Takahashi, Kosei (Kanagawa, JP)
Yamada, Osamu (Tokyo, JP)

Plaque It!

10/974888

10/07/2008

10/28/2004

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Canon Kabushiki Kaisha (Tokyo, JP)

358/3.23

358/504, 382/162, 345/604, 358/518, 382/167, 358/1.9, 345/605, 345/600

G03F3/08; H04N1/46; H04N1/60; G09G5/02; G06K9/00

356/402, 706/1, 382/162, 356/425, 706/13-14, 345/604-605, 358/1.9, 358/3.23, 358/504, 358/518, 382/167, 382/156, 345/600

5742296	Image processing method and apparatus therefor	April, 1998	Yamada et al.	345/431
5915076	Image processing apparatus and method	June, 1999	Sugita	395/109
5929906	Color correcting method and apparatus	July, 1999	Arai et al.	348/223
5933252	Color image processing method and apparatus therefor	August, 1999	Emori et al.	358/500
6052195	Automatic colorant mixing method and apparatus	April, 2000	Mestha et al.	356/425
6061153	Image processing apparatus and method	May, 2000	Sugita	358/518
6072464	Color reproduction method	June, 2000	Ozeki	345/154
6081796	Proportion predicting system and method of making mixture	June, 2000	Takagi et al.	706/1
6342952	Method for matching printing ink colors	January, 2002	Chan	358/1.9
6343137	Method of processing an image such as a still image	January, 2002	Kimura et al.	382/100
6504960	Image processing apparatus and method and memory medium	January, 2003	Takahashi	382/305
6642930	Image processing apparatus, method and computer-readable memory	November, 2003	Matsuura et al.	345/601
6738168	Method and apparatus for reproducing color printer output, and computer-readable recording medium storing color-printer-output reproducing program	May, 2004	Usui et al.	358/520
20020012461	Apparatus and method for measurement, encoding and displaying of object color for digital imaging	January, 2002	MacKinnon et al.	382/164
20020044292	Image processing method and apparatus, and recording medium used therewith	April, 2002	Yamada et al.	358/1.9
20020060803	Image processing apparatus and method thereof	May, 2002	Iida et al.	358/1.13
20020071605	Image processing apparatus and method	June, 2002	Iida et al.	382/165
20020113880	Image processing apparatus, image processing method, and recording medium	August, 2002	Iida et al.	348/222
20030020727	Reducing metamerism in color management systems	January, 2003	Newman	345/604
20030048464	Image processing apparatus, image processing method, program and storage medium	March, 2003	Yamada et al.	358/1.9
20030142222	Colour signal processing	July, 2003	Hordley	348/223.1
20030142377	Image processing apparatus, image processing method, storage medium, and program	July, 2003	Yamada et al.	358/521
20030161530	IMAGE PROCESSING APPARATUS AND METHOD, AND RECORDING MEDIUM	August, 2003	Yamada et al.	382/167
20030202194	Image processing apparatus and information processing apparatus, and method therefor	October, 2003	Torigoe et al.	358/1.9
20030210395	Color evaluation apparatus and method	November, 2003	Takahashi et al.	356/405
20030219155	Resin appearance designing method and apparatus	November, 2003	Azuma et al.	382/156
20030234931	Method for evaluating reproducibility of toning sample by ccm	December, 2003	Sano et al.	356/402

EP0763929	March, 1997			Color seperation method
EP1054560	November, 2000			Spectrum inverter appara
EP1096787	May, 2001			Method and apparatus for reproducing color printer output, and color-printer-output reproducing program
JP6332313	February, 1988
JP2241271	September, 1990
JP5296836	November, 1993
JP6189122	July, 1994
JP0894440	April, 1996
JP8107508	April, 1996
JP0933347	February, 1997
JP9120185	May, 1997
JP9163382	June, 1997
JP10262157	September, 1998			METHOD FOR PREDICTING COLOR TRANSFER CHARACTERISTIC
JP20018047	January, 2001
JP200153976	February, 2001
JP2001128020	May, 2001			METHOD AND DEVICE FOR REPRODUCING COLOR OF COLOR PRINTER OUTPUT AND COMPUTER READABLE RECORDING MEDIUM RECORDING COLOR REPRODUCTION PROGRAM FOR COLOR PRINTER OUTPUT
JP2001186364	July, 2001			COLOR INFORMATION PROCESSING METHOD
JP2002098590	April, 2002			METHOD AND DEVICE FOR COLOR ARRANGEMENT SIMULATION
JP2002136138	May, 2002			SWITCHING POWER CIRCUIT
JP2002136139	May, 2002			SWITCHING POWER CIRCUIT
JP2002221825	August, 2002			TONER AND DEVELOPER FOR ELECTROPHOTOGRAPHY, AND IMAGE FORMING APPARATUS USING THE DEVELOPER
JP2002221826	August, 2002			TONER, TONER PRODUCING METHOD AND IMAGE FORMING METHOD
JP2002290756	October, 2002			COLOR MATCHING DEVICE AND PROVISION METHOD OF COLOR MATCHING SERVICE
JP2002365133	December, 2002			METHOD AND DEVICE FOR CALCULATING COLOR GAMUT OF COLORING MATERIAL, METHOD AND DEVICE FOR DETERMINING COLOR REGENERATION, AND METHOD AND DEVICE FOR CALCULATING BLENDING RATIO OF COLORING MATERIAL
JP2003169224	June, 2003			METHOD FOR CALCULATING COLOR GAMUT OF COLOR MATERIAL, METHOD FOR DISCRIMINATING COLOR REPRODUCTION, METHOD FOR CALCULATING COLOR MATERIAL BLENDING RATIO, APPARATUS FOR CALCULATING COLOR GAMUT OF COLOR MATERIAL, APPARATUS FOR DISCRIMINATING COLOR REPRODUCTION, AND APPARATUS FOR CALCULATING COLOR MATERIAL BLENDING RATIO
WO/2003/095212	November, 2003			REPRODUCTION COLOR PREDICTION APPARATUS AND METHOD

Coles, Edward L.

Baker, Charlotte M.

Fitzpatrick, Cella, Harper & Scinto

CROSS REFERENCE TO RELATED APPLICATION

This is a Continuation of Application No. PCT/JP03/05776 filed on May 8, 2003, and published in English as International Publication No. WO 03/095212 A1 on Nov. 20, 2003, the priority of which is claimed herein (35 U.S.C. § 120) and which claims priority of Japanese Application No. 2002-136138 filed May 10, 2002, Japanese Application No. 2002-136139 filed May 10, 2002, Japanese Application No. 2002-221825 filed Jul. 30, 2002 and Japanese Application No. 2002-221826, filed Jul. 30, 2002, the priorities of which are also claimed herein (35 U.S.C. § 119). International Application No. PCT/JP03/05776 is incorporated by reference herein in its entirety, as if fully set forth herein.

The invention claimed is:

1. A color processing apparatus comprising: a primary-color correction unit configured to correct primary colors of recording agents used on the basis of dot quantities; an estimation unit configured to estimate mixed colors corresponding to respective combinations of dot quantities of the color agents used, using the primary colors corrected by said primary-color correction unit; a multi-order color correction unit configured to correct the mixed colors estimated by said estimation unit using correction coefficients which are determined based on differences between actual colors of patches and colors of the patches as estimated by said estimation unit; and a prediction unit configured to predict a color gamut that can be reproduced by the recording agents on the basis of the mixed colors corrected by said multi-order color correction unit.

2. A color processing method comprising: a primary-color correction step of correcting primary colors of recording agents used on the basis of dot quantities; an estimation step of estimating mixed colors corresponding to respective combination of dot quantities of the color agents used using the primary colors corrected in the primary-color correction step; a multi-order color correction step of correcting the mixed colors estimated in the estimation step using correction coefficients which are determined based on differences between actual colors of patches and colors of the patches as estimated in the estimation step; and a prediction step of predicting a color gamut that can be reproduced by the recording agents on the basis of the mixed colors corrected in the multi-order color correction step.

3. The method according to claim 2, wherein the primary-color correction step includes steps of: generating a lookup table by estimating a relationship between a dot quantity and spectral reflectance on the basis of spectral reflectance at a predetermined dot quantity of a color agent used; and correcting a primary color of the color agent using the lookup table.

4. The method according to claim 3, wherein the estimation step includes a step of estimating the spectral reflectance of the mixed color on the basis of spectral reflectance data of respective color agents obtained in the primary-color correction step using Kubelka-Munk theory.

5. The method according to claim 2, further comprising: a display step of displaying the color gamut predicted in the prediction step on a three-dimensional space based on a predetermined color system.

6. The method according to claim 5, further comprising: a setting step of setting a desired combination of dot quantities; and a step of estimating a mixed color corresponding to the combination of the dot quantities set in the setting step in the primary-color correction step, the estimation step and the multi-odder color correction step, and indicating a position of the estimated mixed color on the three-dimensional space displayed in the display step.

7. The method according to claim 2, further comprising: a determination step of determining whether colors of respective pixels represented by designated image data fall inside or outside the color gamut predicted in the prediction step.

8. The method according to claim 7, further comprising: a step of binarizing and displaying the respective pixels of the image data depending on whether the pixels fall inside or outside the predicted color gamut.

9. A computer-readable memory medium which stores a control program for making a computer execute a color processing method comprising: a primary-color correction step of correcting primary colors of recording agents used on the basis of dot quantities; an estimation step of estimating mixed colors corresponding to respective combination of dot quantities of the color agents used using the primary colors corrected in the primary-color correction step; a multi-order color correction step of correcting the mixed colors estimated in the estimation step using correction coefficients which are determined based on differences between actual colors of patches and colors of the patches as estimated in the estimation step; and a prediction step of predicting a color gamut that can be reproduced by the recording agents on the basis of the mixed colors corrected in the multi-order color correction step.

