation characteristic value of the inflection point, is gradually decreased. In this embodiment, the light emission amount at the inflection point is gradually increased from the initial value. As a result, the gradation threshold value is gradually increased from the initial value. In this embodiment, the initial value, which is the minimum value of the light emission amount at the inflection point, the maximum value, and the increase amount of the light emission amount at the inflection point at each stage are set. The initial inflection point is the inflection point B2 in FIG. 12, and the inflection point of the function changes step by step from the inflection point B2 to the inflection point B0. The conditions for determining the gradation threshold value in the fourth embodiment are rewritten as follows.

[0180] First condition: average light emission amount ≦ light emission threshold value C If the average value of the backlight block light emission amount is equal to or less than the light emission threshold value C over N consecutive frames (a predetermined number of consecutive times), the LD threshold adjustment unit 210 increases the light emission amount at the inflection point by ΔL. ΔL may be a fixed value or a function of the gradation threshold value immediately before the change. N is an integer of 1 or more.

[0181] Second condition: average light emission amount > light emission threshold value D When the average value of the backlight block light emission amount exceeds the light emission threshold value D, the LD threshold adjustment unit 210 determines the inflection point as the initial inflection point B2.

[0182] Third condition: light emission threshold value C < average light emission amount ≦ light emission threshold value D When the average value of the backlight block light emission amount is greater than the light emission threshold value C and equal to or less than the light emission threshold value D, the LD threshold adjustment unit 210 maintains the inflection point (coordinates) of the previous frame. The light emission threshold values C and D may be fixed values (maintaining the initial values) or may be changed according to the gradation threshold value.

[0183] In addition, the first control and the second control in the fifth embodiment can be interchanged by making the changes from the first embodiment to the fourth embodiment. As described above, in the seventh embodiment, when the average emission amount is equal to or less than the emission amount threshold C for N frames continuously, the first conversion function is used. When the average emission amount is greater than the emission amount threshold C and equal to or less than the emission amount threshold D, it is determined to maintain the current conversion function. When the average emission amount exceeds the emission amount threshold D, the second conversion function is used.

[0184] In each embodiment of the present disclosure, the gradation threshold is set to a value smaller than 80 gradations. Since the emission amount of the backlight block becomes smaller for a display image in which the gradation feature value is lower than the gradation threshold, the influence of the luminance distribution of each backlight block and the leakage light from the surrounding blocks also becomes smaller. That is, by setting the gradation threshold to a small value, it is possible to omit the emission amount correction process considering the luminance distribution of each backlight block and the influence of the leakage light from the surrounding blocks. Therefore, the liquid crystal display device 1 does not include a storage unit for storing a luminance distribution as in the prior art. Also, it does not include a correction arithmetic processing circuit adapted to the luminance distribution. Thus, it is possible to prevent the circuit scale from increasing.

[0185] Also, although the gradation feature value in each embodiment of the present disclosure uses the maximum gradation value in the display area block, an example of the means for determining the gradation feature value will be described with reference to FIGS. 19A, 19B, and 20. FIG. 19A shows a plurality of display area blocks 503 constituting the video frame 501, and FIG. 19B is an enlarged view of the display area block 503 of the hatched portion shown in FIG. 19A.

[0186] As shown in FIG. 19B, each display area block 503 of the video frame 501 includes pixels 517 of N rows × M columns × 3 (RGB). Gradation data is given to each of the RGB pixels 517. In FIG. 19B, the numerical values shown for each pixel 517 represent the gradation data given to each pixel 517. For example, in the first row and first column, the gradation data of the R pixel is 50 gradations, the gradation data of the G pixel is 53 gradations, and the gradation data of the B pixel is 46 gradations.

[0187] The display area block 503 is composed of N rows from the block first row 514 to the block last row 515. Each row is composed of R, G, and B pixels 517 arranged cyclically. The row 516 next to the block last row 515 is the block first row of the next display area block. Also, the display area block 503 is composed of M columns from the block first column 511 to the block last column 512. The column 513 next to the block last column 512 is the block first column of the next display area block 503. Each column is composed of R, G, and B pixel columns. Also, FIG. 19B shows the right boundary 519 and the lower boundary 518 of the display area block 503.

[0188] Next, it will be described with reference to FIG. 20. When a video frame is input to the liquid crystal display device 1, the block light emission amount determination unit 202 starts extracting grayscale data from the first row and first column of the video frame. Specifically, the grayscale data (53 grayscales) of the G pixel, which is the maximum value, is extracted from the grayscale data given to the RGB pixels in the first row and first column of the target display area block and temporarily stored (S11-1). Subsequently, it moves to the first row and second column, and the grayscale data (53 grayscales) of the G pixel, which is the maximum value, is extracted from the grayscale data given to the RGB pixels and compared with the maximum value extracted in the first row and first column (S11-2). In this case, since the two maximum values to be compared are the same value, 53 grayscales are temporarily stored as the maximum grayscale (S11-3).

[0189] Subsequently, it moves to the first row and third column, and the grayscale data (70 grayscales) of the G pixel, which is the maximum value, is extracted from the grayscale data given to the RGB pixels (S11-1) and compared with the temporarily stored maximum value (53 grayscales) (S11-2). As a result of the comparison, since the newly extracted 70 grayscales are larger, the maximum value is updated to 70 grayscales and temporarily stored (S11-3). Thereafter, the same operation is repeated until the block last column (M columns). As a result of repeatedly extracting and comparing the maximum value until the block last column, if the grayscale data (70 grayscales) of the G pixel extracted and temporarily stored in the first row and third column is the maximum value, this value is temporarily stored as the maximum value of the first row in the target display area block.

