JP2002044474A - Color conversion processing method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a black tone jump from becoming prominent, when forming black and other output colors from input R, G, and B. SOLUTION: An intermediate parameter, having linear characteristics with respect to the three-dimensional input color space of R, G, and B, without indicating a black output value directly to each lattice point for black is recorded in a color conversion table 10. A black generation means 11 generates a black K used for an actual print, based on a second middle parameter P" outputted from an interpolation operation part 3, and is composed by one-dimensional LUT where for example a K output value has been written to the value of a second intermediate parameter. Although C', M', Y', and P' of eight lattice points outputted from the color conversion table 10 are subjected to linear interpolation operation by the interpolation operation part 3, and C, M, Y, and P" are outputted, as for P" it is inputted to a black generation means 11, and K is generated and is supplied to a print engine.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an image, such as a color printer, which inputs red (R), green (G), and blue (B) data values of each pixel of image data. , Yellow (Y), magenta (M), cyan (C), and black (K).

[0002]

2. Description of the Related Art Various methods for generating C, M, Y, and K from R, G, and B, such as a method of performing a matrix operation, are known. One of them is a color conversion table. There are methods to use. In the method using the color conversion table, R, G, and B are input, and C,
A method of outputting M and Y, and a method of generating K from C, M and Y outputted, and a method of inputting R, G and B and outputting C, M, Y and K directly from a color conversion table There is a method. This application is directed to the latter method.

[0003] Such R, G, B as an input,
FIG. 8 shows a configuration example of a color conversion processing device using a color conversion table for outputting C, M, Y, and K. In FIG. 8, reference numeral 1 denotes a read lattice point address operation unit, 2 denotes a color conversion table, and 3 denotes an interpolation operation unit. A color conversion processing device having a configuration as shown in FIG. 8 is well known, but will be briefly described below. In the following, it is assumed that R, G, and B to be input are each 8 bits and have 256 gradations. It is also assumed that C, M, Y, and K have 8 bits and 256 gradations.

First, the color conversion table 2 will be schematically described. Considering a three-dimensional input color space having three axes of input colors R, G, and B, a combination of predetermined values of R, G, and B is determined as a grid point, and an output is generated for each of the grid points. A set of four color values of C, M, Y, and K is registered. A color conversion table is obtained by registering a set of four color values of C, M, Y, and K output for each grid point. For example, for all of the inputs R, G, B, 0, 15, 30, 45, 60, 75, 9
0, 105, 120, 135, 150, 165, 180, 195, 210, 225, 24
Assuming that 18 gradation values of 0 and 255 are taken and a grid point is determined by a combination of these gradation values, 5832 (= 18 × 18 × 18) grid points are included in the three-dimensional input color space. Will be determined.

Of course, it is desirable to register output values of C, M, Y, and K for all combinations of R, G, and B values that are input. In this case, a color conversion table is used. Since the amount of data of the output color values registered in the color conversion table becomes enormous, the grid points are determined at intervals in the three-dimensional input color space as described above, thereby reducing the amount of data registered in the color conversion table. It is trying.

Next, the operation of the color conversion processing apparatus shown in FIG. 8 will be described. Here, it is assumed that the interpolation operation unit 3 performs a linear interpolation operation by the cubic interpolation method.

When the values of the three colors R, G, and B are input, the read grid point address operation unit 1 outputs the input values of R, G, and B.
8 surrounding a point in the three-dimensional input color space determined by the values of G and B
Are obtained by calculating addresses on the color conversion table 2 in which the output color values of the eight grid points are registered, and are used as inputs to the color conversion table 2. In addition,
In the read-out grid point address calculation unit 1, it is registered in advance at which address on the color conversion table 2 the output color value determined for which grid point is registered.

Thus, from the color conversion table 2,
Output color values determined for these eight grid points are output. FIG. 8 shows these values as C ′,
M ', Y', and K ', but actually C' is C '
_{1, C '2, C'} 3, C '4, C' 5, C '6, C' 7, C '8
8 values are included. The same applies to M ', Y', and K '.

