KR20060074932A - Image contrast improvement apparatus and the method thereof - Google Patents

Abstract

The present invention relates to a device for improving image contrast and a method thereof, wherein the input image has a function characteristic of DeGamma before the black / white stretching, and the input / output mapping function uses the reference value for applying the stretching without a complicated slope calculation method. It is intended to provide a method to improve contrast by applying RGB according to an image to have a color component of pure color so that the RGB component corresponding to the luminance component locked to black does not lose its own color.

Contrast, degamma, black / white stretching, tilt

Description

Image contrast improvement apparatus and method

1 is a block diagram illustrating an embodiment of a conventional black / white stretching system;

2 is a view for explaining a black / white stretching process by the system,

3 is a block diagram illustrating an embodiment of the black / white stretching system of the present invention;

4 is a detailed view of the black / white stretching system,

And,

5 is a diagram illustrating an input / output characteristic graph for each step of the present invention.

* Description of symbols on the main parts of the drawings *

110: degamma part 120: YCbCr conversion part

130: B / W stretching unit 132: calculating unit

134: slope calculation unit 136: stretching unit

140: RGB conversion unit 150: Gamma unit

The present invention relates to an image signal processing system, and more particularly, to an apparatus and a method for preventing the loss of color components occurring when the contrast of luminance is improved in a color image.

In general, the dynamic range of the level of the input video signal is smaller than the hardware range for the video signal processing provided in the video signal processing system, and the black / white stretching system is configured to distribute the video signal smaller than the hardware range. A system that increases resolution by stretching the dynamic range of levels closer to the hardware range.

1 and 2 show this conventional black / white stretching system. FIG. 1 is a block diagram illustrating an embodiment of a black / white stretching system, and FIG. 2 is a view for explaining a black / white stretching process by the system shown in FIG.

As shown in the drawing, the black / white stretching system includes a histogram distribution unit 11, a histogram information calculating unit 13, an average calculating unit 15, a gradient calculating unit 17, a coefficient calculating unit 19, It has the filter part 21 and the stretch part 23.

In the histogram distribution calculation unit 11, the histogram distribution of the input video signal Yin in a predetermined unit, that is, the histogram distribution H (i) _P of the previous video signal and the histogram distribution H (i) of the current video signal. _C ) is calculated and the sum of the gray levels of the entire input image signal and the total number of pixels, and the maximum level Max and the minimum level Min of the input image signal are detected in the histogram distribution calculation process.

The average calculating unit 15 calculates an average level Mean of the input image signal by using the sum of the total gray levels of the input image signal detected by the histogram distribution unit 11 and the total number of pixels.

The slope calculating unit 17 first calculates the black / white stretching points L _B and U _W linked to the average level Mean using the average level Mean and the preset stretching points L and U, respectively. do.

In addition, the minimum level Min and the maximum level Max of the input image signal detected by the histogram distribution unit 11 and the black / white stretching points L _B and U _W calculated by the gradient calculation unit 17 are also included. ) Is used to calculate the black / white stretching slopes SL _B and SL _W.

On the other hand, in the histogram information calculating section 13, the histogram distribution H (i) _C of the current input video signal calculated by the histogram distribution calculating section 11 and the histogram distribution H (i) _P of the previous input video signal. The histo information data Diff_histo is calculated using the following formula, and the ratio calculating section 19 uses the histo information data Diff_histo calculated by the histo information calculating section 13 to calculate the change ratio (Coeff: coefficient). To calculate.

Here, the histo information data (Diff_histo) is calculated using the low gray level part in the case of black stretching, rather than using the total gray level of the input video signal, and uses the high gray level part in the case of white stretching. Calculate.

Thereafter, the filtering unit 21 filters the black / white stretching slopes SL _B and SL _W corresponding to the change ratio Coeff of the screen calculated by the ratio calculating unit 19 to filter the filtered black / white stretching slopes. Outputs (F_SL _W and F_SL _B ).

The stretching unit 23 maps the filtered black stretching slope F_SL _B and the white stretching slope F_SL _W to the input image signal according to the degree of change of the screen, respectively, to the hardware range of the gray level range of the input image signal. Configured to stretch.

As described above, a method of increasing the contrast by converting the low luminance value to 0 and the high luminance value to 1 may change the luminance component to increase the contrast, but in the process, a unique color composed of RGB The ingredients are lost.

That is, a problem occurs in that the image appears black due to the loss of the color value of the black-locked part, and the method of calculating the black / white stretching slopes SL _B and SL _W is complicated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and to provide a method of simply improving the contrast without losing color components by using a method of converting a nonlinear RGB of an input image into a linear RGB.

