JPH07322176A - Video display processing method of electronic display and its device - Google Patents

Abstract

PURPOSE:To improve the contrast of a screen and to improve the image quality of a skin color part when video is displayed on electronic displays such as an LCD and a PDP, etc. CONSTITUTION:When an input/output characteristic conversion is performed for an input video signal to display the video by the input video signal on an electronic display, the luminance signal of the input video signal is detected by a luminance detection circuit 3, the skin color part in the video by the input video signal is detected by a skin color detection circuit 4, signals in which the skin color part is weighted by a weighting device 5 and the luminance signal are added by an addition circuit 6, histograms in which the luminance level histograms of the skin color part are weighted and added to the luminance level histograms of a background by the added signal are prepared for every field in a histogram calculation circuit 7, the input/output characteristic is determined according to the average value and the dispersion of the histograms, the data for the input/output characteristic conversion is obtained at an input/output characteristic calculation circuit 8, the data is written in the RAM 2a to 2c of an input/output characteristic conversion circuit 2 and the input/output characteristic conversion is performed for the input video signal delayed by a one-field delay part 2 in the RAM 2a to 2c.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video display processing technique in an electronic display (LCD (liquid crystal display panel), PDP (plasma display panel), etc.) used in a television or the like, and more particularly, to improve the quality of displayed video. The present invention relates to an electronic display image display processing method and an apparatus thereof.

[0002]

2. Description of the Related Art When an image based on an input image signal is displayed on an electronic display such as a liquid crystal display panel (hereinafter referred to as LCD) or a plasma display panel (hereinafter referred to as PDP), it is adjusted to the characteristics (gamma characteristics, etc.) of the electronic display. Input video signal is processed in a predetermined manner.

In this signal processing, for example, an input / output characteristic conversion process for gamma correction is generally performed on a video signal (RGB digital video signal) of a television or the like, and an appropriate video is electronically produced by the video signal. Can be displayed on the display.

[0004]

By the way, among the above-mentioned electronic displays, LCDs and PDPs generally lack contrast and brightness of displayed images as compared with other electronic displays, so that good images can be obtained. The current situation is that the skin color that is difficult, for example, noticeable to the human eye, is not so good.

Further, in the above-mentioned electronic display, since the power consumption is kept constant in consideration of power consumption, life, etc., for example, when the displayed image is not bright as a whole,
That is, when the entire screen is dark, the brightness of the peak of the display image is also low, the image quality of the display image is degraded, and the skin-colored portion, which is particularly noticeable to the human eye, becomes dark.

The present invention has been made in view of the above problems, and an object of the present invention is to improve the image quality of a display image and to obtain an image with a good skin tone and good contrast. An object of the present invention is to provide a video display processing method and device for an electronic display.

[0007]

In order to achieve the above object, an image display processing method for an electronic display and an apparatus therefor according to the present invention include: when converting an input image signal into an input / output characteristic in accordance with the characteristic of the electronic display; A histogram for the brightness level of the flesh-colored portion of the video image by the input video signal is weighted and added to the histogram of the brightness level of the entire video image to calculate the average value and variance, and according to the average value and variance The gist is that the data for converting the input video signal into the input / output characteristic is calculated.

[0008]

With the above means, the luminance signal of the input video signal is detected, while the flesh color portion of the image due to the input video signal is detected, and the signal of this flesh color portion is weighted and added to the luminance signal, The counter counts the number of pixels for each of the same signal levels of the added signals and sums for each field (or one frame) to create a histogram of the input video signal (same signal level).

In this way, a histogram is obtained in which the histogram for the luminance level of the image (background) and the histogram for the luminance level of the flesh color portion are weighted and added. The average value (APL; average level) and variance of the histogram are calculated by the input / output characteristic calculation means that inputs this histogram, and the input / output characteristic is determined based on this average value and variance to obtain the input / output characteristic data. It is calculated.

In this case, the input / output characteristic data is obtained, for example, by y = 1 / 2 ((x / c) to the γth power), and the c value is determined according to the average value of the histogram, and the γ value Is determined according to the variance of the histogram.

As described above, since the data for converting the input / output characteristics of the input video signal is determined in accordance with the average value and the variance of the histogram, it is possible to suppress the black shadow and the white shadow on the screen. Therefore, an image with good contrast can be obtained.

