KR980013454A - Color compensation method and its circuit according to luminance variation - Google Patents

Abstract

A color compensation method and a circuit therefor according to variation in luminance are provided. In the color compensation method, a color component signal is input, a luminance signal changed by a predetermined process on a luminance signal and a luminance signal, And outputs the corrected color component signal by varying the value of the color component signal based on the luminance signal, thereby providing a distortion-free color signal.

Description

Color compensation method and its circuit according to luminance variation

The present invention relates to a color compensation method and a circuit therefor according to luminance variation, and more particularly to a color compensation method for changing a color value according to a luminance change in a system for independently processing a color signal based on luminance processing, . Red, green, and blue (hereinafter referred to as RGB) color processing can be classified into two basic methods. One method is RGB independent color processing and the other is color processing based on luminance (Y) processing. First, FIG. 1 is a block diagram of a color processing circuit for three independent processes for RGB color signals. The RGB color signals are independently processed by the R processor 11, the G processor 12, and the B processor 13 And outputs the resultant color signal R'G'B '. However, most color system applications are typically used to reduce the complexity of the color processing method based on luminance processing. Color processing based on Y allows a given RGB system to convert to a different color system containing Y components. That is, the RGB signals can be converted into various different color signals such as (Y, I, Q), (Y, U, V), (Y, R-Y, B-Y) In the present invention, for example, (Y, U, V) is defined as a color system, where Y is a luminance component and U and V represent system-defined color signals. In general, the relationship between the RGB signal and the new color signal YUV can be expressed by the following equation (1).

[Equation 1]

Here, aij is a coefficient. Fig. 2 is a block diagram of a color processing circuit based on a conventional Y-processing. The converted color signal is subjected to color processing based on Y-processing. 2, the RGB / YUV converter 21 converts the input RGB signal into a YUV signal, and the double Y signal is output as a luminance signal Y 'changed in the Y processor 22. The YUV / RGB converter 23 receives the Y 'signal output from the Y processor 22 and the UV signal output from the RGB / YUV converter 21, and converts the signal into an R'G'B' signal. The resulting RGB signal is obtained by inverse transformation from the (Y, U, V) signal to the (R, G, B) color system by the relationship shown in the following equation (2).

&Quot; (2) "

Therefore, the Y component is changed to Y 'by the Y processor 22 shown in FIG. 2, and the resulting RGB color signal can be expressed by Equation (3).

&Quot; (3) "

Here, in order to prevent unnatural color distortion, a change in the luminance component should be appropriately taken into consideration when the converted signals (Y, U, V) are inversely transformed into (R, G, B) color signals. However, the color processing circuit shown in Fig. 2 has no color compensation function. For example, it is assumed that the color system is composed of Y, R-Y, and B-Y signals, and Y is changed to Y '= Y +? Y by a predetermined process. The changed color signals (Y ', R-Y, B-Y) are changed to (R, G, B) values without color compensation and the resulting color signals are given by the following equations (4) to (6).

&Quot; (4) "

R '= (R - Y) + Y' = R +

&Quot; (5) "

G '= (G-Y) + Y' = G +

&Quot; (6) "

The need for color compensation is evident from this example if we know the next distortion problem when the pure R, G, B signals are taken into account: B '= (B-Y) + Y' = B + That is, when there is no color compensation, when Y changes to Y ', the pure signal (R, 0,0) is mapped to (R + Δy, Δy, Δy), for example. Thus, the resulting color signal is no longer a pure signal. Similarly, if there is no color compensation, all other pure color signals are distorted. This is clearly an unwanted result. A contrast correction method for extracting Y from the input color signals RGB, extracting a correction signal from the extracted Y, and adding a correction signal to each input RGB signal as shown in the above Equations (4) to (6) 5,345, 277, which is incorporated herein by reference.

