Color converting apparatus and color converting method for converting input image data into converted image data

For each paper type, a plurality of two-dimensional excitation characteristics tables Ti are provided in one to one correspondence with a plurality of colors i. The excitation characteristics table Ti for each color i contains a plurality of sets of excitation-reflectance data Bi (λ0, λ) in a two-dimensional matrix form, for a plurality of combinations of incident light wavelengths λ and reflected light wavelengths λ0. The excitation-reflectance data Bi (λ0, λ) indicates the ratio of the amount of the reflected light wavelength λ0 generated in response to incidence of the incident light wavelength λ, with respect to the amount of the incident light wavelength λ. Using the two-dimensional excitation characteristics table Ti corresponding to the user's selected paper type and using the spectral radiation characteristics S(λ) of the user's selected light source type, Equations (9)-(11) are calculated to create an output profile, and color conversion is performed by using the output profile.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a color converting apparatus and color converting method for converting input image data into converted image data for a color outputting device.

2. Description of Related Art

In order to reproduce a color by using a color outputting device, such as a printer, equivalent to that indicated by input image data, a color matching process is employed in the process of converting the input image data into control signals for the color outputting device. During the conversion process, in order to attain a color matching, the input image data is converted to device-independent XYZ color quantities (X, Y, Z), and then into Lab color quantities (L*, a*, b*), which are also device-independent.

Conventionally, when an arbitrary object color is produced by a color outputting device, such as a printer, using paper, ink, or another color reproducing media, a set of XYZ color values (X, Y, Z) is defined as indicative of the arbitrary color by the following Equation (1):

A set of Lab color quantities (L*, a*, b*) is defined in terms of the XYZ value set (X, Y, Z) by the following Equation (2).
L*=116*(Y/Yn)1/3−16
a*=500*{(X/Xn)1/3−(Y/Yn)1/3)}
b*=200*{(Y/Yn)1/3−(Z/Zn)1/3)}  (2)wherein Xn, Yn, and Zn are tristimulus values of a perfectly diffuse surface (white). In other words, Xn, Yn, and Zn are tristimulus values defined for the case where incident light is illuminated directly on the human eye. These tristimulus values Xn, Yn, and Zn are defined by Equation (3) below:

In recent years, inkjet printers have become widely used as the color outputting device.

SUMMARY OF THE INVENTION

Frequently, fluorescent matter is incorporated in the ink and paper serving as the color reproducing media of inkjet printers. Fluorescent matter is characteristic in that, when light of a certain wavelength is irradiated on the fluorescent matter, the matter not only excites and reflects light of the same wavelength, but also reflects light of a different wavelength, specifically of a longer wavelength.

The conventional Equation (1) is, however, formulated under the assumption that the object color reflects light having the same wavelength as the incident light, and does not account for the generation of reflected light having a wavelength different from that of the incident light. That is, the spectral reflectance characteristics B(λ) merely indicate the ratio of reflected light to incident light, wherein the reflected light has the same wavelength λ as the incident light. In fact, Equation (1) itself only describes cases in which both incident light and reflected light have equivalent wavelengths λ. For this reason, the values X, Y, and Z defined by Equation (1) cannot accurately specify the values of a color having a fluorescent component with excitation characteristics.

Additionally, if the object color contains a fluorescent component, when the spectral wavelength characteristics S(λ) of incident light varies due to changes in the light source, the spectral characteristics of the light reflected from the object color will also vary. In other words, when the light source is changed, the color observed for the same object color will appear differently due to the interaction between the spectral wavelength characteristics S(λ) of the incident light and the excitation effect of the fluorescent component. However, the conventional equations (1) and (2) are established not taking into account the effects from excitation that is based on the changes of the observation environment light. The Lab color quantities (L*, a*, b*) obtained by the conventional Equation (2) cannot accurately specify the actual color observed.

Hence, the color values X, Y, Z and L, a, b determined by conventional Equations (1)-(3) cannot accurately quantify the object color when the object color has excitation characteristics. It is impossible to accurately reproduce colors using these color quantities, even through color matching.

The problem the same as described above occurs not only when the object color generates reflected light through excitation but also when the object color generates transmitted light through excitation.

The problem the same as described above occurs also when the object color is produced by any other color outputting devices so that the object color generates light (reflected or transmitted light) through excitation having a wavelength different from that of the incident light.

In view of the above-described drawbacks, it is an object of the present invention to provide a color converting apparatus and color converting method that is capable of converting input image data into converted image data that accurately reproduces the input image data by a color outputting device, even when the color outputting device reproduces colors with excitation characteristics by using a fluorescent component or the like that excites incident light.

In order to attain the above and other objects, the present invention provides a color converting apparatus, comprising: an image data inputting portion inputting image data; a color converting portion performing color conversion on the image data to generate converted image data, the color converting portion performing the color conversion by using information on output-end color conversion characteristics, which is determined based on information on excitation characteristics of a color that is outputted by a color outputting device; and a converted image data outputting portion outputting the converted image data.

With this construction, even when the color outputted by the color outputting device excites light of a different wavelength than that of the incident light, the color converting apparatus of the present invention performs color conversion using the output-end color conversion characteristics that account for this excitation. The color outputting device can output colors based on the converted image data that accurately reproduce the input image data.

The color converting portion may include: an input-end color converting portion converting the received image data into color quantity data using input-end color conversion characteristics of the image data; and an output-end color conversion portion converting the color quantity data to converted image output data using the output-end color conversion characteristics.

When the color outputting device outputs a color in response to a color control signal i, the color produces light with a generated light wavelength λ0in response to incidence of light with an incident light wavelength λ. In this case, a set of excitation characteristics data Bi (λ0, λ) is defined as indicating a ratio of an amount of the light with the wavelength λ0relative to the amount of the light with the wavelength λ, the generated light wavelength λ0being equal to or different from the incident light wavelength λ. The information on the excitation characteristics of the color corresponding to the color control signal i may include a plurality of sets of excitation characteristics data Bi (λ0, λ) for a combination of a plurality of incident light wavelengths λ and a plurality of generated light wavelengths λ0.

According to another aspect, the present invention provides a color converting apparatus, comprising: a color data inputting portion receiving device-independent color data; a color converting portion performing color conversion on the device-independent color data to generate converted image data by using information on output-end color conversion characteristics, which is determined based on information on excitation characteristics of a color that is outputted by a color outputting device; and a converted image data outputting portion outputting the converted image data, wherein the color outputting device outputs a color in response to a color control signal i, the color producing light with a generated light wavelength λ0in response to incidence of light with an incident light wavelength λ, a set of excitation characteristics data Bi (λ0, λ) being defined as indicating a ratio of an amount of the light with the wavelength λ0relative to the amount of the light with the wavelength λ, the generated light wavelength λ0being equal to or different from the incident light wavelength λ, and wherein the information on the excitation characteristics of the color corresponding to the color control signal i includes a plurality of sets of excitation characteristics data Bi (λ0, λ) for a combination of a plurality of incident light wavelengths λ and a plurality of generated light wavelengths λ0.

When the color outputting device is capable of outputting a plurality of colors according to a plurality of predetermined color control signals i, the output-end color converting portion converts the device-independent color quantity data set into one of the plurality of color control signals. In this case, the information on the output-end color conversion characteristics may be determined based on: the information on the excitation characteristics of the color outputted by the color outputting device, and information on output-end environment characteristics, which indicates an environment on an output end, in which the color outputted by the color outputting device is to be observed. The information on the output-end environment characteristics may include a spectral radiation distribution array indicative of an output-end environment, the spectral radiation distribution array including a plurality of sets of relative spectral radiation characteristics data S(λ) in correspondence with the plurality of incident light wavelengths λ, each relative spectral radiation characteristics data set S(λ) being indicative of a relative amount of power of light at a corresponding incident light wavelength λ in the output-end environment with respect to an amount of power of light at a predetermined incident light obtained in the output-end environment. The output-end color converting portion may convert the device-independent color quantity data set into the one color control signal by using the following relationships:
X=K*∫generated light wavelength range{(∫incident light wavelength rangeBi(λ0, λ)*S(λ)dλ)*x(λ0)}dλ0,
Y=K*∫generated light wavelength range{(∫incident light wavelength rangeBi(λ0, λ)*S(λ)dλ)*y(λ0)}dλ0,
Z=K*∫generated light wavelength range{(∫incident light wavelength rangeBi(λ0, λ)*S(λ)dλ)*z(λ0)}dλ0,wherein K=100/∫incident light wavelength rangeS(λ)*y(λ)dλ, and x(λ0), y(λ0), z(λ0) are the spectral sensitivities X, Y, and Z of the human eye for the light with the wavelength λ0.

According to another aspect, the present invention provides a color converting method, comprising the steps of: inputting image data; performing color conversion on the image data to generate converted image data, the color converting step performing the color conversion by using information on output-end color conversion characteristics, which is determined based on information on excitation characteristics of a color that is outputted by a color outputting device; and outputting the converted image data.

According to still another aspect, the present invention provides a color converting program, comprising: a program of inputting image data; a program of performing color conversion on the image data to generate converted image data, the color converting program performing the color conversion by using information on output-end color conversion characteristics, which is determined based on information on excitation characteristics of a color that is outputted by a color outputting device; and a program of outputting the converted image data.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A color converting apparatus and color converting method according to preferred embodiments of the present invention will be described while referring to the accompanying drawings wherein like parts and components are designated by the same reference numerals to avoid duplicating description.

The color converting apparatus and color converting method according to a first embodiment of the present invention will be described with reference toFIGS. 1-13.

FIG. 1shows a color converting apparatus1according to the preferred embodiment.

The color converting apparatus1is connected to a monitor2and an inkjet printer3, and is designed to reproduce colors displayed on the monitor2with the inkjet printer3.

The monitor2displays colors based on original data (Rin, Gin, Bin), wherein data Rin, Gin, and Bin included in the original data indicate gradations of the three primary colors.

The color converting apparatus1converts the original data (Rin, Gin, Bin) into corrected data (Cout, Mout, Yout, Kout).

The inkjet printer3creates an output image based on the corrected data (Cout, Mout, Yout, Kout).

The color converting apparatus1of the present embodiment includes a personal computer.

As shown inFIG. 2, the color converting apparatus1includes: a CPU10, a RAM12, a ROM14, a hard disk16, an input/output (I/O) interface18, and a buffer memory20. A bus22connects the CPU10, RAM12, ROM14, hard disk16, I/O interface18, and buffer memory20to one another.

The I/O interface18is connected also to an input device24, such as a keyboard and a mouse, a floppy disk drive26(“floppy” is a registered trademark), and a CD-ROM drive28, as well as the monitor2and inkjet printer3. The I/O interface18is further connected to a network30of an arbitrary type. When necessary, the I/O interface18can be connected also to a digital camera4and a scanner5.

The ROM14previously stores therein: a program for the color management system CM and a program for a profile maker PM. These programs may also be stored in the hard disk16instead of the ROM14. It is noted that data of the programs of the color management system CM and the profile maker PM may be originally stored on a computer-readable recording medium, such as a floppy disk or a CD-ROM, and may be installed into the hard disk16via the floppy disk drive26or the CD-ROM drive28. Alternatively, data of the programs of the color management system CM and the profile maker PM may be downloaded from the network30such as the Internet or the like. The ROM14may previously store therein an application program. The application program functions to create desired images.

The ROM14is formed with: a print data storage unit14a, an input profile storage unit14b, an excitation characteristic storage unit14c, and a spectral radiation (illumination) characteristic storage unit14d. These memory areas may be formed on the hard disk16rather than the ROM14.