TECHNICAL FIELD

The present invention relates to a technique for predicting colors reproduced by a multi-color reproduction process using specific color inks, e.g., a multi-color print process or a multi-color print using a color printer, i.e., reproduction colors.

The present invention also relates to a method of predicting a possible color reproduction range, i.e., a color gamut, on the basis of the predicted reproduction colors.

The present invention relates to an information processing apparatus, system, and method, which customize an optimal ink set required for the user to obtain a desired color reproduction result on the basis of the predicted reproduction colors.

BACKGROUND ART

As a conventional method of predicting reproduction colors of an image generated by subtractive color mixing (e.g., a print process), reproduction color prediction using a lookup table (to be abbreviated as an LUT hereinafter) disclosed in Japanese Patent Laid-Open No. 2001-053976, and a reproduction color prediction method using the Kubelka-Munk theory (to be abbreviated as a KM theory hereinafter) disclosed in Japanese Patent Laid-Open No. 09-120185 are known.

In reproduction color prediction using an LUT, a large number of patches formed by changing step by step the dot quantity of ink used in a print process are output, and the obtained colorimetric data are geometrically laid out on a color space such as CIELAB, as shown in FIG. 10 (each vertex of cubes shown in FIG. 10 stores a colorimetric value and the dot quantity of each ink in correspondence with each other). After that, an ink dot quantity corresponding to a desired tristimulus value (a point indicated by an open circle in FIG. 10) is interpolated on the basis of the geometrical layout with neighboring existing points (points indicated by full circles in FIG. 10), thus calculating a desired dot quantity.

The KM theory examines I, ΔI, J, and ΔJ with respect to infinitesimal thickness dx in ink, as shown in FIG. 11, and calculates reflectance (J/I) by solving:
dI =−( S+K ) Idx+SJdx (1)
dJ =( S+K ) Jdx−SIdx (2)

• • S: scattering coefficient of ink
  • K: absorption coefficient of ink

In reproduction color prediction using an LUT, the number N of patches that must be output to generate an LUT is given by:

$\begin{array}{cc}N={\left(\frac{100}{P}+1\right)}^I& \left(3\right)\end{array}$

• • N: number of patches to be output
  • P: interval (%) upon changing dot quantity
  • I: number of inks used

Therefore, when interval P upon changing the dot quantity is decreased or when the number I of inks used upon executing a print process using multi-color inks is increased to improve the prediction precision, the number N of patches to be output increases exponentially, resulting in huge cost of output and colorimetry.

The KM theory predicts reproduction colors when a coloring material such as ink is applied to have a uniform thickness. Therefore, when a print process is made using an area-modulation printer shown in FIG. 12, a mechanical dot gain (a phenomenon that the effective area ratio becomes larger than the theoretical area ratio due to physical spread of ink) and an optical dot gain (a phenomenon that an actual dot looks larger than its original area due to scattering of light in ink or paper) which occurs at the boundaries between portions with and without ink cannot be precisely predicted.

For example, the reproduction color-prediction method of Japanese Patent Laid-Open No. 09-120185 expands the KM theory to apply it to an actual printer, and predicts reproduction colors by independently modeling a portion where a plurality of inks mix, and a portion where a plurality of inks overlap each other. However, since this method does not consider the influence of an optical dot gain, it cannot implement precise reproduction color prediction.

A general color print is printed by a process print method, which uses a total of four color inks (C, M, Y, and. K), i.e., three color inks cyan, magenta, and yellow that are generated from a color document via three-primary color separation, and black. When an identical image is to be printed in large quantity like those of magazines, posters, and the like, a print process is made by adding several different special color inks suited to that original image, thus realizing delicate color appearance and the color gamut that cannot be reproduced by the process print. For example, upon developing an ink-jet or laser printer, C, M, Y, and K inks are normally used. However, C, M, Y, and K inks of various characteristics are available, and many companies have addressed development of inks with higher quality. A technique that adds another ink in addition to the C, M, Y, and K inks, and prints using five or more inks has been studied. In order to improve such ink development efficiency, it is demanded to automatically optimize inks.

For this purpose, recently, a method of automatically and precisely making color separation into respective plates upon using special color inks has been developed. For example, Japanese Patent Laid-Open No. 2001-053976 discloses a special color color-separation method for separating an original image into Y, M, and C plates and a special color plate. On the other hand, as a technique for improving the color reproduction precision, a spectral color reproduction technique that matches spectral distributions themselves in addition to the tristimulus values of colors has been disclosed in Japanese Patent Laid-Open No. 05-296836. In this way, in order to precisely reproduce a target color, there are two different approaches, i.e., a method of using a special color ink (special color color-separation method) and a method of making spectral distribution characteristics as closer as possible although conventional inks are used (spectral color reproduction).

The conventional special color color-separation method makes color separation for given C, M, Y, and K inks and special color ink. For example, Japanese Patent Laid-Open No. 2001-053976 requires colorimetric data of the special color ink for color separation, and is premised on the use of the special color ink manually selected in advance. However, as for a selection method of inks themselves, i.e., a method that specifies combinations of inks which allow optimal color reproduction, no clear method is established yet. For this reason, a skillful engineer selects special color ink by trial and error in practice.

On the other hand, in spectral color reproduction, a spectral distribution is made closer to that of a target color using given inks so as to realize color reproduction closest to the target color. However, it is impossible for spectral approximation to reproduce spectral distribution characteristics of a target image or color using given inks alone. Furthermore, no technique that specifies inks of spectral distribution characteristics that can reproduce those of a target color/image is available.

As described above, a printer as an image output apparatus normally outputs an image using C, M, Y, and K inks (or toners) if it is a four-color printer. A six-color printer outputs an image using two light inks or special color inks in addition to the above four colors. Note that the color gamut of the printer is determined by the colors of color agents such as inks, toners, and the like.

In general, as a method of measuring the color gamut of an image generated by subtractive color mixing (e.g., a print process), for example, a method of approximating the color gamut using a polynomial of higher degree, as disclosed in Japanese Patent Publication No. 63-32313, a method of approximating the color gamut using a neural network, as disclosed in Japanese Patent Laid-Open No. 2-241271, and the like can be used. Also, a method of generating a device model using a method of generating a plurality of patches and predicting the color gamut using the weighted mean of colorimetry results of these patches is available, as disclosed in Japanese Patent Laid-Open No. 10-262157.

As described above, Japanese Patent Laid-Open No. 09-120185 describes the color reproduction prediction method using the KM theory.

However, the aforementioned polynomial of higher degree, neural network, and device model based on the weighted mean normally requires a huge number of patches to attain gamut prediction with higher precision. The KM theory cannot precisely predict a mechanical or optical dot gain if a print process is made using an area-modulation printer, as shown in FIGS. 11 and 12.

As described above, upon printing an identical image in large quantity like those on magazines, posters, and the like, a print process is made by adding several different special color inks suited to that original image so as to reproduce delicate color appearance or the color gamut that cannot be reproduced by process print. Recently, a method of automatically and precisely making color separation into respective plates upon using special color inks has been developed. For example, Japanese Patent Laid-Open No. 2001-053976 discloses a special color color-separation method for separating an original image into Y, M, and C plates and a special color plate.

As described above, as for a selection method of inks themselves, i.e., a method that specifies combinations of inks which allow optimal color reproduction, no clear method is established yet. For this reason, a skillful engineer selects special color ink by trial and error in practice.

Upon reproducing a color which cannot be reproduced by conventional inks, it is difficult to estimate the characteristics of inks to be used.

DISCLOSURE OF INVENTION

The present invention has been proposed to solve the aforementioned problems, and has as its object to allow high-precision reproduction color prediction.

It is another object of the present invention to allow reproduction color prediction that takes the influence of a mechanical or optical dot gain into consideration.

It is still another object of the present invention to allow easy selection of appropriate color agents and their dot quantities so as to precisely reproduce a target color.

It is still another object of the present invention to allow high-precision color gamut prediction that can precisely predict a reproduction color to be reproduced using color agents.

It is still another object of the present invention to automatically set color agents required to reproduce a target color.

Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

FIG. 1 is a block diagram showing the arrangement of a reproduction color prediction apparatus according to the first embodiment;

FIG. 2 is a flow chart for explaining a reproduction color prediction process in the reproduction color prediction apparatus of the first embodiment;

FIG. 3 shows an example of primary color correction patches used in the first embodiment;

FIG. 4A is a graph showing the spectral reflectance measurement results in correspondence with the dot quantities of cyan ink;

FIG. 4B is a graph showing a primary color correction LUT acquired from the measurement result shown in FIG. 4A;

FIG. 5 shows an example of ink overlap correction patches used in the first embodiment;

FIG. 6 shows an example of a user interface according to the first embodiment;

FIG. 7 is a block diagram showing the arrangement of a reproduction color prediction apparatus according to the second embodiment;

FIG. 8 is a flow chart for explaining a reproduction color prediction process in the reproduction color prediction apparatus of the second embodiment;

FIG. 9 shows an example of a user interface according to the second embodiment;

FIG. 10 is a view for explaining a reproduction color prediction method using an LUT;

FIG. 11 is a view for explaining reproduction color prediction using the Kubelka-Munk theory;

FIG. 12 is a view for explaining an optical dot gain;

FIG. 13 is a block diagram showing the arrangement of an ink optimization apparatus according to the third embodiment;

FIG. 14 is a flow chart for explaining an ink optimization process in the ink optimization apparatus of the third embodiment;

FIG. 15 shows an example of a user interface which is presented by the ink optimization apparatus of the third embodiment, and is used to set a target color;

FIG. 16 shows an example of a user interface used to display an ink optimization result in the ink optimization apparatus of the third embodiment;

FIG. 17 is a block diagram showing the arrangement of an ink optimization apparatus according to the fourth embodiment;

