JP4501766B2 - Video processing apparatus and video display apparatus - Google Patents

Description

  The present invention relates to a video display device such as a television receiver or a video processing device such as a DVD player or a set top box including a digital tuner, and particularly has a configuration for correcting the gradation of a video signal. The present invention relates to a video processing apparatus and a video display apparatus.

  Conventional techniques for detecting or calculating a luminance histogram of a video signal and performing gradation correction such as gamma correction in a video display device such as a television receiver are disclosed in, for example, Patent Documents 1 and 2 below. ing.

JP-A-6-90382 JP-A-8-317250

  As means for correcting the gradation of the video, there are brightness correction for controlling the DC component of the video signal (the luminance signal included therein), contrast correction for controlling the amplitude level of the luminance signal, gamma correction, and the like. Here, consider a case where, for example, gradation correction is performed in the order of brightness correction, contrast correction, and gamma correction using a luminance histogram detected or calculated from a luminance signal. Since the gamma correction is performed on the brightness signal subjected to the brightness correction and / or the contrast correction, the brightness histogram of the brightness signal to be gamma corrected may be different from the original brightness histogram detected or calculated. . For example, when the brightness level in the low-brightness area near the black side is reduced or suppressed by brightness correction, the brightness signal immediately before gamma correction is the one in which the brightness level in the low-brightness area is reduced with respect to the original brightness signal It has become. That is, the luminance histogram related to the luminance signal immediately before the gamma correction has a lower frequency or 0 in the low luminance region than the luminance histogram related to the original luminance signal.

  Therefore, in the above case, the luminance histogram used for gamma correction is different from the luminance signal actually subjected to gamma correction. Therefore, if the luminance histogram used for brightness correction and / or contrast correction is the same as the luminance histogram used for gamma correction, appropriate gamma correction cannot be obtained. The above Patent Documents 1 and 2 do not consider such a problem at all.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a technology capable of displaying high-quality video by performing appropriate gradation correction.

  In order to achieve the above object, the present invention provides a luminance histogram used for, for example, brightness correction and / or contrast correction as the first gradation correction, and a luminance histogram used for, for example, gamma correction as the second gradation correction, This is characterized by different brightness histograms. That is, the present invention uses a first luminance histogram for brightness correction and / or contrast correction, and uses a second luminance histogram obtained by changing the first luminance histogram for gamma correction.

  The second luminance histogram is obtained by changing the first luminance histogram in accordance with brightness correction processing and contrast correction processing. For example, when the brightness level in the low brightness region including the black level is reduced or suppressed (for example, 0) by the brightness correction and the contrast correction, the brightness level is reduced or suppressed in the first brightness histogram. The frequency corresponding to the low luminance region is reduced or cut to generate the second luminance histogram.

  According to the present invention, it is possible to display a high-quality image in which gradation correction is performed according to the image.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing an embodiment of a video display device according to the present invention. A luminance signal S1 and color difference signals RY and BY are input to the video display device as input video signals. The color difference signals R-Y and BY are appropriately color-corrected by a color correction circuit (not shown) and supplied to the matrix circuit 60. Since this color correction circuit is a part not directly related to the characteristic part of the present embodiment, its details are omitted here. For details of the color correction processing, refer to, for example, Japanese Patent Laid-Open No. 2003-47020. The luminance signal S1 is input to the detection circuit 10. The detection circuit 10 detects a luminance histogram indicating a luminance frequency distribution in one frame or one field period (hereinafter also referred to as one screen period) of the video from the input luminance signal S1. This luminance histogram has the form shown in FIG. 5, for example. That is, the detection circuit 10 detects the number of pixels having luminance corresponding to each of the plurality of luminance areas divided, that is, the frequency (appearance frequency) of luminance components belonging to each of a plurality of predetermined luminance level ranges, A luminance histogram as shown in FIG. 5 is generated. In FIG. 5, the divided luminance area is divided into five parts HST0 to HST4. The luminance signal S1 is digitized by, for example, an A / D converter (not shown). If this digital signal is represented by 10 bits, one luminance area in FIG. It becomes. If the video signal input to the video display device shown in FIG. 1 is originally in a digital format, an A / D converter is not necessary. In the present embodiment, the luminance region is divided into five. Of course, the luminance region may be larger than this, and it goes without saying that a higher accuracy histogram can be detected as the number of divisions increases. At the same time, the detection circuit 10 detects an average luminance level (hereinafter referred to as APL) for one screen from the input luminance signal S1.

