JP5978811B2 - LUT (LookUpTable) creation device, image data conversion device, LUT creation method, and LUT creation program - Google Patents

Description

  The present invention relates to the technical field of achromatic plate making in color printing.

  Conventionally, in the color printing field, colors are expressed using four inks, C (Cyan), M (Magenta), and Y (Yellow), which are generally chromatic colors, and K (Key Plate), which is an achromatic color. ing. CMYK is called process color and is the basic color for color printing. On the other hand, in recent years, a technique called Achromatic Printing has been established in which a part of colors expressed by the three chromatic colors of CMY is replaced by K. According to the achromatic plate making, the total amount of ink used can be reduced, so that the cost of the ink can be reduced and the cost for drying the ink can be reduced. In addition, it is expected that the gray stability is improved and the ink paste on the paper surface is improved.

  Also, when expressing vivid colors that cannot be expressed with process colors, printing is performed using special color inks that are different from specially generated process colors. Many techniques related to printing are also disclosed. For example, in Patent Document 1, an input signal including a special color or further black K (for example, YMCKO (Orange) G (Green)) is changed to an output signal including a special color or further black K (for example, YMCKR (Red) G). Color conversion processing to be converted, including the input special color amount (O, G amount), black amount (K amount), output special color amount (R, G amount), black amount (K amount) A technique for matching the two is disclosed. As described above, in the field of achromatic printing, many techniques for converting color data to be reproduced with CMYK or CMYKOG into color data in which a part of CMY is replaced with black K are disclosed.

  On the other hand, in some color printing fields, printing may be performed using only spot color ink without using CMYK. For example, in color printing that expresses a wood grain tone, printing may be performed using a plurality of dark brown inks.

Japanese Patent No. 42388992

  However, conventional techniques such as the technique described in Patent Document 1 are not related to printing using only spot color ink without using CMYK, and therefore, when printing using image data that reproduces color using only spot color ink. The amount of special color ink, which is more expensive than CMYK ink, could not be reduced, and it was difficult to control printing costs.

  The present invention has been made in view of such problems and the like, and reduces the amount of spot color ink used when printing image data that reproduces only spot colors other than CMYK, and suppresses printing costs. Let it be an issue.

In order to solve the above problems, the invention according to claim 1 is the first image data for color reproduction by a plurality of special colors other than C (Cyan), M (Magenta), Y (Yellow), and K (Key Plate). , said the plurality of features, a LUT creating apparatus for creating an LUT (Look Up Table) for converting the second image data to the color reproduction by some types of features and K, the first image at least a first obtaining means for color showing the limits to obtain the colorimetric value of a printing product of printing, before Symbol spot inks and K respectively corresponding to the kind of features of a part of a color reproduction range that is color reproduction data Second acquisition means for acquiring color measurement values of a color chart printed with ink, and third acquisition means for acquiring color measurement values of a color chart printed with a plurality of spot color inks respectively corresponding to the plurality of spot colors. , Indicated by the colorimetric value acquired by the second acquisition means When the color reproduction range indicated by the colorimetric value acquired by the first acquisition unit is included in the color reproduction range, the colorimetric value acquired by the second acquisition unit and the third acquisition characterized in that it comprises a creating means for creating the LUT based on the obtained colorimetric values by means.

Further, the present invention is the LUT creation device according to claim 1, wherein the second acquisition means respectively corresponds to some types of spot colors other than the spot color closest to K among the plurality of spot colors. The colorimetric values of the color chart printed with the special color ink and the K ink are acquired.

Furthermore, the present invention is the LUT creation device according to claim 1 or 2, wherein the colorimetric value is an L ^* a ^* b ^* value.

  Furthermore, the present invention includes conversion means for converting the first image data into the second image data based on the LUT created by the LUT creation device according to any one of claims 1 to 3. This is an image data conversion device.

Furthermore, the present invention is, C (Cyan), M ( Magenta), Y (Yellow), the first image data to the color reproduction by a plurality of features other than the K (Key Plate), among the plurality of features, one A LUT creation method in a LUT creation device for creating a LUT (Look Up Table) for converting to a second image data to be reproduced by K type special color and K, and color reproduction is performed with the first image data color color indicating at least limit the range of color reproduction range is printed by the corresponding spot color inks and K ink and first acquisition step of acquiring a colorimetric value of a printing product of printing, the type of feature before Symbol part A second acquisition step of acquiring colorimetric values of the chart; a third acquisition step of acquiring colorimetric values of a color chart printed with a plurality of spot color inks respectively corresponding to the plurality of spot colors; and the second acquisition step. Color reproduction indicated by the colorimetric values acquired by When the color reproduction range indicated by the colorimetric value acquired by the first acquisition step is included in the box, the colorimetric value acquired by the second acquisition step and acquired by the third acquisition step characterized in that it comprises a and a creation step of creating the LUT on the basis of the colorimetric values.

