JP2013121135A - Image processing apparatus, image forming apparatus, program, and image processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a difference in color before and after replacement processing of total amount regulation.SOLUTION: An image processing apparatus of the present invention includes: color information obtaining means for obtaining color information on a color reproduced by a specific single color and a color reproduced by a mixed color of a plurality of fundamental colors adjacent to the specific color in terms of hue; replacement information creating means for creating replacement information indicating a rate of replacement from signal values of the plurality of fundamental colors to a signal value of the specific color on the basis of the color information obtained by the color information obtaining means; and replacement processing means for replacing the signal value of the plurality of fundamental colors with the signal value of the specific color on the basis of the replacement information created by the replacement information creating means, if the total sum of the signal values of the respective colors of the image signal exceeds the set limit value when outputting an image on the basis of an image signal comprising the plurality of fundamental colors and the specific color.

Description

  Embodiments described herein relate generally to an image processing apparatus, an image forming apparatus, a program, and an image processing method.

  Conventionally, printers that print using CMYK in color printing technology are generally known, but in recent years, CMYK (basic color) colorant (toner), which is a process color, has been changed to orange (O), green. A special color material such as (G) is newly added, and a multicolor printer (image processing apparatus) capable of performing multicolor printing using a color material exceeding four colors has attracted attention.

  In order to perform the multicolor printing, it is necessary to determine not only CMYK (basic colors) but also the amount of the special color material, and various methods are known as the determination method. In particular, as a typical method, a look-up table (LUT: conversion table) for converting a CMYK signal into an N color signal (N> 4) based on a colorimetric value of a printed matter printed by combining CMYK (basic color) and a special color. Create a Look-Up Table) and determine the color material amount of the special color using the LUT, and among the CMYK (basic colors), for example, two colors of cyan (C) and magenta (M) There is known a method for determining the color material amount of a special color by replacing it with a certain blue single color.

  By the way, there is a limit to the amount of color material that can be applied to the printing paper, and if the amount of color material (toner amount) adhering per unit area is too large, problems such as image quality deterioration due to color material bleeding occur. For this reason, when converting an RGB signal or CMYK signal input to the image processing apparatus to an N color signal (N> 4) including a special color, the total color material amount after conversion is an upper limit of a predetermined color material amount. It is necessary not to exceed the value (also referred to as the total amount regulation value).

  Therefore, when the sum of the input N color signal values exceeds the total amount regulation value, it is necessary to correct the signal value of each color so as not to exceed the total amount regulation value. Therefore, as a technique for correcting the signal value of each color so as not to exceed the total amount regulation value as described above, when the sum of the signal values of each color including the spot color exceeds the total amount regulation value, the signal value of the basic color is changed to the signal of the special color. A technique for replacing a basic color signal value with a spot color signal value based on a replacement table for replacement with a value (see, for example, Patent Document 1) is known.

  However, in the prior art including the above-mentioned Patent Document 1, the replacement ratio from the CMY basic color to the spot color signal is constant, and the color difference (color tone change) before and after replacement according to the spot color amount generated by the replacement. There is a problem that becomes large. Further, there is a problem that it is difficult to determine the replacement ratio according to the color material to be used.

  Therefore, the present invention solves the above-described conventional problems, and can reduce the color difference before and after the total amount restriction replacement process, and can easily determine the replacement ratio, an image forming apparatus, a program, and An object is to provide an image processing method.

  In order to solve the above-described problems and achieve the object, the image processing apparatus of the present invention provides a color that is reproduced with a single special color and a color that is reproduced with a mixture of a plurality of basic colors that are huewise adjacent to the special color. A color information acquisition unit that acquires color information, and a replacement that generates replacement information indicating a replacement ratio of signal values of a plurality of basic colors to signal values of spot colors based on the color information acquired by the color information acquisition unit When the information generation means and the image signal composed of a plurality of basic colors and special colors are output, if the sum of the signal values of each color of the image signal exceeds a set limit value, the replacement information generation means And replacement processing means for replacing the signal values of a plurality of basic colors with signal values of spot colors based on the replacement information created by the above.

  Further, the image forming apparatus of the present invention includes an output unit that outputs a color patch composed of a single special color and a color patch composed of a mixture of a plurality of basic colors that are huewise adjacent to the special color, and the output A color information acquisition unit that reads each color patch output by the unit and acquires color information of a mixed color of the special color and the plurality of basic colors, and a plurality of color information acquisition units based on the color information acquired by the color information acquisition unit. A replacement information creating means for creating replacement information indicating a ratio of replacement from a basic color signal value to a spot color signal value, and when outputting based on an image signal composed of a plurality of basic colors and spot colors, the image A replacement processing means for replacing the signal values of a plurality of basic colors with signal values of spot colors based on the replacement information created by the replacement information creating means when the sum of the signal values of each color of the signal exceeds a set limit value; Provided.

  Further, the program of the present invention provides a computer with color information acquisition means for acquiring color information of a color reproduced with a single special color and a color reproduced with a mixed color of a plurality of basic colors that are huewise adjacent to the special color; Based on the color information acquired by the color information acquisition means, replacement information creation means for creating replacement information indicating a ratio of replacement of signal values of a plurality of basic colors to signal values of spot colors, and a plurality of basic colors and spot colors When the total sum of the signal values of the respective colors of the image signal exceeds a set limit value when outputting based on the image signal configured by: based on the replacement information generated by the replacement information generating means, a plurality of This is a program that functions as replacement means for replacing the signal value of the basic color with the signal value of the spot color.