The buffer memory20functions as an input unit20a(seeFIG. 6) for receiving original data (Rin, Gin, Bin) from the application program, and for temporarily saving that data. The buffer memory20also functions as an output unit20b(seeFIG. 6) for receiving corrected data (Cout, Mout, Yout, Kout) from a color management system CM, described later, temporarily storing the corrected data, and outputting this data to the inkjet printer3via the I/O interface18thereafter.

The CPU10executes the program for the profile maker PM, stored in the ROM14or the hard disk16, to create an output profile.

The CPU10further executes the program for the color management system CM, stored in the ROM14or the hard disk16, to convert original data (Rin, Gin, Bin) into corrected data (Cout, Mout, Yout, Kout). The CPU10also controls overall operations of the color converting apparatus1. For example, the CPU10executes the application program.

The RAM12is for saving data, which is created by the CPU10when the CPU10performs calculations while executing the various programs. The RAM12is formed with: an output profile saving unit12a, a reference white data saving unit12b, a spectral reflection data saving unit12c, and a calorimetric measurement data saving unit12d. The output profile saving unit12ais for saving an output profile which are created by the CPU10while the CPU10executes the profile maker PM program. The reference white data saving unit12b, the spectral reflection data saving unit12c, and the calorimetric measurement data saving unit12dare for saving reference white color data, spectral reflectance data, and calorimetric measurement data, respectively, all of which are created by the CPU10while the CPU10executes the profile maker PM program.

The input device24enables the user to input various instructions and data. As will be described later, the input device24functions as an environment light characteristic input unit24aand a paper type selecting unit24b(seeFIG. 6). The environment light characteristic input unit24ais for inputting types of light sources to indicate the environment, in which colors outputted by the inkjet printer3will be observed. The paper type selecting unit24bis for selecting a type of paper, onto which the inkjet printer3outputs an image.

Next, the print data storage unit14awill be described in detail.

Print data is prestored in the print data storage unit14a. This print data is used by the CPU10when the CPU10executes the profile maker PM program to create an output profile.

More specifically, the print data storage unit14astores 754 sets of control signals (C, M, Y, K) as print data for designating 754 colors i (O≦i≦753). Here, the 754 sets of control signals (C, M, Y, K) are constructed from: 216 sets of control signals (C, M, Y, K), in which CMY have the values of 0, 10, 20, 40, 70, or 100% and K have a value of 0%; 216 sets of control signals (C, M, Y, K), in which CMY have values of 0, 10, 20, 40, 70, or 100% and K has a value of 20%; 125 sets of control signals (C, M, Y, K), in which CMY have the values of 0, 20, 40, 70, or 100% and K has the value of 40%; 125 sets of control signals (C, M, Y, K), in which CMY have the values of 0, 20, 40, 70, or 100% and K has the value of 60%; 64 sets of control signals (C, M, Y, K), in which CMY have the values of 0, 40, 70, or 100% and K has the value of 80%; and 8 sets of control signals (C, M, Y, K), in which CMY have the values of 0 or 100% and K has the value of 100%. For example, print data designating a 0thcolor (brightest color (i=0)) is constructed from one set of minimum control signals (C=0%, M=0%, Y=0%, and K=0%) indicating the color of white paper.

Next, the input profile storage unit14bwill be described.

The input profile storage unit14bprestores therein an input profile. The input profile is profile data for the monitor2, and is required for converting the original data (Rin, Gin, Bin) into device-independent Lab data (Lin, ain, bin). In order to convert a set of original data (Rin, Gin, Bin) into a set of Lab data (Lin, ain, bin), the color management system CM first determines a set of luminance values (Sr, Sg, Sb) for the three primary colors indicated by the original data set (Rin, Gin, Bin). Based on the set of these luminance values (Sr, Sg, Sb), the color management system CM determines a set of XYZ values (Xin, Yin, Zin), and subsequently determines a set of Lab data (Lin, ain, bin) based on the XYZ value set (Xin, Yin, Zin).

The color management system CM determines luminance values Sr, Sg, and Sb by calculating the following Equation (4) for the original data Rin, Gin, and Bin:
Sr=(Rin/255)γr
Sg=(Gin/255)γg
Sb=(Bin/255)γb(4)

The color management system CM further determines the XYZ values Xin, Yin, and Zin by calculating the following Equation (5):
Xin=Sr*Xr+Sg*Xg+Sb*Xb
Yin=Sr*Yr+Sg*Yg+Sb*Yb
Zin=Sr*Zr+Sg*Zg+Sb*Zb(5)

wherein the * symbol denotes a multiplication symbol.

The color management system CM further determines the Lab values Lin, ain, and bin by calculating the following Equation (6):
Lin*=116*(Yin/Yn)(1/3)−16,
ain*=500*{(Xin/Xn)(1/3)−(Yin/Yn)(1/3)},
bin*=200*{(Yin/Yn)(1/3)−(Zin/Zn)(1/3)}  (6)

Next, the excitation characteristic storage unit14cwill be described.

The excitation characteristic storage unit14cprestores a table of excitation characteristics as shown inFIG. 3.

The excitation characteristics table ofFIG. 3stores therein 754 two-dimensional excitation characteristics tables Ti (where 0≦i≦753) for each of three types of paper which can be used by the inkjet printer3. In this example, the three paper types include: normal paper (type I), glossy paper (type II), and coated paper (type III).

As shown inFIG. 4, each two-dimensional excitation characteristics table Ti (where 0≦i≦753) contains a plurality of sets of excitation-reflectance data Bi (λ0, λ). The plurality of sets of excitation-reflectance data Bi (λ0, λ) are arranged in a two-dimensional matrix form in correspondence with combinations of a plurality of incident light wavelengths λ and a plurality of reflected light wavelengths λ0. The plurality of incident light wavelengths λ are set at 10-nm intervals across the entire wavelength range of incident light (from 300 nm to 780 nm). In other words, the plurality of incident light wavelengths λ are 300, 310, 320, . . . , and 780 nm. The plurality of reflected light wavelengths λ0are set at 10-nm intervals across the entire wavelength range of reflected light (from 380 nm to 780 nm). In other words, the plurality of reflected light wavelengths λ0are 380, 390, 400, . . . , and 780 nm. Each excitation-reflectance data set Bi (λ0, λ) is defined to indicate that when light with the incident light wavelength λ falls incident on an object color that is produced by some control signal i, the object color reflects light with the reflected light wavelength λ0at a ratio Bi (λ0, λ) indicative of the amount of the reflected light with respect to the amount of the incident light.

The 754 two-dimensional excitation characteristics tables T0-T753are prepared for each type of paper in a manner as described below.

First, one type of paper is loaded in the inkjet printer3. Then, 754 color patches are created on the paper based on the 754 sets of print data (C, M, Y, K), indicating 754 colors i (0≦i≦753), stored in the print data storage unit14a.

Next, a two-dimensional excitation characteristics table Ti is created for the color patch of each color i, where 0≦i≦753, by performing the following spectral measurement.

First, a monochromatic light having a wavelength λ of 300 nm is irradiated on one color patch i. A spectral sensor is used to measure reflected light at intervals of 10 nm across the entire reflected light wavelength range from 380 nm to 780 nm in order to determine a plurality of excitation-reflectance data sets Bi (λ0, λ), where λ=300 nm and λ0=380, 390, 400, . . . , 780 nm. The spectrophotometer CM-3800d (product name) manufactured by Minolta and Nisshin Boseki can be used as the spectral sensor.

Next, a monochromatic light having another wavelength λ of 310 nm is radiated on the same color patch i. The same spectral sensor is used to measure reflected light at intervals of 10 nm over the entire reflected light wavelength range from 380 nm to 780 nm in order to determine another plurality of excitation-reflectance data sets Bi (λ0, λ), where λ=310 nm and λ0=380, 390, 400, . . . , 780 nm.

In this way, a single color wavelength across the entire wavelength range of incident light 300 nm to 780 nm is irradiated in order progressively in intervals of 10 nm on a color patch of the single color i. The excitation-reflectance data Bi (λ0, λ), where λ=300, 310, 320, . . . , 780 nm and λ0=380, 390, 400, . . . , 780 nm, is determined by taking spectral measurements of reflected light using the spectral sensor at intervals of 10 nm across the entire wavelength range of reflected light, from 380 nm to 780 nm. As a result, a plurality of sets of excitation-reflectance data Bi (λ0, λ), for the combinations of the plurality of incident light wavelengths λ and the plurality of reflected light wavelengths λ0, are determined in the form of a two-dimensional matrix, as shown inFIG. 4. This two-dimensional matrix is set as the two-dimensional excitation characteristics table Ti.

By determining a two-dimensional excitation characteristics table Ti for the color patch of each of all the 754 colors i (0≦i≦753) using the method described above, 754 two-dimensional excitation characteristics tables T0-T753are created for one type of paper.

Similarly, 754 color patches are created for each of other paper types, and the above-described spectral methods are performed for each of the color patches, thereby creating 754 two-dimensional excitation characteristics tables T0-T753for each of the other paper types. The excitation characteristics table ofFIG. 3is created by arranging the two-dimensional excitation characteristics tables T0-T753for all paper types, as shown inFIG. 3, and is stored in the excitation characteristic storage unit14c.

It is noted that a user will select one paper type from among the types I, II, and III, stored in the excitation characteristic storage unit14c, and input data of this type into the input device24(paper type selecting unit24b) as the paper type to be used by the inkjet printer3.

Next, the spectral radiation characteristic storage unit14dwill be described.

The spectral radiation characteristic storage unit14dprestores therein a spectral radiation characteristics table, such as that shown inFIG. 5.

The spectral radiation characteristics table holds data of a plurality of environment light characteristics in which an image outputted by the inkjet printer3can be observed. In other words, the spectral radiation characteristics table contains a one-dimensional environment light characteristics data array D for each of a plurality of light source types. In this example, the plurality of light source types include: an A light source (type I), a D65 light source (type II), and a xenon light source (type III),

Each environment light characteristics data array D is a relative spectral power distribution, and includes a plurality of sets of relative spectral radiation characteristics data S(λ) in correspondence with a plurality of incident light wavelengths λ (300,310,320, . . . ,780nm), which are set at intervals of 10 nm across the entire incident light wavelength range from 300 nm to 780 nm. Each data set S(λ) denotes the proportion at which the light source irradiates incident light of the wavelength λ. In this example, each data set S(λ) is a normalized value for radiation intensity of the light source in the corresponding wavelength λ, wherein S(560 nm) (radiation intensity of the light source at the wavelength λ=560 nm) is normalized to 1.In other words, each data set S(λ) is indicative of an amount of power of light with the incident light wavelengths λ relative to an amount of power of light with 560 nm. It is noted that S(555 nm) (radiation intensity for the wavelength λ=555 nm) may be normalized to 1 instead of S(560 nm).

In this way, each environment light characteristics data array D holds a plurality of relative spectral radiation characteristics data sets S(λ) for the same incident light wavelength range (300-780 nm) as that for the incident light wavelength λ in the two-dimensional excitation characteristics tables Ti ofFIG. 4. It is noted that the environment light characteristics data array D has to hold data S(λ) for at least a wavelength covering the entire range of the incident light wavelengths λ possessed by the two-dimensional excitation characteristics tables Ti. The environment light characteristics data array D may hold data S(λ) for additional wavelength ranges that exceed the 300-780 nm wavelength range of the incident light wavelengths λ of the tables Ti.

The user will select one of the light source types I, II, and III stored in the spectral radiation characteristic storage unit14dThe user will input the selection information into the input device24(environment light characteristic input unit24a) as the light source used for the environment in which an output image created by the inkjet printer3will be observed.