Furthermore, the present invention is, C (Cyan), M ( Magenta), Y (Yellow), the first image data to the color reproduction by a plurality of features other than the K (Key Plate), among the plurality of features, one Color reproduction that reproduces the color of the first image data from a computer included in the LUT creation device that creates a LUT (Look Up Table) for conversion to the second image data to be reproduced by the special color of the part type and K. measuring the range of at least a first acquisition means for color showing the limits to obtain the colorimetric value of a printing product of printing, the printed color chart with the corresponding spot inks and K ink to the type of feature before Symbol part Second acquisition means for acquiring color values, third acquisition means for acquiring colorimetric values of a color chart printed with a plurality of spot color inks respectively corresponding to the plurality of spot colors, and measurement measurements acquired by the second acquisition means. Within the color reproduction range indicated by the color value When the color reproduction range indicated by the colorimetric value acquired by the first acquisition unit is included, the colorimetric value acquired by the second acquisition unit and the colorimetry acquired by the third acquisition unit a LUT creation program for causing to function as, creating means for creating the LUT based on the value.

  According to the present invention, an LUT is generated for converting first image data that is reproduced with only a spot color other than CMYK into second image data that is reproduced with a part of the plurality of spot colors and K. Therefore, by printing the image after converting the first image data to the second image data using the LUT, it is possible to reduce the usage amount of the special color ink and suppress the printing cost.

3 is a conceptual diagram for explaining functions of the color data conversion apparatus 1. FIG. 2 is a block diagram illustrating a configuration of a color data conversion apparatus 1. FIG. 4 is a flowchart illustrating an example of LUT (Look Up Table) creation processing by the control unit 11 of the color data conversion apparatus 1. 4 is a flowchart illustrating an example of color data conversion processing by a control unit 11 of the color data conversion apparatus 1. FIG. 3 is a diagram illustrating an example of ink usage before and after color data conversion processing by the color data conversion apparatus 1 is performed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present embodiment is an embodiment in which the present invention is applied to the color data conversion apparatus 1.

  As shown in FIG. 1, the color data conversion apparatus 1 (an example of “LUT creation apparatus” and “image data conversion apparatus”) according to this embodiment includes three special colors (special color A, special color B, and special color C). Pre-conversion image data BD (an example of “first image data”) that reproduces colors is converted into post-conversion image data AD (“second image”) that reproduces colors using two special colors (special color A and special color B) and black K. An example of “image data”.) Create a LUT to convert to. The color data conversion apparatus 1 converts the pre-conversion image data BD into post-conversion image data AD using the created LUT. The pre-conversion image data BD reproduces the color for each pixel by a combination of the three special color densities, while the post-conversion image data AD displays the color by the combination of the two special colors and the black K density. It has come to reproduce. The color data conversion apparatus 1 creates an LUT that does not change the appearance of a printed matter printed based on the pre-conversion image data BD and a printed matter printed based on the post-conversion image data AD.

  Next, the configuration of the color data conversion apparatus 1 will be described. As shown in FIG. 2, the color data conversion apparatus 1 includes a control unit 11, a storage unit 12, an interface unit 13, a display unit 14, and an operation unit 15.

  The storage unit 12 includes, for example, a hard disk drive (HDD) and stores various programs such as an operating system and application programs. In particular, the storage unit 12 of the present embodiment stores application programs for executing various processes such as LUT creation processing and color data conversion processing. The various programs may be acquired from other server devices or the like via a network, or may be recorded on a recording medium in a computer-readable manner and read via an external drive device. Also good.

The interface unit 13 serves as a window for data exchanged with other devices and devices. For example, the interface unit 13 performs data conversion when receiving colorimetric value data obtained from a colorimeter (not shown). The colorimeter is a measuring device that measures a color chart printed by a printing machine and acquires an L ^* a ^* b ^* value (an example of “colorimetric value”).

  The display unit 14 is configured by, for example, a liquid crystal display or the like, and displays an operation screen or the like when the operator operates the color data conversion device 1. The operation unit 15 includes, for example, a keyboard, a mouse, and the like. The operation unit 15 receives an operation by the operator and transmits an operation signal indicating the operation content to the control unit 11.

