Display apparatus and method of controlling backlight

Abstract

The invention relates to a display apparatus and a method of controlling a backlight. The display device includes a backlight source including a plurality of backlight blocks; a display panel configured to display an image using light from the backlight source; and a controller. The controller is configured to: acquire a video frame; determining gray level feature values associated with the plurality of backlight blocks according to gray levels of specified pixels in the video frame; determining the luminous quantity of the plurality of backlight blocks from the gray level characteristic values according to a current transfer function; and determining whether to change the current conversion function based on a comparison result of the statistical value of the light emission amounts of the plurality of backlight blocks and one or more predetermined threshold light emission amounts.

Description

Technical Field

[0001] The present invention relates to controlling a backlight of a display device. Background Art

[0002] A technique called local dimming is used to reduce power consumption of a backlight of a liquid crystal display device and to improve contrast of a displayed image. Local dimming divides a light emitting surface of the backlight into a plurality of blocks and individually controls the light emission amount of each block by increasing or decreasing the light emission amount of each block according to the luminance in a video frame.

[0003] For example, when a white window is displayed on an all - black background, local dimming controls the backlight such that regions (blocks) corresponding to the region where the white window is displayed emit more light (at a higher luminance) and regions (blocks) corresponding to the region where the (black) background is displayed emit less light.

[0004] Compared with a case where the entire backlight always emits light at 100%, this control achieves a reduction in power for the backlight. In addition, the luminance difference between the region that emits a large amount of light and the region that emits a small amount of light increases, which provides a higher contrast within the same plane, thereby improving the display quality. Summary of the Invention

[0005] Some implementations of local dimming use a frame memory to temporarily store grayscale data of a video frame in order to grasp luminance differences within the video frame. At the same time, light emitted from each block of the backlight affects adjacent blocks as leakage light. Therefore, controlling the light emission amount of the backlight requires storing a per - block luminance distribution reflecting the leakage light and adjusting the light emission amount based on the luminance differences in the video frame according to this luminance distribution. Therefore, a large amount of memory and a large - scale arithmetic circuit are required to perform strict local dimming to meet the luminance differences of the video frame.

[0006] A local dimming driving method for the backlight can be considered as follows: using only one threshold grayscale level, in a case where the input grayscale level is lower than the threshold grayscale level, this method performs a brightness reduction control of reducing the brightness of the backlight block more for a lower input grayscale level, and in a case where the input grayscale level is equal to or higher than the threshold grayscale level, this control is not performed. Since this method uses one threshold, it can be implemented with a small memory and a small arithmetic circuit.

[0007] However, according to this method, when all grayscale levels of the input image are higher than the threshold grayscale level, the light emission amount of the backlight must be 100%, and the energy - saving effect of the backlight cannot be achieved. If the threshold grayscale level is increased to improve the energy - saving effect, the light emission amount of the backlight for a low - grayscale - level image becomes too small, and thus the display quality may deteriorate.

[0008] A display device according to an aspect of the present invention includes: a backlight including a plurality of backlight blocks; a display panel configured to display an image using light from the backlight; and a controller. The controller is configured to: acquire a video frame; determine a gray-level feature value associated with the plurality of backlight blocks according to the gray level of a specified pixel in the video frame; determine the light emission amounts of the plurality of backlight blocks from the gray-level feature value according to a current conversion function; and determine whether to change the current conversion function based on a comparison result between a statistical value of the light emission amounts of the plurality of backlight blocks and one or more predetermined threshold light emission amounts.

[0009] An aspect of the present invention reduces power consumption of the display device while suppressing a degradation in its display quality.

[0010] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory and do not limit the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 A configuration example of a display device in an embodiment of the present invention is shown.

[0012] Figure 2 A functional configuration example of a video signal processing circuit is schematically shown.

[0013] Figure 3 It is a flowchart of an example of an overall process of a video signal processing circuit that controls the light emission amounts of backlight blocks.

[0014] Figure 4 An example of a function that defines a relationship between a gray-level feature value of a backlight block and its light emission amount is provided.

[0015] Figure 5 A relationship between a threshold light emission amount to be referred to for determining a threshold gray level and a function for determining the light emission amount of a backlight block is shown.

[0016] Figure 6 An example of a gray-level feature value and light emission amounts of backlight blocks for one frame is provided.

[0017] Figure 7 It is a flowchart of a detailed process of a video signal processing circuit.

[0018] Figure 8 An example of a function that defines a relationship between a gray-level feature value of a backlight block and its light emission amount in a second embodiment is provided.

[0019] Figure 9 It is a flowchart of a detailed process of a video signal processing circuit in a second embodiment.

[0020] Figure 10Schematically shows the gradual change of the threshold gray level in the third embodiment.

[0021] Figure 11 Is a diagram for explaining an example of controlling the threshold gray level in the third embodiment.

[0022] Figure 12 Provides an example of a function defining the relationship between the gray level characteristic value and the light emission amount in the fourth embodiment.

[0023] Figure 13 Is a diagram for explaining an example of controlling the folding point (threshold gray level) in the fourth embodiment.

[0024] Figure 14 Is a diagram showing the method of controlling the gray level characteristic value - light emission amount conversion characteristic in the fifth embodiment.

[0025] Figure 15A Is a diagram for explaining an example of controlling the threshold gray level in the first control of the fifth embodiment.

[0026] Figure 15B Is a diagram for explaining an example of gradually reducing the light emission amount at the folding point from 0.95 to 0.85 in the second control of the fifth embodiment.

[0027] Figure 16 Provides the control result of the gray level characteristic value based on some video frames in the fifth embodiment.

[0028] Figure 17A Provides an example of a function in the range of the gray level characteristic value from 0 to the threshold gray level in the sixth embodiment.

[0029] Figure 17B Provides another example of a function in the range of the gray level characteristic value from 0 to the threshold gray level in the sixth embodiment.

[0030] Figure 17C Provides yet another example of a function in the range of the gray level characteristic value from 0 to the threshold gray level in the sixth embodiment.

[0031] Figure 17D Provides yet another example of a function in the range of the gray level characteristic value from 0 to the threshold gray level in the sixth embodiment.

[0032] Figure 17E Provides yet another example of a function in the range of the gray level characteristic value from 0 to the threshold gray level in the sixth embodiment.

[0033] Figure 17F Provides yet another example of a function in the range of the gray level characteristic value from 0 to the threshold gray level in the sixth embodiment.

[0034] Figure 18 Shows the method of gradually reducing the threshold gray level from the initial value in the seventh embodiment.

[0035] Figure 19A Is a diagram showing the relationship between the video frame and the display area block.

[0036] Figure 19B Is a diagram showing the details of the display area block.

[0037] Figure 20 Is a flowchart of the detailed process of determining the gray level feature value according to the video frame.

[0038] Figure 21 Shows another configuration example of the display device in an embodiment of this specification.

[0039] Figure 22 Schematically shows another configuration of the backlight.

[0040] Figure 23 Shows an example of calculating the light emission amount by two video signal processing circuits according to the gray level feature values of each backlight block.

[0041] Figure 24 Shows the calculation of the average light emission amount of two video signal processing circuits.

[0042] Figure 25A Provides the relationship between the gray level feature value and the light emission amount in the first backlight area.

[0043] Figure 25B Provides the relationship between the gray level feature value and the light emission amount in the first backlight area.

[0044] Figure 25C Provides the relationship between the gray level feature value and the light emission amount in the first backlight area.

[0045] Figure 25D Provides the relationship between the gray level feature value and the light emission amount in the first backlight area.

[0046] Figure 25E Provides the relationship between the gray level feature value and the light emission amount in the first backlight area.

[0047] Figure 26A Provides the relationship between the gray level feature value and the light emission amount in the second backlight area.

[0048] Figure 26B Provides the relationship between the gray level feature value and the light emission amount in the second backlight area.

[0049] Figure 26CThe relationship between the gray - level eigenvalue and the luminous flux in the second backlight region is provided.

[0050] Figure 26D The relationship between the gray - level eigenvalue and the luminous flux in the second backlight region is provided.

[0051] Figure 26E The relationship between the gray - level eigenvalue and the luminous flux in the second backlight region is provided.

[0052] Figure 27 Another configuration of the backlight source is schematically shown.

[0053] Figure 28 An example of the gray - level eigenvalue of the backlight block calculated by four video signal processing circuits is provided.

[0054] Figure 29 The luminous flux of the backlight block calculated by four video signal processing circuits is provided.

[0055] Figure 30 The average luminous flux of four backlight regions calculated by four associated video signal processing circuits is provided.

[0056] Figure 31 Final management information regarding the average luminous flux to be maintained by each of the four video signal processing circuits is provided.

[0057] Figure 32 An example of the data to be transmitted between two video signal processing circuits is shown.

[0058] Figure 33 An example of the waveforms of the clock signal, data signal, and control signal is shown. Detailed implementation

[0059] Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that the above - mentioned embodiments are only examples for implementing the present invention and do not limit the technical scope of the present invention. Common elements in the drawings are denoted by the same reference numerals, and some elements in the drawings are exaggerated in size or shape to facilitate clear understanding of the description.

[0060] An embodiment of the present invention describes local dimming (LD) control for a backlight source of a display device. The local dimming control divides the backlight source into multiple blocks (backlight blocks) and controls the luminous flux of the backlight blocks according to the gray - level of each pixel specified in the video data.

[0061] The local dimming control method is considered as follows: only using one threshold gray level, in the case where the input gray level is lower than the threshold gray level, the method performs brightness reduction control that reduces the brightness of the backlight block more for a lower input gray level, and in the case where the input gray level is equal to or higher than the threshold gray level, this control is not performed.

[0062] However, according to this method, when all the gray levels of the input image are higher than the threshold gray level, the luminous amount of the backlight source must be 100%, and the energy-saving effect of the backlight source cannot be achieved. If the threshold gray level is increased to improve the energy-saving effect, the luminous amount of the backlight source of the low-gray-level image becomes too small, so the display quality may deteriorate.

[0063] Hereinafter, the display device in the embodiment of the present invention will be specifically described. The display device in the embodiment of the present invention uses a transfer function to determine the luminous amount of each backlight block according to the gray-level data of the video frame. The display device determines whether to change the transfer function to be used next based on the determined luminous amount, and changes the transfer function if a predetermined condition is satisfied. This configuration achieves effective energy saving while suppressing the deterioration of the display quality.

[0064] First Embodiment

[0065] Figure 1 Fig. shows a configuration example of a display device in an embodiment of the present invention. The display device displays an image by controlling the transmission of light from the backlight source. Figure 1 Fig. 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 13, a video signal source 14, a liquid crystal display panel 20, a display driver 21, and a scan driver 22. The liquid crystal display device 1 further includes a backlight source 30, a backlight driver board 31, and a backlight power supply 32. The signal processing board 10 includes a power generation circuit 11 and a video signal processing circuit 12. The signal processing board 10, the display driver 21, and the scan driver 22 may be included in a controller for controlling the liquid crystal display panel 20.

[0066] The liquid crystal display device 1 displays a screen according to video data input from the outside. The video data includes video frames (also simply referred to as frames) to be displayed in sequence. The liquid crystal display panel 20 is arranged in front of the backlight source 30 (viewer side), and controls the amount of light from the backlight source 30 that is to be transmitted through the liquid crystal display panel 20 to display the video frames (images) input in sequence.

[0067] The power generation circuit 11 may include a DC-DC converter that generates and supplies power to operate other circuits. The video signal processing circuit 12 performs processing related to a display screen, such as generating a signal for displaying an image on the liquid crystal display panel 20 and a signal for controlling the backlight 30. The power supply 13 supplies power to the power generation circuit 11. The video signal source 14 supplies a video signal to the video signal processing circuit 12 based on external video data.

[0068] The power generation circuit 11 generates power to drive integrated circuits (ICs) such as the video signal processing circuit 12, the display driver 21, and the scan driver 22. The display driver 21 and the scan driver 22 are configured to perform their processing using the power supplied from the power generation circuit 11.

[0069] The display driver 21 generates a data signal from the video signal sent from the video signal processing circuit 12 and supplies the data signal to the liquid crystal display panel 20. The scan driver 22 sequentially selects the scan lines of the liquid crystal display panel 20 according to the timing signal sent from the video signal processing circuit 12. The video signal processing circuit 12 also sends the timing signal to the display driver 21, and according to the timing signal, the display driver 21 generates a data signal from the received video signal and supplies the data signal to the liquid crystal display panel 20.

[0070] The video signal processing circuit 12 converts the data arrangement of the video signal input from the outside to send it to the display driver 21, and generates and sends a timing signal for operating the display driver 21 and the scan driver 22 using the power supplied from the power generation circuit 11.

[0071] The video signal processing circuit 12 also generates a drive control signal for controlling the driving of a plurality of backlight blocks included in the backlight 30 and sends the drive control signal to the backlight driver board 31. The backlight blocks may simply be referred to as blocks. Examples of the drive control signal include a backlight on / off control signal and a dimming control signal. The dimming control signal is a signal for controlling the following signals: a pulse width modulation (PWM) signal for time-divisionally controlling the light emission period of the light source and the amount of current flowing through the light source.

[0072] The backlight 30 is a planar light source device arranged behind the liquid crystal display panel 20 to emit light required for the liquid crystal display panel 20 to display an image. The backlight driver board 31 includes a backlight drive circuit and controls the light emission amount (brightness) of the backlight 30 according to the drive control signal sent from the video signal processing circuit 12. The backlight driver board 31 operates using the power supplied from the backlight power supply 32.

[0073] The liquid crystal display device 1 adopts local dimming. In Figure 1 In the configuration example of, the backlight 30 is divided into X blocks (regions) along the x-axis and Y blocks along the y-axis. Each backlight block has a rectangular shape, and multiple backlight blocks are arranged in a matrix.

[0074] The backlight 30 consists of multiple rows of backlight blocks. Each row of backlight blocks consists of backlight blocks aligned in the x-axis direction (row direction). In one example, the backlight blocks in all rows contain the same number of backlight blocks. Although it is stated for ease of explanation that the backlight blocks in all rows have the same number of backlight blocks, each row of backlight blocks can have a different number of backlight blocks.

[0075] From another perspective, the backlight 30 consists of multiple columns of backlight blocks. Each column of backlight blocks consists of backlight blocks aligned in the y-axis direction (column direction). The backlight blocks in all columns have the same number of backlight blocks. Although it is stated for ease of explanation that the backlight blocks in all columns have the same number of backlight blocks, each column of backlight blocks can have a different number of backlight blocks. The backlight blocks can be arranged in a layout other than a matrix layout.

[0076] The liquid crystal display device 1 can individually control the light emission amount of (X×Y) blocks. The liquid crystal display device 1 individually controls the light emission amount of each block by increasing or decreasing the light emission amount of each block according to the brightness of the pixels in the video frame, so as to reduce power consumption and improve contrast.