[0190] When the extraction operation of the maximum value up to the last column (1 row by M columns) of the block is completed in the target display area block, the target is shifted to the adjacent display area block in the x-axis direction, and the extraction of the maximum value is continued. That is, the above-described operation is sequentially performed on the RGB pixels after the first block column (M + 1 column) of the first row. Then, the maximum value of the first row in each display area block is temporarily stored (S11-4).

[0191] When the extraction of the maximum value of the first row of the video frame is completed, the operation shifts to the extraction operation of the gradation data of the RGB pixels included in the second row. For example, as shown in FIG. 19B, it is assumed that the gradation data given to the G pixel in the RGB pixel of the second row and the third column is 72 gradations. At this point, the maximum value temporarily stored is 70 gradations temporarily stored in the first row, and in the second row and the third column, the newly extracted 72 gradations are larger. Therefore, the stored value is updated with 72 gradations as the maximum value (S11-5). Thereafter, the extraction operation of the maximum value, the comparison, and the temporary storage operation are repeated for the third row, the fourth row, and so on.

[0192] The extraction operation of the maximum value is performed up to the last row (Nth row) of the block of the display area block. As shown in FIG. 19B, it is assumed that 90 gradations are extracted as the maximum value in the last row (Nth row) of the block. If the value temporarily stored up to the (N - 1)th row is 72 gradations, the newly extracted 90 gradations in the last row are larger. Therefore, it is updated with 90 gradations as the maximum value and temporarily stored.

[0193] When the extraction operation of the maximum value for the display area block is completed, the maximum value among the maximum values extracted in each row from the first row to the last row of the block can be obtained. The block light emission amount determination unit 202 stores the maximum value among these maximum values in the memory as the gradation feature value (S11-6). For the video frame divided into X in the x-axis direction and Y in the y-axis direction in FIG. 19A, X × Y gradation feature values are determined and stored in the memory.

[0194] In an embodiment of the present disclosure, the maximum value of the gradation data given to each RGB pixel included in each row of the video frame is extracted and temporarily stored for each block section, and the maximum value is further updated for each row. The value to be temporarily stored is one for each display area block, and a register circuit can be used for temporary storage. Since the maximum value of the RGB pixels included in one row is sequentially extracted from the head of the video frame, an extraction circuit can be realized if there is a memory amount of at least about 2 to 10 lines. Therefore, determination of the gradation feature value can be realized by a small-scale circuit without using a frame memory or the like. <Embodiment 8>

[0195] FIG. 21 shows a configuration example of a display device according to an embodiment of the present specification. Hereinafter, differences from the configuration example shown in FIG. 1 will be mainly described. The liquid crystal display device 1 includes video signal sources 14A and 14B, and display drive drivers 21A and 21B. The signal processing board 10 includes video signal processing circuits 12A and 12B. The video signal processing circuit 12A is a first processing circuit, and the video signal processing circuit 12B is a second processing circuit. This configuration can be adopted in a case where the display area has a high resolution and exceeds the resolution that can be driven by one IC, and a plurality of ICs are used to divide the display area into upper, lower, left, and right parts and drive them.

[0196] The liquid crystal display panel 20 includes adjacent first display area 250A and second display area 250B. The video signal processing circuit 12A performs processing related to video display, such as generation of a signal for displaying an image in the first display area 250A and a signal for controlling the backlight 30. The video signal processing circuit 12B performs processing related to video display, such as generation of a signal for displaying an image in the second display area 250B and a signal for controlling the backlight 30. The video signal source 14A supplies a video signal to the video signal processing circuit 12A, and the video signal source 14B supplies a video signal to the video signal processing circuit 12B.

[0197] The display driver 21A generates a data signal from the video signal transmitted from the video signal processing circuit 12A and supplies it to the first display area 250A. The display driver 21B generates a data signal from the video signal transmitted from the video signal processing circuit 12B and supplies it to the second display area 250B. The video signal processing circuit 12A also transmits a timing signal to the display driver 21A, and the display driver 21A generates a data signal from the received video signal according to the timing signal and supplies it to the first display area 250A. The video signal processing circuit 12B also transmits a timing signal to the display driver 21B, and the display driver 21B generates a data signal from the received video signal according to the timing signal and supplies it to the second display area 250B.

[0198] The video signal processing circuit 12A uses the power supplied from the power generation circuit 11 to perform data array conversion for transmitting the externally input video signal to the display driver 21A and generation and transmission of a timing signal for the operation of the drivers 21A and 22. The video signal processing circuit 12A further generates a drive control signal for driving and controlling the backlight 30 and transmits it to the backlight drive board 31.

[0199] The video signal processing circuit 12B uses the power supplied from the power generation circuit 11 to perform data array conversion for transmitting the externally input video signal to the display driver 21B and generation and transmission of a timing signal for the operation of the display drivers 21B and 22. The video signal processing circuit 12B further generates a drive control signal for driving and controlling the backlight 30 and transmits it to the backlight drive board 31.