Moreover, since the histogram of the flesh color portion is weighted and added to the histogram of the image (background), the histogram for the luminance level of the flesh color portion becomes large. That is, since the gamma value of the input / output characteristic in the flesh-colored portion is determined to be a large value, the flesh-colored portion becomes bright and a display image with good contrast can be obtained.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION An image display processing method for an electronic display and an apparatus thereof according to the present invention determine the brightness of a screen based on an average value (APL; average image level) of a histogram with respect to a luminance level of an image and its variance (or standard deviation). It is possible to judge, that is, the brightness and the like of the screen are reflected in the average value and the variance, and the input video signal (R
When input / output characteristics of the input video signal are converted to display the video of the GB digital video signal) on the electronic display, a histogram for the brightness level of the skin color portion of the video by the input video signal is displayed for the brightness level of the entire video (background). Data for the input / output characteristic conversion is determined according to the APL and variance of the histogram obtained by adding the weight to the histogram.

Therefore, as shown in FIG. 1, the image display processing device of this electronic display is designed so that the input image signal (RG
1-field delay unit 1 for delaying B digital video signal) by 1 field, and RAM for performing input / output characteristic conversion processing (gamma correction, etc.) on the delayed video signal.
An input / output characteristic conversion circuit 2 including 2a, 2b, and 2c, and a luminance signal detection circuit 3 that detects a luminance signal of an input video signal.
And a flesh color detection circuit 4 for detecting a flesh color portion of an image based on an input video signal, and a weighting device 5 (multiplication circuit) for multiplying the detected flesh color portion by a predetermined number to obtain a flesh color portion signal.
And an addition circuit (logical sum circuit) 6 for adding the above-mentioned luminance signal and the signal of the flesh color portion, and a histogram for the luminance level of the entire image by weighting the histogram for the luminance level of the flesh color portion by this added signal. A histogram calculation circuit 7 for calculating the added histogram, and an average value of the weighted histograms, that is, APL (average video level) and variance (or standard deviation) are calculated,
An input / output characteristic calculation circuit 8 for calculating input / output characteristic data based on the APL and the variance is provided.

More specifically, the skin color detecting circuit 4 is
When the ratio of the R, G, B signal levels of the input video signal is within a certain range, it is judged as a skin color, and for example, R (red): G
(Green): B (Blue) = (1.3 to 1.7): (1.1 to)
1.3): 1, that is, when B is 1, R is 1.3 to
1.7, G is determined to be a skin color within the range of 1.1 to 1.3. The weighter 5 outputs the R, G, and B signals determined to be the skin color as one signal and by multiplying them by a fixed number.

The addition circuit 6 logically sums the luminance signal from the luminance detection circuit 1 and the skin color signal from the weighter 5 and outputs the result. The histogram calculation circuit 7 is a counter, and counts the number of pixels for each same signal level by the signal (data) obtained by the logical sum, and sums up for each field to calculate the histogram shown by the broken line curve in FIG. In other words, not only the histogram for the brightness level of the image (background), but also the histogram for the brightness level of the flesh-colored part of the image (human face, hands, etc.) is weighted and added to the background brightness level histogram to obtain the histogram. create.

Next, the operation of the image display processing device for the electronic display having the above-mentioned configuration will be described in detail with reference to the characteristic diagrams of FIGS. The histograms shown by the broken line curves in FIGS. 2 and 3 are values relative to the input / output level.

First, for example, a television signal (NTSC
Input video signal (8 bits to 1)
An image based on a 0-bit RGB digital image signal) is displayed on an electronic display (LCD, PDP, etc.).

At this time, the 1-field delay unit 2 delays the input video signal by 1 field and outputs it to the input / output characteristic conversion circuit 2. On the other hand, the luminance signal detection circuit 3 inputs 8-bit data (upper 8 bits data) of the input video signal and detects the luminance signal of the input video signal. In addition, as described above, the R, G, and B signals determined to be the skin color are detected by the skin color detection circuit 4 and the weighter 5, and the signals are multiplied by a certain number and output as one signal (for example, 8-bit data).

The luminance signal and the flesh color signal (8-bit data) are added by the adder circuit 6 and input to the histogram calculation circuit 7. The histogram calculation circuit 4 inputs the input image as shown by the broken line curve in FIG. 3, for example. The histograms A and B for the luminance level of the entire image (background) and the flesh-colored portion of the signal are calculated for each field, that is, the luminance level histogram of the flesh-colored portion is weighted and added to the background luminance level histogram to create a histogram. .

