JP6107232B2 - Color separation processing method, color separation processing apparatus and program - Google Patents

Description

  The present invention relates to a color separation processing method, a color separation processing apparatus, and a program.

  For color image recording, three colors of cyan (C), magenta (M), and yellow (Y), or four color materials (ink, toner) obtained by adding black (K) to these are generally used. Is. However, in recent years, in order to widen the color reproduction range, there is a technology that uses inks of intermediate hues such as orange (O), green (G), and blue (B) (see, for example, Patent Document 1). The former ink is called a process ink, and the latter ink is called a special color (HiFi) ink.

  In a conventional color separation process in which C, M, and Y input signals are converted into output signals representing the recording amounts of process ink and spot color ink, the ink amount (color material recording amount) is used to fully utilize the color reproduction range. ) Is used 100%. For this reason, there has been a problem that a hue shift occurs, the outermost contour of the gamut becomes uneven, and the gradation continuity accompanying continuous changes in the input signal deteriorates.

The present invention has been made in view of the above problems,
An object of the present invention is to provide a color separation processing method, a color separation processing device, and a program that can maintain good tone continuity by using a color material recording amount up to a range that reproduces the maximum saturation. It is in.

  According to the present invention, the color material recording amount data corresponding to the outermost shell representative point of the color reproduction range of the image recording apparatus is represented by the color of the input signal representing the recording amount of the C, M, and Y color materials (hereinafter referred to as process color materials). The color material recording amount data allocated to the surface of the space cube and the interpolation calculation formula based on the allocated position and the interpolation calculation formula based on the allocation position are used, and from the input signal, the color material of the intermediate color of the process color material and the process color material (hereinafter referred to as HiFi color). In the color separation processing method for generating an output signal representing the recording amount of the material), as the color material recording amount data corresponding to the outermost shell representative point of the color reproduction range, the single color maximum color of the process color material and the HiFi color material Color material recording amount data that reproduces the degree of color, and color material recording amount data that reproduces the maximum saturation of the mixed color of the HiFi color material and one process color material that is adjacent to it in hue. Hue order around the highest saturation of The color material recording amount data that reproduces the maximum saturation of the mixed color of the two process color materials that are allocated and hued on both sides of the HiFi color material is positioned closer to the black than the maximum saturation side of the surface of the color space cube. The most important feature is to assign to the.

  According to the present invention, it is possible to maintain good gradation continuity when the CMYK input signal continuously changes.

The example of a 7-color inkjet printer reproduction color is shown. The relationship between the gamut shape when no hue shift occurs and the amount of ink shot is shown. The relationship between the gamut shape in the case where a hue shift occurs and the ink shot amount is shown. A gamut shape when hue shift occurs in C, M, and Y is shown. The gamut shape and ink ejection amount of the present invention are shown. The gamut outermost shell and the gamut outermost shell representative point of the present invention are shown. The processing flowchart of the intermediate signal of the present invention is shown. 3 shows a flowchart of determination processing for a color mixture upper limit value according to the present invention. 3 is a flowchart of mixed color patch printing processing according to the present invention. The γ function is shown. The relationship between the printer raw signal and the standardized printer signal is shown. 5 is a flowchart for explaining a color separation processing method according to the first embodiment of the present invention; It is explanatory drawing of the image output processing system in which color separation processing is included. It is explanatory drawing of allocation of the coloring material recording amount data by Example 1 to the surface of the color space cube of a CMY signal. It is a figure which shows the example of the division | segmentation into the triangular pyramid of the color space cube of a CMY signal. It is a block diagram for demonstrating the functional structure of the color separation processing apparatus which concerns on Example 1 of this invention. It is a flowchart for demonstrating the color separation processing method which concerns on Example 2 of this invention. It is a block diagram for demonstrating the functional structure of the color separation processing apparatus which concerns on Example 2 of this invention. It is a block diagram for demonstrating the functional structure of the color separation processing apparatus which concerns on Example 3 of this invention. It is a block diagram for demonstrating the functional structure of the color separation processing apparatus which concerns on Example 4 of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  The relationship between hue shift and gamut, which is a premise of the present invention, will be described. FIG. 1A shows an example of seven color ink jet printer reproduction colors on the CIELAB, a * b * chromaticity diagram. In addition to process inks (C, M, Y), green (G), orange (O) The change in color reproduction of a single color (primary color) with respect to the ink hit amount of the HiFi ink having an intermediate hue of blue (B) is shown. In the present invention, since the color gamut with high saturation is mainly handled, the black ink K = 0 (%) will be described, but the same applies to the case where K ≠ 0. In addition, the ink ejection amount is set to 100% as a limit value that does not cause bleeding on the paper.

  In FIG. 1A, C, M, O, and G have the highest saturation when the ink placement amount is lower than 100%, and the saturation is lowered when the placement amount is 100%. This state is called “hue shift (hue is bent)”, the color with the highest saturation is called the “highest saturation color”, and the point on the color coordinate of the highest saturation color is called the “highest saturation point”. In FIG. 1A, the maximum saturation point of each ink is indicated by a black circle. In Y and B, no hue shift occurs. That is, the ink includes ink that does not shift hue and ink that does not.

  In general, in an inkjet printer, since solid color reproduction is preferred, the ink placement amount is given priority not to the hue shift condition (which does not occur) in the color space but to the blur condition (which does not occur) on paper. Decide. In addition, since the density increases as the driving amount increases, the shadow color reproduction range increases.

  FIG. 1B shows changes in color reproduction of primary and secondary colors with respect to the ink ejection amount on the CIELAB, a * b * chromaticity diagram. In FIG. 1B, for example, a hue shift occurs in the G single color and no hue shift occurs in the Y single color, but no hue shift occurs in the secondary color (G + Y) composed of G and Y. Further, for M and O, a hue shift occurs in a single color, but a hue shift does not occur in a secondary color (M + O) composed of M and O.

  Thus, regardless of whether or not there is a hue shift in a single color, a hue shift occurs in the secondary color according to the ink to be combined. FIG. 1C shows a combination of the presence / absence of hue shift of primary and secondary colors. In FIG.1 (c), the color in parenthesis () shows the ink color corresponding in FIG.1 (b). Further, since there is no example in which hue shift does not occur in any of the two single colors constituting the secondary color, it is not shown in FIG.

