JP2008193496A - Image processing apparatus, program, and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain color gamut outline of a target device with high visibility of image even when the total amount is limited in the color space of the target device. <P>SOLUTION: The total amount limiting device outline generation part 36 changes color gamut outline without the total amount limitation in the outline changing part 48 with the total amount limitation of a total amount limitation setting part 38 and adjusts steep outline point of color gamut outline in the outline adjusting part 50. By this adjustment, the total amount of color material having reached the total amount limitation is decreased and variation from the total amount of adjacent color material is decreased. Consequently, the outline point of color gamut outline is adjusted to form smooth color gamut outline. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image processing apparatus, a program, and a method for calculating a color gamut outline of a target device.

  When an image is captured by an input device or displayed or printed by an output device, the color range that can be captured and the color range that can be reproduced are limited depending on the characteristics of each device. For example, when an image is output by an image forming apparatus, if the output instructed image includes a color that cannot be reproduced, conversion processing (color gamut compression processing or color correction processing) for keeping this color within a reproducible color range ) Is performed. In order to execute such conversion processing, it is effective to obtain a color range outline (color gamut outline) that can be reproduced by each device. In addition to color gamut compression processing, the color gamut outline is also used for various purposes such as when evaluating the color reproduction of a device.

  In a device such as an image forming apparatus, an image is formed using four or more color materials including black (K), and the color of the image is expressed in a device color space having the colors of these color materials as elements. A CMYK color space or the like is known as an example of the device color space. Further, in the color conversion processing, it is desirable to perform processing in a color space (device-independent color space) that does not depend on the characteristics of individual devices. CIELAB color space, CIEXYZ color space, and the like are known as examples of device-independent color spaces.

  The color in which an image is actually formed is expressed in the device color space, but when conversion processing is performed using the device-independent color space, color space conversion is performed between the device-independent color space and the device color space. There is a need. For example, processing that requires a device color gamut such as color gamut compression processing is performed in a device-independent color space. Therefore, it is necessary to obtain the device color gamut in the device-independent color space. This can be achieved by obtaining a color gamut outline having a corresponding relationship in each of the device color space and the device-independent color space.

  However, when determining the color gamut of a device having four or more colors such as the CMYK space, the three colors of CMY and K are not independent, and thus are composed of primary colors (CMY) and secondary colors (RGB). In the gamut outline, it is not necessary to consider K, but in the tertiary color, CMY and K overlap, and the influence of K cannot be ignored. Therefore, the color gamut outline obtained by conversion from the CMY color space to the device-independent color space cannot be used as it is.

As a technique for solving this, there is known an image processing apparatus that can obtain a color gamut outline in another color space when a restriction is provided in the device color space at high speed, low cost, and high accuracy (for example, , See Patent Document 1). In this technology, when the total amount is limited in the device color space, in order to obtain the color gamut outline in the device-independent color space, the color gamut outline is determined on the device color space, and this is determined by the color conversion model. Converting to a dependent color space.
JP 2005-63093 A

  However, obtaining the color gamut outline in another color space when the restriction is provided in the device color space simply gives the restriction, so that the shape of the color gamut outline in the other color space is complicated. Therefore, when it is converted into a device color space using this, the color reproduction of the image may deteriorate. For example, when the lightness is low, the shape of the color gamut outline in the device-independent color space may change locally (for example, glitches), and lightness inversion or discontinuous gradation may occur in the vicinity. In some cases, an image with a deteriorated appearance of an image is provided.

  The present invention has been made in consideration of the above facts, and an image processing apparatus and program capable of calculating the color gamut outline of a target device with a good image appearance even when the total amount is limited in the color space of the target device And to obtain a method.

  According to the first aspect of the present invention, there is provided a generating means for generating an outline point group constituting a color gamut outline in a color space of a target device capable of expressing a plurality of colors based on a plurality of color elements, and each color in the color space of the target device. A setting unit for setting a total amount limit for limiting the total sum of the elements; a changing unit for changing the outline point group generated by the generating unit according to the total amount limit set by the setting unit; and a sum for each input color element The sum total of each color element in which the change rate variation of the total amount characteristic representing the relationship of the sum of the color elements after the total amount restriction exceeds a predetermined value is obtained, and the total obtained is less than the sum of the color elements after the total amount restriction. Adjusting means for adjusting the outline point group changed by the changing means.

  According to the present invention, each color element is adjusted by the adjusting means so that the outline shape is smoothed by the adjusting means for the outline point group changed according to the total amount restriction by the changing means from the color gamut outline in the color space of the target device generated by the generating means. . That is, the sum total of each color element in which the change rate variation of the total amount characteristic representing the total amount of each color element after the total amount restriction with respect to the total sum of the input color elements exceeds a predetermined value is obtained. The outline point group is adjusted so that the obtained sum is less than the sum of the color elements after the total amount restriction. As a result, a sharp contour change that occurs when the total amount is restricted can be suppressed, and a contour point group that suppresses image appearance deterioration and the like can be obtained in the color space of the target device.

  According to a second aspect of the present invention, in the image processing apparatus according to the first aspect, the adjustment unit converts the outline point group in the color space of the target device into an outline point group constituting a color gamut outline in another color space. A color conversion means, a determination means for determining that a change rate variation of a color gamut outline in another color space exceeds a specified value based on an outline point group in another color space converted by the color conversion means; And the change rate variation of the color gamut outline in the different color space is less than a specified value for the adjusted outline point group based on the outline point group converted by the color conversion means and the determination result of the determination means The outline point group changed by the changing means is adjusted.

  According to the present invention, when each color element is adjusted so that the outline shape is smooth, whether the outline shape is smooth is different from the color space of the target device (for example, it does not depend on the target device). This is determined by the outline shape in the device-independent color space. For this reason, the adjustment means includes a color conversion means and a determination means, and based on the outline point group converted by the color conversion means and the determination result of the determination means, the adjusted outline point group is a color gamut outline in another color space. The outline point group changed by the changing means is adjusted until the change rate fluctuation becomes equal to or less than a specified value (for example, until smooth). The color conversion means converts the outline point group in the color space of the target device into an outline point group constituting a color gamut outline in another color space (for example, a device-independent color space that does not depend on the target device). The determination unit determines that the change rate variation of the color gamut outline in another color space exceeds a specified value based on the outline point group in another color space converted by the color conversion means. In this way, the outline shape is determined in a color space different from the color space of the target device (for example, a device-independent color space that does not depend on the target device), so that the steep outline shape that occurs when the total amount is limited The change can be determined without depending on the color space of the target device, and an outline point group in which deterioration of the appearance of the image is suppressed can be obtained in the color space of the target device.

