JP2012118419A - Image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a display image in which a luminance level difference in a black image part is suppressed by minimizing the unwanted power of a backlight, in an image display device in which the backlight is divided into a plurality of backlight cells and the light intensity of the backlight cells can be individually controlled.SOLUTION: The image display device including a backlight 107 in which a plurality of backlight cells 601 whose light intensity can be individually controlled are two-dimensionally combined and a liquid crystal panel 108 which modulates the light of the backlight 107 for each pixel and displays an image includes a region histogram detection part 102 which detects a luminance histogram for each display region of the liquid crystal panel corresponding to each backlight cell from the input image signal of one frame, to detect maximum luminance information, a region black area detection part 101 which detects a region black area for each display region corresponding to each backlight cell, and a light control value determination part 103 which determines the light emission quantity of each backlight cell according to the detected maximum luminance information and region black area for each region.

Description

  The present invention relates to an image display device that displays an image using a backlight, and in particular, an image in which an image display area is divided into a plurality of areas and the brightness of the backlight corresponding to each area can be individually controlled. The present invention relates to a display device.

  In general, in a non-light-emitting display device such as a liquid crystal display device using a liquid crystal panel as a display device, light is irradiated from the back side of the liquid crystal panel by a backlight in order to form an image on the liquid crystal panel. At this time, if the backlight always emits light at a constant brightness regardless of the image signal, the brightness of the backlight is usually matched to the condition that the screen brightness (also called luminance) is maximum. Even when a black display or a dark image is displayed, light is emitted with the same brightness. For this reason, backlight power that does not contribute to display is consumed. Further, since the contrast of the liquid crystal panel is not infinite (that is, light is slightly transmitted even when the transmittance of the liquid crystal is minimized), black floating occurs in which the black image portion becomes slightly bright due to light leakage.

  Therefore, in order to reduce black float and save power, the image display area is divided into a plurality of areas, and the area corresponding to the image signal is backed according to the feature amount of the image signal corresponding to each area. Various liquid crystal display devices that individually control the luminance of light for each divided region have been proposed. Such partial or local control of the light intensity of the backlight is called area dimming, area control, or local dimming. In such a liquid crystal display device, it is possible to suppress black floating by turning off the backlight corresponding to the black image region. However, when both the bright part and the black image are included in the same image, the halo There is a problem that a luminance step called a black image portion is visually recognized.

  As a conventional technique for solving such a problem, for example, Patent Document 1 discloses that a backlight is turned on so as to suppress a luminance step in an adjacent region so that a luminance step in a black image portion is not visually recognized. ing.

JP 2008-51905 A

  However, the conventional technique described in Patent Document 1 emits the backlight so that the luminance level difference between adjacent regions cannot be visually recognized, and thus has a problem of consuming unnecessary power that does not contribute to display. is doing.

  The present invention has been made in view of the above problems, and provides a technique for making it possible to obtain a display image in which unnecessary power of a backlight is minimized and a luminance step in a black image portion is suppressed. It is in.

  The present invention is characterized by the configurations described in the claims. Specifically, the backlight is configured by two-dimensionally combining a plurality of backlight cells whose light intensity can be individually controlled, and an image is obtained by modulating the light emitted from the backlight for each pixel. An image display device comprising a liquid crystal panel for display, an area histogram detection unit for detecting a histogram of luminance for each display area of the liquid crystal panel corresponding to each backlight cell from an input image signal of one frame, and each backlight A region black area detection unit for detecting a region black area for each display region corresponding to the cell, and brightness control of each backlight cell according to the detected region histogram and the detected region black area It is characterized by determining a value.

  Further, in the display area corresponding to a certain backlight cell, when the area black area value detected by the area black area detection unit is larger than a predetermined black area threshold, the backlight luminance control obtained from the area histogram detection unit The luminance control value of the backlight cell may be determined so that the emission luminance of the backlight cell is lower than the value.

  Further, when the area black area value is a second area value larger than the first area value, the luminance of the backlight is set so that the emission luminance of the backlight cell is relatively lower than that of the first area value. The control value may be determined.

  Further, instead of the region black area detection unit, a region APL detection unit that detects a region APL for each display region corresponding to each backlight cell may be used.

  Furthermore, the control intensity of the emission luminance of the backlight cell corresponding to each region may be switched according to the black area and / or APL of the entire input image signal of one frame.

