JPH0353668A - Color correction method - Google Patents

Abstract

PURPOSE:To attain proper color correction by rewriting a color cube when color correction information defined by a form of the color cube is insufficient to optimize the color correction information. CONSTITUTION:A color correction device consists of a differential computing element 10, correction devices 21-23, and adders 31-33. The combination of the density of 2nd 3 primary colors is corrected into the combination of the density of 3rd 3 primary colors by setting a correction value to 3 sets of the correction devices 21-23 by the operator. Since 3 correction values are set to the correction devices 21-23 as to the primary component and also the secondary component respectively independently, a color cube with optimum color correction information is defined. Thus, proper color correction is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a color correction method, and more particularly to a color correction method for performing leakage correction using a color solid.

[Conventional technology]

Generally, when a color image is output using various output media, the color tones vary depending on the output media. For example, actual printing is performed based on exactly the same color image data that expresses the color information of one pixel by a combination of the density values of the three primary colors C, M, and Y, and the case where a color hard copy is output. When compared, even though the original image data is the same, the color tone is not the same. This is because the colors of ink and the like used are different. Such a difference in color tone may cause problems in the printing process. For example, consider a process in which image data is generated by a computer and printing is performed by cutting a plate based on this image data. At this time, before starting the actual printing process, a color hard copy of the image data created by the computer is output to check whether the image needs to be modified. However, if the color tone of this color hard copy differs from the color tone of the actual print, satisfactory confirmation cannot be made.

In such cases, there is a method to perform color correction on the original image data, output a color hard copy based on the corrected image data, and make the printed result and the color hard copy as similar in tone as possible. is taken. For example, if the original image data is
, M0, YO), the second primary color (C0, M0, YO) corresponds one-to-one to the combination of density values of the first three primary colors (C0, M0, YO).
Cl, Ml, Yl) density value combinations are defined, and when outputting a color hard copy, the second three primary colors (Cl, Ml, Yl) are used instead of the first three primary colors (C0, M0, YO). ) data will be used. The correspondence between the first three primary colors and the second three primary colors is usually defined by a color solid that constitutes a three-dimensional lookup table. With this color solid, the first three primary colors (
From the combination of density values of C0, M0, YO), the combination of density values of the second three primary colors (Cl, Ml, Yl) is
A one-to-one correspondence can be obtained.

To define such a color solid, you need to make a printout and a color hard copy of the same image containing a color standard that can express the golden color reproduction range, and then measure both using a measuring device such as a spectrocolorimeter or densitometer. The correspondence between the two is determined based on the measurement results (for example, in Japanese Patent Application No. 63-60836).
(see specification).

[Problem to be solved by the invention]

However, the color correction method using the color solid defined as described above has a problem in that it is not always possible to perform good color correction. This is considered to be because a color solid with optimal color correction information has not been defined due to reasons such as errors being included in the measurements performed to define the color solid.

Therefore, an object of the present invention is to provide a color correction method that can optimize color correction information and perform more appropriate color correction.

[Means to solve the problem]

(1) The first invention of the present application is based on the first three primary colors (X0, Y
In one-to-one correspondence to the combination of concentration values of ○, zO),
When a combination of density values of the second three primary colors (X1, Y1, Z1) is defined, instead of this combination of density values of the second three primary colors, the combination of the third primary colors (X 2 ,
Y2. Z 2 ) (7) In the color correction method for determining the combination of la degree values, 6 input lines and 6
The corrector has three output lines and outputs a predetermined correction value to each output line according to the differential density value given to each input line.
A set of 3 human power lines and 6 output lines is prepared, and the difference between the largest density value and the second largest density value among the color density values given to the three input lines. is determined as the primary color component, this primary color component is output to the output line corresponding to the color with the largest density value, and the difference between the second largest density value and the smallest density value is determined as the secondary color component. A difference calculator is provided that has the function of calculating this secondary color component and outputting this secondary color component to the output line corresponding to the mixed color of the color with the largest density value and the color with the second largest density value. , connect the six output lines of the difference calculator to the input lines of each of the three sets of correctors, give the combination of density values of the first three primary colors (X0, Y0, ZO) to the difference calculator, 3 The correction value output from each output line of the first corrector of the .1fi corrector is added to the density value of the first color (X1) of the second three primary colors, and the correction value is added to the density value of the first color (X1) of the second three primary colors. The density value is determined, and the correction value output from each output line of the second corrector of the three sets of correctors is calculated as the correction value of the second color (Y1) of the second three primary colors.
), the density value of color (Y2) is determined, and the correction value output from each output line of the third corrector of the three sets of correctors is calculated as the density value of the color (Y2) of the second three primary colors. Color 3 (z1
), the density value of color (z2) is determined, and the determined colors (X2), (Y2) . (Z2) to find the combination of density values of the third three primary colors (X2, Y2.Z2).