  According to a third aspect of the present invention, in the image processing apparatus according to the first or second aspect, the adjustment unit is configured such that the sum of the color elements when the total amount limit set by the setting unit reaches the total amount limit The outline point group changed by the changing means is adjusted so as to be less than the total sum of the color elements.

  According to the present invention, the outline point group is adjusted so that the total sum of the color elements when reaching the set total amount limit is less than the total sum of the color elements after the total amount limit. It is known that the appearance of the image changes greatly when reaching the sum total of each color element when the total amount limit is set, and by reducing the sum at this time, it reaches the set sum The sum of each color element can be made slow.

  According to a fourth aspect of the present invention, in the image processing apparatus according to the third aspect, the adjusting means independently adjusts the color elements such that the sum of the color elements is less than the sum of the color elements after the total amount restriction. It is characterized by adjusting.

  According to the present invention, each color element is adjusted independently in limiting the total amount. Thereby, each color element can be selectively adjusted.

  According to a fifth aspect of the present invention, in the image processing apparatus according to any one of the first to fourth aspects, the color space of the target device is a color value corresponding to a color material amount of each color of CMYK of the image forming device. 4 or more device color spaces, and the adjustment unit prohibits adjustment of the color material amount of any one of the CMYK colors.

  According to the present invention, a device color space of four or more colors can be set, so that a color gamut outline for easily forming a multicolor image can be created for image formation.

  According to a sixth aspect of the present invention, in the image processing apparatus according to the fifth aspect, the one color material amount is a K color material amount.

  According to the present invention, since the amount of the K color material is adjusted, it is possible to adjust to the device color space in which the K color is dominant.

  According to a seventh aspect of the present invention, there is provided a generating means for generating a contour point group constituting a color gamut contour in a color space of a target device capable of expressing a plurality of colors based on a plurality of color elements, and a color of the target device Setting means for setting a total amount limit for limiting the total sum of each color element in the space; changing means for changing the outline point group generated by the generating means according to the total amount limit set by the setting means; and each input color element The sum total of each color element in which the change rate variation of the total amount characteristic representing the relationship of the sum of each color element after the total amount restriction with respect to the sum of the total amount exceeds a predetermined value is obtained, and the obtained sum is less than the sum of each color element after the total amount restriction Thus, the image processing program functions as an adjusting unit that adjusts the outline point group changed by the changing unit.

  According to the present invention, since the computer functions as each of the above means, the computer executes the image processing program, so that the computer functions as the image processing apparatus according to claim 1. Similarly, a sharp outline change that occurs when the total amount is restricted can be suppressed, and an outline point group that suppresses deterioration of image appearance or the like can be obtained in the color space of the target device.

  The invention according to claim 8 is an image processing method for calculating a color gamut outline of a target device, wherein an outline point group constituting a color gamut outline in a color space of the target device capable of expressing a plurality of colors based on a plurality of color elements is obtained. A generating step for generating, a setting step for setting a total amount limit for limiting the total sum of each color element in the color space of the target device, and an outline point group generated by the generating unit according to the total amount limit set by the setting unit. A change step to be changed and a sum of each color element in which the change rate variation of the total amount characteristic representing the total sum of each color element after the total amount restriction with respect to the total sum of each input color element exceeds a predetermined value is obtained. An adjusting step of adjusting the outline point group changed by the changing means so as to be less than the total sum of the respective color elements after the total amount restriction.

  According to the present invention, since the color gamut outline of the target device is calculated in each step, it functions as the image processing apparatus according to claim 1, and the total amount is limited in the same manner as the image processing apparatus. A sharp outline change that sometimes occurs can be suppressed, and an outline point group that suppresses deterioration of image appearance or the like can be obtained in the color space of the target device.

  As described above, according to the present invention, an outline point group changed according to the total amount restriction by the changing means from the color gamut outline in the color space of the target device generated by the generating means so that the outline shape becomes smooth by the adjusting means. Since each color element is adjusted, it is possible to suppress the steep outline shape change that occurs when the total amount is limited, and to determine the outline point group that suppresses the deterioration of the appearance of the image in the color space of the target device. Has an excellent effect.

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a color management system 10 including an image processing apparatus to which the present invention can be applied. The color management system 10 can be built in an image forming apparatus represented by a color copying machine.

  As an image forming apparatus, it is possible to use a configuration in which a color image is formed by electrophotographic method using toners of CMYK colors and then transferred and fixed on paper. However, the present invention is not limited to this. It is also possible to adopt a configuration in which an image is formed on the paper by another method such as an ink jet method in which a color image is formed on the paper by ejecting the ink from the nozzles as recording droplets. Furthermore, the present configuration can be adopted not only for the four colors of CMYK but also for multicolor printing. 1 shows a functional block diagram of the color management system, the color management system 10 has a CPU of a computer (not shown) or a CPU built in a printer connected to the computer via a communication line. This is realized by executing the processing program.

  As shown in FIG. 1, the color management system 10 includes an input side device 12, a color gamut management unit 14, and an output side device 16. The output side device 16 is a device that forms an image based on input image data, and forms (prints) a color image on a sheet using, for example, an image forming apparatus represented by a color copying machine (for example, color materials of CMYK colors). )) Is an example. The output device 16 may function as an image data output unit that outputs image data to the image forming apparatus.

  The input-side device 12 is a device to which image data for forming an image on the output-side device, for example, image data representing an image to be printed is input. The input-side device 12 is a scanner that reads an image or another computer that outputs image data (for example, An example is a device that inputs image data of a color image expressed in colors in RGB or CMYK color spaces. The input side device 12 may function as an image data input unit that inputs image data from the scanner or another computer.