[0077] The backlight 30 can be a direct-lit backlight, which includes a light source array arranged in the backlight plane opposite to the liquid crystal display panel 20 and a diffusion plate located 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 in each block. A desired number of LEDs can be included in one block. Based on the luminous efficiency and brightness distribution of the LEDs, the optimal number of LEDs is arranged at the optimal position.

[0078] Instead of the above direct-lit type, the backlight 30 can be an edge type, which includes a light guide plate and a light source arranged on the side. The light-emitting area of the backlight 30 can be composed of blocks arranged in a matrix or blocks arranged in horizontal or vertical lines.

[0079] 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 sends the drive control signal to the backlight driver board 31. The backlight driver board 31 drives and controls the light sources (such as LEDs) of the backlight 30 so that each block emits light with the light emission amount specified in the drive control signal from the video signal processing circuit 12.

[0080] The video signal processing circuit 12 generates timing signals for the display driver 21 and the scan driver 22 according to the timing signals of the input video signal, and also sequentially sends the signals (frame signals) of each video frame in the video signal to the display driver 21. The frame signal can specify the gray level of each pixel in the video frame. In full-color display, each pixel specifies the gray level of red (R), green (G), or blue (B); in monochrome display, each pixel specifies the gray level of white.

[0081] The video signal processing circuit 12 also analyzes the video frame, generates a drive control signal for illuminating the liquid crystal display panel 20 from behind the liquid crystal display panel 20 by the backlight 30 based on the analysis result, and sends the drive control signal to the backlight 30. The drive control signal sent to the backlight 30 is a drive control signal for the video frame analyzed or the video frame after the analyzed video frame. The following description is based on the assumption that the drive control signal sent to the backlight 30 is for the video frame after the analyzed video frame. This configuration enables processing with less memory.

[0082] As described above, the liquid crystal display device 1 adopts local dimming. The video signal processing circuit 12 determines the temporary light emission amount of each block of the backlight 30 based on the analysis result of the video frame. In addition, the video signal processing circuit 12 also determines the adjusted light emission amount of each backlight block based on the temporary light emission amount of each backlight block. The adjusted light emission amount includes the temporary light emission amount maintained when it is determined that no adjustment is required. The video signal processing circuit 12 determines the adjusted light emission amount as the brightness value for each backlight block to emit light.

[0083] The video signal processing circuit 12 generates a drive control signal corresponding to the adjusted light emission amount and outputs it to each backlight block. For each backlight block, the relationship between the adjusted light emission amount and the drive control signal is determined in advance. The drive control signal specifies the actual light emission amount of the backlight block. In one example, the drive control signal specifies the duty ratio of the pulse width in pulse width modulation (PWM) for power control.

[0084] Hereinafter, the control of the backlight 30 by the video signal processing circuit 12 will be described in detail. Figure 2 An example of the functional configuration of the video signal processing circuit 12 is schematically shown. The video signal processing circuit 12 includes a display control drive signal generator 231, a block light emission amount determiner 202, a block light emission amount arrangement unit 203, a local dimming (LD) threshold coordinator 210, and a backlight drive control signal generator 221. The LD threshold coordinator 210 includes an average comparator 211, a threshold gray level determiner 212, and an average block light emission amount calculator 213.

[0085] The display control driving signal generator 231 generates signals to be sent to the display driver 21 and the scan driver 22 based on the video signal received from the video signal source 14. The display control driving signal generator 231 sends a signal specifying the gray level of each pixel in a video frame and a timing signal to the display driver 21, and sends the timing signal to the scan driver 22.

[0086] The block light emission amount determiner 202 and the block light emission amount arrangement unit 203 determine the light emission amount of each backlight block based on the gray level of the pixels specified in the video frame. Specifically, the block light emission amount determiner 202 determines the light emission amount of each block of the backlight source 30 based on the gray level of the pixels of a video frame.

[0087] The block light emission amount determiner 202 determines a gray level feature value from the gray levels of the pixels in a part of the display area (also referred to as the display area block) opposite to the backlight block by a predetermined method. Each backlight block is associated with a corresponding display area block. The gray level feature value can be a statistical value of the gray levels in the display area block; it can be the maximum value, the average value, or the mode. From the perspectives of display quality and the scale of the arithmetic circuit, the maximum value is preferred.

[0088] The block light emission amount determiner 202 has a function of associating the gray level feature value with the block light emission amount. The block light emission amount determiner 202 calculates the light emission amount of the backlight block by inputting the gray level feature value into a function. The light emission amount of the backlight block is a normalized relative value ranging from 0 to 1. The block light emission amount determiner 202 forwards the light emission amount of each backlight block to the LD threshold coordinator 210.

[0089] The block light emission amount determiner 202 determines a function (relationship) for determining the light emission amount based on the gray level feature value based on the threshold gray level obtained from the LD threshold coordinator 210. In this example, the LD threshold coordinator 210 determines the threshold gray level of the current video frame based on the light emission amount of the backlight block in the previous video frame, and forwards the determined threshold gray level to the block light emission amount determiner 202.

[0090] The average block light emission amount calculator 213 calculates the average value of the light emission amounts of all the backlight blocks of a video frame received from the block light emission amount determiner 202. The average value comparator 211 compares the average value of the light emission amounts calculated by the average block light emission amount calculator 213 with one or more predetermined threshold light emission amounts to make a determination. The threshold gray level determiner 212 determines the threshold gray level based on the determination result of the average value comparator 211 and forwards it to the block light emission amount determiner 202. Details of the processing of the LD threshold coordinator 210 will be described later.

[0091] The block luminous flux arranging unit 203 generates an array of the luminous fluxes of the backlight blocks calculated by the block luminous flux determiner 202. In the array, each block of the backlight source 30 is associated with its luminous flux. The block luminous flux arranging unit 203 forwards the generated array of luminous fluxes to the backlight source drive control signal generator 221.

[0092] The backlight source drive control signal generator 221 obtains the luminous fluxes determined for the respective backlight blocks from the block luminous flux arranging unit 203, and generates drive control signals based thereon. For example, the backlight source drive control signal generator 221 generates drive control signals that cause the specified luminous fluxes to conform to the physical characteristics of the light sources included in the respective backlight blocks. The backlight source drive control signal generator 221 sends the drive control signals for the respective backlight blocks to the backlight source drive board 31. It should be noted that the actual brightness (luminous flux) of different backlight blocks may be the same or different, even if the relative values of the luminous fluxes of different backlight blocks are the same value.

[0093] Figure 3 It is a flowchart of an example of the overall process of the video signal processing circuit 12 controlling the luminous flux of the backlight blocks. Figure 3 The flowchart shows the processing of one video frame.

[0094] The block luminous flux determiner 202 analyzes the gray levels of the pixels of the video frame received from the video signal source 14, and determines the gray level characteristic value associated with each backlight block (S11). The gray level characteristic value is a statistical value determined from the gray levels of the respective pixels in a pixel group (a region composed of a plurality of pixels) previously associated with the backlight block by a predetermined method. The gray level characteristic value in this example is the highest gray level in the pixel group associated with the backlight block.

[0095] Next, the block luminous flux determiner 202 determines the current function (S12) based on the current threshold gray level obtained from the LD threshold coordinator 210. The function defines the relationship between the gray level characteristic value and the luminous flux of the backlight block. The relationship between the threshold gray level and the function is specified in advance. The block luminous flux determiner 202 also determines the luminous flux of each backlight block based on the gray level characteristic value of the backlight block and the current function (S13).

[0096] Next, the backlight source drive control signal generator 221 controls the drive of each backlight block according to the luminous flux determined for the backlight block (S14). Specifically, the luminous flux determined for each backlight block is forwarded to the block luminous flux arranging unit 203. The block luminous flux arranging unit 203 generates an array of the luminous fluxes of the respective backlight blocks. The array associates the backlight blocks with their luminous fluxes. The array of luminous fluxes is forwarded to the backlight source drive control signal generator 221.

[0097] The backlight drive control signal generator 221 obtains the light emission amounts determined for the respective backlight blocks from the block light emission amount arrangement unit 203, and generates drive control signals conforming to these light emission amounts. The backlight drive control signal generator 221 sends the drive control signals for the respective backlight blocks to the backlight drive board 31.

[0098] The light emission amounts of the backlight blocks determined in step S13 are forwarded to the LD threshold coordinator 210. The average block light emission amount calculator 213 calculates the average value (arithmetic mean) of the light emission amounts of the backlight blocks (S15). The average value comparator 211 and the threshold gray level determiner 212 determine the next threshold gray level based on the relationship between the average value of the light emission amounts and the threshold light emission amount (S16). Regarding the average value of the light emission amounts, the arithmetic mean can be calculated with a minimum-scale arithmetic circuit. However, different calculation methods or different statistical values can be adopted.

[0099] For example, when displaying an image with most of the display area being bright and part being dark, the calculation result of the arithmetic mean may be significantly affected by the light emission amounts of the backlight blocks in the bright area. To cope with this situation, the geometric mean can be adopted as the average value. Alternatively, considering that the light emission amounts of the respective backlight blocks are based on the gray level characteristic values of the display area blocks, the harmonic mean can also be adopted. Given the magnitude relationship of arithmetic mean ≥ geometric mean ≥ harmonic mean, if it is known that high-gray-level images will be frequently displayed, adopting the geometric mean or the harmonic mean can save more power for the backlight.

[0100] As another alternative, the root mean square, the weighted average based on the light emission amount distribution (histogram), or the trimmed mean calculated after excluding extreme light emission amounts can be adopted. In the case of using a histogram, the light emission amount can be determined based on the high-frequency category or the median.

[0101] Figure 4 Examples of functions (gray level characteristic value - light emission amount conversion formulas) defining the relationship between the gray level characteristic values and the light emission amounts of the backlight blocks are provided. As described above, the block light emission amount determiner 202 determines the function defining the relationship between the gray level characteristic values and the light emission amounts according to the threshold gray level received from the LD threshold coordinator 210. In Figure 4 the example, the block light emission amount determiner 202 selects one of two functions according to the specified threshold gray level.

[0102] In Figure 4 the graph, the horizontal axis represents the gray level characteristic value of the backlight block or the highest gray level in the associated pixel group. In this example, the gray level of a pixel takes one of the integers from 0 to 255. The vertical axis represents the light emission amount of the backlight block. The light emission amount is represented by a relative value; the maximum value is 1 and the minimum value is 0.

[0103] The function 401 (first conversion function) is the initial function, and its threshold gray level A (first threshold gray level) is 64. The function 402 (second conversion function) is a function modified from the initial function, and its threshold gray level B (second threshold gray level) is 80. For all gray level eigenvalue, the luminous flux according to the function 402 is less than or equal to the luminous flux according to the function 401, and for at least a part of the gray level eigenvalue range, the luminous flux according to the function 402 is less than the luminous flux according to the function 401. The values of the threshold gray levels A and B are examples and can be other values. The threshold gray levels A and B in this example are fixed values.

[0104] The function 401 is represented as a linear function that clips 0 in the range of gray level eigenvalues from 0 to 64, and takes a constant value of the maximum luminous flux of 1.0 in the range of gray level eigenvalues from 64 to 255. In other words, the luminous flux according to the initial function increases from 0 to 1.0 in the range of gray level eigenvalues from 0 to 64, and maintains the maximum value of 1.0 in the range of gray level eigenvalues from 64 to 255.

[0105] The function 402 is represented as a linear function that clips 0 in the range of gray level eigenvalues from 0 to 80, and takes a constant value of the maximum luminous flux of 1.0 in the range of gray level eigenvalues from 80 to 255. In other words, the luminous flux according to the initial function increases from 0 to 1.0 in the range of gray level eigenvalues from 0 to 80, and maintains the maximum value of 1.0 in the range of gray level eigenvalues from 80 to 255.

[0106] In the range where the gray level eigenvalue is from 1 to 79, the luminous flux according to the modified function 402 is less than the luminous flux according to the initial function 401. Therefore, the power consumption can be further reduced. However, since in the low gray level range, the luminous flux according to the modified function 402 is less than the luminous flux according to the initial function 401, the luminous flux of the low gray level image becomes too small to provide good image visibility. An embodiment of the present invention determines the threshold gray level according to the total luminous flux of the backlight. Therefore, the possibility that the luminous flux of the low gray level image becomes too small to provide good image visibility can be reduced.

[0107] Figure 5 The relationship between the threshold luminous flux for determining the threshold gray level to be referred to and the function for determining the luminous flux of the backlight block is shown. In this example, two threshold luminous fluxes C and D are predetermined. For example, the threshold luminous flux C (first threshold luminous flux) is 0.5, and the threshold luminous flux D (second threshold luminous flux) is 0.8.

[0108] The LD threshold coordinator 210 calculates the average value (average luminous amount) of the luminous amounts of the backlight blocks for a frame, and determines the threshold gray level for the next frame based on the relationship between the average luminous amount and the threshold luminous amounts C and D. In an embodiment of the present invention, the LD threshold coordinator 210 determines the threshold gray level in view of the following conditions.

[0109] First condition: average luminous amount ≤ threshold luminous amount C

[0110] If the average luminous amount of the backlight block is less than or equal to the threshold luminous amount C, the LD threshold coordinator 210 determines the threshold gray level as the initial threshold gray level A. When the threshold luminous amount C is 0.5, if the average luminous amount of the backlight block is less than or equal to 0.5, the threshold gray level is determined to be 64.

[0111] Second condition: average luminous amount > threshold luminous amount D

[0112] If the average luminous amount of the backlight block is greater than the threshold luminous amount D for N consecutive frames (a consecutive predetermined number of times), the LD threshold coordinator 210 determines the threshold gray level as the corrected threshold gray level B. The corrected threshold gray level B can be a fixed value or a function of the average luminous amount. The value N is an integer greater than 0. When N is greater than 1 (multiple consecutive frames), it is possible to reduce the degradation of the display quality or the difficulty of backlight control caused by the frequent change of the threshold gray level.

[0113] Third condition: threshold luminous amount C < average luminous amount ≤ threshold luminous amount D

[0114] If the average luminous amount of the backlight block is greater than the threshold luminous amount C and less than or equal to the threshold luminous amount D, the LD threshold coordinator 210 maintains the threshold gray level of the previous frame. Thus, it is possible to reduce the degradation of the display quality or the difficulty of backlight control caused by the frequent change of the threshold gray level.

[0115] The number of predetermined threshold luminous amounts can be only one; if the average luminous amount is greater than the threshold luminous amount, the threshold gray level B is selected, and if the average luminous amount is less than or equal to the threshold luminous amount, the threshold gray level A is selected. The condition for selecting the threshold gray level B can be that for multiple consecutive frames, the average luminous amount is greater than the threshold luminous amount.