  The control unit 11 includes a CPU (Central Processing Unit) having a calculation function, a ROM (Read Only Memory), a working RAM (Random Access Memory), an oscillation circuit (not shown), and the like. Based on the operation signal received from, processing corresponding to the operation content of the operator is performed. Note that the control unit 11 reads and executes an application program that executes LUT creation processing and color data conversion processing, whereby the first acquisition means, the second acquisition means, the third acquisition means, the creation means, and the conversion means of the present invention. Function as.

Next, the LUT creation processing by the control unit 11 will be described with reference to FIG. Note that the following L ^* a ^* b ^* values (i) to (iii) are stored in the storage unit 12 before the processing shown in FIG. 3 is started.
(i) the L ^* a ^* b ^* values: three colors based on the pre-conversion image data BD (spot A, feature B, featured C) objects printed matter printed with special color inks of L ^* a ^* b ^* values
L ^* a ^* b ^* value of (ii): Special color C that most closely approximates black K from the special colors of three colors (special color A, special color B, and special color C) (in this embodiment, special color C is closest to black K) L ^* a ^* b ^* value of a color chart printed with two colors of special color ink and black ink of K ink.
L ^* a ^* b ^* values of (iii): 3-color (spot color A, feature B, featured C) L ^* a ^* b ^* values of printed color chart spot inks Incidentally, most black K in (ii) The identification of the spot color that approximates to may be performed by humans based on vision, or may be performed by a computer based on L ^* a ^* b ^* values. In addition, the printed matter and the color chart printed in (i) to (iii) are printed under the same conditions. Further, the L ^* a ^* b ^* value obtained by colorimetry at colorimeter L ^* a ^* b ^* values each print or color chart (i) ~ (iii). Furthermore, the color charts of (ii) and (iii) are, for example, combinations for the case where the halftone dot density of each color is changed in five steps (0%, 25%, 50%, 75%, 100%) ( In the case of 5 stages, it is assumed that 5 ^ 3 = 125 patches are included.

First, the control unit 11 sets L ^* a ^* b ^* values (L of (i)) of the target printed matter printed with the special color inks of the three colors (special color A, special color B, and special color C) stored in the storage unit 12. ^* a ^* b ^* value) is acquired (step S1). Then, the control unit 11, L ^* a ^* b ^* values of the L ^* a ^* b ^* values of printed color chart in two colors spot inks and black K ink in the storage unit 12 is stored ((ii) ) Is acquired (step S2).

Next, the control unit 11 determines whether or not the target printed matter printed with the special color inks of the three colors (special color A, special color B, and special color C) can be reproduced with the two special color inks and the black K ink. (Step S3). Specifically, the control unit 11, the three colors (spot A, feature B, featured C) object printing product of printing by spot inks of L ^* a ^* b ^* values of ((i) L ^* a ^* b ^* color color reproduction range indicated by the value) is represented in two colors of the spot inks and printed color chart black K ink L ^* a ^* b ^* values ((ii) L ^* a ^* b ^* values) of If it is included in the reproduction range, it is determined that color reproduction is possible. More specifically, the control unit 11 determines whether or not one of the color reproduction range with reference to the a ^* b ^* values in each of the L ^* a ^* b ^* values are included in the other of the color reproduction range .

If the control unit 11 determines in step S3 that the color reproduction is not possible (step S3: NO), the control unit 11 displays an error message indicating that the LUT cannot be created on the display unit 14 (step S6). ), And finish the LUT creation process. On the other hand, if the control unit 11 determines that color reproduction is possible (step S3: YES), L ^* a of the color chart printed with the special color ink of three colors (special color A, special color B, and special color C). ^* b ^* value (L ^* a ^* b ^* value of (iii)) is acquired (step S4). Next, the control unit 11 creates a LUT based on the L ^* a ^* b ^* value acquired in the process of step S2 and the L ^* a ^* b ^* value acquired in the process of step S4 (step S5). The LUT creation process ends.

  Next, color data conversion processing by the control unit 11 will be described with reference to FIG. Before the process shown in FIG. 4 is started, the pre-conversion image data BD and the pre-conversion image data BD LUT created by the LUT creation process are stored in the storage unit 12.

  First, the control unit 11 acquires the pre-conversion image data BD stored in the storage unit 12 (step S11). Next, the control unit 11 converts the acquired pre-conversion image data BD using the LUT for pre-conversion image data BD stored in the storage unit 12, and creates post-conversion image data AD (step S12). . Next, the control unit 11 stores the created post-conversion image data AD in the storage unit 12 (step S13), and ends the color data conversion process.