  The image processing method executed by the image processing apparatus of the present invention obtains color information of a color reproduced with a single special color and a color reproduced with a mixture of a plurality of basic colors that are huewise adjacent to the special color. Based on the acquired color information, a replacement information indicating a replacement ratio from a plurality of basic color signal values to a special color signal value is created, and based on an image signal composed of a plurality of basic colors and special colors. When outputting, if the sum of the signal values of each color of the image signal exceeds a set limit value, a method of replacing the signal values of a plurality of basic colors with signal values of spot colors based on the created replacement information. is there.

  According to the present invention, it is possible to reduce the color difference (color change) before and after the replacement processing from the basic color of the total amount restriction to the spot color, and it is possible to easily determine the replacement ratio.

FIG. 1 is a front view illustrating a schematic configuration of the image processing apparatus according to the present embodiment. FIG. 2 is a block diagram illustrating a configuration example of a controller that controls the processing operation of the image processing apparatus. FIG. 3 is a block diagram illustrating a functional configuration of the image processing apparatus. FIG. 4 is a flowchart showing a flow of processing operation of the color patch generation unit. FIG. 5 is a schematic diagram for explaining an example of a color patch generated by the color patch generation unit. FIG. 6 is a schematic diagram for explaining the relationship between the spot color and the adjacent process color. FIG. 7 is a flowchart showing the flow of processing operations of the spot color replacement LUT calculation unit. FIG. 8 is a graph for explaining the color difference minimum color material configuration of the spot color single color and the adjacent process color secondary color, and the replacement characteristic curve of the process color. FIG. 9 is a flowchart showing the flow of the processing operation of the total amount restriction processing unit. FIG. 10 is a flowchart showing a detailed processing operation flow of step S403 in FIG. FIG. 11 is a schematic diagram for explaining a specific example of the total amount restriction process of FIGS. 9 and 10.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  In the image processing apparatus and the image processing method of the present invention, a special color material such as orange (O) or green (G) is newly added to a basic color material (such as toner) such as CMYK which is a process color. In addition, the present invention can be applied to an image processing apparatus such as a copier (printer) or a multi function peripheral (MFP) capable of performing multicolor printing using color materials exceeding four colors. In the description, a case where the present invention is applied to an image processing apparatus realized by a digital multi-function peripheral will be described.

  First, the configuration of the image processing apparatus 1 according to the present embodiment will be described with reference to FIG. FIG. 1 is a front view showing a schematic configuration of an image processing apparatus 1 of the present embodiment.

  As shown in FIG. 1, the image processing apparatus 1 includes an operation unit 2 having a touch panel type display screen for displaying various function keys such as a start key for instructing start of copying (copying) and operation icons, and an operation unit. When the start key 2 is pressed, an automatic document feeder (ADF) 3 that automatically feeds a document set on the document setting unit 31, an ADF 3, a document table glass (also called contact glass) ) An image reading unit (color measurement means) 4 such as a color scanner for reading an image of a document set on 41 or an image of a color patch (see FIG. 5) described later, and an image forming unit 6 from a paper feed tray (not shown). The sheet feeding device 5 that feeds the transfer paper (recording medium) and the image read by the image reading unit 4 by a method such as electrophotography, thermal sensitivity, thermal transfer, and inkjet are fed from the sheet feeding device 5. An image forming unit (printer unit) 6 to be formed on the transferred transfer paper, a paper discharge unit (also referred to as a paper discharge tray) 7 for discharging the transfer paper on which the image is formed by the image forming unit 6 to the outside, A controller (control unit) 10 for controlling the processing operation of the image processing apparatus 1 is provided.

  Next, the configuration of the controller 10 of the image processing apparatus 1 will be described with reference to FIG. FIG. 2 is a block diagram illustrating a configuration example of the controller 10 that controls the processing operation of the image processing apparatus 1.

  As shown in FIG. 2, the controller 10 includes a CPU 11 that comprehensively controls processing operations of the image processing apparatus 1, a RAM 12, a ROM 13, and a network I / F 14 connected to the CPU 11 via a bus line BL. ing.

  The CPU 11 uses the RAM 12 as a work memory, executes a program stored in the ROM 13, and loads each component such as the ADF 3, the image reading unit 4, the image forming unit 6, and the paper feeding device 5 through the bus line BL. Control.

  The network I / F 14 exchanges various data such as print data and scan commands with an external information processing apparatus such as a server or personal computer connected via a network N such as a LAN (Local Area Network). .

  Next, the functional configuration of the image processing apparatus 1 will be described with reference to FIG. FIG. 3 is a block diagram illustrating a functional configuration of the image processing apparatus 1.

  As illustrated in FIG. 3, the image processing apparatus 1 functions as the image processing unit 100 when the CPU 11 expands and executes a program stored in the ROM 13 or the like on the RAM 12. The image processing unit 100 also includes a spot color replacement LUT creation unit 110, a color separation processing unit 120, and a total amount restriction processing unit 130.