  The luminance histogram and APL detected by the detection circuit 10 are supplied to the control circuit 20. The control circuit 20 is composed of, for example, a microcomputer and generates a control signal to be output to the gradation correction circuit based on the luminance histogram and APL detected by the detection circuit 10. As shown in FIG. 1, the tone correction circuit according to the present embodiment controls the direct current (DC) level of the luminance signal S1 to perform brightness correction, and the brightness correction is performed by the brightness correction circuit 30. It includes a digital amplifier for varying the amplitude level of the luminance signal S1, and controls the amplitude level to perform contrast correction, and the contrast correction circuit 30 and the luminance signal S1 contrast-corrected by the contrast correction circuit 40 are input / output. A gamma correction circuit 50 that performs gamma correction by conversion is included. In the present embodiment, the luminance signal S1 is subjected to correction processing in the order of the brightness correction circuit 30, the brightness correction circuit 30, and the gamma correction circuit 50. The control signal from the control circuit 20 is supplied to each of the brightness correction circuit 30, the brightness correction circuit 30, and the gamma correction circuit 50.

  The luminance signal S1 whose gradation has been corrected by the gradation correction circuit is supplied to the matrix circuit 60. The matrix circuit 60 performs a matrix operation on the luminance signal S1 and the color signals R-Y and B-Y that have been subjected to the color correction processing by the above-described color correction circuit to generate three primary color signals R, G, and B. The primary color signal generated by the matrix circuit 60 is supplied to the display unit 2 constituted by, for example, a liquid crystal panel or a plasma display panel (PDP). The display unit 2 displays an image based on the input primary color signal.

  Next, details of the gradation correction circuit will be described. First, an example of brightness correction in the brightness correction circuit 30 will be described with reference to FIG. The control circuit 20 calculates the correction amount of the brightness correction circuit 30 based on the luminance histogram and APL detected by the detection circuit 10. For example, in the luminance histogram shown in FIG. 5, the control circuit 20 has a frequency of the low luminance region (for example, HST0) near the black side lower than a predetermined threshold value and the frequency of the high luminance region (for example, HST3, HST4). If it is higher than the predetermined threshold value, a control signal is generated by calculating a correction amount that lowers the direct current level of the luminance signal. As a result, as shown in FIG. 2 (a), brightness correction is performed such that the level of the luminance signal indicated by the thin broken line (a) is shifted to the level indicated by the thick dotted line (b). As a result, the luminance level in the vicinity of the low luminance region is reduced or suppressed (0 level), and black can be tightened (black is sunk). That is, as shown in FIG. 6 (a), the DC level is lowered as the frequency of the low luminance region is smaller. In this example, only one luminance area HST0 is referred to in performing the brightness correction in the above example, but two luminance areas HST0 and HST1 may be used. For example, the frequency of HST0 and the frequency of HST1 may be summed, and the shift amount may be determined based on whether or not the total value exceeds a threshold value or the difference between the total value and the threshold value. In this case, when the total value exceeds the threshold value, for example, the shift amount is set to 0 to prevent the image from being crushed in the low-brightness region (no sense of contrast), and the difference between the total value and the threshold value is large As the shift amount is increased, black may be tightened. Further, the relationship between the total value of each luminance region and the brightness correction amount may be the characteristic shown in FIG. 6A, that is, the increase in the total frequency (“HST total value” in FIG. 6A). The correction level (DC level shift amount) may be decreased in proportion to In this example, when the total value is 0, the correction amount is maximized, and the correction amount decreases as it increases. When the total value exceeds a certain predetermined value, the correction amount becomes 0.

  Further, the shift amount of the direct current level of the luminance signal may be adjusted by the detected APL. For example, as shown in FIG. 6B, adjustment is performed such that the shift amount is increased when APL is high, and the shift amount is decreased when APL is low. An adjustment opposite to this may be performed. As shown in FIG. 6 (b), APLSTART and APLEND are set as the variable range of the brightness correction amount. If the detected APL is less than or equal to APLSTART and greater than or equal to APLEND, the brightness correction amount does not change even if the APL changes.If the detected APL is in the range of APLSTART to APLEND, the APL value is Thus, the brightness correction amount may be changed (in this example, increased). In this way, appropriate brightness correction according to the luminance histogram and APL can be performed.