As described above, the color data conversion apparatus 1 according to the present embodiment converts the pre-conversion image data that reproduces colors using a plurality of spot colors other than CMYK using a part of the spot colors and black K. Create a LUT to convert to post-image data. Specifically, the control unit 11 was printed with special color inks and black inks corresponding to some of the special colors (special color A and special color B) in the special colors of three colors (special color A, special color B, and special color C). L color chart L ^* a ^* b ^* value and ((L ^* a ^* b ^* values of ii)), the desired printed matter printed in three colors spot inks L ^* a ^* b ^* values ((i) ^* If the a ^* b ^* values) acquires, it includes color reproduction range indicated by the latter L ^* a ^* b ^* values within the color reproduction range indicated by the former L ^* a ^* b ^* values, featured and L ^* a ^* b ^* values of the color chart printed only ink ((L ^* a ^* b ^* values of iii)), the color chart printed by the spot inks and black K ink L ^* a ^* b ^* A LUT is created based on the value (L ^* a ^* b ^* value of (ii)).

  According to the color data conversion apparatus 1 of the present embodiment, as shown in FIG. 5, the special color A ink and the special color are compared with the case where the pre-conversion image data is printed with the special color A ink, the special color B ink, and the special color C ink. When the converted image data is printed with B ink and black K ink, the amount of each ink used is reduced. In particular, since special color inks are more expensive than CMYK inks, the cost reduction effect is enhanced. In addition, since the printed matter is printed using black ink that is not easily affected by light, the difference in hue when the printed matter is observed under a different light source environment compared to the printed matter printed with only the special color ink. Becomes smaller.

  Note that the present invention is not limited to the above-described embodiment, and various other modifications are possible.

  Next, a modification of this embodiment will be described.

  In the above embodiment, the LUT for converting the pre-conversion image data BD for color reproduction with the three special colors to the post-conversion image data AD for color reproduction with the two special colors and black K is created. Alternatively, an LUT may be created for converting pre-conversion image data for color reproduction with a plurality of spot colors into post-conversion image data for color reproduction with some spot colors and black (K) in the plurality of spot colors.

For example, an LUT may be created for converting pre-conversion image data for color reproduction with five special colors into post-conversion image data for color reproduction with four special colors and black K. In this case, the control unit 11 obtains the L ^* a ^* b ^* value of the target printed matter printed with the five special color inks in the process of step S1, and the special color ink and black ink of the four colors in the process of step S2. The L ^* a ^* b ^* value of the color chart printed with ink shall be obtained. Then, the control unit 11 determines whether or not the target printed matter printed with the five special color inks with the four special color inks and the black K ink can be reproduced in the process of step S3. If the controller 11 determines that color reproduction is possible at this time, the controller 11 acquires L ^* a ^* b ^* values of a color chart printed with five special color inks (step S4), and creates an LUT (step S5). ). In step S2, the control unit 11 acquires the L ^* a ^* b ^* value of the color chart printed by replacing the spot color that is closest to the black K among the five special colors with the black K.

Further, for example, an LUT may be created for converting pre-conversion image data that reproduces with seven special colors into post-conversion image data that reproduces with six special colors and black K. In this case, the control unit 11 obtains the L ^* a ^* b ^* value of the target printed matter printed with the seven special color inks in the process of step S1, and the six special color inks and black ink K in the process of step S2. The L ^* a ^* b ^* value of the color chart printed with ink shall be obtained. In step S3, the control unit 11 determines whether the target printed matter printed with the seven special color inks and the six special color inks and the black K ink can be reproduced. At this time, if it is determined that the color reproduction is possible, the control unit 11 acquires the L ^* a ^* b ^* value of the color chart printed with the seven special color inks (step S4), and creates the LUT (step S5). ). In step S2, the control unit 11 replaces the spot color closest to black K and the spot color closest to black K among the seven special colors with black K, and calculates the L ^* a ^* b ^* values of the color chart printed. It will be acquired.