  Next, the relationship between hue shift and gamut will be described using a single color as an example. FIG. 2 shows a relationship (FIG. 2B) between the gamut shape (FIG. 2A) on the lightness and saturation plane and the ink hit amount when no hue shift occurs in C, M, and Y. . In FIG. 2, the gamut indicates from paper white (point a) to solid monochrome (point b) and black point (point c). In (C) is the amount of cyan ink deposited (%).

  In the case of ink that does not cause a hue shift, the saturation does not decrease even when the amount of ink applied from paper white is increased, so that the linear relationship between brightness and saturation is maintained (FIG. 2 (a) point a → Point b). Further, gradation continuity is maintained even in the region from the highest saturation point to the black point (FIG. 2 (b), point b → point c).

  FIG. 3 shows an example in which a hue shift occurs with M ink. For simplicity of explanation, it is assumed that hue shift does not occur in C and Y inks. The gamut shape in the brightness and saturation plane is shown in FIG. In FIG. 3 (a), only M ink from paper white starts to be ejected, and point d is the maximum saturation point when the ink ejection amount is Xm%. Further, the amount of M ink shot is 100% at point b. From point b to point c, C and Y inks are started to be applied while the amount of M ink applied remains 100%. FIG. 3B shows the relationship between the amount of ink applied at each point.

  As shown in FIG. 3, in the case of ink in which a hue shift occurs, when ink starts to be printed from paper white, the saturation decreases at the highest saturation point (point d), so that the linear relationship between lightness and saturation is maintained. It does not strike (FIG. 3 (a) point a → point d → point b). In effect, the outer area of the gamut becomes a point d, and the point b becomes a depression in the shadow area. That is, tone continuity is not maintained in the region from the highest saturation point to the black point (FIG. 3A, point d → point b → point c).

  In the example of FIG. 3, the hue shift is only for M ink. However, when hue shift occurs in C and Y inks, the gamut shape in the vicinity of the black point where the amount of C and Y ink shots approaches 100% becomes uneven. This is shown in FIG. FIG. 4A shows the gamut shape on the brightness and saturation plane, and FIG. 4B shows the gamut shape on the a * b * plane in the vicinity of the black point. In such a gamut shape, the linear relationship between ink continuity and gradation continuity cannot be maintained.

  That is, in order to maintain the linear relationship between ink continuity and gradation continuity, each ink must be used within a range where no hue shift occurs. In FIG. 5, when hue shift occurs in C, M, and Y, the gamut shape when the ink hit amount is used up to 100% is shown by a solid line, FIG. 5A (lightness and saturation plane), and FIG. ) (A * b * plane).

  As in the present invention, the gamut shape in the case where the ink hit amount corresponding to the maximum saturation point is used is indicated by a dotted line, FIG. 5A (lightness, saturation plane), FIG. 5C (a * b *). Plane). When the ink hit amount corresponding to the maximum saturation point is used (dotted line), the gamut shape becomes smaller (than the solid line), but unevenness is eliminated and gradation continuity is maintained. Further, FIG. 5B shows a change in the ink ejection amount from the point a → the point d → the point e in FIG. Here, in order to simplify the explanation, the ink ejection amount corresponding to the highest saturation point is assumed to be Xm% for all of C, M, and Y.

  The above highlight is an example of a single color, but the same applies to a secondary color. In the case where a primary color is mixed to form a secondary color, in order to smooth the gamut shape and maintain a linear relationship between ink continuity and gradation continuity, in the present invention, ink ejection corresponding to the highest saturation point is performed. Up to an amount (hereinafter referred to as “maximum saturation point ink placement”).

In order to grasp the above-described gamut shape (specifically, the outermost representative point of gamut described later), in the present invention,
(1) For each color ink, an ink placement amount (color material recording amount data) that reproduces the maximum saturation point in a single color is obtained.
(2) In the range of the hit amount, an ink hit amount that reproduces the highest saturation point in the secondary color is obtained for all ink combinations.
(3) A printer gamut is defined as a gamut formed with an ink amount up to an ink placement amount that reproduces the maximum saturation point obtained in (1) and (2) above.
Take steps. Actually, K ink is added to the secondary color instead of the secondary color.

  Here, as shown in FIG. 6, the outermost contour of the printer gamut obtained by the above-mentioned procedure is called the gamut outermost contour, and the primary and secondary color ink combinations constituting the outermost gamut are designated as the gamut outermost representative points. Call.

  FIG. 7 shows a flowchart of the intermediate signal processing (processing until the Cmy intermediate signal is separated into multiple colors (CMYKOG) and printed).

  The cmy intermediate signal is converted into a standardized printer signal D by multicolor separation (step S1). Next, γ conversion using a γ function representing printer characteristics is performed, converted to a printer raw signal Z (step S2), and printed (step S3). Actually, the standardized printer signal D and printer raw signal Z are for each color. Details of each signal will be described later.

  In the present invention, a standardized printer signal D corresponding to the outermost representative point of the gamut is assigned to the surface of the cmy input color space cube, and a color separation matrix using an interpolation operation (tetrahedral interpolation) based on the assigned position. Since color separation is performed using the created matrix, it is necessary to obtain a “color mixture upper limit value” to be assigned to the gamut outermost contour representative point. Further, the color relationship between the assigned outermost contour representative points is preferably a linear relationship without hue shift or reversal. For this reason, for each ink, it is necessary to obtain an ink ejection amount at the highest saturation point and a γ function representing the relationship between the standardized printer signal D and printer raw signal. The γ function is created using the spatial distance of CIELab (uniform color space).

  The calculation method of the color mixture upper limit and γ function according to the present invention will be described with reference to FIGS. FIG. 8 is a flowchart of the color mixture upper limit determination process according to the present invention. First, printing of a single color patch and color measurement are performed (step S11), and the maximum saturation point ink placement amount of each ink is determined (step S12). In the example of FIG. 8, the amount of ink applied at the maximum saturation point of M ink is Xm. Further, a printer raw signal Pm is obtained for the ink placement amount Xm at the highest saturation point (step S13).

  Next, the printer raw signal is standardized by the CIELab spatial distance, and the standardized printer signal D and a γ function that is a printer characteristic are obtained (step S14). Standardization using the CIELab spatial distance will be described later.