FIG. 18 is a flow chart for explaining an ink optimization process in the ink optimization apparatus of the fourth embodiment;

FIG. 19 shows an example of a user interface used to set a target color in the fourth embodiment;

FIG. 20 is a block diagram showing the arrangement of a color gamut prediction apparatus according to the fifth embodiment;

FIGS. 21A and 21B are flow charts for explaining a color gamut prediction process according to the fifth embodiment;

FIG. 22 shows an example of a user interface used to input ink information according to the fifth embodiment;

FIG. 23 shows an example of a user interface used to display a color gamut prediction result according to the fifth embodiment;

FIG. 24 is a block diagram showing the arrangement of a color gamut prediction apparatus of the sixth embodiment;

FIGS. 25A to 25C are flow charts for explaining a color gamut prediction of the sixth embodiment;

FIG. 26 shows an example of a user interface used to display a color gamut prediction result according to the sixth embodiment;

FIG. 27 is a block diagram showing the arrangement of an ink customize system according to the seventh embodiment;

FIGS. 28A and 28B are flow charts for explaining an ink customize process according to the seventh embodiment;

FIG. 29 shows an example of a user interface according to the seventh embodiment;

FIG. 30 is a flow chart for explaining an output estimation process according to the seventh embodiment;

FIG. 31 is a block diagram showing the arrangement of an ink customize system according to the eighth embodiment;

FIGS. 32A and 32B are flow charts for explaining an ink customize process according to the eighth embodiment; and

FIG. 33 shows an example of a user interface in the eighth embodiment.

BEST MODE OF CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings.

First Embodiment

<Arrangement of Reproduction Color Prediction Apparatus>

FIG. 1 is a block diagram showing the arrangement of a reproduction color prediction apparatus according to an embodiment of the present invention. Reference numeral 1 denotes a reproduction color prediction apparatus according to the first embodiment. Reference numeral 2 denotes a spectral reflectance measurement device for measuring printer characteristics. In this embodiment, the spectral reflectance measurement device 2 is used to measure the spectral reflectance characteristics of color patches (to be described later using FIGS. 3 and 5) output by a printer, used in the embodiment. Reference numeral 3 denotes an ink calorimetric value storage unit which stores the spectral reflectance data of inks measured by the spectral reflectance measurement device 2 . The ink calorimetric value storage unit 3 stores primary color and ink overlap colorimetric values. Note that this embodiment uses a plurality of color inks as recording agents, but a plurality of color toners may be used.

Reference numeral 4 denotes a primary color correction LUT generator for generating a primary color correction LUT using the primary color calorimetric values stored in the ink colorimetric value storage unit 3 . Reference numeral 6 denotes a primary color correction LUT storage unit which stores the primary color correction LUT generated by the primary color correction LUT generator 4 . Reference numeral 5 denotes an ink overlap correction coefficient calculator which calculates ink overlap correction coefficients on the basis of the ink overlap colorimetric values stored in the ink colorimetric value storage unit 3 . Reference numeral 7 denotes an ink overlap correction coefficient storage unit which stores the ink overlap correction coefficients calculated by the ink overlap correction coefficient calculator 5 . Processes using the primary color LUT generator 4 and ink overlap correction coefficient calculator 5 will be described in detail later.

Reference numeral 8 denotes an ink dot quantity setting unit. The user sets ink dot quantities using this unit. Reference numeral 9 denotes an ink dot quantity storage unit which stores the ink dot quantities set by the ink dot quantity setting unit 8 . Reference numeral 10 denotes a primary color dot gain correction unit which makes primary color correction in correspondence with the ink dot quantities stored in the ink dot quantity storage unit 9 (the reason why this embodiment uses a term “primary color-correction” is that the general KM theory uses a concept that a parameter (K/S) linearly changes with respect to the dot quantity, and does not consider any influences of nonlinearity of a dot gain, but this embodiment nonlinearly corrects this dot gain. That is, this nonlinear correction will be referred to as primary color dot gain correction). Reference numeral 11 denotes an initial estimated value calculator, which calculates an initial estimated value of spectral reflectance (initial estimated spectral reflectance value) of a mixed color using the above ink dot quantities.

Reference numeral 12 denotes an ink overlap correction unit which corrects the initial estimated spectral reflectance value calculated by the initial estimated value calculator 11 using the ink overlap correction coefficients stored in the ink overlap correction coefficient storage unit 7 , and the ink dot quantities stored in the ink dot quantity storage unit 9 to obtain an estimation result (final estimation result) of spectral reflectance of the mixed color obtained by the above ink dot quantities. Reference numeral 13 denotes an estimation result display unit which displays the final estimation result of the spectral reflectance corrected by the ink overlap correction unit 12 . The estimation result display unit 13 can use a display such as a CRT, LCD, or the like.

<Reproduction Color Prediction Process>

A reproduction color prediction process of the reproduction color prediction apparatus with the above arrangement will be described below.

FIG. 2 is a flow chart showing a reproduction color prediction process executed by the reproduction color prediction apparatus 1 . FIG. 6 shows an example of a user interface used to set ink dot quantities using the ink dot quantity setting unit 8 and to display the estimation result by the estimation result display unit 13 . The reproduction color prediction process according to the first embodiment will be described in detail below using the accompanying drawings. Note that the user interface of this embodiment displays a window shown in FIG. 6 on the display, and instructions are made by operating the cursor using a pointing device. Alternatively, various other known input devices such as a touch panel and the like may be used.

It is checked in step S 201 if the user has pressed (clicked) a primary color patch read button 601 . If YES in step S 201 , the flow advances to step S 202 ; otherwise, the flow jumps to step S 204 . In the process executed when the primary color patch read button 601 has been pressed, sample patches (details will be described later) generated using inks to be used are measured using the spectral reflectance measurement device 2 , and the obtained colorimetric values are stored in the ink colorimetric value storage unit 3 in step S 202 . The flow advances to step S 203 , the primary color correction LUT generator 4 reads the primary color calorimetric values stored in the ink colorimetric value storage unit 3 , calculates a primary color correction LUT (its details will be described later in <Generation of Primary Color Dot Gain Correction LUT>), and stores it in the primary color correction LUT storage unit 6 .

It is checked in step S 204 if the user has pressed an overlap patch read button 602 . If YES in step S 204 , the flow advances to step S 205 ; otherwise, the flow advances to step S 206 . If the overlap patch read button 602 has been pressed, the ink overlap correction coefficient calculator 5 calculates ink overlap correction coefficients, and stores them in the ink overlap correction coefficient storage unit 7 in step S 205 . Note that the ink overlap correction coefficients are used to correct the estimated values calculated by the initial estimated value calculator 11 , and are calculated on the basis of errors between the estimated spectral reflectance values of overlap patches calculated by the initial estimated value calculator 11 , and actually measured spectral reflectance values of that overlap patches. Details of this calculation process will be described later in <Calculation of Ink Overlap Correction Coefficient>.

It is checked in step S 206 if the user has pressed a spectral reflectance estimation button 605 . If YES in step S 206 , the flow advances to step S 207 ; otherwise, the flow returns to step S 201 . If the spectral reflectance estimation button 605 has been pressed, processes in subsequent steps S 207 to S 211 are executed.

In step S 207 , the ink dot quantities set by the user are acquired via the ink dot quantity setting unit 8 , and are stored in the ink dot quantity storage unit 9 . The ink dot quantity setting unit 8 provides a user interface which includes a numerical value input area 603 and slide bars 604 shown in, e.g., FIG. 6, and prompts the user to set desired ink dot quantities. The user can designate dot quantities of respective colors (cyan, magenta, yellow, and black) by numerical values using the numerical value input area 603 or using the slide bars 604 .

In step S 208 , the primary color dot gain correction unit 10 corrects primary color dot gains using the ink dot quantities stored in the ink dot quantity storage unit 9 and the primary color correction LUT (to be described in detail later in <Generation of Primary Color Dot Gain Correction LUT>) stored in the primary color correction LUT storage unit 6 , and calculates spectral reflectance values corresponding to the respective ink dot quantities.

In step S 209 , the initial estimated value calculator 11 predicts a mixed color based on the spectral reflectance values of inks calculated by the primary color dot gain correction unit 10 using the KM theory given by:

$\begin{array}{cc}{\left(\frac{K}{S}\right)}_{i,\lambda }=\frac{{\left(R_{i,\lambda }-1\right)}^2}{\left(2·R_{i,\lambda }\right)}& \left(4\right)\\ {\left(\frac{K}{S}\right)}_{\mathrm{MIX},\lambda }={\left(\frac{K}{S}\right)}_{\mathrm{Paper},\lambda }+\sum _{i=1}^n{\left(\frac{K}{S}\right)}_{i,\lambda }& \left(5\right)\\ R_{\mathrm{MIX},\lambda }=1+{\left(\frac{K}{S}\right)}_{\mathrm{MIX},\lambda }-\sqrt{{\left(\frac{K}{S}\right)}_{\mathrm{MIX},\lambda }^2+2·{\left(\frac{K}{S}\right)}_{\mathrm{MIX},\lambda }}& \left(6\right)\end{array}$

• • K: absorption coefficient
  • S: scattering coefficient
  • (K/S) _i,λ : (K/S) of ink i at wavelength λ
  • (K/S) _MIX,λ : (K/S) at wavelength λ after inks are mixed
  • (K/S) _Paper,λ : (K/S) of paper at wavelength λ
  • R _i,λ : spectral reflectance of ink i at wavelength λ
  • R _MIX,λ : spectral reflectance at wavelength λ after inks are mixed
    In this way, since the mixed color is predicted based on the KM theory using the output values from the primary color dot gain correction unit, the mixed color that reflects corrected dot gains can be predicted. More specifically, in this embodiment, the dot gain of primary color (printed using only one color ink) and that of secondary or higher color (printed when a plurality of inks overlap each other) are independently considered, and dot gain correction in this case indicates the primary color dot gain alone. The dot gain of secondary or higher color will be considered in ink overlap correction.