  The spot color replacement LUT creation unit 110 outputs a plurality of color patches each composed of a spot color single color and a process color secondary color, and based on the colorimetric values (color information) of each color patch, the spot color single color and process A replacement amount between color secondary colors is calculated, and the result is created as a spot color replacement LUT (Look-Up Table) (replacement information). The color patch generation unit 110a, the color patch colorimetry unit 110b, And a spot color replacement LUT calculation unit 110c.

  Here, the color patch generation unit (output unit) 110a applies process colors such as cyan (C), magenta (M), yellow (Y) and achromatic black (K) to orange (O) and green ( The image forming unit (output unit) 6 of the image processing apparatus (multicolor printer) 1 capable of multicolor printing including a chromatic special color such as G) is configured by combining two of process colors. A process of outputting a color patch and a color patch (see FIG. 5) composed of a single special color is performed.

  The color patch colorimetric unit (color information acquisition unit) 110b reads each color patch output from the image forming unit 6 by the color patch generation unit 110a by the image reading device (color measurement unit) 4 and standardizes each color patch. The color of the signal (CIE L * a * b signal) is measured, and the standard signal of each measured color patch is stored in a storage unit such as the RAM 12.

  The spot color replacement LUT calculation unit (replacement information creation unit) 110c is configured to process the secondary color of the process color for the spot color single color based on the standard signal of each color patch stored in the storage unit by the color patch colorimetry unit 110b. A combination of colorants that minimizes the CIE L * a * b color difference is obtained, a spot color replacement LUT that is referred to when the process color secondary color is replaced with a spot color single color is created, and stored in a storage unit such as the RAM 12.

  In addition, when RGB image data is input from the image reading unit 4 or the like, the color separation processing unit 120 converts the RGB image data into N colors obtained by combining four CMYK colors (standard colors) and one or more special colors. (N> 4) Data is converted and output to the total amount restriction processing unit 130.

  Note that the N color data here determines the color material amounts of cyan (C), magenta (M), yellow (Y), black (K), and special colors (green: G, orange: O, etc.). This is a signal value for each color, and each color material amount is in a range of 0 to 100% with 256 gradations for each color.

  The total amount restriction processing unit (replacement processing unit) 130 restricts the amount of each color material attached to a recording medium such as transfer paper based on a preset total amount restriction value (limit value).

  Note that the total amount regulation value in the present embodiment indicates the total amount of color material that can be printed in the image processing apparatus 1 using N colors. The amount of each N color material is determined by the signal value output from the image processing unit 100.

For example, in the case of the image processing apparatus 1 in which the total amount regulation value is set to 200% and the six colors of CMYKOG are used, the output color signals of CMYKOG are set to c, m, y, k, o, and g, respectively, and each color material of CMYKOG When the amounts are T (c), T (m), T (y), T (k), T (o), and T (g), the relationship between the total amount regulation value and each color material amount can be expressed as follows. .
(T (c) + T (m) + T (y) + T (k) + T (o) + T (g)) <200%

The relationship between the output color signal and the color material amount of the image processing apparatus 1 varies depending on the image forming process and the paper type. Here, for the sake of simplicity, it is assumed that the relationship between the output color signal and the color material amount is linear. Assume that the following equation holds.
(Color material amount) = (Output color signal) × 100/255

  Then, when the output color signal exceeds the total amount restriction value, the total amount restriction processing unit 130 corrects each color signal to be equal to or less than the total amount restriction value. Specifically, the total amount restriction processing unit 130 corrects each output color signal by replacing the process color secondary color with a single spot color using the spot color replacement LUT created in advance and stored in the storage unit, Do not exceed the total regulation value. Then, the total amount restriction processing unit 130 outputs the output color signal corrected so as not to exceed the total amount restriction value to the image forming unit 6.

  Next, the processing operation of the image processing apparatus 1 having the above-described configuration will be described with reference to FIGS.

  First, the processing operation of the color patch generation unit 110a will be described with reference to FIGS. FIG. 4 is a flowchart showing a processing operation flow of the color patch generation unit 110a, FIG. 5 is a schematic diagram for explaining an example of the color patch generated by the color patch generation unit 110a, and FIG. FIG. 5 is a schematic diagram for explaining a relationship between a spot color and an adjacent process color.

  As shown in FIG. 4, the color patch generation unit 110a performs a process for generating a spot color single color patch (step S101). That is, in step S101, a color patch of a single color gradation of a special color mounted on the image processing apparatus 1 (particularly, the image forming unit 6) is generated.

  More specifically, in the process of step S101, for example, the image processing apparatus 1 (image forming unit 6) can print in six colors of C, M, Y, K, O (orange), and G (green). In some cases, a single color gradation color patch of each of the special colors O (orange) and G (green) is generated (see FIG. 5A). At this time, each color patch is generated on the basis of a spot color signal sampled by being divided into gradations of a constant interval.

  5A shows an example of the spot color single color patch generated in step S101. In the example of FIG. 5A, each color signal value is composed of 8 bits (0 to 255). In this case, the spot color single color patch when the spot color signal is sampled in 8 steps (32, 64, 96, 128, 160, 192, 224, 255) is shown.

  Subsequently, the color patch generation unit 110a performs processing for generating an adjacent process color secondary color patch (step S102).