(2> The second invention of the present application is based on the first three primary colors (XO.Y
In one-to-one correspondence to the combination of density values of 0, zO), the second three primary colors (Xi, Yl, Z 1) (')i
'For a color solid in which a combination of 1 degree values is defined, a combination of density values of the second three primary colors defined in the vicinity of an arbitrary point Q in this color solid is defined as a combination of density values of the third primary color (X2,
Y2. In the color correction method that corrects the combination of density values of Among the points, point Q
Find the grid point PO closest to and the 26 grid points P1 to P26 around it, and for the grid point PO, calculate the density values of the second three primary colors (X1, Y1, Z1) defined here. By adding correction values (ΔX, ΔY, Δ2) to each of them, the density values of the third three primary colors (X2, Y2, Z2) are calculated and corrected, and the grid points P1 to P26 are defined here. By adding the quotient obtained by dividing the correction value (ΔX.ΔY, ΔZ) by a predetermined number n to each of the density values of the second three primary colors (X1, Y1, Z1), the third three primary colors (X2. Y2, Z2
) is calculated and corrected.

[For production]

According to the first invention of the present application, if the operator sets correction values in three sets of correctors, the second three primary colors (X1, Yl, Zl
) is the third primary color (X2, Y2
．． Z2) is corrected to the combination of density values. Three correction values for the primary color component and three correction values for the secondary color component can be independently set in each corrector. Therefore, the correction value can be easily set based on the operator's intuition.

According to the second invention of the present application, data in the vicinity of any point within the color solid can be rewritten.

In this case, the lattice point serving as the center of rewriting is corrected using the correction value itself, while the surrounding lattice points are corrected using the quotient obtained by dividing the correction value by a predetermined number n. Therefore, even if the data in the color solid is partially rewritten, the spatial change in the data after rewriting can be made gentle.

〔Example〕

The present invention will be described below based on illustrated embodiments.

Embodiment of the First Invention of the Present Application FIG. 1 is a block diagram showing the configuration of a color correction device according to an embodiment of the first invention of the present application. This device is suitable for rewriting all data within a color solid. FIG. 2 shows an example of a color solid to be rewritten. This color solid is
The second three primary colors (Cl, Ml, Yl) correspond one-to-one to the combination of density values of the first three primary colors (COM0, YO).
A three-dimensional lookup table is constructed to find combinations of density values. For example, for a point P in a color solid whose coordinate value is a combination of density values of the first three primary colors (COi.MOi, YOi), there is a combination of density values of the second three primary colors that corresponds one-to-one to this point P. (Cl j, Ml
j, Yl j) is defined. In this color solid,
The density value of each color is expressed by 8 bits from 0 to 255. Therefore, theoretically, a combination of density values of the second three primary colors must be defined for each of the 2563 combinations of density values of the first three primary colors. However, in reality, in order to reduce the number of data, a grid is created in which each concentration axis is divided into eight equal parts, as shown in Figure 2, and only each grid point is defined, and the distance between the grid points is The density value is determined by interpolation.

Now, the gist of the present invention is to rewrite this color solid when the color correction information defined in the form of such a color solid is not sufficient. This rewriting is performed by the device shown in FIG.

