JP2001036760A - Multicolor separation method and multicolor separation system - Google Patents

Abstract

(57) [Problem] To provide a rational method for accurately converting special color plate making data to multi-color separation data including auxiliary colors using multi-color DDCP, and to provide such a multi-color separation system. The task is to To solve the above problem, a first invention is a multi-color separation method of a color sample, and selects three colors from primary colors of a color output device that reproduces colors with four or more component colors. 3
A first step of preparing a plurality of correspondence tables (LUTs) for associating combinations of color halftone percentages (three-color grid points) with chromaticity values of color pieces output by the color output device; A second step of selecting an optimum LUT from the plurality of LUTs from the chromaticity values of the color samples obtained by the measurement, and calculating three of the LUTs by interpolation from the selected LUT and the chromaticity values. A third step of obtaining a color separation value based on color is provided to obtain a color separation value that optimally reproduces a color sample color with a process color and an auxiliary color of a multicolor printer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to C (cyan), M
Process 4 for (magenta), Y (yellow), and K (black)
The present invention relates to a multi-color separation method and a multi-color separation apparatus for faithfully reproducing a color sample specified by chromaticity or the like in a multi-color printer that reproduces a color and one or more other auxiliary colors. The present invention also relates to a multi-color separation system that obtains color separation data that faithfully reproduces color in plate making data created for the purpose of printing using a so-called special color ink other than process colors in the multi-color printer.

[0002]

2. Description of the Related Art Generally, in the printing industry, a proof print is submitted in order to obtain the confirmation of a print orderer regarding color reproduction and design appearance before printing on a printing press. Nowadays, a method of producing a proof with an output of a digital color printer (DDCP) of an ink jet method or a sublimation transfer method without producing a proof with a proof press is being adopted between a printing company and a print orderer. .

[0003] In digital color printers and proofs or main presses, ie offset printing or gravure printing,
The color reproduction is different due to the differences in the hue of the primary colors of the process colors used, the paper, the coloring mechanism, and the like. Therefore, an appropriate color matching process is applied to the original plate making data to create output data for DDCP. , Is usually used.

[0004]

However, in the field of packaging printing, conventionally, for the purpose of stabilizing reproduced colors,
Or, it is common to use an ink called a special color other than the process color in order to appeal to the consumer of the product. In particular, when a special color is used for the latter reason, a color with high lightness and high saturation is often used, and there is a problem that color reproduction cannot be faithfully performed in a DDCP that reproduces colors with CMYK process colors. Therefore, recently, in order to expand the color gamut, multicolor DDCPs that use five or more color materials using auxiliary colors such as green and orange in addition to process colors have also become commercially available, but are reproduced as special colors. A multicolor separation method for converting platemaking data including colors to be processed into multicolor separation data including auxiliary colors with high accuracy and efficiency has not been established, and multicolor DDCP can be effectively utilized. There is a problem that there is no.

The present invention has been made in view of such problems, and is a rational method of converting special color plate making data into multi-color separation data including auxiliary colors with high accuracy using a multi-color DDCP. It is an object to present a method and such a multicolor separation system.

[0006]

In order to solve the above-mentioned problems, a first invention is a multi-color separation method of a color sample, which comprises a color output device for reproducing colors with four or more primary colors.
A plurality of correspondence tables (LUTs) for selecting three colors and associating a combination of halftone percentages of three colors (three-color grid points) with the chromaticity values of color pieces output from the color output device using the three-color grid points. ), A second step of selecting an optimum LUT from the plurality of LUTs from the chromaticity values of the color sample obtained by the measurement, and a step of selecting the selected LUT and the chromaticity. And a third step of obtaining color separation values for the three colors of the LUT from the values by interpolation calculation to obtain color separation values that optimally reproduce the color of the color sample using the process colors and auxiliary colors of the multicolor printer. The point is to obtain.

In the first step, the chromaticity values of the color pieces that are actually output from the multicolor printer with respect to the combination of the halftone values of the three colors of the multicolor printer (three-color grid points). Can be associated with a certain roughness. Three
The more the number of color grid points, the more accurate the correspondence. Since there are generally four or more combinations for selecting three colors from the colors used in a multicolor printer, a plurality of LUTs are prepared.

