JP2007336531A - Image correction circuit, image correction method and image display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image correction circuit capable of realizing effective contrast enhancement irrespectively of contents of an input image. <P>SOLUTION: A black-side intermediate luminance distribution acquisition circuit 22 and a white-side intermediate luminance distribution acquisition circuit 23 acquire luminance a black-side intermediate luminance distribution 61 and a white-side intermediate luminance distribution 62 in each image frame. A characteristic line determining section 24 determines a low-luminance-region input/output characteristic curve LB1 and a high-luminance-region input/output characteristic curve LW1 in each image frame. A gamma correction execution circuit 31 executes image correction for YUV signals (Yin, Uin, Vin) in regions at a low-luminance side and a high-luminance side from a weighed luminance center G1 on the basis of the low-luminance-region input/output characteristic curve LB1 and the high-luminance-region input/output characteristic curve LW1. The low-luminance-region input/output characteristic curve LB1 and the high-luminance-region input/output characteristic curve LW1 are more likely to simple curves irrespectively of contents of input image data. <P>COPYRIGHT: (C)2008,JPO&INPIT

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. 15A, 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. 16A, when the luminance distribution is distributed in a high luminance region (white level region) (luminance distribution 106B), for example, FIG. As shown in FIG. 17, the gamma curve is corrected from L101 to L103, and for example, as shown in FIG. 17A, the luminance distribution is distributed in the intermediate luminance region (luminance distribution 106C). For example, as shown in FIG. 17B, 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 input image data as a histogram distribution and corrects the gamma curve for each distribution peak based on the luminance histogram distribution. Has been.

JP 2006-93753 A JP 2005-175933 A

  Here, the conventional contrast improvement method using the luminance histogram distribution is such that the distribution results detected in all luminance regions are reflected in the contrast improvement of all luminance regions as shown in FIGS. As shown in FIGS. 1 and 2, the distribution result detected in a partial luminance region is reflected in the contrast improvement of that portion. 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 an image frame has only one distribution peak or a small number of distribution peaks, the gamma curve is corrected according to each distribution peak, so that effective contrast improvement can be realized. it is conceivable that. 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 partial luminance region, for example, FIG. Like the gamma curves L105A and L105B shown in (B), the gamma curve becomes complicated. Therefore, for example, as shown in FIG. 18A, 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.

  In this way, the distribution results detected in all luminance regions are reflected in the contrast improvement of all luminance regions, or the distribution results detected in partial luminance regions are reflected in the contrast improvement of that portion. However, it is difficult to effectively improve the contrast regardless of the content of the input image.

  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.

  A first image correction circuit according to the present invention corrects input image data based on input / output characteristic lines for each image frame obtained by adaptively changing a predetermined reference input / output characteristic line. The black side intermediate luminance distribution, which is the luminance distribution of the region between the lowest luminance of the predetermined intermediate luminance region and the reference luminance located at the center of the intermediate luminance region in the luminance distribution of the input image data in the image frame, is acquired. A low-brightness region that passes through the reference point on the reference input / output characteristic line and the lowest luminance point on the reference input / output characteristic line, which are determined in accordance with the reference luminance, based on the luminance distribution acquisition means and the obtained black-side intermediate luminance distribution Determining means for determining an input / output characteristic curve; and correction executing means for executing image correction on input image data in an area on a lower luminance side than the reference luminance based on the determined low luminance area input / output characteristic curve. Those were. The “reference input / output characteristic line” is not limited to a linear characteristic line, and may be a characteristic line represented by a curve.

  A first image correction method of the present invention corrects input image data based on input / output characteristic lines for each image frame obtained by adaptively changing a predetermined reference input / output characteristic line. The black side intermediate luminance distribution that is the luminance distribution of the region between the lowest luminance of the predetermined intermediate luminance region and the reference luminance located at the center of the intermediate luminance region in the luminance distribution of the input image data in the image frame is acquired. Based on the obtained black side intermediate luminance distribution, a low luminance region input / output characteristic curve passing through the reference point on the reference input / output characteristic line determined corresponding to the reference luminance and the lowest luminance point on the reference input / output characteristic line is obtained. Then, based on the determined low luminance area input / output characteristic curve, image correction is performed on the input image data in the area on the lower luminance side than the reference luminance.