  More specifically, in the process of step S102, a color constituted by a combination of two CMY process colors (see FIG. 6) that are hue-adjacent in the device independent color space CIE L * a * b *. A patch is generated (see FIG. 5B). The color signal value of the color patch of each adjacent process color is sampled by dividing it into gradations with a constant interval, and created based on a color signal composed of all combinations of the sampled two color signal values. Is done.

  In the example of FIG. 6, the process colors CMY and spot colors O and G are plotted on the a * b * plane in the CIE L * a * b * color space. For example, the spot color is 0 ( The process color adjacent to the spot color O (orange) is magenta (M) and yellow (Y), and the spot color G is green (G). This indicates that the process colors that are hue adjacent to (green) are yellow (Y) and cyan (C).

  FIG. 5B shows an example of an adjacent process color secondary color patch generated in step S102. In the example of FIG. 5B, when two adjacent process colors for a certain spot color are A and B, the color signals of the color material A and the color material B are sampled in 8 steps. ing.

  That is, in step S102, the color patch generation unit 110a creates a color patch based on the color signals of all combinations of the sampled color material A and color material B, for example. When each color is sampled in 8 steps, the number of color patches to be generated is 64 patches (8 × 8). Further, when two or more special colors are used, it is necessary to create color patches of secondary process color secondary colors corresponding to the number of special colors. When three special colors are used, 192 patches (8 × 8 × 3) of color patches are generated.

  Subsequently, in the color patch generation unit 110a, each color patch (special color single color patch, The adjacent process color secondary color patch is printed (output) (step S103).

  Next, the processing operation of the spot color replacement LUT calculation unit 110c will be described with reference to FIGS. FIG. 7 is a flowchart showing the flow of processing operations of the spot color replacement LUT calculation unit 110c. FIG. 8 is a graph for explaining the color difference minimum color material configuration of the spot color single color and the adjacent process color secondary color, and the replacement characteristic curve of the process color.

  As shown in FIG. 7, in the spot color replacement LUT calculation unit 110c, first, color measurement values (L * a * b * values, XYZ values) corresponding to the respective color signal values stored in the storage unit by the color patch color measurement unit 110b. ) Is read (step S201).

  Subsequently, the spot color replacement LUT calculation unit 110c searches for a combination of signal values that minimize the color difference from the adjacent process color secondary color patches for the color measurement value of the spot color single color (step S202). For example, when spot color single color is sampled in 8 steps (8 patches) and adjacent process color 2 colors are sampled in 8 steps (8 × 8 = 64 patches), respectively, as shown in FIG. The patch having the smallest color difference is searched from the color patches of the process color secondary color. Then, the special color signal value when the color difference is minimum and the signal values of two adjacent process colors are recorded. Although the colorimetric values of the color patches are shown in FIG. 5, the color information may be acquired by a color prediction model and replaced with the measured values.

  FIG. 8A is a diagram in which the signal values of the two adjacent process colors having the smallest color difference are plotted against the signal values of the single color of the special color. In FIG. 8A, the special color single color patch is composed of 8 patches (eight gradations), and the adjacent process color 2 colors constituting the adjacent process color secondary color patch with the smallest color difference for each patch. Color signals A and B are plotted. For example, when the special color signal value = 32, the signal values A and B of the two adjacent process colors that minimize the color difference are 32 and 64, respectively. That is, since the relationship of the special color signal value (32) ≈the process color A signal value (32) + the process color B signal value (64) is established, it is possible to grasp the optimum replacement amount between the special color and the process color. it can.

  Subsequently, the spot color replacement LUT calculation unit 110c uses the signal value data of the spot color and the two adjacent process colors checked in the search in step S202 to determine the relationship between the spot color and the adjacent process color replacement amount (that is, the process color). (Substitution characteristic curve) is obtained (step S203). That is, in the process of step S202, the relationship (replacement amount) of the process color signal value that minimizes the color difference with respect to the spot color signal values (32, 64, 96, 128, 160, 192, 224, 255) sampled at regular intervals Although it has been understood, it is not possible to grasp what values the signal values of the two process colors take for the spot color signal values that have not been sampled. Therefore, for such signal values, the relationship between the spot color and the adjacent process color is calculated by the least square method using the sampled discrete data.

  FIG. 8B is a diagram showing the relationship between the spot color and the replacement amount of the adjacent process color. That is, in step S203, the spot color replacement LUT calculation unit 110c uses the sampling data of the spot color and the adjacent process color shown in FIG. 8A as shown in FIG. The relational expression of the adjacent process color is calculated. From this relational expression, it is possible to calculate the replacement amount of two process colors for all the gradation values (0 to 255) of the special color.

  Subsequently, the spot color replacement LUT calculation unit 110c calculates the replacement amount of the two process colors for all the tone values (0 to 255) of the spot color from the relational expression obtained in step S203, and calculates the LUT (Look-Look- Up Table) (step S204). By using the LUT as the replacement amount of the spot color and the process color, it is possible to save the calculation work of the subsequent total amount restriction processing unit 130.

  Next, the processing operation of the total amount restriction processing unit 130 will be described with reference to FIG. FIG. 9 is a flowchart showing the flow of processing operation of the total amount restriction processing unit 130.

