JP2001169132A - Method and circuit for color correction - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a circuit for color correction, which correct only the saturation (color development) of only a specific color, without breaking the color temperature (white balance) of a black-and-white signal (a signal in a state of no color components) neither changing the hue, while leaving three primary color signal as they are. SOLUTION: This color correction circuit has inputs of three primary color signals and is provided with a comparison means which discriminates which of two input signals is the larger, a subtraction means which generates a difference signal between the input signal discriminated as a larger signal by the comparison means and the other input signal, an operation means for color which operates a color correction coefficient on the basis of this difference signal, a color correction value calculation means which generates a color correction value according to the input signal discriminated as a smaller signal by the comparison means and the color correction coefficients, and a correction means for color, which corrects three input signals on the basis of the color correction value from the color correction value calculation means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a color correction circuit and a color correction method, and more particularly to a color correction circuit and a color correction method for correcting color saturation.

[0002]

2. Description of the Related Art When the color temperature of a video signal to be displayed differs from that of a display device, the video signal is displayed differently from the original color of the video signal. For example, in a liquid crystal display device in which the white temperature of a backlight of a light source or a display liquid crystal panel is set to 6500 °, NTS having a white temperature of 9300 ° is used.
When displaying the C signal, it is displayed differently from the original color of the NTSC signal.

A liquid crystal display device has a narrower color reproduction range than a CRT display device. Therefore, when a video signal such as an NTSC signal is displayed, the color of the signal is different from the original color of the signal.

Further, in order to increase the apparent white radiance of a display device (for example, a CRT display, a liquid crystal display, etc.), the display (for example, an NTSC signal, an HDTV signal, etc.) must have a display temperature higher than the original color temperature. When setting the color temperature, for example, an NTSC signal having a white temperature of 9300 °
When the color temperature of the color display of the RT display is displayed at 11500 °, the color differs from the original color of the NTSC signal.

In order to solve this problem, conventionally, when a display device and a signal to be displayed have different color temperatures, a device for processing a display device or an input signal at the time of a black and white signal (a signal having no color component). (Eg, NTSC signal decoder)
The color temperature (white balance) on the display is changed to the original color temperature of the signal by changing the degree of amplification of each of the amplifiers for amplifying the three primary color signals. As for the display of a signal having a color component, a device for processing an input signal adjusts the color display by changing the hue and the color density of the color component.

Also, in order to increase the apparent white shine,
When the color temperature is changed, a method of changing the demodulation angle, color tone, and color density for demodulating the color signal from the carrier color signal by a signal processing device (for example, an NTSC signal decoder or the like) is known. Has been adopted.

As described above, the conventional color correction circuit adjusts the color temperature by changing the degree of amplification of each of the amplifiers for amplifying the three primary color signals. It was to change the hue and color depth.

As a conventional example, in achromatic data, high-speed calculation is performed by using a color correction coefficient as an m × n matrix coefficient without changing data before and after color correction and without changing luminance before and after color correction. Japanese Unexamined Patent Publication No. Hei 11-17974 and Japanese Unexamined Patent Publication No. Hei 10-313465, which describe that a video signal processing device for a medical endoscope performs color correction with little change in luminance.
And Japanese Patent Application Laid-Open No. 5-328113, in which the R, G, and B spaces are divided into cubes and divided into six tetrahedrons to generate YMCK color correction signals. However, none of the publications describes color correction in consideration of the color temperature.

[0009]

However, the conventional color correction circuit has the following problems.

That is, as a first point, even if the color temperature at the time of a black-and-white signal (a signal without a color component) is changed to change the hue or the color density, the original color cannot be reproduced. Depending on the set value of the color temperature, the coloring of a specific color deteriorates. That is, the display of the color temperature at the time of a black-and-white signal (a signal having no color component) can be accurately performed, but the color reproduction range in a specific color direction is narrowed. In order to change the color temperature by changing the size of the three primary colors, the size of the three primary colors is originally 1: 1: 1 for a black and white signal, but the color temperature is changed by intentionally changing the balance. . Since a strong signal (large signal) and a weak signal (small signal) are generated among the three primary colors, the magnitude at which the weak signal (small signal) can be changed is narrowed, so that the color reproduction range is narrowed and color development is deteriorated.