  A first image display device of the present invention corrects input image data based on input / output characteristic lines for each image frame obtained by adaptively changing a predetermined reference input / output characteristic line. The black side intermediate luminance distribution, which is the luminance distribution of the region between the lowest luminance of the predetermined intermediate luminance region and the reference luminance located at the center of the intermediate luminance region in the luminance distribution of the input image data in the image frame, is acquired. A low-brightness region that passes through the reference point on the reference input / output characteristic line and the lowest luminance point on the reference input / output characteristic line, which are determined in accordance with the reference luminance, based on the luminance distribution acquisition means and the obtained black-side intermediate luminance distribution A determination means for determining an input / output characteristic curve; a correction execution means for executing image correction on input image data in a region on the lower luminance side than the reference luminance based on the determined low luminance region input / output characteristic curve; It is obtained and a display means for displaying an image based on the corrected input image data.

  In the first image correction circuit, the image correction method, and the image display device of the present invention, the black-side intermediate luminance distribution is acquired from the predetermined intermediate luminance region in the luminance distribution of the input image data in the image frame. Also, based on the obtained black side intermediate luminance distribution, a low luminance region input / output characteristic curve passing through the reference point and the lowest luminance point is determined. Based on the determined low luminance region input / output characteristic curve, image correction is performed on the input image data in the region on the lower luminance side than the reference luminance. Therefore, based on the black side intermediate luminance distribution which is the luminance distribution of the local region, the input / output characteristic curve (low luminance region input / output) of the region lower than the reference luminance which is wider than this region. Therefore, the low luminance region input / output characteristic curve tends to be a simple curve regardless of the contents of the input image data.

  In the image correction circuit of the present invention, the low luminance region input / output characteristic curve is preferably a curve that is located below the reference 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. In such a configuration, the input / output characteristic curve of the low luminance area becomes the simplest curve, and the effect of improving the contrast is further increased.

  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 intermediate luminance region and the reference luminance, and the determination unit further includes the obtained white side. 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 based on the intermediate luminance distribution, and the correction execution means determines the determined low luminance region input / output characteristic curve and high It is preferable to perform image correction on the input image data in the lower and higher luminance regions than the reference luminance, respectively, based on the luminance region input / output characteristic curve. When configured in this manner, the low luminance region input / output characteristic curve and the high luminance region input / output characteristic curve are determined based on the acquired black side intermediate luminance distribution and white side intermediate luminance distribution, respectively. Based on this, the image correction is performed on the input image data in both the lower luminance side and the higher luminance side regions than the reference luminance. Therefore, in addition to the low luminance area input / output characteristic curve, the high luminance area input / output characteristic curve tends to be a simple curve regardless of the contents of the input image, and the contrast improvement effect is further increased.

  The second image correction circuit of the present invention corrects input image data based on input / output characteristic lines for each image frame obtained by adaptively changing predetermined reference input / output characteristic lines. The white side intermediate luminance distribution which is the luminance distribution of the region between the maximum luminance of a predetermined intermediate luminance region and the reference luminance located at the center of the intermediate luminance region in the luminance distribution of the input image data in the image frame is acquired. A high-luminance region that passes through the reference point on the reference input / output characteristic line and the highest luminance point on this reference input / output characteristic line determined according to the reference luminance based on the luminance distribution acquisition means and the obtained white-side intermediate luminance distribution A determination means for determining an input / output characteristic curve; and a correction execution means for executing image correction on input image data in a region on the higher luminance side than the reference luminance based on the determined high luminance region input / output characteristic curve. Those were.

  According to a second image correction method of the present invention, input image data is corrected based on an input / output characteristic line for each image frame obtained by adaptively changing a predetermined reference input / output characteristic line. The white side intermediate luminance distribution, which is the luminance distribution of the region between the maximum luminance of the predetermined intermediate luminance region and the reference luminance located at the center of the intermediate luminance region in the luminance distribution of the input image data in the image frame, is acquired. Based on the obtained white side intermediate luminance distribution, a high luminance region input / output characteristic curve passing through the reference point on the reference input / output characteristic line determined corresponding to the reference luminance and the highest luminance point on the reference input / output characteristic line is obtained. Based on the determined high luminance region input / output characteristic curve, image correction is performed on the input image data in the region on the higher luminance side than the reference luminance.

  The second image display device of the present invention corrects input image data based on input / output characteristic lines for each image frame obtained by adaptively changing predetermined reference input / output characteristic lines. The white side intermediate luminance distribution which is the luminance distribution of the region between the maximum luminance of a predetermined intermediate luminance region and the reference luminance located at the center of the intermediate luminance region in the luminance distribution of the input image data in the image frame is acquired. A high-luminance region that passes through the reference point on the reference input / output characteristic line and the highest luminance point on this reference input / output characteristic line determined according to the reference luminance based on the luminance distribution acquisition means and the obtained white-side intermediate luminance distribution A determination means for determining an input / output characteristic curve; a correction execution means for executing image correction on input image data in a region on the higher luminance side than the reference luminance based on the determined high luminance region input / output characteristic curve; It is obtained and a display means for displaying an image based on the corrected input image data.

