JP2011151491A - Device and program for color conversion - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform color conversion into a color signal which colorimetrically coincides with a color signal which includes color components of a basic color material and a light color material and should be subjected to color conversion, wherein the total amount of color materials is kept within a preset limit value. <P>SOLUTION: A forward conversion unit 12 converts an input CMYK color signal into an L*a*b* color signal by using association data between CMYK obtained by a print data acquisition unit 22 and L*a*b*, and a color reproduction area mapping part 13 maps the L*a*b* color signal into an L*'a*'b*' color signal in a color reproduction area of a printer. A black amount calculation unit 14 calculates a black amount K' and a light quantity calculation unit 15 calculates light quantity Lc' and Lm' on the basis of association data between CMYK obtained by a printer data acquisition unit 23 and the L*a*b* and a limit value set by a total amount limit value setter 21. An inverse conversion unit 16 calculates C', M' and Y' by using association data between CMYKLcLm obtained by the printer data acquisition unit 23 and the L*a*b*, and outputs a C'M'Y'K'Lc'Lm' color signal to the printer. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a color conversion device and a color conversion program.

  In Patent Document 1, first, color separation from RGB input to CMYK output is performed, and an increaseable amount of shade total color material amount is obtained from the total color material amount of C, M, Y, K, and output density and shade total color material are obtained. A color separation method is described in which light and dark color separation is performed from the amount.

  Japanese Patent Application Laid-Open No. 2004-26883 discloses a basic configuration in which color conversion processing is performed on a color signal of a basic color material, and the color signal subjected to color conversion processing is color-separated to generate a color signal of a basic color material and a color signal of a light color material The first color patch using the color material and the second color patch using the basic color material and the light color material are formed, and the color conversion table is created based on the difference between the colorimetric values of the first and second color patches. An image processing apparatus to be created is described.

  Japanese Patent Application Laid-Open No. H10-228561 describes a gray color material amount separation image processing method in which a color material having the same color tone and a different density is replaced with a mixed color so that the light color material has a substantially same hue.

JP 2007-288495 A JP 2008-228231 A JP 2009-055196 A

  An object of the present invention is to obtain a color signal that includes color components of a basic color material and a light color material, and whose color material total amount falls within a preset limit value and colorimetrically matches a color signal to be color-converted. Is to perform color conversion.

  The invention according to claim 1 is an association coefficient group in which a color signal in a first color space that does not depend on a device is associated with a color signal in a second color space that depends on the device. An acquisition unit for acquiring a correlation coefficient group obtained by measuring colors of a color sample group including color signals created so that the total amount is less than or equal to the first limit value; and the correspondence acquired by the acquisition unit A first color signal that is a color signal in the first color space accepted as a color signal to be color-converted based on a weighting coefficient group and a second limit value set in advance for the total amount of color material The total color material amount is kept below the second limit value by a predetermined method, and color conversion in the second color space comprising the color components of the basic color material and the light color material is performed. Some color components included in the second color signal that is a color signal And a part of the first color signal and the part after the conversion by the first conversion unit based on the association coefficient group acquired by the acquisition unit. A color conversion apparatus comprising: second conversion means for converting a color signal of a color component into a color signal of a remaining color component included in the second color signal.

The invention according to claim 2 color-separates the color signal of the first color sample group created by combining the color components of the basic color material into the color component of the basic color material and the color component of the light color material, The acquisition unit further includes a generation unit that generates a second color sample group for acquiring the association coefficient group, and the generation unit has a total amount of color material after color separation exceeds the first limit value. In this case, the second color sample group is created by performing the color separation by reducing the total amount of the color material so as to be less than or equal to the first limit value by a predetermined method. The color conversion apparatus according to claim 1.
According to a third aspect of the present invention, the creating means is configured such that the total color material amount after the color separation using the basic density separation coefficient group among the color signals of the first color sample group is the first color sample group. For a color signal exceeding the limit value, the color material total amount is reduced by a predetermined method, and the color separation is performed using the density separation coefficient group corresponding to the reduced color material total amount. A color conversion apparatus according to claim 2.
According to a fourth aspect of the present invention, the acquisition means includes a plurality of types of color materials having different total color material amounts after color separation for each of the color signals of the first color sample group created by combining the color components of the basic color material. Obtaining a plurality of types of association coefficient groups obtained by measuring colors of a plurality of types of second color sample groups created by color separation using a basic density separation coefficient group; 4. The conversion unit according to claim 1, wherein the conversion unit converts the remaining color components included in the second color signal into color signals based on the plurality of types of association coefficient groups. A color conversion apparatus according to claim 1.
According to a fifth aspect of the present invention, the first conversion unit includes the second color signal from the first color signal based on the association coefficient group and the second limit value. From the black amount calculation means for calculating the color component of the black basic color material, the first color signal, and the color signal of the black basic color material calculated by the black amount calculation means, the second color Basic color material signal calculation means for calculating the color components of the remaining basic color materials included in the color signal, and the color components of the basic color material calculated by the black amount calculation means and the basic color material signal calculation means, Color separation means for color-separating into the color component of the basic color material and the color component of the light color material so that the total amount of the color material falls within the second limit value, and the color separation means should be color-separated The total amount of the color material after color separation using the color separation coefficient group based on the color component of the basic color material is the second color material. 2. When the limit value is exceeded, the color material total amount is reduced by a predetermined method, and the color separation is performed using the density separation coefficient group corresponding to the reduced color material total amount. 5. The color conversion device according to any one of 4 to 4.

According to a sixth aspect of the present invention, the color signal after the conversion by the first conversion means is a color signal of the color component of the light color material, and the color of the color component of the light color material converted by the first conversion means 6. The color conversion apparatus according to claim 1, further comprising light color amount adjusting means for adjusting a signal.
According to a seventh aspect of the present invention, the color signal after the conversion by the first conversion means is a color signal of a color component of a basic color material, and the color according to any one of the first to fourth aspects It is a conversion device.
The invention according to claim 8 is that the association coefficient group used by the first conversion unit and the second conversion unit are both the first color signal, all the colors of the basic color material and the light color material. 6. The color conversion apparatus according to claim 1, wherein the second color signal composed of a color component of the material is associated with the second color signal.
According to a ninth aspect of the present invention, the first conversion unit is configured to generate a black ink in the second color signal from the first color signal based on the association coefficient group and the second limit value. Black amount calculation means for calculating a color component of the basic color material, and the first conversion means is calculated by the first color signal and the black amount calculation means created from the association coefficient group. Using a coefficient group in which a set of color signals composed of the basic color material of black ink and the color signals of some of the color components in the second color signal are associated, The color conversion apparatus according to claim 1, wherein the partial color component is converted into a color signal.