An object of the present invention is to provide a color compensation method in which, when RGB is processed independently based on luminance processing, the luminance signal is also adapted to change the luminance signal when the luminance is changed. Another object of the present invention is to provide a color compensating circuit that changes the color signal when the luminance is changed when the R, G, and B are independently processed based on luminance processing. In order to achieve the above object, a color compensation method according to the present invention is a method of processing a color signal based on a luminance signal, the method comprising: (a) inputting a color component signal; (b) And (c) outputting the color component signal as the compensated color component signal by varying the value of the color component signal based on the changed luminance signal. . According to another aspect of the present invention, there is provided a circuit for processing a color signal based on a luminance signal, comprising: first conversion means for converting an input RGB signal into a luminance signal and a color component signal; A luminance signal processing unit for inputting the luminance signal, the color component signal and the changed luminance signal, and changing the value of the color component signal according to a luminance change to generate a compensated color signal And second converting means for receiving the changed luminance signal and the compensated color component signal and outputting the resultant color signal (R'G'B ') by inverse transformation, .

1 is a block diagram of a conventional color processing circuit for RGB independent processing.

2 is a block diagram of a color processing circuit based on a conventional Y-process.

FIG. 3 is a view for explaining a color compensation method according to the luminance variation according to the present invention.

4 is a diagram showing a color compensation line for preventing color saturation.

5 is a block diagram according to one embodiment of a color processing circuit based on Y-processing with color compensation according to the present invention.

6 is a detailed circuit diagram of the color compensator shown in FIG.

7 is another detailed circuit diagram of the color compensator shown in FIG.

8 is a block diagram according to another embodiment of a color processing circuit based on Y-processing with color compensation according to the present invention.

First, the color compensation method will be described with reference to FIGS. 3 and 4. FIG. C = (R, G, B) and Y, and Y is changed to Y 'by a predetermined luminance process. The basic idea of the method for color compensation of the present invention is to change a given color from (R, G, B) space to its color direction. First, the plane in Y is Y = a ₁₁ R + a ₁₂ G + a ₁₃ B (R, G, B) can be represented by, having a constant Y values (R, G, B) space from the equation (1) . That _{is, Y = a 11 R + a} 12 G + a 13 every color signal placed on the plane B have the same luminance value. The change in luminance from Y to Y 'implies that a given color C is shifted to the Y' plane as shown in FIG. At this time, in the present invention, it is assumed that C and C 'have the same color direction, which means that the line OC coincides with the line OC'. Thus, the compensated color C 'on the Y' plane is obtained by finding the intersection of the line OC and the Y 'plane. In summary, the original color signal C shown in FIG. 3 is mapped to C 'when the Y plane lies in the Y' plane, which is the intersection of the line OC and the Y 'plane. Now, to find C ', (l, m, n) is defined as the directional cosine of a given color C, which is given by Equation (7).

&Quot; (7) "

l = R / r, m = G / r, n = B / r

here, Similarly, the direction cosines (l ', m', n ') of the output color signal C' = (R ', G', B ') can be expressed as shown in Equation (8).

&Quot; (8) "

l '= R' / r ', m = G' / r ', n' = B '/ r'

here, to be. In order for these two colors to have the same color direction, the following relation (9) or (10) must be established.

&Quot; (9) "

l = l ', m = m', n = n '

&Quot; (10) "

R '/ r' = R / r, G '/ r' = G / r, B '/ r'

&Quot; (11) "

&Quot; (12) "

&Quot; (13) "

Substituting the relation given in the above equations (11), (12) and (13) into Y '= a ₁₁ R' + a ₁₂ G + a ₁₃ B '

&Quot; (14) "

&Quot; (15) "

&Quot; (16) "

This means that the ratio of change of luminance changes to the ratio of change of color, so that color compensation is performed by changing the color value according to the change of luminance. Equation (11) to Equation (13) can be expressed by the following Equations (18) to (20) using the results of Equation (17).

&Quot; (18) "

&Quot; (19) "

&Quot; (20) "

In conclusion, C 'can be obtained as follows.

