JP2014203034A - Display control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate a need of a special image property evaluation circuit for a compress mode selection of a compression circuit.SOLUTION: A display control device includes: evaluating image property for each of a plurality of areas divided from a display area of a liquid crystal panel with an image property evaluation circuit; generating back-light-control information which controls luminance distribution of back light of the liquid crystal panel based on the evaluation result; and selecting a compress mode of a compression circuit based on the evaluation result by the image property evaluation circuit.

Description

  The present invention relates to a display control device that processes input image data and outputs the processed image data to a display device such as a liquid crystal panel.

  In the display control device using the liquid crystal panel, the backlight of the liquid crystal panel is divided into multiple areas vertically and horizontally, and the local dimming that controls the backlight brightness for each area independently improves the video contrast. Power consumption has been reduced. This local dimming analyzes the spatial luminance distribution of the input image for each frame, evaluates the brightness for each region of the video, and controls the luminance of the backlight for each region according to the evaluation result. The image data is corrected.

  FIG. 8 shows a conventional display control apparatus 200. The local dimming circuit 210 creates a luminance histogram of the input image data in the histogram creation unit 211, takes the histogram into the image characteristic evaluation unit 212, analyzes the spatial luminance distribution, evaluates the image characteristics, and evaluates the results. Thus, a backlight control signal is generated and input to the CPU 220 constituting the backlight control means, whereby the luminance of each area of the backlight 230 is controlled. Further, the input image data is corrected by the image correction circuit 213 according to the evaluation result. The image data corrected by the image correction unit 213 is input to the XY decoder of the timing control circuit 240, whereby display control of the liquid crystal panel 250 is performed. This local dimming technique is described in Patent Document 1.

  On the other hand, in this type of display control apparatus 200, the input image data is written to the memory and read from the memory for various purposes. For example, image data is temporarily stored in a memory for processing for format conversion for 3D display and overdrive processing for displaying a moving image on the liquid crystal panel 250 with limited responsiveness. Reading from there is performed. At this time, in order to reduce the necessary memory capacity, compression processing of image data before writing and decompression processing of read image data are performed.

  However, depending on the compression method and condition setting, the compressed image data may not be accurately restored to the original image data. In particular, when image data of an image having specific characteristics is compressed, a compression error increases, and the display image quality may deteriorate.

  For example, in shipping inspection of the liquid crystal panel 250, a test pattern is displayed in which strips of R, G, and B colors whose luminance continuously changes in the horizontal direction over the entire screen are arranged adjacent to each other in the vertical direction. There are things to do. At this time, there was a problem that noise was conspicuous in the vicinity of the boundary between the horizontal bands of different colors.

  The display control apparatus may include a first compression circuit 10 for compression mode A and a second compression circuit 20 for compression mode B. Specifically, the first compression circuit 10 includes a quantizer 11, an inverse quantizer 12, a line buffer 13, a prediction unit 14, and adders 15 and 16, for example, as shown in FIG. ing. Then, as shown in FIG. 9 (b), prediction is made from the respective pixel data (data subjected to quantization and inverse quantization) of the pixel Dd immediately before the same line as the pixels Da, Db, Dc on the upper line. Based on the pixel data Dy of the pixel Dx and the pixel data of the pixel Dx, compressed data Q of the pixel Dx is generated.

  Specifically, as shown in FIG. 10A, for example, the second compression circuit 20 includes a quantizer 21, an inverse quantizer 22, a one-pixel delay unit 23, a prediction unit 24, and adders 25 and 26. It has. Then, as shown in FIG. 10B, the compressed data Q of the pixel Dx is a pixel of the pixel Dx that is predicted from the pixel data of the pixel Da immediately before the same line (data that has undergone quantization and inverse quantization). The prediction is generated from the data Dy and the image data of the pixel Dx.

  The two compression circuits 10 and 20 are such that the compression method used is a method of quantizing the difference between the image data predicted from adjacent pixels and the image data of the pixel into compressed data having a fixed number of bits. Therefore, the amount of data after compression is the same and can be stored in memories having the same capacity. However, the condition setting (pixels used for prediction) is different. For natural images, the first compression circuit 10 often provides superior image quality.

  However, when the first compression circuit 10 displays the test pattern, as shown in FIG. 9C, there is a possibility that an error may increase when generating compressed data of the pixel of interest Dx near the boundary. There is. For example, when the compressed data is decompressed in the vicinity of the boundary between the green (G) band and the blue (B) band with reference to the image data G60 in the upper line, There is a problem in that image data having a brightness significantly different from that of the surroundings is reproduced, and noise on the boundary is noticeable. The second compression circuit 20 has a characteristic that the error near the boundary is small and noise is not conspicuous in the test pattern.