The invention according to claim 10 is an association coefficient group in which the color signal in the first color space independent of the device and the color signal in the second color space dependent on the device are associated with each other. An acquisition means for acquiring an association coefficient group obtained by measuring colors of a color sample group made up of color signals created so that the total amount is less than or equal to the first limit value, and accepted as a color signal to be color-converted; The color signal in the first color space obtained by converting the obtained color signal is a color signal in the color gamut of the target device, and is a color signal in the first color space. Based on the mapping means for mapping to a color signal, the association coefficient group acquired by the acquisition means, and a second limit value set in advance for the total amount of color material, the first obtained by the mapping means 1 color signal is color-coded by a predetermined method The second color signal is a color signal that is color-converted in the second color space including the color component of the basic color material and the color component of the light color material, with the total amount falling below the second limit value. Based on the first conversion means for converting into color signals of some color components included in the color signal, and the association coefficient group acquired by the acquisition means, the first color signal and the first color signal And second conversion means for converting the color signals of the part of the color components after conversion by the conversion means into color signals of the remaining color components included in the second color signal. Color conversion device.
The invention according to claim 11 further includes color gamut outline generation means for generating a color gamut outline of the target device based on the association coefficient group, and the mapping means includes the color gamut outline generation means. The color conversion apparatus according to claim 10, wherein mapping to the first color signal is performed based on a color gamut outline of the target device generated by the method.

  The invention according to claim 12 is an association coefficient group in which a computer is associated with a color signal in a first color space independent of a device and a color signal in a second color space dependent on the device. A function for obtaining a correspondence coefficient group obtained by measuring colors of a color sample group formed of color signals so that the total amount of color materials falls within a first limit value, and the correspondence coefficient group; A predetermined method for determining a first color signal, which is a color signal in the first color space, accepted as a color signal to be color-converted based on a second limit value set in advance for the total amount of color material Is a color signal that is color-converted in the second color space comprising the color component of the basic color material and the color component of the light color material after the total color material amount falls within the second limit value. Change to color signals of some color components included in the second color signal. And the color signals of the remaining color components included in the second color signal, based on the association coefficient group, the first color signal and the color signal of the partial color component after conversion. A color conversion program characterized by realizing a function of converting into a signal.

According to the first aspect of the present invention, the color signal includes the color components of the basic color material and the light color material, and the total color material amount falls within a preset limit value and colorimetrically matches the color signal to be color-converted. Color conversion into color signals can be performed.
According to the second aspect of the present invention, the color signal to be color-converted is converted into the basic color material and the light color material by using the color sample group of the color signal created by itself so that the total amount of the color material falls within a preset limit value. Can be converted into a color signal that includes the color components and the total color material amount falls within a preset limit value and colorimetrically matches the color signal to be color-converted.
According to the third aspect of the present invention, compared to the case where the present configuration is not provided, the color signal is a color signal including the color components of the basic color material and the light color material, and the total color material amount falls within a preset limit value. It is possible to reduce the number of color sample groups necessary for color conversion to a color signal that is colorimetrically coincident with the color signal to be color-converted.
According to the invention of claim 4, the color signal including the color components of the basic color material and the light color material without outputting the color sample group every time the limit value of the total color material amount is changed, It is possible to perform color conversion to a color signal that falls within the set limit value and colorimetrically matches the color signal to be color-converted.
According to the invention of claim 5, as compared with the case where the present configuration is not provided, the total color material amount is within a limit value that is a color signal including the color components of the basic color material and the light color material. It is possible to improve accuracy when performing color conversion to a color signal colorimetrically coincident with the color signal to be color-converted.

According to the invention of claim 6, the amount of the color component of the light color material included in the color signal after color conversion can be adjusted.
According to the seventh aspect of the present invention, it is possible to control the start of dark color in the gradation of the color component of the color signal subjected to color conversion.
According to the eighth aspect of the present invention, compared with the case where the present configuration is not provided, the accuracy when color conversion to a color signal colorimetrically coincident with the color signal to be color-converted is improved. Can do.
According to the ninth aspect of the invention, compared with the case where the present configuration is not provided, the accuracy when color conversion to a color signal colorimetrically coincident with the color signal to be color-converted is improved. Can do.

According to the tenth aspect of the present invention, the color signal includes the color components of the basic color material and the light color material, and the total color material amount falls within a preset limit value and colorimetrically matches the color signal to be color-converted. Color conversion into color signals can be performed.
According to the eleventh aspect of the invention, compared with the case where the present configuration is not provided, the accuracy when color conversion to a color signal colorimetrically coincident with the color signal to be color-converted is improved. Can do.
According to the twelfth aspect of the present invention, the color signal includes color components of the basic color material and the light color material, and the total color material amount falls within a preset limit value and colorimetrically matches the color signal to be color-converted. Color conversion into color signals can be performed.

It is the block diagram which showed the function structure of the 1st Embodiment of this invention. FIG. 3 is a block diagram illustrating details of a function of a printer data acquisition unit according to the first embodiment of the present invention. It is a graph which shows an example of the density separation LUT used as the basis of cyan. 5 is a flowchart illustrating an operation example of a density separation unit when color separation processing is performed on the basis of a high total density separation LUT in the first embodiment of the present invention. It is a graph for demonstrating the density | concentration decomposition | disassembly LUT when the color material total amount is reduced continuously. It is the block diagram which showed the detail of the function of the light color amount calculation part in the 1st Embodiment of this invention. It is the block diagram which showed the function structure of the 2nd Embodiment of this invention. It is the block diagram which showed the detail of the function of the light color amount calculation part in the 2nd Embodiment of this invention. It is the graph which showed the example of the adjustment coefficient. It is the block diagram which showed the function structure of the 3rd Embodiment of this invention. It is the block diagram which showed the function structure of the 5th Embodiment of this invention. It is the block diagram which showed the function structure of the 6th Embodiment of this invention. It is a hardware block diagram of the computer which can implement | achieve embodiment of this invention.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
In this embodiment, CMYK color signals composed of cyan (C), magenta (M), yellow (Y), and black (K) color components are converted into light cyan (Lc) and light color of similar colors and different densities. A color conversion apparatus that converts CMYKLcLm color signals including magenta (Lm) color components will be described.