Second, for example, in a liquid crystal display device, even if the color temperature at the time of a black and white signal (a signal without a color component) can be changed by a liquid crystal panel or an input signal, a backlight of a light source is not used. The color temperature cannot be changed. For this reason, the coloring of a specific color deteriorates.

Third, since a display device for a computer such as a liquid crystal display device has only inputs of three primary color signals, it is difficult to change the hue and color density.
In order to change the hue and the color density, a complicated and large circuit is required, for example, by converting the three primary color signals into another spatial signal.

[Object of the Invention] Therefore, when the color temperature is changed, the color temperature of a black-and-white signal (a signal having no color component) can be accurately reproduced, but the saturation of a specific color also changes. .

An object of the present invention is to provide three primary color signals,
A color correction circuit capable of correcting only the saturation (coloring) of a specific color without changing the color temperature (white balance) of a black-and-white signal (signal having no color component) and without changing the hue. It is intended to provide a correction method.

[0015]

The present invention employs the following new characteristic constitution means in order to solve the above-mentioned problems. That is, a first feature of the method of the present invention is that, in a color correction circuit having three primary color signal inputs, a comparison means for determining the magnitude of two input signals, and an input signal determined to be large by the comparison means. Subtraction means for generating a difference signal from the remaining one input signal; color calculation means for calculating a color correction coefficient based on the difference signal; and an input signal determined to be small by the comparison means and the color correction coefficient. A color correction circuit comprising: a color correction value calculation unit that calculates a color correction value; and a color correction unit that corrects three input signals based on the color correction values from the color correction value calculation unit. .

According to a second feature of the method of the present invention, the color calculating means includes a subtracting means capable of subtracting a fixed value and a subtraction result of 0.
A color correction circuit comprising means for setting the above positive value, means for externally controlling the strength of color correction, and means for setting the maximum value of the coefficient to 1.

According to a third feature of the method of the present invention, in the color correction circuit, extracting means for extracting a luminance component from three input signals, and calculating a luminance correction coefficient from the luminance component of the extracting means and the color correction value. A color correction circuit, further comprising: a luminance calculating means for correcting the three input signals based on the luminance correction coefficient from the luminance calculating means.

A fourth feature of the apparatus according to the present invention is that, in a color correction method having three primary color signal inputs, a comparing step of determining the magnitude of two input signals, and an input signal determined to be large in the comparing step. Subtracting a difference signal between the input signal and the remaining one input signal; calculating a color correction coefficient based on the difference signal; an input signal determined to be small in the comparing step; and the color correction coefficient A color correction value calculating step of generating a color correction value from the color correction value, a color correcting step of correcting three input signals based on the color correction values from the color correction value calculating step, and extracting a luminance component from the three input signals. An extracting step, a luminance calculating step of calculating a luminance correction coefficient from the luminance component and the color correction value of the extracting step, and a luminance correcting step of correcting three input signals based on the luminance correction coefficient from the luminance calculating step. Correction process A color correction method characterized by.

[Operation] As a result, the color correction coefficient of the black-and-white signal (signal having no color component) becomes 0, and the color correction coefficient is generated only when correcting a color in a specific direction. Therefore, the color temperature (white balance) of a black-and-white signal (a signal having no color component) is not degraded, the hue does not change, and only the saturation (coloring) of a specific color is corrected. The color reproduction range in a specific color direction can be expanded.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described.
This will be described with reference to the drawings.

First Embodiment (1) Description of Configuration A color correction circuit according to a first embodiment of the present invention will be described in detail.

FIG. 1 is a configuration diagram of a color correction circuit and a color correction method according to the first embodiment, FIG. 2 is a configuration diagram and an operation characteristic diagram of a color correction coefficient calculation unit according to the present embodiment, and FIG. FIG. 3 is an operation conceptual diagram of a correction circuit and a color correction method.