In the above embodiment, in the process of step S3 of the LUT creation process, L ^* a ^{* of} the target printed matter printed with the special color ink of three colors (special color A, special color B, and special color C) based on the pre-conversion image data BD ^. b ^* values as ((L ^* a ^* b ^* values of i)), 2-color features ink and color chart was printed in three colors ink black K ink L ^* a ^* b ^* values ((ii) L ^* a ^* b ^* value) is determined by comparing whether or not the image data BD before conversion can be reproduced with the two special color inks and the black K ink. L ^* a ^* b ^* instead of the value obtained by colorimetry at colorimeter prints printed with color indicating at least limit the range of color reproduction range of the pre-conversion image data BD L ^* a ^* b ^* value It is good also as using. That is, in the process of step S3, it is only necessary to determine whether or not the target printed matter can be reproduced with the two special color inks and the black K ink. If the color indicating the color is printed, the color located in the middle of the color reproduction range may not be printed.

In the above embodiment, the L ^* a ^* b ^* value is used as an example of the “colorimetric value”, but an XYZ value may be used.

1 color data conversion device 11 control unit 12 storage unit 13 interface unit 14 display unit 15 operation unit BD image data before conversion AD image data after conversion

Claims (6)

The first image data to be reproduced by a plurality of spot colors other than C (Cyan), M (Magenta), Y (Yellow), and K (Key Plate) , and some kinds of spot colors and K among the plurality of spot colors. A LUT creation device for creating a LUT (Look Up Table) for conversion to second image data that reproduces color by
First acquisition means for acquiring a colorimetric value of a printed matter on which a color indicating at least a limit range of a color reproduction range to be reproduced with the first image data is printed;
A second acquisition means for acquiring a colorimetric value of the spot inks and a color chart printed by the K ink which correspond to the type of feature before Symbol part,
Third acquisition means for acquiring colorimetric values of a color chart printed with a plurality of spot color inks respectively corresponding to the plurality of spot colors;
When the color reproduction range indicated by the colorimetric value acquired by the first acquisition unit is included in the color reproduction range indicated by the colorimetric value acquired by the second acquisition unit, the second acquisition is performed. Creating means for creating the LUT based on the colorimetric value obtained by the means and the colorimetric value obtained by the third obtaining means;
LUT creation apparatus comprising: a. The LUT creation device according to claim 1,
The second acquisition means acquires a colorimetric value of a color chart printed with a spot color ink and a K ink corresponding respectively to some kinds of spot colors other than the spot color closest to K among the plurality of spot colors. ,
LUT creation device characterized by that. The LUT creation device according to claim 1 or 2,
The LUT creation device, wherein the colorimetric value is an L * a * b * value. Based on the LUT generated by the LUT generation apparatus according to any one of claims 1 to 3, the image data, characterized in that it comprises converting means for converting the first image data into the second image data Conversion device. The first image data to be reproduced by a plurality of spot colors other than C (Cyan), M (Magenta), Y (Yellow), and K (Key Plate) , and some kinds of spot colors and K among the plurality of spot colors. A LUT creation method in a LUT creation device that creates a LUT (Look Up Table) for conversion to second image data that reproduces color by:
A first acquisition step of acquiring a colorimetric value of a printed matter on which a color indicating at least a limit range of a color reproduction range reproduced by the first image data is printed;
A second acquisition step of acquiring calorimetric values of spot inks and printed color chart K inks respectively corresponding to the type of feature before Symbol part,
A third acquisition step of acquiring colorimetric values of a color chart printed with a plurality of spot color inks respectively corresponding to the plurality of spot colors;
When the color reproduction range indicated by the colorimetric value acquired by the first acquisition step is included in the color reproduction range indicated by the colorimetric value acquired by the second acquisition step, the second acquisition A creation step of creating the LUT based on the colorimetric value acquired in the step and the colorimetric value acquired in the third acquisition step;
LUT creation method, which comprises a. The first image data to be reproduced by a plurality of spot colors other than C (Cyan), M (Magenta), Y (Yellow), and K (Key Plate) , and some kinds of spot colors and K among the plurality of spot colors. A computer included in the LUT creation device that creates a LUT (Look Up Table) for conversion to second image data that reproduces color by
First acquisition means for acquiring a colorimetric value of a printed matter on which a color indicating at least a limit range of a color reproduction range reproduced by the first image data is printed;
Second acquisition means for acquiring a colorimetric value of the spot color inks and printed color chart K inks respectively corresponding to the type of feature before Symbol part,
Third acquisition means for acquiring colorimetric values of a color chart printed with a plurality of spot color inks respectively corresponding to the plurality of spot colors;
When the color reproduction range indicated by the colorimetric value acquired by the first acquisition unit is included in the color reproduction range indicated by the colorimetric value acquired by the second acquisition unit, the second acquisition is performed. Creating means for creating the LUT based on the colorimetric value obtained by the means and the colorimetric value obtained by the third obtaining means;
LUT creation program for causing to function as.