At this time, as described above, the read grid point address calculation unit 1 calculates the output color values of the eight grid points surrounding the point in the three-dimensional input color space determined by the input R, G, and B values. Is calculated and input to the color conversion table 2 and the input R,
A weighting coefficient used when the interpolation calculation unit 3 performs a linear interpolation calculation by the cubic interpolation method based on the positional relationship between a point on the three-dimensional input color space of G and B and eight grid points surrounding the point. Is calculated and supplied to the interpolation calculation unit 3.

[0010] The interpolation operation unit 3 uses the C ', M', Y ', and K' output from the color conversion table 2 and the weighting factor supplied from the read grid point address operation unit 1 to perform a cubic interpolation method. Performs a linear interpolation operation with
C, M, Y, and K corresponding to the G and B values are calculated and output. Then, C, M, Y and K are supplied to the print engine.

It is well known that an operation for obtaining eight grid points surrounding a point in a three-dimensional input color space determined by input R, G, and B values, an operation for obtaining a weighting coefficient, and a linear interpolation operation using a cubic interpolation method. Therefore, detailed description is omitted.

The above is a case where a point in the three-dimensional input color space determined by the input R, G, and B values does not coincide with a lattice point.
If it matches the grid point, the read grid point address calculator 1 calculates the address on the color conversion table 2 in which the output color value of the grid point is registered, and sends it to the color conversion table 2. Input. At this time, the read-out grid point address calculator 1 supplies the interpolation calculator 3 with a predetermined weighting coefficient for instructing the output from the color conversion table 2 to be output as it is. As a result, from the color conversion table 2, only the value of the output color determined for the one grid point is output, and the interpolation operation unit 3
Outputs it as it is.

In the above description, the interpolation operation unit 3 performs the linear interpolation operation by the cubic interpolation method, but may perform the linear interpolation operation by the tetrahedral interpolation method. In this case, output color values C ′ _{1 to} C ′ ₄ , M defined at four grid points forming a tetrahedron surrounding a point on the three-dimensional input color space determined by the input R, G, and B values. ′
Performing interpolation calculation using _{1 ~M '4, Y' 1} ~Y '4, K' 1 ~K '4, and the weighting factor. When a point determined by the input R, G, and B values coincides with a lattice point, only the value of the output color defined at the lattice point is output from the color conversion table as in the case of the cubic interpolation method. The same is true.

[0014]

However, when printing is performed using C, M, Y, and K generated by the conventional configuration shown in FIG. 8, a black tone jump occurs at a black outline portion of the image. In some cases, the image quality was noticeably degraded.

This is because the black output characteristics with respect to the input R, G, and B values have strong nonlinearity.
That is, first, C, M, Y with respect to the density of the input R, G, B
The output density characteristics are as shown in FIG. 9A, and are substantially linear with respect to the R, G, and B input color spaces. When the linear interpolation operation is performed by the tetrahedral interpolation method, a large error occurs between the values of C, M, and Y obtained as a result of the linear interpolation operation and the values of C, M, and Y that are truly required at that time. Does not occur. Note that the horizontal axis in FIG. 9 indicates the density of one of the inputs R, G, and B, and the characteristics indicated by a in FIG.
The graph shows the density characteristics of one output color of C, M, and Y with respect to the density of one input color of B.

However, as shown in FIG. 9B, the black output density characteristic has a characteristic that the input color density rises sharply from a certain point, and has strong nonlinearity.
Note that the characteristic indicated by B in FIG. 9 indicates the characteristic of the output density of K with respect to the density of one input color of R, G, and B. Since the black output density characteristic with respect to the input R, G, and B densities is such a non-linear characteristic, a black tone jump becomes conspicuous in a black contour portion of an image or the like.

The reason is conceptually described as follows. Here, in order to facilitate understanding, only generation of K is considered, and the input R, G, B
Is output at the two grid points sandwiching the point determined by, and from the two K 'values, the interpolation operation unit 3 takes the average value of the two K' values. It is assumed that K is generated and output by a linear interpolation operation.

Now, when R, G, and B are input, the 2 selected by the read grid point address arithmetic unit 1
Assuming that the density of K ′ at two grid points is K ′ _a , K ′ _b as shown in FIG. 10, and the density of black generated by the linear interpolation operation by the interpolation operation unit 3 is K in FIG. I do. However, according to the output density characteristic of K shown in (b), the required black density at this time is K ₀ in FIG. 10, and as a result, when printing is performed, black is not generated for the pixel. The output will be darker than necessary. This will stand out as a black tone jump.