  The relationship between the ink ejection amount X, the printer raw signal P, and the standardized printer signal D is as shown in FIG. The γ function represents the relationship between the standardized printer signal D and printer raw signal P, as shown in FIG.

  These processes are performed for all inks (CMYKOG), and a γ function is obtained for each ink (step S15).

  Next, mixed color patch printing and colorimetry are performed (step S16). This will be described in detail with reference to FIG. FIG. 9 shows a flowchart of mixed color patch printing processing. In FIG. 9, mixed color printing is performed using Y ink and M ink. First, input signals Yin and Min are set. Yin = Min = i and i = 0 to 255. Here, actually, i corresponds to the printer signal D after standardization (step S21). Next, γ conversion is performed on each of Y and M inks to obtain Yout and Mout which are printer raw signals (step S22). This is transmitted to the printer for printing to obtain a patch (step S23). Printing is performed for all combinations of mixed colors (step S24).

  Returning to FIG. 8, the color mixture patch is printed, color measurement is performed, and the color mixture upper limit value is determined (step S17). Here, the color mixture upper limit value is a standardized printer signal corresponding to the highest saturation point, and the relationship is shown in FIG. In FIG. 11B, the color mixture upper limit value of Y and M inks is denoted by Zym. The mixed color upper limit value is implemented for all combinations of mixed colors (step S18). The data for reproducing the maximum saturation of the mixed color is selected from the mixed colors obtained by mixing equal amounts of data after standardizing the data for reproducing the maximum saturation of the single color ink as the upper limit value. In this way, since the mixed color is reproduced using the standardized single color, the hue shift amount of the mixed color is reduced.

  The creation of a γ function using the CIELab spatial distance will be described. The γ function is a function for converting the standardized printer signal D (0 ≦ D ≦ 255) into a printer raw signal P (0 ≦ D ≦ Pm). FIG. 11C shows the printer raw signal P in the CIELab space, and FIG. 11D shows the printer signal D in the CIELab space.

In the present invention, the γ function is created so that the CIELab spatial distances between adjacent points (level intervals) of the standardized printer signal are equal. That is, in FIG. 11, when the coordinates of the point D0, which is paper white in the CIELab space, are (L0, a0, b0) and the coordinates of the point Di (i = 0 to 255) are (Li, ai, bi), The CIELab spatial distance Line (i) of Di is expressed as follows.
Line (i) = sqrt {(Li-L0) ^ 2 + (ai-a0) ^ 2 + (bi-b0) ^ 2}
The γ function is created so that the CIELab spatial distances between adjacent points of the standardized printer signal are equal.
That is,
A function that satisfies Line (1) −Line (0) = Line (2) −Line (1) = Line (i + 1) −Line (i) = Line (255) −Line (254) is created. In this way, normalization is performed so that the distances in the uniform color space are uniform, so that the gradation continuity is improved.

Examples of the present invention will be described in detail below.
First, a method for performing CMYKOG multi-color separation on the Cmyk input signal will be described. For convenience, let cmyk (lowercase) be the input signal and CMYKOG be the output ink signal.

  FIG. 12 is a flowchart for explaining the color separation processing method according to the present invention. This color separation processing method can be applied to, for example, a color separation processing step 114 in an image output processing system as shown in FIG.

  First, an outline of the image output processing system in FIG. 13 will be described. Reference numeral 111 denotes input image data, and the page image is composed of a set of component data representing components such as characters and images. Examples of the component data constituting the input image data 111 include component data in which colors are expressed in an RGB color space depending on the scanner representing an image read by the scanner, and an operator drawing using a personal computer. In addition, component data of various input color spaces such as component data in which colors are expressed in a CMYK color space representing a graphic image are mixed.

  In the color conversion processing step 112, component data in various input color spaces included in the input image data 111 are converted into component data in a virtual cmyk color space depending on the printer 116, and a set of component data in the cmyk color space. Print image data that is a body is generated. Here, since the printer 116 generally uses four colors of cmyk ink, the color conversion processing step 112 regards the printer 116 as a virtual cmyk printer and generates print image data of cmyk.

  The generated print image data is sent to the rasterization processing step 113. The printer 116 outputs a page image for each scanning line, and the print image data composed of the component data generated in the color conversion processing step 112 cannot be output by the printer 116 as it is. In the rasterization processing step 113, the print image data is subjected to rasterization processing and converted into a raster format cmyk signal suitable for the printer 116.

  This raster-format cmyk signal is sent to the color separation processing step 114. The printer 116 is a printer that uses G (green) and O (orange) inks that are HiFi inks in addition to the process inks (C, M, Y, and K). In the color separation processing step 114, the raster-format cmyk signal is converted into a CMYKGO signal (a signal representing the recording amount of each CMYKOG ink).

  This CMYKOG signal is sent to the gradation processing step 115. The CMYKOG signal represents the ink recording amount by the number of gradations determined according to the data length for each ink (256 gradations from 0 to 255 if the data length is 1 byte for each ink). On the other hand, the printer 116 displays an image by forming dots. However, even if dots are formed for each pixel or the size of the dots is controlled, only a few types of states can be obtained. Therefore, in the gradation processing step 115, the CMYKOG signal is converted into a recording signal representing dot formation for each pixel by a technique such as error diffusion or dithering. This recording signal is sent to the printer 116 and recorded as a multicolor image using CMYKOG ink.

  This will be described with reference to the flowchart of FIG. In FIG. 12, steps S101 to S103 correspond to a preparation process for color separation processing, and steps S104 to S107 correspond to processing steps for actually converting a cmyk signal into a CMYKOG signal (corresponding to the color separation processing step 114 of FIG. 13). Processing step). Therefore, the preparatory processing steps S101 to S103 are performed by a computer or the like different from the means for executing the color separation processing step 114, and the interpolation operation formula and planar data set for each triangular pyramid as the processing result are color-separated. What is necessary is just to make it usable with the execution means of the process step 114. The means for executing the color separation processing step 114 is realized by, for example, a program (such as a printer driver) that operates on a computer connected to the printer 116 or a program that operates on a computer built in the printer 116.

  In steps S101 to S103, steps S101a to S103a are preparation processing steps for color separation from a cmy input signal to a CMYOG output signal under the condition of k = 0. Steps S101b to S103b are preparation processing steps for color separation from a cmy input signal to a CMYOG output signal under the condition of k = 255. In the following description, it is assumed that each ink signal is an 8-bit signal having a value from 0 to 255 in both the cmy input signal and the CMYOG output signal. The K signal representing the K ink recording amount is also an 8-bit signal having a value from 0 to 255.