  According to the configuration of the present invention described above, the brightness of the backlight cell in each region is controlled according to the feature amount of the image signal for each region, thereby reducing the power required for the backlight and the black image portion. It is possible to obtain a display image in which the luminance step is suppressed.

1 is an overall block diagram of Embodiment 1 of the present invention. The schematic diagram which shows the relationship between a histogram detection result and the amount of light emission of a backlight cell. The block diagram of a black area detection part for every area | region. The schematic diagram which shows the relationship between a black area and the backlight cell light emission upper limit. The block diagram of a light control value determination part. The schematic diagram of a display area and a backlight cell. Example of input image The figure which shows an example of the output of the area | region histogram detection part (102) with respect to the image of FIG. 6 in Example 1. FIG. The figure which shows an example of the output of the black area detection part (101) for every area | region with respect to the image of FIG. 6 in Example 1. FIG. FIG. 7 is a diagram illustrating an example of an output of a minimum value detection unit (500) for the image in FIG. 6 according to the first embodiment. The figure which shows an example of the output of the light control value determination part (103) with respect to the image of FIG. 6 in Example 1. FIG. Example of input image The figure which shows an example of the output of the area | region histogram detection part (102) with respect to the image of FIG. 12 in Example 1. FIG. The figure which shows an example of the output of the light control value determination part (103) with respect to the image of FIG. 12 in Example 1. FIG. FIG. 3 is a diagram illustrating a luminance distribution of a backlight in the x-axis direction in the first embodiment. Example of input image The figure which shows an example of the output of the black area detection part (101) for every area | region with respect to the image of FIG. 16 in Example 1. FIG. The figure which shows an example of the output of the light control value determination part (103) with respect to the image of FIG. 16 in Example 1. FIG. The figure which shows an example of the output of the light control value determination part (103) with respect to the image of FIG. 16 in Example 2 of this invention. The block diagram of the black area detection part (101) for every area | region in Example 3 of this invention. FIG. 10 is an overall block diagram of Embodiment 4 of the present invention. The block diagram of the APL detection part for every area | region (218) in Example 4 of this invention. The block diagram of the black area detection part (101) for every area | region in Example 5 of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is an overall circuit block diagram of a liquid crystal display device according to a first embodiment of the present invention.

  The liquid crystal display device of this example includes an image frame receiving unit (100), a black area detecting unit for each region (101), a histogram detecting unit for each region (102), a dimming value determining unit (103), and a filter unit. (104), a backlight control unit (105), a liquid crystal control unit (106), a backlight unit (107), and a liquid crystal panel (108). The backlight unit (107) is divided corresponding to the display area (600) of the liquid crystal panel, and a backlight (hereinafter referred to as a backlight) whose light intensity (light emission amount) can be controlled independently for each area. Cell (601)). That is, the backlight unit (107) is configured by combining a plurality of backlight cells (601), and more specifically, the plurality of backlight cells (601) are arranged in a matrix (two-dimensionally). Assume that they are arranged. As a result, according to the feature amount of the image signal of each display area in the liquid crystal panel (108), the light emission amount of the backlight cell (601) that corresponds to the display area (600) is controlled individually. Control becomes possible. Details of this will be described later.

  In this embodiment, the light source of each backlight cell (601) uses one or a plurality of light emitting diodes (LEDs) that emit white light (for example, 3 to 5). Other light-emitting elements such as three-color LEDs that emit green light and laser diodes may be used. The image frame received by the image frame receiving unit (100) is sent to the black area detecting unit for each region (101) and the histogram detecting unit for each region (102) for detecting the feature amount of the image.

  The histogram detection unit (102) for each region decomposes the input image frame for each region, and based on the luminance information for each pixel, the luminance distribution in the region (that is, the pixel corresponding to each of the plurality of luminance ranges is determined). Histogram showing how much is present). In accordance with the histogram detection result, the light emission amount of each backlight cell (601) is determined, and a control signal (109) is sent to the dimming value determination unit (103).

  FIG. 2 shows an example of the relationship between the light emission amount of the backlight cell (601) and the histogram detection result. A table having such characteristics (LUT (Look up Table)) is held in advance in a storage unit (not shown) such as a ROM, and the table is referred to based on the histogram detection result. It is possible to determine the light emission amount of the light cell. Here, the luminance information for each pixel is a luminance value on the liquid crystal panel obtained from the maximum gradation value or gradation value in each pixel of the image frame, and the histogram detection result is a luminance information value in the display area. , And any value from the top 5% of the luminance information value frequency to the maximum value (maximum luminance information value) is indicated. That is, the area-specific histogram detection unit (102) detects maximum gradation information that substantially has the maximum gradation (luminance) in each display area.