  Next, an example of contrast correction in the contrast correction circuit 40 will be described with reference to FIG. By the brightness correction, a gradation margin corresponding to the shift amount of the DC level is formed. Contrast correction effectively uses the margin of gradation. That is, the contrast correction circuit 40 is indicated by a dotted line (c) connecting the intersection of the line (b) and the horizontal axis of FIG. 2 (b) and the point of the maximum gradation level (1023) of the line (a). The amplitude level of the luminance signal S1 that has been subjected to brightness correction so as to achieve the above characteristics is controlled. The control circuit 20 supplies a control signal for giving the characteristic (c) to the contrast correction circuit 40. The slope of the line (c) may be controlled by the detected APL. For example, when the APL is higher than the threshold value, the slope may be relaxed, and when the APL is low, the slope may be steep. By performing contrast correction in this way, it is possible to effectively use gradation and enhance contrast.

  Next, an example of gamma correction in the gamma correction circuit 50 will be described with reference to FIG. The gamma correction circuit 50 performs gamma correction of the contrast-corrected luminance signal S1 based on the luminance histogram detected by the detection circuit 10, and its basic operation is as follows. That is, the gamma correction circuit 50 adjusts the gradient of the gamma characteristic with respect to the luminance region so as to obtain a high gradation in the luminance region (HST1 to HST2 in the figure) having a high frequency in the luminance histogram shown in FIG. It is steeper than the slope of the gamma characteristic in other luminance regions. This gamma characteristic is shown by a dashed-dotted curve in FIG. As is clear from this, the slopes of the curves in HST2 to HST3 are steeper than those in HST0 and HST4 to 5. The control circuit 20 supplies the gamma correction circuit 50 with a control signal for allowing the gamma correction circuit 50 to have an input / output characteristic according to a gamma curve as shown in FIG. That is, the control circuit 20 refers to the detected luminance histogram, and gives the input / output characteristics to the gamma correction circuit 50 so as to increase the gradation of the characteristic portion of the video, that is, the luminance region having a high frequency. As a result, it is possible to obtain an image with enhanced contrast in the characteristic part of the image. Note that fine adjustment of the gamma curve, for example, local inclination adjustment of a low luminance region, a high luminance region, or the like may be performed based on the detected APL.

  In the above-described configuration, when the brightness histogram detected by the detection circuit 20 is used for each of the brightness correction and the gamma correction, the following problem may occur. That is, when the brightness level of the low brightness area (for example, HPL0) near the black side is suppressed to 0 level as shown in FIG. 2 by the brightness correction, the brightness signal S1 immediately before the gamma correction is The brightness level of the low brightness area is set to zero. That is, the luminance histogram related to the luminance signal immediately before the gamma correction has a lower frequency or 0 in the low luminance region than the luminance histogram related to the original luminance signal. That is, the luminance histogram detected by the detection circuit 20 is different from the luminance signal that is actually subjected to gamma correction. Therefore, if the luminance histogram used for brightness correction is the same as the luminance histogram used for gamma correction, appropriate gamma correction may not be obtained.

The present embodiment has been made in consideration of such a phenomenon, and its characteristic configuration will be described with reference to FIG. In the luminance signal whose DC level has been shifted by the brightness correction circuit 30, the luminance level in the range corresponding to the shift amount is zero. In FIG. 3, the range in which the luminance level is 0 is shown as “brightness level”. That is, in the luminance histogram of the luminance signal S1 input to the gamma correction circuit 50, the frequency of the luminance region corresponding to the brightness level is zero. Therefore, in the present embodiment, when performing gamma correction using the luminance histogram, the luminance histogram detected by the detection circuit 10 is not used as it is, but the frequency (luminance signal) corresponding to the brightness level is cut or reduced. A luminance histogram is generated by the control circuit 20 and used for gamma correction. Hereinafter, the detected luminance histogram is referred to as a first luminance histogram, and the luminance histogram generated for gamma correction is referred to as a second luminance histogram.