The difference calculator 10 has three input lines C0, M0, YO.
and six output lines C, M, Y, R, G, B
has. The difference calculator 10 has the following two functions. First, the first function calculates the difference between the largest density value and the second largest density value among the density values given to the three input lines as a primary color component, and calculates the largest density value. This is a function to output this primary color component to the output line (one of C, M, and Y) corresponding to the color. Then, the second function calculates the difference between the second largest density value and the smallest eyebrow intensity value among the tla intensity values given to the three input lines as a secondary color component, and selects the largest This function outputs this secondary color component to the output line (one of R, G, and B) corresponding to the mixed color of the color with the eyebrow intensity value and the color with the second largest density value. be. Here, the mixed color of C and M is B%M and Y
The mixed color of C and Y is R, and the mixed color of C and Y is G. The operation of the difference calculator 10 will be described more specifically as follows. For example, Co-200, MO-120, YO
Assume that a density value of -90 is input. Then, the primary color component is (200-120)-80. This primary color component 80 is connected to the output line C (the color CO with the largest density value).
). Also, the secondary color component is (120-
90)-30. This secondary color component 30 is connected to the output line B (
(corresponding to a mixed color of the color CO having the largest density value and the color MO having the second largest density value). In this case, the outputs of the other output lines are 0.

The three sets of correctors 21 to 23 have six input lines and six output lines, and have a function of outputting a predetermined correction value to each output line according to the differential density value given to each human force line. has. Each corrector is composed of C, M, Y, R, G, and B parts, and six corresponding output lines of the difference calculator 10 are connected to each of these parts. It has a function of inputting a differential density value, that is, a primary color component or a secondary color component, and outputting a corresponding correction value. In this example, the primary color component or secondary color component is 0 to
Takes values up to 255. In each part, a linear function is defined that outputs a specific correction value for this value of 0 to 255. Normally, the correction value for the input value of O is O. This linear function is set by the operator.

Adders 31 to 33 each add concentration values Cl, M1 . Yl
Add the correction values given from the correctors 21 to 23 to
As a result, the density value C2. It has a function to output M2 and Y2. For example, the adder 31 adds all the correction values output from the six output lines of the corrector 21 to the density value C1, and outputs the result as the density value C2.

The settings of the correctors 21 to 23 by the operator are performed as follows. That is, the operator can obtain information on which colors should be made darker and which colors should be made lighter from the result of color correction using the color solid before correction. For example, if we obtain information that cyan should be made darker and green should be made lighter, we will give a linear function that outputs a positive correction value to the C part of the correctors 21 to 23, and give a negative correction value to the G part of the correctors 21 to 23. All you have to do is give a linear function that outputs a value. The absolute value of the linear function can be determined based on information on how dark or thin the image should be. Further, for portions that do not require correction, O may be output at all times.

Now, in the color solid shown in Figure 2, the first three primary colors (C
The combination of density values of the second three primary colors (CI, Ml, Y1) is defined on a one-to-one basis for the combination of multiple density values of (C0, M0, YO).
0, YO) and (CI, M1, Yl) as the first
Co, M0, Y0, Cl, Ml, in the device shown in the figure
If Yl is given sequentially, (C2
, M2. Y2) is found. Therefore, in the color solid,
data (Cl, Ml, Yl) to data (C2.M2.Y
By rewriting 2), a new color solid can be formed. This new color solid is created by the corrector 2 set by the operator.
It has color correction information that has been corrected according to steps 1 to 23, so that more appropriate color correction can be performed.

Second Embodiment of the Invention The color correction method described herein is suitable for partially correcting color solid information. Generally, a skilled operator can recognize which part of the color solid should be corrected and how, based on the result of color correction using the color solid before correction. For example, in the color solid shown in FIG. 3, it is recognized that the color correction information near the point Q should be corrected, and the correction values are (ΔC, ΔM.ΔY).
Suppose that it is recognized that . In this case, the grid point PO closest to point Q and 26 grid points P1 to P26 around this grid point PO are determined. FIG. 4 shows the extracted 27 lattice points obtained. Then, regarding the grid point PO, the correction value (Δ
C. ΔM, ΔY) are used as they are for correction. For example, if the concentration value defined at grid point PO is (Cla, M
la, Yla), the density value after correction is
(Cla+ΔC, Mla+ΔM, Yla+ΔY). On the other hand, regarding grid points P1 to P26, a predetermined number n is defined, and the correction value (ΔC, ΔM, ΔY
) is used for correction. For example, grid point P
The concentration value defined in 1 is (Clb, Mlb, Ylb
), the density value after correction is (Clb+Δ
C/'n, Mlb+ΔM/n, Ylb+ΔY/n)
becomes.