  In the color printing industry, a proof that simulates the printing color is output using a simple color printer such as an electrophotographic printer or an ink jet printer in the pre-process for creating printed matter with this printing machine, and color proofing is thereby performed. A so-called color proofing system is used. In general, the color reproduction characteristics of the printing machine and color printer differ, so that the color signal that can be reproduced by the printing machine can be reproduced by the color printer by correcting the color signal input to the color printer. It is necessary to keep. Specifically, the color profile color measurement data output by the printing machine and a print profile composed of a combination of the corresponding CMYK data, the color chart color measurement data output by the color printer, and the corresponding device-dependent data A printer profile composed of a combination of (for example, CMYK and RGB) is created, and CMYK data depending on the print color used for color calibration is converted into a device-independent color space such as an XYZ color space or L * a * b by the print profile. * After conversion to the color space, the printer profile is converted to data depending on the color printer. By outputting the device-dependent data converted in this way with a color printer, it is possible to obtain a color calibration sample that is close to the printing color of the printing machine, and it is possible to simulate the printing color using the color printer. Become.

  By the way, in ink jet printers, in addition to basic color materials C, M, Y, and K, the use of light colors Lc and Lm is widely performed for the purpose of reducing graininess, and the same applies to electrophotographic printers. 6-color printing is realized. Various methods have been proposed as a color conversion technique from the color signal of the basic color material to the color signal including the light and dark color material.

However, in general, electrophotographic printers and inkjet printers are often provided with a total amount limit of color materials, and it is necessary to perform color conversion within the total amount limit value. In addition, in an electrophotographic printer, color conversion may be performed with a total amount limit value that is smaller than the maximum total amount limit value that can be output by the printer in order to suppress glossiness and relief caused by an increase in color materials.
Therefore, the color conversion apparatus according to the present embodiment outputs the CMYK color signals, which are input color signals from the printing press, to the printer so as to satisfy the total amount limit value of the printer and to match the input color signals colorimetrically. Color separation is performed into CMYKLcLm color signals that are color signals.

  In the following description, the input color signal is CMYK of the printing press, and the output color signal is CMYKLcLm of the printer. Then, the CMYK color signal is once converted into an L * a * b * color signal (an example of the first color signal), and then the C′M′Y′K′Lc′Lm ′ color signal (second color signal). It is assumed that the data is converted into (example). The input color signal is not limited to this example, but may be XYZ or L * a * b * which is a device-independent color space, or sRGB (standard RGB) or AdobeRGB which is an RGB color space. Also good. Further, the output color signal is not limited to this example, and any output color signal may be used as long as it is a device-dependent output color signal including a plurality of color components having similar colors and different densities.

<First Embodiment>
FIG. 1 is a block diagram showing a functional configuration of the color conversion apparatus according to the first embodiment of the present invention. As shown in the figure, the color conversion apparatus according to the present embodiment includes a color signal reception unit 11, a forward conversion unit 12, a color reproduction area mapping unit 13, a black amount calculation unit 14, a light color amount calculation unit 15, An inverse conversion unit 16, a color signal output unit 17, a total amount limit value setting unit 21, a print data acquisition unit 22, and a printer data acquisition unit 23 are provided.

  The color signal receiving unit 11 receives a CMYK color signal that is an input color signal to be color-converted by the color conversion device.

  The forward conversion unit 12 uses the association data between CMYK and L * a * b * obtained by the print data acquisition unit 22 to convert the input CMYK color signal received by the color signal reception unit 11 into a device-independent manner. The color signal is converted into an L * a * b * color signal. As this conversion method, in the present embodiment, a regression model described in JP-A-10-262157 is used. The conversion method is not limited to this, and conversion using a model such as matrix conversion or a neural network may be used.

  The color gamut mapping unit 13 maps the L * a * b * color signal converted by the forward conversion unit 12 to an L * ′ a * ′ b * ′ color signal in the color gamut of the printer. As this mapping method, various known methods may be used. If the L * a * b * color signal converted by the forward conversion unit 12 is a color signal within the color gamut of the printer, the color gamut mapping unit 13 may not be provided.

  The black amount calculation unit 14 uses the association data of CMYK and L * a * b * obtained by the printer data acquisition unit 23 to obtain the total color material amount limit value set by the total amount limit value setting unit 21. Based on the L * 'a *' b * 'color signal mapped by the color gamut mapping unit 13 and the black amount (K) of the input CMYK color signal, the black amount (K') is calculated. To do. As this calculation method, for example, a technique described in JP 2007-43250 A is applied. Specifically, a four-color regression model described in, for example, Japanese Patent Laid-Open No. 10-262157 is created from the correspondence data between CMYK and L * a * b * obtained by the printer data acquisition unit 23. A black amount calculation model of L * a * b * → K is created using a regression model of four colors. In the present embodiment, the black amount calculation unit 14 is provided as an example of the black amount calculation unit.

  The light color amount calculation unit 15 uses the association data between CMYK and L * a * b * obtained by the printer data acquisition unit 23 to obtain the color material total amount limit value set by the total amount limit value setting unit 21. Based on the L * 'a *' b * 'color signal mapped by the color gamut mapping unit 13 and the black amount (K') calculated by the black amount calculation unit 14, the light color amounts (Lc ', Lm) ') Is calculated. Details of the function of the light color amount calculation unit 15 will be described later. In the present embodiment, a black amount calculation unit 14 and a light color amount calculation unit 15 are provided as an example of the first conversion unit.

  The inverse conversion unit 16 uses the association data of CMYKLcLm and L * a * b * obtained by the printer data acquisition unit 23 to use the L * 'a *' b * 'color signal and the black amount (K'). ) And the light color amount (Lc ′, Lm ′), among the output color signals (C′M′Y′K′Lc′Lm ′ color signals) whose components are the colors of the color materials used by the printer, Color components (C ′, M ′, Y ′) other than black and light colors are calculated. As this conversion method, in the present embodiment, a regression model described in JP-A-10-262157 is used. In the present embodiment, the inverse conversion unit 16 is provided as an example of the second conversion means.