As can be easily understood from the above description, the generation of an unnecessarily large density of black is caused by
Because it is remarkable at the rising part of the black output density characteristic,
In particular, a black tone jump becomes conspicuous in a black outline portion or the like of an image.

In addition, the fact that an unnecessarily large black is generated as described above means that the interpolation operation unit 3
Under color removal (UCR) for C, M, Y output from
Is performed, it means that the undercolor removal amount (UCR amount) becomes unnecessarily large, and together with this, the black tone jump becomes conspicuous.

In the above, a case has been described in which a very simple linear interpolation operation of taking the average of the values of K 'defined at two grid points is performed. The same holds for the case of performing a linear interpolation operation using the body interpolation method.

Therefore, the present invention provides a color conversion processing method and a color conversion processing apparatus which can make tone jumps inconspicuous when generating black and other output colors from inputs R, G, B. It is intended to provide.

[0023]

According to a first aspect of the present invention, there is provided a color conversion processing method comprising the steps of: inputting a predetermined color among cyan, magenta, yellow, and black to a color conversion table; An intermediate parameter having a linear output characteristic with respect to the color space is registered, a new intermediate parameter is generated by performing a linear interpolation operation on the intermediate parameter output from the color conversion table, and based on the new intermediate parameter. An output color value is generated. Claim 2
The color conversion processing method according to claim 1, wherein the means for generating an output color value based on the new intermediate parameter is a one-dimensional lookup table. In the color conversion processing method according to the third aspect, for at least black, an intermediate parameter having a linear output characteristic with respect to the input color space is registered in the color conversion table, and the intermediate parameter output from the color conversion table is registered. It is characterized in that a new intermediate parameter is generated by a linear interpolation operation, a black output color value is generated based on the new intermediate parameter, and an undercolor removal amount is generated. The color conversion processing device according to claim 4, wherein a color conversion table in which intermediate parameters having linear output characteristics with respect to an input color space are registered for a predetermined color among cyan, magenta, yellow, and black; An interpolation unit that performs a linear interpolation operation on the intermediate parameters output from the conversion table to generate new intermediate parameters, and a color that generates an output color value based on the new intermediate parameters generated by the interpolation operation unit Generating means.
According to a fifth aspect of the present invention, in the color conversion processing apparatus according to the fourth aspect, the color generation means is a one-dimensional lookup table. The color conversion processing device according to claim 6, wherein at least with respect to black, a color conversion table in which intermediate parameters having linear output characteristics with respect to an input color space are registered, and an intermediate parameter output from the color conversion table. An interpolation operation unit that performs a linear interpolation operation to generate a new intermediate parameter; a color generation unit that generates an output color value based on the new intermediate parameter generated by the interpolation operation unit; And an under color removal amount generating means for generating an under color removal amount based on the new intermediate parameter.

[0024]

Embodiments of the present invention will be described below with reference to the drawings. In the following description, R, G, B, C ', M', Y ', P', P ", C,
M, Y, and K are all 8 bits and have 256 gradations, and the following values represent gradation values. It is also assumed that when R = G = B = 0, the image is completely black, and when R = G = B = 255, the image is completely white.

FIG. 1 is a diagram showing an embodiment of a color conversion processing device according to the present invention. In the drawing, reference numeral 10 denotes a color conversion table;
Reference numeral 11 denotes a black generation unit. Since the read grid point address calculation unit 1 and the interpolation calculation unit 3 are the same as those in the related art, FIG.
The same reference numerals are used, and the description is kept to a minimum.
Although the interpolation operation unit 3 performs the linear interpolation operation by the cubic interpolation method, the interpolation operation unit 3 may perform the linear interpolation operation by the tetrahedral interpolation method as described above.

First, the color conversion table 10 will be described. In the color conversion table 10, a set of output values of four colors of cyan, magenta, yellow, and black is registered for each grid point defined by a combination of predetermined values of R, G, and B. The output characteristics of cyan, magenta, and yellow registered in the color conversion table 10 for each grid point are the same as those of the related art. In FIG. 1, FIG.
Similarly, the values of cyan, magenta, and yellow output from the color conversion table 10 are indicated by C ', M', and Y ', respectively.