[0116] Figure 6 Examples of the gray level eigenvalue and the luminous amount of the backlight block for a frame are provided. In Figure 6 the disclosed example, the backlight is composed of fifteen backlight blocks (five blocks along the x-axis * three blocks along the y-axis). The video data of one frame is used for fifteen display area blocks corresponding to the fifteen backlight blocks. The gray level eigenvalue is determined according to the gray level data of the pixels included in the display area block, Figure 6The unit matrix 411 therein represents the gray-level eigenvalue of the backlight block. The unit matrix 412 represents the luminous amount of the backlight block when the threshold gray level is 64. The unit matrix 413 represents the luminous amount of the backlight block when the threshold gray level is 80.

[0117] The value in each unit of the unit matrix 411 is the gray-level eigenvalue of each backlight block. The value in each unit of the unit matrices 412 and 413 is the luminous amount of each backlight block.

[0118] Figure 6 It is shown that, when the threshold gray level is 64, the luminous amount of the backlight block with a gray-level eigenvalue of 48 is 48 / 64 = 0.75, and when the threshold gray level is 80, the luminous amount of the backlight block with a gray-level eigenvalue of 48 is 48 / 80 = 0.60. As noted from this example, increasing the threshold gray level results in a reduction in the power consumption of the backlight source.

[0119] However, if the threshold gray level is increased too much, the difference in luminous amount between the low-gray-level backlight blocks and the high-gray-level backlight blocks will increase, and the display quality may deteriorate significantly. Therefore, the adjustment amount of the initial value (threshold gray level B - threshold gray level A) is determined within an appropriate range.

[0120] Figure 7 is a flowchart of the detailed processing of the video signal processing circuit 12. The block luminous amount determiner 202 receives a video frame (S21), and also retrieves the current threshold gray level (S22). The block luminous amount determiner 202 compares the gray-level eigenvalue of each backlight block with the threshold gray level (S23). In the example Figure 5 described, the threshold gray level is 64 or 80.

[0121] If the gray-level eigenvalue is equal to or higher than the threshold gray level (S23: No), the luminous amount of the backlight block is determined to be 1 (S25). If the gray-level eigenvalue is lower than the threshold gray level (S23: Yes), the luminous amount of the backlight block is obtained by dividing the gray-level eigenvalue by the threshold gray level (S24). The block luminous amount determiner 202 determines the luminous amount calculated according to the condition of the relationship between the gray-level eigenvalue and the threshold gray level as the luminous amount of the backlight block, and determines the luminous amount of all backlight blocks (S26).

[0122] The calculated luminous amount is forwarded to the LD threshold coordinator 210. The average block luminous amount calculator 213 calculates the average luminous amount G of the backlight blocks (S31). Next, the average value comparator 211 compares the average luminous amount G with the threshold luminous amounts C and D. As Figure 5 shown, the threshold luminous amount C is less than the threshold luminous amount D.

[0123] First, the average value comparator 211 compares the average luminous amount G with the threshold luminous amount C (S32). If the average luminous amount G is less than or equal to the threshold luminous amount C (S32: No), the threshold gray level determiner 212 determines the threshold gray level as the initial threshold gray level A, and further resets the counter value k to 0 (S33). The determined threshold gray level is forwarded to the block luminous amount determiner 202.

[0124] If the average luminous amount G is greater than the threshold luminous amount C (S32: Yes), the average value comparator 211 compares the average luminous amount G with the threshold luminous amount D (S34). If the average luminous amount G is less than or equal to the threshold luminous amount D (S34: No), the threshold gray level determiner 212 determines to maintain the threshold gray level at the current value, and further resets the counter value k to 0 (S35). The determined threshold gray level is forwarded to the block luminous amount determiner 202.

[0125] If the average luminous amount G is greater than the threshold luminous amount D (S34: Yes), the average value comparator 211 compares the counter value k with a predetermined maximum value N (S36). If the counter value k has reached N (S36: No), the threshold gray level determiner 212 determines whether the current threshold gray level is the corrected value 80 (S37).

[0126] If the current threshold gray level is 64 (S37: No), the threshold gray level determiner 212 changes the threshold gray level from 64 to 80 and maintains the counter value k (S38). The determined threshold gray level is forwarded to the block luminous amount determiner 202. If the current threshold gray level is 80 (S37: Yes), the threshold gray level determiner 212 maintains the threshold gray level at the current value 80 and also maintains the counter value k (S39). The determined threshold gray level is forwarded to the block luminous amount determiner 202.

[0127] If the determination in step S36 is that the counter value k has not reached N (S36: Yes), the threshold gray level determiner 212 maintains the threshold gray level at the current value and increments the counter value k (S40). The determined threshold gray level is forwarded to the block luminous amount determiner 202.

[0128] If sufficient energy-saving effect is achieved through the threshold gray level and the gray level characteristic value - luminous amount conversion formula in the initial setting (for example, if the average luminous amount is less than or equal to the threshold luminous amount C), this embodiment maintains the initial setting because no additional energy-saving is required. If the threshold gray level and the gray level characteristic value - luminous amount conversion formula do not achieve the energy-saving effect, this embodiment appropriately changes the threshold gray level and the gray level characteristic value - luminous amount conversion formula to achieve the energy-saving effect.

[0129] Second Embodiment

[0130] In the following, a second embodiment of the present invention will be described. The differences from the first embodiment will be mainly described below. Unless otherwise specified, the description of the first embodiment applies to the second embodiment.

[0131] Figure 8 An example of a function (gray level characteristic value - light emission amount conversion formula) that defines the relationship between the gray level characteristic value and the light emission amount of the backlight block in the second embodiment is provided. The block light emission amount determiner 202 determines a function that defines the relationship between the gray level characteristic value and the light emission amount based on the threshold gray level received from the LD threshold coordinator 210. In Figure 8 the example, the block light emission amount determiner 202 selects one of two functions based on the specified threshold gray level.

[0132] In Figure 8 the graph, the horizontal axis represents the gray level characteristic value of the backlight block. The vertical axis represents the light emission amount of the backlight block. The function 401 (first conversion function) is an initial function, and its threshold gray level A is 64. The function 401 has the same configuration as that described in reference Figure 4 and Figure 5 . The function 403 (second conversion function) is a function corrected from the initial function, and its threshold gray level E (third threshold gray level) is 70. For all gray level characteristic values, the light emission amount according to the function 403 is less than or equal to the light emission amount according to the function 401, and for at least a part of the gray level characteristic value range, the light emission amount according to the function 403 is less than the light emission amount according to the function 401. The values of the threshold gray levels A and E are examples and can be other values. The threshold gray levels A and E in this example are fixed values.

[0133] The function 401 is represented as a linear function (first linear function) that monotonically increases from 0 to 1.0 in the range of the gray level characteristic value from 0 to 64 and a constant linear function (second linear function) in the range of the gray level characteristic value from 64 to 255. The function 403 is represented as a linear function (third linear function) that monotonically increases from 0 to the light emission amount parameter F in the range of the gray level characteristic value from 0 to 70, and a linear function (fourth linear function) that increases from the light emission amount parameter F to 1.0 in the range of the gray level characteristic value from 70 to 255. The slope in the range of the gray level characteristic value from 70 to 255 is less than the slope in the range of the gray level characteristic value from 0 to 70. The light emission amount parameter F takes a value greater than 0 and less than 1.0; for example, the value is 0.8. Although Figure 8 the value of the light emission amount parameter F (the value of the light emission amount) in the example of

[0134] The function 403 (modified function) in the low gray-level eigenvalue range part where the gray-level eigenvalue ranges from 0 to the threshold gray level E can be expressed by the following formula:

[0135] Luminous flux

[0136] = (luminous flux parameter F / threshold gray level E) × gray-level eigenvalue (conversion formula 1)

[0137] The function 403 (modified function) in the high gray-level eigenvalue range part where the gray-level eigenvalue ranges from the threshold gray level E to the maximum gray level can be expressed by the following formula:

[0138] Luminous flux

[0139] = ((1 - luminous flux parameter F) / (maximum gray level - threshold gray level E)) × (gray-level eigenvalue - maximum gray level) + 1 (conversion formula 2)

[0140] For example, the luminous flux parameter F can be 0.8; the threshold gray level E can be 70; and the maximum gray level can be 255.

[0141] Similarly, the function 401 (initial function) can be expressed by the above conversion formulas 1 and 2, but some parameters have changed. Specifically, the low gray-level eigenvalue range part where the gray-level eigenvalue ranges from 0 to the threshold gray level A can be expressed by conversion formula 1. The high gray-level eigenvalue range part where the gray-level eigenvalue ranges from the threshold gray level A to the maximum gray level can be expressed by conversion formula 2. The luminous flux parameter in conversion formulas 1 and 2 is 1.0, and the threshold gray level A replaces the threshold gray level E. For example, the threshold gray level A can be 64. As can be understood from the above, the following parameters can be used to define these two functions: luminous flux parameter, threshold gray level, and maximum gray level.

[0142] As Figure 8 shown, when the gray-level eigenvalue is 0 or 255, the luminous flux according to the two functions 401 and 403 takes the same value, and within the range between these values (when the gray-level eigenvalue is in the range from 1 to 254), the luminous flux according to the modified function 403 is less than the luminous flux according to the initial function 401. Therefore, the power consumption can be further reduced. Since the slope of the modified function is smaller in the high gray-level range, the influence on the display quality (brightness drop) can be minimized.

[0143] As Figure 8As shown, each function for calculating the luminous amount based on the grayscale feature value has a folding point. The folding point may be located in region 410. Region 410 is a rectangular region having vertices at coordinates (A, 1.0), (0.8A, 0.8), (64, 0.8), and (80, 1.0), where A is the threshold grayscale A, the grayscale 80 is the allowable limit of the folding point, and the luminous amount of 0.8 is the allowable limit of the folding point. When designing the display device, the allowable limit is determined to suppress the degradation of the display quality.

[0144] Similar to the first embodiment, in this embodiment, the threshold grayscale is determined based on the overall luminous amount of the backlight. Similar to the first embodiment, two threshold luminous amounts C and D are determined in advance. The LD threshold coordinator 210 calculates the average luminous amount of the backlight blocks for one frame and determines the threshold grayscale for the next frame based on the relationship between the average luminous amount and the threshold luminous amounts C and D. In this embodiment, the LD threshold coordinator 210 determines the threshold grayscale in view of the following conditions.

[0145] First condition: average luminous amount ≤ threshold luminous amount C

[0146] If the average luminous amount of the backlight blocks is less than or equal to the threshold luminous amount C, the LD threshold coordinator 210 determines the threshold grayscale as the initial threshold grayscale A. When the threshold luminous amount C is 0.5, if the average luminous amount of the backlight blocks is less than or equal to 0.5, the threshold grayscale is determined as 64.

[0147] Second condition: average luminous amount > threshold luminous amount D

[0148] If the average luminous amount of the backlight blocks is greater than the threshold luminous amount D for N consecutive frames (a consecutive predetermined number of times), the LD threshold coordinator 210 determines the threshold grayscale as the corrected threshold grayscale E. The corrected threshold grayscale E can be a fixed value or a function of the average luminous amount. The value N is an integer greater than 0. When N is greater than 1 (multiple consecutive frames), the degradation of the display quality or the difficulty of backlight control caused by the frequent change of the threshold grayscale can be reduced.

[0149] Third condition: threshold luminous amount C < average luminous amount ≤ threshold luminous amount D

[0150] If the average luminous amount of the backlight blocks is greater than the threshold luminous amount C and less than or equal to the threshold luminous amount D, the LD threshold coordinator 210 maintains the threshold grayscale of the previous frame. Thus, the degradation of the display quality or the difficulty of backlight control caused by the frequent change of the threshold grayscale can be reduced.

[0151] The number of predetermined threshold luminances can be only one; if the average luminance is greater than the threshold luminance, the threshold gray level E is selected, and if the average luminance is less than or equal to the threshold luminance, the threshold gray level A is selected. The condition for selecting the threshold gray level E can be that for a plurality of consecutive frames, the average luminance is greater than the threshold luminance.

[0152] Figure 9 is a flowchart of the detailed processing of the video signal processing circuit 12. The block luminance determiner 202 receives a video frame (S51) and also retrieves the current threshold gray level and luminance parameters (S52). The block luminance determiner 202 compares the gray level characteristic value of each backlight block with the threshold gray level (S53). In the example Figure 8 described, the threshold gray level is 64 or 70.

[0153] If the gray level characteristic value is lower than the threshold gray level (S53: Yes), the luminance of the backlight block is calculated by conversion formula 1 for the low gray level characteristic value range (S54). If the gray level characteristic value is equal to or higher than the threshold gray level (S53: No), the luminance of the backlight block is calculated by conversion formula 2 for the high gray level characteristic value range (S55).

[0154] Figure 8 In the example of [], the conversion formula 1 in the initial function is the conversion formula for the range of gray level characteristic values from 0 to 64 in function 401, and the conversion formula 2 is the conversion formula for the range of gray level characteristic values from 64 to 255 in function 401. Similarly, the conversion formula 1 in the corrected function is the conversion formula for the range of gray level characteristic values from 0 to 70 in function 403, and the conversion formula 2 is the conversion formula for the range of gray level characteristic values from 70 to 255 in function 403.

[0155] The block luminance determiner 202 determines the luminance calculated according to the condition of the relationship between the gray level characteristic value and the threshold gray level as the luminance of the backlight block, and determines the luminance of all backlight blocks (S56).

[0156] The calculated luminance is forwarded to the LD threshold coordinator 210. The average block luminance calculator 213 calculates the average luminance G of the backlight blocks (S61). Next, the average value comparator 211 compares the average luminance G with the threshold luminances C and D.

[0157] First, the average value comparator 211 compares the average luminous amount G with the threshold luminous amount C (S62). If the average luminous amount G is less than or equal to the threshold luminous amount C (S62: No), the threshold gray level determiner 212 determines the threshold gray level as the initial threshold gray level A, the luminous amount parameter as 1.0, and further resets the counter value k to 0 (S63). The determined threshold gray level and luminous amount parameter are forwarded to the block luminous amount determiner 202.

[0158] If the average luminous amount G is greater than the threshold luminous amount C (S62: Yes), the average value comparator 211 compares the average luminous amount G with the threshold luminous amount D (S64). If the average luminous amount G is less than or equal to the threshold luminous amount D (S64: No), the threshold gray level determiner 212 determines to maintain the threshold gray level and the luminous amount parameter at the current values, and further resets the counter value k to 0 (S65). The determined threshold gray level and luminous amount parameter are forwarded to the block luminous amount determiner 202.