  The color signal output unit 17 calculates the black amount (K ′) calculated by the black amount calculation unit 14, the light color amounts (Lc ′, Lm ′) calculated by the light color amount calculation unit 15, and the inverse conversion unit 16. The obtained color components (C ′, M ′, Y ′) are output to the printer as output color signals (C′M′Y′K′Lc′Lm ′ color signals).

  The total amount limit value setting unit 21 sets the maximum limit value (an example of the first limit value) of the total color material amount used in the printer, or an arbitrary limit value (an example of the second limit value) smaller than the maximum limit value. Set. For example, when the maximum limit value of the total amount of color materials used in the printer is 280%, the total amount limit value setting unit 21 sets a total amount limit value such as 240% which is smaller than 280%. As a setting method, for example, in addition to designating a preset limit value by the user, a unique limit value is determined in advance for each type of printer or each output mode of the printer, and the type of printer to be used A limit value may be set according to the output mode. Of course, it may be given in advance as a fixed value. Different limit values may be set according to the color area.

  The print data acquisition unit 22 acquires correspondence data between CMYK and L * a * b * necessary for the forward color conversion by the forward conversion unit 12. Specifically, the print data acquisition unit 22 outputs a color patch of a combination of four colors of C, M, Y, and K of about 1000 patches with a printing machine, and measures the output result to measure CMYK and the device. Correlation data with an independent color signal (L * a * b *) is acquired.

  The printer data acquisition unit 23 associates CMYK and L * a * b * data necessary for the black amount calculation by the black amount calculation unit 14 and the light color amount calculation by the light color amount calculation unit 15, and the inverse by the inverse conversion unit 16. Correlation data between CMYKLcLm and L * a * b * necessary for conversion is acquired. Such association data is an example of an association coefficient group. In the present embodiment, the printer data acquisition unit 23 is provided as an example of the creation unit and the acquisition unit.

  The above functions can be realized only by hardware, but can also be realized by a combination of hardware and software. In the latter case, each function is realized by a CPU (not shown) of the color conversion apparatus reading and executing a program stored in a memory (not shown), for example.

In the following, first, the printer data acquisition unit 23 will be described.
FIG. 2 is a block diagram showing details of the function of the printer data acquisition unit 23 (see FIG. 1). As illustrated, the printer data acquisition unit 23 includes a density separation unit 23a and an image output unit 23b.

  The density decomposition unit 23a uses a density decomposition LUT (Look-Up Table) 30 (an example of a coefficient group for density decomposition) to convert C into dark cyan (C ′) and light cyan (Lc ′). Are decomposed into dark magenta (M ′) and light magenta (Lm ′), respectively. In addition, the image output unit 23b includes a CMYKLcLm color patch (second color sample) obtained by the grayscale separation unit 23a separating the color signal of the CMYK color patch (an example of the first color sample group) into CMYKLcLm. Group) is output to the printer. The printer data acquisition unit 23 measures the output result from the image output unit 23b, thereby associating data between CMYK and device-independent color signals (L * a * b *), and CMYKLcLm and device-independent. Correlation data with the color signal (L * a * b *) is acquired.

Here, the density decomposition LUT 30 will be described.
FIG. 3 is a graph showing an example of the density separation LUT 30 that is the basis of cyan. Here, three types of look-up tables with different total color material amounts are shown as the density separation LUT 30. Each graph shows the coverage of dark cyan (C), the coverage of light cyan (Lc), and the total coverage of C and Lc in the cyan gradation.

  FIG. 3A shows an example in the case of a high total amount, in which Lc is positively used in the highlight area, and color separation is performed so as to increase C and reduce Lc as the input coverage approaches 100%. By performing such decomposition, graininess is reduced in the highlight area, and cyan is reproduced in the 100% area as in the case of four colors. On the other hand, FIG.3 (c) is an example in the case of a low total amount, and does not use Lc at all but uses C for all. This is equivalent to the case where reproduction is performed with four colors of CMYK without applying the grayscale separation LUT30. FIG. 3B shows an example in the case of the medium total amount (intermediate between the high total amount and the low total amount). Also, for magenta, such a basic density separation LUT 30 is prepared.

  FIG. 3 shows a three-level density separation LUT 30 of a high total amount, a medium total amount, and a low total amount, but in this embodiment, as will be described later, the color when a CMYK color patch is decomposed into six colors is shown. Depending on the total amount of material, the density decomposition LUT 30 between the three stages shown in FIG. 3 (between the high total amount and the medium total amount, or between the medium total amount and the low total amount) may be used.

Next, the operation of the density separation unit 23a in the printer data acquisition unit 23 will be described.
In order to output a color patch with a coverage that is less than or equal to the maximum limit value of the total amount of color materials used in the printer, the total amount of the four colors of the CMYK color patch is stored in the maximum limit value in advance. In the present embodiment, color separation is performed for each of the CMYK color patches based on the grayscale separation LUT 30 (shown in FIG. 3A) having the maximum total amount (light color amount). If the total amount of the six colors after separation does not fall within the maximum limit value, the total amount (light color amount) is continuously lowered as will be described later, and what is shown in FIG. Decompose with different density decomposition LUT30.

  FIG. 4 is a flowchart showing an example of the operation of the density separation unit 23a when performing color separation processing based on the high total density separation LUT 30. The density separation unit 23a first selects a high total density separation LUT 30 (step 101), and obtains a total amount of six color materials when CMYK is decomposed into CMYKLcLm using it (step 102). When the total amount of the six colors after the separation does not fall within the maximum limit value (No in step 103), the light / dark separation LUT 30 (when the total amount (light color amount) is lowered by a certain amount based on the high total light / dark separation LUT 30) The light / dark separation LUT 30 between the high total amount and the medium total amount is selected (step 104), and the process returns to step 102 again. On the other hand, when the total amount of the six colors after the separation falls within the maximum limit value (Yes in Step 103), the total amount (light color amount) at that time is decomposed into six colors using the density separation LUT 30 (Step 105). . Thus, the operation of the density separation unit 23a when performing the color separation process based on the high total quantity density separation LUT 30 is completed.