However, with respect to black, what is registered in the color conversion table 10 for each grid point does not directly represent the output value of black, but is linearly registered in the three-dimensional input color space of R, G, and B. This is an intermediate parameter having various characteristics.

Here, the linear characteristic with respect to the three-dimensional input color space of R, G, B means that the value obtained by the linear interpolation operation in the interpolation operation unit 3 and the input R, G, B value In the case of, there is no error or a very small characteristic from the value truly required. Therefore, simply, C ′,
The output characteristics may be similar to those of M 'and Y'.

In FIG. 1, intermediate parameters output from the color conversion table 10 are indicated by P '.
As will be described later, the value of P ′ output from the color conversion table 10 is not used directly for printing as a black value, but is used for generating black used for printing.

C ', registered in the color conversion table 10
FIG. 2 shows some examples of the values of M ', Y', and P '. FIG.
(A) shows C ', R, G, and B inputs for the flesh color area.
FIG. 2B shows an example of output values of M ', Y', and P ', and FIG. 2B shows C', M ', and R' for the R, G, and B inputs in a slightly dark blue region.
An example of output values of Y 'and P' is shown.

Next, the black generation means 11 will be described.
For black, the interpolation operation unit 3 performs a linear interpolation operation on the eight intermediate parameters P ′ output from the color conversion table 10 and outputs new intermediate parameters P ″.
In FIG. 1, the new intermediate parameter P ″ is indicated as a second intermediate parameter, but is hereinafter referred to as a second intermediate parameter. Based on P ", a black K actually used for printing is generated, and a predetermined operation may be performed to generate K from the second intermediate parameter P". , A one-dimensional lookup table in which the output value of K is written (hereinafter, the lookup table is referred to as LUT).

In the former case, what kind of function is used to generate K from the second intermediate parameter P ″ is arbitrary, but as described above, K is nonlinear with respect to the inputs R, G, and B. Therefore, the function for generating K from P ″ is
It becomes nonlinear. As an example, for example, a function as shown in the following equation (1) can be used as an operation performed by the black generation unit 11.

[0033]

(Equation 1) That is, in this case, when P ″ is input, the black generation unit 11 automatically performs the operation of the expression (1) to generate and output K.

When a one-dimensional LUT that outputs K using the value of P ″ as an input address is used as the black generation means 11, the one-dimensional LUT includes values of 0 to 255 of P ″. On the other hand, an appropriate value of K may be written. FIG. 3 shows an example of the structure of such a one-dimensional LUT. In the one-dimensional LUT shown in FIG. 3, the relationship between the second intermediate parameter P ″ and the black K is actually nonlinear. In FIG. = 0
K is assigned 1 or 2 for P ″ = 98-109, and K is 2 for P ″ = 111-127.
To 5 are assigned. The same applies to other ranges of P ". However, K for a certain P"
The value, "are made with more than the value of K for. That, P" it smaller P When the value of K when the value of a i (i = 0~255) represented by K _i, K _{i −1} ≦ K _i .

In the case where a one-dimensional LUT is actually used as the black generating means 11, what kind of K value is assigned to each of the values of P ″ from 0 to 255 is determined by the color conversion table 10. In consideration of the characteristics of the intermediate parameter P ′ to be registered in the, it is sufficient to determine what kind of K should be assigned to what kind of P ″ by an experiment or theoretical calculation, and write it into the one-dimensional LUT.

Hereinafter, the operation of the color conversion processing apparatus shown in FIG. 1 will be described. Now, when the values of R, G, and B are input, the read grid point address calculation unit 1 performs the above-described operation to convert the points in the three-dimensional input color space determined by the input values of R, G, and B. The eight surrounding grid points are obtained, and the addresses of the eight grid points on the color conversion table 10 in which the values of C ', M', Y ', and P' are registered are calculated to obtain the color values. A weighting coefficient used when performing a linear interpolation calculation by the cubic interpolation method is calculated and obtained by the interpolation calculation unit 3 as an input to the conversion table 10, and the obtained weighting coefficient is supplied to the interpolation calculation unit 3.