[0159] If the average luminous amount G is greater than the threshold luminous amount D (S64: Yes), the average value comparator 211 compares the counter value k with the predetermined maximum value N (S66). If the counter value k has reached N (S66: No), the threshold gray level determiner 212 determines whether the current luminous amount parameter is the corrected value F (e.g., 0.8) (S67).

[0160] If the current luminous amount parameter is 1.0 instead of F (S67: No), the threshold gray level determiner 212 changes the threshold gray level from 64 (threshold gray level A) to 70 (threshold gray level E), and changes the luminous amount parameter from 1.0 to F. The counter value k remains unchanged (S68). The determined threshold gray level and luminous amount parameter are forwarded to the block luminous amount determiner 202.

[0161] If the current luminous amount parameter is F (S67: Yes), the threshold gray level determiner 212 maintains the threshold gray level at the current value, and also maintains the luminous amount parameter at the current value F. The counter value k remains unchanged (S69). The determined threshold gray level and luminous amount parameter are forwarded to the block luminous amount determiner 202.

[0162] If the determination in step S66 is that the counter value k has not reached N (S36: Yes), the threshold gray level determiner 212 maintains the threshold gray level and the luminous amount parameter at the current values, and increments the counter value k (S70). The determined threshold gray level and luminous amount parameter are forwarded to the block luminous amount determiner 202.

[0163] The energy-saving effect produced by the modified function in the second embodiment is smaller than that of the initial function. The modified function produces an energy-saving effect without significantly reducing the light emission amount of the backlight blocks for all gray levels, and also achieves a reduction in power consumption in the high gray level region.

[0164] Third Embodiment

[0165] Hereinafter, a third embodiment of the present invention will be described. The differences from the first embodiment will be mainly described below. Unless otherwise specified, the description of the first embodiment applies to the third embodiment. When the high light emission of the backlight continues for a certain period of time, this embodiment gradually increases the threshold gray level. This configuration suppresses the degradation of the display quality caused by the sudden decrease in the light emission amount, while reducing the power consumption by reducing the light emission amount.

[0166] Figure 10 The gradual change of the threshold gray level is schematically shown. Figure 10 An example of a function (gray level characteristic value - light emission amount conversion formula) that defines the relationship between the gray level characteristic value and the light emission amount of the backlight block in the third embodiment is provided. The block light emission amount determiner 202 determines the function that defines the relationship between the gray level characteristic value and the light emission amount according to the threshold gray level received from the LD threshold coordinator 210. In Figure 10 the example, the block light emission amount determiner 202 determines the function according to the specified threshold gray level.

[0167] In Figure 10 the graph, the horizontal axis represents the gray level characteristic value of the backlight block. The vertical axis represents the light emission amount of the backlight block. The function 401 (first conversion function) is the initial function, and the initial threshold gray level (fourth threshold gray level) is 64. The function 401 has the same configuration as that described in reference Figure 4 and Figure 5 above.

[0168] The function 404 (second conversion function) is a function modified from the initial function 401, and its threshold gray level (fifth threshold gray level) is 72. The function 404 is expressed as a linear function that increases from 0 to 1.0 in the range of the gray level characteristic value from 0 to 72, and shows a constant value of 1.0 in the range of the gray level characteristic value from 72 to 255. The difference in the threshold gray level between the functions 404 and 401 is 8.

[0169] The function 402 (third conversion function) is a function modified from the function 404, and its threshold gray level (sixth threshold gray level) is 80. The function 402 has the same configuration as that described in reference Figure 4 and Figure 5The same configuration as described above. The threshold gray level difference between functions 402 and 404 is 8. As noted from this description, the incremental step ΔJ for gradually increasing the threshold gray level is a constant. This value does not need to be constant, but can be gradually increased or decreased.

[0170] Although Figure 10 the maximum threshold gray level in the example of is 80, it can be a different value. Additionally, the value of the step ΔJ of the threshold gray level is not limited to 8, but can be, for example, a smaller value.

[0171] Similar to the first embodiment, this embodiment determines the threshold gray level based on the overall light emission amount of the backlight. As in the first embodiment, two threshold light emission amounts C and D are predetermined. The LD threshold coordinator 210 calculates the average light emission amount of the backlight blocks for a frame and determines the threshold gray level for the next frame based on the relationship between the average light emission amount and the threshold light emission amounts C and D. In this embodiment, the LD threshold coordinator 210 determines the threshold gray level in view of the following conditions.

[0172] First condition: Average light emission amount ≤ threshold light emission amount C

[0173] If the average light emission amount of the backlight blocks is less than or equal to the threshold light emission amount C, the LD threshold coordinator 210 determines the threshold gray level as the initial threshold gray level A. In the case where the threshold light emission amount C is 0.5, if the average light emission amount of the backlight blocks is less than or equal to 0.5, the threshold gray level is determined to be 64.

[0174] Second condition: Average light emission amount > threshold light emission amount D

[0175] If the average light emission amount of the backlight blocks is greater than the threshold light emission amount D for N consecutive frames (a consecutive predetermined number of times), the LD threshold coordinator 210 increases the threshold gray level by ΔJ. The step value (adjustment amount) ΔJ can be a fixed value or a function of the latest threshold gray level. The value N is an integer greater than 0.

[0176] Third condition: Threshold light emission amount C < average light emission amount ≤ threshold light emission amount D

[0177] If the average light emission amount of the backlight blocks is greater than the threshold light emission amount C and less than or equal to the threshold light emission amount D, the LD threshold coordinator 210 maintains the threshold gray level of the previous frame.

[0178] The threshold light emission amounts C and D can be fixed values (which can maintain their initial values) or can vary with the threshold gray level.

[0179] Figure 11It is a diagram for explaining an example of the control threshold gray level in this embodiment. For ease of description, the backlight is composed of six backlight blocks, and the number of display area blocks opposite to the backlight blocks is also six. In this example, the threshold gray level is gradually increased from the initial value of 64 to 80. Assume that the maximum threshold gray level is higher than 80; the increment step ΔJ of the threshold luminous amount is 8; the threshold luminous amount C is 0.5; the threshold luminous amount D is 0.8; and the number (count value) N of consecutive video frames for increasing the threshold gray level is 3. That is, if the average luminous amount of three consecutive frames exceeds the threshold luminous amount D = 0.8, the threshold gray level of the next video frame of these three consecutive frames will be increased by ΔJ = 8. If the threshold gray level has reached the maximum value, it will be maintained at that value.

[0180] In state S1, the threshold gray level is the initial value of 64. According to the received video frame, the gray level characteristic value of each backlight block is 64. Therefore, the luminous amount of all backlight blocks is 1.0. The average luminous amount is 1.0, which is greater than the threshold luminous amount D = 0.8. If state S1 lasts for three consecutive video frames, the threshold gray level of the subsequent fourth video frame is determined to be 72.

[0181] In state S2, the threshold gray level is 72. Assume that the display device continues to receive video frames with the same data, then the gray level characteristic value of each backlight block is 64. Since the threshold gray level is 72, the luminous amount for the gray level characteristic value of 64 is 0.89. The average luminous amount is 0.89, which is greater than the threshold luminous amount D = 0.8. If state S2 lasts for three consecutive video frames, the threshold gray level of the subsequent fourth video frame is determined to be 80.

[0182] In state S3, the threshold gray level is 80. Assume that the display device continues to receive video frames with the same data, then the gray level characteristic value of each backlight block is 64. Since the threshold gray level is 80, the luminous amount for the gray level characteristic value of 64 is 0.8. The average luminous amount is 0.8, which is less than or equal to the threshold luminous amount D = 0.8 and greater than the threshold luminous amount C = 0.5. Therefore, the threshold gray level is maintained at 80.

[0183] As described above, the third embodiment is a control that effectively avoids the reduction of the in-plane contrast ratio.

[0184] Fourth Embodiment

[0185] In the following, a fourth embodiment of the present invention will be described. The differences from the first embodiment will be mainly described below. Unless otherwise specified, the description of the first embodiment is applicable to the fourth embodiment. When the high emission of the backlight continues for a certain period of time, in this embodiment, the emission amount at the folding point of the function for converting the gray-level characteristic value into the emission amount of the backlight block along the initial function is gradually reduced. This means that the threshold gray level is reduced. This configuration suppresses the degradation of the display quality caused by the sudden decrease in the emission amount, and also reduces the possibility that the emission amount of the low gray-level image becomes too low to provide good image visibility, while reducing the power consumption by reducing the emission amount.

[0186] Figure 12 An example of a function (gray-level characteristic value - emission amount conversion formula) defining the relationship between the gray-level characteristic value and the emission amount of the backlight block in the fourth embodiment is provided. The block emission amount determiner 202 determines the function defining the relationship between the gray-level characteristic value and the emission amount according to the threshold gray level received from the LD threshold coordinator 210. In Figure 12 the example, the block emission amount determiner 202 determines the function according to the specified threshold gray level.

[0187] In Figure 12 the graph, the horizontal axis represents the gray-level characteristic value of the backlight block. The vertical axis represents the emission amount of the backlight block. The function 431 (first conversion function) is the initial function, and the initial threshold gray level is 80. The function 431 has the same configuration as the function 402 described with reference to Figure 4 and Figure 5 . The emission amount according to the function 431 is represented as a linear function that monotonically increases from the origin (0, 0) to the folding point B0 and shows a constant value of 1.0 in the range from the gray-level characteristic value at the folding point B0 to the maximum gray-level characteristic value. The emission amount in the range from the gray-level characteristic value at the folding point B0 to the maximum gray-level characteristic value can be represented by a monotonically increasing linear function.

[0188] The function 432 (second conversion function) is a function obtained by correcting the initial function 431 one or more times. As described above, one correction reduces the emission amount at the folding point by a predetermined step. The folding point B1 of the function 432 is located at the coordinate where the emission amount in the initial function 431 is 0.9. The gray-level characteristic value at the folding point B1 or the threshold gray level (seventh threshold gray level) in the corrected function 432 is 72.

[0189] The function 432 consists of two linear functions, as in Figure 8is the same as the function 403 in. Specifically, in the function 432, the light emission amount from the point with a grayscale feature value of 0 to the folding point B1 is represented as a monotonically increasing linear function, while the light emission amount from the folding point B1 to the maximum grayscale feature value is represented as another monotonically increasing linear function. The slope from the origin to the folding point B1 is greater than the slope from the folding point B1 to the point at the maximum grayscale feature value.

[0190] The function 433 (the third conversion function) is a function obtained by correcting the function 432 one or more times. The folding point B2 of the function 433 is located at the coordinate where the light emission amount in the initial function 431 is 0.85. The grayscale feature value at the folding point B2 or the threshold grayscale level (the eighth threshold grayscale level) in the corrected function 433 is 68.

[0191] The functions 431, 432, and 433 can be represented by the conversion formulas 1 and 2 described in the second embodiment. The slope from the point with a grayscale feature value of 0 to the folding point is common to all functions, and in each function, the slope from the point with a grayscale feature value of 0 to the folding point is greater than the slope from the folding point to the point with the maximum grayscale feature value. The slope from the folding point to the point at the maximum grayscale feature value increases in the order from the function 431 to the function 433. For example, when correcting the function, the step size (decrement) of reducing the light emission amount at the folding point can be a constant value of 0.01, and the minimum light emission amount at the reduced folding point can be 0.8.

[0192] Similar to the first embodiment, this embodiment determines the threshold grayscale level based on the overall light emission amount of the backlight. As in the first embodiment, two threshold light emission amounts C and D are determined in advance. The LD threshold coordinator 210 calculates the average light emission amount of the backlight blocks for one frame and determines the position of the folding point or the threshold grayscale level for the next frame based on the relationship between the average light emission amount and the threshold light emission amounts C and D. In this embodiment, the LD threshold coordinator 210 determines the threshold grayscale level in view of the following conditions.

[0193] The first condition: the average light emission amount ≤ the threshold light emission amount C

[0194] If the average light emission amount of the backlight blocks is less than or equal to the threshold light emission amount C, the LD threshold coordinator 210 determines the folding point as the initial folding point B0 (the threshold grayscale level is the initial threshold grayscale level). When the threshold light emission amount C is 0.5, if the average light emission amount of the backlight blocks is less than or equal to 0.5, the initial folding point is determined at the coordinate (80, 1.0). In other words, the threshold grayscale level is determined to be 80.

[0195] The second condition: the average light emission amount > the threshold light emission amount D

[0196] If the average luminous amount of the backlight block is greater than the threshold luminous amount D for N consecutive frames (a consecutive predetermined number of times), the LD threshold coordinator 210 reduces the luminous amount at the folding point by ΔL. In other words, the threshold gray level is reduced by ΔR. The step value (adjustment amount) ΔL can be a fixed value or a function of the latest threshold gray level. If ΔL is a constant, then ΔR is also a constant. An example of ΔL can be 0.01, and the value of N is an integer greater than 0.

[0197] Third condition: Threshold luminous amount C < average luminous amount ≤ threshold luminous amount D

[0198] If the average luminous amount of the backlight block is greater than the threshold luminous amount C and less than or equal to the threshold luminous amount D, the LD threshold coordinator 210 maintains the folding point (its coordinates) or function of the previous frame. The threshold luminous amounts C and D can be fixed values (which can maintain their initial values) or can vary with the threshold gray level.

[0199] Figure 13 is a diagram for explaining an example of controlling the folding point (threshold gray level) in the present embodiment. In this example, the luminous amount at the folding point is gradually reduced from 0.95 to 0.85. The luminous amount at the initial folding point is 1.0, and the decrement step ΔL is 0.05. The threshold gray level also varies with the luminous amount at the folding point. In Figure 13 the example, the threshold gray level is gradually reduced from 76 to 68. The decrement step ΔR is 4.

[0200] Assume that the threshold luminous amount C is 0.5; the threshold luminous amount D is 0.88; and the number (count value) N of consecutive video frames for reducing the luminous amount at the folding point is 3. In other words, if the average luminous amount of three consecutive video frames exceeds the threshold luminous amount D = 0.88, the luminous amount at the folding point will be reduced by ΔL = 0.05. If the luminous amount at the folding point has reached the minimum value, that value is maintained.

[0201] In state S101, the threshold gray level is 76, and the luminous amount at the folding point is 0.95. That is to say, state S101 is the corrected state after the initial state. As described above, the threshold gray level (initial function) in the initial state is 80, and the luminous amount at the folding point is 1.0. The gray level characteristic value of each backlight block according to the input video frame is 80.

[0202] Therefore, the luminous amount of each backlight block is calculated by using the conversion formula 2 described in the second embodiment of the applied function, and its value is 0.95. The average luminous amount of the backlight block is 0.95, which is greater than the threshold luminous amount D = 0.88. If state S101 lasts for three consecutive video frames, then for the subsequent fourth video frame, the luminous amount at the folding point becomes 0.9, and the threshold gray level becomes the gray level characteristic value 72 at the folding point.