&Quot; (21) "

C '= (R', G ', B')

&Quot; (22) "

= (kR, kG, kB)

Where k = Y '/ Y, which is the ratio between the original luminance signal and the resulting luminance signal. Using the result of Equation (22), color compensation of other color systems can be easily performed. That is, for example, a given (Y, U, V) signal should be converted to (kY, kU, kV) as shown in the following equations 22 to 28 as a result of the color compensation given in equation do.

&Quot; (23) "

U '= a ₂₁ R' + a ₂₂ G '+ a ₂₃ B'

&Quot; (24) "

_{= K (a 21 R + a} 22 G + a 23 B)

&Quot; (25) "

= kU

And,

&Quot; (26) "

V '= a ₃₁ R' + a ₃₂ G '+ a ₃₃ B'

&Quot; (27) "

k (a ₃₁ R + a ₃₂ G + a ₃₃ B)

&Quot; (28) "

= kV

Now, in order to prevent color saturation by the above-described color compensation method, the following assumption of color compensation is further considered. The luminance ratio is given by k. When the color compensation is performed by the compensation lines (R ', G', B ') = k (R, G, B) shown in FIG. 4, And the maximum (Max) level is compensated with the maximum value Max, which implies saturation. This is because the color between b and Max is mapped to Max as a result of the above-described correction method and can not be distinguished from each other. In order to prevent this color saturation, a compensation line for a color between a (= lb) level and a maximum (Max) level is set as a compensation line (R, G ', B' ', G', B ') = A (R, G, B) + K. Here, 0 1, which can be expressed as A, (29), and (30).

&Quot; (29) "

And,

&Quot; (30) "

The color compensation circuit for performing the above color compensation method will be described with reference to FIGS. 5 to 7. FIG.

FIG. 5 is a block diagram of a color processing circuit based on Y-processing with color compensation according to the present invention, in which a change made in Y is input to the other color components U and V as feeds.

In Fig. 5, the RGB / YUV converter 31 converts the input RGB signal into YUV. The Y processor 32 converts the Y signal output from the RGB / YUV converter 31 into Y 'by a predetermined process and feeds back the Y signal to the color compensator 33. Here, the predetermined processing may be a contrast enhancement using a histogram equalization, a noise reduction, a gain control, or the like as a process for improving a video signal adapted to a screen.

The color compensator 33 receives the YUV signal output from the RGB / YUV converter 31 and the Y 'signal output from the Y processor 32, and changes the UV signal according to the Y change to output the U V' signal.

The YUV / RGB converter 34 receives the Y 'signal output from the Y processor 32 and the U' V signal output from the color compensator 33 and outputs the resulting color signals R ', G', B ').

FIG. 6 is a detailed circuit diagram of the color compensator 33 shown in FIG.

6, the operator 33.1 calculates a ratio (k) between Y signal output from the RGB / YUV converter 31 and Y 'signal output from the Y processor 32, that is, Y' / Y do. The first multiplier 33.2 multiplies the U signal output from the RGB / YUV converter 31 by the ratio k output from the computing unit 33.1 and outputs a U 'signal. The second multiplier 33.3 multiplies the V signal output from the RGB / YUV converter 31 by the ratio k output from the calculator 33.1 and outputs the V 'signal.

FIG. 7 is another detailed circuit diagram of the color compensator 33 shown in FIG.

7, the operator 33.4 calculates a ratio (k) between Y signal outputted from the RGB / YUV converter 31 of FIG. 5 and Y 'signal outputted from the Y processor 32, that is, Y' / Y do. The first approximation adjuster 33.5 and the second approximation adjuster 33.6 are for preventing color saturation with the approximated compensating line shown in FIG.

The first approximate value adjuster 33.5 inputs the U signal output from the RGB / YUV converter 31 of FIG. 5, the ratio k output from the operator 33.4, and the parameter 1, The U 'signal compensated by the compensation lines (R', G and B ') = k (R, G, B) is output from the minimum level to the a (= lb) And outputs the U 'signal compensated by the approximated compensation lines (R', G ', B') = A (R, G, B) + K.

