JP2000343761A - Color correction method - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a color correction method for reducing a difference in gloss of an output image. A color correction method for outputting a color image on recording paper by superimposing a plurality of color materials, wherein the amount of each color material forming a color image is determined, and the color is calculated from each amount of the color material. When the total amount of the color materials is determined and the threshold value is smaller than the total amount of the color materials, the total amount of the color materials is set as a reference table value according to the threshold value, and when the threshold value is larger than the total amount of the color materials. Controls the total amount of the color materials as the reference table value as it is.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a color correction method for a color image output apparatus for controlling the influence of glossiness due to differences in color materials.

[0002]

2. Description of the Related Art A color image output apparatus includes a color display for displaying a color image, a computer for generating a data signal of a color image to be output, and a color image data signal received from a computer and receiving the data signal in cyan (C) and magenta. (M), yellow (Y), and black (K) are converted into respective density signals, and a color printer is configured to output a color image with CMYK toners.

A color image data signal in such a color image output device is subjected to density conversion processing, color correction processing,
And gradation modulation processing are sequentially performed. Then, the color correction processing is performed by a three-dimensional lookup table interpolation method.

The three-dimensional lookup table interpolation method divides an RGB density space, which is the entire input color space from a computer, into a cube including predetermined coordinate points.
CMYK output lookup table values of two vertices (grid points),
An output CMYK signal with respect to an input RGB density signal is obtained by using weights obtained from respective distances between the eight vertices of the cube and the coordinate points.

Here, the reference table used in the conventional color correction processing includes density signals dri, dgi, d at each grid point.
The CMYK values that reproduce the bi color best are determined and created. Also, since black characters are preferred to be matte,
The reference table is created so that only the K toner having a lower gloss than other color toners is output.

In this method, the gloss of each of the C, M, Y, and K toners is not taken into consideration.

Here, with respect to the gloss, the C, M, and Y toners have a property of being more glossy than the K toner.
Gloss increases as the total toner amount of CMYK increases.

As described above, the conventional black output of the reference table is only the matte K toner, but the colors around black in the color space are C, C at the UCR rate.
There is a problem that the amounts of the M and Y toners increase and the gloss suddenly increases.

[0009]

As described above, due to the difference in the material of each color toner and the method of outputting black, a change in gloss appears when a natural image is reproduced, and a high quality image cannot be obtained. .

Accordingly, an object of the present invention is to provide a color correction method capable of reducing the difference in gloss between output images.

[0011]

In order to solve this problem, a color correction method according to the present invention is a color correction method for overlaying a plurality of color materials and outputting a color image on recording paper, The respective amounts of the color materials forming the color image are obtained, the total amount of the color materials is obtained from the respective amounts of the color materials, and when the threshold value is smaller than the total amount of the color materials, the total amount of the color materials is determined by this threshold. The reference table value is set in accordance with the value, and when the threshold value is larger than the total amount of the color material, the total amount of the color material is directly used as the reference table value, and the total amount is controlled.

Thus, the total amount of the color materials to be output is adjusted, so that the difference in gloss between the output images can be reduced.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is a color correction method for outputting a color image on recording paper by superimposing a plurality of color materials, wherein a color forming a color image is provided. The amount of each color material is calculated, the total amount of the color material is calculated from each amount of the color material, and if the threshold value is smaller than the total amount of the color material, the total amount of the color material is adjusted according to the threshold value in the reference table. If the threshold value is larger than the total amount of the color materials, the color correction method is to control the total amount using the total amount of the color materials as the reference table value as it is, and the total amount of the output color materials is adjusted. Therefore, it has the effect that the difference in gloss of the output image can be reduced.

According to a second aspect of the present invention, in the first aspect of the present invention, when one of the plurality of color materials is black, the total amount is adjusted by adjusting the amount of the color material other than the black color material. This is a color correction method that controls the sharpness of the output image by suppressing sudden changes in the amount of black color material and preventing the color from appearing in the achromatic dark areas. It has the effect that it becomes possible.

According to a third aspect of the present invention, in the first or second aspect of the invention, the distance between the coordinate point of the input color and the coordinate point of black in the color space of the input color signal is obtained. Is a color correction method that calculates the threshold value from the distance and uses the threshold value to control the total amount of the color material.The change in the total amount of the color material from the black point in the color space is defined by a smooth function. Therefore, it has the effect that the difference in gloss of the output image can be reduced.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG.

FIG. 1 is a schematic diagram showing a configuration of a color image output apparatus in which a color correction method according to an embodiment of the present invention is executed, and FIG. 2 is a diagram showing processing of a color image data signal in the color image output apparatus of FIG. FIG. 3 is a conceptual diagram showing the contents of color correction processing, and FIG. 4 is a flowchart showing a processing process by a color correction method according to an embodiment of the present invention.

As shown in FIG. 1, a color image output device includes a color display 1 for displaying a color image, a computer 2 for receiving a command and generating a data signal of a color image to be output, and a color image data from the computer 2. Receives signals and converts them to cyan (C), magenta (M), yellow (Y), and black (K) density signals, and outputs a color image on recording paper using CMYK color material toner. And a color printer 3.

As shown in FIG. 2, a color image data signal in such a color image output device is converted into a density conversion processing unit 4 for converting RGB image data into density data.
5, 6, and RGB color density data are converted into C, M, Y, and K data used for color reproduction of a printer. A color correction processing unit 7 and a predetermined gradation modulation processing unit 8 for RGB density data sequentially process the data. Will be applied.

The color correction processing 7 is performed by a three-dimensional lookup table interpolation method.

Here, the three-dimensional lookup table interpolation method will be described.