Similar corrections are made for lattice points P2 to P26.

Through such correction, data in the vicinity of any point within the color solid can be rewritten, and the spatial change in the rewritten data within the color solid can be made gentle.

[Effective period of invention]

As described above, according to the first invention of the present application, the operator
By setting correction values in the set of correctors, the combination of density values of the second three primary colors (Xi, Yl, Zl) becomes the third
is corrected to a combination of density values of the three primary colors (X2, Y2, Z2). Each corrector has three correction values for the primary color component and three correction values for the secondary color component.
Since each can be set independently, the correction value can be easily set based on the operator's intuition, and more appropriate color correction can be performed.

Further, according to the second invention of the present application, data within a color solid can be partially rewritten. In this case, the lattice point that is the center of rewriting is corrected using the correction value itself, while the surrounding lattice points are corrected using the quotient of the correction value divided by a predetermined number n. Spatial changes in data after rewriting can be made gentler, allowing more appropriate color correction.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the basic configuration of an apparatus for performing the color correction method according to the first invention of the present application, FIG. 2 is a diagram showing a color solid to be corrected by the apparatus of FIG. 1, and FIG. FIG. 4 is a partially enlarged view of FIG. 3; FIG. 4 is a partially enlarged view of FIG. 3; 10...Difference calculator, 21-23...Corrector, 31
~33...Adder.

Claims (2)

[Claims] (1) In one-to-one correspondence to the combination of density values of the first three primary colors (X0, Y0, Z0), the second three primary colors (X1, Y
1, Z1) is defined, the color for which the combination of density values of the third three primary colors (X2, Y2, Z2) is sought instead of the combination of density values of the second three primary colors. In the correction method, three sets of correctors are prepared that have six input lines and six output lines and output a predetermined correction value to each output line according to the differential density value given to each input line. has three input lines and six output lines, and the difference between the largest density value and the second largest density value among the color density values given to the three input lines is calculated as Find it as a color component, output this primary color component to the output line corresponding to the color with the largest density value, and find the difference between the second largest density value and the smallest density value as a secondary color component. , a difference calculator having a function of outputting this secondary color component to an output line corresponding to a mixed color of a color having the largest density value and a color having the second largest density value is prepared; six output lines of the difference calculator are connected to input lines of each of the three sets of correctors, and a combination of density values of the first three primary colors (X0, Y0, Z0) is provided to the difference calculator. , The correction value output from each output line of the first corrector of the three sets of correctors is added to the density value of the first color (X1) of the second three primary colors to obtain the color ( Find the density value of In addition to the density value, the density value of color (Y2) is determined, and the correction value outputted from each output line of the third corrector of the three sets of correctors is applied to the correction value outputted from each output line of the third corrector of the three sets of correctors. In addition to the density value of the third color (Z1), the density value of the color (Z2) is determined, and the obtained colors (X2), (Y2), and (Z2) are combined to form the third three primary colors (X2, Y2, Z2) A color correction method characterized by finding a combination of density values. (2) In one-to-one correspondence to the combination of density values of the first three primary colors (X0, Y0, Z0), the second three primary colors (X1, Y
For a color solid in which a combination of density values of X2 , Y2, Z2), the correction values (ΔX, ΔY, ΔZ) and an arbitrary predetermined number n are defined, and the density values are defined within the color solid. Of the grid points that are
The grid point P0 closest to the point Q and the 26 points around it
lattice points P1 to P26 are obtained, and regarding the lattice point P0, the second three primary colors (X1, Y1
, Z1), the correction values (ΔX, Δ
By adding Y, ΔZ), the third primary color (X2,
Y2, Z2) are calculated and corrected, and for the grid points P1 to P26, the correction is applied to each of the density values of the second three primary colors (X1, Y1, Z1) defined here. By adding the quotient of the values (ΔX, ΔY, ΔZ) divided by the predetermined number n, the third primary color (X2
, Y2, Z2) and performs the correction.