  As shown in FIG. 9, in the total amount restriction processing unit 130, first, when an N color signal (N color data) is inputted, a total amount restriction value stored in advance in a storage unit such as the ROM 13 is read and acquired ( Step S401). The total amount regulation value is not limited to a preset value, but may be a value directly input by the user via a user interface (not shown). Alternatively, several modes may be prepared in advance, a plurality of total amount regulation values corresponding to the modes may be stored in advance in the storage unit, and the corresponding total amount regulation value may be selected according to the mode.

  Subsequently, when the total amount restriction value is read in step S401, the total amount restriction processing unit 130 determines whether or not the N-color signal sum exceeds the total amount restriction value (step S402). Here, each of the N color signals is in the range of 0 to 255. In this embodiment, since it is assumed that one or more colors of CMYK and special colors are used, N> 4 is a condition.

  If it is determined in step S402 that the N color signal value sum exceeds the total amount restriction value (step S402: Yes), the total amount restriction processing unit 130 can replace the process color CMY and the spot color input signal. Each input signal is corrected by obtaining a correct signal upper limit value and replacing CMY with a special color (step S403). Details of the CMY to spot color replacement process in step S403 will be described later. On the other hand, if it is determined in step S402 that the N color signal value sum does not exceed the total amount regulation value (step S402: No), the total amount regulation processing unit 130 uses the input color signal as an output signal as it is. Output to the image forming unit 6.

  After the process color to spot color replacement processing in step S403, the total amount restriction processing unit 130 determines whether or not the sum of the corrected N color signal values exceeds the total amount restriction value (step S404).

  If it is determined in step S404 that the total amount regulation value is not exceeded (step S404: No), the total amount regulation processing unit 130 outputs the corrected N color signal value to the image forming unit 6 as an output signal. . On the other hand, if it is determined in step S404 that the N color signal value sum exceeds the total amount restriction value (step S404: Yes), the total amount restriction processing unit 130 applies to all the spot colors included in the N color signal. It is then determined whether or not a replacement process has been performed (step S405). That is, in the replacement process in step S403, one spot color is selected and the process color is replaced with the spot color for that color. Therefore, when the N color signal is CMYKOG, either the spot color O (orange) or G (green) is selected and the replacement process with the selected spot color is performed, but the other color that has not been selected is selected. The spot color is not replaced. Therefore, it is determined whether or not there is a spot color that has not been subjected to the replacement process, so that the replacement process for all the spot colors is performed.

  If it is determined in step S405 that all spot colors have not been replaced (step S405: No), the total amount restriction processing unit 130 performs replacement processing again in step S403. At this time, the spot color that has been subjected to the replacement process is not selected, but the spot color that has not been subjected to the replacement process is selected to correct each color signal value.

  On the other hand, if it is determined in step S405 that replacement processing has been performed for all the spot colors (step S405: Yes), the total amount restriction processing unit 130 corrects each color signal so that the N color signal sum is equal to or less than the total amount restriction value. (Step S406). That is, in the process of step S406, the total amount restriction processing unit 130 has performed the replacement processing on all the spot colors for the N color signal that is sent, and the total signal value exceeds the total amount restriction value. Therefore, processing is performed so that the N-color signal sum is within the range of the total amount regulation value.

Note that the total amount restriction method used in the process of step S406 includes, for example, fixing the output signal value of one of the N colors and keeping the composition ratio of the output signal values of the other colors constant, The process of making it fall within the range is mentioned. That is, in the case of a signal composed of CMYKOG, when K is fixed and the ratio of C: M: Y: O: G is fixed and adjusted to the total amount regulation value S, C, M, Y, K, O, Each output signal value of G is C, M, Y, K, O, G, and each output signal value of C, M, Y, K, O, G after modification considering the total amount regulation is C ′, M When ', Y', K ', O', G ', C', M ', Y', K ', O', G 'are C' = C * (SK) / (C + M + Y + O + G)
M ′ = M × (SK) / (C + M + Y + O + G)
Y ′ = Y × (SK) / (C + M + Y + O + G)
K '= K
O ′ = O × (SK) / (C + M + Y + O + G)
G ′ = G × (SK) / (C + M + Y + O + G)
Is obtained.

  Next, the detailed processing operation of step S403 in FIG. 9 will be described with reference to FIG. FIG. 10 is a flowchart showing a detailed processing operation flow of step S403 in FIG.

  As shown in FIG. 10, the total amount restriction processing unit 130 first performs a replacement color material selection process in the process of step S403 of FIG. 9 (step S501).

  Specifically, in the process of step S501, the total amount restriction processing unit 130 selects two colors, that is, the spot color to be replaced and the process color that is huely adjacent to that color. First, one spot color to be replaced is selected. For example, when two colors of orange and green are used as the spot colors, one of the colors is selected. Next, when a spot color is selected, two colors are selected from the process colors CMY that are huewise adjacent to the spot color. If the selected spot color is orange, magenta and yellow are selected. If the spot color is green, cyan and yellow are selected. In the following description, the selected spot color is referred to as X, and the two process colors are referred to as P1 and P2, respectively.