Next, the functions of the profile maker PM and the color management system CM in the color converting apparatus1will be described with reference toFIG. 6.

As shown inFIG. 6, the profile maker PM includes: a white color calculating unit110, a spectral reflection data calculating unit120, a color value computing unit130, and a profile creating unit140.

The white color calculating unit110functions to read a single environment light characteristics data array D from the spectral radiation characteristic storage unit14d(FIG. 5) in correspondence with the light source type (type I, II, or III) that is inputted into the environment light characteristic input unit24aby the user. The white color calculating unit110then calculates reference white data Xn, Yn, and Zn (tristimulus values of a perfectly diffuse surface) based on the data array D.

More specifically, the white color calculating unit110calculates the following Equation (7), using the plurality of sets of data S(λ) forming the data array D, to determine the tristimulus values Xn, Yn, and Zn for a perfectly diffuse surface. The white color calculating unit110stores these values Xn, Yn, and Zn in the reference white data saving unit12b.

wherein x(λ), y(λ), and z(λ) are color matching functions, which are defined in Table 2.1 of CIE (Commission Internationale de l'Eclairage) 15.2 (appended table 1 of JIS Z8701) and whose values are set to 0 for wavelengths below 380 nm. Also, K is defined by the following Equation (8):

According to Equations (7) and (8), it can be understood that Yn is always 100.

The spectral reflection data calculating unit120functions also to read a single environment light characteristics data array D from the spectral radiation characteristic storage unit14din correspondence with the light source type (type I, II, or III), which is inputted into the environment light characteristic input unit24aby the user. The spectral reflection data calculating unit120also reads 754 two-dimensional excitation characteristics tables T0-T753from the excitation characteristic storage unit14cin correspondence with the paper type (type I, II, or III), which is inputted into the paper type selecting unit24bby the user.

The spectral reflection data calculating unit120calculates a plurality of sets of spectral reflection characteristics data Ri(λ0) for each of the 754 colors (i=0−753) using the data array D and the corresponding table Ti (i=0-753). The plurality of data sets Ri(λ0) are defined for the plurality of reflected light wavelengths λ0, which are defined at intervals 10 nm within the range of 380-780 nm.

More specifically, the calculating unit120calculates, for each color i (i=0 to 753), the following Equation (9) using: the plurality of data sets Bi (λ0, λ) that form the corresponding table Ti, and the plurality of data sets S(λ) that form the data array D. By integrating the product of the value S(λ) and the value Bi (λ0, λ) for one reflected light wavelength λ0with respect to the incident light wavelengths λ at 10-nm intervals in the range of 300-780 nm, the calculating unit120determines one set of spectral reflection characteristics data Ri(λ0) for the corresponding wavelength λ0.

In this way, the calculating unit120determines, for each color i, a plurality of sets of spectral reflection characteristics data Ri(λ0) for the plurality of reflected light wavelengths λ0(=380, 390, 400, . . . , 780 nm) which are defined at 10-nm intervals within the range of 380-780 nm. That is, the calculating unit120determines a plurality of data sets R0(λ0: λ0=380, 390, 400, . . . , 780 nm)-R753(λ0: λ0=380, 390, 400, . . . , 780 nm) for all the 754 colors. The calculating unit120stores all the spectral reflection characteristics data sets Ri(λ0) (here, i=0−753 and λ0=380, 390, 400, . . . , 780 nm) in the spectral reflection data saving unit12c, as shown inFIG. 7.

The color value computing unit130functions to compute a set of Lab color values (L*, a*, b*) for each of the 754 colors i (i=0−753) based on: the set of reference white color values (Xn, Yn, Zn) that are now stored in the reference white data saving unit12b, and the spectral reflection characteristics data sets Ri(λ0) for the corresponding color (i=0−753 and λ0=380, 390, 400, . . . , 780 nm) that are now stored in the spectral reflection data saving unit12c.

More specifically, the color value computing unit130first determines a set of XYZ values (Xi; Yi, Zi) for each color i using the following equation (10):

In this way, the computing unit130integrates the product of the spectral reflection characteristic value Ri(λ0) and the color matching function (x(λ0), y(λ0), or z(λ0)) with respect to the reflected light wavelengths λ0at 10-nm intervals in the range of 380-780 nm, thereby determining the XYZ value Xi, Yi, or Zi.

The computing unit130then determines a set of Lab values (L*, a*, b*) for each color i by calculating the following equation (11) based on the set of XYZ values (Xi, Yi, Zi).
L*=116*(Yi/Yn)(1/3)−16,
a*=500*{(Xi/Xn)(1/3)−(Yi/Yn)(1/3)},
b*=200*{(Yi/Yn)(1/3)−(Zi/Zn)(1/3)}  (11)

wherein values Xn, Yn, and Zn are read from the reference white data saving unit12b.

It is noted that the computing unit130calculates a XYZ values (X0, Y0, Z0) by equation (10) for the 0thcolor control signal (i=0). The 0thcolor control signal is defined by (C=0%, M=0%, Y=0%, K=0%) and represents color of white paper. In order to determine a Lab value set (L*, a*, b*) for the 0thcolor, the computing unit130first resets the values Xn, Yn, and Zn, to be used for the calculation of equation (11) for the 0thcolor, into the values X0,Y0, and Z0, respectively. Accordingly, the computing unit130will calculate the equation (11) as follows:
L*=116*(Y0/Y0)(1/3)−16=100,
a*=500*{(X0/X0)(1/3)−(Y0/Y0)(1/3)}=0,
b*=200*{(Y0/Y0)(1/3)−(Z0/Z0)(1/3)}.

The computing unit130will always determines that a Lab value set for the white paper color is equal to a fixed value set (100, 0, 0). Deposition of ink for the white paper color will be always prevented when performing color reproduction. In this way, because it is ensured that L*=100, a*=0, and b*=0 are always maintained for the color control signal i=0 of the brightest color, the color reproducibility for this brightest color control signal i=0 is improved.

It is noted that for colors other than the 0thcolor, the computing unit130does not execute the resetting operation for the values Xn, Yn, and Zn, but uses the values Xn, Yn, and Zn as they are read from the reference white data saving unit12b.

After computing the Lab value sets (L*, a*, b*) for all the 754 colors i (0≦i≦753), the color value computing unit130saves these Lab values in the calorimetric measurements data saving unit12d, as shown inFIG. 8. In this way, the relationship between the CMYK values (C, M, Y, K) for the 754 colors and the Lab values (L, a, b) is determined by the computing unit130, and stored in the saving unit12d.

It is noted that as is clear from the above Equations (7)-(11), according to the present embodiment, the value Yi can exceed Yn (100), and the value of L* can exceed 100 contrary to the conventional method.

More specifically, conventionally the value of Y is determined by Equation (1), and the value of L is determined by Equation (2). Because of the equations (1) and (3), Yn is always 100. The value B(λ) is defined as the spectral reflectance of an object color, and therefore satisfies the relationship of 0≦B(λ)≦1. Accordingly, the value Y is always less than or equal to Yn (100), and the value of L is always less than or equal to 100. In order to prevent operation errors due to unforeseen arithmetic errors, therefore, the upper limit of 100 can be defined for the values Y and L*. A limiting process can be executed to determine that an error occurs when Y and L* are determined to exceed 100, then to rematch these values to 100.

Contrarily, according to the present embodiment, the excitation characteristics value Bi (λ0, λ) used in the present embodiment itself is a value between 0 and 1. The spectral reflection characteristic value Ri(λ0) is the result of taking the integral of the excitation characteristics values Bi (λ0, λ) over the entire incident light wavelength range. According to Equation (9), the value Ri(λ0) will be always greater than or equal to 0, but can also exceed 1 to indicate excitation. Accordingly, as is clear by Equations (7) and (10), the value Yi can exceed the value Yn, and the value of L* can exceed 100.

Taking into account this specific characteristics of the present embodiment, the color value computing unit130does not determine that an error occurs even when the value Yi exceeds the Yn. In other words, the color value computing unit130does not execute the above-mentioned limiting process. Additionally, the work area in the RAM12for temporarily storing results of calculations is configured to be able to store values of Y that exceed Yn, that is, 100. Similarly, the calorimetric measurements data saving unit12dis configured to store a value for L greater than 100.

In this way, the present embodiment is established to taking into account that the brightness of reflection light resulting from excitation can be greater than that of the incident light depending on the value of the spectral reflection characteristic data Ri(λ0). In this way, according to the present embodiment, excitation is taken into account, enabling the values of Y and L* to exceed 100. Hence, the limiting process is eliminated in the present embodiment, allowing the value for L* to exceed 100. The data retaining range is allocated for the data retaining portion (work area in RAM12) such that the value of Y can be accurately retained even when Y is calculated as a value exceeding Yn and that the value of L* can be accurately retained even when L* exceeds 100. Hence, the process will not generate an overflow error. In this way, it is possible to perform the conversion process even when a value of Y greater than Yn is obtained, without causing an overflow error.

The profile creating unit140functions to calculate an output profile based on a correlation between: print data (C, M, Y, K) of 754 colors i (0≦i≦753), stored in the print data storage unit14a, and Lab color values (L, a, b) for 754 colors, that are now stored in the calorimetric measurements data saving unit12d. The profile creating unit140stores the output profile in the output profile saving unit12a.

The profile creating unit140first determines 1014sets of CMYK print data (C, M, Y, K) for all the 1014colors that include the 754 sets of print data (C, M, Y, K) for 754 colors. The profile creating unit140then determines a correlation between CMYK print data and Lab values.

More specifically, the profile creating unit140sets one set of print data, which is constructed from an arbitrary CMYK combination other than the print data (C, M, Y, K) of the 754 colors. For example, the profile creating unit140sets one set of print data (C=1%, M=0%, Y=0%, K=0%). Next, the profile creating unit140calculates a set of Lab values (L, a, b) for this set of print data (C=1%, M=0%, Y=0%, K=0%) by performing an interpolation using the relationship between and the CMYK values (C, M, Y, K) for the 754 colors and the Lab values (L, a, b) for the 754 colors.

The profile creating unit140repeats this calculation until all the 1014sets of Lab values (L, a, b) are determined for all the 1014sets of print data (C, M, Y, K). In this way, Lab value sets are determined for all print data sets (C, X, Y, K). As a result, a relationship between (C, M, Y, K) and (L, a, b) is determined. This relationship will be referred to as “(C, M, Y, K)-(L, a, b) relationships” hereinafter.

More specifically, the profile creating unit140first defines the Lab space in which the L-axis, a-axis, and b-axis are orthogonal to one another. The profile creating unit140then defines a plurality of lattice points (L, a, b) by three-dimensionally dividing the Lab space into arbitrary equal intervals. The profile creating unit140then selects, for each lattice point (L, a, b), one set of (L, a, b) among all the sets of Lab data (L, a, b) listed in the (C, M, Y, K)-(L, a, b) relationship. The profile creating unit140then selects the one set of (L, a, b) that has the minimum color distance (color difference) from the subject lattice point (L, a, b) in the Lab space.

The profile creating unit140then reads one set, of CMYK data (C, M, Y, K) that corresponds to the selected Lab data set (L, a, b) from the (C, M, Y, K)-(L, a, b) relationship, and stores this CMYK data in correspondence with the lattice point (L, a, b).

By repeating the above-described operations for all the lattice points (L, a, b), the (L, a, b)-(C, M, Y, K) relationship is created in the form of a three-dimensional lookup table. The profile creating unit140stores this three-dimensional lookup table as the output profile in the output profile saving unit12aas shown inFIG. 9.

