JPH0746623A - Chroma correction device - Google Patents

Abstract

PURPOSE:To obtain a chroma correction device which provides natural color reproducibility for both a color with high chroma (deep color) and a color with low chroma (light color) without changing a hue. CONSTITUTION:A luminance coefficient deciding means 1 decides a first correction coefficient ky corresponding to an input luminance signal Y. A color difference coefficient deciding mean 2 decides a second correction coefficient kc corresponding to input color differential signals R-Y, B-Y. A correction coefficient deciding means 3 outputs a chroma coefficient (k) whose value is decreased as increasing luminance and decreasing chroma by the first coefficient ky and the second coefficient kc. A multiplier means 4 outputs the input color differential signal by multiplying by the chroma coefficient. The natural color reproducibility for both the color with high chroma (deep color) and the color with low chroma (light color) can be provided without changing the hue by changing the gain of color difference so that the chroma can be decreased as increasing the luminance and decreasing the chroma by the luminance signal and two color differential signals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a saturation correction device for a video machine such as a television, a video camera, a video camera and a video printer which handles a full color image.

[0002]

2. Description of the Related Art In recent years, with the development of hard copy technology, especially full-color hard copy technology, it has become possible to reproduce images with high fidelity by using a printing technology such as a sublimation type thermal transfer system. In terms of color reproduction, recording materials and image processing have provided a reproduction capability equivalent to that of silver salt photographs, and in terms of resolution, silver salt photographs are approaching by using high-definition video signals such as high definition.

However, the dynamic range of recording of a video printer is several tens of times at most, which is inferior to that of a CRT by one digit or more, so that the color reproduction range is considerably small, which results in a highly saturated color (dark color). The difference between the color) and the color with low saturation (light color) becomes small, resulting in an image with no color contrast.

Further, since colors are reproduced by additive color mixing in the CRT, the more the colors are mixed, the brighter the color becomes. vice versa,
Since the video printer reproduces the colors by subtractive color mixing, the more the colors are mixed, the darker the color becomes. As a result, the reproduction range of particularly bright colors becomes small in the video printer, and the color reproducibility of the bright areas is reduced by CRT without correction.
Markedly worse than

Conventionally, in a photograph, in order to correct the color contrast, the saturation is corrected by a method called an inter-image effect of a color negative film. This is a phenomenon in which the development in the emulsion layer is promoted so that the ratio of R, G and B is large, that is, the color of high saturation is further expanded, and this makes the color reproduction vivid. become,
The shades of colors close to a single color such as red (R), green (G), and blue (B) are emphasized. On the contrary, when considering a color with high saturation as a reference, it can be considered that a color having a smaller ratio, that is, a color with lower saturation, has lower saturation and the color contrast is corrected.

As a method of correcting the saturation according to the luminance, the input color difference signal is multiplied by a gain to reduce the saturation so as not to exceed the dynamic range in which the color can be reproduced near the white peak. There is a system for achieving good color reproduction (Japanese Patent Application Laid-Open No. 3-039264).

[0007]

FIG. 6 shows a change in color in a uniform color space Luv by a method called an inter-image effect, which is performed on a photograph. In the figure, ◯ is an input color and Δ is a color corrected by the inter-image effect. As can be seen from FIG. 6, this method has a problem that the hue and the luminance change when the saturation is increased.

Further, the method of correcting the saturation in accordance with the brightness reduces the saturation by multiplying the input color difference signal by a gain so as not to exceed the dynamic range in which the color can be reproduced near the white peak. Since this is a method for achieving good color reproduction, there is a problem in that the contrast of colors within the dynamic range is not corrected.

In view of the above problems, the present invention does not change the hue and has a high saturation color (dark color) and a low saturation color (light color).
It is an object of the present invention to provide a saturation correction device that realizes both natural color reproducibility.

[0010]

In order to achieve the above object, the saturation correction apparatus of the present invention comprises a color difference coefficient determining means for determining a first correction coefficient according to an input color difference signal, and the color difference coefficient determining means. A correction coefficient determining means for outputting a saturation coefficient whose value becomes smaller as the saturation becomes smaller than an output, and a multiplying means for multiplying the determined saturation coefficient by the input color difference signal are provided.

Further, in order to achieve the above object, the saturation correction device of the present invention responds to a brightness coefficient determining means for determining a correction coefficient according to an input brightness signal and a maximum value of RGB difference according to an input color difference signal. RGB difference coefficient determining means for outputting the second correction coefficient, the output of the brightness coefficient determining means, and the RG.
The brightness is greater than that of the output of the B difference coefficient determination means, and
The correction coefficient determining means outputs a saturation coefficient that decreases as the maximum value of the difference decreases, and the multiplying means that multiplies the determined saturation coefficient by the input color difference signal.