In FIG. 1, R (red), G (green), and B (blue) signals, which are three primary color signals, are input to input units 1, 2, and 3, respectively. The comparator 4 is connected to the input units 2 and 3, and outputs a larger one of the two input signals to the terminal a and a smaller one to the terminal b as a result of the comparison between the two input signals. The subtractor 5 is connected to the input unit 1 and the large signal output terminal a of the comparator 4. The signal of the comparator 4 is subtracted from the signal of the input unit 1 to obtain a difference signal, for example, (input unit 1-
Output the input unit 2).

The color correction coefficient calculating section 7 is connected to the subtractor 5 and receives a correction amount control signal 6 from outside. The color correction coefficient calculation unit 7 performs subtraction processing, half-wave rectification processing, multiplication processing for control amount adjustment, and standardization of coefficients on the difference signal from the subtracter 5, and outputs coefficients. The multiplier 8 is connected to the color correction coefficient calculator 7 and the small signal output b terminal of the comparator 4, and multiplies the signal of the comparator 4, for example, the signal of the input unit 3 by the coefficient of the color correction coefficient calculator 7. Output the color correction values. The subtractors 9, 10, 11 are connected to the multiplier 8 and the input units 1, 2, 3, and subtract the color correction value of the multiplier 8 from the input signal. The subtracted value is used as a corrected signal in the output unit 1.
2, 13 and 14 are output as R ', G' and B '.

FIG. 2 is a configuration diagram and an operation characteristic diagram of the color correction coefficient calculating section 7 of the present embodiment. The input difference signal from the subtractor 5 is input to the subtractor 21. The output characteristic at point c in FIG. 2 is a straight line characteristic passing through the zero point of input and output. The subtracter 21 subtracts a fixed value 20 determined by a range not to operate from the difference signal. Subtraction result is fixed value 20
As a result of the subtraction, the characteristic at point d in FIG. 2 is obtained.
The result of the subtraction is input to the half-wave rectifier 22, is set to a value of 0 or more, and is output to the multiplier 23. The output of the multiplier 23 has a characteristic that rises from the fixed value of the input as point e in FIG. The multiplier 23 obtains a value equivalent to a value obtained by multiplying the input signal by the external correction amount control signal 6 by controlling the degree of amplification for changing the correction amount of the color correction by the external correction amount control signal 6. 25.

The limiter 25 in the coefficient standardizing section 24 prevents the amplified coefficient from exceeding the maximum value of the assumed difference signal. After that, it is input to the multiplier 26. The multiplier 26 multiplies the reciprocal 27 of the assumed maximum value of the difference signal and outputs the result as a color correction coefficient. This correction coefficient is a characteristic limited to 1 which is limited by the limiter 25 of the output characteristic at the point f in FIG.

(2) Description of Operation The operation of the color correction circuit according to the first embodiment of the present invention will be described with reference to the drawings. Here, it is assumed that an R (red) signal of the three primary color signals is input to the input unit 1, a G (green) signal is input to the input unit 2, and a B (blue) signal is input to the input unit 3. Although not shown, a display unit (for example, an LCD display) is provided at a subsequent stage of the output units 12, 13, and 14, and in this display, color reproduction in the R direction is poor. is there.

In FIG. 1, first, the G signal and the B signal input from the input units 2 and 3 are compared in magnitude by a comparator 4. Here, it is assumed that the G signal is larger than the B signal (G signal
Signal> B signal). As a result of the comparison by the comparator 4, the G signal is output to the subtractor 5 through the terminal a of the comparator 4. The B signal is output to the multiplier 8 through the b terminal. The subtractor 5 subtracts the G signal determined to be larger by the comparator 4 from the R signal input from the input unit 1 to calculate a difference signal (difference signal = R signal−G signal). This difference signal is input to the color correction coefficient calculation unit 7 and becomes the characteristic at point f in FIG.
It is output as a color correction coefficient of 0 or a positive value. The color correction coefficient is sent to the multiplier 8 and multiplied by the B signal determined to be small by the comparator 4 to calculate a correction value (correction value = color correction coefficient × B signal).

The corrected values are subtracted from the signals R, G, and B input from the input units 1, 2, and 3 by the subtracters 9, 10, and 11 to obtain the corrected signals R 'and G. ′,
The B ′ signal is calculated and output to the output units 12, 13, 14.