  Subsequently, the total amount restriction processing unit 130 performs a special color replacement LUT reading process (step S502). Specifically, in step S502, the total amount restriction processing unit 130 reads the spot color replacement LUT for the two process colors P1 and P2 selected in step S501. The spot color replacement LUT is created in advance by the spot color replacement LUT creation unit 110.

  Subsequently, the total amount restriction processing unit 130 performs a calculation process of the spot color generation upper limit (Xmax) (step S503).

Specifically, in step S503, the total amount restriction processing unit 130 calculates the upper limit value of the spot color that can be generated by replacement from the input signal value of the spot color X selected in step S501. It is assumed that the input signal is composed of five colors CMYKX, each color signal is c, m, y, k, x, and each signal value is in the range of 0 to 100%. At this time, since the signal upper limit value that can be set for each color is 100%, the spot color upper limit value (Xmax) that can be generated by reducing the two colors P1 and P2 is
Xmax = 100−x (1)
Can be expressed as From this, the spot color generation upper limit (Xmax) is obtained.

  Subsequently, the total amount restriction processing unit 130 performs processing for calculating the adjacent process color decrement upper limit values (P1max, P2max) (step S504).

Specifically, in step S504, the total amount restriction processing unit 130 sets an upper limit value of the process color that can be reduced at the time of replacement from the input signal values of the two process colors (P1, P2) selected in step S501. calculate. When the two colors P1 and P2 are replaced with the spot color X, the CMY signal value necessary for the replacement with the spot color must not exceed the input CMY signal value. Therefore, if the input signals of the two colors (P1, P2) selected from CMY are p1, p2, the upper limit values (P1max, P2max) of P1, P2 that can be reduced at the time of replacement with the spot color are:
P1max = p1 (2)
P2max = p2 (3)
Can be expressed as From this, the adjacent process color decrement upper limit values (P1max, P2max) are obtained.

  Subsequently, the total amount restriction processing unit 130 performs calculation processing of the adjacent process color decrement amounts (P1sub, P2sub) and the spot color generation amount (Xadd) (step S505).

  Specifically, in step S505, the total amount restriction processing unit 130, based on the spot color generation upper limit value calculated in step S503 and the adjacent process color decrement upper limit value calculated in step S504, Specifically, the decrement amounts of the adjacent process colors P1 and P2 and the generation amount of the spot color signal X are calculated. A method for calculating the correction amount of each color signal will be described below.

First, if the spot color generation amount when replacing two process colors with a spot color is Xadd, the decrement amounts of the two process colors are P1sub and P2sub, respectively, and the spot color replacement LUT read in step S502 is used, each color signal at the time of replacement The correction amount can be expressed as follows.
P1sub = P1_LUT (Xadd) (4)
P2sub = P2_LUT (Xadd) (5)
Here, P1_LUT is a spot color replacement LUT for the process color P1, and P2_LUT is a spot color replacement LUT for the process color P2.

Next, the correction amount of each color signal is calculated using the spot color generation upper limit value Xmax and the adjacent process color decrement upper limit values P1max and P2max. However, when correcting each color signal by replacement, the range of color signal values before and after replacement must be taken into consideration. The first point to consider is that the spot color signal value after replacement must not exceed 100%. Since the upper limit of the signal value is determined in advance, a value exceeding it (> 100%) cannot be taken. Therefore, when the spot color generation upper limit value Xmax is used as the spot color generation amount Xadd,
0 <Xadd ≦ Xmax (6)
Must meet the requirements. The second point to consider is that the amount of signal to reduce the two process colors at the time of replacement must not exceed the input signal value. If the amount to be reduced exceeds the input signal value, the signal value after replacement becomes negative, and becomes an inappropriate value as the signal value. For this reason, when the adjacent process color decrement upper limit values P1max and P2max are used as the signal amounts P1sub and P2sub for subtracting two process colors at the time of replacement,
P1sub ≦ P1max (7)
P2sub ≦ P2max (8)
Must meet the requirements. Here, equations (7) and (8) can be rewritten as follows using equations (4) and (5).
P1_LUT (Xadd) ≦ P1max (9)
P2_LUT (Xadd) ≦ P2max (10)
From these conditions, in order to efficiently replace the process color with the spot color, the maximum spot color generation amount Xadd satisfying the expressions (9) and (10) and satisfying the expression (6) can be obtained. That's fine. Then, by substituting the obtained Xadd into the equations (4) and (5), the adjacent process color decrement amounts P1sub and P2sub are obtained.

  Subsequently, the total amount restriction processing unit 130 corrects each input signal value (step S506).

Specifically, in step S506, the total amount restriction processing unit 130 corrects each input signal using the adjacent process color decrement amounts P1sub and P2sub and the spot color generation amount Xadd calculated in step S505. The signal values p1 ′ and p2 ′ and the spot color signal value x ′ of the two adjacent process colors after correction can be expressed as follows.
p1 '= p1-P1sub (11)
p2 '= p2-P2sub (12)
x ′ = x + Xadd (13)
In this way, each input signal value is corrected by replacing two adjacent process colors with one special color.

  Next, a specific example of the total amount restriction process of FIGS. 9 and 10 will be described with reference to FIG. FIG. 11 is a schematic diagram for explaining a specific example of the total amount restriction process of FIGS. 9 and 10.

