JP5012195B2 - Image correction circuit, image correction method, and image display apparatus - Google Patents

Description

  The present invention relates to an image correction circuit, an image correction method, and an image display device having a function of performing correction processing on an image signal.

  Usually, a television receiver, a VTR (Video Tape Recorder), a digital camera, a television camera, a printer, or the like has an image processing function (for example, adjustment of light and darkness, contrast, contour, etc.) after image quality correction is performed on an input image. Functions such as correction). Such a function is effectively applied mainly to an image that is dark overall and has low contrast, or an image in which details are blurred.

  Among these functions, contrast adjustment is usually performed by correcting a gamma curve representing a so-called gamma characteristic. As an example, there is a method using a luminance distribution based on a histogram distribution of an input image. Specifically, for example, as shown in FIG. 14A, when the luminance distribution is distributed in a low luminance region (black level region) (luminance distribution 106A), for example, FIG. ), The gamma curve is corrected from L101 to L102. Similarly, for example, as shown in FIG. 15A, when the luminance distribution is distributed in a high luminance region (white level region) (luminance distribution 106B), for example, FIG. As shown in FIG. 16, when the gamma curve is corrected from L101 to L103, for example, as shown in FIG. 16A, the luminance distribution is distributed in the intermediate luminance region (luminance distribution 106C). For example, as shown in FIG. 16B, the gamma curve is corrected from L101 to L104. Note that the degree of correction amount set for each luminance level when correcting this gamma curve is called a gain.

  For example, Patent Documents 1 and 2 propose a contrast improvement method that detects the luminance distribution of an input image as a histogram distribution and corrects the gamma curve for each distribution peak based on the luminance histogram distribution. ing.

JP 2006-93753 A JP 2005-175933 A

  Here, the conventional contrast improvement method using the luminance histogram distribution, as shown in FIGS. 14 to 16, reflects the distribution results detected in all the luminance regions in the contrast improvement of all the luminance regions, or the above-mentioned patent document. As shown in FIGS. 1 and 2, the distribution result detected in the partial luminance region is reflected in the contrast improvement of the portion, and the luminance region for detecting the luminance histogram distribution is a fixed region set in advance. However, in the case of such a contrast improvement method, for example, as described below, depending on the content of the input image, there may be cases where effective contrast improvement is not performed or the display image becomes unnatural. It was.

  That is, for example, when the luminance histogram distribution in the image frame has only one distribution peak or a small number of distribution peaks, the gamma curve is corrected according to each distribution peak detected in the fixed luminance region, It is considered that effective contrast improvement can be realized. However, when there are many distribution peaks in the luminance histogram distribution, if correction is performed for each of such many distribution peaks using the distribution result in the fixed luminance region, for example, FIG. The gamma curve becomes complicated like the gamma curves L105A and L105B shown in B). Therefore, for example, as shown in FIG. 17A, the effect of improving the contrast is reduced, and when the slope of the curve is increased in order to increase the effect, for example, as shown in the gamma curve L105B shown in FIG. It becomes a curve with a negative slope, and the display image becomes unnatural.

  As described above, in the conventional technique in which the distribution result detected in the preset fixed luminance region is reflected in the contrast improvement, it is difficult to effectively improve the contrast regardless of the contents of the input image. there were.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an image correction circuit, an image correction method, and an image display device that can realize effective contrast improvement regardless of the contents of an input image. It is to provide.

The image correction circuit of the present invention obtains, for each image frame, an area determination unit that determines an intermediate luminance area for each image frame according to the content of the input image data, and a luminance distribution of the input image data in the determined intermediate luminance area. Input / output characteristics that define image correction content for input image data by adaptively changing a predetermined reference input / output characteristic line based on the obtained luminance distribution acquisition means and the luminance distribution of the obtained intermediate luminance region A determining unit that determines a line for each image frame; and a correction executing unit that executes image correction on input image data based on the determined input / output characteristic line. The determining means determines the gain value in the input / output characteristic line corresponding to the change amount in the adaptive change according to the total distribution amount in the luminance distribution of the intermediate luminance region, and determines the gain value. In addition, when the total distribution amount is equal to or smaller than the predetermined first distribution threshold, the gain value increases as the total distribution amount increases, while when the total distribution amount is larger than the first distribution threshold. The gain value is limited to a predetermined gain threshold value or less. The “reference input / output characteristic line” is not limited to a linear characteristic line, and may be a characteristic line represented by a curve.

According to the image correction method of the present invention, an intermediate luminance region is determined for each image frame according to the content of the input image data, and the luminance distribution of the input image data in the determined intermediate luminance region is obtained for each image frame. By applying an adaptive change to a reference input / output characteristic line determined in advance based on the luminance distribution of the intermediate luminance region, an input / output characteristic line that defines image correction content for input image data is determined for each image frame, The image correction is performed on the input image data based on the determined input / output characteristic line. Further, the gain value in the input / output characteristic line corresponding to the change amount in the adaptive change is determined according to the distribution total amount in the luminance distribution of the intermediate luminance region, and the distribution total amount is predetermined when determining the gain value. When the total distribution amount is larger than the first distribution threshold, the gain value is set to a predetermined value. It should be limited to below the gain threshold.

An image display apparatus according to the present invention includes an area determination unit that determines an intermediate luminance area for each image frame according to the content of input image data, and acquires the luminance distribution of the input image data in the determined intermediate luminance area for each image frame. And an input / output characteristic line that prescribes image correction content for input image data by adaptively changing a predetermined reference input / output characteristic line based on the obtained luminance distribution of the intermediate luminance region. Determination means for determining each image frame, correction execution means for executing image correction on the force image data based on the determined input / output characteristic line, and display means for displaying an image based on the input image data subjected to image correction It is equipped with. The determining means determines the gain value in the input / output characteristic line corresponding to the change amount in the adaptive change according to the total distribution amount in the luminance distribution of the intermediate luminance region, and determines the gain value. In addition, when the total distribution amount is equal to or smaller than the predetermined first distribution threshold, the gain value increases as the total distribution amount increases, while when the total distribution amount is larger than the first distribution threshold. The gain value is limited to a predetermined gain threshold value or less.

  In the image correction circuit, the image correction method, and the image display device of the present invention, an intermediate luminance region is determined for each image frame in accordance with the content of the input image data, and the luminance distribution of the input image data in the intermediate luminance region is the image frame. Get every. In addition, the reference input / output characteristic line is adaptively changed based on the obtained luminance distribution of the intermediate luminance region, whereby the input / output characteristic line is determined for each image frame. Then, based on the determined input / output characteristic line, image correction is performed on the input image data. Therefore, since the input / output characteristic line is determined based on the luminance distribution in the intermediate luminance region for each image frame corresponding to the content of the input image data, the input / output characteristic line is simple regardless of the content of the input image data. It becomes easy to become a curve.

  In the image correction circuit of the present invention, the region determination means obtains the luminance centroid of the luminance distribution of the input image data for each image frame, and has predetermined predetermined values on the low luminance side and the high luminance side with the obtained luminance centroid as the center. A range determined by setting the width may be determined as the intermediate luminance region. The “luminance centroid” means a luminance position corresponding to a value obtained by dividing the sum of products of luminance and frequency (total integrated value) by the sum of frequencies in the luminance distribution of one image frame.