  Therefore, normally, when the first compression circuit 10 is used and the liquid crystal panel 250 is inspected using the test pattern in question, the second compression circuit is used instead of the first compression circuit 10. 20 may be used to generate compressed data. In this way, it is considered that the generation of noise can be suppressed. However, in order to do this, it is determined that the test pattern is the above-described test pattern by extracting the features of the target image, and the compression circuit to be used is changed from the first compression circuit 10 to the second compression circuit 20. A means to do this is required.

  Incidentally, the display control apparatus 200 does not include a circuit for evaluating the characteristics of an image for the purpose of selecting the first compression circuit 10 or the second compression circuit 20 as described above. An image characteristic evaluation unit 212 for independently adjusting the luminance of the backlight for each of a plurality of horizontal regions is provided.

  The image characteristic evaluation unit 212 analyzes the luminance distribution of the entire screen, and can detect that a pattern in which the luminance continuously changes over the entire screen is displayed. Therefore, it seems that the compression circuit can be selected based on the evaluation result of the image characteristic evaluation unit 212 for adjusting the backlight luminance.

  Here, the problem that the compression error increases in the case of a specific image has been conventionally recognized. For example, there is a conventional technique that describes that a “gradation image” whose luminance continuously changes in the horizontal direction is detected and the selection of the compression circuit is switched (Patent Document 2).

JP 2010-175913 A JP 2006-31474 A

  However, the detection of a “gradation image” in Patent Document 2 is performed for each minute region (based on the difference between four pixels adjacent in the horizontal direction). Here, not only the test pattern in which the luminance continuously changes in the horizontal direction over the entire screen, which is a problem in the display control apparatus 200 described above, but also in the case where there is a horizontal luminance change in a small area in the screen. Detection is performed. Even if there is a change in luminance in the horizontal direction in a small area and noise occurs only in that area, it is difficult for the human eye to detect, and it is not essential to change the selection of the compression circuit. Rather, if the selection of the compression circuit is changed for each area in the screen, there may be side effects such as the discontinuity between the areas being noticeable.

  An object of the present invention is to provide a display control apparatus that does not require special image characteristic evaluation means for changing processing conditions such as a compression mode.

In order to achieve the above object, the invention according to claim 1 is a display control device that performs processing including first processing on input image data and outputs the display data as display data to the display device. An image characteristic evaluation circuit for evaluating the characteristics of the image data for each area obtained by dividing the display area of the apparatus into a plurality of areas, and the backlight of the display device based on the evaluation result by the image characteristic evaluation circuit A backlight control means for generating a backlight control signal for controlling the luminance distribution, and the first process based on an evaluation result by the image characteristic evaluation circuit under one processing condition selected from a plurality of processing conditions And a processing means for performing the processing.
According to a second aspect of the present invention, in the display control device according to the first aspect, the image data is data of a plurality of frames that are continuously input, and the selection of the processing condition is performed for each of the plurality of frames. It is characterized in that it is performed in common in the whole.
According to a third aspect of the present invention, in the display control device according to the first or second aspect, the image data is data of a plurality of frames that are continuously input, and the evaluation result by the image characteristic evaluation circuit Based on the above, the backlight control signal and the signal for selecting the processing condition are alternately obtained for image data of one or more consecutive frames of the plurality of frames.
According to a fourth aspect of the present invention, in the display control device according to any one of the first to third aspects, the processing means has the evaluation result within a set range preset for each of the regions. When the ratio is a predetermined ratio, the first process condition is selected as the first process, and the second process condition is selected otherwise.
According to a fifth aspect of the present invention, in the display control apparatus according to any one of the first to fourth aspects, the first process is a compression process of the image data, and the plurality of processing conditions obtain the same compression rate. The processing conditions are different from each other.

  According to the present invention, since the processing conditions such as the compression mode are selected based on the evaluation result by the image characteristic evaluation unit that originally adjusts the backlight luminance distribution, a special image characteristic evaluation unit is provided for changing the processing conditions. Do not need. In addition, since the brightness of each area of the entire screen is evaluated for backlight luminance distribution adjustment, the evaluation result of each area can be synthesized to determine the necessity of changing the processing conditions for the entire screen, It becomes possible to select processing conditions such as a common compression mode for the entire screen.