  FIG. 11A shows that the total amount restriction value is 200% and the input color signal values are C = 40, M = 100, Y = 80, K = 50, and R = 30. Shows the value. In FIG. 11A, each color signal takes a value in the range of 0 to 100%.

  FIG. 11B shows a replacement characteristic curve of adjacent process colors used when two process colors are replaced with spot colors. In the example of FIG. 11, the image processing apparatus 1 capable of printing using CMYKR five color materials is assumed.

  That is, in the example of FIG. 11, when the total amount restriction value (200%) is read in step S401 of FIG. 9, it is determined in step S402 whether or not the total input color signal exceeds the total amount restriction value. In this case, as shown in the left diagram of FIG. 11A, the total sum of the input color signals is 300%, which indicates that the total amount regulation value is exceeded. Therefore, in step S403, a process color to spot color replacement process is performed to reduce the total amount.

  That is, as the replacement process, two colors are selected from the spot color to be replaced and the process color CMY that is huewise adjacent to the spot color in step S501 of FIG. In the example of FIG. 11, the spot color to be replaced is red (R) (see FIG. 11A), and the adjacent process colors are two colors (magenta (M) and yellow (Y) that are hue-adjacent to red (R) ( 11B) is selected.

  Subsequently, in the special color replacement LUT reading process in step S502 of FIG. 10, the replacement LUT from the selected magenta (M) and yellow (Y) to the special color red (R) is read. Here, the replacement LUT for the spot color is calculated in advance, and in the example of FIG. 11, a replacement LUT as shown in FIG. 11B is prepared.

  Subsequently, in the process of calculating the spot color generation upper limit value (Xmax) in step S503 in FIG. 10, a spot color upper limit value that can be generated is calculated when the process color is replaced with the spot color. Xmax can be obtained from equation (1), and Xmax = 70.

  Subsequently, in the process of calculating the adjacent process color decrement upper limit value in step S504 of FIG. 10, the upper limit value of the process color that can be reduced at the time of replacement is calculated from the input signal values of the two process colors. Assuming that the upper limit values of the selected magenta (M) and yellow (Y) are Msub and Ysub, the respective values are Msub = 100 and Ysub = 80 from the equations (2) and (3).

Subsequently, in the process of calculating the adjacent process color decrement amount and the spot color generation amount in step S505 of FIG. 10, the decrement amounts of magenta (M) and yellow (Y), which are adjacent process colors, and the generation amount of the spot color red (R). Is calculated. Assuming that the generation amount of the special color red (R) is Radd, Radd is obtained from the equation (6).
0 <Radd ≦ 70 (I)
You must meet the conditions. Similarly, the decrement amounts Msub and Ysub of the adjacent process colors magenta (M) and yellow (Y) are obtained from the equations (9) and (10).
Msub = M_LUT (Radd) ≦ 100 (II)
Ysub = Y_LUT (Radd) ≦ 80 (III)
You must meet the conditions. When the maximum Radd that simultaneously satisfies the conditions of the expressions (I) to (III) is obtained, Radd = 70. Then, referring to the special color replacement LUTs of magenta (M) and yellow (Y) from this value, Msub = 80 and Ysub = 70 are obtained.

Subsequently, in the correction processing of each input signal value in step S506 in FIG. 10, each input is calculated from the calculated magenta (M), yellow (Y) decrement amounts Msub, Ysub, and spot red (R) generation amount Radd. Correct the signal. The corrected values M ′, Y ′, and R ′ of magenta (M), yellow (Y), and red (R) are obtained as follows from equations (11) to (13).
M ′ = 100−80 = 20
Y ′ = 80−70 = 10
R ′ = 30 + 70 = 100

  By the replacement process, each input signal value is corrected, and the corrected CMYKR values are C = 40, M = 20, Y = 10, K = 50, and R = 100, respectively. However, since the total color signal is 220 at this point, it can be seen that the total amount regulation value 200 has been exceeded (see the central diagram in FIG. 11A). Further, the replacement process with the spot color cannot be performed any more. Therefore, in such a case, the black amount K is held, and the other color signal values are reduced so that the ratio is held constant before and after the correction. Accordingly, the corrected signal values C′M′Y′K′R ′ are C ′ = 35, M ′ = 18, Y ′ = 9, K ′ = 50, and R ′ = 88, respectively (FIG. 11). (See the right figure in (A)). The total amount can be reduced by correcting the signal value in this way.

  That is, according to the image processing apparatus of the present embodiment described above, the replacement ratio is determined based on the colorimetric values of the color patch printed with the combination of the CMY basic colors and the color patch printed with the spot color single color. It is possible to reduce the color difference (color change) before and after the replacement process from the CMY basic colors to the special colors when the total amount restriction is performed on the color signals exceeding four colors.

  As mentioned above, although demonstrated based on exemplary embodiment, this embodiment is not limited by above-described embodiment.

  For example, in the above-described embodiment, the spot color replacement LUT creation unit 110 (see FIG. 3) generates a color patch and calculates the spot color replacement LUT based on the colorimetric value of the color patch. However, the present invention is not limited to this, and it is possible to adopt a form in which color information is acquired using a color prediction model.