  In the second image correction circuit, the image correction method, and the image display device of the present invention, the white side intermediate luminance distribution is acquired from the predetermined intermediate luminance region in the luminance distribution of the input image data in the image frame. Further, 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 is determined. Then, based on the determined high luminance region input / output characteristic curve, image correction is performed on the input image data in the region on the higher luminance side than the reference luminance. Therefore, based on the white side intermediate luminance distribution that is the local region luminance distribution, the input / output characteristic curve (high luminance region input / output) of the region that is wider than this region and that is higher than the reference luminance Therefore, the high luminance region input / output characteristic curve is likely to be a simple curve regardless of the contents of the input image.

  According to the first image correction circuit, the image correction method, or the image display device of the present invention, the black side intermediate luminance distribution is acquired from the predetermined intermediate luminance region in the luminance distribution of the input image data in the image frame. Based on the black side intermediate luminance distribution, a low luminance region input / output characteristic curve passing through the reference point and the lowest luminance point is determined, and the luminance lower than the reference luminance is determined based on the determined low luminance region input / output characteristic curve. Since the image correction is performed on the input image data in the side region, the low luminance region input / output characteristic curve can be easily made a simple curve regardless of the content 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.

  In addition, according to the second image correction circuit, the image correction method, or the image display device of the present invention, the white side intermediate luminance distribution is acquired from the predetermined intermediate luminance region in the luminance distribution of the input image data in the image frame. In addition, a high luminance region input / output characteristic curve passing through the reference point and the highest luminance point is determined based on the white side intermediate luminance distribution, and based on the determined high luminance region input / output characteristic curve, Since the image correction is performed on the input image data in the region on the high luminance side, the high luminance region input / output characteristic curve can be easily made a simple curve regardless of the content 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. As shown in FIG. 4A, for example, an input / output characteristic line (γ curve) obtained by adaptively changing the reference input / output characteristic line L0 representing the input luminance signal Yin = the output luminance signal Yout as shown in FIG. ) Lout1 is determined. Specifically, the γ curve Lout1 includes a luminance centroid G1 and a centroid point P1 determined by a value on the reference input / output characteristic line L0 at the luminance centroid G1 and a minimum luminance point P3 on the reference input / output characteristic line L0. A low luminance region input / output characteristic curve LB1 that passes through, and a high luminance region input / output characteristic curve LW1 that passes through the center of gravity P1 and the highest luminance point P4 on the reference input / output characteristic line 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 line L0, respectively, and are curves having no inflection points ( For example, it is expressed by a quadratic curve), and the S curve is shown as the entire γ curve Lout1.

  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 line L0, to the black side. An appropriate value is determined based on the total distribution amount in the intermediate luminance distribution 61 and the total distribution amount in the white side intermediate luminance distribution 62.

  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) in this way are output to the matrix circuit 41.

  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. Further, the black side distribution threshold values Bt1 and Bt2 correspond to specific examples of “first black side distribution threshold value” and “second black side distribution threshold value” in the present invention, respectively, and the black side gain threshold value Bg2 corresponds to the present invention. Corresponds to a specific example of “black side gain threshold” in FIG. The white side distribution threshold values Wt1 and Wt2 correspond to specific examples of the “first white side distribution threshold value” and the “second white side distribution threshold value” in the present invention, respectively, and the white side gain threshold value Wg2 corresponds to the present invention. This corresponds to a specific example of “white side gain threshold” in FIG.

  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. Further, 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, The reference input / output characteristic line L0 is adaptively changed to determine 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. At this time, the gains (black side gain Bg and white side gain Wg) in the low luminance region input / output characteristic curve LB1 and the high luminance region input / output characteristic curve LW1, that is, adaptive changes from the reference input / output characteristic line L0. Based on the distribution total amount in the black-side intermediate luminance distribution 61 and the distribution total amount in the white-side intermediate luminance distribution 62, for example, the amounts are appropriate as shown in FIGS. 5 (A) and 5 (B), for example. To be 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 becomes small (FIG. 15A), or the display image becomes unnatural as a curve with a negative slope (FIG. 15B). 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, in the black side intermediate luminance distribution acquisition circuit 22 and the white side intermediate luminance distribution acquisition circuit 23, of 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 obtained for each image frame, and the characteristic line determination unit 24 determines the reference point based on the black-side intermediate luminance distribution 61 and the white-side intermediate luminance distribution 62. A low luminance region input / output characteristic curve LB1 passing through (luminance centroid G1) and the lowest luminance point P3 and a high luminance region input / output characteristic curve LW1 passing through the luminance centroid G1 and the highest luminance point P4 are determined for each image frame; In the γ correction execution circuit 31, based on the determined low luminance region input / output characteristic curve LB1 and high luminance region input / output characteristic curve LW1, Since the image correction is performed on the YUV signals (Yin, Uin, Vin) in the lower luminance side and the higher luminance side than the luminance center of gravity G1, the low luminance region is input regardless of the contents of the input image data. Each of the output characteristic curve LB1 and the high luminance region input / output characteristic curve LW1 can be easily made simple. 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.