It is a block diagram of the display control apparatus of one Example of this invention. It is a detailed block diagram of the local dimming circuit of FIG. FIG. 3 is a characteristic diagram of a histogram created by the histogram creating unit in FIG. 2. It is explanatory drawing of the timing of backlight control and image pattern identification. It is a flowchart of a process of backlight control and image pattern identification. It is explanatory drawing of image pattern identification. It is a block diagram of the display control apparatus of another Example of this invention. It is a block diagram of the conventional display control apparatus. It is explanatory drawing of the compression mode A. FIG. It is explanatory drawing of the compression mode B. FIG.

  FIG. 1 shows a display control apparatus 100 according to one embodiment of the present invention. Reference numeral 110 denotes a 3D format conversion circuit, which outputs image data obtained by performing 3D format conversion processing on input image data. In order to temporarily store the image data in the memory 111 during the conversion processing, an encoder / decoder 112 that performs compression and expansion processing is provided. Reference numeral 120 denotes a local dimming circuit, which is configured as shown in FIG. 2 to be described later, and generates corrected image data and a backlight control signal. Reference numeral 130 denotes a CPU, which constitutes a backlight control means for inputting the backlight control signal obtained by the local dimming circuit 120 to adjust the brightness of the backlight, and a processing means for selecting a compression mode of the compression circuit. Configure. 150 is an overdrive circuit for improving the low response of the liquid crystal panel with respect to the screen change speed, 170 is a timing controller, and 180 is a liquid crystal panel.

  FIG. 2 shows the configuration of the local dimming circuit 120. A luminance histogram creation circuit 121 creates a luminance histogram for each area obtained by dividing a screen of one frame represented by input image data into a plurality of vertical and horizontal areas. Reference numeral 122 denotes an image characteristic evaluation circuit, which evaluates the image characteristic for each area from the obtained histogram for each area. In this image characteristic evaluation, for example, as shown in FIG. 3, a predetermined evaluation result can be obtained by taking an average value and a maximum value of luminance from the obtained histogram and performing arithmetic processing using predetermined parameters. it can.

  Reference numeral 123 denotes an image correction circuit, which corrects the image for each area according to the evaluation result. For example, when the evaluation result of a certain area is to reduce the luminance of the backlight, the luminance of the image of the area is increased so as to compensate for it.

  124 is a time axis filter that can be switched on / off, and when it is set to on, filtering is performed to reduce a large luminance difference in the evaluation result of the same region between adjacent frames when evaluated for each region. Do. When set to OFF, the evaluation result signal obtained by the image characteristic evaluation circuit 122 passes as it is. The processing result of the time axis filter 124 is also input to the image correction unit 123 as a correction signal. Reference numeral 125 denotes a backlight LUT, which generates backlight control information corresponding to the evaluation result using a lookup table.

  Reference numeral 126 denotes a spatial filter that can be switched on / off. When a large luminance difference is generated in the backlight control information for each area in the frame when the ON is set, filtering is performed to reduce the difference. When set to OFF, the backlight control information for each area obtained by the backlight LUT passes as it is.

  Reference numeral 127 denotes a dimming circuit, which applies control based on backlight control information obtained from the spatial filter 126 for each area to PWM data indicating the backlight collective luminance set by the user or the like, and outputs it to the control information buffer 128. To do.

  The backlight control information output from the control information buffer 128 is taken into the CPU 130, and the backlight 190 is controlled for each area. Further, as will be described later, the backlight control information obtained when the time axis filter 124 and the spatial filter 126 are turned off is used by the CPU 130 to identify the image pattern. Depending on the identification result, the compression circuit of the encoder / decoder 112 is switched to the compression mode A or B.

  The feature of the present embodiment is that the image pattern of the input image is identified using the evaluation result by the image characteristic evaluation circuit 122 for local dimming. However, the backlight control information generated from the evaluation result is only for backlight control, and is not a value that appropriately represents the luminance distribution of the input image. If this is used as it is, the image pattern identification accuracy is not sufficient. Therefore, in this embodiment, in order to improve the identification accuracy, the operation mode of the local dimming circuit 120 is switched between the backlight control mode and the image pattern identification mode.

  First, in the backlight control mode, the time axis filter 124 and the spatial filter 126 are set to be on. As a result, the evaluation result by the image characteristic evaluation circuit 122 is filtered by the time axis filter 124 and the spatial filter 126, and the control information output from the spatial filter 126 is further converted into PWM signals that are luminance information set by the user or the like in the dimming circuit 127. Then, backlight control is performed using the control information finally obtained. This is the same operation as the conventional local dimming.