As shown in FIG. 3, the three-dimensional RGB density space 9 which is a cube showing the range of the entire input color space from the computer 2 is divided into small cubes. Then, the CMYK data corresponding to the RGB density values at the vertices of each cube is stored as a reference table.

Then, for a cube 11 composed of divided portions of the RGB density three-dimensional space 9 and including the coordinate points 10 on the RGB density three-dimensional space 9 of the input RGB density signal, refer to the CMYK outputs of the eight vertices of the cube 11. An output CMYK signal with respect to the input RGB density signal is obtained from the table value and the weight obtained from each distance between the eight vertices of the cube 11 and the coordinate point 10. In the following, RGB
The vertices of each cube when the density three-dimensional space 9 is divided into cubes are called grid points.

Next, a processing process according to the color correction method of this embodiment will be described with reference to FIG.

In the reference table creation flowchart shown in FIG. 4, first, RGB density values dri, dgj, dbk, which are coordinate values of grid points, are obtained (step 1).

Next, the RGB density values dri, dgj, db
CMYK value C1i that reproduces the best color for k color
jk, M1ijk, Y1ijk, and K1ijk are obtained (step 2).

Then, the CMYK value C obtained in step 2
The sum SUM of 1ijk, M1ijk, Y1ijk, and K1ijk is obtained (step 3), and the sum SUM thus obtained is compared with the magnitude of the threshold value T (step 4).

If the threshold value T is smaller than the total sum SUM, normalization is performed so that the total sum SUM of the CMYK values becomes equal to the threshold value T (step 5). Also, sum SUM
If the threshold value T is larger, the process proceeds to step 6 described later.

Here, in step 5, an expression for normalizing the CMYK values is shown.

[0030]

(Equation 1)

Next, if the threshold value T is larger than the sum SUM, step 3 is performed. If the threshold value T is smaller than the sum SUM, step 5 is performed.
1ijk, M1ijk, Y1ijk, and K1ijk are set as reference table values (step 6).

When the reference table value is obtained, it is determined whether another reference table value must be calculated, that is, whether or not the reference table value is the last grid point (step 7). If another reference table value is calculated in step 7, the process returns to step 1, and if the calculation of the reference table value is completed, the process ends.

As described above, according to the present embodiment, since the total amount of the color materials to be output is adjusted, the difference in gloss between the place of only the K toner single color and the other colors in the output image is reduced. And a high quality color image output can be obtained.

Here, in step 5 of FIG.
Normalization was performed without changing the mixing ratio of C, M, Y, and K. However, normalization may be performed by reducing the amount of glossy toners C, M, and Y without changing the amount of K. it can.

The equation for normalizing at this time is shown below.

[0036]

(Equation 2)

By performing the processing using this equation, the amount of the C, M, and Y toners having a large gloss is reduced, the color tone in the achromatic dark portion is suppressed, and the change in the gloss becomes smooth. A high-quality color image can be obtained.

Further, in these cases, the gloss can be adjusted by setting the threshold value T used in step 4 of FIG. 4 to a different value in the RGB density space.

That is, the RGB density values dri, dgj, dbk input in step 1 of FIG.
The distance d of the B density values drK, dgK, dbK in the RGB density three-dimensional space is calculated by the following equation.

[0040]

(Equation 3)

Then, using the distance d obtained by this equation, a threshold value T is obtained by a function f of the distance d shown in the following equation.

[0042]

(Equation 4)

By obtaining the threshold value T in this manner, the change in the total amount of the color materials from black (drK, dgK, dbK) is defined by a smooth function, so that a good image quality with a smooth gloss change is obtained. A color image output can be obtained.

[0044]

As described above, according to the present invention, since the total amount of the color materials to be output is adjusted, it is possible to obtain an effective effect that the difference in gloss between output images can be reduced. .

As a result, an effective effect that a high quality color output image can be obtained can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of a color image output apparatus in which a color correction method according to an embodiment of the present invention is executed.

FIG. 2 is an explanatory diagram showing processing of a color image data signal in the color image output device of FIG. 1;

FIG. 3 is a conceptual diagram showing the contents of a color correction process.

FIG. 4 is a flowchart showing a processing process according to a color correction method according to an embodiment of the present invention;

[Explanation of symbols]

 4, 5, 6 density conversion processing section 7 color correction processing section 8 gradation modulation processing section 9 RGB density three-dimensional space 10 coordinate point 11 cube

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C262 AA24 AA26 AA27 AB13 BA02 BA14 BC01 BC07 2H030 AD11 BB32 BB63 5C077 LL19 MP08 PP33 PP37 PP38 PP42 PP43 PP58 PQ23 RR14 TT02 TT06 5C079 HB03 LA01 LA21 LB00 MA05 PA06

Claims (3)

[Claims] 1. A color correction method for outputting a color image on a recording sheet by superimposing a plurality of color materials, wherein an amount of each of the color materials forming a color image is determined. When the threshold value is smaller than the total amount of the color materials, the total amount of the color materials is set to a reference table value in accordance with the threshold value, and the total amount of the color materials is calculated from the total amount of the color materials. When the threshold value is large, the total amount of the color materials is directly used as a reference table value, and the total amount is controlled. 2. When one of the plurality of coloring materials is black,
2. The color correction method according to claim 1, wherein the total amount is controlled by adjusting the amount of a color material other than the black color material. 3. A distance between a coordinate point of an input color and a coordinate point of black in a color space of an input color signal, a threshold value is determined from the determined distance, and a sum of color materials is calculated using the threshold value. 3. The color correction method according to claim 1, wherein the amount is controlled.