[0200] The backlight drive board 31 includes a backlight drive circuit and controls the lighting (brightness) of the backlight 30 according to the drive control signals transmitted from the video signal processing circuits 12A and 12B.

[0201] The image signal processing circuits 12A and 12B each generate a drive control signal for controlling the luminance of each block of the backlight 30 and transmit it to the backlight drive substrate 31. The backlight drive substrate 31 drives and controls the light sources of the backlight 30 so that the blocks emit light at the luminance values of the blocks indicated by the drive control signals from the image signal processing circuits 12A and 12B.

[0202] The image signal processing circuit 12A generates a timing signal for the display drive driver 21A and the scan driver 22 in accordance with the timing signal of the input image signal, and sequentially transmits the signal (frame signal) of each image frame in the image signal to the display drive driver 21A. The image signal processing circuit 12B generates a timing signal for the display drive driver 21B and the scan driver 22 in accordance with the timing signal of the input image signal, and sequentially transmits the signal (frame signal) of each image frame in the image signal to the display drive driver 21B.

[0203] The image signal processing circuit 12A analyzes the image frame and generates and transmits a drive control signal to the backlight 30 that illuminates the first display area 250A from the back based on the analysis result. The image signal processing circuit 12B analyzes the image frame and generates and transmits a drive control signal to the backlight 30 that illuminates the second display area 250B from the back based on the analysis result.

[0204] FIG. 22 schematically shows the configuration of the backlight 30. The backlight 30 is composed of a first backlight area 350A on the left side and a second backlight area 350B on the right side. In the example described below, each of the first backlight area 350A and the second backlight area 350B is composed of 12 backlight blocks.

[0205] The first backlight area 350A is located directly below the first display area 250A. The first backlight area 350A faces the first display area 250A on the back side of the first display area 250A and irradiates the first display area 250A with light. The second backlight area 350B is located directly below the second display area 250B. The second backlight area 350B faces the second display area 250B on the back side of the second display area 250B and irradiates the second display area 250B with light.

[0206] As described in the other embodiments above, the video signal processing circuit 12A determines the gradation characteristic values and the light emission amounts of the backlight blocks in the first backlight area 350A. Similarly, as described in the other embodiments above, the video signal processing circuit 12B determines the gradation characteristic values and the light emission amounts of the backlight blocks in the second backlight area 350B.

[0207] Here, the video signal processing circuits 12A and 12B use the same conversion function for calculating the light emission amount from the gradation characteristic values. Specifically, the video signal processing circuits 12A and 12B select the same conversion function in the initial state. Further, the video signal processing circuits 12A and 12B determine whether to change or maintain the conversion function based on the average value of the light emission amounts of the entire backlight 30 including the first backlight area 350A and the second backlight area 350B.

[0208] As a result, the video signal processing circuits 12A and 12B can always select a common conversion function, and can determine the same light emission amount for the backlight blocks with the same gradation characteristic values in the first backlight area 350A and the second backlight area 350B.

[0209] The video signal processing circuits 12A and 12B each receive only the video data of only one of the first display area 250A and the second display area 250B, and individually control the first backlight area 350A and the second backlight area 350B. In the form of the present embodiment, the video signal processing circuits 12A and 12B communicate with each other the information for determining the average value of the light emission amounts of the backlight blocks calculated by the other video signal processing circuit. Thereby, the video signal processing circuits 12A and 12B can each efficiently calculate the average light emission amount of the entire backlight 30.

[0210] In the example described below, the average light emission amount of the first backlight area 350A and the average light emission amount of the second backlight area 350B are each transmitted from the responsible video signal processing circuit to the other video signal processing circuit. Note that any information that can determine the average light emission amount of the other backlight area, for example, the light emission amounts of all the backlight blocks in the backlight area, may be communicated between the video signal processing circuits 12A and 12B.

[0211] The video signal processing circuits 12A and 12B each calculate the average light emission amount of the entire backlight 30 from the average light emission amount of the responsible backlight area and the average light emission amount of the other backlight area. Further, the video signal processing circuits 12A and 12B each determine, based on the average light emission amount of the entire backlight 30, a function for calculating the light emission amount from the gradation characteristic value to be used next for the current conversion function. As described above, the conversion function to be used is maintained or changed to another conversion function.

[0212] Hereinafter, a specific example will be described. Assume that the conversion functions currently used by the video signal processing circuits 12A and 12B are the conversion function 401 shown in FIG. 14. Note that any conversion function described in other embodiments can be used.

[0213] FIG. 23 shows an example of calculating the light emission amount from the gradation characteristic values of the backlight blocks by each of the video signal processing circuits 12A and 12B. The video signal processing circuit 12A calculates the gradation characteristic value of each backlight block in the first backlight region 350A based on the video data acquired from the video signal source 14A. The matrix 601A shows the calculation result, and the value of each cell indicates the gradation characteristic value of the corresponding backlight block.

[0214] Similarly, the video signal processing circuit 12B calculates the gradation characteristic value of each backlight block in the second backlight region 350B based on the video data acquired from the video signal source 14B. The matrix 601B shows the calculation result, and the value of each cell indicates the gradation characteristic value of the corresponding backlight block.