In step S 210 , the ink overlap correction unit 12 corrects the initial estimated spectral reflectance value estimated by the initial estimated value calculator 11 using the ink overlap correction coefficients (to be described in detail later) stored in the ink overlap correction coefficient storage unit 7 , and calculates a final estimation result of the spectral reflectance (to be referred to as a spectral reflectance final estimation result).

In step S 211 , the estimation result display unit 13 displays the spectral reflectance final estimation result calculated by the ink overlap correction unit 12 using a display method indicated by a spectral reflectance final estimation result display area 607 shown in, e.g., FIG. 6. By setting a light source using a light source name display area 606 , tristimulus values under that light source are displayed on a tristimulus value display area 608 . For example, since light source D 50 is set in the light source name display area 606 in FIG. 6, L*a*b* tristimulus values are calculated and displayed on the tristimulus value display area 608 .

<Generation of Primary Color Dot Gain Correction LUT>

Details of generation of the primary color dot gain correction LUT by the primary color correction LUT generator 4 (step S 203 ) and primary color dot gain correction by the primary color dot gain correction unit 10 (step S 208 ) will be described below using FIGS. 2, 3 , 4 A, 4 B, and 6 .

Upon generation of the primary color dot gain correction LUT, primary color correction patches, which are output in advance using a printer that is to undergo reproduction color prediction, are measured by the spectral reflectance measurement device 2 , and the results (spectral reflectance data) are stored in the ink colorimetric value storage unit 3 . The primary color correction patches used in this process are prepared by changing the ink dot quantity of each color in 20%-increments from 0% to 100%, as shown in, e.g., FIG. 3.

The spectral reflectance data of the primary color correction patches, which are stored in the ink colorimetric value storage unit 3 , are reflectance values at respective wavelengths corresponding to discrete ink dot quantities, as shown in FIG. 4A. FIG. 4A shows the spectral reflectance measurement results in correspondence with respective dot quantities (20%, 40%, 60%, 80%, 100%) of cyan ink. Also, the dot quantity=0% indicates an ink-less state, i.e., the spectral reflectance of paper.

These spectral reflectance data are input to the primary color correction LUT generator 4 , and are converted into an LUT which indicates the relationship between the dot quantities and reflectance values at respective wavelengths, as shown in FIG. 4B. Since only discrete measurement results in 20%-increments of ink dot quantity are available, the primary color correction LUT is generated using a general interpolation method such as linear interpolation, spline interpolation, or the like.

The primary color dot gain correction unit 10 (step S 208 ) makes primary color dot gain correction in correspondence with the input ink dot quantities using the LUT to estimate spectral reflectance characteristics of primary colors. Note that FIG. 4B illustrates only four graphs for the sake of simplicity. However, in practice, tables of all wavelengths (41 wavelengths in 10-nm increments from 380 to 780 nm) sampled in the visible wavelength range are generated.

<Calculation of Ink Overlap Correction Coefficient>

Details of the ink overlap correction coefficient calculation process by the ink overlap correction coefficient calculator 5 . (step S 205 ) will be described below using FIG. 5.

In the ink overlap correction coefficient calculation process, ink overlap correction patches, which are output in advance using a printer that is to undergo reproduction color prediction, are measured by the spectral reflectance measurement device 2 , and the results (spectral reflectance data) are stored in the ink colorimetric value storage unit 3 . The ink overlap correction patches used in this process are prepared by changing the dot quantity of each ink in 20%-increments from 0% to 100%, and printing patches using two or more color inks to overlap each other, as shown in FIG. 5. The patches shown in FIG. 5 are printed using four inks (C, M, Y, and K).

The initial-estimated value calculator 11 calculates initial estimated spectral reflectance values of the respective overlap correction patches using the data (respective color dot quantities) of the overlap correction patches, and equations (4) to (6) above. The calculated initial estimated spectral reflectance values have errors from actually measured data, which are obtained by actually measuring the correction patches by the spectral reflectance measurement device 2 and storing them in the ink calorimetric value storage unit 3 . In order to correct errors from the actually measured data, correction coefficients a _h,λ , b _i,j,λ , and c _k,l,m,λ are determined using a method of least squares or the like to minimize the errors by:

$\begin{array}{cc}\begin{array}{c}{R}_{\mathrm{mod},\lambda }=\sum _{h=1}^n{a}_{h,\lambda }{R}_{p,\lambda }^h+\sum _{\underset{j=1}{i=1}}^n{b_{i,j,\lambda }\left(\frac{K}{S}\right)}_{i,j,\lambda }+\\ \mathrm{ }\sum _{\begin{array}{c}k=1\\ \begin{array}{c}l=1\\ m=1\end{array}\end{array}}^n{c_{k,l,m,\lambda }\left(\frac{K}{S}\right)}_{k,l,m,\lambda }\\ \mathrm{for}{\left(\frac{K}{S}\right)}_{i,j,\lambda }={c_i\left(\frac{K}{S}\right)}_{i,\lambda }+{c_j\left(\frac{K}{S}\right)}_{j,\lambda }\\ {\left(\frac{K}{S}\right)}_{k,l,m,\lambda }={c_k\left(\frac{K}{S}\right)}_{k,\lambda }+{c_l\left(\frac{K}{S}\right)}_{l,\lambda }+{c_m\left(\frac{K}{S}\right)}_{m,\lambda }\end{array}& \left(7\right)\end{array}$

• • R _mod,λ : corrected spectral reflectance at wavelength λ
  • R _p,λ : spectral reflectance at wavelength λ, which is estimated by the KM theory
  • a _h,λ , b _i,j,λ , c _k,l,m,λ : ink overlap correction coefficients
  • (K/S) _i,j,λ : (K/S) when only inks i and j at wavelength λ are considered
  • (K/S) _k,l,m,λ : (K/S) when only ink k, l, and m at wavelength λ are considered

In equation (7), R _p,λ is an estimated value of a secondary color using the spectral reflectance that has undergone primary color correction, and the KM theory given by equations (4) to (6), and R _mod,λ is a corrected estimated value after ink overlap correction. Coefficients a _h,λ , b _i,j,λ , and c _k,l,m,λ are determined to minimize errors between R _mod,λ and the actually measured values of color patches. Also, i and j of the second term, and k, l, and m of the third term indicate arbitrary inks. For example, if four, C, M, Y, and K colors are used as n-color inks, i=C, M, Y, K, j=C, M, Y, K, . . . (for i≠j, k≠l≠m). Furthermore, (K/S) is as defined by equation (4). The ink overlap correction coefficients obtained by the above process are stored in the ink overlap correction coefficient storage unit 7 .

<Ink Overlap Correction>

Details of the ink overlap correction process by the ink overlap correction unit 12 (step S 210 ) will be described below. The ink overlap correction unit 12 (step S 210 ) corrects the initial estimated spectral reflectance values, which are calculated by the initial estimated value calculator 11 (step S 209 ) in association with the ink dot quantities set by the ink dot quantity setting unit 8 , using the ink overlap correction coefficients stored in the ink overlap correction coefficient storage unit 7 and equation (7), thus removing estimation errors due to ink overlap.

As described above, according to this embodiment, reproduction color estimation is done with respect to the set ink dot quantities in the following procedures.

(1) The primary color dot gain correction unit 10 calculates spectral reflectance values corresponding to set dot quantities for respective inks. Since this calculation uses the LUT stored in the primary color correction LUT storage unit 6 , dot gain correction is applied.

(2) The initial estimated value calculator 11 predicts a mixed color (initial estimation) using the KM theory on the basis of the spectral reflectance values of inks obtained by the primary color dot gain correction unit 10 and the set ink dot quantities (equations (4) to (6)).

(3) Furthermore, the ink overlap correction unit 12 makes ink overlap correction of secondary or higher color for the initial estimation result using the correction coefficients stored in the ink overlap correction coefficient storage unit 7 (equation (7)).

As described above, since spectral reflectance after inks are mixed is initially estimated by applying the spectral reflectance values of respective inks that have undergone dot gain correction to the mixed color predicted using the KM theory, and the obtained initial estimation result undergoes ink overlap correction, high-precision reproduction color estimation can be implemented.

Second Embodiment

The second embodiment according to the present invention will be described in detail below with reference to the accompanying drawings. FIG. 7 is a block diagram showing the arrangement of a reproduction color prediction apparatus 701 according to the second embodiment.

Reference numeral 702 denotes a spectral reflectance measurement device for measuring printer characteristics. Reference numeral 703 denotes an ink calorimetric value storage unit which stores spectral reflectance data of inks measured by the spectral reflectance measurement device 702 . Reference numeral 704 denotes a primary color correction LUT generator, which generates a primary color correction LUT on the basis of calorimetric values of primary color stored in the ink calorimetric value storage unit 703 . Reference numeral 706 denotes a primary color correction LUT storage unit which stores the primary color correction LUT generated by the primary color correction LUT generator 704 .

Reference numeral 705 denotes an ink overlap correction coefficient calculator, which calculates ink overlap correction coefficients on the basis of ink overlap calorimetric values stored in the ink colorimetric value storage unit 703 . Reference numeral 707 denotes an ink overlap correction coefficient storage unit which stores the ink overlap correction coefficients calculated by the ink overlap correction coefficient calculator 705 .

Reference numeral 708 denotes an ink dot quantity setting unit that provides an interface with which the user sets ink dot quantities. Reference numeral 709 denotes an ink dot quantity storage unit, which stores the ink dot quantities set using the ink dot quantity setting unit 708 .