Accordingly, the respective outputs in this case are: R 'signal = R signal-correction value, G' signal = G signal-correction value, B 'signal = B signal-correction value.

Here, the color correction coefficient output from the color correction coefficient calculating section 7 is a value of 1 or less, and becomes a value of 0 unless R signal> G signal. Since the G signal> B signal, if a correction value is generated, the B signal is the minimum value. The correction value is
Since the signal of the minimum value is a value obtained by multiplying the signal by a color correction coefficient of 1 or less, the result of subtracting this value is always a positive value, and therefore does not become a negative value that is not necessary as a signal. In addition, since the relationship of R signal> G signal> B signal is satisfied, subtracting the same correction value from each of the R, G, and B signals means that the largest signal is the G signal and the B signal. The ratio of subtraction is lower than that of. As a result, the ratio of the R signal to the G and B signals increases, and the saturation can be corrected. Further, when the coordinates on the CIE chromaticity diagram are obtained from the values of the R, G, and B signals, and the angle with respect to the coordinates of white is obtained, it is understood that there is no change before and after the correction. This means that the hue has not changed.

FIG. 3 is a conceptual diagram of the operation of the color correction circuit and the color correction method according to the present embodiment. The graph shows a CIE chromaticity diagram. By the operation of the present embodiment, a signal having coordinates such as point X can be corrected to point Y which is an extension of a line connecting the white coordinates and the coordinates of point X. This means that only the saturation can be corrected without changing the hue.

FIG. 2 is a configuration diagram and an operation characteristic diagram of the color correction coefficient calculating section 7 of the present embodiment. The operation of the color correction coefficient calculator 7 will be described. The difference signal from the subtractor 5, which is an input signal of the color correction coefficient calculator 7, is input to the subtractor 21. The subtracter 21 subtracts a fixed value 20 set in advance according to a range in which it is not desired to operate from the difference signal, and the characteristic becomes like a point d (difference signal-fixed value).

By the operation of subtracting the fixed value 20, a range in which the coefficient becomes 0 or less, that is, a range in which the coefficient does not operate is created. When the R signal ≦ G signal, when the difference between the R and G signals is small, when the monochrome signal and the saturation are small, the difference signal has a value of 0 or less. The subtraction result is input to the half-wave rectifier 22,
Although positive values are output as they are for half-wave rectification, all negative values become 0 and output to the multiplier 23 (characteristic at point e).

As a result, when the R signal is smaller than the G signal, the operation is stopped. The multiplier 23 amplifies to change the correction amount by the external correction amount control signal 6 and outputs the amplified signal to the limiter 25. The limiter 25 prevents the amplified coefficient from exceeding the assumed maximum value of the difference signal. The assumed difference signal is a constant (the maximum value of the difference signal = the maximum value of the R signal−the minimum value of the G signal) determined when considering the entire system including the present invention.

For example, when the input units 1, 2, 3 are input terminals of a computer device, the maximum value of the R signal is 0.7V, the minimum value of the G signal is 0V, The maximum value of the difference signal is necessarily determined to be 0.7V. Therefore, in the reciprocal of the maximum value, 1 / 0.7V = 1.
43. After that, it is input to the multiplier 26. The multiplier 26 multiplies the reciprocal 27 of the assumed maximum value of the difference signal and outputs the result as a color correction coefficient. The standardization is performed so that the color correction coefficient becomes 1 when the difference signal has the maximum value. The color correction coefficient has a value of 0 or more and 1 or less, and the value changes depending on the difference signal (the characteristic at point f).

When the difference is large (when the influence of the R signal is strong)
Is strong, and when it is small (when the influence of the R signal is weak), the correction can be made weakly. As described above, the color correction coefficient becomes 0 for signals other than R signal> G signal, and no correction operation is performed. That is, since the operation is performed only when the influence of the R signal is greater than that of the other signals, only the correction in the R direction can be performed. Further, since the operation is not performed even when the monochrome signal or the saturation is low, the color temperature (white balance) of the monochrome signal is not lost.

