JPH05103335A - Method and device for correcting color - Google Patents

Abstract

PURPOSE:To perform precise color correction by preparing N sets of 3X3 matrix coefficients and performing the color correction by selecting the optimum 3X3 matrix coefficient at every picture element to be subjected to the color correction. CONSTITUTION:A matrix circuit 12 inputs such color information as hue, saturation, luminance, etc., and performs matrix operation based on 3X3 matrix coefficients given to each picture element. In addition, a look-up table 14 inputs such color information as hue, saturation, luminance, etc., and discriminates that the color information belongs to which color group among preset prescribed N color groups. N sets of 3X3 matrix coefficients are prepared for performing excellent color correction on the N color groups and one set of 3X3 matrix coefficients is selected out of the N sets based on the group discriminated by the table 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color correction method and apparatus, and more particularly to a color correction method and apparatus for correcting a color image signal in order to reproduce a color well in color display or color copying.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram showing an image signal processing system including a conventional color correction device. In the figure, the color camera 1 photographs a subject, and three color image signals R of red (R), green (G), and blue (B) indicating the subject are shown.
₁ , ₁ , G ₁ and B ₁ are output to lookup tables (hereinafter, referred to as LUTs) 2, 3 and 4 for each color. still,
These signals R ₁ , G ₁ and B ₁ are signals that have already been subjected to white balance adjustment and converted into 8-bit digital signals.

The LUTs 2, 3 and 4 are respectively preset with tables showing the input / output relations.
Reference numeral 4 reads out the output signals R ₂ , G ₂ and B ₂ from the table according to the input signals R ₁ , G ₁ and B ₁ . FIG. 6 is a graph showing an example of the input / output relationship of the LUT 2, showing the linear correction with offset. When the subject is a negative film, it is necessary to prepare an LUT having an input / output relationship for negative-positive conversion as shown in FIG.

The signals R ₂ , G ₂ , B ₂ output from these LUTs ₂ , ₃ , 4 are applied to the matrix circuit 5. The matrix circuit 5 has the following equation: As shown in (3), the matrix operation of the preset 3 × 3 matrix coefficients a _{11 to} a ₃₃ and the input signals R ₂ , G ₂ and B ₂ is performed to obtain the signals R ₃ , G ₃ and B ₃ . I am trying. Here, the above 3 × 3 matrix coefficient a
_{11 to} a ₃₃ are set so that the most suitable color correction can be performed on average for all the colors.

Each of the color-corrected signals R ₃ ,
G ₃ and B ₃ are output to the color TV 6 and displayed in color here.

[0006]

However, in the above-described conventional color correction apparatus, nine fixed coefficients a _{11 to} a _{33 are used.}
In all color spaces (R, G, B; 256 × 256 × 256
= 16,777,216 color spaces), the average color correction is performed over all color spaces, and therefore good color correction is not always performed for each color.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a color correction method and apparatus capable of performing fine color correction within a practical range.

[0008]

In order to achieve the above object, the present invention performs a matrix operation based on a predetermined 3 × 3 matrix coefficient for three color information including information on hue, saturation and luminance. Thus, in the color correction method for performing color correction, N sets of 3 × 3 matrix coefficients that perform good color correction for each group of predetermined N colors set in advance are prepared, and information on hue, saturation, and luminance is provided. Is input, and it is determined for each pixel which color group of the N color groups the color information belongs to, and the color information is determined from the N sets of 3 × 3 matrix coefficients. A 3 × 3 matrix coefficient corresponding to a color group is selected for each pixel, and the predetermined 3 × 3 matrix coefficient is switched to the 3 × 3 matrix coefficient selected for each pixel. It is set to.

[0009]

According to the present invention, N sets of 3 × 3 matrix coefficients capable of good color correction are prepared for each of a plurality of important colors (groups of N colors), and each pixel to be color-corrected is prepared. The optimum 3 × 3 matrix coefficient is selected for each pixel, and the color correction is performed with the selected 3 × 3 matrix coefficient for each pixel for practical use.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a color correction method and apparatus according to the present invention will be described in detail below with reference to the accompanying drawings. 1 is a block diagram showing an image signal processing system including a first embodiment of a color correction apparatus according to the present invention. The same parts as those in FIG. 5 are designated by the same reference numerals, and detailed description thereof will be omitted.