  In the image correction circuit of the present invention, the luminance distribution acquisition unit is configured to obtain a black side intermediate luminance which is a luminance distribution of a region between the determined minimum luminance of the intermediate luminance region and a reference luminance located at the center of the intermediate luminance region. The distribution is acquired for each image frame, and the above determination means determines the reference point on the reference input / output characteristic line and the minimum luminance on the reference input / output characteristic line determined according to the reference brightness based on the obtained black-side intermediate brightness distribution. A low luminance region input / output characteristic curve passing through the point is determined, and the correction execution means performs image correction on the input image data in the region on the lower luminance side than the reference luminance based on the determined low luminance region input / output characteristic curve. Can be configured to perform. When configured in this manner, the low luminance region input / output characteristic curve, which is a part of the input / output characteristic line, tends to be a simple curve regardless of the content of the input image data.

  In this case, the luminance distribution acquisition unit further acquires a white side intermediate luminance distribution that is a luminance distribution of a region between the maximum luminance of the determined intermediate luminance region and the reference luminance, and the determination unit further obtains the luminance distribution. Based on the obtained white side intermediate luminance distribution, a high luminance region input / output characteristic curve passing through the reference point and the highest luminance point on the reference input / output characteristic line is determined, and the correction execution means includes the determined low luminance region input. Based on the output characteristic curve and the high luminance region input / output characteristic curve, it is preferable to perform image correction on the input image data in the region on the lower luminance side and the higher luminance side than the reference luminance. When configured in this way, the high luminance region input / output characteristic curve, which is a part of the input / output characteristic line, tends to be a simple curve regardless of the content of the input image data. The low-brightness region input / output characteristic curve is more preferably a curve that is located below the reference input / output characteristic line and has no inflection point. More preferably, the curve is located above the input / output characteristic line and has no inflection point. The “inflection point” means a point at which the sign of the second derivative of the function defining the curve changes from positive to negative or from negative to positive. When configured as described above, the low luminance region input / output characteristic curve and the high luminance region input / output characteristic curve are the simplest curves, and the effect of improving contrast is further increased.

  According to the image correction circuit, the image correction method, or the image display device of the present invention, an intermediate luminance region is determined for each image frame in accordance with the contents of the input image data, and the luminance distribution of the input image data in the intermediate luminance region is displayed as an image. It is acquired for each frame, input / output characteristic lines are determined for each image frame based on the obtained luminance distribution of the intermediate luminance region, and image correction is performed on input image data based on the determined input / output characteristic lines. Therefore, the input / output characteristic line can be easily made a simple curve regardless of the contents of the input image data. Therefore, for example, even when the luminance histogram distribution in the image frame has a large number of distribution peaks, it is possible to realize effective contrast improvement without producing an unnatural display image.

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

[First Embodiment]
FIG. 1 shows the overall configuration of an image display apparatus according to the first embodiment of the present invention. The image display device includes an tuner 11, a Y / C separation circuit 12, a chroma decoder 13, a switch 14, a delay circuit 15, an input / output characteristic line generation unit 2 and an image processing unit 3, and a matrix circuit 41. And an image display function unit including a driver 42 and a display 5. The image correction circuit and the image correction method according to the first embodiment of the present invention are embodied by the image display device according to the present embodiment, and will be described below together.

  The image signal input to the image display device may be a television signal from a TV (TeleVision), or an output from a VCR (Video Cassette Recorder), a DVD (Digital Versatile Disc), or the like. It has become common in recent televisions and personal computers (PCs) to capture image information from a plurality of types of media and perform screen display for each of them.

  The tuner 11 receives and demodulates a television signal from the TV and outputs it as a composite signal (CVBS; Composite Video Burst Signal).

  The Y / C separation circuit 12 separates the composite signal from the tuner 11 or the composite signal from the VCR or DVD 1 into a luminance signal Y1 and a color signal C1 and outputs them.

  The chroma decoder 13 outputs the luminance signal Y1 and the color signal C1 separated by the Y / C separation circuit 12 as a YUV signal (Y1, U1, V1) composed of the luminance signal Y1 and the color difference signals U1, V1. .

  The YUV signal is image data of a two-dimensional digital image, and is a set of pixel values corresponding to positions on the image. Among them, the luminance signal Y represents a luminance level, and takes an amplitude value between a white level which is 100% white and a black level which is 100% black. Further, 100% of white of the image signal is defined as 100 (IRE) in a unit representing a relative ratio of image signals called IRE (Institute of Radio Engineers). In the Japanese NTSC (National Television Standards Committee) signal standard, the white level is 100 IRE and the black level is 0 IRE. On the other hand, the color difference signals U and V correspond to a signal BY obtained by subtracting the luminance signal Y from blue (B) and a signal RY obtained by subtracting the luminance signal Y from red (R). By combining these U signal and V signal with the luminance signal Y, colors (hue, saturation, luminance) are expressed.

  The switch 14 switches the selected signal to a YUV signal by switching YUV signals from a plurality of types of media (here, YUV signals (Y1, U1, V1) and YUV signals (Y2, U2, V2) from DVD2). (Yin, Uin, Vin) is output.

  The input / output characteristic line generation unit 2 adaptively generates an input / output characteristic line (γ curve) used in a γ correction execution circuit 31 in the image processing unit 3 to be described later. A black side intermediate luminance distribution acquisition circuit 22, a white side intermediate luminance distribution acquisition circuit 23, and a characteristic line determination unit 24 are provided.

  The luminance distribution acquisition circuit 21 acquires a luminance distribution consisting of a histogram distribution based on the luminance signal Yin of the YUV signals (Yin, Uin, Vin) output from the switch 14 and calculates the luminance centroid of the acquired luminance distribution. The intermediate luminance region centered on the luminance gravity center is determined. The luminance centroid is a luminance position corresponding to a value obtained by dividing the sum of the products of luminance and frequency (total integration value) by the total sum of frequencies in the luminance distribution of one image frame.

  FIG. 2 shows an example of the luminance distribution (luminance distribution 6) acquired by the luminance distribution acquisition circuit 21. The vertical axis represents the frequency of the histogram distribution, and the horizontal axis represents the luminance level.

  The luminance distribution acquisition circuit 21 uses the luminance distribution 6 for each frame data (image data constituting one screen), which is data for one frame when displaying an image and data for one field, for example. To get to. Further, the luminance centroid of the luminance distribution (for example, the luminance centroid G1 in FIG. 2) is obtained for each image frame based on the luminance distribution 6, and the low luminance side and the high luminance are obtained with the obtained luminance centroid G1 as the center. A range in which a predetermined width is set on each side (in the example of FIG. 2, a width corresponding to three gradations) is determined as an intermediate luminance region with each image frame. Here, the luminance centroid G is obtained, for example, by the following equation (1), and the luminance distribution is obtained for each image frame. Therefore, the luminance centroid G is also obtained for each image frame. . The data of the luminance distribution 6, the luminance gravity center G, and the intermediate luminance region 6M obtained in this way are output to the black-side intermediate luminance distribution acquisition circuit 22 and the white-side intermediate luminance distribution acquisition circuit 23.

  Based on the data of the luminance distribution 6, the luminance centroid G, and the intermediate luminance region 6M acquired by the luminance distribution acquisition circuit 21, the black-side intermediate luminance distribution acquisition circuit 22, as shown in FIG. Of the intermediate luminance region 6M determined for each frame, a black-side intermediate luminance distribution 61 that is a luminance distribution of a region (black-side intermediate luminance region 6BM) lower than the luminance gravity center G is acquired for each image frame It is. Similarly, the white side intermediate luminance distribution acquisition circuit 23 is shown in FIG. 3B based on the data of the luminance distribution 6, the luminance centroid G, and the intermediate luminance region 6M acquired by the luminance distribution acquisition circuit 21, for example. As described above, the white-side intermediate luminance distribution 62 that is the luminance distribution of the region (white-side intermediate luminance region 6WM) higher than the luminance gravity center G among the intermediate luminance regions 6M determined for each image frame is displayed for each image frame. To get to.