Reference numeral 710 denotes a primary color dot gain correction unit which makes primary color correction in correspondence with the ink dot quantities stored in the ink dot quantity storage unit 709 . Reference numeral 711 denotes an initial estimated value calculator which estimates a color mixing result using the KM theory on the basis of respective primary color values corrected by the primary color dot gain correction unit 710 . Reference numeral 712 denotes an ink overlap correction unit, which corrects an initial estimated spectral reflectance value calculated by the initial estimated value calculator 711 using the ink overlap correction coefficients stored in the ink overlap correction coefficient storage unit 707 and the ink dot quantities stored in the ink dot quantity storage unit 709 , so as to obtain an estimated spectral reflectance value.

Reference numeral 713 denotes a target color setting unit, which sets spectral reflectance data or tristimulus values of a target color. When the spectral reflectance data is set, a user interface shown in, e.g., FIG. 9 can be used. This interface allows the user to change a graph display using a pointing device such as a mouse or the like on a display area 905 . Reference numeral 714 denotes a color reproduction error calculator, which calculates an error between the estimated spectral reflectance value calculated by the ink overlap correction unit 712 and the target color set by the target color setting unit 713 . Reference numeral 715 denotes a color reproduction result display unit which displays the estimated spectral reflectance value corrected by the ink overlap correction unit 712 . The color reproduction result display unit 715 comprises a CRT, LCD, or the like, and makes a display, as shown in FIG. 9.

<Reproduction Color Prediction Process>

FIG. 8 is a flow chart of a reproduction color prediction process executed by the reproduction color prediction apparatus 701 . FIG. 9 shows an example of a user interface used to set a target color using the target color setting unit 713 and to display the color reproduction estimation result by the color reproduction result display unit 715 .

It is checked in step S 801 if the user has pressed (clicked) a primary color dot gain read button 901 . If YES in step S 801 , the flow advances to step S 802 ; otherwise, the flow jumps to step S 804 . If the primary color dot gain read button 901 has been pressed, sample patches are measured using the spectral reflectance measurement device 702 , and the obtained calorimetric values are stored in the ink colorimetric value storage unit 703 in step S 802 . In step S 803 , the primary color correction LUT generator 704 reads the primary color colorimetric values stored in the ink colorimetric value storage unit 703 , calculates a primary color correction LUT, and stores it in the primary color correction LUT storage unit 706 . The primary color correction LUT, its generation sequence, and sample patches used to generate the LUT are the same those in the first embodiment.

It is checked in step S 804 if the user has pressed an overlap patch read button 902 . If YES in step S 804 , the flow advances to step S 805 ; otherwise, the flow advances to step S 806 . If the overlap patch read button 902 has been pressed, the ink overlap correction coefficient calculator 705 calculates ink overlap correction coefficients, and stores them in the ink overlap correction coefficient storage unit 707 in step S 805 . Details of the correction coefficient calculation process are as has already explained in the first embodiment.

It is checked in step S 806 if the user has pressed a color matching button 903 . If YES in step S 806 , the flow advances to step S 807 ; otherwise, the flow returns to step S 801 . If the color matching button 903 has been pressed, processes in subsequent steps S 807 to S 815 are executed.

In step S 807 , the target color setting unit 713 inputs spectral reflectance data or tristimulus values of a target color which is set by the user. The target color setting unit 713 is implemented as a target color spectral reflectance input area 905 or target color tristimulus value input area 907 provided in the user interface shown in FIG. 9. By inputting a desired value to one of these areas, the spectral reflectance data or tristimulus values of the target color can be set.

In step S 808 , initial values of ink dot quantities of all inks or ink dot quantities updated in step S 814 are set and stored in the ink dot quantity storage unit 709 . In step S 809 , primary color dot gains are corrected using the ink dot quantities stored in the ink dot quantity storage unit 709 and the primary color correction LUT stored in the primary color correction LUT storage unit 706 , thus calculating spectral reflectance values corresponding to the given ink dot quantities.

In step S 810 , the initial estimated value calculator 711 predicts a mixed color using the spectral reflectance values of inks calculated by the primary color dot gain correction unit 710 and the KM theory given by equations (4) to (6) above. In step S 811 , the ink overlap correction unit 712 corrects an initial estimated spectral reflectance value estimated by the initial estimated value calculator 711 (step S 810 ) using the ink overlap correction coefficients stored in the ink overlap correction coefficient storage unit 707 and equation (7), and calculates a spectral reflectance final estimation result.

In step S 812 , the color reproduction error calculator 714 calculates an error between the spectral reflectance of the target color and the spectral reflectance final estimation result (for example, such error includes an RMS error, color difference ΔE, and the like, but the present invention is not limited to them). It is checked in step S 813 if the error calculated by the color reproduction error calculator 714 is larger than a pre-set threshold value. If the error is larger than the threshold value, the flow advances to step S 814 ; if the error is equal to or smaller than the threshold value, the flow advances to step S 815 .

In step S 814 , the ink dot quantities are updated using a general optimization method such as a steepest descent method or the like to minimize the error between the spectral reflectance of the target color and the spectral reflectance final estimation result. The processes in steps S 808 to S 813 are then executed using the updated ink dot quantities. In this way, the processes in steps S 809 to S 814 are repeated until the error between the spectral reflectance of the target color and the spectral reflectance final estimation result becomes equal to or smaller than the threshold value.

In step S 815 , the color reproduction result display unit 715 displays the spectral reflectance final estimation result calculated by the ink overlap correction unit 712 . On this display, as shown in, e.g., FIG. 9, the spectral reflectance final estimation result is displayed on a spectral reflectance final estimation result display area 906 , and tristimulus values under a light source designated by a light source name display area 904 are displayed on a tristimulus value display area 907 . Furthermore, color difference ΔE from the target color at that time and the ink dot quantities are respectively displayed on a color difference display area 908 and ink dot quantity display area 910 .

<Number and Type of Inks Used>

In the first and second embodiments, four color inks, i.e., cyan (C), magenta (M), yellow (Y), and black (K) are used. However, the present invention is not limited to these inks. For example, the present invention can be applied to an arrangement including light inks (light cyan and light magenta) prevalently used in ink-jet printers, an arrangement including special color inks different from the above inks, and an arrangement using only three, C, M, and Y colors without using K ink.

As described above, according to the above embodiments, in reproduction color prediction of an image output device, since a reproduction color prediction model is combined with correction of a portion that cannot be predicted by a model, high-precision reproduction color estimation can be implemented. Especially, upon applying the KM theory to prediction of a mixed color, the spectral reflectance that has undergone primary color dot gain correction is used, and correction using correction coefficients, which are obtained based on the actually measured values and predicted values, is applied, thus implementing high-precision reproduction color prediction.

As described above, according to the above mentioned embodiment, high-precision reproduction color prediction can be implemented.

Third Embodiment

In the third and fourth embodiments to be described hereinafter, a process for optimizing (determining) ink dot quantities will be explained.

FIG. 13 is a block diagram showing the arrangement of an ink optimization apparatus according to the third embodiment of the present invention.

Referring to FIG. 13, reference numeral 2001 denotes an ink optimization apparatus according to the third embodiment. Reference numeral 2002 denotes an ink design unit, which designs ink characteristics of a given target color. Reference numeral 2003 denotes a primary color dot gain estimation unit, which estimates a primary color dot gain of the ink designed by the ink design unit 2002 . Reference numeral 2004 denotes a primary color dot gain LUT storage unit, which stores a primary color dot gain LUT estimated by the primary color dot gain estimation unit 2003 . Note that this embodiment uses a plurality of inks as color agents. However, the optimization method of this embodiment can be applied when other color agents such as toners and the like are used.

Reference numeral 2005 denotes a calorimetric value data storage unit, which stores the colorimetric values of output patches of a printer used in an ink optimization process. Reference numeral 2006 denotes an ink overlap correction coefficient calculator, which calculates ink overlap correction coefficients on the basis of the colorimetric values stored in the colorimetric value data storage unit 2005 . Reference numeral 2007 denotes an ink overlap correction coefficient storage unit, which stores the ink overlap correction coefficients calculated by the ink overlap correction coefficient calculator 2006 .

Reference numeral 2008 denotes an ink dot quantity setting unit, which sets ink dot quantities of the designed ink. Reference numeral 2009 denotes a primary color dot gain correction unit, which makes primary color correction, which considers a dot gain to be described later, for the ink dot quantities set by the ink dot quantity setting unit 2008 (the reason why this embodiment uses a term “primary color correction” is that the general KM theory uses a concept that a parameter (K/S) linearly changes with respect to the dot quantity, and does not consider any influence of nonlinearity of the dot gain, but this embodiment nonlinearly corrects this dot gain). Reference numeral 2010 denotes an initial estimated value calculator, which calculates a color mixing result (initial estimated spectral reflectance value) on the basis of primary color values corrected by the primary color dot gain correction unit 2009 . Reference numeral 2011 denotes an ink overlap correction unit, which corrects the initial estimated spectral reflectance value calculated by the initial estimated value calculator 2010 using the ink overlap correction coefficients stored in the ink overlap correction coefficient storage unit 2007 , and the ink dot quantities stored in the ink dot quantity storage unit 2009 , thus obtaining an estimated spectral reflectance value.

Reference numeral 2012 denotes a predicted output data storage unit which stores a predicted output value (the estimation result obtained by the ink overlap correction unit 2011 ; details will be described later using the flow chart of FIG. 14). Reference numeral 2013 denotes a target color data storage unit, which stores a target color set by the user. Reference numeral 2014 denotes a target color data setting unit which provides a user interface, with which the user sets a target color. Reference numeral 2015 denotes an ink optimization result display unit, which controls a display device 2019 to display optimized ink information. Reference numeral 2016 denotes an ink characteristic storage unit, which stores characteristics of paper used in a print process, and ink characteristics obtained by measuring those of some existing inks, in advance. Reference numeral 2017 denotes an error calculator, which calculates an error between predicted output data and target color data. Reference numeral 2018 denotes a minimum error determination unit, which compares a minimum value of the error (minimum error value) calculated by the error calculator 2017 with a threshold value. Reference numeral 2019 denotes a display device, which displays a target color designated by the user, and an ink optimization result under the control of the ink optimization result display unit 2015 . The display device 2019 can use a CRT, LCD, or the like.