  The color gamut management unit 14 is a functional unit that converts the image data input from the input side device 12 into image data for the output side device 16 having a color gamut that matches or is different from that of the input side device 12. The color gamut management unit 14 includes an input side color conversion unit 18, a color gamut conversion unit 20, and an output side color conversion unit 22. The color gamut conversion unit 20 is connected to an output side color gamut outline definition unit 26 in order to grasp the color gamut outline of the output side device 16 for color gamut conversion.

  When the color space of the image data input from the input side device 12 is different from the color space used in the subsequent stage, the input side color conversion unit 18 performs a color space conversion process to the color space used in the subsequent stage. Here, the processing from the input side color converter 18 to the output side color converter 22 uses a device-independent color space, for example, a color space such as CIE-L * a * b *. Here, it is assumed that the image data input from the input side device 12 is CMYK image data. Therefore, the input side color conversion unit 18 performs conversion from the CMYK color space to the L * a * b * color space. The conversion from the CMYK color space to the L * a * b * color space is performed based on the ICC profile, for example, with an ICC profile describing image device characteristics attached thereto. If the image data is image data in a device-independent color space, the processing in the input side color conversion unit 18 is not necessary, and the input side color conversion unit 18 may be omitted.

  When the color space of the input image data is different from the color space used in the subsequent stage, the output side color conversion unit 22 performs the color space conversion process to the color space used in the subsequent stage. For example, when the output device 16 is a printer or the like, image data in the YMC color space or the YMCK color space is often received. In such a case, the output side color conversion unit 22 performs a color space conversion process from a device-independent color space, for example, a color space such as CIE-L * a * b *, to a YMC color space or a YMCK color space.

  That is, a device-independent color space is used to perform conversion processing such as color correction processing and color gamut compression processing, and a device color space is used when an image is actually formed. For this reason, it is necessary to perform color space conversion between the device-independent color space and the device color space. As a procedure for creating a color conversion coefficient for this color space conversion, for example, modeling is performed in the forward direction from the CMYK color space, which is a device color space, to the CIELAB color space, which is a device-independent color space, and vice versa. Thus, a color conversion coefficient for performing conversion from the CIE-L * a * b * color space, which is a device-independent color space, to the CMYK color space, which is a device color space, is obtained. As a method for creating a model, for example, it is described in “Makoto Sasaki and Hiroaki Ikegami,“ Proc. Of International Congress of Imaging Science 2002 ”, (2002), p.413-141” (hereinafter referred to as technical literature). A method or the like can be used.

  The color gamut conversion unit 20 converts the image data of the input-side device 12 converted into the device-independent color space into image data of the output-side device 16 in the device-independent color space. That is, when the color based on the image data in the color space of the input side device 12 cannot be reproduced as the color in the color space of the output side device 16, the output side color reproducible area (color gamut outline of the output side device) is used. Then, conversion processing (color gamut compression processing and color correction processing) is performed for keeping the color of the input side device 12 within the color range reproducible by the output side device 16.

  Although detailed description is omitted, this conversion process includes various predetermined conversion processes by known methods such as hue maintenance, brightness maintenance, and saturation maintenance. An example is the technology already filed by the applicant. In order to perform this conversion processing in the color gamut conversion unit 20, the data on the color gamut outline is stored in advance in the input side color gamut outline definition unit 24 and the output side color gamut outline definition unit 26, respectively.

  In this embodiment, a color gamut outline in the case where a total amount restriction of a plurality of color elements is provided in the device color space of the output side device 16 is used. For this reason, in this embodiment, the output side color gamut outline defining unit 26 is configured as an image processing apparatus 30 (FIG. 2) for obtaining a color gamut outline, which will be described in detail later.

  As shown in FIG. 2, the image processing apparatus 30 that executes processing for holding output-side color gamut outline data in the output-side color gamut outline definition unit 26 includes a device outline generation unit 32, a limit amount setting unit 34, a total amount A restricted device outline generation unit 36, a total amount restriction setting unit 38, a color conversion unit 42, and a color gamut outline generation unit 46 are provided. Although FIG. 2 shows a functional block diagram of the image processing apparatus 30, the image processing apparatus 30 includes a CPU of a computer (not shown) or a CPU built in a printer connected to the computer via a communication line. This is realized by executing a predetermined processing program.

  In this embodiment, as an application example of the present invention, a color gamut outline obtained by limiting the total amount of a plurality of color elements in the device color space of the output side device 16 is used. Therefore, in the following description, the color space of the output side device 16 is made to correspond as the color space of the target device, and the color space of the color gamut conversion unit 20 is made to correspond to another color space. The color space of the target device and another color space are not limited. As an example, the color space of the target device is a CMYK color space (primary colors are C, Y, M, K), and another color space is a device. The CIE-L * a * b * color space that is an independent color space is adopted.

  The device outline generation unit 32 generates an outline point group constituting a color gamut outline in the color space of the target device restricted by conditions such as the maximum restriction amount and the minimum restriction amount specified by the restriction amount setting unit 34. At this time, the points on the color gamut outline in the color space of the target device to be extracted as the outline point group are arbitrary. For example, at least vertices constituting the color gamut outline and points on each axis connecting the vertices should be extracted. At this time, the points on each axis are extracted at equal intervals, and the gamut outline is unequally allocated so that the outline points generated by the gamut outline generation unit 46 described later can be easily used. The top point may be extracted. Further, contour points can be extracted at equal intervals or evenly on the color gamut contour surface. For example, the color gamut outline may be expressed by a polygon or the like. In such a case, when the outline point group is generated by the device outline generation unit 32, the relationship between the outline points in the extracted outline point group is expressed. Build it. Since the construction of the relationship between the outline points is performed in the color space of the target device, it can be easily performed.

  The limit amount setting unit 34 accepts designation of an arbitrary condition in the color space of the target device as necessary, and sets the accepted condition. Although the conditions for accepting are arbitrary, for example, conditions such as the maximum restriction amount and the minimum restriction amount for each color can be accepted.

  The total amount restriction device outline generation unit 36 is configured to generate a color gamut outline in the case where the total amount of the color material amount is restricted in the color gamut of the target device. Here, an example is shown in which the outline point group is generated by the device outline generation unit 32 and then the outline point group is changed to meet the total amount restriction condition. However, the entire outline point group is regenerated. Also good.

  The color conversion unit 42 selects an outline point group of another color space (here, an outline of the CIE-L * a * b * color space) from the outline point group of the color space of the target device changed by the total amount restriction device outline adjustment unit 36. Point cloud). For this conversion, a forward model of the target device can be used.