When the input video signal is an NTSC signal, the brightness signal Y detected by the brightness signal detection circuit 3 is usually Y = 0.30R + 0.59G + 0.11B.
In the present invention, the luminance signal is Ya = R.
Even with + G + B, almost the same effect can be obtained.

Further, the signal level for creating the histogram is 6 bits to 8 bits when the output signal, that is, the signal output by converting the input / output characteristics has an 8-bit structure.

Further, the pixel block for obtaining the frequency (output level) of the histogram is 3 when the image by the NTSC signal is displayed by general 480 × 680 pixels.
Even if the APL and the variance value are calculated with one 2 × 32 pixel block, that is, one pixel of the pixel block as a representative, it is not so different from the case of the histogram obtained by counting the number of pixels for each same signal level. Absent. Therefore, 1/16 × 1/16 or 1/32 × 1/32
The histogram may be calculated by taking one pixel from the pixels.

The input / output characteristic calculation circuit 8 calculates the variance and APL from the histograms A and B (weighted and added histograms) calculated for each field, and according to the variance. The γ value (0.1 to 6.0) of the input / output characteristic is determined, and the value c at which the output level of the device is ½ of the maximum is determined according to the APL. Furthermore, the determined γ value and value c
Based on the above, the data for input / output characteristic conversion is calculated by the following equation 1 and each RAM 2a, 2b,
2c, respectively.

[0025]

[Equation 1] In the above formula 1, y is the output level of the input / output characteristic conversion,
x means an input level of input / output characteristic conversion, c means a value of y = 1/2, and γ means a γ (gamma) value.

In this case, in the input / output characteristic calculation circuit 8, the calculated histogram is once stored in the internal RAM, and then the data in this RAM is fetched by the arithmetic processing unit (MPU) to obtain the constant value shown in the above mathematical expression 1. Input / output characteristic data is calculated according to a mathematical formula. When the output level exceeds the output level with the value (data) at the high level in the above mathematical expression 1, for example, an elliptic expression smoothly connected to the mathematical expression 1 may be used.

In this way, a luminance level histogram of the input video signal is created, input / output characteristics are determined according to the average value and variance of this histogram, and data for input / output characteristic conversion (input / output characteristic data) is obtained. Since the input video signal is calculated and the input / output characteristic is converted (gamma correction) based on this data, it is possible to suppress the blackout and whiteout of the displayed image even in an electronic display such as a PDP having a small dynamic range. In addition, it is possible to improve the contrast of the displayed image and thus obtain a high quality image.

By the way, when the whole image (background) is relatively bright but the flesh color part is dark, if a human sgram is created only by the luminance signal of the input image signal, the histogram for the luminance level of the entire image is shown by the broken line A in FIG. Although it is large as shown, the histogram for the luminance level of the flesh color part becomes small as shown by the broken line B in FIG.

When the input / output characteristic is determined based on the average value and the variance of the histograms shown by the broken lines A and B in FIG. 2 and the data for the input / output characteristic conversion is calculated, the shape shown by the solid line curve in the figure is obtained. That is, the γ (gamma) value of the skin-colored portion is small, and the skin-colored portion (face, hand, etc.) that is easily noticed by the human becomes darker than the original signal.

However, in the present invention, as described above,
Since the histogram for the luminance level of the flesh-colored portion is added to the luminance level of the entire image to obtain the histogram, the histogram of the flesh-colored portion becomes large as shown by the broken line B in FIG.

When the input / output characteristic is determined according to the average value and the variance of the histograms shown by the broken lines A and B in FIG. 3 and the data for the input / output conversion is calculated, the shape shown by the solid curve in FIG. The γ (gamma) value of the skin-colored portion is large, and the skin-colored portion (face, hands, etc.) that is easily noticed by humans becomes brighter than the original signal, and the skin-colored portion becomes clean, and the contrast of the resulting display image is enhanced.

Further, when the flesh-colored portion is in a relatively bright place, the histogram for the luminance level of this flesh-colored portion is weighted and summed with the histogram for the luminance level of the entire image. The flesh-colored part becomes brighter and cleaner, and more favorable results can be obtained.

In this way, when the input video signal is converted into the input / output characteristics in accordance with the characteristics of the electronic display, the luminance level histogram of the skin color portion is weighted and added to the luminance level histogram of the image (background) to obtain a histogram. , The input / output characteristics are determined according to the average value and variance of this histogram.