In the second step, only one optimal LUT for performing color separation calculation is selected. The LUT having three-color grid points associated with the chromaticity value of the special color sample and the chromaticity value of the minimum chrominance may be selected based on any criteria.
The most natural choice is UT.

Then, in a third step, interpolation calculation is performed using the three-color grid points on the optimal LUT having chromaticity values close to the chromaticity values of the color sample as a clue, and the chromaticity values of the color sample are converted into the optimal LUT. 3
Calculate the value separated by color. Since the conversion from the three-color grid points to the chromaticity values may be regarded as a smooth continuous function, it is reasonable to use the three-color grid points of the LUT having chromaticity values near the chromaticity values of the color sample as a clue. It is a target. By setting the separation values of the primary colors other than the three colors of the optimum LUT to zero in the three-color separation values of the interpolation calculation result, the multi-color separation values of the color sample are finally obtained.

In order to further efficiently perform multi-color separation, the first step is configured to include only LUTs of all combinations of three adjacent hues from all component colors except K. Can be. In general, color samples often target bright and bright colors. Therefore, there is no practical problem even if a color combination LUT including K is excluded, and the configuration is simple and preferable.

In order to further efficiently and accurately perform multi-color separation, the first step is to perform an LUT of all combinations of three adjacent hues from all component colors except K.
, And one or more LUTs of a combination of three colors including K. By adding LUTs of three colors including K, it becomes possible to accurately separate vivid colors having relatively high density. For example, if the color sample also includes a vivid color having a relatively high density, such as a dark brown color, a dark blue / dark purple color, a sepia color, and the like, M
YK LUT, CMK LUT, MOrangeK LUT
Is provided, accurate decomposition can be performed. Omitting the LUTs of other color combinations does not cause any practical problems, and the configuration is simple and preferable.

A second aspect of the present invention for solving the above-mentioned problem is to provide four auxiliary processes of C (cyan), M (magenta), Y (yellow) and K (black) and one or more other colors. Regarding a color proofing device that reproduces a color as a component color, the color proofing is performed by a combination of three halftone percentages (three-color grid points) formed by selecting three of the component colors and the three-color grid points. A multi-color separation apparatus comprising a plurality of LUTs for associating chromaticity values of color pieces obtained by the apparatus and a color sample separation means for a calibration printer, wherein the color sample separation means for a calibration printer comprises: An optimal LUT selecting means for selecting an optimal LUT for performing the decomposition calculation;
The gist of the present invention is to include an interpolation calculating means for calculating a separation value of three colors with respect to the chromaticity value designated by the interpolation calculation with reference to the UT.

Since the color sample separation means for the proof printer is configured to execute the second step and the third step of the first invention, it is possible to obtain a multi-color separation value for the color sample.

A third aspect of the present invention for solving the above-mentioned problem is a special color-compatible multicolor separation system. Regarding a color proofing apparatus that reproduces four process colors of C (cyan), M (magenta), Y (yellow), and K (black) and one or more auxiliary colors as component colors, three of the primary colors are used. A plurality of correspondence tables which correspond to combinations of three-color halftone percentages (three-color grid points) formed by selecting colors and the chromaticity values of color pieces obtained by the color proofing device using the three-color grid points. (LUT), further comprising: a calibration printer color sample separation unit for calculating the separation data for the calibration printer using four process colors and auxiliary colors by referring to the LUT from the chromaticity values of the designated spot color sample; It is provided with a proof printer special color separation plate creating unit that receives image data and converts the separation data obtained by the proof printer color sample separation unit into process image and auxiliary color separation image data. The the gist.

By the function of the color sample separation means for the proof printer, a multi-color separation value is obtained from the chromaticity values of the special color sample, and the special color separation plate creating means for the proof printer uses the RIP means from the plate making image data including the special color portion. By receiving the converted special color plate image data and applying the multicolor separation value to the data, the special color plate 1 plate can be converted to the multicolor separation plate of the proof printer.

The color sample separation means for a proof printer of the multi-color separation system for spot colors corresponds to the most suitable LUT for performing the multi-color separation calculation so as to execute the second and third steps of the first invention. LUT selection means for selecting the
It is preferable to include an interpolation calculating means for calculating a separation value of three colors with respect to the chromaticity value designated by the interpolation calculation with reference to T.

[0017]

Embodiments of the present invention will be described below based on examples.