G ', B') = k (R, G, B) according to the value of the parameter l and the compensated lines R ', G' ') = A (R, G, B) + K. That is, if l = 1, compensation is performed by the compensation lines R ', G', B '= k (R, G, B) (R ', G', B ') = k (R, G, B) from the minimum level to the a (R, G, B) = A (R, G, B) + K from the a level to the maximum level.

The second approximate value adjuster 33.6 receives the V signal output from the RGB / YUV converter 31, the ratio k output from the calculator 33.4, and the parameter 1 to the compensation line R G ', B') = k (R, G, B) = k (R, G, B) ) = A (R, G, B) + K.

8 is a circuit diagram according to another embodiment of the color processing circuit based on the Y-process with color compensation according to the present invention. The R, G, and B signals according to the Y- Circuit diagram for implementing the compensation method.

8, the matrix circuit 41 extracts the Y signal from the input RGB signal. The Y processor 42 converts the Y signal output from the matrix circuit 41 into Y 'by a predetermined process.

The arithmetic unit 43.1 of the color compensator 43 calculates the ratio k between the Y signal output from the matrix circuit 41 and the Y 'signal output from the Y processor 42, that is, Y' / Y.

The first to third multipliers 43.2-43.4 multiply the input RGB color signals by the ratio k output from the operator 43.1 to output the output color signal R 'G' B '.

Here, the color compensator 43 may be constituted by an approximation adjuster as shown in FIG. 7 instead of the multiplier.

The color compensation method and its circuit of the present invention can provide a distortion-free color signal by changing a color value according to a change in luminance when a color signal is processed based on luminance processing.

Claims (32)