Thus, from the color conversion table 10, C ′, C ′,
The values of M ', Y', P 'are output. Then, the interpolation operation unit 3 outputs C ′,
A linear interpolation operation is performed by the cubic interpolation method using M ', Y', P 'and the weighting factor supplied from the read grid point address operation unit 1, and C, C, and C corresponding to the input R, G, B values are obtained.
M, Y, and P ″ are calculated and output. At this time, C, M, and Y output from the interpolation calculation unit 3 are supplied to the print engine, but the second intermediate parameter P ″ is input to the black generation unit 11. Then, K is generated and supplied to the print engine.

The above is a case where a point in the three-dimensional input color space determined by the input R, G, and B values does not coincide with a lattice point.
If it matches the grid point, the read grid point address calculation unit 1 calculates and calculates an address on the color conversion table 10 in which the output color value of the grid point is registered. In addition to input,
A predetermined weighting coefficient is supplied to instruct that the output from the color conversion table 10 be output as it is.
As a result, only the values of C ′, M ′, Y ′, and P ′ determined for the one grid point are output from the color conversion table 10, and are directly output from the interpolation calculation unit 3. Then, C ', M', and Y 'are supplied to the print engine as they are, and P' is directly input to the black generation means 11, where K is generated and supplied to the print engine.

For example, if the black generation means 11 is the one-dimensional LUT shown in FIG. 3 and a part of the color conversion table 10 is as shown in FIG. 2, the input values of R, G, and B are Assuming that (R, G, B) = (89, 46, 49), the read-out grid point address calculation unit 1 performs the operation shown in FIG.
The addresses of the grid points are input to the color conversion table 10, and the weighting coefficients are obtained and supplied to the interpolation calculation unit 3. Then, (C, M, Y, P ″) = (177, 2) is obtained by the linear interpolation operation by the cubic interpolation method in the interpolation operation unit 3.
19, 191 and 51), the value of K generated by the black generating means 11 becomes 0 from FIG.

Assuming that the input values of R, G, B are (R, G, B) = (50, 66, 66) representing a slightly dark blue region, the read grid point address calculation unit 1 will be described with reference to FIG. The addresses of the eight grid points shown in (b) are input to the color conversion table 10, and the weighting coefficients are obtained and supplied to the interpolation calculation unit 3. Then, (C, M, Y, P ″) = (220, 1) is obtained by the linear interpolation calculation by the cubic interpolation method in the interpolation calculation unit 3.
83, 177, 174), the value of K generated by the black generation means 11 is 34 from FIG.

The following is a comparison of these black values with the black values generated by the conventional black generation method. Conventionally, as a method of generating K from the values of C, M, and Y, a method of setting the minimum value of C, M, and Y generated from inputs R, G, and B to the value of K is known. According to the method, K = 177 in both cases. On the contrary,
According to this color conversion processing device, it is possible to suppress the occurrence of black in a skin color region where black dots are more conspicuous, and in a slightly darker blue region where a sharp color including black is required, a lower density step is required. It can be seen that good color reproducibility can be obtained in both the skin color region and the slightly darker blue region since black can be added from the image.

The values of K generated by the color conversion processing device and the input R,
A comparison with the value of K generated by the method of generating C, M, Y, and K from G and B is as follows.

First, a method of generating C, M, Y, and K from conventional inputs R, G, and B using the configuration shown in FIG. 1 will be considered. Obviously, when the values of the inputs R, G, and B coincide with the lattice points, C'M'Y'P 'of the lattice point is output from the color conversion table. Further, a desirable value of K for each P ″ can be obtained from the relationship in FIG.
Therefore, by describing the value of K with respect to P ′ at each grid point instead of P ″ of the one-dimensional LUT of the black generation unit 11,
A conventional color conversion table can be imitated. That is, the relationship between P ′ and K is described in the one-dimensional LUT of the black generation unit 11. FIG. 4 shows an example of a part of the conventional color conversion table simulated in this manner. FIG. 4 shows an example of output values of C ', M', Y ', and K for R, G, and B inputs in a slightly dark blue region, as in FIG. 2B.