  The second luminance histogram is generated in the control circuit 20 as follows, for example. That is, assuming that the brightness level is 0 to 200, for example, the brightness level is 0, the second brightness histogram is obtained by recounting the frequency of each brightness area again with 201 as a base point (that is, 0), for example. It is generated by correcting one luminance histogram. For example, 201 to 400 is set as a new (corrected) HST0, and the number of pixels belonging to the brightness area is detected from the brightness signal in which the brightness level in the range of 0 to 200 (that corresponds to the brightness level range) is cut. And count. In addition, 401 to 600 are corrected as HST1, and the number of pixels belonging to HST1 is counted in the same manner. For HST2 and HST3 after correction, the number of pixels is obtained by the same process. The process of generating the second luminance histogram can use the luminance histogram data detected first. By such processing, a second luminance histogram shown in gray in FIG. Since the shift amount of the DC level in the brightness correction is obtained by the control circuit 20, the brightness level can be easily obtained by the control circuit 20. As described above, in the present embodiment, the first luminance histogram is corrected and changed in accordance with the DC level shift amount in the brightness correction to generate the second luminance histogram. In the above example, the frequency of the brightness level is cut when the second luminance histogram is generated. However, the frequency is reduced to a certain level without being cut, and the second luminance histogram is generated in consideration of this. Also good.

  The gamma correction circuit 50 performs gamma correction as shown in FIG. 4 using the second luminance histogram. When the newly generated second luminance histogram has the highest frequency of the luminance region (corrected HST0) adjacent to the brightness level as shown in FIG. 3, for example, the gradation of the luminance region is increased. The inclination of the luminance region is sharpened as shown by the solid line (d) in FIG.

  As described above, in this embodiment, when the brightness correction circuit 30 performs the brightness correction so as to suppress the low luminance region near the black side, a new luminance histogram is generated based on the luminance signal in which the low luminance region is suppressed. Then, gamma correction can be performed based on the new luminance histogram. Therefore, according to the present embodiment, the characteristic portion of the luminance signal that has been subjected to the brightness correction can be extracted in character, and more appropriate gamma correction can be performed. Therefore, according to the present embodiment, it is possible to display a high-quality image by performing gradation correction with higher accuracy.

  In the above description, the contrast correction does not use the luminance histogram, but the contrast correction may be performed using this. In addition to the brightness correction, the second luminance histogram for gamma correction may be generated in consideration of the result of contrast correction. Furthermore, in the above description, gradation correction is performed in the order of brightness correction, contrast correction, and gamma correction, but this order may be changed. It goes without saying that the present invention is applicable even if the order is changed.

  In the above description, the video processing apparatus such as a television receiver has been described as an example of the video processing apparatus. However, the present invention can be applied to a set top box equipped with a DVD player or a digital tuner, or a hard disk record. Needless to say, the video display unit can be applied not only to the liquid crystal panel and the PDP but also to an FED or a rear projection display device.

The block diagram of the gradation correction circuit which concerns on one Embodiment of this invention. FIG. 5 is a diagram illustrating an example of output characteristics of a brightness correction circuit and a contrast correction circuit according to the present embodiment. FIG. 6 is a diagram illustrating an example of output characteristics of the gamma correction circuit according to the present embodiment. FIG. 6 is a diagram showing an example of output characteristics of the gradation correction circuit according to the present embodiment. The figure which shows an example of the detected brightness | luminance histogram. The figure which shows the relationship between brightness correction amount and APL.

Explanation of symbols

2 ... display unit, 10 ... detection circuit, 20 ... control circuit, 30 ... brightness correction circuit, 40 ... contrast correction circuit, 50 ... gamma correction circuit, 60 ... matrix circuit.