[0203] In state S102, the threshold gray level is 72, and the light emission amount at the folding point is 0.90. Assuming that the display device continues to receive video frames with the same data, the gray level characteristic value of each backlight block is 80. The light emission amount of each backlight block is calculated by conversion formula 2 of the applied function 432, and its value is 0.90. The average light emission amount of the backlight blocks is 0.90, which is greater than the threshold light emission amount D = 0.88. If state S102 continues for three consecutive video frames, then for the subsequent fourth video frame, the light emission amount at the folding point becomes 0.85, and the threshold gray level becomes the gray level characteristic value 68 at the folding point.

[0204] In state S103, the threshold gray level is 68, and the light emission amount at the folding point is 0.85. Assuming that the display device continues to receive video frames with the same data, the gray level characteristic value of each backlight block is 80. The light emission amount of each backlight block is calculated by conversion formula 2 of the applied function 433, and its value is 0.86. The average light emission amount of the backlight blocks is 0.86, which is less than the threshold light emission amount D = 0.88 and greater than the threshold light emission amount C = 0.5. Therefore, the coordinates of the folding point are maintained, or the light emission amount and the threshold gray level at the folding point are maintained.

[0205] As described above, the fourth embodiment is a control that effectively suppresses the unnaturalness of the display quality of an image with continuous gray level changes.

[0206] Fifth Embodiment

[0207] Hereinafter, the fifth embodiment of the present invention will be described. The fifth embodiment performs control (first control) according to the gray level characteristic value - light emission amount conversion characteristic of the third embodiment, and then performs control (second control) according to the gray level characteristic value - light emission amount conversion characteristic of the fourth embodiment. The first control can be control according to the gray level characteristic value - light emission amount conversion characteristic of the first embodiment, and the second control can be control according to the gray level characteristic value - light emission amount conversion characteristic of the second embodiment. This embodiment suppresses the deterioration of the display quality caused by too much reduction in the light emission amount in the low gray level region, while reducing the overall light emission amount of the backlight source. The following describes an example of first performing the control according to the third embodiment and then entering the control according to the fourth embodiment.

[0208] Figure 14 is a diagram showing a method of controlling the gray level characteristic value - light emission amount conversion characteristic in this embodiment. When the display device continuously receives video frames that require high light emission of the backlight source, this embodiment corrects the gray level characteristic value - light emission amount conversion function according to the first control, and then further corrects the gray level characteristic value - light emission amount conversion function according to the second control.

[0209] The first control is the control described in the third embodiment, and the second control is the control described in the fourth embodiment. In Figure 14 , the curve graph of the first control is the same as that of Figure 10 , and the curve graph of the second control is the same as that of Figure 12 . The final function 402 in the first control is the same as the initial function 431 in the second control. Therefore, the first control can seamlessly continue to the second control.

[0210] As described above, as the high emission of the backlight continues, the gray level characteristic value - luminous flux conversion function to be used in the first control is corrected from function 401 to function 404 (the first conversion function), and further corrected to function 402 (the second conversion function). The threshold gray level of function 401 is 64; the threshold gray level (the ninth threshold gray level) of function 404 is 72; the threshold gray level (the tenth threshold gray level) of function 402 is 80.

[0211] As described above, function 402 and function 431 in the second control are the same function (the second conversion function). When the first control continues to the second control, the gray level characteristic value - luminous flux conversion function to be used in the second control is corrected from function 402 (i.e., function 431) to function 432 (the third conversion function). The threshold gray level (the eleventh threshold gray level) of function 432 is the gray level characteristic value 72 at the folding point B1.

[0212] This embodiment executes the first control until the threshold gray level reaches the maximum value (80 in this example), and then enters the second control. A specific example of the control in this embodiment is described below. Figure 15A is a diagram for explaining an example of controlling the threshold gray level in the first control. In this example, the threshold gray level is gradually increased from the initial value 64 to 80, assuming that the maximum threshold gray level is 80.

[0213] Assume that the increment step ΔJ of the threshold gray level is 8; the threshold luminous flux C is 0.5; the threshold luminous flux D is 0.8; and the number (count value) N of consecutive video frames for increasing the threshold gray level is 3. That is, if the average luminous flux of three consecutive frames exceeds the threshold luminous flux D = 0.8, the threshold gray level of the next video frame of these three consecutive frames will be increased by ΔJ = 8.

[0214] As Figure 15A shown, the threshold gray level in state S151 is the initial value 64. According to the received video frame, the gray level characteristic value of each backlight block is 80. Therefore, the luminous flux of all backlight blocks is 1.0. The average luminous flux of the backlight blocks is 1.0, which is greater than the threshold luminous flux D = 0.8. If state S151 lasts for three consecutive video frames, the threshold gray level of the subsequent fourth video frame is determined to be 72.

[0215] In state S152, the threshold gray level is 72. Assuming that the display device keeps receiving video frames with the same data, the gray level eigenvalue of each backlight block is 80. Since the threshold gray level is 72, the luminous intensity for the gray level eigenvalue of 80 is 1.0. The average luminous intensity is 1.0, which is greater than the threshold luminous intensity D = 0.8. If state S152 continues for three consecutive video frames, the threshold gray level of the subsequent fourth video frame is determined to be 80.

[0216] In state S153, the threshold gray level is 80. Assuming that the display device keeps receiving video frames with the same data, the gray level eigenvalue of each backlight block is 80. Since the threshold gray level is 80, the luminous intensity for the gray level eigenvalue of 80 is 1.0. The average luminous intensity is 1.0, which is greater than the threshold luminous intensity D = 0.8. Since the threshold gray level has reached the maximum value of 80, the control of the gray level eigenvalue - luminous intensity conversion characteristic changes from the first control to the second control.

[0217] Figure 15B is a diagram for explaining an example in which the luminous intensity at the folding point is gradually decreased from 0.95 to 0.85 in the second control. The luminous intensity at the initial folding point is 1.0; the initial threshold gray level is 80; the decrement step ΔL is 0.05. The threshold gray level also changes with the luminous intensity at the folding point. In Figure 15B the example, the threshold gray level is gradually decreased from 76 to 68. The decrement step ΔR is 4.

[0218] Assume that the threshold luminous intensity C is 0.5 and the threshold luminous intensity D is 0.88. The values of the threshold luminous intensities C and D can be the same or different between the first control and the second control. The number (count value) N of consecutive video frames for reducing the threshold gray level is 3. That is, if the average luminous intensity of three consecutive video frames exceeds the threshold luminous intensity D = 0.88, the luminous intensity at the folding point will be decreased by ΔL = 0.05. The value of ΔL can be 0.01. If the luminous intensity at the folding point has reached the minimum value, that value is maintained. The threshold N of the number of consecutive video frames can be the same or different between the first control and the second control. For example, the value N in the second control can be 1.

[0219] State S154 is the state changed from state S153 by the second control. State S153 is the initial state in the second control. In state S154, the threshold gray level is 76 and the luminous intensity at the folding point is 0.95. That is, state S154 is the corrected state after the initial state S153. The threshold gray level in state S153 is 80 and the luminous intensity at the folding point is 1.0. The gray level eigenvalue of each backlight block according to the input video frame is 80, which is the same as before.

[0220] The light emission amount of each backlight block is calculated by using the conversion formula 2 described in the second embodiment of the applied function, and its value is 0.95. The average light emission amount of the backlight blocks is 0.95, which is greater than the threshold light emission amount D = 0.88. If the state S154 lasts for three consecutive video frames, then for the subsequent fourth video frame, the light emission amount at the folding point becomes 0.9, and the threshold gray level becomes the gray level eigenvalue 72 at the folding point.

[0221] In state S155, the threshold gray level is 72, and the light emission amount at the folding point is 0.90. Assuming that the display device continues to receive video frames with the same data, the gray level eigenvalue of each backlight block is 80. The light emission amount of each backlight block is calculated by using the conversion formula 2 of the applied function 432, and its value is 0.90. The average light emission amount of the backlight blocks is 0.90, which is greater than the threshold light emission amount D = 0.88. If the state S155 lasts for three consecutive video frames, then for the subsequent fourth video frame, the light emission amount at the folding point becomes 0.85, and the threshold gray level becomes the gray level eigenvalue 68 at the folding point.

[0222] In state S156, the threshold gray level is 68, and the light emission amount at the folding point is 0.85. Assuming that the display device continues to receive video frames with the same data, the gray level eigenvalue of each backlight block is 80. The light emission amount of each backlight block is calculated by using the conversion formula 2 of the applied function 433, and its value is 0.86. The average light emission amount is 0.86, which is less than the threshold light emission amount D = 0.88 and greater than the threshold light emission amount C = 0.5. Therefore, the coordinates at the folding point are maintained, or the light emission amount and the threshold gray level at the folding point are maintained.

[0223] Figure 16 The control results based on the gray level eigenvalues of certain video frames in this embodiment are provided. Specifically, Figure 16 represents the light emission amount of each backlight block and the average light emission amount of the backlight blocks calculated based on the gray level eigenvalues of continuously received video frames. Assume that the threshold light emission amount D is 0.88.

[0224] Case C1 provides the control results for consecutive video frames that have gray level eigenvalues slightly higher than the initial threshold gray level (= 64). For all backlight blocks, the light emission amount according to the initial function with a threshold gray level of 64 is 1.0, and its average value is 1.0. The threshold gray level is increased by the first control, so the light emission amount of the backlight blocks decreases, and its average value decreases to 0.87. This amount is less than the threshold light emission amount D of 0.88, so there is no need to change the control to the second control.

[0225] Case C2 provides the control result for consecutive video frames having a mixture of a low gray - level eigenvalue (= 48) and a relatively high gray - level eigenvalue (= 160). The average luminous intensity according to the initial function with a threshold gray - level of 64 is 0.97. By the first control, the threshold gray - level is increased. Thus, the luminous intensity of the backlight block decreases, and its average value decreases to 0.95. This value is greater than the threshold luminous intensity D of 0.88. Therefore, the control changes from the first control to the second control. By the second control, the threshold gray - level is decreased. Thus, the luminous intensity of the backlight block decreases, and its average value decreases to 0.85. This value is less than the threshold luminous intensity D of 0.88.

[0226] Case C3 provides the control result for consecutive video frames having a mixture of a low gray - level eigenvalue (= 48) and a high gray - level eigenvalue (= 200). The average luminous intensity according to the initial function with a threshold gray - level of 64 is 0.95. By the first control, the threshold gray - level is increased. Thus, the luminous intensity of the backlight block decreases, and its average value decreases to 0.92. This value is greater than the threshold luminous intensity D of 0.88. Therefore, the control changes from the first control to the second control. By the second control, the threshold gray - level is decreased. Thus, the luminous intensity of the backlight block decreases, and its average value decreases to 0.87. This value is less than the threshold luminous intensity D of 0.88.

[0227] This embodiment increases the possibility that the backlight block can maintain its luminous intensity at 80% or more of the initial amount. In particular, this embodiment can control the backlight source so that the luminous intensity is not excessively reduced in the low gray - level range.

[0228] Sixth Embodiment

[0229] Hereinafter, the sixth embodiment of the present invention will be described. The sixth embodiment describes various characteristics in the range from 0 to the threshold gray - level of the gray - level eigenvalue after the threshold gray - level is corrected from the initial value, or the conversion formula from the gray - level eigenvalue to the luminous intensity. All functions (conversion formulas) described below are monotonically increasing functions.

[0230] Figures 17A to 17F An example of a function in the range from 0 to the threshold gray - level of the gray - level eigenvalue is provided. Figure 17A A function composed of an upward - concave curve is provided. As a comparative example, a monotonically increasing linear function is also provided. The linear function can be implemented with a small - scale circuit and minimizes the part that causes unnatural display quality because the change rate of the function is fixed. The upward - concave curve requires a relatively large - scale circuit, but achieves a smaller reduction in luminous intensity around the inflection point. Therefore, it is effective to prioritize display quality around the threshold.

[0231] Figure 17BA function composed of a downward concave curve is provided. As a comparative example, a monotonically increasing linear function is also provided. Although the downward concave curve requires a relatively large-scale circuit, it is effective to prioritize energy-saving effects over the luminous intensity around the inflection point.

[0232] Figure 17C A function forming a convex fold is provided, in which two linear functions with different slopes are connected. As a comparative example, a monotonically increasing linear function is also provided. This function can be implemented with a relatively small-scale circuit and achieve a small reduction in luminous intensity around the inflection point. Therefore, it is effective to prioritize display quality around the threshold.

[0233] Figure 17D A function forming a concave fold is provided, in which two linear functions with different slopes are connected. As a comparative example, a monotonically increasing linear function is also provided. This function can be implemented with a relatively small-scale circuit, and it is effective to prioritize energy-saving effects over the luminous intensity around the inflection point.

[0234] Figure 17E A function connecting an upward concave curve and a downward concave curve is provided. As a comparative example, a monotonically increasing linear function is also provided. Although such a function requires a relatively large-scale circuit, it is effective to control so as not to reduce the luminous intensity in the low gray level region as much as possible.

[0235] Figure 17F A function connecting a downward concave curve and an upward concave curve is provided. As a comparative example, a monotonically increasing linear function is also provided. Such a function can effectively prioritize the brightness around the inflection point over the brightness in the low gray level region.

[0236] The Seventh Embodiment

[0237] Hereinafter, the seventh embodiment of the present invention will be described. The seventh embodiment modifies the gray level eigenvalue-luminous intensity conversion function described in the first to fourth embodiments in the opposite direction.

[0238] As referred to Figure 5 As described, the first embodiment changes the gray level eigenvalue-luminous intensity conversion function from the initial function 401 to the modified function 402. This embodiment uses the threshold B as the initial threshold gray level, uses the function 402 as the initial function, and selects the function to be used from the initial function 402 and the function 401 based on the relationship between the average luminous intensity and the threshold luminous intensity. The conditions for determining the threshold gray level in the first embodiment can be rewritten as follows.

[0239] The First Condition: The average luminous intensity ≤ the threshold luminous intensity C

[0240] If the average light emission amount of the backlight block is less than or equal to the threshold light emission amount C (the first threshold light emission amount) for N consecutive frames (a consecutive predetermined number of times), the LD threshold coordinator 210 determines the threshold gray level as the corrected threshold gray level A. The value of N is an integer greater than 0. The corrected threshold gray level A can be a fixed value or a function of the average light emission amount.

[0241] Second condition: average light emission amount > threshold light emission amount D

[0242] If the average light emission amount of the backlight block is greater than the threshold light emission amount D, the LD threshold coordinator 210 determines the threshold gray level as the initial threshold gray level B.

[0243] Third condition: threshold light emission amount C < average light emission amount ≤ threshold light emission amount D

[0244] If the average light emission amount of the backlight block is greater than the threshold light emission amount C and less than or equal to the threshold light emission amount D, the LD threshold coordinator 210 maintains the threshold gray level of the previous frame.