  The color gamut outline generation unit 46 selectively extracts, for example, outline points suitable for use from the outline point group generated by the color conversion unit 42, and is connected by only a part of the extracted outline point groups. Generate data. This makes it possible to obtain color gamut contour data that is easy to use.

  The total amount restriction setting unit 38 receives the designation of the total amount restriction that restricts the sum of each color element in the color space of the target device, and passes it to the total amount restriction device outline generation unit 36. The total amount restriction device outline generation unit 36 changes the outline point group generated by the device outline generation unit 32 according to the total amount restriction specified by the total amount restriction setting unit 38. Note that the color gamut outline generation unit 46 selectively extracts, for example, outline points suitable for use from the outline point group generated by the color conversion unit 42 in response to the designation of the total amount restriction, and extracts a part of the extracted outlines. Generates color gamut outline data connected only by point clouds.

  The color gamut outline data generated by the color gamut outline generation unit 46 is connected to be input to the total amount restriction device outline generation unit 36. Note that the color gamut outline generation unit 46 has a memory for temporarily storing the generated color gamut outline data, and finally outputs the data to the color gamut conversion unit 20.

  The total amount restriction device outline generation unit 36 includes an outline change unit 48, an outline adjustment unit 50, and a determination unit 52. The outline change unit 48 restricts the outline point group generated by the device outline generation unit 32 when the total amount of color material set by the total amount restriction setting unit 38 is restricted in the color gamut of the target device. This is a functional unit that changes the outline point group to meet the conditions. The outline adjustment unit 50 is a functional unit that adjusts the color gamut outline data corresponding to the device outline that is designated by the total amount restriction changed by the outline change unit 48 so that the color gamut outline is smooth.

  The outline adjustment unit 50 uses a part of the data of the color gamut outline that has been designated by the total amount restriction changed by the outline change unit 48, and uses the position of the outline points that constitute the color gamut outline, the inclination of lines and surfaces, Adjust the shape data representing the position. This adjustment is made according to the determination result of the determination unit 52. The determination unit 52 has a determination condition such as whether or not the inclination of adjacent ridge lines of the outline points constituting the color gamut outline generated by the color gamut outline generation unit 46 falls within a predetermined range. As an example of the adjustment trend, emphasis on gradation is an example. To achieve this, as an example of the determination condition described above, the inclination of adjacent ridge lines of outline points constituting the color gamut outline falls within a predetermined range. Conditions can be adopted.

  Next, each of the above configurations will be described in more detail. First, the device outline generation unit 32 will be described. In the following description, it is necessary to consider the upper half of the color gamut outline where the lightness is higher than the pure color in the color gamut outline in the device-independent color space and the K does not need to be considered, and the lightness is low. The part of the outer gamut is called the lower half.

  FIG. 3 is an explanatory diagram of an example of the color gamut outline in the color space of the target device. FIG. 3A shows the upper half of the CMYK color space, and FIG. 3B shows the lower half of the CMYK color space. In the case of a four-dimensional color space, the color gamut outline in the color space of the target device is a 12-sided polyhedron combining the figures shown in FIGS. 3 (A) and 3 (B). Here, for simplicity, CMYK is assumed to be 0 to 100%.

  In the upper half shown in FIG. 3A, K is always 0%. Further, the center is a point where CMYK is 0%, and the sides from the center to the vertices C, M, and Y are point sequences in which only the respective color elements change from 0 to 100%. In this side, the other three elements are zero. The vertex CY (= G (green)) is a point at C = Y = 100% (M = K = 0%), and the side C-CY remains at C = 100% (M = K = 0%), Y Is a point sequence varying from 0 to 100%. Similarly, side Y-CY is a point sequence in which C changes from 0 to 100% while Y = 100%. The same applies to the vertex MY (= R (red)) and the vertex CM (= B (blue)). Further, the plane OC-CY-Y is a set of points with M = 0%. The other two surfaces are also a set of points with C = 0% and Y = 0%. That is, the upper half of the color gamut outline in the color space of the target device is a set of points where K and any one of the other colors are 0%.

  In the lower half shown in FIG. 3B, the peripheral vertices C, CY, Y, MY, M, and CM are the same as those in FIG. The central CMYK is a point where C = M = Y = K = 100%. Further, the vertex CK is a point where C = K = 100% and M = Y = 0%. Similarly, the vertex YK is a point where Y = K = 100% and M = C = 0%, and the vertex MK is M = K. = 100%, C = Y = 0%. The vertex CYK is a point where C = Y = K = 100% and M = 0%. Similarly, the vertex MYK is a point where M = Y = K = 100% and C = 0%, and the vertex CMK is C = M = K = 100% and Y = 0%.

  The side CMYK-CYK is a point sequence in which M changes from 0 to 100% when C = Y = K = 100%. Similarly, the side CMYK-MYK is a point sequence in which C changes from 0 to 100% when M = Y = K = 100%, and the side CMYK-CMK has C = M = K = 100% and Y is 0-100. It is a point sequence that changes to%. Side CYK-CY is a point sequence in which K = Y = 100%, M = 0%, and K changes from 0 to 100%. Similarly, the side MYK-MY is a point sequence where M = Y = 100% and C = 0% and K changes from 0 to 100%, and the side CMK-CM is C = M = 100%, Y = 0% And K is a point sequence varying from 0 to 100%. Further, the side CK-C is a point sequence in which K changes from 0 to 100% when C = 100% and M = Y = 0%. Similarly, the side YK-Y is a point sequence in which Y = 100%, M = C = 0% and K changes from 0 to 100%, the side MK-M is M = 100%, C = Y = 0% and K Is a point sequence varying from 0 to 100%.

  Furthermore, the plane CMYK-CYK-CK-CMK is a set of points where C = K = 100%. The other two surfaces are also a set of points where Y = K = 100% and M = K = 100%. That is, these three surfaces are a set of points where K and any one of the other colors are 100%. The plane C-CK-CYK-CY is a set of points where C = 100% and M = 0%. Similarly, the plane CYCYK-YK-Y is a set of points where Y = 100% and M = 0%, the plane Y-YK-MYK-MY is a set of points where Y = 100% and C = 0%, and the plane MY− MYK-MK-M is a set of points with M = 100% and C = 0%, plane M-MK-CMK-CM is a set of points with M = 100%, Y = 0%, and plane CMCMK-CK-C is A set of points where C = 100% and Y = 0%. That is, these six surfaces are a set of points where any one color of C, M, and Y is 100% and any one color is 0%.