[0012]

According to the present invention, the first correction coefficient is determined according to the input color difference signal according to the above-described structure, and the saturation coefficient that becomes smaller as the saturation becomes smaller is calculated from the first correction coefficient. The saturation is corrected by multiplying the saturation coefficient by the input color difference signal.

Further, according to the present invention, the correction coefficient is determined according to the brightness from the input brightness signal, the maximum value of the RGB difference is calculated according to the input color difference signal, and the maximum difference between the correction coefficient and the RGB is obtained. From the value, a saturation coefficient that becomes smaller as the luminance is larger and the maximum value of the RGB difference is smaller is obtained, and the saturation is corrected by multiplying the saturation coefficient by the input color difference signal.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A saturation correction device according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the arrangement of a saturation correction apparatus according to the first embodiment of the present invention. In FIG. 1, reference numeral 1 is a brightness coefficient determination for determining a second correction coefficient ky according to an input brightness signal Y. A means 2 is a color difference coefficient determining means for obtaining a first correction coefficient kc in accordance with the two input color difference signals RY and BY.
Is a correction coefficient determining means 4 that determines a saturation coefficient k that lowers the saturation of the input signal as the brightness is higher and the saturation is lower, according to the outputs of the brightness coefficient determining means 1 and the color difference coefficient determining means 2.
Is a multiplication means for multiplying the saturation coefficient k determined by the correction coefficient determination means 3 and the input color difference signals RY and BY, and 5 is the input luminance signal Y and the input color difference signals RY and BY. The delay means delays the timing until the saturation coefficient k is determined.

The operation of the saturation correction device configured as described above will be described below with reference to FIG.

Input luminance signal Y and input color difference signal R
-Y and BY are 8-bit digital signals.

The input luminance signal Y is converted by the luminance coefficient determining means 1 into the second correction coefficient ky from the equation (1).
Here, Y0 is the input luminance signal, Ymax is the maximum value that the input luminance signal can take, and Yoff is for adjusting so that the second correction coefficient ky does not become too large when the luminance is small. Is. The final multiplication of 255 is for conversion to 8 bits.

Ky = (Y0 + Yoff) / (Ymax + Yoff) * 255 (1) In this embodiment, a ROM in which the equation (1) is calculated in advance is created, and the ROM is read out to realize high speed and circuit reduction. is doing. This ROM has an address of 8 bits,
When the data is 8 bits and Y0 is input as an address, the second correction coefficient ky is output as data.

Further, in the color difference coefficient determining means 2, the two input color difference signals RY and BY are converted as shown in equations (2) and (3), respectively. Where C01,
C02 corresponds to the two input color difference signals RY and BY. C11 and C12 are the converted color difference signals, and Cmax1 and Cmax2 are the maximum values that the respective input color difference signals can take.

C11 = | C01 | / Cmax1 (2) C12 = | C02 | / Cmax2 (3) Then, from the converted two color difference signals C11 and C12, the following formula (4) is used. A correction coefficient kc of 1 is determined. Here, Coff is adjusted so that the saturation does not become low when the saturation is higher than a certain level. Also, the multiplication by 255 is for converting to 8 bits.

Kc = {√ (C11 ^ 2 + C12 ^ 2) + Coff} / {√ (Cmax1 ^ 2 + Cmax2 ^ 2) + Coff} * 255 (4) In this embodiment, the equations (2) and (3) are used. , Equation (4) is calculated in advance, address is 16 bits, data is 8 bits
The ROM is used. When C01 is input to the upper address and C02 is input to the lower address, the first correction coefficient kc is output as data.

Then, in the correction coefficient determining means 3, the second correction coefficient ky determined by the brightness coefficient determining means 1
By using the first correction coefficient kc determined by the color difference coefficient determining means 2 as shown in the equation (5), the saturation coefficient is inversely proportional to the saturation, so that the saturation coefficient is small when the saturation is high and the brightness is high. Is smaller and the saturation is lower, the saturation coefficient k is determined. Here, a is a coefficient for adjusting the saturation coefficient k. However, since the saturation is not expanded, k> 2
In the case of 55, the value of k is limited to k = 255. Also,
The factor of 255 is for converting to 8 bits.

K = a × kc / ky * 255 (5) However, when k> 255, k = 255.

In the present embodiment, a ROM having the characteristics of the equation (5) and having an address of 16 bits and data of 8 bits is used. When ky is input to the upper address and kc is input to the lower address, the saturation coefficient k is output as data.

Then, in the multiplying means 4, the saturation coefficient k determined by the correction coefficient determining means 3 is multiplied by the input color difference signal delayed by the delay means 5 for a time sufficient to obtain the saturation coefficient k. Then, a color difference signal whose color contrast is corrected is output.