Claims (10)

In video processing equipment,
A histogram generation unit that generates a luminance histogram indicating a frequency distribution of luminance in a predetermined period of video using the input video signal;
A first gradation correction unit that performs first gradation correction of the video signal based on the luminance histogram generated by the histogram generation unit;
A second tone correction unit that performs second tone correction on the signal that has been tone-corrected by the first tone correction unit, based on the luminance histogram generated by the histogram generation unit;
The histogram generation unit generates a first luminance histogram and a second luminance histogram, and uses the second luminance histogram according to the first gradation correction in the first gradation correction unit. Generated from
It said first gradation correction unit is configured perform said first gradation correction based on the first brightness histogram, the second tone correction unit, said second gradation correction based on the second luminance histogram An image processing apparatus characterized in that:   The video processing apparatus according to claim 1, wherein the histogram generation unit generates a luminance histogram in one frame or one field period of the video. 2. The video processing device according to claim 1, wherein the first gradation correction unit is a brightness correction unit that corrects the brightness of the video signal as the first gradation correction, or the first gradation correction is performed on the video signal as the first gradation correction. Including at least one of a contrast correction unit for correcting contrast,
The video processing apparatus, wherein the second gradation correction unit includes a gamma correction unit that performs gamma correction of the video signal as the second gradation correction. The video processing apparatus according to claim 1, further comprising an average luminance detection unit that detects an average luminance level in one frame or one field period of the video,
The first gradation correction unit performs first gradation correction based on the detected average luminance level and the first luminance histogram, and the second gradation correction unit calculates the detected average luminance level and A video processing apparatus that performs second gradation correction based on the second luminance histogram. 2. The video processing apparatus according to claim 1 , wherein the first gradation correction unit is capable of performing gradation correction for reducing the level of the video signal in a low luminance region near the black side based on the first luminance histogram. And
The histogram generation unit is configured to reduce the level of the first luminance histogram when the first gradation correction unit performs correction to reduce the level of the video signal in the low luminance region. An image processing apparatus, wherein the second luminance histogram is generated by reducing or cutting a frequency corresponding to a low luminance region. In video processing equipment,
A contrast correction unit that performs contrast correction on the input video signal;
A gamma correction unit that performs gamma correction on the contrast-corrected video signal;
A histogram generation unit that generates a luminance histogram indicating a frequency distribution of luminance in a predetermined period of the video using the video signal;
The histogram generation unit includes a first luminance histogram for use in the contrast correction process in the contrast correcting section, the at gamma correction unit and the second stimulable histogram used in the gamma correction processing to generate respectively, and the first An image processing apparatus , wherein a two-luminance histogram is generated by changing the first luminance histogram in accordance with a contrast correction process in the contrast correction unit. In video processing equipment,
A brightness correction unit that performs brightness correction on the input video signal;
A gamma correction unit that performs gamma correction on the brightness-corrected video signal;
A histogram generation unit that generates a luminance histogram indicating a frequency distribution of luminance in a predetermined period of the video using the video signal;
The histogram generation unit, the brightness and the first luminance histogram for use in brightness correction processing in the correction unit, wherein the gamma correction unit and a second brightness histogram used in the gamma correction processing to generate respectively, and the second An image processing apparatus, wherein a luminance histogram is generated by changing the first luminance histogram in accordance with a brightness correction process in the brightness correction unit. In the video display device,
A brightness correction unit that performs brightness correction by controlling the DC level of the luminance signal included in the input video signal;
A contrast correction unit that performs contrast correction by controlling an amplitude level of the brightness signal subjected to the brightness correction;
A gamma correction unit that performs gamma correction on the contrast-corrected luminance signal;
A display unit for displaying a video based on the corrected video signal generated using the brightness signal subjected to the brightness correction, the contrast correction, and the gamma correction;
A second luminance histogram generated by controlling the brightness correction unit and changing the first luminance histogram using a first luminance histogram indicating a luminance frequency distribution obtained from luminance signals of the same frame or the same field. A control unit that controls the gamma correction unit using
The control unit generates the second luminance histogram by changing the first luminance histogram according to a brightness correction process in the brightness correction unit and a contrast correction process in the contrast correction unit. Display device. 9. The video display device according to claim 8 , further comprising a detection unit for detecting an average luminance level in one frame or one field period of the video signal from the luminance signal,
The video display device, wherein the control unit controls the brightness correction unit, the contrast correction unit, and the gamma correction unit using the average luminance level detected by the detection unit. The video processing apparatus according to claim 8 , wherein when the brightness level in the low brightness area including the black level is reduced by the brightness correction unit and the contrast correction unit,
The control unit generates the second luminance histogram by reducing or cutting a frequency corresponding to the low luminance region in which the luminance level is reduced in the first luminance histogram. .

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