  In this way, the points of the color gamut outline in the color space of the target device can be represented by a plane as shown in FIG. The points constituting the color gamut outline as described above are points that satisfy a predetermined condition, and points other than the points that satisfy the above condition are points inside the color gamut.

  Note that the outline point group in the color space of the target device to be generated is extracted so as to be evenly arranged on the sides and surfaces shown in FIG. 3 or unevenly considering the arrangement in the device-independent color space. be able to. In any case, one or more outline points may be selected as the outline point group in the color space of the target device, and only a necessary region may be selected.

  Next, the limit point setting unit 34 and the outline point group generated by the device outline generation unit 32 when conditions are set by the limit amount setting unit 34 will be described. For example, conditions such as the maximum limit amount and the minimum limit amount of arbitrary color elements can be added in the color gamut simulation of the target device. Here, as an example, black K is described as a restriction target.

  When the maximum amount limit Ka and the minimum amount limit Km of the K amount are specified in the limit amount setting unit 34, the device outline generation unit 32 generates the outline group of the target device as described above. Set the limit range of K amount at. The limitation on the maximum amount is dealt with by changing the vertex configuration in FIG. 3B from 100% to Ka%. On the other hand, the minimum amount restriction affects the sides and faces of the figure in FIG. 3B, but the color gamut outline may be a similarity transformation, so that an outline point group in the color space of the target device can be easily created. . Visually, it can be considered that the length of each side shown in FIG.

  In the above description, the case where the maximum limit amount and the minimum limit amount are added to black K has been described as an example. However, since individual color elements can be handled independently, the same applies to other color elements as well. Can be added. Specifically, for color elements other than K, an outline point group in the color space of the target device can be generated by controlling the lower half range and the upper half range. Of course, when no limiting condition is added, an outline point group may be generated from the color gamut outline shown in FIG.

  Next, the color conversion unit 40 will be described. In order for the color conversion unit 40 to perform color conversion from the outline point group to the outline point group in the CIE L * a * b * color space, it is necessary to obtain a color profile (color conversion coefficient) in advance. This may be a definition formula determined in the standard or one obtained in the past. Further, the coefficient may be created by a method using a neural network, a linear regression model, principal component analysis, or the like, and a color patch or the like may be directly output and measured by a measured value. A 3D LUT (three-dimensional lookup table) that stores these correspondences in advance may be used. Here, the printer model in the forward direction was created by using the method described in the above technical document. Using this printer model, the outline point group in the CIE L * a * b * color space is obtained using the outline point group in the color space of the target device described above as an input. By performing color conversion using the forward model in this way, the outline point group can be obtained with high accuracy.

  FIG. 4 is a schematic diagram of a color gamut outline composed of outline points obtained in the CIE L * a * b * color space. Each vertex, each side, and each surface shown in FIG. 3 is converted into each vertex, each side, and each surface shown in FIG. Each side and each surface are not limited to straight lines and planes in the CIE L * a * b * color space, and are generally configured as curves and curved surfaces.

  As described above, it is possible to obtain the outline point group constituting the color gamut outline of the target device in the device-independent color space (CIE L * a * b * color space). Such outline points can be used even if the color space of the target device is not a CMYK color space or a multicolor such as hexachrome expressed in six colors, and the present invention is effective with a multicolor. .

  On the other hand, in order to visualize, evaluate, quantify, etc. the color gamut of the target device in the device-independent color space obtained as described above, the outline point group is used as a 3D polygon. Easy to do. Therefore, the color gamut outline generation unit 44 connects the outline point groups in the CIE L * a * b * color space as vertices to form a polygon by forming a surface. Thus, the color gamut outline of the target device can be visualized three-dimensionally using a general-purpose visualization tool. Further, when creating three-dimensional information in which outline points are connected, there are cases where it is desired to arrange vertices at equal intervals or configure a detailed color gamut, excluding unnecessary areas. In such a case, a color gamut outline may be configured from a part of outline points selected from the outline point group obtained by the color conversion unit 40.

  Polygon generation is configured as a relationship between outline points when the outline point group is generated by the device outline generation unit 32, and between outline points when the outline point group is generated by the color conversion unit 40. It is also possible to hold the relationship as a relationship between corresponding outline points. Thus, it is possible to easily form a polygon in the color space of the target device without forming the polygon in the device-independent color space.

  In this way, by generating outline points in the color space of the target device and converting them into outline points in the device-independent color space using a forward model, exploratory iterative processing is unnecessary. It is possible to obtain a color gamut outline in a device-independent color space with high speed and simplicity.

Next, the total amount limited device outline generation unit 36, the color conversion unit 42, and the color gamut outline generation unit 46 will be described. First, the total amount G of the color material is designated in the total amount restriction setting unit 38. That is,
C + M + Y + K ≦ total amount G (1)
C + M + Y + K> Total amount G (2)
Specify one of the conditions. Here, the expression (1) is used.

After the outline point group is generated by the device outline generation unit 32, the outline point group in the color space of the target device is set so that the total amount limit device outline generation unit 36 does not exceed the total amount G with respect to the generated outline point group. Update. Specifically, it is processed in the outline changing unit 48 of the total amount restriction device outline generating unit 36. At this time, if an arbitrary outline point of the outline point group satisfies the condition of the total amount G (Equation (1)), nothing is performed. If not, processing for limiting the total amount is performed. The processing for limiting the total amount can be realized, for example, by fixing the color material amount of one color and keeping the composition ratio of the other color material amounts constant to match the total amount. That is, when the fixed color material amount is I, the outline points of the device are (I, A1, A2, A3), and the outline points of the devices that have been subjected to the total amount restriction are (I, A1 ′, A2 ′, A3 ′) The device outline points A1 ′, A2 ′, A3 ′ are Ai ′ = (Ai × (GI)) / (A1 + A2 + A3) (3)
{However, i = 1, 2, 3}
Is obtained.