  Returning to the description of FIG. 1, the characteristic line determination unit 24 includes the black side intermediate luminance distribution 61 obtained by the black side intermediate luminance distribution acquisition circuit 22 and the white side intermediate luminance distribution obtained by the white side intermediate luminance distribution acquisition circuit 23. Based on 62, for example, as shown in FIG. 4A, an input / output characteristic line (γ curve) obtained by adaptively changing the reference input / output characteristic L0 representing the input luminance signal Yin = the output luminance signal Yout. Lout1 is determined. Specifically, the γ curve Lout1 is a low luminance region passing through the luminance gravity center G1 and the gravity center point P1 determined by the value of the reference input / output characteristic L0 at the luminance gravity center G1 and the lowest luminance point P3 of the reference input / output characteristic L0. The input / output characteristic curve LB1 is composed of a high luminance region input / output characteristic curve LW1 passing through the center of gravity P1 and the highest luminance point P4 of the reference input / output characteristic L0. Further, the low luminance region input / output characteristic curve LB1 and the high luminance region input / output characteristic curve LW1 are located below or above the reference input / output characteristic L0, respectively, and are curves having no inflection points (for example, A secondary curve), and the entire γ curve Lout1 is an S-shaped curve.

  Since the luminance centroid is obtained for each image frame as described above, for example, as shown in FIG. 4B, the centroid point, the low luminance area input / output characteristic curve, the high luminance area input / output characteristic curve, and γ Curves are also obtained for each image frame, and may differ depending on the image frame (for example, luminance center of gravity G2, center of gravity point P2, low luminance region input / output characteristic curve LB2, high luminance region input / output characteristic curve LW2 and γ) Curve Lout2).

  Further, the characteristic line determination unit 24 sets the gain values in the low luminance region input / output characteristic curve LB1 and the high luminance region input / output characteristic curve LW1, that is, the adaptive change amount from the reference input / output characteristic L0, to the black-side middle, respectively. Based on the total distribution amount in the luminance distribution 61 and the total distribution amount in the white side intermediate luminance distribution 62, an appropriate value is determined.

  Here, FIG. 5A shows the relationship between the distribution total amount in the black side intermediate luminance region 6BM and the gain (black side gain Bg) in the low luminance region input / output characteristic curve LB1. 5 (B) shows the relationship between the total distribution amount in the white side intermediate luminance region 6WM and the gain (white side gain Wg) in the high luminance region input / output characteristic curve LW1.

  In FIG. 5A and FIG. 5B, five regions B0 to B4 corresponding to the value of the distribution total amount on the horizontal axis and the black distribution thresholds Bt0 to Bt3 and the white distribution thresholds Wt0 to Wt3, respectively, Regions W0 to W4 exist.

  Specifically, in FIG. 5A, in the region B0 where the total distribution amount is equal to or less than the black side distribution threshold Bt0, the value of the black side gain Bg is “0”, and the total distribution amount is larger than the black side distribution threshold Bt0. At the same time, in the region B1 which is equal to or less than the black side distribution threshold Bt1, the value of the black side gain Bg increases (in this case, increases linearly) as the total distribution amount increases. In the region B2 in which the total distribution amount is larger than the black side distribution threshold value Bt1 and equal to or less than the black side distribution threshold value Bt2, the black side gain Bg is limited to the black side gain threshold value Bg2 and becomes a constant value. In the regions B3 and B4 larger than the distribution threshold Bt2, the black side gain Bg is limited to less than the black side gain threshold Bg2. That is, in the region B3 where the total distribution amount is larger than the black side distribution threshold value Bt2 and less than or equal to the black side distribution threshold value Bt3, the value of the black side gain Bg decreases (in this case, linearly decreases) as the total distribution amount increases. In the region B4 where the total distribution amount is larger than the black side distribution threshold value Bt3, the black side gain Bg is limited to the black side gain threshold value Bg1 having a smaller value than the black side gain threshold value Bg2, and has a constant value.

  On the other hand, similarly in FIG. 5B, in the region W0 where the total distribution amount is equal to or less than the white side distribution threshold value Wt0, the value of the white side gain Wg is “0”, and the total distribution amount is larger than the white side distribution threshold value Wt0. At the same time, in the region W1 that is equal to or smaller than the white side distribution threshold Wt1, the value of the white side gain Wg increases (in this case, increases linearly) as the total distribution amount increases. In the region W2 in which the total distribution amount is larger than the white side distribution threshold value Wt1 and is equal to or less than the white side distribution threshold value Wt2, the white side gain Wg is limited to the white side gain threshold value Wg2 and becomes a constant value. In the regions W3 and W4 larger than the distribution threshold value Wt2, the white side gain Wg is limited to be less than the white side gain threshold value Wg2. That is, in the region W3 in which the total distribution amount is larger than the white side distribution threshold value Wt2 and equal to or less than the white side distribution threshold value Wt3, the value of the white side gain Wg decreases (in this case, linearly decreases) as the total distribution amount increases. In the region W4 where the total distribution amount is larger than the white side distribution threshold value Wt3, the white side gain Wg is limited to the white side gain threshold value Wg1 having a value smaller than the white side gain threshold value Wg2, and has a constant value.

  In this way, depending on the total distribution amount in the black side intermediate luminance region 6BM and the white side intermediate luminance region 6WM, up to the black side distribution threshold value Bt1 and the white side distribution threshold value Wt1, depending on the total distribution amount, the black side gain Bg and white While the side gain Wg also increases, when the total distribution amount is larger than the black side distribution threshold value Bt1 and the white side distribution threshold value Wt1, the values of the black side gain Bg and the white side gain Wg are limited. However, the gain in the intermediate luminance region 6M is adjusted so as not to be excessive.

  Returning to the description of FIG. 1, the delay circuit 15 delays the color difference signals Uin and Vin output from the switch 14 and synchronizes with the γ curve Lout output from the input / output characteristic line generator 2. Thus, the data is output to the image processing unit 3.

  The image processing unit 3 uses the γ curve Lout adaptively generated by the input / output characteristic line generation unit 2 to output a YUV signal (Yin, Uin, Vin) output from the switch 14 via the delay circuit 15. The image display apparatus according to the present embodiment is configured by a γ correction execution circuit 31 that performs a contrast improvement process on the YUV signals (Yin, Uin, Vin). .

  The γ correction execution circuit 31 uses the γ curve Lout adaptively generated by the input / output characteristic line generator 2 to perform contrast improvement processing on the YUV signal (Yin, Uin, Vin). . Specifically, for example, as shown in FIGS. 4 (A) and 4 (B), the γ curves Lout1 and Lout2 determined for each image frame are input at a degree represented by the gain for each luminance level. Brightness / darkness adjustment of the luminance signal Yin is performed. The YUV signals (Yout, Uout, Vout) after image processing (contrast adjustment) are output to the matrix circuit 41 in this way.

  The matrix circuit 41 reproduces the YUV signals (Yout, Uout, Vout) after the image processing by the image processing unit 3 into RGB signals and outputs the reproduced RGB signals (Rout, Gout, Bout) to the driver 42. It is.

  The driver 42 generates a drive signal for the display 5 based on the RGB signals (Rout, Gout, Bout) output from the matrix circuit 41 and outputs the drive signal to the display 5.