  Also, several types of tables representing the relationship between the light emission amount of the backlight cell and the histogram detection result as shown in FIG. 2 are prepared in advance, the video mode set by the user, the video genre information of the input video, the ambient illuminance, the ambient Needless to say, the temperature may be switched according to the presence / absence of a person, the viewing position of the person, and the like.

  Next, the region-specific black area detection unit (101) having the function of determining the upper limit light emission amount of the backlight cell will be described with reference to FIGS. FIG. 3 is a detailed block diagram of the black area detection unit (101) for each region, and FIG. 4 is a graph showing an example of the relationship between the upper limit light emission amount of the backlight cell and the black area.

  The black area detection unit (101) for each region uses the luminance information detection unit (300) to calculate the maximum gradation value at each pixel of the input image frame or the luminance value on the liquid crystal panel (108) obtained from the gradation value. To detect. This luminance information is compared with the threshold value 1 held in advance or settable from the outside by the comparison unit (301). The area counter 302 is controlled by the input horizontal / vertical synchronization signal. In the threshold value comparison by the comparison unit (301), when the luminance information is lower than the threshold value 1, the counter of the region counter (302) is advanced so that the pixel whose luminance information is lower than the threshold value 1 in the display region. The number, that is, the number of black pixels is counted. From the relationship between the final counter value (the number of black pixels) and the number of pixels of the liquid crystal panel (108) corresponding to one display area, it is possible to determine the proportion of the black image in each display area. Of course, in the threshold comparison, the case where the luminance information is higher than the threshold 1 is counted, and after obtaining the number other than the black pixels, the difference from the total number of pixels may be calculated to obtain the black area. By referring to the LUT (303) according to the black area of each display area, the light emission upper limit (110) of each backlight cell (601) corresponding to each area is determined, and the dimming value determination unit ( 103) as a control signal.

  Here, the characteristics as shown in FIG. 4 are desirable for the LUT (303). That is, the light emission upper limit when the black area in the display area is 100% is minimized (L2), and the value of L2 is 10 to 40 of the light emission upper limit (L1) when the black area in the display area is 0%. Set as%. That is, in this example, even if a certain display area is black, the light emission upper limit amount of the backlight cell (601) corresponding to the display area is not set to 0, and a slight light emission is allowed. In a region where the black area in the region is from 0% to an arbitrary value (P1), it is desirable that the light emission amount limitation by the black area is not functioned. Here, the value of P1 is preferably 60 to 97% of the black area, for example.

  Similarly to FIG. 2, several types of tables representing the relationship between the upper limit light emission amount of the backlight cell and the black area as shown in FIG. 4 are prepared in advance, the video mode set by the user, the video genre of the input video Needless to say, the information may be switched according to information, ambient illuminance, ambient temperature, presence / absence of a person, viewing position of a person, and the like.

  The backlight cell emission amount (109) calculated and output by the histogram detection unit for each region (102), and the backlight cell emission upper limit amount calculated and output by the black area detection unit for each region (101) ( 110) is sent to the dimming value determination unit (103), and the light emission amount of the corresponding backlight cell (601) is determined. A configuration example and operation of the dimming value determination unit (103) will be described with reference to FIGS.

  5 is a detailed block diagram of the dimming value determining unit (103), FIG. 6 is a schematic diagram of a backlight cell in a liquid crystal display device, FIG. 7 is an example of an input image signal, and FIG. 8 is an input of FIG. FIG. 9 shows the output of the black area detection unit (101) for each region, FIG. 10 shows the output of the minimum value detection unit (500), and FIG. 11 shows the light control. It is a schematic diagram which shows a value determination part (103) output. As an example, four backlight cells (601) are arranged in the vertical direction (vertical direction of the liquid crystal panel (108)) and in the horizontal direction (horizontal direction of the liquid crystal panel (108)), whereby the backlight unit (107) is arranged. It is assumed that it consists of a total of 16 areas. The input image signal is composed of a black image (for example, 0 in 8-bit representation) region and a white image (for example, 255 in 8-bit representation) region, and each display corresponding to the backlight cells B2, B3, C2, and C3. Assume that the area includes a white image at a rate of 25%.