[0215] Next, the video signal processing circuit 12A calculates the light emission amount 603A of each backlight block from the gradation characteristic value 601A using the conversion function 401. As shown in FIG. 14, the gradation threshold of the conversion function 401 is 64, which is a linear increasing function in the range below it, and outputs the upper limit value (1.0) in the range above it. Similarly, the video signal processing circuit 12B calculates the light emission amount 603B of each backlight block from the gradation characteristic value 601B using the conversion function 401.

[0216] Next, the video signal processing circuits 12A and 12B calculate the average light emission amount of the backlight 30. FIG. 24 shows the calculation process of the average light emission amount by the video signal processing circuits 12A and 12B. First, the video signal processing circuit 12A calculates the average light emission amount (G_ave) of the first backlight region 350A from the backlight light emission amount 603A and includes it in the management information 605A. In this example, the value is 0.904. Similarly, the video signal processing circuit 12B calculates the average light emission amount (G_ave) of the second backlight region 350B from the backlight light emission amount 603B and includes it in the management information 605B. In this example, the value is 1.0.

[0217] The video signal processing circuit 12A transmits the calculated average light emission amount of the first backlight area 350A to the video signal processing circuit 12B. The video signal processing circuit 12B includes the received value in the management information 605B. The video signal processing circuit 12B transmits the calculated average light emission amount of the second backlight area 350B to the video signal processing circuit 12A. The video signal processing circuit 12A includes the received value in the management information 605A. The video signal processing circuits 12A and 12B each calculate the average light emission amount of the entire backlight 30 from the average light emission amounts of the two backlight areas 350A and 350B and include it in the management information 605A and 605B. In this example, the average light emission amount (Unified_G_ave) of the entire backlight 30 is 0.952.

[0218] Both the video signal processing circuits 12A and 12B determine the following conversion function based on the average light emission amount of the entire backlight 30. Since the currently used conversion function is common, the next selected conversion function is also common to the video signal processing circuits 12A and 12B. As a result, a common conversion function is always used for the first backlight area 350A and the second backlight area 350B, and the same light emission amount can be assigned to backlight blocks with the same gradation characteristic value. If different light emission amounts are assigned to backlight blocks with the same gradation characteristic value, the luminance difference is felt as an image quality discomfort, so it is preferable to assign the same light emission amount.

[0219] Hereinafter, the change in the light emission amount of each backlight block in the first backlight area 350A and the second backlight area 350B for consecutive video frames of the same gradation data will be described. It is assumed that the video signal processing circuits 12A and 12B execute the control example shown in FIG. 14. Also, it is assumed that the conversion function 401 is used at the start of the process.

[0220] First, the change in the light emission amount of the backlight block in the first backlight area 350A will be described. The steps LS1 to LS5 described below are executed, for example, every predetermined number of video frames.

[0221] Referring to FIG. 25A, in step LS1, the video signal processing circuit 12A determines the gradation characteristic value 611A of the backlight block in the first backlight region 350A from one input video frame. The video signal processing circuit 12A calculates the light emission amount 613A of the backlight block in the first backlight region 350A from the gradation characteristic value 611A by the conversion function 401.

[0222] The average light emission amount (G_ave) of the light emission amount 613A is 0.904. The average light emission amount (G_ave) of the second backlight region 350B is 1.0 as will be described later. Therefore, the average light emission amount (Unified_G_ave) of the entire backlight 30 is 0.952. This value is larger than the light emission amount threshold D = 0.88 shown in FIG. 14. Therefore, the conversion function to be used is switched from the conversion function 401 to the conversion function 404.

[0223] Referring to FIG. 25B, in step LS2, the gradation characteristic value 611B of the video frame is the same as the gradation characteristic value 611A of the video frame in step LS1. The video signal processing circuit 12A calculates the light emission amount 613B from the gradation characteristic value 611B by the conversion function 404.

[0224] The average light emission amount (G_ave) of the light emission amount 613B is 0.877. The average light emission amount (G_ave) of the second backlight region 350B is 1.0 as will be described later. Therefore, the average light emission amount (Unified_G_ave) of the entire backlight 30 is 0.938. This value is larger than the light emission amount threshold D = 0.88 shown in FIG. 14. Therefore, the conversion function to be used is switched from the conversion function 404 to the conversion function 402.

[0225] Referring to FIG. 25C, in step LS3, the gradation characteristic value 611C of the video frame is the same as the gradation characteristic value 611B of the video frame in step LS2. The video signal processing circuit 12A calculates the light emission amount 613C from the gradation characteristic value 611C by the conversion function 402.

[0226] The average emission amount (G_ave) of the emission amount 613C is 0.856. The average emission amount (G_ave) of the second backlight region 350B is 1.0, as will be described later. Therefore, the average emission amount (Unified_G_ave) of the entire backlight 30 is 0.928. This value is greater than the emission amount threshold D = 0.88 shown in FIG. 14. Accordingly, the conversion function to be used is switched from the conversion function 402 of the first control to the conversion function 432 of the second control.

[0227] Referring to FIG. 25D, in step LS4, the gradation feature value 611D of the video frame is the same as the gradation feature value 611C of the video frame in step LS3. The video signal processing circuit 12A calculates the emission amount 613D from the gradation feature value 611D by the conversion function 432.

[0228] The average emission amount (G_ave) of the emission amount 613D is 0.845. The average emission amount (G_ave) of the second backlight region 350B is 0.982, as will be described later. Therefore, the average emission amount (Unified_G_ave) of the entire backlight 30 is 0.914. This value is greater than the emission amount threshold D = 0.88 shown in FIG. 14. Accordingly, the conversion function to be used is switched from the conversion function 432 to the conversion function 433.