As shown in FIG. 1, the color correction apparatus according to the present invention mainly comprises matrix circuits 10 and 12, an LUT 14, and a register 16. To the matrix circuit 10, 8-bit signals R ₂ , G ₂ and B _{2 which} are appropriately corrected from LUTs ₂ , 3 and 4 for each color are added,
The matrix circuit 10 has the following equation: As shown in (3), the matrix calculation of the preset 3 × 3 matrix coefficient and the input signals R ₂ , G ₂ and B ₂ is performed to obtain the signals RY, Y and BY.
Here, as shown in the vector diagram of FIG.
The hue is represented by the direction of the vector formed by combining Y, and the saturation is represented by the size of the vector. Also, the Y axis is BY
It is a direction perpendicular to the axis and the RY axis, that is, a direction perpendicular to the paper surface. Then, the signals R ₂ , G ₂ , and B ₂ are 0 to 25, respectively.
When changed up to 5, the signals RY and BY can take the range within the dotted line in FIG.

That is, the matrix circuit 10 decomposes the combination of the signals R ₂ , G ₂ , and B ₂ into hue, saturation, and luminance, which facilitates grouping for each similar color as described later. The signals RY, Y, and BY thus converted by the matrix circuit 10 are output to the matrix circuit 12 and the LUT 14, respectively.

The LUT 14 is a signal R input for each pixel.
Based on Y, Y, and BY, the pixel is divided into a group of a plurality of important colors (32 colors in this embodiment), and a signal indicating the divided group is output to the register 16. That is,
In the LUT 14, a table is set for the upper 6 bits of the signals RY and BY and the upper 3 bits of the signal Y to divide this information into 32 sets.
4 outputs a 5-bit signal indicating the divided group from the table to the register 16 according to the input information.

In the register 16, good color correction can be performed in advance for each of the 32 important colors in advance.
A set of 3 × 3 matrix coefficients is stored, and the register 16 indicates a color group to be input from the LUT 14.
Of the 32 sets of 3 × 3 matrix coefficients, one set of 3 × 3 matrix coefficients capable of performing good color correction for the group is read out based on the bit signal, and the matrix coefficient is used as a matrix circuit. Twelve.

The input stage of the matrix circuit 12 includes:
Although a delay circuit corresponding to the phase delay by the LUT 14 and the register 16 is included, it is omitted in the figure. The matrix circuit 12 performs a matrix operation on the 3 × 3 matrix coefficient set by the register 16 and the signals RY, Y, BY input from the matrix circuit 10 to generate signals R ₃ , G ₃ , B ₃ .

In this way, for each pixel, the respective signals R ₃ and G color-corrected by the matrix coefficient optimum for the color of the pixel.
₃ and B ₃ are output to the color TV 6 and displayed in color here. FIG. 3 is a block diagram showing an image signal processing system including a second embodiment of the color correction apparatus according to the present invention. The same parts as those in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted.

The second embodiment shown in FIG. 3 is a matrix circuit 12 'corresponding to the matrix circuit 12 of the first embodiment.
Are signals R ₂ , G ₂ output from LUTs ₂ , ₃ , and ₄ ,
This is different from the first embodiment in that B ₂ is directly input.
Therefore, the register 16 'is the register 16 of the first embodiment.
The matrix coefficients different from the 32 sets of 3 × 3 matrix coefficients stored in FIG. Further, the matrix circuit 10 has LUTs 2 ', 3', 4'for each color.
The signals RY, Y and BY are generated based on the signals R ₂ ′, G ₂ ′ and B ₂ ′ input from