  In step S101, color material recording amount data (color data) corresponding to the outermost feature point of the color reproduction range of the image recording apparatus is assigned to the surface of the color space cube of the cmy input signal. It is explanatory drawing. Here, the color material recording amount data to be allocated is the printer signal D after the standardization described above, and has the format in which the recording amount of each ink of C, M, Y, K, O, which is the same as the CMYOG signal, is represented by 8 bits. It will be explained as a thing. That is, the allocated color material recording amount data corresponds to a CMYOG output signal value corresponding to the color. In FIG. 14, each coordinate axis of the color space cube of the cmy signal is represented by a small letter cmy to distinguish it from the CMY of the output signal. Hereinafter, processing contents will be described along the processing flow shown in FIG.

  Steps S101a to S103a corresponding to k = 0 will be described. First, in step S101a, white color material recording amount data (C = M = Y = O = G = 0) at the vertex 120, which is the origin of the color space cube (hereinafter abbreviated as the cmy color space cube) of the cmy input signal. ) And black color material recording amount data [C + M + Y] (C = M = Y = 255, O = G = 0) is assigned to the vertex 121 opposite to the vertex 120. A straight line connecting the vertex 120 and the vertex 121 is an achromatic color axis that is a collection of achromatic colors.

  In the cmy color space cube, sides 122, 123, 124, 125, 126, and 127 that do not pass through any of the vertices 120 and 121 are sides corresponding to the highest saturation point of each hue, and are called sides of the highest saturation. . These maximum saturation sides are assigned color material recording amount data (standardized printer signal solid (= 255)) that reproduces the maximum saturation of C, M, Y, O, and G, which are single colors. . Further, the color mixture is color material recording amount data ([YG color mixture upper limit value: Zyg], [GC color mixture upper limit value) that reproduces the maximum saturation of the color mixture of each HiFi ink and one process ink that is huewise adjacent thereto. Value: Zgc], [YO color mixture upper limit: Zyo], and [OM color mixture upper limit: Zom]) are assigned in order of hue.

That is, an upper limit value [YG mixed color upper limit value: Zyg] of the mixed color YG of the HiFi ink G and one process ink Y adjacent in hue is allocated to the side 122 of the highest saturation. An upper limit value [GC mixed color upper limit value: Zgc] of the mixed color GC of the HiFi ink G and one process ink C huewise adjacent thereto is assigned to the edge 123 of the highest saturation. 124 is assigned the YO mixed color upper limit [YO mixed color upper limit: Zyo], and the highest saturation side 125 is assigned the OM mixed color upper limit [OM mixed color upper limit: Zom]. This eliminates the nonlinearity of the reproduced color with respect to the input cmy. Color material recording amount data for reproducing the maximum saturation of the mixed color of the two process inks is assigned. That is, color material recording amount data (upper limit [YC mixed color upper limit: Zyc]) that reproduces the highest saturation of the mixed colors of Y and C inks that are adjacent to the HiFi ink G in terms of hue is the highest saturation of the hue. (The mixed color obtained by adding C ink for hue adjustment to the solid G is the highest saturation point of the hue), so the data of [YC mixed color upper limit value: Zyc] is the surface of the cmy color space cube It is assigned at a position closer to the black than the highest saturation side.

  Similarly, the upper limit value [MY mixed color upper limit value: Zmy] of the mixed colors of M and Y inks on both sides of the O ink is not the highest saturation point of the hue (the M ink for adjusting the hue is placed on the solid O). The added mixed color is the highest saturation point of the hue), and [MY mixed color upper limit value: Zmy] data is assigned to a position closer to the black than the side of the highest saturation on the surface of the cmy color space cube.

  The upper limit value of the mixed colors of C and M ink [CM mixed color upper limit value: Zcm] is the highest saturation point of the hue without using the HiFi ink corresponding to the hue, and the data is shown in FIG. Is assigned on the side of the highest saturation.

  Also, the hue of the upper limit [YC color mixture upper limit: Zyc] of the mixed colors of the two process inks adjacent to the G ink in terms of hue, ie, (1) [YC color mixture upper limit: Zyc], (2) Mixed color [G solid (+ C)] in which C ink for hue adjustment is added to the solid of G ink at the intersection of 3 points with the plane passing through the achromatic color axis and (3) the highest saturation side (C = required amount for hue adjustment, other ink = 0) is allocated. Here, “solid” indicates a solid (= 255) of the standardized printer signal. Similarly, the highest saturation of the O ink at the intersection of the same hue plane and the maximum saturation side of the saturation maximum point [M + Y mixed color upper limit value] of the two process inks adjacent to the O ink in terms of hue. Data of mixed color [solid solid of O (+ M)] (M = required amount for hue adjustment, other colors = 0) obtained by adding M ink for hue adjustment to a color that reproduces the degree is allocated.

  Note that it is possible to omit the allocation of [G solid (+ C)] and [O solid (+ M)]. However, when the assignment is omitted, the position does not become the apex of the triangular pyramid that is an interpolation solid, and the output signal value at that position is calculated by interpolation calculation. Naturally, the calculation accuracy of the CMYOG output signal in the vicinity of the position is slightly lowered.

  The color data corresponding to the outermost shell representative point of the color reproduction range as described above is allocated. The solid data of the process inks C, M, and Y (standardized printer signal solid (= 255)) data is As shown in FIG. 14, it is better to allocate them on the corresponding c, m, y coordinate axes of the cmy input color space cube. In this case, for example, when a single color of c is input, a single color corresponding to the single color input is output, such as a single color of C is output by interpolation calculation, so that there is an advantage that so-called pure color guarantee can be easily realized. .

  Further, on the side of the highest saturation, the solid color of the HiFi ink, the color mixture upper limit value of the HiFi ink and one process ink that is adjacent to the hue are assigned in order of hue, and the assignment position (position in the hue direction) is It may be determined based on the color difference between the colors or the ratio of the hue differences when arranged in the order of hue. For this purpose, the single color and the mixed color are output in advance by the printer 116 (or the same type of printer) and colorimetric, and the colorimetric data (for example, CIELAB L * a * b * value) is prepared. However, these colors are output with k = 0. Then, when determining the allocation position of the color data, a color difference or a hue difference between adjacent colors when the colors are arranged in the hue order is obtained from the colorimetric data. In order to realize color separation with little color difference distortion with respect to the cmy input, it is preferable to determine the allocation position based on the color difference. In order to realize color separation with little hue distortion with respect to the cmy input, the allocation position may be determined based on the hue difference.