[0229] Referring to FIG. 25E, in step LS5, the gradation feature value 611E of the video frame is the same as the gradation feature value 611D of the video frame in step LS4. The video signal processing circuit 12A calculates the emission amount 613E from the gradation feature value 611E by the conversion function 433.

[0230] The average emission amount (G_ave) of the emission amount 613E is 0.839. The average emission amount (G_ave) of the second backlight region 350B is 0.947, as will be described later. Therefore, the average emission amount (Unified_G_ave) of the entire backlight 30 is 0.893. This value is greater than the emission amount threshold D = 0.88 shown in FIG. 14. Since the emission amount at the inflection point has reached the subtraction limit value, the conversion function 433 is maintained.

[0231] Next, the change in the light emission amount of the backlight blocks in the second backlight region 350B will be described. Steps RS1 to RS5 described below correspond to steps LS1 to LS5 above.

[0232] Referring to FIG. 26A, in step RS1, the video signal processing circuit 12B determines the gradation characteristic value 631A of the backlight blocks in the second backlight region 350B from one input video frame. The video signal processing circuit 12B calculates the light emission amount 633A of the backlight blocks in the second backlight region 350B from the gradation characteristic value 631A by the conversion function 401.

[0233] The average light emission amount (G_ave) of the light emission amount 633A is 1.0. The average light emission amount (G_ave) of the first backlight region 350A is 0.904 as described above. Therefore, the average light emission amount (Unified_G_ave) of the entire backlight 30 is 0.952. This value is larger than the light emission amount threshold D = 0.88 shown in FIG. 14. Therefore, the conversion function to be used is switched from the conversion function 401 to the conversion function 404.

[0234] Referring to FIG. 26B, in step RS2, the gradation characteristic value 631B of the video frame is the same as the gradation characteristic value 631A of the video frame in step RS1. The video signal processing circuit 12B calculates the light emission amount 633B from the gradation characteristic value 631B by the conversion function 404.

[0235] The average light emission amount (G_ave) of the light emission amount 633B is 1.0. The average light emission amount (G_ave) of the first backlight region 350A is 0.877 as described above. Therefore, the average light emission amount (Unified_G_ave) of the entire backlight 30 is 0.938. This value is larger than the light emission amount threshold D = 0.88 shown in FIG. 14. Therefore, the conversion function to be used is switched from the conversion function 404 to the conversion function 402.

[0236] Referring to FIG. 26C, in step RS3, the gradation characteristic value 631C of the video frame is the same as the gradation characteristic value 631B of the video frame in step RS2. The video signal processing circuit 12B calculates the light emission amount 633C from the gradation characteristic value 631C by the conversion function 402.

[0237] The average light emission amount (G_ave) of the light emission amount 633C is 1.0. The average light emission amount (G_ave) of the first backlight region 350A is 0.856 as described above. Therefore, the average light emission amount (Unified_G_ave) of the entire backlight 30 is 0.928. This value is greater than the light emission amount threshold D = 0.88 shown in FIG. 14. Therefore, the conversion function to be used is switched from the conversion function 402 of the first control to the conversion function 432 of the second control.

[0238] Referring to FIG. 26D, in step RS4, the gradation characteristic value 631D of the video frame is the same as the gradation characteristic value 631C of the video frame in step RS3. The video signal processing circuit 12B calculates the light emission amount 633D from the gradation characteristic value 631D by the conversion function 432.

[0239] The average light emission amount (G_ave) of the light emission amount 633D is 0.982. The average light emission amount (G_ave) of the first backlight region 350A is 0.845 as described above. Therefore, the average light emission amount (Unified_G_ave) of the entire backlight 30 is 0.914. This value is greater than the light emission amount threshold D = 0.88 shown in FIG. 14. Therefore, the conversion function to be used is switched from the conversion function 432 to the conversion function 433.

[0240] Referring to FIG. 26E, in step RS5, the gradation characteristic value 631E of the video frame is the same as the gradation characteristic value 631D of the video frame in step RS4. The video signal processing circuit 12B calculates the light emission amount 633E from the gradation characteristic value 631E by the conversion function 433.

[0241] The average emission amount (G_ave) of the emission amount 633E is 0.947. The average emission amount (G_ave) of the first backlight region 350A is 0.839 as described above. Therefore, the average emission amount (Unified_G_ave) of the entire backlight 30 is 0.893. This value is larger than the emission amount threshold D = 0.88 shown in FIG. 14. Since the emission amount at the bending point has reached the subtraction limit value, the conversion function 433 is maintained.

[0242] By comparing step LS1 to LS5 and step RS1 to RS5, the conversion functions used in each pair of steps for processing the same video frame are common. Therefore, the emission amounts for the same gradation feature values in different backlight regions are the same.

[0243] In the above example, the display region and the backlight region are divided into two, and each of the divided regions is controlled by two video signal processing circuits. In other examples, the number of divisions of the display region and the backlight region and the number of video signal processing circuits may be three or more. Information is communicated between the video signal processing circuits that control adjacent display regions and backlight regions. Hereinafter, an example of controlling a display region and a backlight region divided into four will be described.