  The display 5 performs image display based on YUV signals (Yout, Uout, Vout) after image processing by the image processing unit 3 in accordance with the drive signal output from the driver 42. The display 5 may be any type of display device, for example, a CRT (Cathode-Ray Tube) 51, an LCD (Liquid Crystal Display) 52, a PDP (Plasma Display Panel) (not shown), or the like.

  Here, the input / output characteristic line generation unit 2 and the image processing unit 3 correspond to a specific example of the “image correction circuit” in the present invention, and include a luminance distribution acquisition circuit 21, a black side intermediate luminance distribution acquisition circuit 22, and a white side. The intermediate luminance distribution acquisition circuit 23 corresponds to a specific example of “luminance distribution acquisition means” in the present invention. The characteristic line determination unit 24 corresponds to a specific example of “determination means” in the present invention, and the γ correction execution circuit 31 corresponds to a specific example of “correction execution means” in the present invention.

  Next, the operation of the image display apparatus according to the present embodiment will be described with reference to FIGS.

  First, an image signal input to the image display device is demodulated into a YUV signal. Specifically, the TV signal from the TV is demodulated by the tuner 11 to become a composite signal, and the composite signal is directly input from the VCR or DVD 1 to the image display device. These composite signals are separated into a luminance signal Y1 and a color signal C1 in the Y / C separation circuit 12, and decoded into YUV signals (Y1, U1, V1) in the chroma decoder 13. On the other hand, the YUV signal (Y2, U2, V2) is directly input from the DVD 2 to the image display device.

  Next, in the switch 14, one of the YUV signals (Y1, U1, V1) and the YUV signals (Y2, U2, V2) is selected and output as a YUV signal (Yin, Uin, Vin). The Among the YUV signals (Yin, Uin, Vin), the luminance signal Yin is output to the γ correction execution circuit 31 in the input / output characteristic line generation unit 2 and the image processing unit 3, while the color difference signals Uin, Vin. Are respectively output to the delay circuit 15.

  Here, the input / output characteristic line generation unit 2 performs the following generation operation of the γ curve Lout based on the input luminance signal Yin.

  Specifically, first, in the luminance distribution acquisition circuit 21, based on the luminance signal Yin of the YUV signals (Yin, Uin, Vin) output from the switch 14, for example, from the histogram distribution as shown in FIG. A luminance distribution is acquired for each image frame. Also, based on the acquired luminance distribution, a luminance centroid G1 is obtained for each image frame, and by setting a predetermined width on each of the low luminance side and the high luminance side with the luminance centroid as the center, for each image frame An intermediate luminance region is determined.

  Next, in the black side intermediate luminance distribution acquisition circuit 22 and the white side intermediate luminance distribution acquisition circuit 23, based on the data of the luminance distribution 6, the luminance centroid G, and the intermediate luminance region 6M acquired by the luminance distribution acquisition circuit 21, respectively. A black side intermediate luminance distribution 61 and a white side intermediate luminance distribution 62 are acquired for each image frame.

  Next, the characteristic line determination unit 24, based on the black side intermediate luminance distribution 61 obtained by the black side intermediate luminance distribution acquisition circuit 22 and the white side intermediate luminance distribution 62 obtained by the white side intermediate luminance distribution acquisition circuit 23, An adaptive change is applied to the reference input / output characteristic L0, and an input / output characteristic line (γ curve) Lout1 composed of the low luminance area input / output characteristic curve LB1 and the high luminance area input / output characteristic curve LW1 is determined. At this time, the values of the gains (black side gain Bg and white side gain Wg) in the low luminance region input / output characteristic curve LB1 and high luminance region input / output characteristic curve LW1, that is, the amount of adaptive change from the reference input / output characteristic L0. However, based on the total distribution amount in the black-side intermediate luminance distribution 61 and the total distribution amount in the white-side intermediate luminance distribution 62, respectively, for example, as shown in FIG. 5A and FIG. It is determined. Specifically, depending on the total distribution amount in the black side intermediate luminance region 6BM and the white side intermediate luminance region 6WM, up to the black side distribution threshold value Bt1 and the white side distribution threshold value Wt1, depending on the total distribution amount, the black side gain Bg and white While the side gain Wg also increases, when the total distribution amount is larger than the black side distribution threshold Bt1 and the white side distribution threshold Wt1, the values of the black side gain Bg and the white side gain Wg are gains in the intermediate luminance region 6M. Is limited so as not to become excessive. The γ curve Lout adaptively generated for each image frame in this way is output to the γ correction execution circuit 31 in the image processing unit 3.

  On the other hand, the delay circuit 15 delays the color difference signals Uin and Vin, and as a result, is synchronized with the γ curve Lout output from the input / output characteristic line generator 2.

  Next, in the γ correction execution circuit 31 of the image processing unit 3, input / output characteristics based on the luminance signal Yin output from the switch 14 and the color difference signals Uin and Vin output from the switch 14 and passed through the delay circuit 15. By using the γ curve Lout supplied from the line generation unit 2, a contrast improvement process is performed on these YUV signals (Yin, Uin, Vin). Specifically, brightness adjustment is performed for each luminance level to the extent represented by the black side gain Bg in the low luminance region input / output characteristic curve LB1 and the white side gain Wg in the high luminance region input / output characteristic curve LW1.

  Here, the γ curve Lout is based on the black-side intermediate luminance distribution 61 and the white-side intermediate luminance distribution 62 based on the black-side intermediate luminance distribution 61 and the white-side intermediate luminance distribution 62 that are local region luminance distributions. Is composed of a low luminance region input / output characteristic curve LB1 and a high luminance region input / output characteristic curve LW1 which are input / output characteristic lines in a wide range of regions (regions on the lower and higher luminance sides than the luminance center of gravity G1). The low luminance region input / output characteristic curve LB1 and the high luminance region input / output characteristic curve LW1, and hence the γ curve Lout, become simple curves regardless of the contents of the input image (YUV signal (Yin, Uin, Vin)). It becomes easy. Specifically, in the present embodiment, these low-luminance area input / output characteristic curve LB1 and high-luminance area input / output characteristic curve LW1 are composed of quadratic curves having no inflection points. The γ curve Lout is always a simple S-shaped curve regardless of the content of the image, that is, the histogram distribution of the input luminance signal Yin for each image frame.

  Therefore, for example, in the case of an input image in which a large number of peaks exist in the luminance distribution, the conventional image display apparatus uses gamma curves as shown in the gamma curves L105A and L105B shown in FIGS. Becomes complicated and the effect of improving the contrast is reduced (FIG. 14A), or the display image becomes unnatural as a curve with a negative slope (FIG. 14B). On the other hand, in the image display apparatus according to the present embodiment, the γ curve Lout tends to be a simple S-curve at all times. Avoiding natural images.

  Further, as shown in FIGS. 5A and 5B, depending on the total distribution amount in the black side intermediate luminance region 6BM or the white side intermediate luminance region 6WM, up to the black side distribution threshold Bt1 and the white side distribution threshold Wt1. Since the black side gain Bg and the white side gain Wg also increase according to the total distribution amount, the gain is appropriately set so that the contrast increases according to the total distribution amount. When the total distribution amount is larger than the black side distribution threshold value Bt1 or the white side distribution threshold value Wt1, the values of the black side gain Bg and the white side gain Wg are set so that the gain in the intermediate luminance region 6M does not become excessive. For example, even if the image is such that the skin of a person is enlarged and displayed, the unevenness of the skin is not excessively emphasized, resulting in a more natural image display. When the total distribution amount is larger than the black side distribution threshold Bt2 or the white side distribution threshold Wt2, the values of the black side gain Bg and the white side gain Wg are further limited (less than the black side gain threshold Bg2 or the white side gain threshold Wg2). Therefore, even if the total distribution amount is further increased, the gain in the intermediate luminance region 6M is surely limited so as not to be excessive.