The color management system CM converts each set of original data (Rin, Gin, Bin), inputted into the buffer memory20(input unit20a), into a set of Lab data (Lin, ain, bin) based on the input profile stored in the input profile storage unit14b. The color management system CM subsequently converts the Lab data set (Lin, ain, bin) into a set of corrected data (Cout, Mout, Yout, Kout) based on the output profile which is now stored in the output profile saving unit12a. The color management system CM outputs the corrected data set (Cout, Mout, Yout, Kout) to the inkjet printer3via the buffer memory20(output unit20b).

It is noted that when performing color conversion on one set of original data (Rin, Gin, Bin), the color management system CM converts this data to a device-independent Lab data set (Lin, ain, bin). The color management system CM converts the data by performing the above Equations (4)-(6) based on the input profile.

Next, the color management system CM converts the Lab data set (Lin, ain, bin) into a corrected data set (Cout, Mout, Yout, Kout) using the output profile (FIG. 9). More specifically, the color management system CM first finds out, in the Lab space, several Lab lattice points (eight lattice points, for example) that surround an input color point that is specified by the Lab data set (Lin, ain, bin). The color management system CM then searches for several sets of CMYK data (C, M, Y, K) that correspond to the several sets of Lab data (L, a, b) at the several Lab lattice points from the output profile. Next, the color management system Cm determines the corrected data set (Cout, Mout, Yout, Kout) corresponding to the inputted Lab data set (Lin, ain, bin) by performing an interpolation calculation based on the several CMYK data sets (C, M, Y, K) searched as described above. Details of this interpolation method is disclosed in the U.S. Pat. No. 5,835,624.

The color management system CM outputs the corrected data (Cout, Mout, Yout, Kout) to the inkjet printer3via the buffer memory20. The user loads paper of the paper type inputted into the paper type selecting unit24b(one of types I, II, or III ofFIG. 3) into the inkjet printer3. Hence, the inkjet printer3outputs an output image through a printing process based on the corrected data (Cout, Mout, Yout, Rout) on the paper of the selected paper type. The user views the outputted image under the light source type (one of types I, II, III ofFIG. 5) that the user has inputted into the environment light characteristic input unit24a. In this way, the user can observe the output image at the same colors as those displayed by the monitor2based on the original data (Rin, Gin, Bin).

The operations of the color converting apparatus1having the above configuration will be described below.

A user operates the color converting apparatus1to create image data (Rin, Gin, Bin) to be displayed on the monitor2by using an image-creating application program. When the user wishes to print out that image on the inkjet printer3, the user inputs his/her command to start up the profile maker PM. The profile maker PM stores the image data (Rin, Gin, Bin) created by the user in the buffer memory20.

These operations of the color converting apparatus1will be described with reference to the flowchart inFIG. 10.

When the profile maker PM is started, the CPU10controls the monitor2in S10to display names of all the light source types (in this example, an A light source, D65light source, and xenon light source set as types I, II, and III, respectively) stored in the, spectral radiation characteristics table (FIG. 5) in the spectral radiation characteristic storage unit14d. The user is prompted to select one of the displayed light source types.

By manipulating the input device24, the user selects a light source type that is used in the environment in which the user will view the printed image. For example, the user aligns the cursor with the name of a desired light source on the monitor2and clicks the mouse button to select the light source type. In this way, operation of the color converting apparatus1is extremely simple, since the user need only select a desired light source.

In S20, the CPU10reads a single environment light characteristics data array D, which corresponds to the selected light source type, from the spectral radiation characteristics table (FIG. 5) in the spectral radiation characteristic storage unit14d. The CPU10stores the environment light characteristics data array D in a work area (not shown) of the RAM12.

In S30, the CPU10calculates the tristimulus values Xn, Yn, and Zn for a perfectly diffuse surface according to Equations (7) and (8) using a plurality of sets of relative spectral radiation characteristics data S(λ) that form the environment light characteristics data array D, which is read in S20The CPU10stores the tristimulus values Xn, Yn and Zn in the reference white data saving unit12bof the RAM12.

In S40, the CPU10controls the monitor2to display the names of all paper types (in the present embodiment, normal paper, glossy paper, and coated paper set to types I, II, and III, respectively) stored in the excitation characteristics table (FIG. 3) of the excitation characteristic storage unit14c. The CPU10prompts the user to select a single type of paper. By operating the input device24, the user selects a desired type of paper. That is, the user aligns the cursor with a desired name of paper type on the monitor2and clicks the mouse button to select the paper type.

In S50, the CPU10reads the 754 two-dimensional excitation characteristics tables T0-T753corresponding to the selected paper type from the excitation characteristics table (FIG. 3) in the excitation characteristic storage unit14c, and stores the data in a work area of the RAM12.

In S60, the CPU10determines a plurality of sets of spectral reflection characteristic data Ri(λ0), where 0≦i≦753 and λ0=380, 390, 400, . . . , 780 nm, and stores these values in the spectral reflection data saving unit12c. It is noted that the CPU10determines, for each color i (0≦i≦753), a plurality of sets of spectral reflection characteristic data Ri(λ0where λ0=380, 390, 400, . . . , 780 nm) by calculating Equation (9) using: the plurality of sets of excitation-reflectance data Bi (λ0, λ) in the corresponding two-dimensional excitation characteristics table Ti (0≦i≦753) that has been stored in the work area of the RAM12in S50; and the plurality of sets of relative spectral radiation characteristics data S(λ) making up the environment light characteristics data array D that has been stored in the work area of the RAM12in S20.

In S70, the CPU10determines an XYZ value set (Xi, Yi, Zi) for each color i (0≦i≦753) by calculating Equation (10) based on the values Xn, Yn, and Zn that have been stored in the reference white data saving unit lib in S30and the spectral reflection characteristic data Ri(λ0) (0≦i≦753) that has been stored in the spectral reflection data saving unit12cin S60. The CPU10further determines an Lab value set (L*, a*, b*) for each color i (0≦i≦753) by calculating Equation (11) based on the XYZ value set (X, Y, Z).

It is noted that when performing calculations for the 0thcolor (i=0), the CPU10calculates the Equation (11) after determining the XYZ value set (X0, Y0, Z0) and by resetting the values Xn, Yn, Zn to X0, Y0, Z0. Accordingly, the Lab value set for the 0thcolor (i=0) is always fixed at is (100, 0, 0). The CPU10will not cause an error during the calculations of S70, even when the calculated value Yi exceeds Yn and the obtained value L* exceeds 100.

In S80, the CPU10saves the Lab data sets (L, a, b) calculated in S70for all the 754 colors as calorimetric measurements data in the calorimetric measurements data saving unit12d.

In S90, the CPU10determines the (C, M, Y, K)-(L, a, b) relationships (that is, correlations between 1014CMYK print data sets and Lab data sets) based on the relationships between the 754 sets of CMYK print data (C, M, Y, K) for 754 colors, which are stored in the print data storage unit14a, and the 754 sets of Lab data (L, a, b) for the 754 colors, which have been stored in the calorimetric measurements data saving unit12din S80.

In S110, the CPU10stores the three-dimensional lookup table showing the (L, a, b)-(C, M, Y, K) relationships in the output profile saving unit12aas an output profile.

After the profile maker PM completes its process in this way, the user starts up the color management system CM program and issues an instruction to perform a print operation.

After the color management system CM starts up, as shown in the flowchart ofFIG. 11, the CPU10reads each set of original data (Kin, Gin, Bin) from the buffer memory20in S200.

In S210, the CPU10determines one set of Lab data (Lin, ain, bin) for each set of original data (Rin, Gin, Bin) based on the input profile stored in the input profile storage unit14b. To do this, the CPU10calculates the above Equations (4)-(6) based on each set of original data (Rin, Gin, Bin).

In S220, the CPU10converts each set of Lab data (Lin, ain, bin) to a set of corrected data (Cout, Mout, Yout, Kout) by performing interpolation calculation using the output profile now stored in the output profile saving unit12a.

In S230, the CPU10outputs the corrected data (Cout, Mout, Yout, Kout) to the inkjet printer3via the buffer memory20.

The color management system CM process is completed after all the sets of original data (Rin, Gin, Bin) are converted to corrected data (Cout, Mout, Yout, Kout) and outputted.

The inkjet printer3produces an output image by performing a printing operation on paper of the paper type selected by the user based on the corrected data (Cout, Mout, Yout, Kout).

In this way, the color converting apparatus1of the present embodiment converts image data (Rin, Gin, Bin) to Lab data (Lin, ain, bin) based on the input profile. The color converting apparatus1further converts the Lab data (Lin, ain, bin) to corrected data (Cout, Mout, Yout, Kout) based on the output profile. Here, the output profile has been created by calculating Equations (9)-(11) based on: the excitation-reflectance data Bi (λ0, λ) in the two-dimensional excitation characteristics tables Ti that correspond to the paper type used in the inkjet printer3; and the relative spectral radiation characteristics data S(λ) for the light source type used when viewing the outputted image. Accordingly, output images created using corrected data (Cout, Mout, Yout, Kout) will have the same colors as those displayed in the monitor2when observed in the observation environment of the light source type selected by the user, even when the created image includes a fluorescent light component.

In the embodiment described above, the original data (Rin, Gin, Bin) is created by the application program on the color converting apparatus1to produce images for the monitor2. The original data (Rin, Gin, Bin) is temporarily stored in the buffer memory20before being subjected to color conversion. However, this original data (Rin, Gin, Bin) may not be created by the color converting apparatus1, but can be prestored on a storage medium, such as a floppy disk or a CD-ROM. In this case, the original data (Rin, Gin, Bin) will be read by the floppy disk drive26or the CD-ROM drive28and temporarily stored in the buffer memory20via the I/O interface18for color conversion. It is also possible to perform color conversion after inputting the original data (Rin, Gin, Bin) for the monitor2via the I/O interface18from the network30and temporarily storing the data in the buffer memory20.

As described above, according to the present embodiment, for each paper type, a plurality of two-dimensional excitation characteristics tables Ti are provided in one to one correspondence with a plurality of colors i. The excitation characteristics table Ti for each color i contains a plurality of sets of excitation-reflectance data Bi (λ0, λ) in a two-dimensional matrix form, for a plurality of combinations of incident light wavelengths λ and reflected light wavelengths λ0. The excitation-reflectance data Bi (λ0, λ) indicate the ratio of the amount of the reflected light wavelength λ0generated in response to incidence of the incident light wavelength λ, with respect to the amount of the incident light wavelength λ. Using the two-dimensional excitation characteristics table Ti corresponding to the user's selected paper type and using the spectral radiation characteristics S(λ) of the user's selected light source type, Equations (9)-(11) are calculated to create an output profile, and color conversion is performed by using the output profile.

Next, several modifications of the first embodiment of the present invention will be described.

In the embodiment described above, the two-dimensional excitation characteristics table Ti (FIG. 4) includes not only the excitation-reflectance data Bi (λ0, λ) for incident light wavelengths λ in the visible range from 400-780 nm, but also the excitation-reflectance data Bi (λ0, λ) for incident light wavelengths λ in the ultraviolet range smaller than 400 nm.

However, it is sufficient that each excitation-reflectance data set Bi (λ0, λ) is in the form of a two-dimensional data for two wavelengths (reflected wavelength λ0and incident light wavelength λ) and therefore can contain information on excitation for generating a reflected light wavelength λ0different from the incident light wavelength λ. It is sufficient that the two-dimensional excitation characteristics table Ti be configured to list up the plurality of excitation-reflectance data sets (excitation characteristics data sets) Bi (λ0, λ) for the two wavelengths λ0and λ. It is unnecessary that the two-dimensional excitation characteristics table Ti contains the ultraviolet range in the incident light wavelength λ. The two-dimensional excitation characteristics table Ti may be configured from the excitation characteristics data Bi (λ0, λ) for incident light wavelengths λ in the visible range from 400-780 nm and for reflected light wavelengths λ0in the visible range from 400-780 nm.