  There are the following two regulation methods depending on the color material to be fixed at this time. In the regulation method 1, K is fixed and the ratio of C: M: Y is fixed and adjusted to the total amount G. That is, in this method, the fixed amount I in equation (3) is the K amount and A1, A2, and A3 are the CMY amounts. The regulation method 2 is a method in which one of the maximum values among C, M, Y, and K is fixed and the ratio of the other three colors is fixed and adjusted to the total amount G. For example, if the color material indicating the maximum amount is C, the fixed amount I in equation (3) may be the C amount, and A1, A2, and A3 may each be the KMY amount.

  In this way, the outline changing unit 48 can obtain an outline point group that satisfies the total amount restriction. Note that the color represented by each outline point is visually different due to the total amount limitation as described above, but it is still a point on the color gamut outline that satisfies the total amount limitation in the color space of the target device. . Therefore, there is no problem for the purpose of obtaining the color gamut outline.

  In the above description, the outline point group that satisfies the total amount restriction condition in proportion to the fixed amount is obtained, but in addition, the outline point group that satisfies the total quantity restriction condition can be obtained by various methods. For example, in the device color space, the total amount restriction is a process for generating a new surface, or is the same as the enlargement / reduction conversion of the surface that performs the total amount restriction, and generates and controls the surface subject to the total amount restriction. But you can get the same effect. When performing the total amount restriction process, care must be taken so that the relationship between the outline points of the outline point group before the change and the relation between the outline points of the outline point group after the change are not different. is there.

  The outline point group changed by the outline change unit 48 of the total amount limiting device outline generation unit 36 is sent to the outline adjustment unit 50, and the outline point group is adjusted so as to be a smooth outline based on the determination result of the determination unit 52. The outline point group adjusted by the outline adjustment unit 50 is sent to the color conversion unit 42 and converted into the outline point group of the device-independent color space in the same manner as the color conversion unit 40. As a result, the color gamut outline in the device-independent color space can be obtained. In this way, the color gamut outline in the device-independent color space that satisfies the condition of the total amount restriction can be obtained.

  The adjustment process in the outline adjustment unit 50 will be described. First, the total amount limitation in this embodiment will be described. Here, in order to simplify the description, the color element is described as the color material amount, and an example is described using the ink amount.

<Total amount restriction method>
FIG. 5 shows the color material amount after the conventional total amount limitation. Conventionally, since regulation is performed with a constant total amount limit value regardless of the input ink amount, the change suddenly occurs before and after the portion where the input ink amount reaches the total amount limit value (250% in the example of FIG. 5). Become.

  FIG. 6 is an example of the total amount limitation of the present embodiment. In the present embodiment, the total amount limit value is changed according to the input color material amount. The maximum limit value is 250% as in FIG. 5, but is smoothly changed so as not to cause an abrupt change in the vicinity of a region where the conventional change becomes abrupt. The total amount limit value in FIG. 6 is the total amount of input color material that reaches the maximum limit total amount (here, 250%): 290%, and the total amount of input color material that starts the smoothing process for limiting the color material amount: 210. % Is specified, and the ink limit amount is determined so that the interval changes smoothly.

  An example of determining the total amount limit value will be described.

First, when the total amount of input ink is Ctotal, the maximum total amount of ink is Max, the total amount of input ink at the start of the limit is Cstart, the total amount of input ink reaching the maximum total amount of ink is Cend, and the value of the total limit amount is Climit, The total amount of ink can be expressed (see FIG. 7).
1) If Ctotal ≤ Cstart,
Climit = Ctotal
2) If Cstart <Ctotal <Cend,
Climit = Cstart
+ (Max-Cstart) / (Ctotal-Cstart) / (Cend-Cstart)
This formula is a formula connecting Cstart and Cend with a straight line, and it can be made smoother by increasing the number of intermediate points.
3) If Ctotal ≥ Cend,
Climit = Max
That is, it can be understood that the value of the total limit amount changes according to the total amount of input ink. Here, the total amount limit value is Max, but the processing of the above equation can be restated as the content of the processing based on the total amount limit value. Accordingly, the outline adjusting unit 50 determines (or inputs) the maximum ink total amount Max (the value obtained by the total amount limit setting unit 38) by determining (or inputting) the input ink total amount Cstart for starting the restriction and the input ink total amount reaching the maximum ink total amount Cend. ), The adjustment for obtaining the limit total amount value Climit is executed by the above equations.

  By the way, although the relationship between the total amount of input ink (color material amount) and the total amount of ink after limiting the total amount (color material amount) can be smoothed as described above, the determination process is performed in a device space or a device-independent color space. May be performed. In this embodiment, the smoothness is determined in the device-independent color space. Next, this determination will be described. In order to simplify the following description, the device-independent color space is the C * axis indicating the saturation in the cross section obtained by cutting the color gamut along the plane including the L * axis in the CIE L * a * b * color space. A two-dimensional figure with the horizontal axis as a horizontal axis.

  As an example, FIG. 8 shows a two-dimensional figure in which the color gamut is cut along an arbitrary plane including the L * axis in the CIE L * a * b * color space, with the C * axis indicating saturation as the horizontal axis. . In FIG. 8, the color gamut outline without the total amount limitation is a line figure connecting the points Ds1-Ds2-Ds3. In addition, the color gamut outline with total amount restriction generated by the color gamut outline generation unit 46 is a line figure connecting the points Dt1-Dx-Dt2-Dt3. That is, when the total amount is restricted, the point Ds1 changes to the point Dt1. Along with this, a part of the characteristics of the points Ds1-Ds2 is changed to be a color gamut outline in which a part of the lower half of the color gamut outline with no total amount restriction is cut.

  FIG. 9 is an enlarged view of the boundary portion (Area) of the color gamut outline in which a part of the lower half of the color gamut outline without limitation on the total amount in FIG. 8 is cut. The outline point Dx (D3) at which the total amount restriction is started is included on the outline points D1 to D6 on the color gamut outline without the total amount restriction. The outline points D7 to D9 on the color gamut outline with the total amount restriction are continuous from the outline point Dx. The determination unit 52 determines whether or not the color gamut outline is smooth depending on whether or not the difference in inclination of the straight line connecting the outline points D7 and D2 before and after the outline point Dx exceeds a predetermined value. . When it is determined that it is not smooth, the outline adjusting unit 50 adjusts the outline points by adjusting the color elements as the color material amount in the color space of the device. As a result, as shown in FIG. 9, the outline point Dx ′ is adjusted, and the color gamut outline can be formed to be smooth by the outline point Dx ′ where no steep fluctuation occurs.