Now, (R, G, B) = (48, 6
Taking as an example the generation of K at a transition portion where blue gradually deepens from (4, 70) to (48, 64, 90), the generation of K in this color conversion processing device and the generation of K by the conventional method When compared with the result, the result was as shown in FIG. In addition, based on the comparison result shown in FIG. 5, the output value of K with respect to the value of input B is plotted and graphed as shown in FIG.
In FIG. 6, the solid line shows a graph of the output value of K with respect to the value of input B in the color conversion processing device, and the broken line shows a graph of the output value of K with respect to the value of input B in the conventional method. .

FIGS. 5 and 6 show that in the conventional method, when the input B value falls below 80, the K output value sharply increases. Then, when printing is performed, such a rapid change in K is recognized as a tone jump and causes a deterioration in image quality. On the other hand, according to this color conversion processing device, since the output of K changes gently with respect to the input B value, the tone jump which occurs in the conventional method is not recognized. Printing can be performed with good image quality.

As described above, according to this color conversion processing apparatus, regarding the generation of black K, the output characteristics of P ′ defined at each grid point registered in the color conversion table 10 are as follows:
Since it is linear with respect to the three-dimensional input color space of R, G, and B, no error is caused by the linear interpolation operation by the interpolation operation unit 3, or even if the error is caused, the error is smaller than the conventional one. . Then, based on the second intermediate parameter P ″ obtained as a result of the linear interpolation operation by the interpolation operation unit 3, the black generation unit 11 generates black K for printing. , Independent of the values of the inputs R, G, B, the relationship between the second intermediate parameter P ″ and K can be a desired non-linear relationship.

As a result, no distortion occurs at the time of black generation due to the linear interpolation operation in the interpolation operation unit 3 as conventionally occurred, so that the amount of black to be printed can be optimized. A black tone jump is not conspicuous at the black outline portion of the image, and a high-quality image can be obtained.

In the above description, the generation of black has been described, but the generation of cyan, magenta, and yellow can be similarly performed. That is, although the output characteristics of cyan, magenta, and yellow defined for the grid points can be treated as substantially linear characteristics, the errors at the time of generating cyan, magenta, and yellow by the linear interpolation operation in the interpolation operation unit 3 are obtained. Alternatively, when the distortion is to be reduced, the output characteristics of cyan, magenta, and yellow registered in the color conversion table 10 for each grid point are also similar to the black generation of the color conversion processing device shown in FIG. , G, and B, registering intermediate parameters having more linear characteristics in the three-dimensional input color space, and further generating cyan, magenta, and yellow having desired characteristics based on the output from the interpolation operation unit 3. A generator, a magenta generator, and a yellow generator may be provided. As with the black generation unit 11, the cyan generation unit, the magenta generation unit, and the yellow generation unit perform a predetermined calculation based on new intermediate parameters obtained by performing linear interpolation calculation in the interpolation calculation unit 3. , Magenta, and yellow output values can be generated.
, A one-dimensional LUT in which cyan, magenta, and yellow output values are written for new intermediate parameters obtained by performing a linear interpolation operation.

In the above description, the UCR has not been described, but the generation of the UCR amount can be performed by the same means as the black generation. FIG. 7 shows a configuration example in that case. In FIG. 7, the read grid point address calculation unit 1, the color conversion table 10, the interpolation calculation unit 3, and the black generation unit 11
Is the same as described above.

In the configuration shown in Fig. 7, there is provided a UCR amount generating means 12 for generating a UCR amount from the second intermediate parameter P "output from the interpolation operation unit 3. This UCR is provided.
The amount generating means 12 may generate the UCR amount from the second intermediate parameter P ″ by a predetermined operation, similarly to the black generating means 11, and the UCR amount is written to the value of the second intermediate parameter. The UCR amount generated by the UCR amount generating means 12 is subtracted from C, M, and Y output from the interpolation operation unit 3 by subtractors 13, 14, and 15. UCR can be performed by subtraction.

Also in this case, the intermediate parameter P 'registered in the color conversion table 10 for each grid point has a linear characteristic with respect to the three-dimensional input color space.
There is an effect that the characteristics of the UCR amount can be made smooth.