Excitation generally occurs to shift in the longer wavelength, only. Accordingly, the excitation-reflectance data sets Bi (λ0, λ), where λ0<λ, are normally always zero (0) That is, the excitation-reflectance data sets Bi (λ0, λ) in the upper-right region of the two-dimensional excitation characteristics table Ti with respect to the diagonal line (λ0=λ) inFIG. 4are always zero (0) in general. It is therefore sufficient to list up only those excitation-reflectance data sets Bi (λ0, λ) for λ0≧λ in the two-dimensional excitation characteristics table Ti. In other words, the two-dimensional excitation characteristics table Ti (FIG. 4) may list up only those data Bi (λ0, λ) that are located on the diagonal line of λ0=λ and on the lower left side of the diagonal line. In this case, it is possible to reduce the amount of data required to be stored in the excitation characteristic storage unit14c.

Papers, such as normal paper, glossy paper, and coated paper, reproduce colors by generating a reflected light in response to incident light. However, there are other types of paper that reproduce colors by generating transmitted light in response to incident light. Examples of these paper types include transparencies for use on overhead projectors.

The excitation characteristic storage unit14c(FIG. 3) may be prestored with store 754 two-dimensional excitation characteristics tables T0-T753for each paper type that generates transmitted light. In this case, excitation characteristics data sets Bi (λ0, λ) forming each two-dimensional excitation characteristics table Ti (i=0-753) can be set as transmittance. When some paper type generates transmitted light at a wavelength λ0in response to incidence of incident light at a wavelengths λ, the transmittance indicates a ratio of the amount of the transmitted light at a wavelength λ0with respect to the amount of the incident light at a wavelength λ. A two-dimensional excitation characteristics table Ti for each color i is created by arranging a plurality of excitation-transmittance data sets Bi (λ0, λ) two-dimensionally for combinations of a plurality of incident light wavelengths λ and a plurality of transmitted light wavelengths λ0.

When printing on a transparency sheet loaded in the inkjet printer3, in S10in the process for creating an output profile (FIG. 10), the user can select a type of light source that will illuminate the transparency when using the overhead projector. In S40, the user can select “transparency sheet” as the paper type. The values Ri(λ0) obtained in S60by Equation (9) for each color i are indicative of spectral transmission characteristics of the subject color i. Based on the spectral transmission characteristics values Ri(λ0), the Lab values are calculated in S70according to Equations (10) and (11).

In the embodiment described above, 754 two-dimensional excitation characteristics tables T0-T753are stored in the excitation characteristic storage unit14c, as shown inFIG. 3, in correspondence with each paper type that can be used in the inkjet printer3. However, the excitation characteristics vary not only according to types of paper, but also according to types of ink.

In the present modification, therefore, the 754 two-dimensional excitation characteristics tables T0-T753are stored in the excitation characteristic storage unit14cin correspondence with each of a plurality of combinations of paper types and ink types that can be used in the inkjet printer3. Each two-dimensional excitation characteristics table Ti (0≦i≦753,FIG. 4) is configured of a plurality of excitation characteristics data sets Bi (λ0, λ) for a plurality of incident light wavelengths λ and reflected light wavelengths λ0. Each data set Bi (λ0, λ) has been determined by producing a color patch by using a corresponding color control signal i and by using a corresponding paper type and a corresponding ink type. A reflectance (or transmittance) of the color patch is measured at a corresponding incident light wavelength λ and at a corresponding reflected light wavelength λ0.

In this modification, the user selects in S40ofFIG. 10both of the paper type and ink type to be used in the printing process. In S50, the CPU10can select the 754 two-dimensional excitation characteristics tables T0-T753in correspondence with the combination of the paper type and ink type selected by the user.

In the embodiment described above, original data (Rin, Gin, Bin) used to drive the monitor2is subjected to color conversion. However, original data (Rin, Gin, Bin) produced by other image data handling devices may be subjected to a color conversion process. For example, original data (Rin, Gin, Bin) may be produced by the digital camera4or the scanner5shown inFIG. 1and may be inputted into the color converting apparatus1for color conversion.

In this case, the input profile storage unit14bis prestored with a three-dimensional lookup table as an input profile. The three-dimensional lookup table includes correlations between a plurality of RGB data sets (R, G, B) and a plurality of Lab data sets (L, a, b). The plurality of RGB data sets (R, G, B) are those that can be inputted from an input-end device (digital camera4, scanner5, or the like) to the color converting apparatus1. The three-dimensional lookup table is created in advance and stored in the input profile storage unit14b.

In the present modification, the buffer memory20functions as the input unit20a(seeFIG. 6) for receiving and temporarily storing original data (Rin, Gin, Bin) from the digital camera4or scanner5via the I/O interface18.

When input data (Rin, Gin, Bin) is inputted from the digital camera4or scanner S in S200ofFIG. 11, the color management system CM calculates Lab data (Lin, ain, bin) in S210by performing an interpolation calculation using the three-dimensional lookup table in the input profile storage unit14b.

In the embodiment described above, the environment light characteristics data array D is stored in the spectral radiation characteristic storage unit14dfor each of the plurality of light source types. Accordingly, the user selects a desired light source in S10ofFIG. 10. In S20, one environment light characteristics data array D is read from the spectral radiation characteristic storage unit14dfor the selected light source type.

In the present modification, however, the user produces a desired environment light characteristics data array D′, as shown inFIG. 12. The data array D′ is indicative of spectral distribution of light illumination in a desired environment, in which the user will observe images created by the inkjet printer3. The data array D′ includes a plurality of sets of relative spectral radiation characteristics data S′(λ) for the plurality of wavelengths λ (300, 310, 320 . . . , 780 nm) within the incident light wavelength range of 300-780 nm. In order to produce each data set S′(λ), the user uses a measuring instrument, such as a spectrophotometer, to actually measure the power of light with wavelength λ in the desired environment. Each data set S′(λ) has a value obtained by normalizing the measured radiation intensity of the light with wavelength λ so that the a reference data set S′(λ=600 nm or 555 nm) is set to 1.

In the present modification, the process of the profile maker PM is modified as shown inFIG. 13by omitting520inFIG. 10and by providing the process of S10′ in place of S10.

As shown inFIG. 13, according to the present modification, in S10′, the user inputs his/her desired environment light characteristics data array D′ into the color converting apparatus1. That is, the user inserts a floppy disk or a CD-R storing the prescribed data array D′ ofFIG. 12into the floppy disk drive26or the CD-ROM drive28. The CPU10drives the floppy disk drive26or CD-ROM drive28, reads the data array D′, and stores the data array D′ in a work area of the RAM12. Alternatively, the user can download the data array D′ from the network30into the work area of the RAM12. Hence, in the present-modification, the floppy disk drive26, CD-ROM drive28, network30, or the like functions as the environment light characteristic input unit24a.

Subsequently, the processes of S30-S110are executed in the same manner as described in the first embodiment. It is noted, however, that when calculating Equation (7) in S30and Equation (9) in S60, the plurality of sets of relative spectral radiation characteristics data S′(λ) forming the data array D′ inputted in S10′ is used in place of the relative spectral radiation characteristics data sets S(λ).

In this way, according to this modification, the user can input an array of desired environment data indicating his/her desired output-end observation environment. Accordingly, it is possible to generate converted data that accurately reproduces a color specified by the input data under any desired environment.

Next, a color converting apparatus and color converting method according to a second embodiment of the present invention will be described with reference toFIGS. 14-18.

In the first embodiment, the user selects an observation environment (light source types I, II, or III inFIG. 5). In response to this selection, the CPU10reads a corresponding environment light characteristics data array D from the spectral radiation characteristic storage unit14d. Further, the user selects a paper type (type I, II, or III inFIG. 3). In response to this selection, the CPU10reads corresponding 754 two-dimensional excitation characteristics tables Ti (0≦i≦753) from the excitation characteristic storage unit14c. The CPU10creates an output profile based on a plurality of relative spectral radiation characteristics data sets S(λ) forming the data array D and a plurality of excitation-reflectance data sets Bi (λ0, λ) forming each table Ti. The CPU10stores this output profile in the output profile saving unit12a.

In the present embodiment, however, the ROM14is provided with an output profile storage unit14e, as indicated by the broken line inFIG. 2.

As shown inFIG. 14, the output profile storage unit14eis prestored with nine output profiles in correspondence with nine combinations of the three light source types (types I, II, and III) and the three paper types (types I, II, and III) that can be selected by the user. Each output profile is a three-dimensional lookup table designating (L, a, b)-(C, M, Y, K) correlations, as is created in the first embodiment (FIG. 9).

These nine output profiles are created in advance for the combinations of light source types and paper types by executing the profile maker PM on another computer that is separate from the color converting apparatus1. In other words, operations of the profile maker PM (FIG. 10) of the first embodiment are repeatedly executed on the separate computer. Each time the operations of the profile maker PM are executed, the light source type selected in S10and the paper type selected in S40are changed in sequence. The plurality of output profiles created in this way are stored in the output profile storage unit14ein the color converting apparatus1.

In this way, according to the present embodiment, the color converting apparatus1is prestored with all the output profiles that can be used in color conversion. The color converting apparatus1does not need to store a program for the profile maker PM. Accordingly, as shown inFIG. 15, the color converting apparatus1of the present embodiment is no longer provided with the print data storage unit14a, spectral radiation characteristic storage unit14d, excitation characteristic storage unit14c, reference white data saving unit12b, spectral reflection data saving unit12c, and colorimetric measurements data saving unit12d, all of which are used to create the output profiles in the first embodiment.

In the present embodiment, the color management system CM functions as shown inFIG. 15. More specifically, the color management system CM converts the original data (Rin, Gin, Bin) in the buffer memory20into Lab data (Lin, ain, bin) based on the input profile. The color management system CM then selects a single output profile from the output profile storage unit14e(FIG. 14) based on the combination of light source type that the user inputs into the environment light characteristic input unit24aand the paper type selected by the user with the paper type selecting unit24b. The color management system CM stores the output profile read from the output profile storage unit14ein the output profile saving unit12a. The color management system CM then converts the Lab data (Lin, ain, bin) into corrected data (Cout, Mout, Yout, Kout) based on the output profile now stored in the output profile saving unit12a. The color management system CM outputs the corrected data to the inkjet printer3via the buffer memory20(output portion20b).

The operation of the color converting apparatus1of the present embodiment will be described in greater detail with reference toFIG. 16.

When the user wishes to use the inkjet printer3to print image data (Rin, Gin, Bin) created and displayed on the monitor2, the user starts the color management system CM. The image data (Rin, Gin, Bin) is inputted into the buffer memory20.

After the color management system CM is started, the CPU10controls the monitor2in S150ofFIG. 16to display names of the three light source types (A light source, D65light source, and xenon light source set as types I, II, and III, respectively) that correspond to all the nine output profiles stored in the output profile storage unit14e(FIG. 14). The color management system CM then prompts the user to select a single light source type. The user manipulates the input device24to select a light source type that will be used in the environment in which the user views the outputted image.

In S160, the CPU10controls the monitor2to display names of the three paper types (normal paper, glossy paper, and coated paper set as types I, II, and III, respectively) that correspond to all the nine output profiles stored in the output profile storage unit14e(FIG. 14). The CPU10prompts the user to select a single paper type The user operates the input device24to select a desired paper type.