[0245] As referenced Figure 8 As described, the second embodiment changes the gray level eigenvalue - light emission amount conversion function from the initial function 401 to the corrected function 403. This embodiment uses the threshold E as the initial threshold gray level, uses the function 403 as the initial function, and selects the function to be used from the initial function 403 and the function 401 based on the relationship between the average light emission amount and the threshold light emission amount. The conditions for determining the threshold gray level in the second embodiment can be rewritten as follows.

[0246] First condition: average light emission amount ≤ threshold light emission amount C

[0247] If the average light emission amount of the backlight block is less than or equal to the threshold light emission amount C for N consecutive frames (a consecutive predetermined number of times), the LD threshold coordinator 210 determines the threshold gray level as the threshold gray level A. The threshold gray level A can be a fixed value or a function of the average light emission amount. The value of N is an integer greater than 0.

[0248] Second condition: average light emission amount > threshold light emission amount D

[0249] If the average light emission amount of the backlight block is greater than the threshold light emission amount D, the LD threshold coordinator 210 determines the threshold gray level as the initial threshold gray level E.

[0250] Third condition: threshold light emission amount C < average light emission amount ≤ threshold light emission amount D

[0251] If the average light emission amount of the backlight block is greater than the threshold light emission amount C and less than or equal to the threshold light emission amount D, the LD threshold coordinator 210 maintains the threshold gray level of the previous frame.

[0252] As referencedFigure 10 As described above, in the third embodiment, the threshold gray level is gradually increased from the initial value. As Figure 18 shown, in this embodiment, the threshold gray level is gradually decreased from the initial value. In this embodiment, the maximum threshold gray level, the minimum threshold gray level, and the decrement per step of the threshold gray level are predetermined as the initial values. The conditions for determining the threshold gray level in the third embodiment are rewritten as follows.

[0253] First condition: average luminous flux ≤ threshold luminous flux C

[0254] If the average luminous flux of the backlight block is less than or equal to the threshold luminous flux C for N consecutive frames (a consecutive predetermined number of times), the LD threshold coordinator 210 decreases the threshold gray level by ΔJ. The value ΔJ can be a fixed value or a function of the latest threshold gray level. The value N is an integer greater than 0.

[0255] Second condition: average luminous flux > threshold luminous flux D

[0256] If the average luminous flux of the backlight block is greater than the threshold luminous flux D, the LD threshold coordinator 210 determines the threshold gray level as the initial threshold gray level (the maximum value).

[0257] Third condition: threshold luminous flux C < average luminous flux ≤ threshold luminous flux D

[0258] If the average luminous flux of the backlight block is greater than the threshold luminous flux C and less than or equal to the threshold luminous flux D, the LD threshold coordinator 210 maintains the threshold gray level of the previous frame. The threshold luminous fluxes C and D can be fixed values (their initial values can be maintained), or they can vary with the threshold gray level.

[0259] As referred to Figure 12 above, in the fourth embodiment, the luminous flux at the folding point is gradually decreased from the initial value. In other words, in the fourth embodiment, the threshold gray level or the gray level characteristic value at the folding point is gradually decreased. In this embodiment, the luminous flux at the folding point is gradually increased from the initial value. Therefore, the threshold gray level is gradually increased from the initial value. In this embodiment, the minimum luminous flux at the folding point, the maximum luminous flux at the folding point, and the increment per step of the luminous flux at the folding point are predetermined as the initial values. The initial folding point is Figure 12 the folding point B2 in

[0260] First condition: average luminous flux ≤ threshold luminous flux C

[0261] If the average light emission amount of the backlight block is less than or equal to the threshold light emission amount C for N consecutive frames (a predetermined number of consecutive times), the LD threshold coordinator 210 increases the light emission amount at the folding point by ΔL. The value ΔL can be a fixed value or a function of the latest threshold gray level. The value N is an integer greater than 0.

[0262] Second condition: average light emission amount > threshold light emission amount D

[0263] If the average light emission amount of the backlight block is greater than the threshold light emission amount D, the LD threshold coordinator 210 determines that the folding point is the initial folding point B2.

[0264] Third condition: threshold light emission amount C < average light emission amount ≤ threshold light emission amount D

[0265] If the average light emission amount of the backlight block is greater than the threshold light emission amount C and less than or equal to the threshold light emission amount D, the LD threshold coordinator 210 maintains the folding point (its coordinates) of the previous frame. The threshold light emission amounts C and D can be fixed values (which can maintain their initial values) or can vary with the threshold gray level.

[0266] As described above, by modifying the first to fourth embodiments, the first control and the second control in the fifth embodiment can be modified. As described above, the seventh embodiment determines to use the first transfer function when the average light emission amount of N or more consecutive frames is less than or equal to the threshold light emission amount C, determines to maintain the current transfer function when the average light emission amount is greater than the threshold light emission amount C and less than or equal to the threshold light emission amount D, and determines to use the second transfer function when the average light emission amount is greater than the threshold light emission amount D.

[0267] Embodiments of the present invention use a gray level not higher than 80 as the threshold gray level. When displaying an image with a gray level feature value lower than the threshold gray level, the light emission amount of the backlight block decreases. Therefore, the brightness distribution of each backlight block and the influence of the leakage light from adjacent blocks are also reduced. Therefore, in considering the brightness distribution of each backlight block and the influence of the leakage light from adjacent blocks, by adopting a low threshold gray level, the adjustment of the light emission amount can be eliminated. Therefore, the liquid crystal display device 1 of the present invention neither includes a storage unit for storing the brightness distribution nor includes an arithmetic circuit for adjusting to conform to the brightness distribution as in the prior art. Embodiments of the present invention can avoid an increase in the circuit scale.

[0268] Embodiments of the present invention use the highest gray level within the display area block as the gray level feature value. Hereinafter, reference Figure 19A 、 Figure 19B and Figure 20 describe examples of methods for determining the gray level feature value. Figure 19A Shows a plurality of display area blocks 503 corresponding to the video frame 501, Figure 19B is Figure 19AAn enlarged view of the shaded display area block 503 in

[0269] As Figure 19B shown, each display area block 503 of the video frame 501 includes pixels 517 of M columns * N rows * 3 (R, G, B). Each R, G, or B pixel 517 is assigned grayscale data. Figure 19B The numerical value in each pixel 517 in

[0270] represents the grayscale data assigned to the pixel 517. For example, in the first column of the first row, the grayscale data of the R pixel is 50; the grayscale data of the G pixel is 53; the grayscale data of the B pixel is 46. The display area block 503 consists of N rows from the block start row 514 to the block end row 515. Each row consists of R pixels, G pixels, and B pixels 517 arranged in a cycle. The row 516 after the block end row 515 is the block start row of the next display area block 503. The display area block 503 also consists of M columns from the block start column 511 to the block end column 512. The column 513 after the block end column 512 is the block start column of the next display area block 503. Each column consists of an R pixel column, a G pixel column, and a B pixel column. Figure 19B The right boundary 519 and the lower boundary 518 of the display area block 503 are also indicated.

[0271] Next, referring to Figure 20 the determination of the grayscale feature value is described. When the liquid crystal display device 1 receives a video frame, the block luminous amount determiner 202 starts extracting grayscale data from the first column in the first row of the video frame. Specifically, the block luminous amount determiner 202 extracts the highest value, i.e., the grayscale value data (53) of the G pixel, from the grayscale data to be assigned to the RGB pixels in the first column of the first row in the target display area block, and temporarily stores this data (S11-1). Moving to the second column of the first row, the block luminous amount determiner 202 extracts the highest value, i.e., the grayscale value data (53) of the G pixel, from the grayscale data to be assigned to the RGB pixels there, and compares this value with the highest value extracted from the first column of the first row (S11-2). In this case, the two highest values being compared are the same value, and the value 53 is temporarily stored as the highest grayscale level (S11-3).

[0272] Moving to the first row and the third column, the block luminance determiner 202 extracts the highest value, i.e., the gray-scale value data of the G pixel, from the gray-scale data of the RGB pixels to be assigned there (70) (S11-1), and compares this value with the temporarily stored highest data (53) (S11-2). Since the comparison result shows that the newly extracted gray-scale value 70 is higher, the block luminance determiner 202 updates the highest value to 70 and temporarily stores it (S11-3). The block luminance determiner 202 repeats the above process until the end column of the block (the Mth column). In the case where the gray-scale data (70) of the G pixel in the first row and the third column, which is extracted and temporarily stored, is the highest value, as a result of repeatedly extracting the highest value and comparing until the end column of the block, this value is temporarily stored as the highest value in the first row of the display area block.

[0273] When the extraction of the highest value is completed up to the end column of the target display area block (the first row and the Mth column), the block luminance determiner 202 changes the target display area block to an adjacent display area block in the x-axis direction and continues to extract the highest value. In other words, the block luminance determiner 202 performs the above process on the RGB pixels in the start column of the block (the (M + 1)th column) and subsequent columns in the first row, and temporarily stores the highest value in the first row of each display area block (S11-4).

[0274] When the extraction of the highest value is completed in the first row of the video frame, the block luminance determiner 202 moves to the extraction of the gray-scale data of the RGB pixels in the second row. For example, as Figure 19B shown, assume that the gray-scale data of the G pixel in the RGB pixels to be assigned to the second row and the third column is 72. At this time, the temporarily stored highest value is 70, and the newly extracted 72 in the second row and the third column is higher. Therefore, the block luminance determiner 202 updates the stored value to the highest value 72 (S11-5). After that, the block luminance determiner 202 advances to the third row, the fourth row, and subsequent rows, repeats the extraction of the highest value, compares this value with the stored value, and temporarily stores the highest value.

[0275] The block luminance determiner 202 performs the extraction of the highest value until the end row of the display area block (the Nth row). As Figure 19B shown, assume that the value 90 is extracted as the highest value from the end row (the Nth row). If the temporarily stored value in the (N - 1)th row is 72, the newly extracted value 90 from the last row is higher. Therefore, the block luminance determiner 202 updates the highest value to 90 and temporarily stores it.

[0276] When the operation of extracting the highest value is completed on one display area block, the highest value among the multiple highest values extracted from each row from the start row to the end row of the block is obtained. The block luminance determiner 202 stores this highest value among the multiple highest values as the gray-scale feature value in the memory (S11-6). ForFigure 19A A video frame divided into X blocks in the x-axis direction and Y blocks in the y-axis direction determines X×Y grayscale feature values and stores them in a memory.

[0277] Embodiments of the present invention extract and temporarily store the highest value in the grayscale data of the RGB pixels in a row of a video frame block by block, and also update the highest value of each block row by row. Since the number of values to be stored is one for each display area block, a register circuit can be used for temporary storage. In addition, the extraction circuit can be implemented with a memory of at least two to ten rows because the highest grayscale level of the RGB pixels included in one row is extracted one by one from the start of the video frame. Therefore, grayscale feature values can be determined with a small-scale circuit without using a frame memory.

[0278] Eighth Embodiment

[0279] Figure 21 Shows another configuration example of the display device in an embodiment of this specification. The following mainly describes the differences from the Figure 1 configuration example. The liquid crystal display device 1 includes a video signal source 14A and a video signal source 14B, and a display driver 21A and a display driver 21B. The signal processing board 10 includes a video signal processing circuit 12A and a video signal processing circuit 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 when the display area is divided horizontally or vertically to be driven by different ICs because the resolution of the display area is too high to be driven by one IC.

[0280] The liquid crystal display panel 20 includes a first display area 250A and a second display area 250B adjacent to each other. The video signal processing circuit 12A performs processing related to the display screen, such as generating 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 the display screen, such as generating 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 provides a video signal to the video signal processing circuit 12A, and the video signal source 14B provides a video signal to the video signal processing circuit 12B.

[0281] The display driver 21A generates a data signal based on the video signal sent from the video signal processing circuit 12A, and supplies the data signal to the first display area 250A. The display driver 21B generates a data signal based on the video signal sent from the video signal processing circuit 12B, and supplies the data signal to the second display area 250B. The video signal processing circuit 12A also sends a timing signal to the display driver 21A, and the display driver 21A generates a data signal based on the received video signal, and supplies the data signal to the first display area 250A according to the timing signal. The video signal processing circuit 12B also sends a timing signal to the display driver 21B, and the display driver 21B generates a data signal based on the received video signal, and supplies the data signal to the second display area 250B according to the timing signal.

[0282] The video signal processing circuit 12A converts the data arrangement of the video signal input from the outside to send it to the display driver 21A, and generates and sends a timing signal for operating the display driver 21A and the scan driver 22 using the power supplied from the power generation circuit 11. The video signal processing circuit 12A also generates a drive control signal for controlling the drive of the backlight 30, and sends the drive control signal to the backlight driver board 31.

[0283] The video signal processing circuit 12B converts the data arrangement of the video signal input from the outside to send it to the display driver 21B, and generates and sends a timing signal for operating the display driver 21B and the scan driver 22 using the power supplied from the power generation circuit 11. The video signal processing circuit 12B also generates a drive control signal for controlling the drive of the backlight 30, and sends the drive control signal to the backlight driver board 31.

[0284] The backlight driver board 31 includes a backlight drive circuit, and controls the light emission (brightness) of the backlight 30 according to the drive control signals sent from the video signal processing circuit 12A and the video signal processing circuit 12B.

[0285] Each of the video signal processing circuit 12A and the video signal processing circuit 12B generates a drive control signal for controlling the brightness of each block of the backlight 30, and sends the drive control signal to the backlight driver board 31. The backlight driver board 31 drives and controls the light sources of the backlight 30 so that each block emits light at the brightness value specified in the drive control signals from the video signal processing circuit 12A and the video signal processing circuit 12B.

[0286] The video signal processing circuit 12A generates timing signals for the display driver 21A and the scan driver 22 according to the received timing signal for the video signal, and also sequentially sends the signal (frame signal) of each video frame in the video signal to the display driver 21A. The video signal processing circuit 12B generates timing signals for the display driver 21B and the scan driver 22 according to the received timing signal for the video signal, and also sequentially sends the signal (frame signal) of each video frame in the video signal to the display driver 21B.

[0287] The video signal processing circuit 12A analyzes the video frame, generates a drive control signal for illuminating the first display area 250A from behind the first display area 250A by the backlight 30 based on the analysis result, and sends the drive control signal to the backlight 30. The video signal processing circuit 12B analyzes the video frame, generates a drive control signal for illuminating the second display area 250B from behind the second display area 250B by the backlight 30 based on the analysis result, and sends the drive control signal to the backlight 30.

[0288] Figure 22 The configuration of the backlight 30 is schematically shown. The backlight 30 has 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 twelve backlight blocks.