  Also, the C ink recording amount of [G solid (+ C)] is the same as the printer signal solid (= 255) after standardization of the G ink, for which the allocation position is determined as described above, and the G and C inks. It may be determined based on the hue difference or the ratio of the color difference with the mixed color upper limit [GC mixed color upper limit: Zgc]. Similarly, the M ink recording amount of [O solid (+ M)] is the O ink solid whose allocation position is determined as described above and the mixed color upper limit value of O and Y ink [YO mixed color upper limit value: It may be determined based on the hue difference or the ratio of the color difference with respect to Zyo].

  Also for the mixed color that reproduces the highest saturation point of the two process inks, k = 0 is output in advance by the printer 116 (or the same type of printer) and measured, and based on the measured color data, these mixed colors Allocation positions (lightness direction, hue direction position) are determined. However, the mixed color [YC mixed color upper limit value: Zyc] and [MY mixed color upper limit value: Zmy] data for reproducing the maximum saturation point are represented in CMY colors as shown in FIG. 14 regardless of the measured hue. It is also possible to arrange them on the sides 129 and 130 corresponding to the hue of the space cube. In this case, the triangular pyramid division process in the next step S102a is facilitated. [G solid color], [YG color mixture upper limit value: Zyg], [GC color mixture upper limit value: assigned to the side of the highest saturation according to the measured hue of [YC color mixture upper limit value: Zyc]: [Zgc] allocation position and [G solid (+ C)] C ink recording amount are adjusted. Similarly, according to the measured hue of [MY color mixture upper limit: Zmy], the maximum saturation Adjust the [O solid], [YO mixed color upper limit: Zyo], and [MO mixed upper limit: Zmo] assigned positions and the M ink recording amount of [O solid (+ M)] To do.

  In the next step S102a, the cmy color space cube is divided into a plurality of triangular pyramids (interpolated solids) whose apexes are the positions where colors are assigned. As described above, since the color corresponding to the outermost shell representative point in the color reproduction range is assigned to a position on the side of the highest saturation or a position closer to the black side, the origin 120 of the cmy color space cube, that is, the assignment of white The position can be easily divided into a plurality of triangular pyramids with the common vertex of all the triangular pyramids. For example, select the smallest triangle that can be generated by the vertex assigned with black and another color assignment position, combine this triangle and the white vertex into one triangular pyramid, and then the rest of the triangles that can be generated The input color space cube can be divided into triangular pyramids by a method of repeating the procedure of selecting the smallest one from among them and combining the vertexes of white with a triangular pyramid. Part of the triangular pyramid thus divided is illustrated in FIG.

  Next, in step S103a, for each divided triangular pyramid, the plane formula of the four surfaces constituting the triangular pyramid is determined based on the cmy color space position of the apex of the triangular pyramid. As will be described later, this planar formula is used to determine which triangular pyramid the cmy input signal belongs to. Further, in this step S103a, for each divided triangular pyramid, a CMYOG output signal for a cmy input signal belonging to the triangular pyramid is generated based on the cmy color space position of each apex of the triangular pyramid and the assigned color data. Determine the interpolation formula.

  The interpolation equation is expressed as follows.

Here, X11 to X54 are interpolation coefficients. The interpolation coefficient of such an interpolation calculation formula is determined as follows.

The cmy color space position of the four apexes of the triangular pyramid and the color data (the combination of ink recording amounts) assigned thereto are as follows:
(C1, m1, y1) => (C1, M1, Y1, O1, G1)
(C2, m2, y2) => (C2, M2, Y2, O2, G2)
(C3, m3, y3) => (C3, M3, Y3, O3, G3)
(C4, m4, y4) => (C4, M4, Y4, O4, G4)
Then, the interpolation calculation for the four vertices can be expressed as follows.

Therefore, the interpolation coefficients X11 to X54 can be determined as follows.

Moreover, the general formula of the plane in the cmy color space is

Here, since Pc to Pm are coefficients, for example, the plane expression passing through the first three points (c1, m1, y1), (c2, m2, y2), (c3, m3, y3) is

Therefore,

Can be determined as follows.

  The preparation process for the case of k = 0 has been described above. Next, steps S101b to S103b of the preparation process for the case of k = 255 will be described.

  In step S101b, the same solid and mixed color upper limit values as in step S101a are assigned to the surface of the cmy color space cube. However, in step S101a, when determining the allocation position of the solid, color mixture upper limit value, etc., data obtained by measuring these solid colors, the color mixture upper limit value, etc. in advance by setting k = 0 is used. However, in step S101b, the solid color is used in advance. The color measurement data obtained by outputting the color mixture upper limit value k = 255 (overlaid on the solid K single color) and measuring the color are used for determining the allocation position of the output signal values. That is, in the case of k = 255 and k = 0, the solid and color mixture upper limit value allocation position (position in the hue direction) allocated on the side of the maximum saturation and the process ink color mixture upper limit value allocation position Further, there is a difference in the (G solid (+ C)) C ink recording amount and the [O solid (+ M)] M ink recording amount (in the hue direction and brightness direction).

  In step S102b, the same processing to the triangular pyramid as in step S102a is performed. In step S103b, processing for determining a plane expression and an interpolation calculation expression similar to those in step S103a is performed.

  Next, for example, the color separation processing (FIG. 12, steps S104 to S107) that is actually executed in the color separation processing step 114 of FIG. 13 will be described.

  First, in step S104, a one-pixel cmyk signal is input. In step S105a, for the cmy signal in the cmyk input signal, the triangular expression for k = 0 divided in step S102a is evaluated by evaluating the plane formula of each triangular pyramid when k = 0 determined in step S103a. One triangular pyramid to which the cmy signal belongs is determined from the cones. That is, the four planes constituting the triangular pyramid are evaluated with respect to the cmy signal, and when it is determined that the cmy color space position of the cmy signal is inside all the four planes, it belongs to the triangular pyramid. judge. Similarly, in step S105b, the planar formula of each triangular pyramid determined in the case of k = 255 determined in step S103b is evaluated, and the cmy signal belongs to the triangular pyramid for k = 255 divided in step S102b. Determine one triangular pyramid.