In S170, the CPU10reads, from the output profile storage unit14e, a single output profile that corresponds to the combination of the light source selected in S150and the paper type selected in S160, and stores the output profile in the output profile saving unit12a.

Subsequently, color conversion is performed by executing the processes of S200-S230similarly to the process (FIG. 11) of the first embodiment.

According to the color converting apparatus1of the present embodiment, the entire color conversion operation can be performed extremely quickly, since an output profile corresponding to the combination of light source and paper type selected by the user can be simply selected. Moreover, the selected output profile is created in advance by performing Equations (9)-(11) based on: the excitation-reflectance data Bi (λ0, λ) in the two-dimensional excitation characteristics tables Ti corresponding to the user-specified paper type, and the relative spectral radiation characteristics data S(λ) for the user's specified light source type. Accordingly, when the corrected data (Cout, Mout, Yout, Kout) obtained based on the output profile is used to create an output image on the user's specified paper type, the output image will appear to have the same colors as that displayed on the monitor2when observed in an environment having the user's specified light source, even when the output image contains a fluorescent component.

Next, modifications of the second embodiment will be described.

In the second embodiment described above, the print data storage unit14a, spectral radiation characteristic storage unit14d, excitation characteristic storage unit14c, reference white data saving unit12b, spectral reflection data saving unit12c, and calorimetric measurements data saving unit12dused to create the output profiles are omitted from the color converting apparatus1, as shown inFIG. 15. In the present modification, however, the spectral radiation characteristic storage unit14dis retained in the color converting apparatus1, as shown inFIG. 17. The spectral radiation characteristic storage unit14dis prestored with the environment light characteristics data arrays D for the three light source types I, II, and II, as shown inFIG. 5.

As in the fifth modification of the first embodiment, according to this modification, the floppy disk drive26, CD-ROM drive28, network30, or the like of the present modification functions as the environment light characteristic input unit24afor inputting the desired environment light characteristics data array D′ (FIG. 12) that is created by the user through actual measurements.

In the present modification, the color management system CM functions as shown inFIG. 17.

That is, the color management system CM converts the original data (Rin, Gin, Bin) inputted into the buffer memory20into Lab data (Lin, ain, bin) based on the input profile.

The color management system CM selects, from among the plurality of environment light characteristics data arrays D in the spectral radiation characteristic storage unit14d(seeFIG. 5), one data array D that indicates the environment characteristics closest to the data array D′ that the user has inputted into the environment light characteristic input unit24a.

More specifically, the color management system CM determines, for each wavelength λ (300, 310, 320, . . . , 780 nm) in the incident light wavelength range (300-780 nm), the difference between a data set S′(λ) in the inputted data array D′ (FIG. 12) and a data set S(λ) in one data array D in the storage unit14d(FIG. 5). The color management system CM calculates the total sum of differences by adding together the differences for all the wavelengths λ of 300, 310, 320, . . . , 780 nm.

The color management system CM performs the above-described calculation for each of all the three data arrays D stored in the storage unit14d(FIG. 5). In this way, the color management system CM calculates., the total sum of differences between the desired data array D′ and a data array D for light source I; the total sum of differences between the desired data array D′ and a data array D for light source IT; and the total sum of differences between the desired data array D′ and a data array D for light source III.

The color management system CM then selects, as a data array that is closest to the data array D′, one data array D having the smallest total sum of differences among the three data arrays D. The color management system CM then determines a light source type that corresponds to the selected data array D.

Next, the color management system CM reads, from the output profile storage unit14e(FIG. 14), one output profile that corresponds to the combination of the selected light source type and the paper type selected by the user with the paper type selecting unit24b. The color management system CM stores the output profile in the output profile saving unit12a.

The color management system CM then converts the Lab data (Lint ain, bin) to corrected data (Cout, Mout, Yout, Kout) based on the output profile now stored in the saving unit12a. The color management system CM outputs this corrected data to the inkjet printer3via the buffer memory20.

The operation of the color converting apparatus1according to the present modification will be described below in greater detail with reference toFIG. 18.

In S140, the user inputs the user's desired environment light characteristics data array D′ into the color converting apparatus1. That is, the user inserts a floppy disk or a CD-R that stores the data array D′ into the floppy disk drive26or the CD-ROM drive28. The CPU10drives the floppy disk drive26or CD-ROM-drive28to store the data array D′ in a work area of the RAM12. Alternatively, the CPU10can download the data array D′ into the work area of the RAM12from the network30.

In S150′, the CPU10selects one environment light characteristics data array D that is closest to the inputted data array D′ from the spectral radiation characteristic storage unit14d(FIG. 5), and determines a corresponding light source type.

In S160, as in the second embodiment, the CPU10prompts the user to select a paper type. The user selects a paper type.

In S170, the CPU10reads from the output profile storage unit14ea single output profile that corresponds to the combination of the light source type selected in S150and the paper type selected in S160, and stores the output profile in the output profile saving unit12aSubsequently, steps S200-S230are executed to perform color conversion, in the same manner as described in the first embodiment.

In this way, the color converting apparatus1of the present modification can perform extremely quick color conversion, since the apparatus need only select an output profile for one light source type the most similar to the environment characteristics inputted by the user.

The output profile storage unit14e(FIG. 14) may be prestored with a plurality of output profiles corresponding to a combination of all ink types, all paper types, and all light source types by taking into account a plurality of ink types as in the third modification of the first embodiment. In this case, the user selects both a paper type and ink type in S160ofFIG. 16. In S170, the CPU10can select an output profile corresponding to a combination of the light source type selected by the user in S150and the paper type and ink type selected in S160

Next, a color converting apparatus and color converting method according to a third embodiment of the present invention will be described with reference toFIGS. 19-26.

The color converting apparatus1according to the third embodiment functions to create on the inkjet printer3color samples of printed materials that are to be created using a printing device6shown by the broken line inFIG. 1.

More specifically, the printing device6produces printed materials by using the original data (Cin, Min, Yin, Kin). The color converting apparatus1according to the present embodiment converts the original data (Cin, Min, Yin, Kin) into corrected data (Cout, Mout, Yout, Kout) so that the inkjet printer3will create the same colors as the printed materials by using the corrected data (Cout, Mout, Yout, Rout).

In this case, the user can store original data (Cin, Min, Yin, Kin), to be inputted to the printing device6, on a data storing medium, such as a floppy disk or CD-R. The user inserts this floppy disk or CD-R into the floppy disk drive26or CD-ROM drive28of the color converting apparatus1(FIG. 2). The original data (Cin, Min, Yin, Kin) is read and stored in the buffer memory20via the I/O interface18.

Alternatively, the user can input the original data (Cin, Min, Yin, Kin) into the color converting apparatus1from the network30. This original data (Cin, Min, Yin, Kin) is read and stored in the buffer memory20via the I/O interface18.

In this way, the buffer memory20functions as the input unit20a(seeFIG. 19) for receiving the original data (Rin, Gin, Bin) via the I/O interface18from the floppy disk drive26, the CD-ROM drive28, or a type of network30. The buffer memory20temporarily stores the original data (Rin, Gin, Bin).

Next, the portions of the color converting apparatus1according to the present embodiment differing from the first embodiment will be described.

As shown inFIG. 19, the profile maker PM of the present embodiment not only creates an output profile, but also an input profile. Therefore, the ROM14is not provided with the input profile storage unit14b. Instead, the RAM12is provided with an input profile saving unit12eas indicated by the broken lines inFIG. 2. The input profile is created by the profile maker PM, and then is stored in the input profile saving unit12e.

In the present embodiment, in addition to the excitation characteristic storage unit14c, another excitation characteristic storage unit14fis formed in the ROM14, as shown inFIG. 2. As shown inFIG. 20, 754 two-dimensional excitation characteristics tables T0′-T753′ are prestored in the excitation characteristic storage unit14fin correspondence with all paper types used by the printing device6(in the present embodiment, normal paper, glossy paper, and coated paper set as types I, II, and III, respectively).

As shown inFIG. 21, one two-dimensional excitation characteristics table Ti′ (0≦i≦753) corresponding to each paper type used in the printing device6contains a plurality of sets of excitation-reflectance data Bi (λ0, λ). Similarly as in the first embodiment, the two-dimensional excitation characteristics table Ti′ (0≦i≦753) contains a plurality of data sets Bi (λ0, λ) in correspondence with combinations of a plurality of incident light wavelengths λ and a plurality of reflected light wavelengths λ0. The plurality of incident light wavelengths λ are defined at 10-nm intervals within the incident light wavelength range of 300-780 nm, and the plurality of reflected light wavelengths λ0are defined at 10-nm intervals within the reflected light wavelength range of 380-780 nm.

It is noted that in the first embodiment, the 754 two-dimensional excitation characteristics tables T0-T753(FIG. 3) for the inkjet printer3are created in advance for each paper type used on the inkjet printer3. That is, the inkjet printer3is driven to produce 754 color patches on each corresponding paper type based on the 754 sets of print data (C, M, Y, K), and measurements are taken of these color patches. Similarly, the 754 two-dimensional excitation characteristics tables T0′-T753′ for the printing device6are created in advance for each paper type used on the printing device6. The tables T0′-T753′ for the printing device6are created according to the same method used to create the tables T0-T753for the inkjet printer3. That is, the inkjet printer3is driven to produce 754 color patches on each corresponding paper type based on the 754 sets of print data (C, M, Y, K), and measurements are taken of these color patches.

In the present embodiment, the environment light characteristic input unit24anot only functions for inputting a type of light source indicating the environment in which color samples outputted by the inkjet printer3will be observed, but also functions for inputting a type of light source indicating the environment in which printed materials outputted by the printing device6will be observed.

Similarly, the paper type selecting unit24bnot only functions for selecting a type of paper used on the inkjet printer3for outputting color samples, but also functions for selecting a type of paper used for outputting printed materials on the printing device6.

As in the first embodiment, the white color calculating unit110, spectral reflection data calculating unit120, color value computing unit130, and profile creating unit140serve to create an output profile in the present embodiment. However, these components also function to create an input profile in the present embodiment, in a manner as described below.

The white color calculating unit110functions to read, from the spectral radiation characteristic storage unit14d(FIG. 5), a single environment light characteristics data array D that corresponds to the light source type (type I, II, or III) to be used when viewing printed materials created on the printing device6. It is noted that the light source type is designated at the environment light characteristic input unit24aby the user,. The white color calculating unit110calculates white reference values Xn, Yn, and Zn according to Equation (7) based on the relative spectral radiation characteristics data sets S(λ) in the data array D. The white reference values Xn, Yn, and Zn are saved in the reference white data saving unit12b.

The spectral reflection data calculating unit120functions to read, from the spectral radiation characteristic storage unit14d, the single environment light characteristics array D that corresponds to the light source type (type I, II, or III) to be used when viewing printed materials created on the printing device6. It is noted that the light source type is inputted into the environment light characteristic input unit24aby the user. The spectral reflection data calculating unit120reads, from the other excitation characteristic storage unit14f(FIG. 20), 754 two-dimensional excitation characteristics tables T0′-T753′ that correspond to the paper type (type I, II, or III) to be used in the printing device6. It is noted that the paper type is designated at the paper type selecting unit24bby the user. Equation (9) is used to calculate the spectral reflection characteristic values Ri(λ) (i=0−753 and λ0=380, 390, 400, . . . , 780 nm) for 754 colors i (i=0−753) based on the relative spectral radiation characteristics data sets S(λ) in the data array D and the excitation-reflectance data sets Bi (λ0, λ) in the 754 tables T0′-T753′. The spectral reflection characteristic values Ri(λ0) are saved in the spectral reflection data saving unit12cas shown inFIG. 7.