  At this time, since each display area corresponding to the backlight cells B2, B3, C2, and C3 includes a white image, the output of the histogram detection unit for each area is maximized from the relationship of FIG. On the other hand, since no white image is detected in the display areas corresponding to the other backlight cells, the output of the histogram detection unit (102) for each area is the lowest value (10 in the example of FIG. 8), which is shown in FIG. The amount of light emitted from the backlight cell (109) is obtained.

  The black area detection unit (101) for each area detects that the black area is 75% in each display area corresponding to the backlight cells B2, B3, C2, and C3, and the backlight is based on the relationship shown in FIG. The cell light emission upper limit (“60” in the example of FIG. 9) is output. On the other hand, since the black area is 100% in the other backlight cell regions, L2 (“25” in the example of FIG. 9) is output to obtain the backlight cell emission upper limit (110) shown in FIG. .

  The backlight cell emission amount (109) and the backlight cell emission upper limit amount (110) obtained as described above are input in parallel to the minimum value selection unit (500) and the difference detection unit (501). . In the minimum value selection unit (500), in order to limit the light emission amount of the backlight cell by the backlight cell light emission upper limit amount (110), as shown in FIG. The smaller one (that is, the minimum value) of the backlight cell emission amount (109) and the backlight cell emission upper limit amount (110) is selected and output.

  On the other hand, the difference detection unit (501) detects a limited light emission amount. That is, the difference is detected when the backlight cell light emission upper limit (109) is smaller than the light emission amount of the backlight cell which is the original light emission amount in each display area. In this example, in each display area corresponding to the backlight cells B2, B3, C2, and C3, “40” (= 100−60) is a limited light emission amount, and the other areas are “0”. . Differences in each display area are all input to the area product-sum operation unit (502), and product-sum operation is performed to obtain an insufficient amount of light emission (40 × 4 = 160) for the image frame. This shortage is distributed to each area in the distribution processing unit (503). The output from the distribution processing unit (503) and the smaller one of the backlight cell emission amount (109) and the backlight cell emission upper limit (110) selected by the minimum value selection unit (500) are added. By adding in (504), the final dimming value from the dimming value determination unit (103) as shown in FIG. 11 is output.

  With such a process, it is possible to obtain an image in which black float is suppressed while suppressing a decrease in luminance on the screen. In the distribution processing in the distribution processing unit (503), 160, which is a limited light emission amount in this example, is evenly redistributed in 16 display areas. Therefore, in this example, the value “10” is distributed to each display area. Therefore, as shown in FIG. 11, in the backlight cell D4, for example, “10” distributed by the distribution processing unit (503) and “10” selected by the minimum value selection unit (500) are added. A dimming value of “20” is obtained.

  Next, the effect of the present embodiment will be described using a screen example different from FIG. Here, for simplification of explanation, consider the case where the input image is shown in FIG. The input image includes white images at a ratio of 25% in each display area corresponding to the backlight cells A2, A3, B2, B3, C2, C3, D2, and D3. By the processing similar to that described with reference to FIGS. 6 to 11, the region-specific histogram detection unit (102) performs backlight processing for backlight cells corresponding to a display region including a white image, for example, as shown in FIG. “100” is output as the light cell emission amount (109), and “10” is output as the backlight cell emission amount (109) for the backlight cell corresponding to the display area including only the black image. The difference detection unit (501) sets “60” for the backlight cell corresponding to the display area including the white image and “10” for the backlight cell corresponding to the display area including only the black image as the difference output. Output. The distribution processing unit (503) receives the shortage of light emission amount (40 × 8 = 320) for the image frame, and redistributes the 16 areas evenly to obtain “20” (= 320 ÷ 16) for all areas. ) Is added to the output of the minimum value selection unit (500) by the adder (504) to output a backlight cell emission amount as shown in FIG. 14, for example.

  FIG. 15A shows the distribution of light in the x-axis direction when the backlight cell (601) is controlled to be turned on in FIG. 13, and FIG. 14 shows the light distribution when the backlight cell (601) is controlled to be turned on. The distribution is shown in FIG. In each figure, the light distribution of a single backlight cell is indicated by a broken line, and the light distribution obtained by adding all the backlight cells is indicated by a solid line. Comparing the backlight luminance difference (700 and 701) and the luminance gradient in the black image region of FIG. 15A and FIG. 15B, FIG. 15A is larger than FIG. It can be seen that it is.

  In this way, by setting and controlling the upper limit of the light emission luminance (light emission amount) of each backlight cell (601) in accordance with the black area of the image signal for each display region, the luminance step in the black image region can be kept low. Is possible.