  In other words, when the high-density total decomposition LUT 30 cannot perform decomposition, the gray-scale decomposition unit 23a increases the total amount (high total amount → medium total amount → low total amount) until the total amount of the six colors after decomposition falls within the maximum limit value. (Light color amount) is continuously reduced. Then, decomposition is performed using a density decomposition LUT 30 between the high total amount and the medium total amount (or the intermediate total amount or possibly between the medium total amount and the low total amount) that falls within the maximum limit value.

  Similarly, the density decomposition unit 23a decomposes CMYK into CMYKLcLm based on the medium total quantity and the low total quantity density decomposition LUT30. The low total amount density decomposition LUT 30 is the same as the case where the density decomposition LUT 30 is not applied, so the values of Lc and Lm are 0.

Here, the density separation LUT 30 when the total amount (light color amount) is continuously reduced will be specifically described.
FIG. 5 is a graph for explaining the density separation LUT 30 when the total color material amount (light color amount) is continuously reduced. FIG. 5A shows dark cyan (C) and light cyan (Lc) in the cyan gradation when the high total amount and medium total amount shown in FIGS. 3A and 3B are used. The total coverage is shown in an overlapping manner. FIG. 5B shows the coverage of C and Lc in the case of a high total amount and a medium total amount in an overlapping manner.

  In the present embodiment, based on the density decomposition LUT 30 (shown in FIG. 3A) at the time of the high total amount, the sum (total amount) of C and Lc is set in the direction of the arrow A1 in FIG. 5A. , Continuously lower by a certain amount. That is, the C + Lc curve in the graph of FIG. 5A is continuously deformed in the direction of the arrow A1. This is realized by increasing the amount of C in the direction of arrow A2 in FIG. 5B and decreasing the amount of Lc in the direction of arrow A3 in FIG. 5B. In the present embodiment, such a method of lowering the total sum (total amount) of C and Lc (how to deform the C + Lc curve in the graph) is determined in advance, and the lowering method together with the information of the light / dark separation LUT 30 is determined. Store it in a memory or the like.

Next, a specific example of color separation performed by the density separation unit 23a will be described.
Here, an example will be described in which the maximum limit value is 280% (an example of the first limit value), and the density separation LUT 30 that is the basis of cyan and magenta is that of FIG. The color separation performed on the basis of the high total density contrast LUT 30 is as follows.

  In the case of (C, M, Y, K) = (40, 40, 100, 30), C, Lc when the input coverage in FIG. Are 3% and 69%, respectively, (C, M, Y, K, Lc, Lm) = (3, 3, 100, 30, 69, 69). The total amount of color material at this time is 274%, which is within 280% of the maximum limit value. For this reason, it decomposes using a high total amount light and dark decomposition LUT30.

  In the case of (C, M, Y, K) = (50, 50, 100, 30), when decomposing with the high total amount density decomposition LUT 30, (C, M, Y, K, Lc, Lm) = (12, 12, 100, 30, 76, 76). Since the total color material amount does not fall within 280% of the maximum limit value, the density separation LUT 30 between the high total amount and the medium total amount, which is obtained in accordance with a predetermined method of deformation of the C + Lc curve and the M + Lm curve, is used. And it decomposes | disassembles into (C, M, Y, K, Lc, Lm) = (25,25,100,30,50,50) that the total amount becomes 280%.

  In the case of (C, M, Y, K) = (60, 60, 100, 30), if the decomposition is performed with the high total amount of light and shade decomposition LUT 30, it does not fall within 280% of the maximum limit value. Even if it is not within 280% of the maximum limit. For this reason, the light / dark separation LUT 30 between the medium total amount and the low total amount, which is obtained in accordance with the predetermined deformation method of the C + Lc curve and the M + Lm curve, is used. And it decomposes | disassembles into (C, M, Y, K, Lc, Lm) = (47,47,100,30,28,28) which becomes total amount 280%.

  As described above, in the present embodiment, a method for lowering the total amount to be within the total amount limit value is determined in advance. Then, the printer data acquisition unit 23 applies the above three types of density separation LUTs 30 to the CMYK color patches, outputs the CMYKLcLm color patches with the printer, and measures the output result. In order to obtain the correspondence data between CMYK and L * a * b * necessary for the black amount calculation and the light color amount calculation, the colorimetric data for one of the three types of light / dark separation LUT 30 is used. To do. In addition, in order to obtain the correspondence data between CMYKLcLm and L * a * b * necessary for performing the inverse transformation, the colorimetric data for all three types is used. For example, when the number of CMYK color patches is 1000, 1000 pieces of association data between CMYK and L * a * b * and 3000 pieces of association data between CMYKLcLm and L * a * b *. However, depending on the coverage of the CMYK color patch, even when the high total density separation LUT 30 is used as a base, only the low total quantity separation LUT 30 can be included in the maximum limit value, that is, Lc and Lm cannot be added. is there. In such a case, overlapping color patches appear in the association data between CMYKLcLm and L * a * b *, and the number of patches is reduced accordingly.

  The basic density decomposition LUT 30 is not limited to that shown in FIG. 3, and may be a decomposition LUT in which Lc increases until the input coverage reaches 100%, for example. In addition, as for the type of the density decomposition LUT 30, there should be at least two types of decomposition LUTs of high total amount and low total amount (same as in the case of four colors), and if there is a decomposition LUT between the two types of decomposition LUTs, the total amount Still good.

Next, the light color amount calculation unit 15 will be described.
FIG. 6 is a block diagram showing details of the function of the light color amount calculation unit 15 (see FIG. 1). As shown in the figure, the light color amount calculation unit 15 includes an inverse conversion unit 15a and a light / dark separation unit 15b.

  Based on the association data between CMYK and L * a * b * obtained by the printer data acquisition unit 23, the inverse conversion unit 15a performs L * 'a *' b * 'K' (color reproduction area mapping unit). C ″ M ″ Y ″ is calculated from L * ′ a * ′ b * ′ obtained in Step 13 and K ′) calculated by the black amount calculation unit 14. For example, when the black amount (K ′) is given by applying the technique described in Japanese Patent Laid-Open No. 2007-43250, C ″, M ″, Y ′ calculated by the light color amount calculation unit 15. The total amount of “, K” falls within the limit value set by the total amount limit value setting unit 21 and coincides colorimetrically with L * ′ a * ′ b * ′. In the present embodiment, an inverse conversion unit 15a is provided as an example of a basic color material signal calculation unit.