<Ink Optimization Process>

FIG. 14 is a flow chart showing an ink optimization process by the ink optimization apparatus 2001 of the third embodiment. FIG. 15 shows an example of a user interface which is provided by the target color setting unit 2014 to allow the user to set a target color. FIG. 16 shows an example of a user interface which is provided by the ink optimization result display unit 2015 to display an ink optimization result. The ink optimization process according to the third embodiment will be described below using these figures.

In step S 2201 , the user sets a desired target color using the target color setting unit 2014 , and the set target color is stored in the target color data storage unit 2013 . The target color setting unit 2014 provides a user interface shown in, e.g., FIG. 15, and the user sets the target color via this interface (details will be described later). It is checked in step S 2202 if the user has input all target colors. This checking process is implemented by seeing if an ink optimization button 2306 has been pressed, on the interface shown in FIG. 15. Each target color set using an area 2301 , slide bars 2302 , and the like is stored in the target color data storage unit 2013 upon depression of a target color addition button 2305 .

Upon depression of the ink optimization button 2306 , the flow advances to step S 2203 . In step S 2203 , spectral reflectance data of C, M, Y, and K inks, which are normally used, and those of special color inks such as green, orange, and the like when the dot quantity=100%, of the ink characteristics stored in the ink characteristic storage unit 2016 are set as initial values in the ink design unit 2002 . Assume that ink design using six color inks are to be made in this embodiment.

In step S 2204 , the primary color dot gain estimation unit 2003 estimates dot gains at arbitrary dot quantities on the basis of the spectral reflectance data when the ink dot quantity=100%, which are set by the ink design unit, and stores them as an LUT in the primary color correction LUT (details will be described later).

In step S 2205 , the ink overlap correction coefficient calculator 2006 reads the ink overlap colorimetric values stored in the calorimetric value data storage unit 2005 , and calculates ink overlap correction coefficients. The calculated ink overlap correction coefficients are stored in the ink overlap correction coefficient storage unit 2007 (details will be described later). Since the ink overlap correction coefficients use identical values in all ink combinations, the process in step S 2205 may be skipped after it is executed once. In step S 2206 , all ink dot quantities are set to initial values (e.g., 0%) to prepare for processes in step S 2207 and subsequent steps.

In step S 2207 , the primary dot gain correction unit 2009 corrects primary color dot gains using the ink dot quantities set by the ink dot quantity setting unit 2008 and the primary color dot gain LUT stored in the primary color dot gain LUT storage unit 2004 , thus calculating spectral reflectance values corresponding to the given ink dot quantities. In step S 2208 , the initial estimated value calculator 2010 predicts a mixed color based on the spectral reflectance values of inks calculated by the primary color dot gain correction unit 2009 using the KM theory given by equations (4) to (6) above. Note that (K/S) at wavelength λ of paper is held in the ink characteristic storage unit 2016 .

In step S 2209 , the ink overlap correction unit 2011 corrects initial estimated spectral reflection values estimated by the initial estimated value calculator 2010 using the ink overlap correction coefficients stored in the ink overlap correction coefficient storage unit 2007 , thereby calculating a spectral distribution final estimation result (details will be described later).

In step S 2210 , the error calculator 2017 calculates an error between the spectral distribution final estimation result calculated in step S 2209 , and each target color set in step S 2201 . If the error is smaller than a minimum value, a minimum error value in the predicted output data storage unit 2012 is updated by that error, and ink characteristics and dot quantities at that time are stored in the predicted output data storage unit 2012 . It is checked in step S 2211 if all combinations of dot quantities of the currently set inks have been checked. If all combinations have been checked, the flow advances to step S 2213 ; if combinations to be checked still remain, the flow advances to step S 2212 . In step S 2212 , the dot quantities are changed by a given change amount, and the flow returns to step S 2207 . Note that combinations of dot quantities in the above process basically undergo full search. For example, when six color inks are used, all combinations of all ink dot quantities are checked within the range from 0% to 100%. Note that an increment value used to change the dot quantity from 0% to 100% may be determined as a default, or an arbitrary value may be set by user's operation.

The minimum error determination unit 2018 checks in step S 2213 if the minimum error value stored in the predicted output data storage unit 2012 is larger than a set threshold value. If the minimum error value is larger than the threshold value, the flow advances to step S 2214 ; otherwise, the flow advances to step S 2215 . In step S 2214 , at least one of the currently set inks is replaced by ink having other characteristics. Note that ink having other characteristics is read out from the characteristic storage unit 2016 .

If the minimum error value stored in the predicted output data storage unit 2012 becomes smaller than the set threshold value, the minimum error value stored in the predicted output data storage unit 2012 , and the ink characteristics and dot quantities at that time, are displayed in a format shown in, e.g., FIG. 16 (details will be described later) in step S 2215 . If a plurality of target colors are set in step S 2201 , the process in FIG. 14 is repeated for all the set target colors. More specifically, the processes in steps S 2206 to S 2214 in FIG. 14 are repeated for each target color. Upon replacing by ink with other characteristics in step S 2214 , all combinations of a predetermined number of colors (e.g., six colors) chosen from ink candidates stored in the ink characteristic storage unit 2016 may be used as inks to be replaced.

<Target Color Setting User Interface>

The user interface to be provided by the target color setting unit 2014 will be described below. FIG. 15 shows an example of the user interface with which the user sets a target color using the target color data setting unit 2014 . A target color setting method will be described in detail below using FIG. 15.

The user can set a target color to be output by a printer using tristimulus values or spectral reflectance data. When the user sets a target color using tristimulus values, he or she sets a desired light source in a light source setting area 2307 , and can set desired tristimulus values under that light source using a numerical value input area 2301 or slider bars 2302 . Upon setting a target color using spectral reflectance data, a user interface that allows the user to change a graph displayed on a target color spectral reflectance input area 2304 using a pointing device such as a mouse or the like is provided. With this interface, the user makes setups to obtain desired spectral reflectance characteristics. The set target color is displayed on a target color confirmation area 2303 . If the user wants to add another target color, he or she can add a target color by pressing the target color addition button 2305 after the desired target color is set. When the user has input all target colors and wants to start ink optimization using each input target color, he or she can press the ink optimization button 2306 .

<Primary Color Dot Gain Estimation>

Normally, the ink dot quantities and spectral reflectance characteristics do not have a linear relationship in a print process, and a phenomenon that the area of ink on a sheet surface becomes larger than a theoretical area ratio occurs. This phenomenon is well known as a dot gain. In this embodiment, the primary dot gain estimation unit 2003 estimates the dot gain of ink designated by the ink design unit 2002 .

FIGS. 4A and 4B show the relationship between the ink dot quantities and spectral reflectance characteristics of arbitrary cyan ink. As can be seen from FIGS. 4A and 4B, the spectral reflectance characteristics change nonlinearly with respect to each dot quantity. In order to estimate this dot gain, the following estimation formulas are used:

$\begin{array}{cc}\begin{array}{c}{\left(\frac{K}{S}\right)}_{100\%,\lambda }=\frac{{\left(R_{100\%,\lambda }-1\right)}^2}{2·R_{100\%,\lambda }}\\ {\left(\frac{K}{S}\right)}_{\mathrm{Est},\lambda }={\left(\frac{K}{S}\right)}_{100\%,\lambda }·{\left(\frac{x}{100}\right)}^{\gamma }\\ R_{\mathrm{Est},\lambda }=1+{\left(\frac{K}{S}\right)}_{\mathrm{Est},\lambda }-\sqrt{{\left(\frac{K}{S}\right)}_{\mathrm{Est},\lambda }+2·{\left(\frac{K}{S}\right)}_{\mathrm{Est},\lambda }}\\ \mathrm{for}\gamma =a·{\log \left(\frac{K}{S}\right)}_{100\%,\lambda }+b\end{array}& \left(8\right)\end{array}$

• • R _100%,λ : spectral reflectance when dot quantity=100%
  • K: absorption coefficient
  • S: scattering coefficient
  • x: dot quantity (%)
  • R _Est,λ : estimated spectral reflectance value when dot quantity x
  • a, b: constants

In the above estimation formulas, constants a and b can use identical values for all inks. These constants can be determined by, e.g., a method of least squares using calorimetric data of arbitrary inks. In this embodiment, spectral reflectance values corresponding to respective dot quantities are estimated with reference to those when the dot quantity=100%, but other dot quantities may be used as a reference. However, estimation using spectral reflectance when the dot quantity=100% can assure higher estimation precision. Using the above estimation formulas, estimated values obtained upon changing the dot quantities of respective inks are calculated for respective wavelengths, and are stored as an LUT in the primary color dot gain LUT storage unit 2004 . Note that estimated values are calculated using equations (8) for all wavelengths (41 wavelengths in 10-nm increments from 380 to 780 nm) sampled in the visible wavelength range.

Note that the method of actually measuring patches shown in FIG. 3 (the method explained in the first embodiment) may be used as a method of generating the primary color dot gain LUT.

<Calculation of Ink Overlap Correction Coefficient>

The calculation process of the ink overlap correction coefficients in step S 2205 will be described below. The process in step S 2205 is the same as that in the first embodiment (step S 205 ), and colorimetric data of ink overlap correction patches (FIG. 5) which are output and measured in advance using a printer which is to undergo color reproduction prediction, are stored in the colorimetric value data storage unit 2005 .