  Next, the operation of the image processing apparatus 30 will be described as an operation of the present embodiment. Here, a case will be described in which the processing in the total amount restriction device outline generation unit 36 in the above configuration executed in the image processing apparatus 30 is programmed and the program is executed. The computer can also function as each of the above-described components by programming the processing in each of the above-described components.

  The image processing device 30 stores a color gamut outline generation processing routine shown in FIG. 9 in a memory in advance, and this processing routine is executed according to a user instruction from an input device such as a keyboard.

  First, in step 100, the color gamut outline data in the color space of the target device generated by the device outline generation unit 32 is read, and in the next step 102, the total amount limit set by the total amount limit setting unit 38 is read. In the next step 104, the color gamut outline without the total amount restriction is changed to the color gamut outline based on the set total quantity restriction. At this point, the shape of the color gamut outline may change locally due to the total amount limitation (for example, glitches), and the appearance of the image may deteriorate due to inversion of brightness or discontinuous gradation in the vicinity. Images may be provided.

  In the next step 106, an adjustment range for suppressing a region in which a local change (for example, erosion) occurs due to the total amount restriction on the shape of the color gamut outline is set, and in the next step 108, the adjustment amount is obtained. These adjustment amounts and adjustment ranges can be obtained as follows. Obtaining the adjustment amount and the adjustment range means obtaining the above-mentioned total input ink amount Ctotal, maximum ink total amount Max, input ink total amount Cstart of restriction start, input ink total amount Cend reaching the maximum ink total amount, and limit total amount value Climit. is there.

  FIG. 11 shows the relationship between the color material amount without the total amount limitation and the relationship between the color material amount with the total amount fixed and 250% as the total amount limitation to obtain the color gamut outline connecting CYK-CMYK in FIG. Is. When the total amount is not limited, the amount of each color material changes from 0 to 100% for K color while maintaining 100% for Y color and C color. On the other hand, the color material amount whose total amount is fixed is reduced from 100% for the Y color and the C color while maintaining the increase in the K color.

  In this embodiment, paying attention to the point that the color material amount due to the conventional fixed total amount limit fixed reaches a total amount limit value (250% in the example of FIG. 11), the total amount limit value is reached. The total amount (250%) of the portion (Y: C: K = 100: 100: 50) is set as the adjustment point (maximum ink total amount Max). Then, a combination of a total color material amount within an upper limit and a lower limit (for example, immediately before and after) of a predetermined range is determined as a restriction start color material total amount (restriction start input ink total amount Cstart) and a limit reached color material total amount (input ink total amount reaching the maximum ink total amount). Cend). That is, the range from the total restriction start color material amount (restriction start input ink total amount Cstart) to the limit arrival color material total amount (input ink total amount Cend reaching the maximum ink total amount) is obtained as the adjustment range. The adjustment amount can be obtained according to the above formula.

  Since the adjustment amount is determined as the total amount of the color material, here, the K color is fixed and the adjustment amount for adjusting the Y color and the C color is obtained. In addition, the combination of the total amount of color material at the upper and lower limits of the predetermined range described above includes, for example, the combination of the total amount of color material immediately before and after the adjustment point, and in the case of a setting requiring more smoothness, There are a combination of a total amount of color material in which the predetermined total amount is reduced and a combination of an increase in total amount of color material.

  In FIG. 12, as an example of the first total amount restriction, a combination of the total color material amount immediately before and after the adjustment point (maximum ink total amount Max) is defined as a restriction start color material total amount (Cstart) and a limit reached color material total amount (Cend). As a result of obtaining the adjustment amount, and as an example of the second total amount restriction, a combination of the color material total amount of plus or minus 40% from the adjustment point (maximum ink total amount Max) is set as the restriction start color material total amount (Cstart) and the limit reaching color material. The result of obtaining the adjustment amount as the total amount (Cend) is shown.

  Next, in step 110 of FIG. 10, a verification range for verifying whether the color gamut outline is smooth in the device-independent color area when the color gamut outline is adjusted by the adjustment amount in the obtained adjustment range. Set. This setting may include at least the adjustment range. In the next step 112, color conversion is instructed by obtaining a contour point group in a device-independent color space (CIE L * a * b * color space) using the forward device model. This processing is performed in the color conversion unit 42 and the color gamut outline generation unit 46, and the total amount restriction device outline generation unit 36 sends the outline point data of the verification range set in step 110 to the color conversion unit 42. Is output.

  As a result, the color gamut outline generation unit 46 can form the color gamut outline in the device-independent color area for the color gamut outline adjusted by the adjustment amount in the adjustment range. The color gamut contour is read in the device independent color region. In the next step 116, it is determined whether or not the outline shape is good based on the color gamut outline of the verification range in the device-independent color area. This determination can be executed based on whether or not the fluctuation (change rate) of the straight line connecting the outline points in the color gamut outline of the verification range exceeds a predetermined value (or falls within the predetermined range). If the result in Step 116 is negative, the process returns to Step 106, and if the result is positive, the process proceeds to Step 118.

  FIG. 13 shows the color gamut outline within the verification range of the device-independent color space. As can be seen from the figure, when the total amount limit is fixed (thin dotted line in FIG. 13), steep fluctuations are forced at the outline point Dx, but the outline point Dx is changed (as in the first total amount limit). By adjusting (bold line in FIG. 13), a smooth color gamut outline can be obtained. Further, by enlarging the adjustment range (second total amount limitation), it is possible to obtain a color gamut outline having further smoothness.

  Next, in step 118, the outline point group including the verification range determined to have a good outline shape is defined as the final color gamut outline in the device color space, and is output to the color conversion unit 42 in the next step 120. . Thereby, the color gamut outline generation unit 46 suppresses color reproduction deterioration of the image as a smooth color gamut outline, for example, the shape of the color gamut outline in the device-independent color space changes locally at a low lightness. It is possible to provide a color gamut outline that can suppress image formation in which the appearance of an image is deteriorated by suppressing (for example, glitching) and causing an inversion of lightness or discontinuous gradation in the vicinity.