[0244] FIG. 27 schematically shows the configuration of the backlight 30. The backlight 30 is composed of a first backlight region 350A on the upper left side, a second backlight region 350B on the upper right side, a third backlight region 350C on the lower left side, and a fourth backlight region 350D on the lower right side. In the example described below, each of the backlight regions 350A - 350D is composed of 12 backlight blocks.

[0245] The backlight regions 350A - 350D are respectively arranged directly below four different display regions and face each other. The backlight regions 350A - 350D respectively irradiate the opposing display regions. Four video signal processing circuits for controlling each pair of the four display regions and the backlight regions are implemented.

[0246] Figure 28 shows an example of the gradation characteristic values of the backlight blocks calculated by the four video signal processing circuits 12A - 12D. The video signal processing circuit 12A calculates the gradation characteristic value of each backlight block in the first backlight region 350A based on the video data acquired from the corresponding video signal source. The matrix 621A shows the calculation result, and the value of each cell indicates the gradation characteristic value of the corresponding backlight block.

[0247] The video signal processing circuit 12B calculates the gradation characteristic value of each backlight block in the second backlight region 350B based on the video data acquired from the corresponding video signal source. The matrix 621B shows the calculation result, and the value of each cell indicates the gradation characteristic value of the corresponding backlight block.

[0248] The video signal processing circuit 12C calculates the gradation characteristic value of each backlight block in the third backlight region 350C based on the video data acquired from the corresponding video signal source. The matrix 621C shows the calculation result, and the value of each cell indicates the gradation characteristic value of the corresponding backlight block.

[0249] The video signal processing circuit 12D calculates the gradation characteristic value of each backlight block in the fourth backlight region 350D based on the video data acquired from the corresponding video signal source. The matrix 621D shows the calculation result, and the value of each cell indicates the gradation characteristic value of the corresponding backlight block.

[0250] Figure 29 shows the light emission amounts of the backlight blocks calculated by the video signal processing circuits 12A - 12D respectively. The video signal processing circuits 12A - 12D calculate the light emission amounts 623A - 623D of the backlight blocks from the backlight gradation characteristic values 621A - 621D using the conversion function 401 respectively.

[0251] Next, the video signal processing circuits 12A and 12B calculate the average light emission amount of the backlight 30. FIG. 30 shows the calculation results of the average light emission amount of the corresponding backlight regions 350A - 350D by the video signal processing circuits 12A - 12D.

[0252] The video signal processing circuit 12A calculates the average light emission amount of the first backlight region 350A from the backlight light emission amount 623A and includes it in the management information 625A. In this example, the value is 0.904. The video signal processing circuit 12B calculates the average light emission amount of the second backlight region 350B from the backlight light emission amount 623B and includes it in the management information 625B. In this example, the value is 1.0.

[0253] The video signal processing circuit 12C calculates the average light emission amount of the third backlight region 350C from the backlight light emission amount 623C and includes it in the management information 625C. In this example, the value is 0.904. The video signal processing circuit 12D calculates the average light emission amount of the fourth backlight region 350D from the backlight light emission amount 623D and includes it in the management information 625D. In this example, the value is 1.0.

[0254] Next, the video signal processing circuits 12A - 12D transmit the information on the average light emission amount they calculated to other video processing circuits. For example, the information on the average light emission amount is communicated between the video signal processing circuits 12A and 12C, and the information on the average light emission amount is communicated between the video signal processing circuits 12B and 12D. After that, the information on the average light emission amount is communicated between the video signal processing circuits 12A and 12B, and the information on the average light emission amount is communicated between the video signal processing circuits 12C and 12D. Note that if each video signal processing circuit can obtain the information on the average light emission amount of all the backlight regions 350A - 350D, the exchange of information between the video signal processing circuits 12A - 12D is arbitrary.

[0255] FIG. 31 shows the management information of the average light emission amount finally held by each of the video signal processing circuits 12A - 12D. As described above, since the information on the average light emission amount of the backlight regions 350A - 350D is communicated among the video signal processing circuits 12A - 12D, the content of the management information of the average light emission amount is common. In this example, the average light emission amount (Unified_G_ave) of the entire backlight 30 is 0.952.

[0256] The video signal processing circuits 12A - 12D determine the following conversion function based on the average light emission amount of the entire backlight 30. Since the currently used conversion function is common, the next selected conversion function is also common to the video signal processing circuits 12A - 12D. As a result, a common conversion function is always used for all the backlight regions 350A - 350D, and the same light emission amount can be assigned to the backlight blocks with the same gradation characteristic value.

[0257] FIG. 32 shows an example of the data communicated between the video signal processing circuits 12A and 12B. Note that the following description is applicable to the communication between any two video signal processing circuits. The video signal processing circuit 12A uses the clock signal SCK1 and the control signal CS1 to transmit the data signal SDA1 indicating the average light emission amount to the video signal processing circuit 12B. The video signal processing circuit 12B uses the clock signal SCK2 and the control signal CS2 to transmit the data signal SDA2 indicating the average light emission amount to the video signal processing circuit 12A. For data transmission, for example, serial transmission can be used. Also, some signal lines may be shared between the video signal processing circuits 12A and 12B to reduce the number of signal transmission lines.