The color value computing unit130functions to compute the Lab color values (L*, a*, b*) for the 754 colors using Equations (10) and (11) based on; the reference white color values Xn, Yn, Zn that are now stored in the reference white data saving unit12b, and the spectral reflection characteristic values Ri(λ0) (i=0−753 and λ0=380, 390, 400, . . . , 780 nm) for the 754 colors that are now stored in the spectral reflection data saving unit12c. The Lab color values (L*, a*, b*) for the 754 colors are stored in the calorimetric measurement data saving unit12d.

The profile creating unit140functions to create a correlation between all the 1014colors of CMYK print data and Lab data in the form of a four-dimensional lookup table. The correlation is established based on the relationship between print data (C, M, Y, K) of 754 colors i (0≦i≦753) stored in the print data storage unit14aand Lab color values (L*, a*, b*) for the 754 colors stored in the colorimetric measurements data saving unit12d. The profile creating unit140stores data of this correlation as an input profile in the input profile saving unit12e, as shown inFIG. 22.

Except for the description given above, the color converting apparatus1of the present embodiment has the same configuration as the color converting apparatus1in the first embodiment.

Next, the operations of the color converting apparatus1according to the present embodiment having the construction described above will be described.

It is noted that prior to printing with original data (Cin, Min, Yin, Kin) on the printing device6, the user would like to create samples of the printed material on the inkjet printer3and to let a person requesting the printed material (hereinafter referred to as “client”) to check the state of colors. In such a case, before creating samples of the printed material, the user first starts the profile maker PM. It is noted that the original data (Cin, Min, Yin, Kin) is read from a floppy disk or the like and stored in the buffer memory20.

Once the profile maker PM is started, the CPU10first creates an input profile according to substantially the same method used in the first embodiment to create the output profile.

More specifically, as shown inFIG. 23, the CPU10prompts the user in S310to select a light source type for the environment in which printed material created on the printing device6will be observed, just as in step S10of the first embodiment (FIG. 10).

In S320, as in S20, the environment light characteristics data array D of the selected light source type is read from the spectral radiation characteristic storage unit14d(FIG. 5) and stored in a work area of the RAM12.

In S330, as in S30, Equation (7) is used to calculate the tristimulus values Xn, Yn, and Zn of a perfectly diffuse surface based on the plurality of data sets S(λ) forming the data array D of the selected light source type.

In S340, as in S40, the CPU10prompts the user to select a type of paper to be used by the printing device6.

In S350, as in S50, the CPU10reads the 754 two-dimensional excitation characteristics tables T0′-T753′ (Ti′ (0≦i≦753)) that correspond to the paper type selected by the user from the other excitation characteristic storage unit14f(FIG. 20) and stores these tables Ti′ (0≦i≦753) in the work area of the RAM12.

In S360, as in S60, the CPU10uses Equation (9) to calculate the spectral reflection characteristic values Ri(λ0) based on the plurality of data sets Bi (λ0, λ) that make up the tables Ti′ (0≦i≦753)) now stored in the RAM12, and saves the result in the spectral reflection data saving unit12cas shown inFIG. 7.

In S370-S380, as in S70-S80, the CPU10calculates the XYZ values (Xi, Yi, Zi) and the Lab values (L*, a*, b*) for each color i according to Equations (10) and (11) and stores the results in the colorimetric measurements data saving unit12das shown inFIG. 8

In S390, as in S90, the CPU10calculates Lab value sets corresponding to all the 1014sets of CMYK data that include the 754 CMYK print data in the print data storage unit14a. The CPU10creates correlations between all the 1014CMYK data sets (C, X, Y, K) and the corresponding1014Lab data sets (L, a, b) in the form of a 4-dimensional lookup table. Unlike the first embodiment, the reverse calculation of S100(FIG. 10) is not executed in the present embodiment.

Accordingly, the program proceeds directly from S390to S410. In S410, the CPU10stores, as an input profile, all the 1014CMYK data sets (C, M, Y, K) and their corresponding1014Lab data sets (L, a, b) determined in S390in the colorimetric measurements data saving unit12das shown inFIG. 22.

After creation of the input profile is complete, the CPU10creates an output profile according to the operations in the same manner as in the first embodiment (FIG. 10).

It is noted that according to the present embodiment, the user selects in S10the light source type that will be used in the environment in which the client will view the sample created by the inkjet printer3. In S40, the user selects a paper type that will be used for creating the sample on the inkjet printer3.

After creating the output profile, the profile maker PM process ends, as in the first embodiment, and the color management system CM process is initiated.

As shown inFIG. 24, after the color management system CM is started, the CPU10reads in S500original data (Cin, Min, Yin, Kin) that has been inputted into the buffer memory20for output on the printing device6.

In S510, the CPU10converts the original data (Cin, Min, Yin, Kin) to Lab data (Lin, ain, bin) based on the input profile stored in the calorimetric measurements data saving unit12d. More specifically, the original data (Cin, Min, Yin, Kin) is converted to Lab data (Lin, ain, bin) based on a correlation between the CMYK data and Lab data in the input profile (FIG. 22).

In S520-S530, processes equivalent to the steps S220-S230of the first embodiment (FIG. 11) are executed to convert the Lab data (Lin, ain, bin) to corrected data (Cout, Mout, Yout, Kout) based on the output profile and to output this converted data to the inkjet printer3.

The inkjet printer3performs a printing process based on the corrected data (Cout, Mout, Yout, Kout) on a paper type selected in S40(FIG. 10) to produce a sample. The client views the sample under a light source type selected in S10(FIG. 10) The color observed in this way will appear to be the same as the color on printed material to be printed by the printing device6on paper selected in S340(FIG. 23) and observed under a light source selected in S310(FIG. 23). Accordingly, the client can accurately determine the color state of the printed material to be printed by the printing device6by viewing the sample.

In the present embodiment described above, the color converting apparatus1converts the original data (Cin, Min, Yin, Kin) to Lab data (Lin, ain, bin) based on the input profile. The input profile has been created by calculating Equations (9)-(11) based on: the excitation characteristics Bi (λ0, λ) for the two-dimensional excitation characteristics tables Ti′ corresponding to the paper type used on the printing device6, and the relative spectral radiation characteristics S(λ) for the light source used in the printed-material observation environment. The color converting apparatus1converts the Lab data (Lin, ain, bin) to corrected data (Cout, Mout, Yout, Kout) based on the output profile. The output profile has been created by calculating Equations (9)-(11) based on the excitation characteristics Bi (λ0, λ) for the two-dimensional excitation characteristics tables Ti corresponding to the paper type to be used on the inkjet printer3, and the relative spectral radiation characteristics S(λ) for the light source used in the sample observation environment. Accordingly, when a sample created according to the corrected data (Cout, Mout, Yout, Kout) is observed under the observation environment for the sample, the colors of the sample will appear the same as those observed on the final printed material under the observation environment for the final printed material, even when the sample and/or final printed material contains a fluorescent component.

It is noted that the output profile can be created in the present embodiment as in the fifth modification of first embodiment (FIG. 13). That is, the desired environment light characteristics data array D′ (FIG. 12) can be inputted into the color converting apparatus1in S10′, shown inFIG. 13, and used for creating the output profile.

More specifically, the client uses a spectrophotometer to measure a plurality of relative spectral radiation characteristics data sets S′(λ) for a plurality of incident light wavelengths λ at 10-nm intervals across the incident light wavelength range (300-780 nm) in the environment in which the client will check the samples. A desired environment light characteristics data array D′ (FIG. 12) is formed from the plurality of data sets S′(λ), and is stored on a floppy disk or a CD-R. The user can receive the floppy disk or CD-R from the client and insert the floppy disk or CD-R into the floppy disk drive26or the CD-ROM drive28of the color converting apparatus1. Alternatively, the client can transmit the desired data array D′ to the color converting apparatus1via the network30. The CPU10downloads the desired data array D′ from the network30in S10′ and stores the data array D′ in a work area of the RAM12.

Similarly, when creating the input profile, a desired environment light characteristics data array D′ can be inputted into the color converting apparatus1in S310. In this case, the process of S320inFIG. 23is omitted. More specifically, a spectrophotometer is used to measure a plurality of sets of relative spectral radiation characteristics S′(λ) for a plurality of incident light wavelengths λ across the incident light wavelength range (300-780 nm) for the environment in which the printed material created by the printing device6will be observed. A desired environment light characteristics data array D′ is formed from the plurality of data sets S′(λ). This data array D′ is inputted into the color converting apparatus1via the floppy disk drive26, the CD-ROM drive28, or the network30.

As described above, according to the present embodiment, the type of paper used to produce the printed material and the type of light source in which the printed material will be observed are designated, and the input profile is created based on the designated paper type and light source type. Similarly, the type of paper used to produce the sample and the type of light source in which the sample will be observed are designated, and the output profile is created based on the designated paper type and light source type.

Image data (Cin, Min, Yin, Kin) is converted into Lab data (Lin, ain, bin) by using the input profile. The Lab data (Lin, ain, bin) is then converted into corrected image data (Cout, Mout, Yout, Kout) by using the output profile. Accordingly, although the samples are printed on the inkjet printer3that is different from the printing device6used for producing the final printed material, the samples can accurately show the color state of the printed materials, despite the fact that the samples are produced on a sheet type different from that of the final printed material and that the samples are observed in an environment different from the final observation environment. In this way, colors to be outputted by the printer6and to be observed in the input-end observation environment are accurately reproduced by the inkjet printer3in the output-end observation environment. Accordingly, it is possible to accurately check the state of colors for final printed materials by viewing the samples.

According to the present embodiment, the input profile is created by taking account for the combinations of input-end observation environment and excitation characteristics of colors produced on the printing device6. Accordingly, it is possible to convert CMYK image data for the printing device6into Lab color quantities that account for the interaction between this excitation and input-end observation environment, even when the color produced on the printing device6excites light of a wavelength different from that of the incident light. Similarly, the output profile-is created by taking into account the combinations of the output-end observation environment and excitation characteristics of colors produced on the inkjet printer3. Accordingly, it is possible to convert the Lab color quantities into converted CMYK image data that accounts for the interaction between this excitation and the output-end observation environment, even when the color produced on the inkjet printer3excites light of a wavelength different from that of the incident light. By outputting this converted image data to the inkjet printer3, the color outputted by the inkjet printer3and observed in the output-end observation environment appears the same as the so color outputted by the printing device6and observed in the input-end observation environment.

It is noted that the color converting apparatus1may be connected to both of the printer6and the inkjet printer3. In this case, the user controls the color converting apparatus1to produce the input profile and the output profile, to convert original image data (Cin, Min, Yin, Kin) into corrected image data (Cout, Mout, Yout, Kout) by using the input and output profiles, and to output the corrected image data (Cout, Mout, Yout, Kout) to the inkjet printer3to produce samples After the client checks the samples and confirms that he/she is satisfied with the color state of the sample, the user controls the color converting apparatus1to output the original image data (Cin, Min, Yin, Kin) to the printing device6to produce final printed materials.

However, it is unnecessary to connect the color converting apparatus1to the printer6or the inkjet printer3. The color converting apparatus1may not be connected to any of the printing device6and the inkjet printer3. For example, the user has the printing device6installed in his/her printing shop, while the client has an ink jet printer3installed in his/her home. The color converting apparatus1is provided in the user's printing shop but separate from the printing device6.