Next, consider the case where the input image is shown in FIG. FIG. 16 differs from FIG. 7 in the position of the white image, and the display area corresponding to the backlight cells B2, B3, C2, and C3 has a white image at a ratio of 5%, 15%, 15%, and 65%. Shall be included. Similar to the examples of FIGS. 6 to 11, since each display area corresponding to the backlight cells B2, B3, C2, and C3 includes a white image, the output of the per-area histogram detection unit (102) is as shown in FIG. The same black area detection unit (101) for each area detects that the black area is 95% for the display area corresponding to the backlight cell B2, and based on the relationship shown in FIG. As shown in FIG. 17, the backlight cell emission upper limit (46 in the example of FIG. 17) is output. Similarly, the backlight cell emission upper limit amount (“55”, “55”, “100” in the example of FIG. 17) is output for each display region corresponding to B3, C2, and C3 according to the value of the black area. Similar to the examples of FIGS. 6 to 11, the product-sum operation unit (502) calculates the shortage of the light emission amount for the image frame (54 + 45 + 45 = 144), and distributes the limited light emission amount “144”. (503) is redistributed equally in the 16 display areas (in this case, “9” is distributed to one display area), and the adder (504) of the minimum value selection unit (500) When added to the output, a dimming value corresponding to each backlight cell as shown in FIG. 18 is obtained.

  In this way, by setting and controlling the upper limit of the light emission luminance of the backlight cell corresponding to each display region according to the black area for each display region, the backlight luminance of the region with a large black area including the white image is lowered. Therefore, it is possible to suppress unnatural black floating in which the black image portion becomes slightly bright due to light leakage, and to make it difficult to visually recognize the luminance step in the black image portion. Even in the same APL image, by controlling the upper limit of the light emission luminance in accordance with the value of the black area for each display region, a different backlight cell light emission amount distribution can be obtained for each display region.

  The distribution processing unit (503) preferably performs the above-described distribution processing. However, power may be given priority from the viewpoint of power consumption, and the redistribution processing may not be performed or the redistribution ratio may be reduced. Good.

  Returning to FIG. 1 again, the filter unit (104) filters in the time direction so as to suppress a steep luminance variation with respect to the light emission amount of the backlight cell determined by the dimming value determination unit (103) as described above. Process. This process is, for example, a process of obtaining a weighted average of the light emission amount obtained at the timing of the frame of the current image signal and the timing of the previous frame, or the light emission amount obtained at the timing of the previous frame and the previous frame. . In addition, the filter unit (104) can perform not only a time direction process but also a spatial filter process. For example, spatial filtering may be performed by performing integration processing so that the change in the amount of light emitted from a certain backlight cell and the amount of light emitted from a backlight cell adjacent in the vertical and / or horizontal direction is moderated. it can.

  The backlight control unit (105) receives the final light emission amount determined by the filter unit (104) and controls lighting of the backlight cells in the backlight unit (107). The signal for driving the backlight is a PWM (Pulse Width Modulation) signal or an amplitude modulation signal. In the case of a PWM signal, the PWM frequency is constant, and the LED of the backlight cell (602) is driven by changing the ratio (duty ratio) between the ON period and the OFF period according to the light emission intensity. Further, it is desirable that the PWM frequency is equal to or higher than the frame frequency of the liquid crystal display device.

  The liquid crystal control unit (106) receives the final light emission amount determined by the filter unit (104), calculates a luminance distribution immediately below the liquid crystal panel (106), and performs image correction based on an appropriate gain amount. For example, here, if the final light emission amount is controlled to about half of the maximum luminance of the light source, the liquid crystal control unit (106) doubles the amplitude of the image signal and reduces the luminance of the image by reducing the emission luminance. Image correction is performed so as to cancel out the decrease. The corrected image signal is supplied to the liquid crystal panel (108), and the liquid crystal panel (108) is driven.

  By doing in this way, a liquid crystal panel (108) modulates the light radiate | emitted from the backlight part (107) for every pixel, and forms an image according to the signal which follows.

  As described above, according to this embodiment, the light emission amount of the corresponding backlight cell is controlled by the luminance histogram of each display region, and the light emission luminance of the corresponding backlight cell is determined according to the black area of each display region. Since the upper limit is set, the backlight luminance of a large black area including a white image can be suppressed low, and the unnatural black float that makes the black image portion slightly bright due to light leakage can be suppressed. Thus, it is possible to make it difficult to visually recognize the luminance step in the black image portion. Therefore, according to the present embodiment, it is possible to provide a high-quality image with less black floating while suppressing the power consumption of the backlight.