[0289] The first backlight area 350A is directly below the first display area 250A. The first backlight area 350A is behind the first display area 250A and opposite to the first display area 250A to illuminate the first display area 250A. The second backlight area 350B is directly below the second display area 250B. The second backlight area 350B is behind the second display area 250B and opposite to the second display area 250B to illuminate the second display area 250B.

[0290] The video signal processing circuit 12A determines the gray level characteristic value and the luminous amount of each backlight block in the first backlight area 350A as described in the other embodiments above. Similarly, the video signal processing circuit 12B determines the gray level characteristic value and the luminous amount of each backlight block in the second backlight area 350B as described in the other embodiments above.

[0291] In the present embodiment, the video signal processing circuits 12A and 12B use the same conversion function when calculating the light emission amount based on the gray level characteristic value. Specifically, the video signal processing circuits 12A and 12B select the same conversion function in their initial states. In addition, the video signal processing circuits 12A and 12B determine whether to change or maintain the conversion function based on the average light emission amount of the entire backlight source 30 including the first backlight region 350A and the second backlight region 350B.

[0292] This configuration enables the video signal processing circuits 12A and 12B to always select the same conversion function, so that they can determine the same light emission amount for the backlight blocks having the same gray level characteristic value in the first backlight region 350A and the second backlight region 350B.

[0293] The video signal processing circuit 12A only receives the video data of the first display region 250A and independently controls the first backlight region 350A. The video signal processing circuit 12B only receives the video data of the second display region 250B and independently controls the second backlight region 350B. The video signal processing circuits 12A and 12B in the present embodiment transmit information to each other so that one video signal processing circuit can determine the average value of the light emission amount of the backlight blocks calculated by the other video signal processing circuit. This configuration enables the video signal processing circuits 12A and 12B to effectively calculate the average light emission amount of the entire backlight source 30.

[0294] In the example described below, each of the average light emission amount of the first backlight region 350A and the average light emission amount of the second backlight region 350B is sent from the video signal processing circuit assigned with the backlight region to the other video signal processing line. The information to be transmitted between the video signal processing circuits 12A and 12B can be any information that enables one video signal processing circuit to determine the average light emission amount of the backlight region assigned to the other video signal processing circuit (for example, the light emission amount of all backlight blocks in the assigned backlight region).

[0295] Each of the video signal processing circuits 12A and 12B calculates the average light emission amount of the entire backlight source 30 based on the average light emission amount of the backlight region assigned to itself and the average light emission amount of the other backlight region. In addition, each of the video signal processing circuits 12A and 12B determines the function for determining the light emission amount based on the gray level characteristic value to be used after the current conversion function based on the average light emission amount of the entire backlight source 30. As described above, the conversion function to be used is maintained or changed to a different function.

[0296] A specific example is described below. Assume that the conversion functions currently used by the video signal processing circuits 12A and 12B are Figure 14The conversion function 401 in it. The conversion function can be any other conversion function described in other embodiments.

[0297] Figure 23 FIG. shows an example in which the video signal processing circuits 12A and 12B calculate the light emission amount based on the gray level characteristic values of the respective backlight blocks. The video signal processing circuit 12A calculates the gray level characteristic values of the backlight blocks in the first backlight area 350A based on the video data obtained from the video signal source 14A. The matrix 601A is the calculation result; the value in each cell represents the gray level characteristic value of the corresponding backlight block.

[0298] Similarly, the video signal processing circuit 12B calculates the gray level characteristic values of the backlight blocks in the second backlight area 350B based on the video data obtained from the video signal source 14B. The matrix 601B is the calculation result; the value in each cell represents the gray level characteristic value of the corresponding backlight block.

[0299] Next, the video signal processing circuit 12A calculates the light emission amount 603A of each backlight block according to the gray level characteristic value 601A by using the conversion function 401. As Figure 14 shown, the threshold gray level of the conversion function 401 is 64; the conversion function 401 is a linearly increasing function in the range where the gray level characteristic value is lower than 64, and outputs the upper limit value (1.0) in the range where the gray level characteristic value is not lower than 64. Similarly, the video signal processing circuit 12B calculates the light emission amount 603B of each backlight block according to the gray level characteristic value 601B by using the conversion function 401.

[0300] Next, the video signal processing circuits 12A and 12B calculate the average light emission amount of the backlight 30. Figure 24 FIG. shows the calculation 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 area 350A according to the light emission amount 603A of the backlight blocks, and includes it in its 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 area 350B according to the light emission amount 603B of the backlight blocks, and includes it in its management information 605B. In this example, the value is 1.0.

[0301] The video signal processing circuit 12A sends the calculated average luminous 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 sends the calculated average luminous 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. Each of the video signal processing circuits 12A and 12B calculates the average luminous amount of the entire backlight source 30 based on the two average luminous amounts of the backlight areas 350A and 350B, and includes the calculated value in its own management information 605A or 605B. In this example, the average luminous amount (Unified_G_ave) of the entire backlight source 30 is 0.952.

[0302] Each of the video signal processing circuits 12A and 12B determines the next transfer function based on the average luminous amount of the entire backlight source 30. Since the transfer function used is common to the video signal processing circuits 12A and 12B, the next transfer function to be selected is also common to them. Therefore, the first backlight area 350A and the second backlight area 350B always use the same transfer function, so that the same luminous amount can be assigned to the backlight blocks with the same gray-level characteristic value. Preferably, the backlight blocks with the same gray-level characteristic value are assigned the same luminous amount, because if they are assigned different luminous amounts, the user will feel the difference in brightness as unnatural display quality.

[0303] The following describes the change in the luminous amount of the backlight blocks in the first backlight area 350A and the second backlight area 350B in response to consecutive video frames with the same gray-level data. Assume that the video signal processing circuits 12A and 12B perform Figure 14 the control example shown and start their processing using the transfer function 401.

[0304] First, the change in the luminous amount of the backlight blocks in the first backlight area 350A is described. For example, every time a predetermined number of video frames are received, steps LS1 to LS5 in the following description are executed.

[0305] Refer to Figure 25A , in step LS1, the video signal processing circuit 12A determines the gray-level characteristic value 611A of the backlight blocks in the first backlight area 350A from a received video frame. The video signal processing circuit 12A calculates the luminous amount 613A of the backlight blocks in the first backlight area 350A based on the gray-level characteristic value 611A using the transfer function 401.

[0306] The average luminous flux (G_ave) of the luminous flux 613A is 0.904. As will be described later, the average luminous flux (G_ave) of the second backlight region 350B is 1.0. Therefore, the average luminous flux (Unified_G_ave) of the entire backlight 30 is 0.952. This quantity is greater than Figure 14 the threshold luminous flux D = 0.88 in

[0307] Reference Figure 25B , the gray-level eigenvalue 611B of the video frame in step LS2 is the same as the gray-level eigenvalue 611A of the video frame in step LS1. The video signal processing circuit 12A calculates the luminous flux 613B based on the gray-level eigenvalue 611B using the transfer function 404.

[0308] The average luminous flux (G_ave) of the luminous flux 613B is 0.877. As will be described later, the average luminous flux (G_ave) of the second backlight region 350B is 1.0. Therefore, the average luminous flux (Unified_G_ave) of the entire backlight 30 is 0.938. This quantity is greater than Figure 14 the threshold luminous flux D = 0.88 in

[0309] Reference Figure 25C , the gray-level eigenvalue 611C of the video frame in step LS3 is the same as the gray-level eigenvalue 611B of the video frame in step LS2. The video signal processing circuit 12A calculates the luminous flux 613C based on the gray-level eigenvalue 611C using the transfer function 402.

[0310] The average luminous flux (G_ave) of the luminous flux 613C is 0.856. As will be described later, the average luminous flux (G_ave) of the second backlight region 350B is 1.0. Therefore, the average luminous flux (Unified_G_ave) of the entire backlight 30 is 0.928. This quantity is greater than Figure 14 the threshold luminous flux D = 0.88 in

[0311] Reference Figure 25D , the gray-level eigenvalue 611D of the video frame in step LS4 is the same as the gray-level eigenvalue 611C of the video frame in step LS3. The video signal processing circuit 12A calculates the luminous flux 613D based on the gray-level eigenvalue 611D using the transfer function 432.

[0312] The average luminous flux (G_ave) of the luminous flux 613D is 0.845. As will be described later, the average luminous flux (G_ave) of the second backlight region 350B is 0.982. Therefore, the average luminous flux (Unified_G_ave) of the entire backlight source 30 is 0.914. This value is greater than Figure 14 the threshold luminous flux D = 0.88 in

[0313] Reference Figure 25E , the gray level eigenvalue 611E of the video frame in step LS5 is the same as the gray level eigenvalue 611D of the video frame in step LS4. The video signal processing circuit 12A calculates the luminous flux 613E based on the gray level eigenvalue 611E using the transfer function 433.

[0314] The average luminous flux (G_ave) of the luminous flux 613E is 0.839. As will be described later, the average luminous flux (G_ave) of the second backlight region 350B is 0.947. Therefore, the average luminous flux (Unified_G_ave) of the entire backlight source 30 is 0.893. This value is greater than Figure 14 the threshold luminous flux D = 0.88 in

[0315] Next, the change in the luminous flux of the backlight blocks in the second backlight region 350B is described. Steps RS1 to RS5 in the following description correspond to steps LS1 to LS5 above.

[0316] Reference Figure 26A , in step RS1, the video signal processing circuit 12B determines the gray level eigenvalue 631A of the backlight blocks in the second backlight region 350B from a received video frame. The video signal processing circuit 12B calculates the luminous flux 633A of the backlight blocks in the second backlight region 350B based on the gray level eigenvalue 631A using the transfer function 401.

[0317] The average luminous flux (G_ave) of the luminous flux 633A is 1.0. As described above, the average luminous flux (G_ave) of the first backlight region 350A is 0.904. Therefore, the average luminous flux (Unified_G_ave) of the entire backlight source 30 is 0.952. This value is greater than Figure 14 the threshold luminous flux D = 0.88 in

[0318] Reference Figure 26B, the gray - level eigenvalue 631B of the video frame in step RS2 is the same as the gray - level eigenvalue 631A of the video frame in step RS1. The video signal processing circuit 12B calculates the luminous flux 633B according to the gray - level eigenvalue 631B using the transfer function 404.

[0319] The average luminous flux (G_ave) of the luminous flux 633B is 1.0. As described above, the average luminous flux (G_ave) of the first backlight area 350A is 0.877. Therefore, the average luminous flux (Unified_G_ave) of the entire backlight 30 is 0.938. This value is greater than Figure 14 the threshold luminous flux D = 0.88 in []. Therefore, the transfer function to be used is changed from the transfer function 404 to the transfer function 402.

[0320] Reference Figure 26C , the gray - level eigenvalue 631C of the video frame in step RS3 is the same as the gray - level eigenvalue 631B of the video frame in step RS2. The video signal processing circuit 12B calculates the luminous flux 633C according to the gray - level eigenvalue 631C using the transfer function 402.

[0321] The average luminous flux (G_ave) of the luminous flux 633C is 1.0. As described above, the average luminous flux (G_ave) of the first backlight area 350A is 0.856. Therefore, the average luminous flux (Unified_G_ave) of the entire backlight 30 is 0.928. This value is greater than Figure 14 the threshold luminous flux D = 0.88 in []. Therefore, the transfer function to be used is changed from the first - controlled transfer function 402 to the second - controlled transfer function 432.

[0322] Reference Figure 26D , the gray - level eigenvalue 631D of the video frame in step RS4 is the same as the gray - level eigenvalue 631C of the video frame in step RS3. The video signal processing circuit 12B calculates the luminous flux 633D according to the gray - level eigenvalue 631D using the transfer function 432.

[0323] The average luminous flux (G_ave) of the luminous flux 633D is 0.982. As described above, the average luminous flux (G_ave) of the first backlight area 350A is 0.845. Therefore, the average luminous flux (Unified_G_ave) of the entire backlight 30 is 0.914. This value is greater than Figure 14 the threshold luminous flux D = 0.88 in []. Therefore, the transfer function to be used is changed from the transfer function 432 to the transfer function 433.

[0324] Reference Figure 26E, the gray-level eigenvalue 631E of the video frame in step RS5 is the same as the gray-level eigenvalue 631D of the video frame in step RS4. The video signal processing circuit 12B calculates the light emission amount 633E based on the gray-level eigenvalue 631E using the transfer function 433.

[0325] The average light emission amount (G_ave) of the light emission amount 633E is 0.947. As described above, the average light emission amount (G_ave) of the first backlight area 350A is 0.839. Therefore, the average light emission amount (Unified_G_ave) of the entire backlight 30 is 0.893. This amount is greater than Figure 14 the threshold light emission amount D = 0.88 in []. Since the light emission amount at the folding point has reached the lower limit, the transfer function 433 is maintained.

[0326] Comparing steps RS1 to RS5 with steps LS1 to LS5, the transfer functions used when processing the same video frame are the same between each pair of steps. Therefore, the light emission amounts of the same gray-level eigenvalues in different backlight areas become the same.

[0327] In the above example, each of the display area and the backlight area is divided into two areas controlled by two different video signal processing circuits. In another example, the number of divisions of the display area and the backlight area and the number of video signal processing circuits can be three or more. Information is transmitted between the video signal processing circuits that control adjacent display areas and backlight areas. The following describes a control example in the case where both the display area and the backlight area are divided into four areas.

[0328] Figure 27 Another configuration of the backlight 30 is schematically shown. The backlight 30 has a first backlight area 350A in the upper left, a second backlight area 350B in the upper right, a third backlight area 350C in the lower left, and a fourth backlight area 350D in the lower right. In the example described below, each of the backlight areas 350A to 350D consists of twelve backlight blocks.

[0329] Each of the backlight areas 350A to 350D is located directly below and opposite to a different display area to illuminate the opposite display area. The display device includes four video signal processing circuits for controlling four pairs of display areas and backlight areas.

[0330] Figure 28Examples of the gray-level characteristic values of the backlight blocks calculated by the four video signal processing circuits 12A to 12D are provided. The video signal processing circuit 12A calculates the gray-level characteristic values of the backlight blocks in the first backlight area 350A based on the video data obtained from the associated video signal source. Matrix 621A is the calculation result; the value in each cell represents the gray-level characteristic value of the corresponding backlight block.

[0331] The video signal processing circuit 12B calculates the gray-level characteristic values of the backlight blocks in the second backlight area 350B based on the video data obtained from the associated video signal source. Matrix 621B is the calculation result; the value in each cell represents the gray-level characteristic value of the corresponding backlight block.

[0332] The video signal processing circuit 12C calculates the gray-level characteristic values of the backlight blocks in the third backlight area 350C based on the video data obtained from the associated video signal source. Matrix 621C is the calculation result; the value in each cell represents the gray-level characteristic value of the corresponding backlight block.