  In the above-described embodiment, the spot color replacement LUT creation unit 110 (see FIG. 3) creates a replacement table (LUT) (replacement information) indicating the ratio of replacement of the CMY basic color signal values to the spot color signal values. However, the present invention is not limited to this, and it is also possible to create a function (replacement information) indicating the ratio of replacement from the CMY basic color signal value to the spot color signal value.

  In the above-described embodiment, the mode in which the color patch output from the image forming unit 6 is read using the image reading device 4 has been described. However, the present invention is not limited to this, and a dedicated reading unit separate from the image reading device 4. (A colorimeter, a color scanner, or the like) may be provided, and the color patch may be read using the reading unit.

  The program for executing the processing procedure in the above-described embodiment can be provided by being incorporated in advance in a storage unit such as a ROM of the image processing apparatus. Further, the above-described program can be provided by being stored in a computer-readable storage medium as a file in an installable or executable format. Furthermore, the above-described program can be provided or distributed via a network such as the Internet.

  Moreover, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

1 Image processing device (multicolor printer)
4 Image reading device (reading means, colorimetric means)
6 Image forming unit (image forming device, multicolor printer)
10 Controller (Information processing device)
100 Image Processing Unit 110 Spot Color Replacement LUT Creation Unit (Color Information Acquisition Unit, Replacement Information Creation Unit)
110a Color patch generator (output means)
110b Color patch colorimetry unit (color information acquisition means)
110c Spot color replacement LUT calculation unit (replacement information creation means)
120 color separation processing unit 130 total amount regulation processing unit (replacement processing means)

Japanese Patent No. 4412733

Claims (8)

Color information acquisition means for acquiring color information of a color reproduced with a single special color and a color reproduced with a mixed color of a plurality of basic colors huewise adjacent to the special color;
Based on the color information acquired by the color information acquisition means, replacement information creation means for creating replacement information indicating a ratio of replacement from the signal values of a plurality of basic colors to signal values of spot colors;
When outputting based on an image signal composed of a plurality of basic colors and special colors, if the sum of the signal values of each color of the image signal exceeds a set limit value, the replacement created by the replacement information creating means An image processing apparatus comprising: replacement processing means for replacing signal values of a plurality of basic colors with signal values of spot colors based on information.   The replacement information creation means searches the color information acquired by the color information acquisition means for a color signal value of a combination that minimizes the color difference between a mixed color of a plurality of basic colors and a single special color, and the searched color signal The image processing apparatus according to claim 1, wherein replacement information indicating the replacement ratio is created based on a value.   The replacement processing means, based on the replacement information created by the replacement information creating means, performs a replacement process for replacing the signal values of a plurality of basic colors with signal values of spot colors, so that the sum of the signal values does not exceed the limit value. 3. The image processing apparatus according to claim 1, wherein when the number exceeds, the total of the signal values is adjusted so as to be within the range of the limit value. Output means for outputting a color patch composed of a single spot color and a color patch composed of a mixture of a plurality of basic colors huewise adjacent to the spot color;
Color information acquisition means for reading each color patch output by the output means and acquiring color information of a mixed color of the special color and the plurality of basic colors;
Based on the color information acquired by the color information acquisition means, replacement information creation means for creating replacement information indicating a ratio of replacement from the signal values of a plurality of basic colors to signal values of spot colors;
When outputting based on an image signal composed of a plurality of basic colors and special colors, if the sum of the signal values of each color of the image signal exceeds a set limit value, the replacement created by the replacement information creating means An image forming apparatus comprising: replacement processing means for replacing signal values of a plurality of basic colors with signal values of spot colors based on information.   The replacement information creation means searches the color information acquired by the color information acquisition means for a color signal value of a combination that minimizes the color difference between a mixed color of a plurality of basic colors and a single special color, and the searched color signal The image forming apparatus according to claim 4, wherein replacement information indicating the replacement ratio is created based on a value.   The replacement processing means, based on the replacement information created by the replacement information creating means, performs a replacement process for replacing the signal values of a plurality of basic colors with signal values of spot colors, so that the sum of the signal values does not exceed the limit value. 6. The image forming apparatus according to claim 4, wherein, if it exceeds, the total of the signal values is adjusted to fall within the range of the limit value. Computer
Color information acquisition means for acquiring color information of a color reproduced with a single special color and a color reproduced with a mixed color of a plurality of basic colors huewise adjacent to the special color;
Based on the color information acquired by the color information acquisition means, replacement information creation means for creating replacement information indicating a ratio of replacement from the signal values of a plurality of basic colors to signal values of spot colors;
When outputting based on an image signal composed of a plurality of basic colors and special colors, if the sum of the signal values of each color of the image signal exceeds a set limit value, the replacement created by the replacement information creating means A program that functions as replacement processing means for replacing signal values of a plurality of basic colors with signal values of spot colors based on information. An image processing method executed by an information processing apparatus,
Obtaining color information of a color reproduced with a single special color and a color reproduced with a mixed color of a plurality of basic colors huewise adjacent to the special color;
Based on the acquired color information, create replacement information indicating a replacement ratio of signal values of a plurality of basic colors to signal values of spot colors,
When outputting based on an image signal composed of a plurality of basic colors and special colors, if the sum of the signal values of each color of the image signal exceeds a set limit value, a plurality of values are generated based on the created replacement information. Image processing method for replacing the signal value of the basic color with the signal value of the spot color.

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