  A second embodiment of the present invention will be described with reference to FIG. The second embodiment is different from the first embodiment in the distribution processing method in the dimming value determination unit (103).

  For example, consider the case where the input image is shown in FIG. In this case, the outputs of the per-region histogram detection unit (102) and the per-region black area detection unit (101) are the same as those in FIGS. 8 and 17, respectively.

  Here, the light emission amount restricted for each backlight cell (601) is distributed to the backlight cells corresponding to the surrounding display regions around the restricted display region. Considering the display area B2 as an example, the light emission amount restricted for the display region B2 is “54” (= 100−46), and this restricted light emission amount is set to A1 adjacent to the B2 with the B2 as the center. , A2, A3, B1, B2, B3, C1, C2, and C3 are distributed to backlight cells corresponding to a total of nine regions. In the case of uniform distribution, the light emission amount distributed to the backlight cells corresponding to the respective display areas is “6” (= 54 ÷ 9). Similarly, when calculating the display area B3, the light emission amount “5” (= 45 ÷ 9) is distributed to the backlight cells corresponding to the nine areas centered on B3. A similar process is performed on the display area C2, and the backlight cell emission amount as shown in FIG. 19 is finally obtained.

  In this way, by redistributing the light emission amount around the region where the light emission amount is limited, there are many black images, and the area around the region (in this example, the display region B2) where black floating is likely to occur due to light leakage. It is possible to raise the light emission amount relatively higher than the light emission amount around the area (in this example, the display area C3) where there is little black image and hardly causes black floating due to light leakage. Can be made difficult to visually recognize.

  A third embodiment of the present invention will be described with reference to FIG. The third embodiment differs from the first and second embodiments in that the control is performed taking into account the black area ratio of the entire image frame.

  FIG. 20 shows the black area of the entire image frame detected by the area black area detection unit (101) shown in FIG. 3, and the backlight cell obtained by the LUT (303) according to the value of the black area. A control system (210) for multiplying the upper limit of light emission by a constant is added. Elements other than the control system (210) that have the same reference numerals as those in FIG. 3 are the same as those described in FIG.

  In the control system (210) of FIG. 20, the luminance information detection unit (300) determines the maximum gradation value in each pixel of the input image frame or the luminance value on the liquid crystal panel (108) obtained from the gradation value. To detect. The luminance information is compared by the threshold value 2 and the threshold value comparison unit (211), which is held in advance or can be set from the outside. In this comparison, when it is determined that the luminance information is lower than the threshold value 2, the overall counter (212) is operated to count the number of pixels having luminance information lower than the threshold value 2, that is, the number of black pixels. From the relationship between the final counter value (the number of black pixels) and the number of pixels of the liquid crystal panel (108), it is possible to obtain the ratio of the black image in one entire image frame. Of course, the threshold value comparison unit (211) may count pixels higher than the threshold value 2 with the overall counter (212), determine the number of pixels other than black pixels, and subtract this from the total pixels to determine the black area. . By referring to the LUT (213) according to the obtained black area, the intensity coefficient 1 (214) for multiplying the backlight cell emission upper limit obtained by the LUT (303) by a constant is determined. The multiplier coefficient (215) multiplies the intensity coefficient 1 (214) obtained with reference to the LUT (213) and the backlight cell emission upper limit amount obtained by the LUT (303) to obtain the final backlight. It is output as the light cell emission upper limit (110).

  As an example, consider a case where the white images in the display areas B2 and B3 in the input image of FIG. 7 are all black images. In this image, the black area of the entire screen is different from that in FIG. 7, but the black areas of the display areas C2 and C3 are the same.

  Since the black area of the entire screen increases, the amount of light incident on the human eye decreases, and the sensitivity of the visual system increases, making it easier to visually recognize the luminance step in the black image portion. For this reason, when the black area increases on the entire screen, it is desirable to reduce the luminance of the backlight.

  Therefore, in the present embodiment, the above-described intensity coefficient 1 is set to a relatively small value when the ratio of the black image in the entire image frame is larger than a predetermined threshold value, as compared with the case where it is small. Control is performed to reduce the upper limit of light emission.