  On the other hand, in the image pattern identification mode, the time axis filter 124 and the spatial filter 126 described above are set to the operation-off state and set to the through state. As a result, the evaluation result obtained by the image characteristic evaluation circuit 122 is directly input to the control information buffer 128 without being affected by the filtering for local dimming, and image pattern identification is performed using this. Even in this case, since the backlight needs to be locally dimmed, control is performed by the information source of the backlight control obtained immediately before and cached in the memory 131 of the CPU 139. At this time, the dimming circuit 127 performs dimming not with the input PWM data but with the contents specially set for image pattern identification inside. Alternatively, the output signal of the spatial filter 126 is sent to the control information buffer 128 through.

  As shown in FIG. 4, alternating switching between the backlight control mode and the image pattern identification mode is performed with four consecutive frames of input image data as one cycle, and is switched every two frames.

  However, since the backlight control information obtained in the frame immediately after switching to the backlight control mode is inaccurate, it is discarded and the information used in the previous local dimming and cached in the memory 131 of the CPU 130 is used. The cached information is also used as backlight control information in the image pattern identification mode. That is, the frames using the backlight control information cached in the CPU 130 in FIG. In these frames, correction by the image correction circuit 123 is also performed using the cached information. In frame number 0, the original local dimming is performed using the backlight control information obtained in the backlight control mode in the previous frame. Image pattern identification is performed at the next frame number 2 using control information detected in the image pattern identification mode at frame number 1.

  As described above, the backlight control information is updated based on the evaluation result collected at frame number 3. Further, the image pattern identification is performed based on the evaluation result collected at frame number 1. Thus, the update frequency of the backlight control information and the frequency of image pattern identification are every four frames.

  FIG. 5 shows a flowchart of processing in the CPU 130 for performing the control described above. First, the frame number is initialized (S1), and the frame number FR = 0 is set. When the vertical synchronization signal is detected (S2), if FR = 0 (S3-YES), the backlight control information used in the immediately preceding backlight control is cached in the memory 131 (S4), and the local dimming is performed. The circuit 120 is set to the image pattern identification mode (S5). Then, the backlight control information cached in the memory 131 is read (S6), backlight control is performed based on the backlight information information (S7), and the frame number is updated to the remainder of (FR + 1) / 4 (S8). That is, the frame number update is performed with FR + 1 when FR = 0 to 2, but is returned to FR = 0 when FR = 3. As a result, the frame numbers 0 to 3 are repeated.

  At this time, since FR = 0, FR = 1 is obtained by updating. Therefore, although step S3 is NO, since step S9 is also NO, steps S6 → S7 → S8 → are repeated when FR = 1.

  As a result, if FR = 2, step S9 is YES, and therefore the compression of the encoder / decoder 112 is performed when the image pattern identification result does not match the specific pattern (the test pattern described above) (S10-NO). After the circuit is set to the compression mode A (S12), the local dimming circuit 120 is set to the backlight control mode, and the process returns to step S6. On the other hand, when the image pattern identification result matches the specific pattern (the test pattern described above) (S10-YES), the compression circuit of the encoder / decoder 112 is set to the compression mode B described above (S11), The local dimming circuit 120 is set to the backlight control mode (S13), and the process returns to step S6.

  FIG. 6 shows an image pattern identification method. Here, as a test pattern, a gradation pattern is used in which bands of each color of R, G, and B that change so that the luminance sequentially increases in the right lateral direction over the entire screen are arranged adjacent to each other in the vertical direction, Whether it matches this is identified.

  At this time, as shown in FIG. 6A, the screen of the liquid crystal panel is divided into W = 8 and H = 8 to create 64 areas, and each of the areas a1 to a8 on the lines L1 to L8. For each, as described with reference to FIG. 3, the evaluation value is calculated from the average value and the maximum value of the luminance. For example, in the case of eight areas a1 to a8 of the line L2, evaluation values as shown in FIG. 6B are calculated. A circle indicates the calculated value. The vertical line (I-shaped line) indicates the allowable range (normal range) of the evaluation value calculated in the area when the test pattern is displayed. If there is a circle mark, the evaluation value of the area is identified as normal. In FIG. 6B, the evaluation value of the area a6 deviates from this “I-shaped line” and is not normal, but the other areas a1 to a5, a7, and a8 are normal.