  In the above description, the aspect in which the present invention is applied in the case of performing color space conversion for converting L * a * b * values into CMYK values on the assumption that image formation is performed using color materials of CMYK colors. However, the color elements in the present invention are not limited to the above. For example, on the premise that image formation is performed using a larger number of color materials, color conversion that converts CMYK values into a greater number of color values is performed. It is also possible to apply it when performing. The present invention includes such a mode as described above. In the above description, the L * a * b * color space has been described as an example of the device-independent color space according to the present invention. However, the present invention is not limited to this, and a color appearance model such as a CAM02 space, It is also possible to apply a color space such as CIEXYZ tristimulus values or iCAM.

1 is a block diagram illustrating a schematic configuration of a color management system including an image processing apparatus to which the present invention is applicable. 1 is a block diagram illustrating a schematic configuration of an image processing apparatus to which the present invention is applicable. It is explanatory drawing of an example of the color gamut outline in the color space of an object device. It is a schematic diagram of a color gamut outline composed of outline points obtained in the CIE L * a * b * color space. It is a diagram which shows the conventional input color material total amount and the color material total amount after total amount restriction | limiting. It is explanatory drawing of a total amount restriction | limiting value changing according to an input color material amount about the total amount restriction | limiting of this embodiment. It is explanatory drawing about the process of the total amount restriction | limiting of this embodiment. It is explanatory drawing of the color gamut outline in CIE L * a * b * color space at the time of total amount restriction | limiting. FIG. 9 is a partially enlarged view of FIG. 8. It is a flowchart which shows the flow of a process of an image processing apparatus. FIG. 5 is a correspondence diagram showing a relationship between color material amounts without a total amount limitation for obtaining a color gamut outline and a relationship between color material amounts with a total amount limitation fixed with 250% as a total amount limitation. FIG. 6 is a correspondence diagram showing a relationship between a first total amount-limited color material amount and a second total amount-limited color material amount for obtaining a color gamut outline according to the present embodiment. FIG. 10 is a comparative explanatory view of the presence or absence of total amount limitation of the present embodiment and the color gamut outline in the CIE L * a * b * color space at the time of conventional total amount limitation.

Explanation of symbols

Dx ... Outline point 10 ... Color management system 12 ... Input side device 14 ... Color gamut management unit 16 ... Output side device 18 ... Input side color conversion unit 20 ... Color gamut conversion unit 22 ... Output side color conversion unit 24 ... Input side color Area outline definition section 26 ... Output side color gamut outline definition section 30 ... Image processing device 32 ... Device outline generation section 34 ... Limit amount setting section 36 ... Total amount restriction device outline generation section 38 ... Total amount restriction setting section 40 ... Color conversion section 42 Color conversion unit 44 Color gamut outline generation unit 46 Color gamut outline generation unit 48 Outline change unit 50 Outline adjustment unit 52 Determination unit

Claims (8)

Generating means for generating outline points constituting a color gamut outline in a color space of a target device capable of expressing a plurality of colors based on a plurality of color elements;
Setting means for setting a total amount limit for limiting the total sum of each color element in the color space of the target device;
Changing means for changing the outline point group generated by the generating means according to the total amount limit set by the setting means;
The sum total of each color element in which the change rate variation of the total amount characteristic indicating the relationship of the total amount of each color element after the total amount restriction to the total sum of each input color element exceeds a predetermined value is obtained, and the obtained sum is each color element after the total amount restriction Adjusting means for adjusting the outline point group changed by the changing means so as to be less than the sum of
An image processing apparatus. The adjusting means includes
Color conversion means for converting from an outline point group in the color space of the target device to an outline point group constituting a color gamut outline in another color space;
A determination unit that determines that the change rate variation of the color gamut outline in another color space exceeds a specified value based on the outline point group in another color space converted by the color conversion unit;
Including
Based on the outline point group converted by the color conversion means and the determination result of the determination means, the change until the change rate variation of the color gamut outline in the different color space becomes equal to or less than a predetermined value for the adjusted outline point group. The image processing apparatus according to claim 1, wherein the outline point group changed by the means is adjusted. The adjusting means adjusts the outline point group changed by the changing means so that the total sum of the color elements when reaching the total amount limit set by the setting means is less than the total sum of the color elements after the total amount limit. The image processing apparatus according to claim 1, wherein the image processing apparatus is an image processing apparatus. The image processing apparatus according to claim 3, wherein the adjustment unit independently adjusts the color elements such that a sum of the color elements is less than a sum of the color elements after the total amount restriction. The color space of the target device is a device color space of four or more colors corresponding to color values corresponding to the color material amounts of CMYK colors of the image forming device,
5. The image processing apparatus according to claim 1, wherein the adjustment unit prohibits adjustment of any one of the CMYK colors. The image processing apparatus according to claim 5, wherein the one color material amount is a K color material amount. Computer
Generating means for generating outline points constituting a color gamut outline in a color space of a target device capable of expressing a plurality of colors based on a plurality of color elements;
Setting means for setting a total amount limit for limiting the total sum of each color element in the color space of the target device;
Changing means for changing the outline point group generated by the generating means according to the total amount limit set by the setting means;
The sum total of each color element in which the change rate variation of the total amount characteristic indicating the relationship of the total amount of each color element after the total amount restriction to the total sum of each input color element exceeds a predetermined value is obtained, and the obtained sum is each color element after the total amount restriction Adjusting means for adjusting the outline point group changed by the changing means so as to be less than the sum of
An image processing program that functions as In the image processing method for calculating the color gamut outline of the target device,
Generating a contour point group constituting a color gamut contour in a color space of a target device capable of expressing a plurality of colors based on a plurality of color elements;
A setting step for setting a total amount limit for limiting the total sum of each color element in the color space of the target device;
A changing step of changing the outline point group generated by the generating unit according to the total amount limit set by the setting unit;
The sum total of each color element in which the change rate variation of the total amount characteristic indicating the relationship of the total amount of each color element after the total amount restriction to the total sum of each input color element exceeds a predetermined value is obtained, and the obtained sum is each color element after the total amount restriction An adjustment step of adjusting the outline point group changed by the changing means so as to be less than the sum of
An image processing method including:

Images