  In the next step S106a, a CMYOG signal in the case of k = 0 is generated using the interpolation calculation formula of the triangular pyramid for k = 0 determined in step S105a. Similarly, in step S106b, a CMYOG signal for k = 255 is generated using the triangular pyramid interpolation equation for k = 255 determined in step S105b.

  In the next step S107, from the CMYOG signal in the case of k = 0 generated in step S106a and the CMYOG signal in the case of k = 255 calculated in step S106b, the next corresponding to the k signal in the cmyk input signal The CMYOG output signal is determined by interpolation calculation.

X = ((Xa × (255−k) + Xb × k)) / 255 (7)
However, X is each ink signal in the CMYOG output signal which is the interpolation calculation result, Xa is each ink signal in the CMYOG signal when k = 0, and Xb is each ink signal in the CMYOG signal when k = 255. is there. A CMYKOG output signal is output as a final color separation processing result by combining the KMY signal with the CMYOG output signal thus calculated.

  The processes in steps S104 to S107 are repeatedly executed until it is determined in step S108 that the final pixel has been processed.

  A program for executing the color separation processing method described above using a computer having a general configuration including a CPU, a memory, and the like, that is, a program for causing a computer to execute each processing step of the color separation processing method is also included in the present invention. Is included.

  FIG. 16 is a block diagram for explaining a functional configuration of the color separation processing apparatus according to the first embodiment of the present invention. This color separation processing apparatus can be applied to, for example, the color separation processing step 114 in FIG.

  The color separation processing apparatus shown in FIG. 16 performs color separation processing by the color separation processing method of the present invention, and includes a signal input unit 151, data set storage units 152a and 152b, determination units 153a and 153b, and an interpolation calculation unit. 154a and 154b, an interpolation calculation unit 155, and a signal output unit 156.

  The signal input unit 151 is a unit that captures the cmyk signal 160. The data set storage unit 152a stores the data set of the plane formula and the interpolation calculation formula for each triangular pyramid determined in step S103a of FIG. 12, and the data set storage unit 152a is determined in step S103b of FIG. A data set of plane formulas and interpolation calculation formulas for each triangular pyramid is stored.

  The determination unit 153a is a unit that performs the determination process of step S105a in FIG. 12, and the determination unit 153b is a unit that performs the determination process of step S105b in FIG. The interpolation calculation unit 154a is a unit that performs the interpolation calculation in step S106a in FIG. 12, and the interpolation calculation unit 154b is a unit that performs the interpolation calculation in step S106b in FIG. The interpolation calculation unit 155 is a means for performing the interpolation calculation in step S107 in FIG. 12, that is, the calculation of the equation (7).

  The signal output unit 156 is a unit that outputs the final CMYKOG output signal 165 by combining the CMYOG signal 164 output from the interpolation calculation unit 155 with the k signal 162 in the cmyk signal 160.

  The overall operation is as follows. The raster-format cmyk signal 160 is input pixel by pixel through the signal input unit 151 (step S104 in FIG. 12). The cmy signal 161 in the input cmyk signal 160 is sent to the determination units 153a and 153b and the interpolation calculation units 154a and 154b, and the k signal 162 in the cmyk signal 160 is sent to the interpolation calculation unit 155 and the signal output unit 156. The determination unit 153a determines the triangular pyramid for k = 0 to which the cmy signal 161 belongs by the evaluation of the planar expression stored in the data set storage unit 152a (step S105a). Similarly, the determination unit 153b sets the data set storage unit. The triangular pyramid for k = 255 to which the cmy signal 161 belongs is determined by the evaluation of the planar expression stored in 152b (step S105b). In the interpolation calculation unit 154a, an interpolation calculation formula corresponding to the triangular pyramid determined by the determination unit 153a is fetched from the data set storage unit 152a, and the CMYOG signal in the case of k = 0 corresponding to the cmy signal 161 by this interpolation calculation formula. 163a is generated (step S106a). Similarly, in the interpolation calculation unit 154b, an interpolation calculation formula corresponding to the triangular pyramid determined by the determination unit 153b is fetched from the data set storage unit 152b, and k = 255 corresponding to the cmy signal 161 by this interpolation calculation formula. CMYOG signal 163b is generated (step S106b). In the interpolation calculation unit 155, the CMYOG signal 163a and the CMYOG signal 164b are subjected to the interpolation calculation of the equation (7) according to the K signal 162, and the CMYOG signal 164 corresponding to the k signal 164 is generated. And the k signal 162 are combined with the signal output unit 156 and output as the final CMYKOG output signal 165 (step S107).

  Such a color separation processing apparatus can be realized by hardware, but can also be realized by using a computer having a general configuration including a CPU and a memory. A program for realizing the color separation processing apparatus using a computer, that is, a program for causing a computer to function as each component of the color separation processing apparatus is also included in the present invention.

  FIG. 17 is a flowchart for explaining the color separation processing method according to the second embodiment of the present invention. This color separation processing method can be applied to, for example, a color separation processing step 114 in an image output processing system as shown in FIG.

  In FIG. 17, steps S201 to S208 correspond to a preparation process for color separation processing, and steps S210 to S212 correspond to the processing steps for actually converting the cmyk signal to the CMYKOG signal (corresponding to the color separation processing step 114 of FIG. 13). Processing step). Accordingly, the preparation processing steps S201 to S208 are performed by a computer or the like different from the means for executing the color separation processing step 114, and the LUT (lookup table) as the processing result is executed by the means for executing the color separation processing step 114. Make it available. The means for executing the color separation processing step 114 is realized by, for example, a program (such as a printer driver) that operates on a computer connected to the printer 116 or a program that operates on a computer built in the printer 116.

  In steps S201 to S208, steps S201a to S208a are preparation processing steps for color separation from a cmy input signal to a CMYOG output signal under the condition of k = 0. Steps S201b to S208b are preparation processing steps for color separation from a cmy input signal to a CMYOG output signal under the condition of k = 255.