Next, the effect of this embodiment will be described. FIG. 2 shows changes in color in the uniform color space Luv of this embodiment. In this figure, ○ is the input color,
Δ is the color corrected by this example. From this figure,
It can be seen that the color is changing toward the origin and the hue is not changing, that the color with higher brightness and lower saturation changes more greatly, and the color with higher saturation does not change regardless of the brightness.

As a result, according to the present invention, it is possible to correct the color contrast without changing the hue and the color having high saturation, and the color having high saturation (dark color) and the color having low saturation (light color). It is possible to realize both natural color reproducibility.

FIG. 3 shows the structure of a saturation correction apparatus according to the second embodiment of the present invention. In FIG. 3, 1 is a brightness coefficient determining means for obtaining a first correction coefficient ky from an input brightness signal Y. , 32 are RGB difference coefficient determining means for outputting a second correction coefficient kc from the two input color difference signals R-Y, BY for the respective maximum values of the differences of RGB, and 33 is an output of the brightness coefficient determining means 1. And the RGB difference coefficient determining means 32 output, the correction coefficient determining means 4 outputs the saturation coefficient k that becomes smaller as the luminance is higher and the maximum value of the RGB difference is smaller. Saturation coefficient k
Multiplication means for multiplying the input color difference signals R-Y and BY
Reference numeral 5 is an input luminance signal Y and input color difference signals RY and BY
Is a delaying means for delaying until the timing at which the saturation coefficient is determined. The operation of the saturation correction device configured as described above will be described below with reference to FIG.

Input luminance signal Y and input color difference signal R
-Y and BY are 8-bit digital signals.

The input luminance signal Y is converted by the luminance coefficient determining means 1 into the first correction coefficient ky from the equation (1).
The brightness coefficient converting means 1 has the same structure as that of the first embodiment.

The two input color difference signals RY and BY
In the RGB difference coefficient determination means 32, the second correction coefficient kc corresponding to the absolute value of the RGB difference is obtained.

Then, in the correction coefficient determining means 33,
First correction coefficient ky determined by the brightness coefficient determining means 1
And the saturation coefficient k is smaller than the second correction coefficient kc determined by the RGB difference coefficient determining means 32 so that the saturation coefficient becomes smaller and the saturation becomes lower when the saturation is higher and the luminance is higher.
Is determined. This correction coefficient determining means is the same as in the first embodiment.

Then, in the multiplication means 4, the saturation coefficient k determined by the correction coefficient determination means 33 is multiplied by the input color difference signal delayed by the delay means 5 for a time sufficient to obtain the saturation coefficient k. Then, a color difference signal whose color contrast is corrected is output.

Next, the RGB difference coefficient determination means 32 will be described in detail with reference to FIG. In FIG. 4, 40 is 2
RGB difference conversion means for obtaining RGB differences from the two input color difference signals RY and BY, 41 is a multiplication means, and 42 is a multiplication means.
Is an adding means, 43 is a subtracting means, 44 is an absolute value means for obtaining an absolute value, 45 is a maximum value determining means for obtaining a maximum value among the absolute values of the differences of RGB, and 46 is a maximum value determining means 4
It is a coefficient determining means for obtaining the second correction coefficient kc from the output of 5.

The two input color difference signals RY and BY are RG.
In the B-difference conversion means 40, the RGB differences RG,
Converted to G-B and B-R. And the required RG
The difference between the B values is the absolute value | R in the absolute value means 44.
-G |, | GB |, | BR |, and the maximum value determining means 45 outputs the largest value D of the absolute values of these differences. The maximum value D of the difference is converted into the second correction coefficient kc according to the equation (6). Here, Dmax is the maximum possible absolute value of the difference between RGB converted from the input signal, S
off is for adjusting so that the second correction coefficient does not become small when the difference is large to some extent. Also, the multiplication by 255 is for converting to 8 bits.

Kc = (D + Soff) / (Dmax + Soff) * 255 (6) In this embodiment, the equation (6) is calculated in advance, and this coefficient is calculated using a ROM having an address of 8 bits and data of 8 bits. It constitutes the determination means 46. And D at the address
Is input, the second correction coefficient kc is output as data.

Next, the effect of this embodiment will be described. FIG. 5 shows changes in color in the uniform color space Luv of this embodiment. In this figure, ○ is the input color,
Δ is the color corrected by this example. From this figure,
It can be seen that the color is changing toward the origin and the hue is not changing, that the color with higher brightness and lower saturation changes more greatly, and the color with higher saturation does not change regardless of the brightness.

Thus, according to the present invention, it becomes possible to correct the color contrast without changing the hue and the color having high saturation, and the color having high saturation (dark color) and the color having low saturation (light color). It is possible to realize both natural color reproducibility.