Further, in this color conversion processing device, as described above, the generation amount of K can be changed for each color gamut determined by the inputs R, G, and B. When the generation amount of K is changed for each area, it is generally difficult to match the generation amount of K with the UCR amount. But,
Since the intermediate parameter is also used for the generation of the UCR amount, it is easy to match the K generation amount with the UCR amount, and therefore, the inversion of the gradation concentration caused by the mismatch between the K generation amount and the UCR amount. And other image quality defects can be prevented.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a color conversion processing device according to the present invention.

FIG. 2 is a diagram illustrating C ′ and C ′ registered in a color conversion table 10 of FIG. 1;
It is a figure showing some examples of the value of M ', Y', and P '.

FIG. 3 is a diagram illustrating an example of a structure of a one-dimensional LUT when the black generation unit 11 of FIG. 1 is configured by a one-dimensional LUT.

FIG. 4 is a diagram showing an example of a part of a conventional color conversion table.

FIG. 5 is a diagram showing a result of comparing the occurrence of K in the color conversion processing device with the occurrence of K according to a conventional method.

FIG. 6 is a graph obtained by plotting the output value of K with respect to the value of input B from the result of the comparison shown in FIG. 5;

FIG. 7 is a diagram illustrating another configuration example of the color conversion processing device according to the present invention, and is a diagram illustrating a configuration example in a case where black K is generated and a UCR amount is generated.

FIG. 8 is a diagram illustrating a conventional configuration example of a color conversion processing device using a color conversion table that outputs R, G, and B as inputs and outputs C, M, Y, and K;

FIG. 9 is a diagram for explaining output density characteristics of C, M, and Y with respect to input R, G, and B densities.

FIG. 10 is a diagram for explaining a problem to be solved by the invention.

[Explanation of symbols]

1 ... Reading grid point address calculation unit, 2 ... Color conversion table,
3 ... interpolation operation unit, 10 ... color conversion table, 11 ... black generation means, 12 ... UCR amount generation means.

 ──────────────────────────────────────────────────の Continued on front page F term (reference) 2C262 AC02 BA02 BA07 BC01 BC03 BC15 BC19 5B057 AA11 CA01 CA08 CA12 CA16 CB01 CB08 CB12 CB16 CC01 CE17 CE18 CH01 CH07 5C077 LL19 MP08 PP15 PP32 PP33 PP37 PP38 PQ12 PQ18 PQ23B1919 HB12 LA21 LB02 MA04 MA11 NA02 PA03

Claims (6)

[Claims] An intermediate parameter having a linear output characteristic with respect to an input color space is registered in a color conversion table for a predetermined color among cyan, magenta, yellow, and black, and output from the color conversion table. A color conversion processing method, wherein a new intermediate parameter is generated by performing a linear interpolation operation on the set intermediate parameter, and an output color value is generated based on the new intermediate parameter. 2. The color conversion processing method according to claim 1, wherein said means for generating an output color value based on said new intermediate parameter is a one-dimensional lookup table. 3. For at least black, an intermediate parameter having a linear output characteristic with respect to an input color space is registered in a color conversion table, and the intermediate parameter output from the color conversion table is linearly interpolated and newly registered. A color conversion processing method for generating an intermediate parameter, generating an output color value of black based on the new intermediate parameter, and generating an undercolor removal amount. 4. A color conversion table in which intermediate parameters having linear output characteristics with respect to an input color space are registered for a predetermined color among cyan, magenta, yellow, and black, and output from the color conversion table. An interpolation operation unit that performs a linear interpolation operation on the intermediate parameter to generate a new intermediate parameter, and a color generation unit that generates an output color value based on the new intermediate parameter generated by the interpolation operation unit A color conversion processing device characterized by the above-mentioned. 5. The color conversion processing method according to claim 4, wherein said color generating means is a one-dimensional lookup table. 6. For at least black, a color conversion table in which intermediate parameters having linear output characteristics with respect to an input color space are registered, and a linear interpolation operation is performed on the intermediate parameters output from the color conversion table. An interpolation operation unit that generates a new intermediate parameter by using a new intermediate parameter generated by the interpolation operation unit; a color generation unit that generates an output color value based on the new intermediate parameter generated by the interpolation operation unit; A color conversion processing device comprising: an undercolor removal amount generation unit that generates an undercolor removal amount based on the undercolor removal amount.