A method for improving image contrast by using black white stretching according to the present invention for achieving the above object is characterized by using a linear RGB value degammaed the input video signal as the input signal of the black white stretch. And input the luminance signal corresponding to the degamma RGB value as the input signal of the black white stretch.

The black white stretching method may be configured to map the gray stretching slope min'_Tilt and the white stretching tilt max'_Tilt with the input image signal to stretch the gray level range of the input image signal to the hardware range, respectively. do.

The black stretching slope (min'_Tilt) and the white stretching slope (max'_Tilt) are represented by the following equations, respectively.

min'_Tilt = (mean-min ') / 2 + min'

max'_Tilt = (max'-mean) / 2 + mean

Where max 'and min' are the maximum and minimum levels of the degammaed input video signal, and mean is the average level of the input video signal using the sum of the total gray levels of the input video signal and the total number of pixels.

An apparatus for improving image contrast using black white stretching according to the present invention for achieving the above object is a degamma unit for converting an input image signal into a degamma linear RGB value, the degamma linear RGB value The gray level range of the input image signal into the hardware range by mapping the luminance signal conversion unit, black stretching slope (min'_Tilt), and white stretching slope (max'_Tilt) to the input image signal, respectively. A black white stretching unit for outputting a stretched signal, an RGB converter for converting the luminance signal converted for the black white stretching into an RGB value, and a gamma for converting the output signal of the RGB converter into a gamma nonlinear RGB value It should be configured to include a wealth.

The black stretching slope (min'_Tilt) and the white stretching slope (max'_Tilt) are expressed as follows.

min'_Tilt = (mean-min ') / 2 + min'

max'_Tilt = (max'-mean) / 2 + mean

Where max 'and min' are the maximum and minimum levels of the degammaed input video signal, and mean is the average level of the input video signal using the sum of the total gray levels of the input video signal and the total number of pixels.

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

3 is a block diagram showing an embodiment of the black / white stretching system of the present invention, in which a degamma unit 110 and an R'G'B 'to YCbCr converter converting R'G'B' into a composite video signal. 120, a B / W stretching unit 130, an R'G'B 'conversion unit 140 for converting a composite video signal into RGB, and a Gamma unit 150.

Since the image displayed on the monitor is a nonlinear RGB in which gamma correction is performed by 0.45 powers of the linear RGB value, the degamma image 110 is degammed by 2.22 of the input image 112 to have a linear RGB value. (122), it is configured to output R'G'B '. Referring to FIG. 5, a degammed image 122 is shown compared to an input image 112. In the present invention, degammed RGB is referred to as R'G'B '.

The R'G'B 'to YCbCr converter 120 includes a luminance signal converter for converting an RGB signal into a luminance signal. That is, the luminance of the YCrCb image, which is a composite signal corresponding to the R'G'B 'image of the degammed image 122 output from the degamma unit 110, for black / white stretching Convert it to a signal and output it.

The B / W stretching unit 130 stretches the gray level range of the input image signal to the hardware range by mapping the black / white stretching slope and the input image signal using the minimum level, the maximum level, and the average value of the input image signal. It is configured to.

A detailed structure of the B / W stretching unit 130 will be described with reference to FIG. 4. The B / W stretching unit 130 is composed of a calculating unit 132 that calculates a maximum / minimum value and an average value, a slope calculating unit 134, and a stretching unit 136 (see FIG. 4). The calculation unit 132 calculates an average level of the input image signal by using the sum of the maximum level max 'and minimum level min' of the input image signal and the total gray levels of the input image signal and the total number of pixels. ) Is calculated. In the following description, the maximum and minimum levels of the degammed image are represented by max 'and min', respectively, in order to distinguish them from the conventional maximum level max and minimum level min. The slope calculator 134 uses the max ', min', and mean values output from the calculator 132 to determine the stretch range according to the image characteristic when the black white stretch is applied. '_Tilt value is obtained by adaptive method as follows.

min'_Tilt = (mean-min ') / 2 + min'

max'_Tilt = (max'-mean) / 2 + mean

As in the above equation, min'_Tilt and max'_Tilt are intermediate values between mean values of images and min 'and max' values. As a result, min'_Tilt and max'_Tilt are adaptively determined according to the luminance characteristics of the image. Therefore, the slope of min 'and min'_Tilt has the characteristic characteristic of DeGamma because the input / output mapping function has the function characteristic of DeGamma without the complicated slope calculation method, which results in the natural contrast improvement. The BWS algorithm is applied in the stretching unit 136 using the determined threshold value.