  The gray separation unit 15b uses the high total amount gray separation LUT 30 based on the limit value set by the total amount limit value setting unit 21, and converts C ″ into dark cyan (C ′ ″) and light cyan. (Lc ′), M ″ is decomposed into dark magenta (M ′ ″) and light magenta (Lm ′). At this time, the density separation is performed so that the total amount of C ″ ″, M ″ ″, Y ″, K ′, Lc ′, and Lm ′ is within the limit value set by the total amount limit value setting unit 21. In other words, as in the case of the density separation unit 23a of the printer data acquisition unit 23, the density separation unit 15b, when the high-total amount of density separation LUT 30 cannot be decomposed, increases until the total amount of the six colors after the separation falls within the limit value. The total amount (light color amount) is continuously reduced so that the total amount → the medium total amount → the low total amount. And it decomposes | disassembles using the density | concentration decomposition | disassembly LUT30 which fits in a limit value. In the present embodiment, a density separation unit 15b is provided as an example of color separation means.

Specifically, for example, when the limit value set by the total amount limit value setting unit 21 is 240% (an example of the second limit value), and the density separation LUT 30 that is the basis of cyan and magenta is FIG. The color separation performed on the basis of the high total density contrast LUT 30 is as follows.
In the case of (C, M, Y, K) = (40, 40, 80, 10), when decomposing with the high total amount density decomposition LUT 30, (C, M, Y, K, Lc, Lm) = (3, 3, 80, 10, 69, 69). At this time, the total amount of the color material is 234%, which falls within the limit value of 240%.

  In the case of (C, M, Y, K) = (50, 50, 80, 10), when the decomposition is performed with the high total amount density decomposition LUT 30, (C, M, Y, K, Lc, Lm) = (12, 12, 80, 10, 76, 76). Since the total amount of the color material does not fall within the limit value of 240% at this time, the light / dark separation LUT 30 between the high total amount and the medium total amount, which is obtained in accordance with a predetermined modification method of the C + Lc curve and the M + Lm curve, is used. And it decomposes | disassembles into (C, M, Y, K, Lc, Lm) = (25,25,80,10,50,50) that the total amount becomes 240%.

  In the case of (C, M, Y, K) = (60, 60, 80, 10), if the decomposition is performed with the high total amount decomposition decomposition LUT30, it does not fall within 240% of the limit value, but the medium total amount decomposition decomposition LUT30 decomposes. However, it does not fall within 240% of the limit value. For this reason, the light / dark separation LUT 30 between the medium total amount and the low total amount, which is obtained in accordance with the predetermined deformation method of the C + Lc curve and the M + Lm curve, is used. And it decomposes | disassembles into (C, M, Y, K, Lc, Lm) = (47, 47, 80, 10, 28, 28) for which the total amount is 240%.

  In this way, the light color amount calculation unit 15 calculates light color amounts (Lc ′, Lm ′) from the L * ′ a * ′ b * ′ color signal and the black amount (K ′). C ″, M ″, Y ″, C ′ ″, M ′ ″ are not final output color signals, but intermediate values necessary for calculating light color amounts (Lc ′, Lm ′). Color signal. Finally, the inverse conversion unit 16 calculates C ′, M ′, and Y ′, and the C′M′Y′K′Lc′Lm ′ color signal of the final output color signal is calculated.

<Second Embodiment>
FIG. 7 is a block diagram showing a functional configuration of the color conversion apparatus according to the second embodiment of the present invention. As shown in the figure, the color conversion apparatus according to the present embodiment has a light color amount for adjusting the color signal of the light color material in addition to the same configuration as the color conversion apparatus according to the first embodiment shown in FIG. A setting unit 15c is provided.

  FIG. 8 is a block diagram showing details of the function of the light color amount calculation unit 15 (see FIG. 7) according to the second embodiment of the present invention. As illustrated, the light color amount calculation unit 15 of the present embodiment includes a light color amount adjustment unit 15d in addition to the same configuration as the light color amount calculation unit 15 in the first embodiment illustrated in FIG. Yes.

The light color amount setting unit 15c sets adjustment coefficients (k _Lc , k _Lm ) for adjusting the light color amount. Here, k _Lc and k _Lm are adjustment coefficients for Lc and Lm, respectively, and each value ranges from 0 to 1. Further, the light color amount adjustment unit 15d multiplies Lc ′ and Lm ′ obtained by the light and shade separation unit 15b of the light color amount calculation unit 15 by adjustment coefficients k _Lc and k _Lm , respectively. As a result, when the coefficient is 0, the light color amount is 0, that is, four colors are reproduced, and when the coefficient is 1, the maximum light color amount is within the limit value set by the total amount limit value setting unit 21. In the present embodiment, a light color amount setting unit 15c and a light color amount adjustment unit 15d are provided as an example of a light color amount adjustment unit.

  In the light color amount setting unit 15c, the same coefficient may be set for all the color areas, or different adjustment coefficients may be set according to the color areas. FIG. 9 is a graph showing an example of the adjustment coefficient. For example, as shown in FIG. 9, by setting an adjustment coefficient that increases with the input L *, it is possible to reduce the light color consumption in the shadow area where the influence of the graininess is small while keeping the graininess of the highlight area good. You may make it reduce.

  Further, in the first embodiment, since the gradation separation LUT 30 that falls within the total amount limit value is changed in the CMYK color space, a gradation jump occurs in the L * a * b * color space close to the visual environment. There is. In such a case, this gradation jump may be suppressed by setting an appropriate adjustment coefficient in the L * a * b * space.

<Third Embodiment>
FIG. 10 is a block diagram showing a functional configuration of the color conversion apparatus according to the third embodiment of the present invention. As shown in the figure, the color conversion apparatus according to the present embodiment includes a dark color amount calculation unit 18 instead of the light color amount calculation unit 15 of the color conversion apparatus according to the first embodiment shown in FIG. .

  The dark color amount calculation unit 18 performs the same processing as that of the light color amount calculation unit 15, and the dark color amount separation unit calculates the dark color amounts C ′ and M ′. In this way, the dark color amount calculation unit 18 calculates the dark color amount before the light color amount, thereby controlling the start of dark color in the gradation such as cyan and suppressing the gradation jump. May be. Also in the present embodiment, dark color amount adjusting means for adjusting the dark color amount may be provided as in the second embodiment.