On the other hand, the initial estimated value calculator 2010 estimates initial estimated spectral reflectance values of the overlap correction patches by equations (4) to (6) using data of the overlap correction patches shown in FIG. 5. The calculated initial estimated spectral reflectance values have errors from actually measured data, which are obtained by measuring overlap correction patches in practice and are stored in the colorimetric value data storage unit 2005 . Hence, in order to correct these errors from the actually measured data, correction coefficients a _h,λ , b _i,j,λ , and c _k,l,m,λ are determined using equation (7) above and a method of least squares or the like to minimize the errors.

The ink overlap correction coefficients obtained in this way are stored in the ink overlap correction coefficient storage unit 2007 .

<Ink Overlap Correction>

Details of the ink overlap correction process in step S 2209 will be described below. In step S 2209 , estimation errors due to ink overlap are corrected by equation (7) above from the initial estimated spectral reflectance value calculated in step S 2208 using the ink overlap correction coefficients (calculated in step S 2205 ) stored in the ink overlap correction coefficient storage unit 2007 .

<Estimation Result Display User Interface>

FIG. 16 shows an example of the user interface used to display the ink optimization result by the ink optimization result display unit 2015 . A display method of the ink optimization result will be described in detail below using FIG. 16.

Upon displaying the ink optimization result, the spectral reflectance of each target color set by the user is displayed on a target color spectral reflectance display area 2401 , and its tristimulus values are displayed on a target color tristimulus value display area 2403 . The output spectral reflectance, which is estimated using inks optimized to reproduce this target color, is displayed on a reproduction color spectral reflectance display area 2402 , and tristimulus values at that time are displayed on a reproduction color tristimulus value display area 2405 .

Also, the types and dot quantities of inks required to output this reproduction color are displayed on an ink dot quantity display area 2407 . An error (e.g., color difference ΔE) between the target color and reproduction color is displayed on an error display area 2404 . Note that light source information is required to calculate tristimulus values. Hence, the user can select a desired light source from a light source selection area 2406 . When the user selects an ink number of the optimized inks from an ink number selection area 2408 , the spectral reflectance of the selected ink is displayed on an optimized ink spectral reflectance display area 2409 .

As described above, according to the third embodiment, color agents as candidates and their characteristics are set, a reproduction color is estimated using the set color agents, and an error between a target color and the reproduction color is checked, thereby determining color agents to be used.

Fourth Embodiment

The fourth embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 17 is a block diagram showing the arrangement of a color reproduction prediction apparatus according to the fourth embodiment. Referring to FIG. 17, reference numeral 2701 denotes an ink optimization apparatus according to the fourth embodiment.

Reference numeral 2702 denotes an ink design unit, which designs the ink characteristics of a given target color. Reference numeral 2703 denotes a primary color dot gain estimation unit, which estimates a primary color dot gain LUT of the ink designed by the ink design unit 2702 . Reference numeral 2704 denotes a primary color dot gain LUT storage unit, which stores the primary color dot gain LUT estimated by the primary color dot gain estimation unit 2703 .

Reference numeral 2705 denotes a calorimetric value data storage unit, which stores the colorimetric values of output patches of a printer used in an ink optimization process. Reference numeral 2706 denotes an ink overlap correction coefficient calculator, which calculates ink overlap correction coefficients on the basis of the calorimetric values stored in the calorimetric value data storage unit 2705 . Reference numeral 2707 denotes an ink overlap correction coefficient storage unit, which stores the ink overlap correction coefficients calculated by the ink overlap correction coefficient calculator 2706 .

Reference numeral 2708 denotes an ink dot quantity setting unit, which sets ink dot quantities of the designed ink. Reference numeral 2709 denotes a primary color dot gain correction unit, which makes primary color correction in correspondence with the ink dot quantities set by the ink dot quantity setting unit 2708 . Reference numeral 2710 denotes an initial estimated value calculator, which calculates, as a color mixing result, an initial estimated spectral reflectance value on the basis of primary color values corrected by the primary color dot gain correction unit 2709 . Reference numeral 2711 denotes an ink overlap correction unit, which corrects the initial estimated spectral reflectance value calculated by the initial estimated value calculator 2710 using the ink overlap correction coefficients stored in the ink overlap correction coefficient storage unit 2707 , and the ink dot quantities stored in the ink dot quantity storage unit 2709 , thus calculating an estimated spectral reflectance value.

Reference numeral 2712 denotes a predicted output data storage unit which stores a predicted output value. Reference numeral 2713 denotes a target color data storage unit, which stores a target color set by the user. Reference numeral 2714 denotes a target color data measurement unit which provides a user interface, with which the user measures a target color. Reference numeral 2715 denotes an ink optimization result display unit, which displays optimized ink information on a display device 2719 . Reference numeral 2716 denotes an ink characteristic storage unit, which stores characteristics of paper used in a print process, and ink characteristics obtained by measuring those of some existing inks, in advance. Reference numeral 2717 denotes an error calculator, which calculates an error between predicted output data and a target color. Reference numeral 2718 denotes a minimum error determination unit, which compares a minimum error value with a threshold value. Reference numeral 2719 denotes a display device, which comprises a CRT, LCD, or the like. Reference numeral 2720 denotes a spectral distribution measurement device which comprises, e.g., a spectrophotometer or the like and measures a target color.

<Ink Optimization Process>

FIG. 18 is a flow chart showing an ink optimization process executed by the ink optimization apparatus 2701 of the fourth embodiment. FIG. 19 shows an example of a user interface which is provided by the target color measurement unit 2714 to allow the user to measure a target color. Note that the user interface for displaying the ink optimization result is displayed on the display device 2719 under the control of the ink optimization result display unit 2715 , and its contents are the same as those of the third embodiment (FIG. 16). The ink optimization process according to the fourth embodiment will be described below.

In step S 2801 , the user measures a desired target color using the target color measurement unit 2714 , and stores it in the target color data storage unit 2713 . It is checked in step S 2802 if the user has measured all target colors. If YES in step S 2802 , the flow advances to step S 2803 . Whether or not the user has measured all target colors is determined by examining if an ink optimization start instruction is issued upon depression of an ink optimization button 2906 (FIG. 19). Note that the target color measurement operation and the like using the user interface provided by the target color measurement unit 2714 will be described later.

If the ink optimization start instruction is issued, the ink design unit 2702 reads out and sets, as initial values, spectral reflectance data of C, M, Y, and K inks, which are normally used, and those of special color inks such as green, orange, and the like when the dot quantity=100%, of the ink characteristics stored in the ink characteristic storage unit 2716 in step S 2803 .

In step S 2804 , the primary color dot gain estimation unit 2703 estimates dot gains at arbitrary dot quantities on the basis of the spectral reflectance data when the ink dot quantity=100%, which are set by the ink design unit 2702 , and generates an LUT. This LUT is stored in the primary color correction LUT storage unit 2704 .

In step S 2805 , the ink overlap correction coefficient calculator 2706 reads the ink overlap calorimetric values stored in the colorimetric value data storage unit 2705 , and calculates ink overlap correction coefficients. The calculated ink overlap correction coefficients are stored in the ink overlap correction coefficient storage unit 2707 . Since the ink overlap correction coefficients use identical values in all ink combinations, the process in step S 2805 may be skipped after it is executed once. In step S 2806 , all ink dot quantities are set to initial values (e.g., 0%) to prepare for processes in step S 2807 and subsequent steps.

In step S 2807 , the primary dot gain correction unit 2709 corrects primary color dot gains using the ink dot quantities set by the ink dot quantity setting unit 2708 and the primary color dot gain LUT stored in the primary color dot gain LUT storage unit 2704 , thus calculating spectral reflectance values corresponding to the given ink dot quantities. In step S 2808 , the initial estimated value calculator 2710 predicts a mixed color based on the spectral reflectance values of inks calculated by the primary color dot gain correction unit 2709 using the KM theory given by equations (4) to (6) above, thus calculating an initial estimated spectral reflectance value. Furthermore, in step S 2809 the ink overlap correction unit 2711 corrects the initial estimated spectral reflectance value estimated by the initial estimated value calculator 2710 using the ink overlap correction coefficients stored in the ink overlap correction coefficient storage unit 2707 , thereby calculating a spectral distribution final estimation result.

In step S 2810 , the error calculator 2717 calculates an error between the calculated spectral distribution final estimation result, and each target color. If the error is smaller than a minimum value stored in the predicted output data storage unit 2712 at that time, the minimum error value is updated by that calculated error, and ink characteristics and dot quantities at that time are stored in the predicted output data storage unit 2712 .

It is checked in step S 2811 if all combinations of dot quantities of the currently set inks have been checked. If all combinations have been checked, the flow advances to step S 2813 ; otherwise, the flow advances to step S 2812 . In step S 2812 , the dot quantities are changed by a given change amount.

The minimum error determination unit 2718 checks in step S 2813 if the minimum error value stored in the predicted output data storage unit 2712 is larger than a set threshold value. If the minimum error value is larger than the threshold value, the flow advances to step S 2814 ; otherwise, the flow advances to step S 2815 . In step S 2814 , at least one of the currently set inks is replaced by an ink having other characteristics, which is read out from the ink characteristic storage unit 2716 . After replacement, the flow returns to step S 2805 to repeat the above processes. In step S 2815 , the minimum error value stored in the predicted output data storage unit 2712 and the ink characteristics and dot quantities that that time are displayed by a display method shown in, e.g., FIG. 16.

<Target Color Measurement User Interface>

FIG. 19 shows an example of the user interface that allows the user to measure a target color using the target color data measurement unit 2714 . The method of measuring a target color will be described in detail below using FIG. 19.