The stretching unit 136 maps the black stretching slope min'_Tilt and the white stretching slope max'_Tilt to the input image signal in response to the degree of change of the screen in the gradient calculator 134 and the gray of the input image signal. It is configured to stretch the level range to the hardware range respectively. As a result, an enhanced image 132 is improved (see FIG. 5).

Referring to FIG. 5, when the BWS is applied as in the related art, the RGB component of the luminance portion that is locked with black is composed of values of R of 30%, G of 60%, and B of 10%, respectively. The RGB of luminance will have a larger range of Color components equal to zero. Therefore, the original color is lost and the color of this part becomes close to black. To improve this, the front end DeGamma processing is applied before applying BWS.

In the linear input / output mapping relationship, the input and output values are the same, but the input / output function characteristics of DeGamma are very small compared to the input values, and the output and input values become similar to the larger input value part, which becomes 255 at 255. This means, for example, if a pixel consists of a large value of R and a small value of G or B, it looks red in the eye, and if B / W Stretching is applied, then R is a large value, so the DeGamma Mapping function Although the value is slightly reduced by the characteristic, the values of G and B are small, so the values are much smaller and are converted into pure R components without G and B. Therefore, although the value is lower due to B / W stretching than the original R (min '), it is made clearer by being composed of pure R components. In other words, even in the case of green and blue colors, other color components are mixed so that the color becomes clearer because only the largest color component is left and the remaining color values are almost 0.

On the other hand, if two values among the RGB components are high and one value is not low, that is, for example, a yellow color with high luminance, the B value does not become very small even through DeGamma. If the B value is included in the max'_Tilt value or more, the value becomes larger and becomes closer to white. Therefore, max 'should be made smaller than the existing BWS.

The R'G'B 'converter 140 restores and outputs a YCrCb image, which is a converted composite signal, to R'G'B "for B / W stretching.

In addition, the gamma unit 150 multiplies the converted linear R'G'B 'value by 0.45 to have a non-linear RGB value for B / W stretching the image output from the R'G'B' conversion unit 140. It is configured to output the gamma correction as much as possible so that the image suitable for the visual characteristics can be seen on the display.

Therefore, it is possible to prevent the loss of color components that occur when improving the contrast of the luminance in the color image, thereby realizing the optimum contrast effect.

While the invention has been described in detail only with respect to the described embodiments, it will be apparent to those skilled in the art that various modifications and variations are possible within the spirit of the invention, and such modifications and variations belong to the appended claims.

As described above, according to the apparatus and method for improving image contrast according to the present invention, by applying a reference value for applying stretching according to an image, it is possible to improve contrast reflecting image characteristics, and by applying an algorithm using DeGamma. It has a color component of pure color, so that the RGB component corresponding to the luminance component that is locked with black does not lose its own color and can be prevented from appearing black.

Claims (5)

 In a method for improving image contrast using black white stretching, And a linear RGB value obtained by degammaing an input video signal as the input signal of the black white stretch. The method of claim 1, The black white stretching method And mapping the black stretching slope (min'_Tilt) and the white stretching slope (max'_Tilt) to the input video signal so as to stretch the gray level range of the input video signal to the hardware range, respectively. The method of claim 2, The black stretching slope (min'_Tilt) and the white stretching slope (max'_Tilt) are represented by the following equations. min'_Tilt = (mean-min ') / 2 + min' max'_Tilt = (max'-mean) / 2 + mean Where max 'and min' are the maximum and minimum levels of the degammaed input video signal, and mean is the average level of the input video signal using the sum of the total gray levels of the input video signal and the total number of pixels. An apparatus for improving image contrast using black white stretching, A degamma unit for converting an input video signal into a degammaed linear RGB value; A luminance signal converting unit converting the degamma linear RGB value into a luminance signal; A black white stretching unit for outputting a signal obtained by stretching the gray level range of the input image signal into a hardware range by mapping the black stretching slope min'_Tilt and the white stretching slope max'_Tilt to the input image signal; An RGB converting unit converting the converted luminance signal to an RGB value to perform the black white stretching; And And a gamma part for converting the output signal of the RGB converter into a gamma nonlinear RGB value. The method of claim 4, wherein The black stretching slope (min'_Tilt) and the white stretching slope (max'_Tilt) are represented by the following equations. min'_Tilt = (mean-min ') / 2 + min' max'_Tilt = (max'-mean) / 2 + mean Where max 'and min' are the maximum and minimum levels of the degammaed input video signal, and mean is the average level of the input video signal using the sum of the total gray levels of the input video signal and the total number of pixels.

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