Then, for a total of 64 areas of the lines L1 to L8, whether or not the image pattern matches the above-described test pattern is identified according to the number of areas where the circles are in the “I-shaped line”. To do. Here, Np is the number of regions where the circle is in the “I-shaped line”,
Np ≧ W × (H−2) −W (1)
Thus, it is identified whether or not the displayed image is a test pattern. “H-2” is for excluding the eight areas a1 to a8 of the uppermost line L1 where the menu bar and the like are displayed and the eight areas L8 of the lowermost line where the status bar and the like are displayed. “−W” is for excluding the context menu.

  When the above expression (1) is satisfied, the displayed image is identified as matching the test pattern, so that the compression circuit is set to the compression mode B as shown in FIG. Thereby, it is possible to prevent a compression error due to noise generated at the upper and lower boundary portions of the horizontal band of the test pattern. When the expression (1) is not satisfied, it indicates that the pattern is not a test pattern, so the compression circuit is set to the compression mode A (normal operation mode).

  When using a gradation pattern in which strips of R, G, and B colors that change so that the luminance sequentially decreases in the right lateral direction over the entire screen are arranged adjacent to each other in the vertical direction as the test pattern. The characteristics of the evaluation value as shown in FIG. 6C are used.

  Furthermore, in order to improve the pattern identification accuracy, the following method can be used. As for the backlight, the number of individually controllable backlights may not be so large (for example, 16 divisions of 8 vertically and 2 horizontally). In this case, in the local dimming control, the number of areas where the backlight control information should be calculated is small, and may be insufficient for image pattern identification. On the other hand, in many cases, the local dimming circuit can flexibly change the number of divisions, the size, etc. of the area so as to be compatible with various backlight specifications.

  Therefore, in the method for improving detection accuracy by alternately switching between backlight control and image pattern identification described with reference to FIG. 4, when setting the image pattern identification mode, the number of regions should be set larger than the actual number of backlights. Accordingly, it is possible to obtain luminance information for each finer region and improve detection accuracy.

  In the above description, the example in which the backlight control information obtained by the local dimming circuit 120 is used when the compression mode of the compression circuit of the encoder / decoder 112 is switched during the processing by the 3D format conversion circuit 110 has been described. However, the present invention is not limited to such an example. As shown in FIG. 7, an encoder / decoder 152 for temporarily storing image data in the memory 151 for processing in the overdrive circuit 150. Of course, it can be used in the same manner when the compression mode of the compression circuit is switched.

100: Display control device 110: 3D format conversion circuit, 111: Memory, 112: Encoder / decoder 120: Local dimming circuit, 121: Histogram creation unit, 122: Image characteristic evaluation unit, 123: Image correction unit, 124: Time axis Filter: 125: Backlight LUT, 126: Spatial filter, 127: Dimming circuit, 128: Image information buffer 130: CPU, 131: Memory 150: Overdrive circuit, 151: Memory, 152: Encoder / decoder 170: Timing control circuit 180: LCD panel 190: Backlight

Claims (5)

A display control apparatus that performs a process including a first process on input image data and outputs the processed image data as display data to a display apparatus,
An image characteristic evaluation circuit for evaluating the characteristics of the image data for each area obtained by dividing the display area of the display device into a plurality of areas;
Backlight control means for generating a backlight control signal for controlling the luminance distribution of the backlight of the display device based on the evaluation result by the image characteristic evaluation circuit;
Processing means for performing the first processing under one processing condition selected from a plurality of processing conditions based on an evaluation result by the image characteristic evaluation circuit;
A display control apparatus comprising: The image data is data of each of a plurality of frames input continuously,
Selecting the processing condition in common for each of the plurality of frames;
The display control apparatus according to claim 1. The image data is data of each of a plurality of frames input continuously,
Based on the evaluation result by the image characteristic evaluation circuit, the backlight control signal and the signal for selecting the processing condition are alternately used for image data of one or more consecutive frames of the plurality of frames. To get into the
The display control apparatus according to claim 1, wherein the display control apparatus is a display control apparatus.   The processing means selects the first processing condition as the first processing when the ratio that the evaluation result is within a preset setting range for each of the areas is a predetermined ratio. 4. The display control apparatus according to claim 1, wherein the second processing condition is selected in other cases.   5. The display according to claim 1, wherein the first processing is compression processing of the image data, and the plurality of processing conditions are different processing conditions for obtaining the same compression rate. Control device.

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