After the user selects a desired light source from a light source selection area 2902 , he or she sets a target color patch to be output by a printer, and presses a colorimetry start button 3907 . Then, the tristimulus values of the measured target color under the selected light source are displayed on a target color tristimulus value display area 2901 , and spectral reflectance is displayed on a target color spectral reflectance display area 2904 . The tristimulus values are converted into R, G, and B values of a monitor via an ICC profile or the like, and a color specified by the converted R, G, and B values is displayed on a target color confirmation area 903 . Note that the ICC profile is a file that describes a method (i.e., a specific color space) for reproducing a color by a specific device (monitor, scanner, printer, or the like), i.e., describes R, G, and B values required to reproduce the same color as device-independent color information (in this case, L*a*b*) using a given device. When the user wants to add another target color, he or she can add a target color by pressing a target color addition button 2905 . When the user has input all target colors and wants to start ink optimization, he or she can press the ink optimization button 2906 .

As described above, according to the third and fourth embodiments, upon setting color agents required to reproduce a target color, color agent characteristics as candidates are set, a reproduction color is estimated using the set color agents, and color agents to be used are determined on the basis of the checking result of an error between the target color and reproduction color. Therefore, color agents which can best reproduce the target color can be automatically selected.

<Number and Type of Inks Used>

In the third and fourth embodiments, a combination of six color inks are to be optimized. However, the number of colors is not limited to six. For example, a combination of five or less or seven or more color inks may be optimized. Alternatively, when conventional C, M, Y, and K inks are used as default inks, and one or a plurality of color inks are to be added, only ink or inks to be added can be optimized.

<Ink Characteristics Used in Ink Optimization>

In the third and fourth embodiments, as ink characteristics used as optimization candidates, the measurement results of existing ink characteristics pre-stored in the ink characteristic storage unit 2016 or 2716 are used. Alternatively, after ink optimization, ink having other characteristics may be additionally stored to make re-calculation. Also, by changing the characteristics (e.g., peak wavelength or reflectance) of existing ink in a computer as needed, ink having virtual characteristics may be set. Furthermore, the user may freely designate desired ink characteristics, and may add them as an ink candidate. That is, the characteristics of inks to be used in these embodiments may be those of either existing or virtual inks, and the present invention is not-limited to them.

<Change in Ink Dot Quantity>

In the third and fourth embodiments, the ink dot quantity is changed by a given amount to search for a dot quantity that can minimize an error from the target color. The change amount of the dot quantity is not limited to a specific value, and the same value need not always be used in the whole processes. For example, a large change amount may be used within a large error range to make searches at coarse intervals. As an error becomes smaller, the change amount is decreased to make fine searches. That is, since such process is a combination optimization problem that determines optimal ink dot quantities when an error between a target color and estimated output value is considered as an evaluation function, general methods of solving the combination optimization problem such as the steepest descent method, simulated annealing, genetic algorithm, and the like may be used. (Note that variations associated with the change amount of the dot quantity can be applied to the process in step S 814 of the second embodiment.)

As described above, according to the third and fourth embodiments, appropriate color agents required to precisely reproduce a target color can be easily selected.

Fifth Embodiment

In the fifth and sixth embodiments to be described below, a color gamut prediction process will be explained.

FIG. 20 is a block diagram showing the arrangement of a color gamut prediction apparatus according to the fifth embodiment. Reference numeral 3001 denotes a color gamut prediction apparatus according to the fifth embodiment. Respective units will be briefly explained below. Detailed operations and the like of these units will become more apparent from a description of a color gamut prediction process that will be explained later with reference to the flow charts of FIGS. 21A and 21B.

Reference numeral 3002 denotes a spectral reflectance measurement device which measures ink and printer characteristics by measuring spectral reflectance data of color patches output by a printer, the color gamut of which is to be predicted. Reference numeral 3003 denotes an ink calorimetric value storage unit, which stores ink spectral reflectance data measured by the spectral reflectance measurement device 3002 . Reference numeral 3004 denotes a primary color dot gain estimation unit, which estimates primary color dot gains from the ink colorimetric values stored in the ink calorimetric value storage unit 3003 . Reference numeral 3005 denotes a primary color dot gain LUT storage unit, which stores the primary color dot gains estimated by the primary color dot gain estimation unit 3004 as an LUT. Note that the printer characteristics indicate correction coefficients obtained based on the difference between an estimated value estimated using the KM theory and an actual output value when different inks overlap each other in a printer output. In other words, the printer characteristics are parameters for an ink overlap correction unit 3012 to be described later. By contrast, the ink characteristics are parameters for a primary dot gain correction unit 3010 to be described later.

Reference numeral 3006 denotes an overlap patch calorimetric value storage unit, which stores the calorimetric values of overlap patches measured by the spectral reflectance measurement device 3002 . Reference numeral 3007 denotes an ink overlap correction coefficient calculator, which calculates ink overlap correction coefficients on the basis of the calorimetric values of ink overlap patches stored in the overlap patch calorimetric value storage unit 3006 . Reference numeral 3008 denotes an ink overlap correction coefficient storage unit, which stores the ink overlap correction coefficients calculated by the ink overlap correction coefficient calculator 3007 .

Reference numeral 3009 denotes an ink dot quantity setting unit, which sets the dot quantities of inks used in color gamut estimation. Reference numeral 3010 denotes a primary color dot gain correction unit, which makes primary color correction in correspondence with the ink dot quantities set by the ink dot quantity setting unit 3009 . Reference numeral 3011 denotes an initial estimated value calculator, which estimates a color mixing result from the primary color values corrected by the primary color dot gain correction unit 3010 . Reference numeral 3012 denotes an ink overlap correction unit, which corrects an initial estimated spectral reflectance value calculated by the initial estimated value calculator 3011 using the ink overlap correction coefficients stored in the ink overlap correction coefficient storage unit 3008 and the ink dot quantities stored in the ink dot quantity storage unit 3009 .

Reference numeral 3013 denotes an estimation result storage unit, which stores an estimated output result corrected by the ink overlap correction unit 3012 . Reference numeral 3014 denotes a color gamut prediction unit, which predicts a color gamut on the basis of the spectral distribution (spectral reflectance) stored in the estimation result storage unit 3013 . Reference numeral 3015 denotes a prediction result display unit, which displays a color gamut prediction result and the like on a display device 3016 . Reference numeral 3016 denotes a display device, which comprises a CRT, LCD, or the like, and displays the color gamut prediction result under the control of the prediction result display unit 3015 .

<Color Gamut Prediction Process>

The color gamut prediction process by the color gamut prediction apparatus 3001 with the above arrangement will be explained below. FIGS. 21A and 21B are flow charts showing the color gamut prediction process executed by the color gamut prediction apparatus 3001 . FIG. 22 shows an example of a user interface which can be used upon inputting ink characteristics. FIG. 23 shows an example of a user interface which can be used to display the color gamut prediction result.

It is checked in step S 3201 if the user has pressed an ink data measurement button 3301 . If YES in step S 3201 , the flow advances to step S 3202 . In step S 3202 , the spectral reflectance data of a patch when the dot quantity of the ink used is 100% is measured using the spectral reflectance measurement device 3002 , and the calorimetric value is stored in the ink calorimetric value storage unit 3003 . At this time, an ink number is displayed on an ink number display area 3307 , and the measured spectral reflectance is displayed on an ink spectral reflectance display area 3308 . Note that a default number “user set No. ΔΔ” may be assigned as the ink number of ink data measured by the user, and that default number may be used after user makes measurement, or the name of a dye used in the ink may be newly assigned. The flow then advances to step S 3206 .

If the user has not pressed the ink data measurement button 3301 , the flow jumps to step S 3203 . It is checked in step S 3203 if the user has pressed an ink file read button 3302 . If YES in step S 3203 , the flow advances to step S 3204 . In step S 3204 , ink data is read from a file designated by the user in an ink data file designation area 3303 , and is stored in the ink calorimetric value storage unit 3003 . At this time, an ink number is displayed on the ink number display area 3307 , and spectral reflectance obtained from the ink data is displayed on the ink spectral reflectance display area 3308 .

If neither the ink data read button 3301 nor the ink file read button 3303 have been pressed, the flow jumps to step S 3205 . In step S 3205 , ink data, which is measured in advance by the user or is delivered from, e.g., a manufacturer or the like, is stored as default ink data in the ink calorimetric value storage unit 3003 . Then, an ink number is displayed on the ink number display area 3307 , and spectral reflectance obtained from the ink data is displayed on the ink spectral reflectance display area 3308 . Note that the user can modify ink information stored in the ink calorimetric value storage unit 3003 in step S 3202 , S 3204 , or S 3205 to desired characteristics using a user interface (ink spectral reflectance display area 3308 ) (details will be described later).

In step S 3206 , the primary color dot gain estimation unit 3004 estimates dot gains at arbitrary dot quantities on the basis of the spectral reflectance data (that at 100%) of the ink stored in the ink calorimetric value storage unit 3003 , and stores the estimation results as an LUT in the primary color dot gain LUT storage unit 3005 (details will be described later).

It is checked in step S 3207 if the user has pressed an overlap patch measurement button 3304 . If YES in step S 3207 , the flow advances to step S 3208 . In step S 3208 , spectral reflectance data of overlap patches are measured using the spectral reflectance measurement device 3002 , and the measurement results are stored in the overlap patch calorimetric value storage unit 3006 . The overlap patches will be described later.

If the user has not pressed the overlap patch measurement button 3304 , the flow jumps to step S 3209 . It is checked in step S 3209 if the user has pressed an overlap file read button 3305 . If YES in step S 3209 , the flow advances to step S 3210 . In step S 3210 , overlap patch data are read from a file designated by the user in an overlap file designation area 3306 , and are stored in the overlap patch calorimetric value storage unit 3006 . If neither the overlap patch measurement button 3304 nor the overlap file read button 3305 have been pressed, the flow jumps to step S 3211 . In step S 3211 , ove