  Further, since the luminance centroid and the intermediate luminance region are determined for each image frame, it is possible to perform optimal contrast improvement regardless of the distribution mode of the luminance distribution 6, that is, the content of the display video.

  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 the 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.

  In the above-described embodiment, the luminance center of gravity, which is the reference luminance when determining the intermediate luminance region 6M, has been described for each image frame. However, for example, as illustrated in FIG. Further, the intermediate luminance area 6M based thereon may be fixed in advance. Even in such a configuration, the γ curve can be simplified as compared with the conventional case, such as the γ curve Lout10 shown in FIG. Contrast improvement can be realized.

  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. 14, 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. 14, 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 W2, 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 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, G10 ... reference luminance, 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 characteristic line, Lout, Lout0 to Lout6, Lout10, Lout11, Lout21 ... input / output characteristic line ( γ curve), LB0-L 6, LB11 ... low luminance region input-output characteristic line, LW0~LW6, LW11 ... high luminance region input-output characteristic line.

Claims (17)

An apparatus for correcting input image data based on input / output characteristic lines for each image frame obtained by adaptively changing predetermined reference input / output characteristic lines,
A black-side intermediate luminance distribution that is a luminance distribution of a region between a minimum luminance of a predetermined intermediate luminance region in a luminance distribution of input image data in an image frame and a reference luminance located at the center of the intermediate luminance region is acquired. Luminance distribution acquisition means;
Based on the obtained black-side intermediate luminance distribution, a low luminance region input / output characteristic curve passing through a reference point on the reference input / output characteristic line and a lowest luminance point on the reference input / output characteristic line determined corresponding to the reference luminance A determination means for determining
An image correction circuit, comprising: a correction execution unit that performs image correction on input image data in a region lower than the reference luminance based on the determined low luminance region input / output characteristic curve . The image correction circuit according to claim 1, wherein the low luminance region input / output characteristic curve is located below the reference input / output characteristic line and has no inflection point. 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,
The image correction circuit according to claim 1, wherein the determination unit determines the input / output characteristic curve of the low luminance region in consideration of the obtained black side luminance distribution. The determining means further includes a low luminance region input / output characteristic curve so that a gain in the low luminance region input / output characteristic curve is not excessive by adding the black side luminance distribution in addition to the black side intermediate luminance distribution. The image correction circuit according to claim 3, wherein the image correction circuit is determined. When the distribution amount of the black-side intermediate luminance distribution is equal to or less than a predetermined first black-side distribution threshold, the determination unit increases the gain in the low-luminance region input / output characteristic curve as the distribution amount increases. On the other hand, when the distribution amount of the black-side intermediate luminance distribution is larger than the first black-side distribution threshold and equal to or smaller than the predetermined second black-side distribution threshold, a gain in the low-luminance region input / output characteristic curve is predetermined. The image correction circuit according to claim 1, wherein the image correction circuit is limited to a black-side gain threshold value. The determining means restricts the gain in the low luminance region input / output characteristic curve to be less than the black side gain threshold when the distribution amount of the black side intermediate luminance distribution is larger than the second black side distribution threshold. The image correction circuit according to claim 5, wherein: The luminance distribution acquisition unit further acquires a white side intermediate luminance distribution that is a luminance distribution of a region between the highest luminance of the intermediate luminance region and the reference luminance,
The determining means further determines a high luminance area input / output characteristic curve passing through the reference point and the highest luminance point on the reference input / output characteristic line based on the obtained white side intermediate luminance distribution,
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, respectively. The image correction circuit according to claim 1, wherein correction is executed. The image correction circuit according to claim 7, wherein the high luminance region input / output characteristic curve is a curve that is located above the reference input / output characteristic line and has no inflection point. 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,