FIG. 1 is an overall block diagram of a special color-compatible multicolor separation system according to an embodiment of the present invention. Reference numeral 1 denotes a special color-compatible multicolor separation system, which is calibrated by a separation LUT 11, a color sample separation unit 12 for a calibration printer, and a special color separation plate creating unit 13 for a calibration printer. The decomposition LUT 11 is
A table in which chromaticity values corresponding to combinations of various halftone% values (three-color grid points) of three of the primary colors of the proof printer targeted by the multicolor separation system are associated. is there. Color sample separation means 12 for proof printer
Are the optimum LUT selection means 121 and the interpolation calculation means 12
2 which receives the colorimetric value of the color sample and
By properly referring to T11, a separation value of the color sample separated into the primary colors of the proof printer is calculated. Reference numeral 13 denotes a proof printer special color separation plate creating unit which receives the special color plate data 3 and converts the special color plate data 3 into multicolor separation plate data 4 in accordance with the separation value calculated by the proof printer color sample separation unit 12. .

In the present embodiment, a CI and a CIE (International Commission on Illumination) define the display space for the chromaticity of color samples and special color inks.
An ELAB (CIE1976L * a * b * display) space is used. Therefore, the measurement value of the colorimetric form is represented by (L *, a *, b *). The color difference ΔE representing the closeness of the two colors C1 and C2 is C1 = (L
When 1,2, (a1, b1) and C2 = (L2, a2, b2), it is calculated by ΔE = √ ((L1-L2) ** 2+ (a1-a2) ** 2+ (b1-b2) ** 2) Is done. Where A ** 2 is the square of A and √B is B
Means the square root of

In the present embodiment, the target multicolor proof printer uses the C, M, Y, and K process colors and the six primary colors of green (G) and orange (O). FIG. 2 is a flowchart showing the flow of the operation procedure of the spot color compatible multicolor separation system. Hereinafter, the operation of the present system will be described with reference to FIG.

First, as a preparation, an LUT for disassembly is prepared in step S10. Of the six component colors, five colors excluding K, one separation L from three adjacent colors of hue.
Create a UT. FIG. 3 shows the chromaticity coordinates of the gradation scale of each of the five colors, excluding K, projected on the a * b * plane of the LAB space. The circumferential direction of the concentric circle centered on the origin corresponds to the hue. Therefore, CMO, MOY, OYG, Y
It is necessary to create five types of decomposition LUTs, GC and GCM. Further, a separation LUT composed of three colors of CYK corresponding to the conversion of dark green is also created.

For each of the three LUTs, for each of the three colors, a halftone% value of each color (a value expressing a halftone as a percentage with solid being 100% and white being 0%) is set, for example, in 10 steps. All combinations of the three colors (1000 ways)
Is output by the target multicolor printer, and the obtained color patches are measured for chromaticity by a colorimeter.
It is created as a table in which three color combinations (three-color grid points) are associated.

Now that the preparation is completed, multicolor separation can be performed. In step S20, the color sample 2 is measured by the colorimeter. This measured value is used as the chromaticity value S (L
0, a0, b0). Now, assume that S is at the position indicated by the ★ mark in FIG. 3 as an example.

Next, in step S30, the LUT having a three-color grid point corresponding to the chromaticity value having the smallest color difference is provided in S (L0, a0, b0) by the operation of the optimum LUT selection means 121.
Select For example, the symbol “★” in FIG.
The UT is selected as the optimal LUT.

Next, at step S40, the interpolation calculation means 1
LUT that gives the chromaticity value S of the color sample by the operation of 22
A three-color separation value is determined. If there is a three-color grid point having a chromaticity value whose color difference from S is smaller than a predetermined color difference ε in the optimal LUT, it is set as the LUT three-color separation value. If not, at least four or more three-color grid points having a chromaticity value close to the chromaticity value S of the color sample are selected from the optimum LUT, and an LUT 3 that provides the chromaticity value S by appropriate interpolation calculation. Find the color separation value. With respect to the star mark in FIG. 3, the decomposition values of Y, G, and C are obtained.