<Fourth embodiment>
The color conversion apparatus according to the fourth embodiment has the same configuration as the color conversion apparatus according to the first embodiment shown in FIG. However, in the fourth embodiment, the black amount and the light color amount are calculated using the association data between CMYKLcLm and L * a * b * obtained by the printer data acquisition unit 23. This is different from the first embodiment in which the black amount and the light color amount are calculated using the association data between CMYK and L * a * b *.

  The black amount calculation unit 14 uses the association data between CMYKLcLm and L * a * b * obtained by the printer data acquisition unit 23 based on the limit value set by the total amount limit value setting unit 21. A black amount (K ′) is calculated from the L * ′ a * ′ b * ′ color signal mapped by the color gamut mapping unit 13 and the black amount (K) of the input CMYK color signal. As this calculation method, for example, a technique described in Japanese Patent Application Laid-Open No. 2007-43250 is applied. Specifically, a six-color regression model described in, for example, Japanese Patent Laid-Open No. 10-262157 is created from the association data between CMYKLcLm and L * a * b * obtained by the printer data acquisition unit 23. Then, a black amount calculation model of L * a * b * → K is created using a regression model of six colors.

  The light color amount calculation unit 15 uses the association data between CMYKLcLm and L * a * b * obtained by the printer data acquisition unit 23 based on the limit value set by the total amount limit value setting unit 21. A light color amount (Lc ′, Lm ′) is calculated from the L * ′ a * ′ b * ′ color signal mapped by the color gamut mapping unit 13 and the black amount (K ′) calculated by the black amount calculation unit 14. To do. Specifically, a six-color regression model described in, for example, Japanese Patent Laid-Open No. 10-262157 is created from the association data between CMYKLcLm and L * a * b * obtained by the printer data acquisition unit 23. The inverse transformation of L * ′ a * ′ b * ′ K′LcLm → CMY is performed using a regression model of six colors. At this time, calculation is performed with Lc = 0 and Lm = 0. Then, the same processing as that of the light / dark separation unit 15b of the first embodiment shown in FIG. 6 is performed to calculate the light color amount.

  As described above, all of the black amount calculation, the light color amount calculation, and the inverse conversion may be performed using the six-color regression model, and the color conversion processing performed by the color conversion device may be performed with higher accuracy.

<Fifth embodiment>
FIG. 11 is a block diagram showing a functional configuration of the color conversion apparatus according to the fifth embodiment of the present invention. As shown in the figure, the color conversion apparatus according to the present embodiment has the same configuration as the color conversion apparatus according to the first embodiment shown in FIG. However, in the fifth embodiment, the light color amount calculation unit 15 in the first embodiment calculates the light color amount (that is, the processing performed by the inverse conversion unit 15a and the density separation unit 15b). Model 19 does.

  Specifically, from the association data of CMYKLcLm and L * a * b * obtained by the printer data acquisition unit 23, for example, by applying the technique described in Japanese Patent Laid-Open No. 10-262157, six colors are applied. A regression model is created, and a light color amount calculation model 19 of L * a * b * K → LcLm is created using the regression models of six colors. Then, using this light color amount calculation model 19, LcLm is directly calculated from L * a * b * K. Thus, the color conversion processing performed by the color conversion device may be made more accurate by calculating the light color amount using the regression model of six colors.

<Sixth Embodiment>
FIG. 12 is a block diagram showing a functional configuration of the color conversion apparatus according to the sixth embodiment of the present invention. As shown in the figure, the color conversion apparatus according to the present embodiment includes a printer color gamut outline generation unit 24 in addition to the same configuration as that of the color conversion apparatus according to the first embodiment shown in FIG.

  The printer color gamut outline generation unit 24 uses the association data between CMYK and L * a * b * or the association data between CMYKLcLm and L * a * b * obtained by the printer data acquisition unit 23 to calculate the total amount. A printer color gamut outline is generated based on the limit value set by the limit value setting unit 21. Specifically, for example, a printer color gamut outline is generated by applying a technique described in Japanese Patent Application Laid-Open No. 2006-352475. Then, the color reproduction area mapping unit 13 (an example of mapping means) maps the device-independent color signal so as to be within the printer color gamut outline. In the present embodiment, a printer color gamut outline generation unit 24 is provided as an example of a color gamut outline generation unit. Thereby, the color conversion processing performed by the color conversion device may be made more accurate.

  By the way, in the present embodiment, the hardware for performing color conversion is not particularly limited. However, for example, it may be realized in a computer such as a personal computer or in an image processing unit of the image forming apparatus. You may make it do. Hereinafter, the hardware configuration of such a computer 90 will be described.

FIG. 13 is a diagram illustrating a hardware configuration of the computer 90.
As shown in the figure, the computer 90 includes a CPU (Central Processing Unit) 91 as a calculation means, a main memory 92 as a storage means, and a magnetic disk device (HDD: Hard Disk Drive) 93. Here, the CPU 91 executes various types of software such as an OS (Operating System) and applications to realize the above-described functions. The main memory 92 is a storage area for storing various software and data used for execution thereof, and the magnetic disk device 93 is a storage area for storing input data for various software, output data from various software, and the like. .
Further, the computer 90 includes a communication interface 94 for performing communication with the outside, a display mechanism 95 including a video memory and a display, and an input device 96 such as a keyboard and a mouse.

  It should be noted that the program for realizing the present embodiment may be provided by being stored in a recording medium such as a CD-ROM, as well as provided by communication means.