  By controlling in this way, the luminance step in the black image portion is easily noticeable, that is, in an image with many black portions on the entire screen, the luminance step can be suppressed by controlling the light emission upper limit of the backlight cell to be low. It becomes possible. On the other hand, in the case where the luminance difference is not conspicuous, that is, the image has a small black portion on the entire screen, the upper limit light emission amount of the backlight cell can be controlled to be high, and a sharper image can be provided.

  A fourth embodiment of the present invention will be described with reference to FIGS. The fourth embodiment is different from the first and second embodiments in that the upper limit light emission amount of the backlight cell is controlled using the APL for each display area.

  FIG. 21 is an overall circuit block diagram of the liquid crystal display device according to the fourth embodiment of the present invention. In the liquid crystal display device of this embodiment, the black area detection unit (101) for each area in the first embodiment is replaced with the APL detection section (218) for each area, and the operation of other blocks is the same as that of the first embodiment. The description is omitted. Hereinafter, details and operations of the APL detection unit for each region will be described with reference to FIG.

  In the area-specific APL detection unit (218) shown in FIG. 22, the image frame received by the image frame reception unit (100) is input, and the luminance value detection unit (220) obtains the liquid crystal panel (from the gradation value). 108) The above luminance value is detected. This luminance information is subjected to a product-sum operation by a product-sum operation unit (221) for each display area based on the input horizontal / vertical synchronization signal. The relationship between the final product-sum value and the total number of pixels of the liquid crystal display panel corresponding to one display area (for example, the ratio between the product-sum value and the total number of pixels. The higher the ratio, the higher the APL. ), The APL of each region can be obtained by the APL arithmetic circuit (222). By referring to the LUT (203) using the APL obtained for each display area, the light emission upper limit amount of each backlight cell corresponding to each display area is determined and controlled by the dimming value determination unit (103). A signal (219) is sent out.

  In this way, it is possible to detect a dark region by using APL to calculate the upper limit light emission amount of the backlight cell. By suppressing the backlight luminance in the low APL region, it is possible to suppress the luminance step in the black image portion.

  A fifth embodiment of the present invention will be described with reference to FIG. The fifth embodiment is different from the third embodiment in that the amount of light emitted from the backlight cell is controlled in consideration of the APL of the entire image frame.

  23, instead of the control system (210) for detecting and controlling the black area of the entire image frame by the black area detection unit (101) for each area shown in FIG. 20, APL detection and control is performed for the entire image frame. A control system (239) is added. Elements other than the control system (239) and having the same reference numerals as in FIG. 3 or FIG. 10 are the same as those described in FIG. 3 or FIG.

  The area-specific APL detection unit (218) receives the image frame received by the image frame reception unit (100), and the luminance value detection unit (220) obtains the luminance on the liquid crystal panel (108) from the gradation value. Detect value. This luminance information is subjected to product-sum operation by the product-sum operation unit (230), and the relationship between the final product-sum value and the total number of pixels of the liquid crystal panel (108) (for example, the product-sum value and the total number of pixels). From the ratio (the higher the ratio, the higher the APL), the APL calculation circuit (231) can determine the APL of the entire image frame. By referring to the LUT (232) using this APL, the intensity coefficient 2 (233) for multiplying the backlight cell light emission upper limit obtained by the LUT (303) by a constant is determined. The multiplier (234) multiplies the intensity coefficient 2 (233) obtained by referring to the LUT (233) and the backlight cell light emission upper limit obtained by the LUT (303) to obtain the final backlight. It is output as the light cell emission upper limit (110).

  As an example, consider a case where all the white images in the display areas B2 and B3 in the input image of FIG. 7 are black images. At this time, the APL of the entire screen is different from that in FIG. 7, but the black areas of the display areas C2 and C3 do not change.

  However, since the APL is low on the entire screen, the amount of light incident on the human eye is reduced, and the sensitivity of the visual system is increased, so that the luminance step in the black image portion is easily visible. For this reason, it is desirable to reduce the luminance of the backlight when the APL is lowered over the entire screen.

  Therefore, in this embodiment, the intensity coefficient 2 (233) is set to a relatively small value when the APL of the entire image frame is smaller than a predetermined threshold value, so that the backlight cell emission upper limit amount is set. Control to make it smaller.

  By controlling in this way, in an image where black floating is conspicuous, that is, the APL of the entire screen is low, it is possible to suppress the luminance step by controlling the light emission upper limit amount of the backlight cell to be low. On the other hand, it is possible to control the light emission upper limit amount of the backlight cell to be high for an image in which the luminance difference is not conspicuous, that is, the APL is high, and a sharp image can be provided.