Therefore, the luminance level histogram of the flesh-colored part becomes large, that is, the gamma value of the flesh-colored part can be increased. Does not become dark, good image display is possible, and when the skin color part is relatively bright, the skin color part becomes brighter,
It is possible to display a more preferable result image.

In the above embodiment, 1 of the input video signal is used.
The input / output characteristic data of the input / output characteristic conversion circuit 2 is calculated for each field, and the input / output characteristic conversion (including gamma correction) of the input video signal is performed for each field, but for each frame of the input video signal. Data of input / output characteristics may be obtained. In this case, if each circuit can be processed for each frame, the same operation and effect as those of the above-described embodiment can be obtained.

[0036]

As described above, according to the present invention, there is provided a video display processing method and apparatus for an electronic display, which can display an image by converting input / output characteristics of an input video signal according to the characteristics of the electronic display. When the input video signal is converted into input / output characteristics in order to display the video based on the input video signal on the electronic display, the luminance signal of the input video signal is detected while the skin color part in the video (background) based on the input video signal is detected. Detects and weights the brightness signal and the skin color part to calculate a histogram for the brightness level, creates a histogram in which the brightness level histogram of the skin color part is weighted to the background brightness level histogram, and the average value and variance of this histogram are created. Since the input / output characteristics are determined according to the above, data for input / output characteristics conversion is obtained.
For example, even in a PDP having a small dynamic range, it is possible to suppress blackout and whiteout of a display image, improve the contrast of the display image, and thus obtain a high-quality image, and If there is a flesh-colored part inside the), it is possible to increase the brightness of the flesh-colored part that is easily noticed by the human eye, that is, it is possible to improve the contrast of the screen, and it is very close to the original image and an image with high contrast can get.

[Brief description of drawings]

FIG. 1 is a schematic partial block diagram of an image display processing device of an electronic display showing an embodiment of the present invention.

FIG. 2 is a schematic input / output characteristic diagram for explaining the operation of the video display processing device shown in FIG.

FIG. 3 is a schematic input / output characteristic diagram for explaining the operation of the video display processing device shown in FIG.

[Explanation of symbols]

 1 1 field delay unit 2 input / output characteristic conversion circuit 2a, 2b, 2c RAM 3 luminance signal detection circuit 4 skin color detection circuit 5 weighter (multiplication circuit) 6 addition circuit 7 histogram calculation circuit 8 input / output characteristic calculation circuit

Claims (3)

[Claims] 1. When converting input / output characteristics of an input video signal according to the characteristics of an electronic display, a histogram for the brightness level of the skin color portion of the video by the input video signal is weighted and added to the histogram of the brightness level of the entire video. An average value and a variance are calculated from the histograms obtained together, and data for converting the input / output characteristics of the input video signal is calculated according to the average value and the variance. Video display processing method. 2. A video display processing method for an electronic display, wherein input / output characteristics are converted according to the characteristics of the electronic display, wherein the input video signal is delayed by one field or one frame, while the input video signal is delayed. Of the input video signal, the signal of the detected skin color portion and the detected luminance signal are weighted and added to obtain a signal for each same signal level of the video signal. The number of pixels is counted to create a histogram, the average value and the variance of the created histogram are calculated, and the input / output characteristic data is calculated according to the average value and the variance. A video table of an electronic display, characterized in that the video signal delayed by one field or one frame is converted by using the input / output characteristics. Processing method. 3. A video display processing device for an electronic display, which converts input / output characteristics of an input video signal according to the characteristics of the electronic display, the delay means delaying the input video signal by one field or one frame, and the input. Luminance signal detecting means for detecting a luminance signal of a video signal, flesh color detecting means for detecting a flesh color portion of an image based on the input video signal, weighting means for multiplying a signal of the flesh color portion by a predetermined number, and the detected luminance A logical sum means for adding a signal and the signal of the flesh color portion multiplied by the fixed number, and a histogram calculating means for counting the number of pixels for each same signal level of the video signal by the added signal to calculate a histogram, An input / output characteristic for calculating an average value and a variance of the calculated histogram and calculating input / output characteristic data according to the average value and the variance An electronic display comprising: an output unit and an input / output characteristic conversion unit for converting an input / output characteristic of the video signal delayed by one field or frame by using the input / output characteristic data. Video display processing method.