[0333] The video signal processing circuit 12D calculates the gray-level characteristic values of the backlight blocks in the fourth backlight area 350D based on the video data obtained from the associated video signal source. Matrix 621D is the calculation result; the value in each cell represents the gray-level characteristic value of the corresponding backlight block.

[0334] Figure 29 The light emission amounts of the backlight blocks calculated by the video signal processing circuits 12A to 12D are provided. The video signal processing circuits 12A to 12D calculate the light emission amounts 623A to 623D of the backlight blocks according to the gray-level characteristic values 621A to 621D by using the transfer function 401.

[0335] Next, the video signal processing circuits 12A to 12D calculate the average light emission amount of the backlight 30. Figure 30 The average light emission amounts of the backlight areas 350A to 350D calculated by the associated video signal processing circuits 12A to 12D are provided.

[0336] The video signal processing circuit 12A calculates the average light emission amount of the first backlight area 350A according to the light emission amount 623A of the backlight block and includes it in its 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 area 350B according to the light emission amount 623B of the backlight block and includes it in its management information 625B. In this example, the value is 1.0.

[0337] The video signal processing circuit 12C calculates the average luminous intensity of the third backlight region 350C based on the luminous intensity 623C of the backlight block, and includes it in its management information 625C. In this example, the value is 0.904. The video signal processing circuit 12D calculates the average luminous intensity of the fourth backlight region 350D based on the luminous intensity 623D of the backlight block, and includes it in its management information 625D. In this example, the value is 1.0.

[0338] Next, each of the video signal processing circuits 12A to 12D sends information about the average luminous intensity it has calculated to the other video signal processing circuits. For example, the video signal processing circuits 12A and 12C transmit their information about the average luminous intensity, and the video signal processing circuits 12B and 12D transmit their information about the average luminous intensity. After that, the video signal processing circuits 12A and 12B transmit their information about the average luminous intensity, and the video signal processing circuits 12C and 12D transmit their information about the average luminous intensity. The method of exchanging information is not limited as long as each video signal processing circuit can obtain information about the average luminous intensity of all the backlight regions 350A to 350D.

[0339] Figure 31 Final management information about the average luminous intensity to be held by each of the video signal processing circuits 12A to 12D is provided. Since the information about the average luminous intensity of the backlight regions 350A to 350D is transmitted among the video signal processing circuits 12A to 12D as described above, the final information about the average luminous intensity is common to the management information of the video signal processing circuits 12A to 12D. In this example, the average luminous intensity (Unified_G_ave) of the entire backlight 30 is 0.952.

[0340] The video signal processing circuits 12A to 12D determine the next transfer function based on the average luminous intensity of the entire backlight 30. Since the transfer function in use is common to the video signal processing circuits 12A to 12D, the next transfer function to be selected is also common to them. Therefore, a common transfer function is always used for all the backlight regions 350A to 350D, so that the same luminous intensity can be assigned to the backlight blocks having the same gray level characteristic value.

[0341] Figure 32An example of data to be transmitted between the video signal processing circuits 12A and 12B is shown. The following description applies to 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 send the data signal SDA1 specifying 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 send the data signal SDA2 specifying the average light emission amount to the video signal processing circuit 12A. For example, serial transmission can be used for data transmission. The number of signal transmission lines can be reduced by sharing one or more signal lines between the video signal processing circuits 12A and 12B.

[0342] Figure 33 An example of waveforms of the clock signal SCK, the data signal SDA, and the control signal CS is shown. The data signal SDA represents the average light emission amount of the backlight area (e.g., the first backlight area). For Figure 31 example, the value "0.904" of G_ave calculated by the video signal processing circuit 12A is sent through 16-bit serial transmission. For example, the average light emission amount value 0.904 can be represented as "3702" with 12-bit resolution.

[0343] As described above, embodiments of the present invention have been described; however, the present invention is not limited to the above embodiments. Those skilled in the art can easily modify, add, or transform each element in the above embodiments within the scope of the present invention. A part of the configuration of one embodiment can be replaced with the configuration of another embodiment, or the configuration of one embodiment can be incorporated into the configuration of another embodiment.

Claims

1. A display device, comprising: A backlight source, the backlight source comprising a plurality of backlight blocks; a display panel configured to display an image using light from the backlight source; as well as Controller, Wherein, the controller is configured as: Get video frames; determining grayscale feature values ​​associated with the plurality of backlight blocks according to grayscale levels of specified pixels in the video frame; determining the light emission amounts of the plurality of backlight blocks from the grayscale characteristic values ​​according to a current conversion function; and Whether to change the current conversion function is determined based on a comparison result between the statistical value of the light emission amounts of the plurality of backlight blocks and one or more predetermined threshold light emission amounts.

2. The display device according to claim 1, wherein: The statistical value of the light emission amount is an average value of the light emission amount.

3. The display device according to claim 2, in, The one or more threshold luminous amounts include a first threshold luminous amount and a second threshold luminous amount greater than the first threshold luminous amount, Wherein, the current conversion function is the first conversion function or the second conversion function, wherein, for all grayscale characteristic values, the luminous amount according to the second conversion function is less than or equal to the luminous amount according to the first conversion function, wherein, for at least a portion of the grayscale characteristic value range, the luminescence amount according to the second conversion function is less than the luminescence amount according to the first conversion function, and Wherein, the controller is configured as: using the first conversion function when the average value of the luminous intensity is less than or equal to the first threshold luminous intensity; In a case where the average value of the luminous intensity is greater than the first threshold luminous intensity and less than or equal to the second threshold luminous intensity, determining to maintain the current conversion function; and The second conversion function is used when the average value of the light emission amount is greater than the second threshold light emission amount for a predetermined number of consecutive times.

4. The display device according to claim 3, in, Each gray level feature value is the highest gray level among the gray levels of the pixels associated with the backlight block, The first conversion function is defined as such that the luminous amount increases monotonically from zero to a maximum amount within a grayscale characteristic value range from zero grayscale to a first threshold grayscale, and always remains at the maximum amount within a grayscale characteristic value range above the first threshold grayscale, wherein the second conversion function is defined such that the luminous amount increases monotonically from zero to the maximum amount within the grayscale characteristic value range from zero grayscale to the second threshold grayscale, and always remains at the maximum amount within the grayscale characteristic value range above the second threshold grayscale, and The second threshold gray level is higher than the first threshold gray level.

5. The display device according to claim 3, in, The first conversion function is defined as a minimum luminous amount showing a minimum grayscale characteristic value and a maximum luminous amount showing a maximum grayscale characteristic value, wherein the second conversion function is defined as showing a minimum luminous amount of the minimum grayscale characteristic value and a maximum luminous amount of the maximum grayscale characteristic value, and In which, within a grayscale characteristic value range that is higher than a third threshold grayscale level and lower than the maximum grayscale characteristic value, the luminescence amount according to the second conversion function is smaller than the luminescence amount according to the first conversion function.

6. The display device according to claim 3, in, The first conversion function is defined as a minimum luminous amount showing a minimum grayscale characteristic value and a maximum luminous amount showing a maximum grayscale characteristic value, wherein the second conversion function is defined as a minimum luminous amount showing the minimum grayscale characteristic value and a maximum luminous amount showing the maximum grayscale characteristic value, wherein the first conversion function is composed of a first linear function that increases monotonically in the grayscale characteristic value range from the minimum grayscale characteristic value to the first threshold grayscale level and a second linear function that is constant or monotonically increases in the grayscale characteristic value range from the first threshold grayscale level to the maximum grayscale characteristic value, The second conversion function is composed of a third linear function that increases monotonically in the grayscale characteristic value range from the minimum grayscale characteristic value to the third threshold grayscale level and a fourth linear function that increases monotonically in the grayscale characteristic value range from the third threshold grayscale level to the maximum grayscale characteristic value. Wherein, the third threshold gray level is lower than the first threshold gray level, wherein the slope of the third linear function is less than or equal to the slope of the first linear function, and The slope of the fourth linear function is greater than the slope of the second linear function.

7. The display device according to claim 2, in, The one or more threshold luminous amounts include a first threshold luminous amount and a second threshold luminous amount greater than the first threshold luminous amount, wherein the current conversion function is the first conversion function, Wherein, the controller is configured as: When the average value of the luminous intensity is greater than the second threshold luminous intensity for a predetermined number of consecutive times, changing the current conversion function from the first conversion function to the second conversion function; After the current conversion function is changed to the second conversion function, if the average value of the luminous intensity is greater than the second threshold luminous intensity for a predetermined number of consecutive times, changing the current conversion function from the second conversion function to a third conversion function; wherein, for all grayscale characteristic values, the luminous amount according to the second conversion function is less than or equal to the luminous amount according to the first conversion function, wherein, for at least a portion of the grayscale characteristic value range, the luminous amount according to the second conversion function is less than the luminous amount according to the first conversion function, wherein, for all grayscale characteristic values, the luminescence amount according to the third conversion function is less than or equal to the luminescence amount according to the second conversion function, and For at least a portion of the grayscale characteristic value range, the luminescence amount according to the third conversion function is smaller than the luminescence amount according to the second conversion function.

8. The display device according to claim 7, in, Each gray level feature value is the highest gray level among the gray levels of the pixels associated with the backlight block, The first conversion function is defined as such that the luminous amount increases monotonically from zero to a maximum amount within a grayscale characteristic value range from zero grayscale to a fourth threshold grayscale, and always remains at the maximum amount within a grayscale characteristic value range above the fourth threshold grayscale, The second conversion function is defined so that the luminous amount increases monotonically from zero to the maximum amount within the grayscale characteristic value range from zero grayscale to the fifth threshold grayscale, and always remains at the maximum amount within the grayscale characteristic value range above the fifth threshold grayscale, Wherein, the fifth threshold gray level is higher than the fourth threshold gray level, wherein the third conversion function is defined so that the luminous amount increases monotonically from zero to the maximum amount within the grayscale characteristic value range from zero grayscale to a sixth threshold grayscale, and always remains at the maximum amount within the grayscale characteristic value range above the sixth threshold grayscale, and Wherein, the sixth threshold gray level is higher than the fifth threshold gray level.

9. The display device according to claim 7, in, Each gray level feature value is the highest gray level among the gray levels of the pixels associated with the backlight block, wherein the first conversion function is defined as a minimum luminous amount showing a minimum grayscale characteristic value and a maximum luminous amount showing a maximum grayscale characteristic value, wherein the second conversion function is defined as a minimum luminous amount showing the minimum grayscale characteristic value and a maximum luminous amount showing the maximum grayscale characteristic value, wherein the third conversion function is defined as showing the minimum luminous amount of the minimum grayscale characteristic value and the maximum luminous amount of the maximum grayscale characteristic value, wherein, within a grayscale characteristic value range that is higher than a seventh threshold grayscale level and lower than the maximum grayscale characteristic value, the luminous amount according to the second conversion function is less than the luminous amount according to the first conversion function, wherein, within a grayscale characteristic value range above an eighth threshold grayscale level and below the maximum grayscale characteristic value, the luminescence amount according to the third conversion function is less than the luminescence amount according to the second conversion function, and Wherein, the eighth threshold gray level is lower than the seventh threshold gray level.

10. The display device according to claim 7, in, Each gray level feature value is the highest gray level among the gray levels of the pixels associated with the backlight block, The first conversion function is defined as such that the luminous amount increases monotonically from zero to a maximum amount within a grayscale characteristic value range from zero grayscale to a ninth threshold grayscale, and always remains at the maximum amount within a grayscale characteristic value range above the ninth threshold grayscale, The second conversion function is defined so that the luminous amount increases monotonically from zero to the maximum amount within the grayscale characteristic value range from zero grayscale to the tenth threshold grayscale, and always remains at the maximum amount within the grayscale characteristic value range above the tenth threshold grayscale, Wherein, the tenth threshold gray level is higher than the ninth threshold gray level, wherein the third conversion function is defined as a zero luminous amount showing a zero grayscale characteristic value and a maximum luminous amount showing a maximum grayscale characteristic value, wherein, within a gray level characteristic value range above an eleventh threshold gray level and below the maximum gray level characteristic value, the luminescence amount according to the third conversion function is less than the luminescence amount according to the second conversion function, and Wherein, the eleventh threshold gray level is lower than the tenth threshold gray level.

11. The display device according to claim 2, in, The one or more threshold luminous amounts include a first threshold luminous amount and a second threshold luminous amount greater than the first threshold luminous amount, Wherein, the current conversion function is the first conversion function or the second conversion function, wherein, for all grayscale characteristic values, the luminous amount according to the second conversion function is less than or equal to the luminous amount according to the first conversion function, wherein, for at least a portion of the grayscale characteristic value range, the luminescence amount according to the second conversion function is less than the luminescence amount according to the first conversion function, and Wherein, the controller is configured as: using the first conversion function when the average value of the luminous intensity is less than or equal to the first threshold luminous intensity for a predetermined number of consecutive times; In a case where the average value of the luminous intensity is greater than the first threshold luminous intensity and less than or equal to the second threshold luminous intensity, determining to maintain the current conversion function; and The second conversion function is used when the average value of the light emission amount is greater than the second threshold light emission amount.

12. The display device according to claim 1, in, The controller includes a plurality of processing circuits, wherein each of the plurality of processing circuits is configured to control different backlight areas of the backlight source corresponding to different display areas of the display panel, and Wherein, each of the plurality of processing circuits is configured to: determining a statistical value of the light emission amount of the backlight blocks of the backlight area allocated for control; acquiring information from one or more other processing circuits for determining statistics of light emission amounts of backlight blocks of backlight areas other than the assigned backlight area; Determining a statistical value of the luminous amounts of all backlight blocks of the backlight source according to the statistical values ​​of the luminous amounts of the backlight blocks of the assigned backlight area and the backlight areas other than the assigned backlight area; and Based on the comparison result of the statistical value of the luminous intensity of all the backlight blocks of the backlight source with one or more predetermined threshold luminous intensity, it is determined whether to change the current conversion function.

13. The display device according to claim 12, wherein: Each of the plurality of processing circuits is configured to receive statistical values ​​of light emission amounts of backlight blocks in backlight areas other than the assigned backlight area, which are transmitted from the one or more other processing circuits through serial transmission.

14. A method for controlling a backlight source of a display device, The backlight source includes a plurality of backlight blocks, and The method comprises: Get video frames; determining grayscale feature values ​​associated with the plurality of backlight blocks according to grayscale levels of specified pixels in the video frame; determining the light emission amounts of the plurality of backlight blocks from the grayscale characteristic values ​​according to a current conversion function; as well as Whether to change the current conversion function is determined based on a comparison result between the statistical value of the light emission amounts of the plurality of backlight blocks and one or more predetermined threshold light emission amounts.

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