  The present invention is suitable for application to a liquid crystal display device configured to divide a backlight into a plurality of regions and individually control the backlight, for example, a liquid crystal television or a portable display.

DESCRIPTION OF SYMBOLS 100 Image frame receiving part 101 Histogram detection part for every area | region 102 Black area detection part for every area | region 103 Dimming value determination part 104 Filter part 105 Backlight control part 106 Liquid crystal control part 107 Backlight part 108 Liquid crystal panel 109 Backlight cell light emission 110 Backlight cell emission upper limit 300 Brightness information detection unit 301 Threshold comparison unit 302 Area counter 303 LUT
500 Minimum value selection unit 501 Difference detection unit 502 Product-sum operation unit 503 Distribution processing unit 600 Display area 601 Backlight cell 700 Luminance difference in black image area 701 Luminance difference in black image area 212 Overall counter 213 LUT
214 Strength coefficient 1
218 APL detection unit for each region 219 Backlight cell light emission upper limit 220 Brightness value detection unit 221 Region product sum operation unit 222 APL operation circuit 223 LUT
230 Product-sum operation unit 231 APL operation circuit 2232 LUT
233 Strength coefficient 2

Claims (9)

A backlight configured by two-dimensionally combining a plurality of backlight cells whose light intensity can be individually controlled, and a liquid crystal panel that displays light by modulating light emitted from the backlight for each pixel In the provided image display device,
A maximum luminance information detector for detecting maximum luminance information for each display area of the liquid crystal panel corresponding to each backlight cell from one frame of the input image signal; and a black area for each display area corresponding to each backlight cell The area black area detection unit for detecting the amount of light emitted from each backlight cell is determined according to the detected maximum luminance information of the image for each display area and the area black area for each detected display area. A dimming value determination unit for
An image display device comprising: The image display device according to claim 1,
When the area black area value detected by the area black area detection unit in a display area corresponding to a certain backlight cell is larger than a predetermined black area threshold, the dimming value determination unit An image display device characterized in that a light emission amount of a backlight cell is lowered. The image display device according to claim 1,
When the area black area value detected by the area black area detection unit in a display area corresponding to a certain backlight cell is larger than a predetermined black area threshold, the dimming value determination unit is smaller than An image display device characterized in that the amount of light emitted from surrounding backlight cells centering on the backlight cell is increased. The image display device according to any one of claims 1 to 3,
The maximum luminance information detection unit obtains a luminance histogram of an image signal for each display area, and detects the maximum gradation information from the luminance histogram. The image display device according to any one of claims 1 to 4,
An overall black area detector that detects a black area corresponding to one frame of the input image signal;
The dimming value determination unit detects the area black area in a display area corresponding to a certain backlight cell, when the total black area in the total black area detection unit is larger than a predetermined black area threshold, compared to a case where it is small Even if the area black area value detected in the part is the same, the light emission amount of the backlight cell is reduced. The image display device according to any one of claims 1 to 4,
An overall APL detection unit for detecting an overall average luminance corresponding to one frame of the input image signal;
The dimming value determination unit detects the area black area in a display area corresponding to a certain backlight cell, when the total APL detected by the total APL detection unit is smaller than a predetermined APL threshold, compared to a case where the total APL is large. Even if the area black area value detected in the part is the same, the light emission amount of the backlight cell is reduced. A backlight configured by two-dimensionally combining a plurality of backlight cells whose light intensity can be individually controlled, and a liquid crystal panel that displays light by modulating light emitted from the backlight for each pixel In the provided image display device,
An area feature amount detection unit that detects maximum luminance information for each display area corresponding to each backlight cell from one frame of the input image signal;
An area APL detection unit that detects average luminance for each display area corresponding to each backlight cell;
A dimming value determining unit that determines the light emission amount of each backlight cell according to the detected maximum luminance information for each display region and the average luminance for each detected display region;
An image display device comprising: The image display device according to claim 7,
In the display area corresponding to a certain backlight cell, the dimming value determination unit is configured so that when the area average luminance detected by the area APL detection unit is smaller than a predetermined APL threshold, the backlight cell An image display device characterized in that the amount of emitted light is reduced. The image display device according to claim 7 or 8,
The image display apparatus, wherein the maximum luminance information detecting unit obtains a luminance histogram of the image signal and detects the maximum gradation information from the luminance histogram.

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