  Next, the matrix circuit 41 reproduces the YUV signals (Yout, Uout, Vout) after the contrast processing into RGB signals (Rout, Gout, Bout), and the driver 42 based on the RGB signals (Rout, Gout, Bout). Thus, a drive signal is generated, and an image is displayed on the display 5 based on the drive signal.

  As described above, in the present embodiment, the luminance distribution acquisition circuit 21 determines the intermediate luminance region 6M for each image frame in accordance with the input luminance signal Yin, and the black-side intermediate luminance distribution acquisition circuit 22 and the white-side intermediate. The luminance distribution acquisition circuit 23 acquires the luminance distribution (the black side intermediate luminance distribution 61 and the white side intermediate luminance distribution 62) in the intermediate luminance region 6M for each image frame, and the characteristic line determination unit 24 acquires these black side intermediate luminances. The γ curve Lout is determined for each image frame by adaptively changing the reference input / output characteristic line L0 based on the distribution 61 and the white-side intermediate luminance distribution 62, and the γ correction execution circuit 31 determines the γ curve Lout based on the γ curve Lout. Since the image correction for the YUV signal (Yin, Uin, Vin) is executed, the γ curve Lout is simplified regardless of the contents of the input image data. The curve can be made easy. Therefore, for example, even when the luminance histogram distribution in the image frame has a large number of distribution peaks, it is possible to realize effective contrast improvement without producing an unnatural display image.

  Specifically, among the intermediate luminance region 6M in the luminance distribution 6 of the luminance signal Yin in the image frame, the black-side intermediate luminance distribution 61 and the white-side intermediate luminance distribution 62 are acquired for each image frame, and the characteristic line is obtained. In the determination unit 24, based on the black side intermediate luminance distribution 61 and the white side intermediate luminance distribution 62, the low luminance region input / output characteristic curve LB1 and the luminance centroid G1 passing through the reference point (luminance centroid G1) and the lowest luminance point P3. And the high luminance area input / output characteristic curve LW1 passing through the maximum luminance point P4 are determined for each image frame, and the determined low luminance area input / output characteristic curve LB1 and high luminance area input / output are determined in the γ correction execution circuit 31. Based on the characteristic curve LW1, images for YUV signals (Yin, Uin, Vin) in the lower luminance side and higher luminance side regions than the luminance gravity center G1, respectively. Since the correction is executed, the low luminance area input / output characteristic curve LB1 and the high luminance area input / output characteristic curve LW1 can be easily made simple curves regardless of the contents of the input image data.

  When the total distribution amount in the black side intermediate luminance region 6BM or the white side intermediate luminance region 6WM is larger than the black side distribution threshold Bt1 or the white side distribution threshold Wt1, the values of the black side gain Bg and the white side gain Wg are set. Since the limitation is made, it is possible to avoid an excessive gain in the intermediate luminance region 6M. Therefore, for example, even in an image that displays an enlarged human skin, the unevenness of the skin is not excessively emphasized, and a more natural video display can be achieved.

  When the total distribution amount in the black side intermediate luminance region 6BM or the white side intermediate luminance region 6WM is larger than the black side distribution threshold Bt2 or the white side distribution threshold Wt2, the values of the black side gain Bg and the white side gain Wg are set. Since the restriction is further limited (restricted to less than the black side gain threshold value Bg2 or the white side gain threshold value Wg2), even if the total distribution amount is further increased, the gain in the intermediate luminance region 6M is surely restricted so as not to be excessive. be able to.

  Further, since the black side intermediate luminance distribution acquisition circuit 22 and the white side intermediate luminance distribution acquisition circuit 23 are provided separately, the contrast improvement operation in the low luminance region and the contrast improvement operation in the high luminance region are performed respectively. It can be done independently.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. The image display device of the present embodiment is further provided with a black side luminance distribution acquisition circuit 25 and a white side luminance distribution acquisition circuit 26 in the input / output characteristic line generator 2 in the image display device of the first embodiment. It is a thing.

  FIG. 6 shows the configuration of the input / output characteristic line generator 2A according to this embodiment. The input / output characteristic line generation unit 2A of the present embodiment includes a luminance distribution acquisition circuit 21, a black side intermediate luminance distribution acquisition circuit 22, a white side intermediate luminance distribution acquisition circuit 23, a characteristic line determination unit 24, a black side The luminance distribution acquisition circuit 25 and the white side luminance distribution acquisition circuit 26 are configured. In addition, the same code | symbol is attached | subjected to the same thing as the component in 1st Embodiment, and description is abbreviate | omitted suitably.

  For example, as shown in FIG. 7A, the black side luminance distribution acquisition circuit 25 is based on the data of the luminance distribution 6, the luminance gravity center G, and the intermediate luminance region 6M acquired by the luminance distribution acquisition circuit 21. A black-side luminance distribution 63, which is a luminance distribution of a region on the lower luminance side (black-side luminance region 6B) than the intermediate luminance region 6M determined every time, is acquired for each image frame. Similarly, the white side luminance distribution acquisition circuit 26 is based on the data of the luminance distribution 6, the luminance centroid G, and the intermediate luminance region 6M acquired by the luminance distribution acquisition circuit 21, as shown in FIG. 7B, for example. In addition, a white side luminance distribution 64 that is a luminance distribution of a region on the higher luminance side (white side luminance region 6W) than the intermediate luminance region 6M determined for each image frame is acquired for each image frame.

  Here, the luminance distribution acquisition circuit 21, the black side intermediate luminance distribution acquisition circuit 22, the white side intermediate luminance distribution acquisition circuit 23, the black side luminance distribution acquisition circuit 25, and the white side luminance distribution acquisition circuit 26 are referred to as “luminance distribution in the present invention. This corresponds to a specific example of “acquiring means”.

  In the input / output characteristic line generator 2A of the present embodiment, the following γ curve Lout is generated based on the input luminance signal Yin.

  First, in the luminance distribution acquisition circuit 21, the luminance distribution 6 including the histogram distribution is acquired for each image frame based on the luminance signal Yin, as in the first embodiment, and based on the acquired luminance distribution. Thus, the luminance centroid G1 and the intermediate luminance region 6M are determined for each image frame. Next, in the black-side intermediate luminance distribution acquisition circuit 22 and the white-side intermediate luminance distribution acquisition circuit 23, as in the first embodiment, based on the data of the luminance distribution 6, the luminance centroid G, and the intermediate luminance region 6M, A black side intermediate luminance distribution 61 and a white side intermediate luminance distribution 62 are acquired for each image frame. On the other hand, in the black side luminance distribution acquisition circuit 25 and the white side luminance distribution acquisition circuit 26, the black side luminance distribution 63 and the white side luminance distribution 64 are images based on the data of the luminance distribution 6, the luminance centroid G, and the intermediate luminance region 6M. Get every frame.

  Next, the characteristic line determination unit 24 obtains the black-side intermediate luminance distribution 61 obtained by the black-side intermediate luminance distribution acquisition circuit 22 and the white-side intermediate luminance distribution acquisition circuit 23 in the same manner as in the first embodiment. Based on the white side intermediate luminance distribution 62, a low luminance region input / output characteristic curve LB1 and a high luminance region input / output characteristic curve LW1 are created.