[0258] FIG. 33 shows an example of the waveforms of the clock signal SCK, the data signal SDA, and the control signal CS. The data signal SDA indicates the average light emission amount of a partial backlight region. The example in FIG. 31 transmits G_ave = 0.904 of the video signal processing circuit 12A using 16 - bit serial transmission. For example, at a 12 - bit resolution, the average light emission amount 0.904 can be represented as 3702.

[0259] As described above, embodiments of the present disclosure have been described, but the present disclosure is not limited to the above embodiments. A person skilled in the art can easily change, add, or transform each element of the above embodiments within the scope of the present disclosure. It is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment.

Explanation of Reference Numerals

[0260] 1 Liquid crystal display device 10 Signal processing substrate 11 Power generation circuit 12 Video signal processing circuit 13 Power supply source 14 Video signal supply source 20 Liquid crystal display panel 21 Display driving driver 22 Scanning driver 30 Backlight 31 Backlight driving substrate 32 Power supply source for backlight 202 Block light emission amount determination unit 203 Block light emission amount arrangement unit 210 LD threshold adjustment unit 211 Average value determination unit 212 Tone threshold determination unit 213 Block light emission amount average value calculation unit 221 Backlight driving control signal generation unit 231 Display control driving signal generation unit

Claims

1. A backlight including a plurality of backlight blocks, a display panel that performs display by light from the backlight, a control device, comprising: wherein the control device acquires a video frame, determines a gradation feature value corresponding to each of the plurality of backlight blocks from the pixel gradations indicated by the video frame, determines the light emission amount of each of the plurality of backlight blocks according to a current conversion function from the corresponding gradation feature value, determines whether to change the current conversion function based on a comparison result between a light emission amount statistical value of the plurality of backlight blocks and one or more preset light emission amount threshold values. A display device.

2. The display device according to Claim 1, wherein the light emission amount statistical value is an average light emission amount. A display device.

3. The display device according to Claim 2, wherein the one or more threshold values include a first light emission amount threshold value and a second light emission amount threshold value greater than the first light emission amount threshold value, the current conversion function is a first conversion function or a second conversion function, for all gradation feature values, the light emission amount by the second conversion function is less than or equal to the light emission amount by the first conversion function, in at least a partial gradation feature value region, the light emission amount by the second conversion function is less than the light emission amount by the first conversion function, wherein the control device uses the first conversion function when the average light emission amount is less than or equal to the first light emission amount threshold value, determines to maintain the current conversion function when the average light emission amount is greater than the first light emission amount threshold value and less than or equal to the second light emission amount threshold value, uses the second conversion function when the average light emission amount continuously exceeds the second light emission amount threshold value a predetermined number of times or more. A display device.

4. The display device according to Claim 3, wherein the gradation feature value is the maximum gradation in pixels corresponding to each backlight block, the first conversion function indicates that the light emission amount monotonically increases from zero to the maximum light emission amount in a range from zero gradation to below a first gradation threshold value, and the maximum light emission amount is constant in a range greater than the first gradation threshold value, the second conversion function indicates that the light emission amount monotonically increases from zero to the maximum light emission amount in a range from zero gradation to below a second gradation threshold value, and the maximum light emission amount is constant in a range greater than the second gradation threshold value, the second gradation threshold value is greater than the first gradation threshold value. A display device.

5. The display device according to Claim 3, The first conversion function indicates the minimum light emission amount at the minimum gradation feature value and indicates the maximum light emission amount at the maximum gradation feature value. The second conversion function indicates the minimum light emission amount at the minimum gradation feature value and indicates the maximum light emission amount at the maximum gradation feature value. In a range greater than the third gradation threshold and less than the maximum gradation feature value, the light emission amount by the second conversion function is smaller than the light emission amount by the first conversion function. Display device.

6. The display device according to claim 3, The first conversion function indicates the minimum light emission amount at the minimum gradation feature value and indicates the maximum light emission amount at the maximum gradation feature value. The second conversion function indicates the minimum light emission amount at the minimum gradation feature value and indicates the maximum light emission amount at the maximum gradation feature value. The first conversion function is composed of a first linear function that monotonically increases in a range from the minimum gradation feature value to the first gradation threshold, and a second linear function that is constant or monotonically increases in a range from the first gradation threshold to the maximum gradation feature value. The second conversion function is composed of a third linear function that monotonically increases in a range from the minimum gradation feature value to the third gradation threshold, and a fourth linear function that monotonically increases in a range from the third gradation threshold to the maximum gradation feature value. The third gradation threshold is smaller than the first gradation threshold. The slope of the third linear function is less than or equal to the slope of the first linear function. The slope of the fourth linear function is greater than the slope of the second linear function. Display device.

7. The display device according to claim 2, The one or more light emission amount thresholds include a first light emission amount threshold and a second light emission amount threshold greater than the first light emission amount threshold. The current conversion function is the first conversion function. The control device, When the average light emission amount continuously exceeds the second light emission amount threshold a predetermined number of times or more, changes the current conversion function from the first conversion function to the second conversion function. After changing the current conversion function to the second conversion function, when the average light emission amount continuously exceeds the second light emission amount threshold a predetermined number of times or more, changes the current conversion function from the second conversion function to the third conversion function. For all gradation feature values, the light emission amount by the second conversion function is less than or equal to the light emission amount by the first conversion function. In at least a part of the gradation feature value region, the light emission amount by the second conversion function is less than the light emission amount by the first conversion function. For all gradation feature values, the light emission amount by the third conversion function is less than or equal to the light emission amount by the second conversion function. In at least a part of the gradation characteristic value region, the light emission amount by the third conversion function is less than the light emission amount by the second conversion function. Display device.