FIG. 4 is a block diagram showing an image signal processing system including a third embodiment of the color correction apparatus according to the present invention. still,
The same parts as those in FIG. 3 are designated by the same reference numerals, and detailed description thereof will be omitted. The third embodiment shown in FIG. 4 is different from the second embodiment shown in FIG. 3 in that a portion indicated by an alternate long and short dash line is added. That is, the LUTs 2 ″, 3 ″, and 4 ″ are input signals R ₁ , G ₁ , and B ₁ to signals R ₂ ″, G ₂ ″, and B ₂ ″.
Is read out and these signals R ₂ ″, G ₂ ″ and B ₂ ″ are output to the matrix circuit 12 ″. Matrix circuit 1
2 ″ has a register 16 ″ corresponding to the register 16 ′.
Matrix coefficient is given by the matrix circuit 12 ″ and the matrix circuit 12 ″ is set by the register 16 ″.
The matrix operation of the matrix coefficient of × 3 and the signals R ₂ ″, G ₂ ″, B ₂ ″ input from the LUTs 2 ″, 3 ″, and 4 ″ is performed to obtain the signals R ₃ ″, G ₃ ″, and B ₃ ″. To generate.

In this way, for each pixel, each signal R ₃ ″ is color-corrected with a matrix coefficient optimum for the color of that pixel,
The G ₃ ″ and B ₃ ″ are output to the color copying machine 18 where they are color copied. In the present embodiment, the pixels that are sequentially input are divided into a plurality of groups based on the signals RY, Y, and BY converted by the matrix circuit 10. However, the present invention is not limited to this. The signals may be classified based on the signals (RY) and (BY), and any classification may be performed as long as the classification is based on color information including information on hue, saturation, and brightness. Good.
Further, the group of a plurality of colors to be divided is not limited to 32 colors.

[0020]

As described above, according to the color correction method and apparatus according to the present invention, it is possible to perform good color correction for each of a plurality of important colors (groups of N colors).
Since the 3 × 3 matrix coefficient is prepared, the optimum 3 × 3 matrix coefficient is selected for each pixel to be color-corrected, and the color correction is performed by the 3 × 3 matrix coefficient selected for each pixel. Fine color correction can be performed within a practical range.

[Brief description of drawings]

FIG. 1 is a block diagram showing an image signal processing system including a first embodiment of a color correction apparatus according to the present invention.

FIG. 2 is a vector diagram used for explaining the signals BY and RY in FIG.

FIG. 3 is a block diagram showing an image signal processing system including a second embodiment of the color correction apparatus according to the present invention.

FIG. 4 is a block diagram showing an image signal processing system including a third embodiment of the color correction apparatus according to the present invention.

FIG. 5 is a block diagram showing an image signal processing system including a conventional color correction device.

FIG. 6 is a graph showing an example of the input / output relationship used to explain the LUT of FIG.

FIG. 7 is a graph showing another example of the input / output relationship used for explaining the LUT of FIG.

[Explanation of symbols]

 10, 12, 12 ', 12 "... Matrix circuit 14 ... Look-up table (LUT) 16, 16', 16" ... Register

Claims (2)

[Claims] 1. A color correction method for performing color correction by performing a matrix operation based on a predetermined 3 × 3 matrix coefficient on three color information including information on hue, saturation, and luminance, and a preset predetermined value. 3 sets of 3 × 3 matrix coefficients for performing good color correction for each N color group are prepared, color information including information on hue, saturation, and luminance is input, and the color information is the N color. Which color group among the groups is determined for each pixel, and a 3 × 3 matrix coefficient corresponding to the determined color group is selected from the N sets of 3 × 3 matrix coefficients for each pixel. The color correction method is characterized in that the predetermined 3 × 3 matrix coefficient is selected for each pixel and the predetermined 3 × 3 matrix coefficient is switched to the 3 × 3 matrix coefficient selected for each pixel. 2. Three pieces of color information including information on hue, saturation, and brightness are input, and matrix calculation is performed on the basis of 3 × 3 matrix coefficients sequentially given to each pixel for the three pieces of color information. A matrix circuit to be performed and color information including information on hue, saturation, and brightness are input, and for each pixel, it is determined which color group the input color information belongs to among a preset group of N colors. Based on the color groups determined by the color determining means, and stores N sets of 3 × 3 matrix coefficients that perform good color correction for each of the N color groups in advance. One set of 3 × out of the N sets of 3 × 3 matrix coefficients
3. A color correction device comprising: matrix coefficient switching means for selecting three matrix coefficients and applying the selected matrix coefficient to the matrix circuit.