In the CIE characteristic shown in FIG. 3, since only correction in the R direction can be performed, the color at point X moves in the direction of R and is corrected by the present color correction circuit without changing the hue. Indicates that you can do it.

Further, in the above-described embodiment, the case where the reproduction of the color in the R direction is deteriorated has been described. However, the reproduction of the color in the G and B directions is also performed by the input signal of the color correction circuit shown in FIG. By inputting a color signal to be corrected to the input terminal 1 and other color signals to the input units 2 and 3, it is possible to correct a color having poor color reproduction.
It is also possible to provide a changeover switch in front of the input units 1, 2, 3 so that a signal to be corrected can be arbitrarily selected. Also, when you want to emphasize a specific color signal,
It is possible to enhance only the color signal without affecting other hues.

Second Embodiment (1) Description of Configuration Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 4 is a configuration diagram of a color correction circuit and a color correction method according to the second embodiment.

In the description of the second embodiment, FIG.
The same parts as those in the first embodiment shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. Only different parts will be described. The same is true for color correction.

In FIG. 4, the difference from FIG. 1 will be mainly described. The luminance component extraction unit 15 is connected to the input units 1, 2, 3 and includes three primary color signals (R, G, B signals). A luminance component calculated by a specific expression is extracted. Brightness correction coefficient calculator 1
Reference numeral 6 is connected to the output of the luminance component extraction unit 15 and the output of the multiplier 8 for calculating a color correction value, and calculates a luminance correction coefficient from the luminance component and the color correction value. The multipliers 17, 18, and 19 are connected to the luminance correction coefficient calculator 16 and the subtractors 9, 10, and 11 for color correction, multiply the color-corrected three primary color signals by the luminance correction coefficient, and output the signals to the output unit 12 (R '), 13 (G'), 14 (B ')
Output to

(2) Description of Operation The operation of the second embodiment of the present invention will be described with reference to the drawings.
The luminance components of the R, G, and B signals input from the input units 1, 2, and 3 are extracted by a luminance component extraction unit 15. The luminance component is extracted based on the formula of “luminance component = 0.30 × R signal + 0.59 × G signal + 0.11 × B signal”. The luminance component is input to the luminance correction coefficient calculator 16 and calculates a luminance correction coefficient based on the luminance component and the color correction value. As the luminance correction coefficient, a luminance correction coefficient is calculated based on a formula of “luminance correction coefficient = luminance component ÷ (luminance component−color correction value)”. Multipliers 17, 18, and 19 are determined by the brightness correction coefficient.
Corrects the signals from the subtractors 9, 10, and 11 for color correction.

Thus, a decrease in luminance due to color correction can be corrected. Since the same color correction value is subtracted for each of the R, G, and B signals, the change in the luminance component becomes a color correction value from the expression of the luminance component. Therefore, if the color correction value is corrected, the luminance becomes the same as the input signal, and a decrease in luminance due to the color correction can be corrected.

As described above, according to the present invention, the color temperature (white balance) of the black-and-white signal (a signal having no color component) is maintained without any change in color tone without changing the color tone of the black-and-white signal (signal without any color component). Only the saturation of the color can be corrected.

In the first and second embodiments described above, the correction of the R signal direction has been described. However, the present invention is not limited to this, and the signals of the three primary colors to be input to the input unit are interchanged. The color direction can also be corrected.

In the present invention, either an analog circuit or a digital circuit may be used.

[0048]

As described above, by employing the color correction circuit and the color correction method of the present invention, the first point is that the color correction coefficient becomes a value of 0 or more and 1 or less, and a specific color direction is obtained. Otherwise, it is 0. The color correction coefficient is also 0 at the time of a monochrome signal (a signal having no color component). Further, there is no change in the color tone due to the operation of subtracting the common correction value.
As a result, it is possible to correct only the saturation of a specific color without disturbing the color temperature (white balance) of the black-and-white signal (signal having no color component) and without changing the hue.

Secondly, since the correction processing can be performed with the three primary color signals as they are, there is no need to perform processing by converting to another color space.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a color correction circuit and a color correction method according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a color correction coefficient calculation unit according to the first embodiment of the present invention.