This interpolation calculation can be performed, for example, as follows. Now, let the three colors of the optimal LUT be XYZ. The optimal three-color lattice point having the chromaticity Q closest to the chromaticity value S is defined as Q ′. At the grid point adjacent to Q ', the difference between the chromaticity value of the grid point Q'x, which has increased only the X component, and the chromaticity value of Q for each L * a * b * is divided by each increment. By doing so, the partial differential coefficients (∂L / ∂X, ∂a / ∂X, ∂) near Q ′ of the mapping from XYZ space to L * a * b * space
b / ∂X) is obtained. Similarly, by taking the difference between the chromaticity value of the adjacent grid point Q'y in which only the Y component has increased and the adjacent grid point Q'z in which only the Z component has increased and Q, and dividing the difference by each increment. And partial derivatives near Q '(∂L / ∂Y, ∂a / ∂Y, ∂b / ∂
Y), (∂L / ∂Z, ∂a / ∂Z, ∂b / ∂Z). As a result, the transformation matrix (） Lab) / (∂XYZ) of the mapping from the XYZ space near Q ′ to the L * a * b * space becomes ∂L / ∂X ∂a / ∂X ∂b / ∂X ∂L / ∂Y ∂a / ∂Y ∂b / ∂Y ∂L / ∂Z ∂a / ∂Z ∂b / ∂Z. By calculating the inverse matrix of this matrix, the transformation matrix (∂XYZ) / (∂Lab) =＝ X / ∂L∂Y / of the mapping from the L * a * b * space near the chromaticity value Q to the XYZ space ∂L ∂X / ∂L ∂X / ∂a ∂Y / ∂a ∂Y / ∂a ∂X / ∂b ∂Y / ∂b ∂Y / ∂b. From this conversion matrix, the XYZ value S ′ for the chromaticity S near Q can be obtained from the following equation from S−Q = (ΔL Δa Δb) and the inverse conversion matrix (∂XYZ) / (∂Lab). ΔX = (∂X / ∂L) ΔL + (∂X / ∂a) Δa + (∂X / ∂b) Δb ΔY = (∂Y / ∂L) ΔL + (∂Y / ∂a) Δa + (∂ Y / ∂b) Δb ΔZ = (∂Z / ∂L) ΔL + (∂Z / ∂a) Δa + (∂Z / ∂b) Δb S '= Q' + (ΔX, ΔY, ΔZ) Thus LUT 3 colors A decomposition value is determined. And optimal L
Assuming that the halftone% value of each primary color not in the UT is 0, a multicolor separation value of a color sample is obtained. FIG. 4 shows the relationship among S, Q, S ', and Q' to help understand the above description.

Finally, in step S50, the special color separation data is received and the multicolor separation data is generated by the operation of the special color separation generation means 13 for the proof printer. The special color plate data is the plate making data created by printing the color sample color with the special color ink and converted into bitmap data for each pixel of the special color by a RIP (Raster Image Processor) device or the like. Each gradation value is shown. Therefore, if the tone value of the pixel is 100% (special color solid), S40
The multi-color separation data is created using the multi-color separation values obtained in step (1) as the gradation values of the primary colors as the pixel data. When the tone value of the pixel of the special color plate is not 100%, a value obtained by multiplying the multicolor separation value by the gradation value is set as the value of the pixel of each multicolor separation plate.

If the multi-color separation data created in this way is output by a multi-color proof printer, a digital color proof similar to a printed matter actually printed with special color inks can be obtained by the wide color reproduction range of the multi-color configuration printer. can get.

Although the embodiment according to the present invention has been described above, various embodiments are possible without departing from the gist of the present invention. For example, the space representing the chromaticity value is not limited to L * a * b *. The calculation method for calculating an appropriate decomposition value from the three-color grid points of the LUT is not limited to this method, as the method described above is shown as one specific example. The number of grid points of the LUT may also be determined depending on the required accuracy and the cost required for realizing the device.

[0030]

As described above, according to the multicolor separation conversion method shown in the present invention, regardless of the number of component colors,
With the same technique, multicolor separation of an arbitrary color can be performed reasonably accurately. Further, by using the special color compatible multi-color separation system shown in the present invention, it is possible to convert the special color plate making data into multi-color separation data of the process color and the auxiliary color with high accuracy, and thus the color reproduction range is wide. Multicolor DD
A digital color proof for a special color plate can be accurately and rationally created using the CP. Until now, the DCCP that handles only CMYK process colors could not produce high-saturation, high-brightness special color digital proofs with sufficient accuracy.
The effect of the present invention is very large.