The image correction circuit according to claim 7, wherein the determination unit determines the high luminance area input / output characteristic curve in consideration of the obtained white side luminance distribution. The determination means further determines the high luminance region input / output characteristic curve so that the gain in the high luminance region input / output characteristic curve does not become excessive by taking the white side luminance distribution into consideration. 10. The image correction circuit according to 9. When the distribution amount of the white side intermediate luminance distribution is equal to or less than a predetermined first white side distribution threshold, the determination unit increases the gain in the high luminance region input / output characteristic curve as the distribution amount increases. On the other hand, when the distribution amount of the white-side intermediate luminance distribution is larger than the first white-side distribution threshold and equal to or smaller than a predetermined second white-side distribution threshold, a gain in the high-luminance region input / output characteristic curve is predetermined. The image correction circuit according to claim 7, wherein the image correction circuit is limited to a white-side gain threshold value. The determining means restricts the gain in the high luminance region input / output characteristic curve to be less than the white side gain threshold when the distribution amount of the white side intermediate luminance distribution is larger than the second white side distribution threshold. The image correction circuit according to claim 11, wherein An apparatus for correcting input image data based on input / output characteristic lines for each image frame obtained by adaptively changing predetermined reference input / output characteristic lines,
A white side intermediate luminance distribution which is a luminance distribution of an area between a maximum luminance of a predetermined intermediate luminance area in a luminance distribution of input image data in an image frame and a reference luminance located at the center of the intermediate luminance area is acquired. Luminance distribution acquisition means;
Based on the obtained white side intermediate luminance distribution, a high luminance region input / output characteristic curve passing 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 correspondence with the reference luminance A determination means for determining
An image correction circuit comprising: correction execution means for performing image correction on input image data in a region higher than the reference luminance based on the determined high luminance region input / output characteristic curve . A method of correcting input image data based on an input / output characteristic line for each image frame obtained by adaptively changing a predetermined reference input / output characteristic line,
A black side intermediate luminance distribution that is a luminance distribution of a region between a minimum luminance of a predetermined intermediate luminance region and a reference luminance located at the center of the intermediate luminance region in the luminance distribution of input image data in an image frame is obtained. ,
Based on the obtained black-side intermediate luminance distribution, a low luminance region input / output characteristic curve passing through a reference point on the reference input / output characteristic line and a lowest luminance point on the reference input / output characteristic line determined corresponding to the reference luminance Decide
An image correction method comprising: executing image correction on input image data in a region on a lower luminance side than the reference luminance, based on the determined low luminance region input / output characteristic curve. A method of correcting input image data based on an input / output characteristic line for each image frame obtained by adaptively changing a predetermined reference input / output characteristic line,
A white side intermediate luminance distribution that is a luminance distribution of a region between a maximum luminance of a predetermined intermediate luminance region in a luminance distribution of input image data in an image frame and a reference luminance located at the center of the intermediate luminance region is acquired. ,
Based on the obtained white side intermediate luminance distribution, a high luminance region input / output characteristic curve passing 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 correspondence with the reference luminance Decide
An image correction method comprising: executing image correction on input image data in a region on a higher luminance side than the reference luminance, based on the determined high luminance region input / output characteristic curve. A display device that corrects input image data based on an input / output characteristic line for each image frame obtained by adaptively changing a predetermined reference input / output characteristic line,
A black-side intermediate luminance distribution that is a luminance distribution of a region between a minimum luminance of a predetermined intermediate luminance region in a luminance distribution of input image data in an image frame and a reference luminance located at the center of the intermediate luminance region is acquired. Luminance distribution acquisition means;
Based on the obtained black-side intermediate luminance distribution, a low luminance region input / output characteristic curve passing through a reference point on the reference input / output characteristic line and a lowest luminance point on the reference input / output characteristic line determined corresponding to the reference luminance A determination means for determining
Based on the determined low-luminance area input / output characteristic curve, correction execution means for executing image correction on input image data in an area on the lower luminance side than the reference luminance;
An image display device comprising: display means for displaying an image based on input image data subjected to image correction. A display device that corrects input image data based on an input / output characteristic line for each image frame obtained by adaptively changing a predetermined reference input / output characteristic line,
A white side intermediate luminance distribution which is a luminance distribution of an area between a maximum luminance of a predetermined intermediate luminance area in a luminance distribution of input image data in an image frame and a reference luminance located at the center of the intermediate luminance area is acquired. Luminance distribution acquisition means;
Based on the obtained white side intermediate luminance distribution, a high luminance region input / output characteristic curve passing 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 correspondence with the reference luminance A determination means for determining
Based on the determined high-luminance area input / output characteristic curve, correction execution means for performing image correction on input image data in an area higher than the reference luminance,
An image display device comprising: display means for displaying an image based on input image data subjected to image correction.

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