A method of processing a color signal based on a luminance signal, the method comprising: (a) inputting a color component signal; (b) inputting a luminance signal changed by a predetermined process on the luminance signal and the luminance signal; And (c) outputting the color component signal as a compensated color component signal by varying the value of the color component signal based on the changed luminance signal. The method of claim 1, wherein the compensated color component signal changes in the same direction as the input color component signal. 2. The method of claim 1, wherein the changed luminance signal forms a plane in a color signal space, and the luminance values of all color signals in a formed luminance plane are the same. 4. The color compensation method of claim 3, wherein the compensated color component signal is obtained by an intersection of a line connecting the direction of the input color component signal and a changed luminance plane. A method of processing a color signal based on a luminance signal, comprising the steps of: (a) converting an input RGB signal into a luminance signal and a color component signal; (b) outputting the luminance signal changed by a predetermined process (C) outputting the compensated color component signal by varying the value of the color component signal based on the changed luminance signal, and (d) outputting the corrected luminance component signal and the compensated color component And outputting the resulting color signal (R'G'B '). 6. The method of claim 5, wherein the RGB signals are converted into Y, U, and V signals in step (a). 6. The color compensation method of claim 5, wherein in step (a), the input RGB signals are converted into Y, R-Y, and B-Y signals. 6. The color compensation method of claim 5, wherein the RGB signals are converted into Y, I, and Q signals in step (a). 6. The method of claim 5, wherein the compensated color component signal changes in the same direction as the input color component signal. 6. The method of claim 5, wherein the changed luminance signal forms a plane in the RGB space, and the luminance values of all the color signals in the formed luminance plane are the same. 11. The method of claim 10, wherein the compensated color component signal is obtained by an intersection of a modified luminance plane and a compensating line connecting the direction of the input color component signal. 12. The method of claim 11, wherein when the ratio of the input luminance signal and the changed luminance signal is given as k, the compensation line is given by: (R ', G', B ') = k (R, G, B) 12. The method of claim 11, wherein when the ratio of the input luminance signal and the changed luminance signal is given as k, the compensation line is given as follows. (R ', G', B ') = A (R, G, B) + K A method of processing a color signal based on a luminance signal, comprising the steps of: (a) extracting a luminance signal from an input RGB signal; (b) outputting a luminance signal changed by a predetermined processing of the luminance signal; and (c) changing the value of the input RGB signal based on the converted luminance signal to output the compensated RGB signal. 15. The method of claim 14, wherein the compensated RGB signal changes in the same direction as the input RGB signal. 15. The method of claim 14, wherein the changed luminance signal forms a plane in the RGB space, and the luminance values of all the color signals in the formed luminance plane are the same. 17. The method of claim 16, wherein the compensated RGB signal is obtained by an intersection of a compensated line connecting the direction of the input RGB signal and a changed luminance plane. 18. The method of claim 17, wherein when the ratio of the input luminance signal to the changed luminance signal is given as k, the compensation line is given by: (R ', G', B ') = k (R, G, B) 18. The method of claim 17, wherein when the ratio of the input luminance signal and the changed luminance signal is given by k, the compensation line is given by: (R ', G', B ') = A (R, G, B) + K A circuit for processing a color signal based on a luminance signal, comprising: first conversion means for converting an input RGB signal into a luminance signal and a color component signal; a first conversion means for converting the luminance signal into a luminance signal for outputting a luminance signal changed by a predetermined luminance process A color compensation means for receiving the luminance signal, the color component signal and the changed luminance signal to output a corrected color component signal by varying a value of a color component signal according to a luminance change; And a second conversion means for receiving the color component signal and outputting the resultant color signal (R'G'B) by inverse transformation. 21. The color compensation circuit according to claim 20, wherein the first conversion means converts the input RGB signals into Y, Y, and V signals. 21. The color compensation circuit according to claim 20, wherein the first conversion means converts the input RGB signals into Y, R-Y, and B-Y signals. 21. The color compensation circuit according to claim 20, wherein the first conversion means converts the input RGB signals into Y, I, Q signals. The image processing apparatus according to claim 20, wherein the color compensating means comprises arithmetic means for calculating a ratio between a luminance signal output from the first converting means and a luminance signal output from the luminance processing means, And a multiplier for multiplying a component signal by a ratio output from said calculating means and outputting the compensated color component signal. The image processing apparatus according to claim 24, wherein the color compensating means comprises arithmetic means for calculating a ratio between a luminance signal outputted from the first converting means and a luminance signal changed from the luminance processing means, And adjusting means for receiving the component signal and the ratio output from the calculating means and outputting the compensated color component signal by varying the value of the color component signal by a predetermined compensation line. 26. The color compensation circuit of claim 25, wherein when the ratio of the input luminance signal and the changed luminance signal is given as k, the compensation line is given by: (R ', G', B ') = k (R, G, B) 26. The color compensation circuit of claim 25, wherein when the ratio of the input luminance signal and the changed luminance signal is given as k, the compensation line is given by: (R ', G', B ') = A (R, G, B) + K A circuit for processing a color signal based on a luminance signal, comprising: a matrix circuit for extracting a luminance signal from an input RGB signal; luminance processing means for outputting a luminance signal changed by a predetermined process on the luminance signal; And color compensating means for varying the value of the RGB signal based on the changed luminance signal to output the compensated RGB signal. The image processing apparatus according to claim 28, wherein the color compensating means comprises arithmetic means for calculating a ratio between a luminance signal outputted from the matrix circuit and a luminance signal changed from the luminance processing means, And a multiplier for multiplying each of the output ratios and outputting the compensated RGB signals. The image processing apparatus according to claim 28, wherein the color compensating means comprises arithmetic means for arithmetically operating a ratio between a luminance signal output from the matrix circuit and a luminance signal output from the luminance processing means, And an adjusting unit for changing the value of the input RGB signal and outputting the compensated RGB signal by the compensation line of the color compensating circuit. 31. The circuit of claim 30, wherein when the ratio of the input luminance signal to the modified luma / non-signal is given as k, the compensation line is given by: (R ', G', B) = k (R, G, B) 31. The method of claim 30, wherein when a ratio of the input luminance signal to the changed luminance signal is given as k, a compensation line is given as follows. (R ', G', B) = A (R, G, B) + K ※ Note: It is disclosed by the contents of the first application.