DESCRIPTION OF SYMBOLS 11 ... Color signal reception part, 12 ... Forward conversion part, 13 ... Color reproduction area mapping part, 14 ... Black amount calculation part, 15 ... Light color amount calculation part, 15a ... Inverse conversion part, 15b ... Light / dark separation part, 15c ... Light color Amount setting unit, 15d ... light color amount adjustment unit, 16 ... reverse conversion unit, 17 ... color signal output unit, 18 ... dark color amount calculation unit, 19 ... light color amount calculation model, 21 ... total amount limit value setting unit, 22 ... printing Data acquisition unit 23 ... Printer data acquisition unit 23a ... Tint separation unit 23b ... Image output unit 24 ... Printer color gamut outline generation unit 30 ... Tone separation LUT

Claims (12)

An association coefficient group in which a color signal in the first color space that does not depend on the device and a color signal in the second color space that depends on the device correspond to each other, and the total color material amount is equal to or less than the first limit value. Acquisition means for acquiring an association coefficient group obtained by measuring colors of color sample groups formed of color signals so as to fit;
The color in the first color space received as a color signal to be color-converted based on the association coefficient group acquired by the acquisition unit and a second limit value set in advance for the total amount of color material The first color signal, which is a signal, is made up of the color component of the basic color material and the color component of the light color material after the total amount of the color material falls within the second limit value by a predetermined method. First conversion means for converting into a color signal of a part of color components included in the second color signal, which is a color signal subjected to color conversion in the second color space;
Based on the association coefficient group acquired by the acquisition unit, the first color signal and the color signal of the partial color component after the conversion by the first conversion unit are converted into the second color. A color conversion apparatus comprising: second conversion means for converting into a color signal of a remaining color component included in the signal. The color signal of the first color swatch group created by combining the color components of the basic color material is color-separated into the color component of the basic color material and the color component of the light color material. Further comprising creating means for creating a second color sample group for obtaining
When the total color material amount after color separation exceeds the first limit value, the creating means reduces the total color material amount so as to be less than or equal to the first limit value by a predetermined method. The color conversion apparatus according to claim 1, wherein the second color sample group is created by performing decomposition.   For the color signal in which the total color material amount after the color separation using the basic density separation coefficient group exceeds the first limit value among the color signals of the first color sample group, 3. The color conversion apparatus according to claim 2, wherein the color material total amount is reduced by a predetermined method, and the color separation is performed using a density separation coefficient group corresponding to the reduced color material total amount. . The acquisition means obtains a plurality of basic density separation coefficient groups having different total color material amounts after color separation for each of the color signals of the first color sample group created by combining the color components of the basic color material. Obtaining a plurality of types of association coefficient groups obtained by measuring colors of a plurality of types of second color sample groups created by the color separation used;
2. The second conversion unit performs conversion of a remaining color component included in the second color signal into a color signal based on the plurality of types of association coefficient groups. 4. The color conversion device according to any one of items 1 to 3. The first conversion means includes
A black amount calculating means for calculating a color component of a black basic color material included in the second color signal from the first color signal based on the association coefficient group and the second limit value; ,
A basic color for calculating the color components of the remaining basic color material included in the second color signal from the first color signal and the color signal of the basic color material of black calculated by the black amount calculation means. A material signal calculating means;
The color components of the basic color material calculated by the black amount calculation unit and the basic color material signal calculation unit are combined with the color component of the basic color material and the light color so that the total color material amount is less than or equal to the second limit value. Color separation means for color separation into the color components of the material,
When the total color material amount after color separation using the color separation coefficient group that is based on the color component of the basic color material to be color separated exceeds the second limit value, the color separation means 5. The color material total amount is reduced by a predetermined method, and the color separation is performed using a density separation coefficient group corresponding to the reduced color material total amount. Color conversion device. The color signal after conversion by the first conversion means is a color signal of a color component of a light color material,
6. The color conversion apparatus according to claim 1, further comprising a light color amount adjusting means for adjusting a color signal of a color component of the light color material converted by the first conversion means.   5. The color conversion apparatus according to claim 1, wherein the color signal after conversion by the first conversion means is a color signal of a color component of a basic color material.   The association coefficient group used by the first conversion unit and the second conversion unit are both the first color signal and the second color component composed of the color components of all the basic color materials and light color materials. The color conversion apparatus according to claim 1, wherein the color signal is associated with the color signal. The first conversion means calculates a color component of a basic black color material in the second color signal from the first color signal based on the association coefficient group and the second limit value. A black ink amount calculating means
The first conversion unit includes a set of color signals formed from the association coefficient group and including the first color signal and the color component of the black basic color material calculated by the black amount calculation unit. And converting a set of the color signals into a color signal of the partial color component using a coefficient group in which the color signals of the partial color components in the second color signal are associated with each other. The color conversion device according to claim 1. An association coefficient group in which a color signal in the first color space that does not depend on the device and a color signal in the second color space that depends on the device correspond to each other, and the total color material amount is equal to or less than the first limit value. Acquisition means for acquiring an association coefficient group obtained by measuring colors of color sample groups formed of color signals so as to fit;
A color signal in the first color space obtained by converting a color signal received as a color signal to be color-converted is a color signal in a color gamut of a target device, and the first color Mapping means for mapping to a first color signal that is a color signal in space;
Based on the association coefficient group acquired by the acquisition unit and a second limit value set in advance for the total color material amount, the first color signal obtained by the mapping unit is determined in advance. A color signal obtained by color conversion in the second color space composed of the color component of the basic color material and the color component of the light color material after the total color material amount falls within the second limit value by the method. First conversion means for converting into color signals of some color components included in a certain second color signal;
Based on the association coefficient group acquired by the acquisition unit, the first color signal and the color signal of the partial color component after the conversion by the first conversion unit are converted into the second color. A color conversion apparatus comprising: second conversion means for converting into a color signal of a remaining color component included in the signal. Further comprising color gamut outline generation means for generating a color gamut outline of the target device based on the association coefficient group;
The said mapping means performs mapping to said 1st color signal based on the color gamut outline of the said apparatus made into the object produced | generated by the said color gamut outline production | generation means. Color conversion device. On the computer,
An association coefficient group in which a color signal in the first color space that does not depend on the device and a color signal in the second color space that depends on the device correspond to each other, and the total color material amount is equal to or less than the first limit value. A function for obtaining a correspondence coefficient group obtained by measuring colors of a color sample group composed of color signals created so as to fit;
A first color that is a color signal in the first color space accepted as a color signal to be color-converted based on the association coefficient group and a second limit value set in advance for the total amount of color material The color in the second color space consisting of the color component of the basic color material and the color component of the light color material after the total amount of color material falls within the second limit value by a predetermined method. A function of converting into a color signal of a part of color components included in the second color signal which is the converted color signal;
Based on the association coefficient group, the first color signal and the converted color signals of the partial color components are converted into color signals of the remaining color components included in the second color signal. A color conversion program characterized by realizing functions.

Images