  Here, in the characteristic line determination unit 24 of the present embodiment, when the γ curve Lout is finally determined, in addition to the low luminance region input / output characteristic curve LB1 and the high luminance region input / output characteristic curve LW1, the black side The determination is made in consideration of the black side luminance distribution 63 obtained by the luminance distribution acquisition circuit 25 and the white side luminance distribution 64 obtained by the white side luminance distribution acquisition circuit 26. Specifically, for example, as in the γ curve Lout11 shown in FIG. 8A, the gains of the low luminance region input / output characteristic curve LB1 and the high luminance region input / output characteristic curve LW1 are based on the black luminance distribution 63. By superposing the gains of the input / output characteristic line L10B and the input / output characteristic line L10W created based on the white side luminance distribution 64, the low luminance region input / output characteristic curve LB11 and the high luminance region are finally entered. A γ curve Lout11 composed of the output characteristic curve LW11 is determined. Therefore, in addition to the luminance distribution in the intermediate luminance region 6M, the γ curve Lout11 is determined in consideration of the luminance distribution in the black side luminance region 6B and the white side luminance region 6W, so that the γ curve is adjusted more finely. The

  For example, as shown in FIG. 8B, the gains of the input / output characteristic line L10B and the input / output characteristic line L10W are set to the gains of the low brightness area input / output characteristic curve LB1 and the high brightness area input / output characteristic curve LW1. As a result of the superimposition, the gain of the low luminance area input / output characteristic curve LB11 or the high luminance area input / output characteristic curve LW11 becomes excessive, and some of the luminance areas of the black side luminance area 6B and the white side luminance area 6W are crushed. In such a case, the gain of the input / output characteristic line L10B and the input / output characteristic line L10W is corrected to be small, and finally the low luminance area input / output characteristic curve LB11 or the high luminance area is entered. The gain of the output characteristic curve LW11 is not excessive. Therefore, the black side luminance region 6B and the white side luminance region 6W are prevented from being partially collapsed, and the gradation expression is reliably ensured.

  In addition to this, for example, as shown in FIG. 9A, an input / output characteristic line created based on the black side luminance distribution 63 or the white side luminance distribution 64 is an input / output characteristic line L20 in the figure. Also in the case of such a shape, it is similarly determined as the γ curve Lout21 in the figure, and when the gain at this time becomes excessive, the input / output characteristic line L21 shown in FIG. In addition, the gain of the γ curve Lout21 is corrected so as not to be excessive.

  As described above, in the present embodiment, when the γ curve Lout is finally determined, in addition to the low luminance region input / output characteristic curve LB1 and the high luminance region input / output characteristic curve LW1, the black side luminance distribution acquisition circuit 25 is provided. Since the black side luminance distribution 63 obtained in the above and the white side luminance distribution 64 obtained by the white side luminance distribution acquisition circuit 26 are also taken into consideration, the determination is made in the black side luminance region 6B and the white side luminance region 6W. The γ curve can be adjusted more finely by determining the γ curve Lout11 in consideration of the luminance distribution.

  Specifically, for example, as a result of superimposing the gains of the input / output characteristic line L10B and the input / output characteristic line L10W, the gain of the low luminance area input / output characteristic curve LB11 or the high luminance area input / output characteristic curve LW11 becomes excessive, and the black side luminance Since the gradation of a part of the area 6B and the white luminance area 6W cannot be expressed, the gains of the input / output characteristic line L10B and the input / output characteristic line L10W are corrected to be small. A part of the black side luminance region 6B and the white side luminance region 6W is prevented from being crushed, and the gradation expression can be reliably ensured.

  In addition, since the black side luminance distribution acquisition circuit 25 and the white side luminance distribution acquisition circuit 26 are provided separately, also in this embodiment, the contrast improvement operation in the low luminance region and the contrast improvement in the high luminance region. The operations can be performed independently.

  Although the present invention has been described with reference to the first and second embodiments, the present invention is not limited to these embodiments, and various modifications can be made.

  For example, in the above embodiment, when the luminance centroid G1 is obtained based on the luminance distribution 6 in the entire luminance region as shown in FIG. 2, and the intermediate luminance region 6M is determined based on this, the luminance centroid G1 In the middle of each image frame, a range that is set to an equal predetermined width (in the example of FIG. 2, a width corresponding to three gradations in each case) on the black side that is the low luminance side and the white side that is the high luminance side. Although the case of determining as the luminance region 6M has been described, the variable intermediate luminance region 6Mv, the variable black-side intermediate luminance region 6BMv, and the variable white-side intermediate, which are regions for acquiring the intermediate luminance distribution, according to the luminance level position of the luminance gravity center G1. The luminance area 6WMv may be varied as follows. Specifically, for example, as shown in FIG. 10A, when the luminance centroid is near the intermediate luminance (luminance centroid G1c), for example, as shown in FIG. 10B, the variable intermediate luminance area 6Mv Variable black-side intermediate luminance region 6BMv (equal to the region width of the variable white-side intermediate luminance region 6WMv below) and variable white-side intermediate luminance region 6WMv (equal to the region width of the variable black-side intermediate luminance region 6BMv) in The intermediate black side luminance distribution and the intermediate white side luminance distribution are acquired in a uniform region around the luminance gravity center G1c. As a result, an appropriate intermediate luminance region in the state of the luminance center of gravity G1c can be obtained, and the input / output characteristic curve composed of the low luminance region input / output characteristic curve LB0 and the high luminance region input / output characteristic curve LW0 passing through the reference point P20. With Lout0, it is possible to perform more effective contrast improvement without excessively correcting black and white gains. On the other hand, for example, as shown in FIG. 11A, when the luminance centroid is located on the lower luminance side than the luminance centroid G1c (luminance centroid G1l), the low luminance region passing through the reference point P30 based on the intermediate luminance region 6M. In the correction by the input / output characteristic curve Lout3 composed of the input / output characteristic curve LB3 and the high luminance area input / output characteristic curve LW3, the black gain is adjusted by the low luminance area input / output characteristic curve LB3 as shown in FIG. Since it will be lowered excessively, black details cannot be reproduced and blackout will be caused. For example, as shown in FIG. 12A, when the luminance centroid is located on the higher luminance side than the luminance centroid G1c (luminance centroid G1h), the low luminance region passing through the reference point P50 based on the intermediate luminance region 6M. In the correction by the input / output characteristic curve Lout5 composed of the input / output characteristic curve LB5 and the high luminance area input / output characteristic curve LW5, the white gain is set by the high luminance area input / output characteristic curve LW5 as shown in FIG. Since it will be raised excessively, the white details cannot be reproduced, resulting in white collapse. Therefore, when the luminance gravity center G1 is biased to the black side or the white side in this way, the area width of the variable intermediate luminance area 6Mv is set to the same width as the intermediate luminance area 6M. For example, FIG. ), The variable black-side intermediate luminance region 6BMv (which is narrower than the region width of the variable white-side intermediate luminance region 6WMv below) and the variable white-side intermediate luminance region 6WMv (the above-described variable) in the variable intermediate luminance region 6Mv. An intermediate black side luminance distribution and an intermediate white side luminance distribution are obtained in an unequal area centered on the luminance center of gravity G11, which is wider than the area width of the black side intermediate luminance area 6BMv, for example, as shown in FIG. As described above, the variable black side intermediate luminance region 6BMv (wider than the variable white side intermediate luminance region 6WMv described below) and the variable white side intermediate luminance region 6WMv (in the variable black side middle) The narrower) than the area width of the luminance area 6BMv, so as to or retrieve intermediate black-side luminance distribution and intermediate white-side luminance distribution in unequal area around the luminance center G1H. That is, the width of the region on the side where the luminance center of gravity is biased is narrowed, and the width of the region on the opposite side is widened. As a result, an appropriate intermediate luminance region in the state of the luminance centroid G1l and the luminance centroid G1h can be obtained, and the low luminance region input / output characteristic curve LB4 and the high luminance region input / output characteristic curve LW4 passing through the reference point P30 are formed. The input / output characteristic curve Lout6 (FIG. 11 (B)) and the input / output characteristic curve Lout6 (FIG. 12 (B)) composed of the low luminance region input / output characteristic curve LB6 and the high luminance region input / output characteristic curve LW6 passing through the reference point P50. ) Makes it possible to improve the contrast more effectively without excessively correcting the black or white gain.