  In steps S201a and S201b, the same color allocation process as that in steps S101a and S101b in FIG. 12 is executed. In steps S202a and S202b, the same process of dividing into triangular pyramids as in steps S102a and S102b in FIG. 12 is executed. In steps S203a and S203b, processing for determining the same plane expression and interpolation calculation expression as in steps S103a and S103b in FIG. 12 is executed.

  Steps S204 to S208 are processing steps for generating an LUT used for decomposing a cmy signal into a CMYOG signal by a memory map interpolation calculation method. First, in step S204, the cmy color space cube is divided into a number of interpolation cubes by dividing the coordinate axes of the cmy color space cube.

  In step S205, an address and a cmy signal corresponding to one divided grid point (corresponding to one vertex of an interpolation cube) are generated. In step S206a, the generated cmy signal is evaluated by the same planar formula as in step S105a of FIG. 12, so that the triangular pyramid to which the cmy signal belongs among the triangular pyramids for k = 0 divided in step S202a. Is determined. Similarly, in step S206b, the triangular pyramid to which the cmy signal belongs is determined from the triangular pyramids for k = 255 as in step S105b of FIG. In step S207a, a CMYOG signal value (recording amount of each CMYOG ink) corresponding to the k = 0 signal is generated by the interpolation calculation formula for k = 0 corresponding to the triangular pyramid determined in step S206a. Similarly, in step S207b, the CMYOG signal value (recording amount of each CMYOG ink) corresponding to the k = 255 condition corresponding to the cmy signal is obtained by the interpolation equation for k = 255 corresponding to the triangular pyramid determined in step S206b. Generated. In step S208a, the CMYOG signal value generated in the previous step S207a is stored in the LUT format in the grid point corresponding address generated in step S205. Similarly, in step S208b, the CMYOG signal value generated in the previous step S207b is stored in the LUT format at the grid point corresponding address generated in step S205. Steps S204 to S208 are repeated until it is determined in step S209 that the processing has been completed up to the final lattice point, whereby an LUT for k = 0 is finally generated in step S208a, and finally k = in step S208b. A LUT for 255 is generated. Note that the color separation processing LUT generation method in steps S201 to S208 is also included in the present invention.

  Next, steps S211 to S212 will be described. This processing step corresponds to, for example, the color separation processing actually executed in the color separation processing step 114 of FIG.

  In step S210, a cmyk signal for one pixel is input. In step S211a, the cmy signal in the input cmyk signal is decomposed into a CMYOG signal by memory map interpolation using a k = 0 LUT. More specifically, output signal values (recording amount of each CMYOG ink) corresponding to eight lattice points which are the vertices of the interpolation cube corresponding to the cmy signal are read from the LUT. Then, for example, the interpolation cube is subdivided into eight small cubes at coordinates corresponding to the cmy signal, and the cmy signal is obtained by linear interpolation based on the weighted average of the output signal values of the eight vertices with the volume of the small cube as a weight. Generate CMYOG signals for. In step S211b, a CMYOG signal is generated by a similar memory map interpolation operation using an LUT for k = 255. In the next step S212, the CMYOG signal generated in steps S211a and S211b is subjected to the same interpolation calculation as in step S107 in FIG. 12, and the resulting CMYOG signal and the K signal are combined to output a CMYKOG signal. is there. The processes in steps S210 to S212 are repeatedly executed until it is determined in step S213 that the final pixel has been processed.

  A program for implementing the color separation processing method and the color separation processing LUT generation method described above using a computer having a general configuration including a CPU, a memory, and the like, that is, the color separation processing method and the color separation processing LUT A program that causes a computer to execute each processing step of the generation method is also included in the present invention.

  FIG. 18 is a block diagram for explaining a functional configuration of the color separation processing apparatus according to the second embodiment of the present invention. This color separation processing apparatus can be applied to, for example, the color separation processing step 114 in FIG.

  The color separation processing apparatus shown in FIG. 18 performs color separation processing by the color separation processing method according to the second embodiment of the present invention, and includes a signal input unit 251, LUT storage units 252a and 252b, and a lattice point address generation unit 253a. 253b, interpolation calculation units 254a and 254b, an interpolation calculation unit 255, and a signal output unit 256.

  The signal input unit 251 is a unit that captures the cmyk signal 260. The LUT storage unit 252a stores the k = 0 LUT created in step S208a of FIG. 17, and the LUT storage unit 252b stores the k = 255 LUT created in step S208b of FIG. doing.

Based on the cmy signal 261 in the cmyk signal 260, the grid point address generation unit 253a generates a grid point address of the k = 0 LUT corresponding to the eight vertices of the interpolation cube to which the cmy signal belongs, and the cmy is generated from the LUT. This is means for reading output signal values corresponding to the eight vertices of the interpolation cube to which the signal 261 belongs. Similarly, the lattice point address generation unit 253b is a unit that generates a lattice point address of the LUT for k = 255, and reads out output signal values corresponding to the eight vertices of the interpolation cube to which the cmy signal 261 belongs from the LUT. The addresses of the LUT storage units 252a and 252b can be shared, and the lattice point address generation units 253a and 253b can be integrated into one.

  The interpolation calculation unit 254a is a unit that generates the CMYOG signal 263a by performing the above-described interpolation calculation on the eight sets of output signal values read from the k = 0 LUT. The interpolation calculation unit 254b is means for generating the CMYOG signal 263b by performing the above-described interpolation calculation on the eight sets of output signal values read from the LUT for k = 255. That is, the grid point address generation units 253a and 253b and the interpolation calculation units 254a and 254b generate the CMYOG signals 263a and 263b from the cmy signal 261 by the memory map interpolation calculation using the LUT stored in the storage units 252a and 252b. It constitutes a means to do.

  The interpolation calculation unit 255 is a means for performing the interpolation calculation in step S212 of FIG. 17, that is, the calculation of the equation (7). The signal output unit 256 is a unit that combines the CMYOG signal 264 output from the interpolation calculation unit 255 with the k signal 262 in the cmyk signal 260 and outputs the final CMYKOG signal 265.

  Such a color separation processing apparatus can be realized by hardware, but can also be realized by using a computer having a general configuration including a CPU and a memory. A program for realizing the color separation processing apparatus using a computer, that is, a program for causing a computer to function as each component of the color separation processing apparatus is also included in the present invention.