8. The display device according to claim 7, wherein the gradation characteristic value is the maximum gradation in pixels corresponding to each backlight block, the first conversion function indicates that the light emission amount monotonically increases from zero to the maximum light emission amount in a range from zero gradation to equal to or less than a fourth gradation threshold value, and the maximum light emission amount is constant in a range greater than the fourth gradation threshold value, the second conversion function indicates that the light emission amount monotonically increases from zero to the maximum light emission amount in a range from zero gradation to equal to or less than a fifth gradation threshold value, and the maximum light emission amount is constant in a range greater than the fifth gradation threshold value, the fifth gradation threshold value is greater than the fourth gradation threshold value, the third conversion function indicates that the light emission amount monotonically increases from zero to the maximum light emission amount in a range from zero gradation to equal to or less than a sixth gradation threshold value, and the maximum light emission amount is constant in a range greater than the sixth gradation threshold value, the sixth gradation threshold value is greater than the fifth gradation threshold value, Display device.

9. The display device according to claim 7, wherein the gradation characteristic value is the maximum gradation in pixels corresponding to each backlight block, the first conversion function shows the minimum light emission amount at the minimum gradation characteristic value and the maximum light emission amount at the maximum gradation characteristic value, the second conversion function shows the minimum light emission amount at the minimum gradation characteristic value and the maximum light emission amount at the maximum gradation characteristic value, the third conversion function shows the minimum light emission amount at the minimum gradation characteristic value and the maximum light emission amount at the maximum gradation characteristic value, in a range greater than a seventh gradation threshold value and less than the maximum gradation characteristic value, the light emission amount by the second conversion function is smaller than the light emission amount by the first conversion function, in a range greater than an eighth gradation threshold value and less than the maximum gradation characteristic value, the light emission amount by the third conversion function is smaller than the light emission amount by the second conversion function, the eighth gradation threshold value is smaller than the seventh gradation threshold value, Display device.

10. The display device according to claim 7, wherein the gradation characteristic value is the maximum gradation in pixels corresponding to each backlight block, the first conversion function indicates that the light emission amount monotonically increases from zero to the maximum light emission amount in a range from zero gradation to equal to or less than a ninth gradation threshold value, and the maximum light emission amount is constant in a range greater than the ninth gradation threshold value, The second conversion function indicates that the light emission amount monotonically increases from zero to the maximum light emission amount in the range from zero gradation to the tenth gradation threshold or less, and the maximum light emission amount is constant in the range greater than the tenth gradation threshold. The tenth gradation threshold is greater than the ninth gradation threshold. The third conversion function indicates a light emission amount of zero at zero gradation and the maximum light emission amount at the maximum gradation feature value. In the range greater than the eleventh gradation threshold and less than the maximum gradation feature value, the light emission amount by the third conversion function is smaller than the light emission amount by the second conversion function. The eleventh gradation threshold is smaller than the tenth gradation threshold. Display device.

11. The display device according to claim 2, wherein the one or more thresholds include a first light emission amount threshold and a second light emission amount threshold greater than the first light emission amount threshold. wherein the current conversion function is the first conversion function or the second conversion function. For all gradation feature values, the light emission amount by the second conversion function is less than or equal to the light emission amount by the first conversion function. In at least a part of the gradation feature value region, the light emission amount by the second conversion function is less than the light emission amount by the first conversion function. The control device, uses the first conversion function when the average light emission amount is less than or equal to the first light emission amount threshold for a predetermined number of times or more in succession. determines to maintain the current conversion function when the average light emission amount is greater than the first light emission amount threshold and less than or equal to the second light emission amount threshold. uses the second conversion function when the average light emission amount exceeds the second light emission amount threshold. Display device.

12. The display device according to claim 1, wherein the control device includes a plurality of processing circuits. The plurality of processing circuits respectively control different backlight regions of the backlight that face different display regions on the display panel. Each processing circuit of the plurality of processing circuits, determines the light emission amount statistical value of the backlight region to be controlled. acquires information for determining the light emission amount statistical value of a backlight region different from the backlight region to be controlled from one or more other processing circuits in the plurality of processing circuits. determines the light emission amount statistical value of the entire backlight from the light emission amount statistical values of the backlight region to be controlled and the backlight region different from the backlight region to be controlled. determines whether to change the current conversion function based on the comparison result between the light emission amount statistical value of the entire backlight and the one or more preset light emission amount thresholds. Display device.

13. The display device according to claim 12, each of the plurality of processing circuits receives the light emission amount statistical value of a backlight area different from the control target backlight area from the one or more other processing circuits by serial transmission. Display device.

14. A method for controlling a backlight of a display device, wherein the backlight includes a plurality of backlight blocks, the control method comprising: acquiring a video frame, determining a gradation feature value corresponding to each of the plurality of backlight blocks from the pixel gradation indicated by the video frame, determining the light emission amount of each of the plurality of backlight blocks according to a current conversion function from the corresponding gradation feature value, determining whether to change the current conversion function based on a comparison result between the light emission amount statistical value of the plurality of backlight blocks and one or more preset light emission amount threshold values. Control method.

Images