[Brief description of the drawings]

FIG. 1 is an overall view of an embodiment of a special color-compatible multicolor separation system according to the present invention.

FIG. 2 is a diagram showing an operation procedure flow of the special color-compatible multicolor separation system according to the present invention.

FIG. 3 shows C of each monochromatic scale of primary colors of a proof printer.
IELAB coordinate diagram

FIG. 4 is a reference diagram for describing a method of calculating a three-color separation value using an optimal LUT.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Multicolor separation system for special colors 2 Color samples 3 Special color plate data 4 Multicolor separation data 11 LUT for separation 12 Color sample separation unit for proof printer 13 Special color separation plate creation unit for proof printer 121 Optimal LUT selection unit 122 Interpolation calculation unit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5C077 LL12 LL20 MM27 PP31 PP33 PP36 PP38 PP41 PP43 PQ08 PQ23 RR19 TT08 5C079 HB00 HB03 KA04 KA12 LA02 LA28 LA31 MA04 MA10 NA29 PA07

Claims (7)

[Claims] 1. A three-color grid point which is a combination of three halftone percentages of three colors selected from component colors of a color output device that reproduces four or more colors, and the three-color grid point is used as the color output device. A first step of preparing a plurality of correspondence tables (LUTs) for associating the chromaticity values of the color pieces obtained by the above-mentioned steps, and the chromaticity values of the designated color samples from the plurality of LUTs. A second step of selecting the optimal LUT, and the selected LUT
Based on the UT and the chromaticity values, the 3
A third step of obtaining a color separation value by color. 2. The multicolor sampler according to claim 1, wherein the first step is to prepare an LUT of all combinations of three adjacent colors of hues of other component colors except K. Color separation method. 3. The method according to claim 1, wherein the first step is a LUT of all combinations of three adjacent colors of hues of other component colors except K.
And a method of preparing one or more LUTs of a combination of three colors including K and three colors including K. 4. The color according to claim 1, wherein in the second step, an LUT including a three-color grid point having a chromaticity value of a color sample and a chromaticity value of a minimum chrominance is selected as an optimal LUT. Sample multicolor separation method. 5. A color proofing apparatus that reproduces four process colors of C (cyan), M (magenta), Y (yellow), and K (black) and one or more other auxiliary colors as component colors. A three-color grid point, which is a combination of halftone percentages of the three colors, formed by selecting three of the component colors, and a chromaticity value of a color piece obtained by outputting the three-color grid point by the color proofing device A proof printer comprising a plurality of correspondence tables (LUTs) for associating the four color values of the process with the chromaticity values of the color samples obtained by the measurement by referring to the plurality of LUTs. A multi-color separation apparatus further comprising color sample separation means for use, wherein the color sample separation means for a proof printer includes an optimum LUT selection means for selecting an optimum LUT for performing multi-color separation calculation, and an optimum LUT. Color indicated by interpolation calculation with reference A multi-color separation apparatus configured to include interpolation calculation means for calculating three-color separation values for degree values. 6. A color proofing device that reproduces four process colors of C (cyan), M (magenta), Y (yellow), and K (black) and one or more other auxiliary colors as component colors. A three-color grid point, which is a combination of halftone percentages of the three colors, formed by selecting three of the component colors, and a chromaticity value of a color piece obtained by outputting the three-color grid point by the color proofing device And a plurality of correspondence tables (LUTs) for associating the LU with the chromaticity value of the designated spot color sample.
A color sample separation unit for a calibration printer for calculating separation data for a calibration printer using four process colors and auxiliary colors with reference to T, and a separation obtained by the color sample separation unit for a calibration printer after receiving special color image data. A special color-compatible multicolor separation system, comprising: a special color separation plate creating unit for a proof printer that converts data into separation image data of process colors and auxiliary colors based on data. 7. The color sample separation means for a proof printer,
An optimum LUT selecting means for selecting an optimum LUT for performing multi-color separation calculation, and an interpolation calculating means for calculating a separation value of three colors with respect to the chromaticity value designated by the interpolation calculation with reference to the optimum LUT. The spot color-compatible multi-color separation system according to claim 6, wherein the system is configured.