FIG. 3 is an operation conceptual diagram of a color correction circuit and a color correction method according to the first embodiment of the present invention.

FIG. 4 is a configuration diagram of a color correction circuit and a color correction method according to a second embodiment of the present invention.

[Explanation of symbols]

 1, 2, 3 input unit 4 comparator 5 subtractor 6 correction amount control signal 7 color correction coefficient operation unit 8 multiplier 9, 10, 11 subtractor 12, 13, 14 output unit 15 luminance component extraction unit 16 luminance correction coefficient Operation unit 17, 18, 19 Multiplier 20 Fixed value 21 Subtractor 22 Half-wave rectification 23 Multiplier 24 Coefficient normalization unit 25 Limiter 26 Multiplier 27 Reciprocal of maximum value of difference signal R, G, B Input signal R ', G ', B' Output signal a, b Output terminal of comparator 4 X Color coordinate point before correction Y Color coordinate point after correction

Claims (7)

[Claims] In a color correction circuit having three primary color signal inputs, a comparison means for judging the magnitude of two input signals, an input signal judged to be large by the comparison means and the remaining one input signal Subtraction means for producing a difference signal, a color calculation means for calculating a color correction coefficient based on the difference signal, and a color for calculating a color correction value from the input signal determined to be small by the comparison means and the color correction coefficient. A color correction circuit comprising: a correction value calculation unit; and a color correction unit that corrects the three input signals based on a color correction value from the color correction value calculation unit. 2. The color calculating means is capable of subtracting a fixed value from the difference signal, a means for setting the result of the subtraction to a positive value of 0 or more, and the intensity of color correction can be externally controlled. 2. The color correction circuit according to claim 1, further comprising: means for setting the maximum value of the color correction coefficient to one. 3. Extraction means for extracting a luminance component from the three input signals, luminance calculation means for calculating a luminance correction coefficient from the luminance component of the extraction means and the color correction value,
3. The color correction circuit according to claim 1, further comprising a luminance correction unit that corrects the three input signals based on a luminance correction coefficient from the luminance calculation unit. 4. A subtracting means for subtracting a fixed value for coring from the difference signal, and a positive rectifying means for making the result of the subtracting means a positive value of 0 or more. An amplifier of the output of the rectifying means whose variable amplification degree is controlled by a correction amount control signal from the outside, a limiter for setting the intensity of the color correction to a constant level, and an output of the limiter which is the maximum value of the difference signal. The color correction circuit according to claim 1, further comprising: a multiplier for multiplying a reciprocal. 5. The input signal to be emphasized among the three input signals is directly input to the subtraction means, and the remaining two input signals of the three input signals are directly input to the comparison means, and as a result, 5. The color correction circuit according to claim 2, wherein the color correction means can enhance the color tone of the input signal to be enhanced. 6. A color correction method having three primary color signal inputs, a comparing step of determining the magnitude of the two input signals, and an input signal determined to be large in the comparing step and the remaining one input signal. A subtraction step of generating a difference signal of the following; a color calculation step of calculating a color correction coefficient according to a correction amount control signal in accordance with an external instruction based on the difference signal; an input signal and the color determined to be small in the comparison step A color correction value calculation step of calculating a color correction value from a correction coefficient, and a color correction step of correcting the three input signals based on the color correction values from the color correction value calculation step; A color correction method, wherein the color temperature of an image can be adjusted by adjusting the hue of one input signal. 7. A color correction method having three primary color signal inputs, wherein a comparing step of determining the magnitude of the two input signals, and an input signal determined to be large in the comparing step and one of the remaining input signals Subtraction step of generating a difference signal of the following, a color calculation step of calculating a color correction coefficient based on the difference signal, and a color of calculating a color correction value from the input signal determined to be small in the comparison step and the color correction coefficient. A correction value calculation step, a color correction step of correcting three input signals based on the color correction values from the color correction value calculation step, an extraction step of extracting a luminance component from the three input signals, and the extraction step And a luminance correction step of correcting three input signals based on the luminance correction coefficient from the luminance calculation step. To be Color correction method.