  Further, in the above embodiment, the case where the luminance center of gravity G1 is obtained based on the luminance distribution 6 in the entire luminance region as shown in FIG. 2 and the intermediate luminance region 6M is determined based on this is described. However, as shown in FIG. 13, for example, the luminance centroid (intermediate luminance centroid G1M) is obtained based on the luminance distribution in the predetermined initial intermediate luminance area 6M0, and the low luminance side and the high luminance are centered on the intermediate luminance centroid 6M. A range in which a predetermined width is set on the luminance side (in the example of FIG. 13, a width corresponding to three gradations) may be determined as an intermediate luminance region 6M with each image frame. Even in such a configuration, it is possible to obtain the same effect as the above embodiment.

  In the above embodiment, the relationship between the total distribution amount in the black side intermediate luminance region 6BM or the white side intermediate luminance region 6WM and the black side gain Bg or the white side gain Wg is shown in FIGS. ), But is not limited to this. For example, in the regions B2 and W2 and the regions B4 and W4, the black side gain Bg and the white side gain Wg may not be constant values, but may be slightly increased to an extent that the gain is not excessive, or conversely decreased. . Further, the black side gain Bg and the white side gain Wg may be increased from the regions B0 and W0, and the gains are directly increased from the regions B2 and W2 to the regions B4 and W4 without providing the regions B3 and W3. You may make it decrease.

  In the above embodiment, the input / output characteristic line generator 2 includes the black intermediate luminance distribution acquisition circuit 22 and the white intermediate luminance distribution acquisition circuit 23 in the input / output characteristic line generator 2A. As described above, the luminance distribution acquisition circuit 25 and the white side luminance distribution acquisition circuit 26 are provided, and the contrast improvement processing on the low luminance side and the contrast improvement processing on the high luminance side are performed simultaneously. Only one of the acquisition circuit 22 and the white side intermediate luminance distribution acquisition circuit 23 is provided, or in addition to this, only one of the black side luminance distribution acquisition circuit 25 and the white side luminance distribution acquisition circuit 26 is provided. Contrast improvement processing may be performed only on one side of the high luminance side. Even in such a configuration, it is possible to achieve effective contrast improvement without producing a display image that is unnatural compared to the conventional art.

  Further, in the above-described embodiment, the case where the image processing unit 3 includes the γ correction execution circuit 31 has been described. However, the configuration of the image processing unit 3 is not limited to this, and other image processing circuits, for example, An example may be included, and a plurality of such circuits may be provided.

1 is a circuit block diagram illustrating an overall configuration of an image display device according to a first embodiment of the present invention. It is a characteristic view for demonstrating the relationship between a luminance distribution, a luminance centroid, and an intermediate luminance region. FIG. 6 is a characteristic diagram for explaining a black side intermediate luminance distribution and a white side intermediate luminance distribution. It is a characteristic view showing the specific example of the input-output characteristic line which concerns on 1st Embodiment. It is a characteristic view for demonstrating the specific example of the relationship between the distribution total amount and gain in an intermediate | middle luminance area | region. It is a circuit block diagram showing the structure of the input-output characteristic line generation part which concerns on the 2nd Embodiment of this invention. It is a characteristic view for demonstrating a black side luminance distribution and a white side luminance distribution. It is a characteristic view showing the specific example of the input-output characteristic line which concerns on 2nd Embodiment. It is a characteristic view showing the other specific example of the input-output characteristic line which concerns on 2nd Embodiment. It is a characteristic view for demonstrating the relationship between the luminance distribution which concerns on the modification of this invention, reference | standard luminance, and an intermediate | middle luminance area | region. It is a characteristic view for demonstrating the relationship between the luminance distribution which concerns on the modification of this invention, reference | standard luminance, and an intermediate | middle luminance area | region. It is a characteristic view for demonstrating the relationship between the luminance distribution which concerns on the modification of this invention, reference | standard luminance, and an intermediate | middle luminance area | region. It is a characteristic view for demonstrating the relationship between the luminance distribution and the initial reference luminance, the initial intermediate luminance region, and the intermediate luminance gravity center according to the modification of the present invention. It is a characteristic view for demonstrating an example of the relationship between the luminance distribution in the conventional image display apparatus, and the change aspect of a gamma curve. It is a characteristic view for demonstrating the other example of the relationship between the luminance distribution in the conventional image display apparatus, and the change aspect of a gamma curve. It is a characteristic view for demonstrating the other example of the relationship between the luminance distribution in the conventional image display apparatus, and the change aspect of a gamma curve. It is a characteristic view showing the other example of the change aspect of the gamma curve in the conventional image display apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Tuner, 12 ... Y / C separation circuit, 13 ... Chroma decoder, 14 ... Switch, 15 ... Delay circuit, 2, 2A ... Input / output characteristic line generation unit, 21 ... Luminance distribution acquisition circuit, 22 ... Black side intermediate luminance Distribution acquisition circuit, 23 ... white side intermediate luminance distribution acquisition circuit, 24 ... characteristic line determination unit, 25 ... black side luminance distribution acquisition circuit, 26 ... white side luminance distribution acquisition circuit, 3 ... image processing unit, 31 ... gamma correction execution Circuit, 41 ... Matrix circuit, 42 ... Driver, 5 ... Display, 51 ... CRT, 52 ... LCD, 6 ... Luminance distribution, 61 ... Black side intermediate luminance distribution, 62 ... White side intermediate luminance distribution, 63 ... Black side luminance distribution 64 ... White side luminance distribution, 6M ... Intermediate luminance region, 6Mv ... Variable intermediate luminance region, 6M0 ... Initial intermediate luminance region, 6BM ... Black side intermediate luminance region, 6BMv ... Variable black side intermediate luminance region, 6WM ... White side intermediate Brightness area, WMv ... variable white side intermediate luminance region, 6B ... black side luminance region, 6W ... white side luminance region, Y1, Y2, Yin, Yout ... luminance signal, C1 ... color signal, U1, U2, Uin, Uout, V1, V2 , Vin, Vout ... color difference signal, Rout, Gout, Bout ... RGB signal, G0 ... initial reference luminance, G1, G1c, G11, G1h, G2 ... luminance centroid, G1M ... intermediate luminance centroid, P1, P2 ... centroid point, P10 , P20, P30, P50 ... reference point, P3 ... lowest luminance point, P4 ... highest luminance point, Bt0 to Bt3 ... black side distribution threshold, Wt0 to Wt3 ... white side distribution threshold, Bg ... black side gain, Bg1, Bg2 ... Black side gain threshold, Wg ... White side gain, Wg1, Wg2 ... White side gain threshold, L0 ... Reference input / output characteristics, Lout, Lout0 to Lout6, Lout11, Lout21 ... Input / output characteristic lines (γ curve), LB0 to LB6 LB11 ... with low brightness area Force characteristic line, LW0~LW6, LW11 ... high luminance region input-output characteristic line.