  FIG. 19 is a block diagram for explaining a functional configuration of the color separation processing apparatus according to the third embodiment of the present invention. This color separation processing device color-separates the CMY input signal 305 into a CMYOG signal 306, and converts this CMYOG signal 306 into a CMYKOG signal 307 through black generation / undercolor removal processing.

  For color separation processing from the Cmy input signal 305 to the CMYOG signal 306, a data set storage unit 301, a determination unit 302, and an interpolation calculation unit 303 are provided. The data set storage unit 301 is a unit that stores the same triangular pyramid plane type and interpolation calculation type data sets as the data set storage unit 152a in FIG. The determination unit 302 is a means for performing the same determination process as the determination unit 153a in FIG. The interpolation calculation unit 303 is means for performing the same interpolation calculation as the interpolation calculation unit 154a in FIG. Further, a black generation / under color removal processing unit 304 is provided as means for black generation / under color removal processing for the CMYOG signal 306.

  As is clear from the above description, the color separation processing method from the cmy signal 305 to the CMYOG signal 306 in the third embodiment is the same as the color separation processing method corresponding to k = 0 in the first embodiment.

  FIG. 20 is a block diagram for explaining a functional configuration of the color separation processing apparatus according to the fourth embodiment of the present invention. This color separation processing device separates the CMY input signal 355 into a CMYOG signal 356, and converts this CMYOG signal 356 into a CMYKOG signal 357 by black generation / under color removal processing.

  For color separation from the Cmy input signal 355 to the CMYOG signal 356, an LUT storage unit 351, a grid point address generation unit 352, and an interpolation calculation unit 353 are provided. The LUT storage unit 351 is means for storing the same LUT as the LUT storage unit 252a in FIG. The lattice point address generation unit 352 is the same lattice point address generation means as the lattice point address generation unit 253a in FIG. The interpolation calculation unit 353 is means for performing the same interpolation calculation as the interpolation calculation unit 254a in FIG. That is, the lattice point address generation unit 352 and the interpolation calculation unit 353 constitute a unit that generates the CMYOG signal 356 from the cmy signal 355 by memory map interpolation calculation using the LUT stored in the storage unit 351.

  This color separation processing apparatus further includes a black generation / under color removal processing unit 354 as means for black generation / under color removal processing for the CMYOG signal 356.

  As is clear from the above description, the color separation processing method from the cmy signal 355 to the CMYOG signal 356 in the fourth embodiment is the same as the color separation processing method corresponding to k = 0 in the second embodiment.

  The color separation processing apparatus described with reference to FIGS. 19 and 20 can be realized by hardware, but can also be realized by using a computer having a general configuration including a CPU and a memory. . A program for realizing the color separation processing apparatus using a computer, that is, a program for causing a computer to function as each component of the color separation processing apparatus is also included in the present invention.

  As described above, according to the present invention, as the data, the outermost representative point data of the color gamut of the process, the HiFi (spot color) single color ink, and the mixed color reproduced by them, the saturation is the highest. Since the point to reproduce is set, the outermost gamut shape becomes smooth and the color design becomes easy. In addition, by performing processing so that the standardized level intervals are equal in distance in the color space, tone continuity inside the gamut is also improved.

120 Vertex to which white is assigned 121 Vertex to which black is assigned 122 to 127 Highest saturation side 151 Signal input unit 152a, 152b Data set storage unit 153a, 153b Determination unit 154a, 154b Interpolation operation unit 155 Interpolation operation unit 156 Signal output unit 251 Signal input unit 252a, 252b Storage unit 253a, 153b Grid point address generation unit 254a, 254b Interpolation operation unit 255 Interpolation operation unit 256 Signal output unit 301 Data set storage unit

JP 2003-11432 A

Claims (6)

  The color material recording amount data corresponding to the outermost shell representative point of the color reproduction range of the image recording apparatus is the surface of the color space cube of the input signal representing the recording amount of the C, M, Y color materials (hereinafter referred to as process color materials). The process color material and the color material of the intermediate color of the process color material (hereinafter referred to as HiFi color material) are recorded from the input signal using the interpolation calculation formula based on the assigned color material recording amount data and the assigned position. In the color separation processing method for generating an output signal representing the quantity, the single color maximum saturation of the process color material and the HiFi color material is reproduced as color material recording amount data corresponding to the outermost shell representative point of the color reproduction range. The color material recording amount data and the color material recording amount data that reproduces the maximum saturation of the mixed color of the HiFi color material and one process color material adjacent to it in the hue are the maximum saturation of the surface of the color space cube. Are assigned to the sides in order of hue Color material recording amount data that reproduces the maximum saturation of the mixed color of the two process color materials that are adjacent to the HiFi color material in terms of hue is assigned to a position closer to the black than the maximum saturation side of the surface of the color space cube. And a color separation processing method. Color material recording amount data that reproduces the maximum saturation of the mixed color is a mixture obtained by mixing equal amounts of data after standardizing the color material recording amount data that reproduces the maximum saturation of the single color as an upper limit value. 2. The color separation processing method according to claim 1, wherein the color separation processing method is selected from colors. The color separation processing method according to claim 2, wherein the standardization in the single color is performed by equalizing the distances in the uniform color space of the level intervals after the standardization.   A color separation processing apparatus for performing color separation processing by the color separation processing method according to claim 1, wherein a color space cube of an input signal representing a recording amount of a process color material is divided. A storage means for storing an interpolation calculation formula determined for each interpolation solid whose apex is a position where material recording amount data is assigned and a plane formula of a component surface of the interpolation solid, and a plane formula stored in the storage means A process color from the input signal using a determination unit that determines an interpolated solid to which the input signal belongs, and an interpolation calculation expression stored in the storage unit that corresponds to the interpolated solid determined by the determination unit. A color separation processing apparatus comprising interpolation calculation means for generating an output signal representing the recording amount of the material and the HiFi color material.   4. A color separation processing apparatus for performing color separation processing by the color separation processing method according to claim 1, wherein an interpolation solid obtained by dividing a color space cube of an input signal representing a recording amount of a process color material. Means for storing a look-up table in which the vertexes of the image data and the recording amounts of the process color material and the HiFi color material are associated, and a memory map interpolation operation using the look-up table, the process color material and the HiFi are obtained from the input signal. Means for generating an output signal representing a recording amount of the color material.   A program that causes a computer to function as each means of the color separation processing apparatus according to claim 4 or 5.