In such a case, the user prepares the original image data (Cin, Min, Yin, Kin), which is to be inputted into the printing device6. The user then loads the original image data (Cin, Min, Yin, Kin) into the color converting apparatus1by using a floppy disk, CD-R, network30, or the like. The user controls the color converting apparatus1to produce the input profile and the output profile, and to convert the original image data (Cin, Min, Yin, Kin) into corrected image data (Cout, Mout, Yout, Kout) by using the input and output profiles. The user then records the corrected image data (Cout, Mout, Yout, Kout) on a floppy disk or a CD-R, or uploads the corrected image data (Cout, Mout, Yout, Kout) to the network30. The client receives the floppy disk or the CD-R, and loads the corrected image data (Cout, Mout, Yout, Kout) into his/her own computer that is connected to the inkjet printer3. The client can download the corrected image data (Cout, Mout, Yout, Kout) into his/her computer from the network30. The client's computer controls the inkjet printer3to produce samples. After the client checks the samples and informs the user of his/her satisfaction of the color state, the user controls his/her printing device6by the original image data (Cin, Min, Yin, Kin) to produce final printed materials.

It is noted that the color converting apparatus1may be connected to the printing device6or the inkjet printer3. When the color converting apparatus1is connected to the printing device6, the color converting apparatus1can perform not only the profile-making and color-converting operation but also control of the printing device6Similarly, when the color converting apparatus1is connected to the inkjet printer3, the color converting apparatus1can perform not only the profile-making and color-converting operation but also control of the inkjet printer3.

Next, a modification of the present embodiment will be described.

When color forming media, such as paper and ink, used by the printing device6do not contain a fluorescent component, the color produced by the printing device6will occur no excitation, but generates only the reflected light of the wavelength λ0equivalent to that of the incident light wavelength λ. In such a case, the two-dimensional excitation characteristics table Ti′ (0≦i≦753) is created as shown inFIG. 25. That is, all the sets of excitation-reflectance data Bi (λ0, λ), except for those for λ0=λ, are set to zero (0).

In this case, a one-dimensional reflectance tables Ti″ (0≦i≦753), as shown inFIG. 26, can be stored in the excitation characteristic storage unit14f(FIG. 20) in place of the two-dimensional table Ti′ (00≦i≦753) ofFIG. 25. Each one-dimensional table Ti″ stores a plurality of reflectance data sets (non-excitation reflectance data sets) Bi (λ) in correspondence with a plurality of incident light wavelengths λ (=300, 310, 320, . . . , 780 nm) at 10-nm intervals within the wavelength range of 300-780 nm of the incident light wavelength λ. In this case, the incident light wavelength λ is equivalent to the reflected light wavelength λ0. Each reflectance data set Bi (λ) is indicative of the ratio of the amount of the reflected light at the wavelength λ, which is generated in response to incidence of the incident light with the same wavelength λ, with respect to the amount of the incident light at the wavelength λ.

In order to create an input profile in this case, the flowchart ofFIG. 23is modified so as to omit step S360, and the process proceeds directly from S350to S370. In S370, XYZ values Xi, Yi, and Zi are calculated using the following Equation (12):

Subsequently, the values L*, a*, and b* are calculated based on Equation (11).

In the above-described embodiment, the input profile is created, and stored in the input profile saving unit12e. However, in the same manner as in the second embodiment, a plurality of input profiles may be created in advance in correspondence with a plurality of paper types and a plurality of light source types. The plurality of input profiles are stored in the ROM14in the same manner as shown inFIG. 14. One input profile may be simply selected according to a user's selected light source type and paper type.

While the invention has been described in detail with reference to specific embodiments thereof, it would be apparent to those skilled in the art that many modifications and modifications may be made therein without departing from the spirit of the invention, the scope of which is defined by the attached claims.

For example, in the first and third embodiments, a plurality of paper types can be used on the inkjet printer3. Accordingly, the excitation characteristic storage unit14cstores 754 tables T0-T753(FIG. 3) in correspondence with each paper type. When the user selects one paper type in S40of the output profile creating process (FIG. 10), the CPU10reads the corresponding 754 tables T0-T753from the storage unit14cin S50.

However, when only a single paper type can be used on the inkjet printer3, the storage unit14cneed only store 754 tables T0-T753for that paper type. Hence, the paper type selecting step S40is no longer needed in the output profile creating process ofFIG. 10. After completing S30, the program may directly proceed to S50, wherein the 754 tables T0-T753are read from the storage unit14c.

In this case, when taking into account a plurality of ink types, such as in the third modification of the first embodiment, the excitation characteristic storage unit14ccan store 754 tables T0-T753in correspondence with each type of ink that can be used in the inkjet printer3. Each table Ti (0≦i≦753) is configured of a plurality of data sets Bi (λ0, λ) for a plurality of incident light wavelengths λ and for a plurality of reflected light wavelengths λ0. Each data set Bi (λ0, λ) is determined by measuring a color patch of the corresponding color i created using the corresponding ink type. In this case, the user selects an ink type in S40ofFIG. 10. In S50, CPU10can select the 754 tables T0-T753corresponding to the ink type selected by the user.

Similarly, a plurality of paper types can be used on the inkjet printer3in the second embodiment. Accordingly, the output profile storage unit14estores nine output profiles (FIG. 14) corresponding to combinations of the plurality of (three) paper types and a plurality of (three) light source types. Therefore, when the user selects a single paper type in S160during the color conversion process ofFIG. 16, the CPU10reads the corresponding output profile from the output profile storage unit14ein S170.

However, when only a single paper type can be used on the inkjet printer3, the output profile storage unit14eneed only store three output profiles corresponding to the combinations of the single paper type and the three light source types. Hence, the paper type selecting step of S160is no longer necessary in the color converting process ofFIG. 16. After selecting a light source type in S150, the CPU10can execute the process of S170to read the output profile corresponding to the selected light source type from the output profile storage unit14e.

In this case, if considering a plurality of ink types, such as in the second modification of the second embodiment, the output profile storage unit14ecan store a plurality of output profiles corresponding to all the combinations of ink types and light source types. In this case, the user selects an ink type in S160ofFIG. 16. In S170, the CPU10can select an output profile corresponding to the combination of light source type and ink type selected by the user.

There are cases when the output image created by the inkjet printer3will be observed always under a single type of light source. In this case, the spectral radiation characteristic storage unit14d(FIG. 5) in the first and third embodiments can store only a single environment light characteristics data array D for a single light source. The light source type selecting step of S10is no longer necessary in the output profile creating step ofFIG. 10. In S20, the CPU can read the single data array D from the storage unit14d. In the second embodiment, the output profile storage unit14e(FIG. 14) can store only three output profiles for the combination of the single light source type and the three paper types. Hence, the light source type selecting step of S150is no longer necessary in the color conversion process ofFIG. 16. After a paper type is selected in S160, the CPU10can read in S170the output profile corresponding to the selected paper type.

It is also possible to modify the step of S10′ in the fifth modification of the first embodiment inFIG. 13to operate similar to S140-S150′ in the first modification of the second embodiment inFIG. 18. Hence, when the user inputs the desired environment light characteristics data array D′ in S10′ ofFIG. 13, the CPU10selects the environment light characteristics data array D nearest the inputted desired environment light characteristics data array D′ from the spectral radiation characteristics table (FIG. 5) and stores the environment light characteristics data array D in the work area of the RAM12. Steps from S30on create the output profile based on this environment light characteristics data array D.

When creating an output profile in the first embodiment, the spectral reflection data calculating unit120calculates the spectral reflection characteristic data Ri(λ0) for each color i using Equation (9). After the spectral reflection characteristics data Ri(λ0) is saved in the spectral reflection data saving unit12c, the color value computing unit130calculates the XYZ values (Xi, Yi, Zi) based on Equation (10). However, the spectral reflection data calculating unit120and spectral reflection data saving unit12ccan be omitted. In this case, the color value computing unit130determines the XYZ values (Xi, Yi, Zi) corresponding to each color i directly by calculating the following Equation (13):

Equation (13) takes a double integral of the excitation reflectance characteristics data Bi (λ0, λ) for the user's selected paper type and the relative spectral radiation characteristics data S(λ) for the user's selected light source type.

The embodiments described above use the inkjet printer3as an example of the color outputting device. However, the color outputting device can be another type of color printer. That is, the present invention can be applied to any other color printers that employ ink, toner, ink ribbons, or other image developing material having a component material with excitation characteristics, such as a fluorescent matter.

In the above-described embodiments, the color converting apparatus1serves as a host computer that outputs CMYK print data (Cout, Mout, Yout, Kout) to the printer3. In this way, the color converting apparatus1may be integrated in the host computer. It is noted that the color converting apparatus1can be incorporated in a printer driver program called a print driver. That is, the computer programs for executing each process of the color converting method (FIGS. 10,11,13,16,18,23, and24) may be included in the print driver program. Before outputting image data, created by a suitable application program on the host computer, to the printer, the printer driver program converts the image data to print data. During this conversion process, the host computer1selects excitation characteristics of the developing materials (color reproducing medium) and output-end observation environment. In this case, the host computer performs these selections.

It is noted that the printer driver program can be prestored in the host computer. Preferably, the printer driver program may be installed on a suitable host computer as a software program to be executed when necessary. In such a case, the printer driver program functions to support changes in the output-end observation environment, color reproducing media and the like. For example, the printer driver program can be stored on a computer-readable recording medium, such as a floppy disk or a CD-ROM. The computer can read the recording medium and install the program on a nonvolatile recording medium, such as the hard disk16of the host computer. When necessary, the printer driver is read and executed. In addition to reading the program from a recording medium, the driver program may be installed on the host computer via the network30such as the Internet, or the like.

In the embodiments described above, the color converting apparatus1is provided separately from the color printer3. However, it is also possible to integrally incorporate the color converting apparatus1in the printer3. In this case, the printer3receives RGB image data used by the image display device2from an external device. The built-in color converting apparatus converts the RGB image data into corrected CMYK image data according to the color characteristics of the developing materials used by the printer3and the observation environment.

In the above-described third embodiment, the CPU10stores, in S410(FIG. 23), a correlation between all the 1014sets of CMYK data and the corresponding 1014Lab data sets as the input profile. In this case, the 1014sets of CMYK data are made up from: (0,0,0,0), (0,0,0,1), (0,0,0,2), . . . , (100, 100, 100, 100), which are set at (1)-value interval from 0 to 100. However, the CPU10may store, as the input profile, a correlation between only the 114sets of CMYK data and corresponding114Lab data sets. In this case, the 114sets of CMYK data are made up from: (0,0,0,0), (0,0,0,10), (0,0,0,20), . . . , (100, 100, 100, 100), which are set at (10)-value interval from 0 to 100. In this case, in S510(FIG. 24), the CPU10converts the original data (Cin, Min, Yin, Kin) to Lab data (Lin, ain, bin) through interpolation based on the input profile.

Similarly, in the above-described embodiments, a correlation between all the 1014sets of CMYK data and the corresponding1014Lab data sets are first produced, and then an inverse calculation is performed to obtain the output profile. The thus produced output profile shows the correlation between 1014Lab data sets and the 1014sets of CMYK data, wherein the 1014sets of CMYK data are made up from: (0,0,0,0), (0,0,0,1), (0,0,0,2), . . . , (100, 100, 100, 100), which are set at (1)-value interval from 0 to 100. The output profile is stored in the output profile saving unit12a. However, the CPU10may store, as the output profile, a correlation between only 114Lab data sets and the 114sets of CMYK data, wherein the 114sets of CMYK data are made up from: (0,0,0,0), (0,0,0,10), (0,0,0,20), . . . , (100, 100, 100, 100), which are set at (10)-value interval from 0 to 100.