In the first and second embodiments, the second
The correction coefficient of is obtained as a value according to the distance from the origin on the plane of the color difference or the maximum absolute value of the RGB difference, but other values can be used if they represent the saturation. Also has the same effect.

Further, in this embodiment, the luminance coefficient determining means, the color difference coefficient determining means, the correction coefficient determining means and a part of the RGB difference coefficient determining means are constituted by using the ROM, but some or all of them are software. It is clear that the same effect can be obtained by performing the treatment.

[0042]

As described above, according to the present invention, the hue is not changed by changing the gain of the color difference so that the higher the brightness and the smaller the saturation are, the lower the saturation is. Natural color reproducibility of both highly saturated colors (dark colors) and lowly saturated colors (light colors) can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a saturation correction device according to a first embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a color change characteristic in a uniform color space Luv in the embodiment.

FIG. 3 is a block diagram showing a configuration of a saturation correction device according to a second embodiment of the present invention.

FIG. 4 is a block diagram showing an internal configuration of RGB difference coefficient determination means in the embodiment.

FIG. 5 is a characteristic diagram showing a color change characteristic in the uniform color space Luv in the embodiment.

FIG. 6 is a characteristic diagram of color change due to the conventional inter-image effect.

[Explanation of symbols]

 1 luminance coefficient determining means 2 color difference coefficient determining means 3 correction coefficient determining means 4 color difference correcting means 5 delay means 32 RGB difference coefficient determining means 33 correction coefficient determining means 40 RGB difference converting means 41 multiplying means 42 adding means 43 subtracting means 44 absolute value Means 45 Maximum value determining means 46 Coefficient determining means

Claims (11)

[Claims] 1. An apparatus for controlling a color difference signal according to the level of an input color difference signal, comprising: a color difference coefficient determining means for determining a first correction coefficient according to the input color difference signal; and an output of the color difference coefficient determining means. Correction coefficient determining means for outputting a saturation coefficient whose value decreases as the saturation decreases, and multiplication means for multiplying the determined saturation coefficient by the input color difference signal. A saturation correction device characterized by outputting as a signal. 2. A brightness coefficient determining means for determining a second correction coefficient according to an input brightness signal, and a value that is larger and smaller in saturation than the output of the brightness coefficient determining means and the output of the color difference coefficient determining means. 2. The saturation correction apparatus according to claim 1, further comprising a correction coefficient determination unit that outputs a saturation coefficient that reduces. 3. The color difference coefficient determining means includes a squaring means, an adding means, and a means for obtaining a square root, and outputs a value obtained by adding a predetermined value to the distance from the origin on the color difference plane. The saturation correction device according to claim 1. 4. The correction coefficient determining means includes a dividing means,
3. The saturation correction device according to claim 1, wherein a value obtained by dividing the output of the color difference coefficient determining means by the output of the luminance converting means is output. 5. The saturation correction apparatus according to claim 2, wherein the brightness coefficient determining means includes means for adding a predetermined value to the brightness signal. 6. The saturation correction device according to claim 4, further comprising saturation coefficient limiting means for limiting the saturation coefficient to a value that does not increase the saturation. 7. An apparatus for controlling a color difference signal according to the levels of an input luminance signal and a color difference signal, wherein a luminance coefficient determining means for determining a correction coefficient according to the input luminance signal and RGB difference according to the input color difference signal. The RGB difference coefficient determining means for outputting a second correction coefficient corresponding to the maximum value of, and the output of the brightness coefficient determining means and the output of the RGB difference coefficient determining means have a larger brightness and a maximum value of RGB difference. The correction coefficient determination means outputs a saturation coefficient that decreases in value, and a multiplication means that multiplies the determined saturation coefficient by the input color difference signal, and outputs the output of the multiplication means as a color difference signal. A saturation correction device characterized by the following. 8. The saturation correction device according to claim 7, wherein the brightness coefficient determining means includes means for adding a predetermined value to the brightness signal. 9. The RGB difference coefficient determining means includes an RGB difference converting means for converting into an RGB difference, a subtracting means, an absolute value means for taking an absolute value of an output of the RGB difference converting means, and an output of the absolute value means. A maximum value determining means for taking the maximum value, and
The saturation correction device according to claim 7, wherein a value obtained by adding a predetermined value to the maximum absolute value of the respective differences is output. 10. The correction coefficient determining means includes a dividing means, and outputs a value obtained by dividing the output of the RGB difference coefficient determining means by the output of the luminance coefficient determining means.
The saturation correction device described. 11. The saturation correction device according to claim 10, further comprising saturation coefficient limiting means for limiting the saturation coefficient to a value that does not increase the saturation.