Claims (16)

Area determining means for determining an intermediate luminance area for each image frame according to the content of the input image data;
A luminance distribution acquisition means for acquiring the luminance distribution of the input image data in the determined intermediate luminance region for each image frame;
Input / output characteristic lines that define image correction content for input image data are determined for each image frame by adaptively changing predetermined reference input / output characteristic lines based on the obtained luminance distribution of the intermediate luminance region. A decision means to
Correction execution means for executing image correction on input image data based on the determined input / output characteristic line ,
The determining means includes
According to the distribution total amount in the luminance distribution of the intermediate luminance region, determining a gain value in the input / output characteristic line corresponding to the change amount in the adaptive change,
In determining the gain value,
When the total distribution amount is equal to or less than a predetermined first distribution threshold, the gain value increases as the total distribution amount increases,
An image correction circuit configured to limit the gain value to a predetermined gain threshold value or less when the total distribution amount is larger than the first distribution threshold value . The determining means includes
When the total distribution amount is larger than the first distribution threshold and not more than a predetermined second distribution threshold, the gain value is limited to the gain threshold and becomes a constant value,
If the total distribution amount is greater than the second distribution threshold, the gain value is further limited to be less than the gain threshold.
The image correction circuit according to claim 1. The area determination means obtains a luminance centroid of the luminance distribution of the input image data for each image frame, and sets ranges determined by setting predetermined widths on the low luminance side and the high luminance side with the obtained luminance centroid as the center. that determine as the intermediate luminance region
The image correction circuit according to 請 Motomeko 1 or claim 2. The area determining means sets the width of the low-luminance side and the high-luminance side area equally or non-uniformly when the luminance centroid is centered according to the luminance level position of the luminance centroid, Determine the intermediate luminance region
The image correction circuit according to claim 3. The region determining means includes
When the luminance centroid is located near the intermediate luminance level, while setting the width of the low-luminance side and the high-luminance side regions equally around the luminance centroid,
When the luminance centroid is biased to the low luminance level side or the high luminance level side, the width of the region on the side where the luminance centroid is biased is selected from the low luminance side and the high luminance side regions. Set it relatively narrow and set the width of the opposite area relatively wide
The image correction circuit according to claim 4. The luminance distribution acquisition unit acquires, for each image frame, a black-side intermediate luminance distribution that is a luminance distribution of a region between the determined minimum luminance of the intermediate luminance region and a reference luminance located at the center of the intermediate luminance region. ,
The determination means is a low luminance that passes through a reference point on the reference input / output characteristic line and a lowest luminance point on the reference input / output characteristic line determined in accordance with the reference luminance based on the obtained black-side intermediate luminance distribution Determine the area input / output characteristic curve,
The correction execution unit was determined on the basis of the low luminance region input-output characteristic curve, that perform image correction on the input image data of the low-luminance side region than the reference brightness
The image correction circuit according to any one of 請 Motomeko 1 to claim 5. The low luminance region input-output characteristic curve, as well as positioned below the reference output characteristic line, Ru curve der no inflection point
The image correction circuit according to 請 Motomeko 6. The luminance distribution acquisition means further acquires a black side luminance distribution that is a luminance distribution of a region on the lower luminance side than the lowest luminance of the intermediate luminance region,
Said determining means, in consideration also the black-side luminance distribution obtained, that determine the low luminance region input-output characteristic curve
The image correction circuit according to 請 Motomeko 6 or claim 7. The determining means superimposes a gain value obtained based on the black side luminance distribution on a gain value obtained based on the black side intermediate luminance distribution, thereby obtaining a final value in the low luminance area input / output characteristic curve. A typical gain value
The image correction circuit according to claim 8. The luminance distribution acquisition means further acquires a white side intermediate luminance distribution that is a luminance distribution of a region on the higher luminance side than the reference luminance among the determined intermediate luminance regions,
The determining means further determines a high luminance region input / output characteristic curve which is an input / output characteristic line passing through the reference point and the highest luminance point of the reference input / output characteristic based on the obtained white side intermediate luminance distribution. And
The correction execution means, based on the determined low-luminance area input / output characteristic curve and high-luminance area input / output characteristic curve, respectively, images for input image data in areas on the lower-luminance side and higher-luminance side than the reference luminance. to run a correction
The image correction circuit according to any one of 請 Motomeko 6 through claim 9. The high luminance region input-output characteristic curve, as well as positioned on the upper side than the reference output characteristic line, Ru curve der no inflection point
The image correction circuit according to 請 Motomeko 10. The luminance distribution acquisition means further acquires a white side luminance distribution which is a luminance distribution of a region on the higher luminance side than the intermediate luminance region,
Said determining means, in consideration also the white-side luminance distribution obtained, that determine the high luminance region input-output characteristic curve
The image correction circuit according to 請 Motomeko 10 or claim 11. The determining means superimposes a gain value obtained based on the white side luminance distribution on a gain value obtained based on the white side intermediate luminance distribution, thereby obtaining a final value in the high luminance region input / output characteristic curve. A typical gain value
The image correction circuit according to claim 12. The luminance distribution acquisition unit acquires, for each image frame, a white-side intermediate luminance distribution that is a luminance distribution of a region between the determined maximum luminance of the intermediate luminance region and a reference luminance located at the center of the intermediate luminance region. ,
The determination means has a high luminance that passes through a reference point on the reference input / output characteristic line and a highest luminance point on the reference input / output characteristic line determined in accordance with the reference luminance based on the obtained white side intermediate luminance distribution Determine the area input / output characteristic curve,
The correction execution unit, based on the determined the high luminance region input-output characteristic curve, that perform image correction on the input image data of the high brightness side area than the reference luminance
The image correction circuit according to any one of 請 Motomeko 1 to claim 5. Determine the intermediate luminance area for each image frame according to the content of the input image data,
The luminance distribution of the input image data in the determined intermediate luminance area is acquired for each image frame,
Input / output characteristic lines that define image correction content for input image data are determined for each image frame by adaptively changing predetermined reference input / output characteristic lines based on the obtained luminance distribution of the intermediate luminance region. And
Based on the determined input / output characteristic line, performing image correction on the input image data ,
According to the distribution total amount in the luminance distribution of the intermediate luminance region, determine a gain value in the input / output characteristic line corresponding to the amount of change in the adaptive change,
In determining the gain value,
When the total distribution amount is equal to or less than a predetermined first distribution threshold, the gain value increases as the total distribution amount increases,
An image correction method in which the gain value is limited to a predetermined gain threshold value or less when the total distribution amount is larger than the first distribution threshold value . Area determining means for determining an intermediate luminance area for each image frame according to the content of the input image data;
A luminance distribution acquisition means for acquiring the luminance distribution of the input image data in the determined intermediate luminance region for each image frame;
A decision is made to adaptively change a predetermined reference input / output characteristic line based on the obtained luminance distribution of the intermediate luminance region, and to determine an input / output characteristic line for defining image correction contents for input image data for each image frame Means,
Correction execution means for performing image correction on input image data based on the determined input / output characteristic line;
Display means for displaying an image based on the input image data subjected to the image correction ,
The determining means includes
According to the distribution total amount in the luminance distribution of the intermediate luminance region, determining a gain value in the input / output characteristic line corresponding to the change amount in the adaptive change,
In determining the gain value,
When the total distribution amount is equal to or less than a predetermined first distribution threshold, the gain value increases as the total distribution amount increases,
An image display device configured to limit the gain value to a predetermined gain threshold value or less when the total distribution amount is larger than the first distribution threshold value .

Images