JP4650535B2 - Printing using chromatic primary color ink and chromatic secondary color ink - Google Patents

Description

  The present invention relates to a color printing technique using a plurality of types of ink.

  In recent years, color ink jet printers have been widely used as image output devices. A normal color inkjet printer uses a plurality of types of inks having hues of cyan C, magenta M, and yellow Y in addition to black (K) ink. Any color of the color image can be reproduced using these plural types of ink.

  In such a printer, the ink amount of each usable ink is determined according to an arbitrary color of the color image. In this specification, processing for determining the ink amount of each ink used for printing for color reproduction is called “separation processing” or “ink color separation processing”. The relationship between the color data of the color image and the ink amount of each color is stored in advance as a color conversion look-up table (LUT: Look Up Table). At the time of printing, the ink amount of each color at each pixel position is determined according to the LUT. (For example, refer to Patent Document 1).

JP-A-10-91089

  Incidentally, color reproducibility by a printer is determined by the type of ink that can be used by the printer. Typically, an arbitrary color can be reproduced by combining three chromatic primary color inks (for example, cyan C, magenta M, and yellow Y ink). In some cases, chromatic secondary color ink having a hue different from that of each chromatic primary color ink is used. Here, “chromatic secondary color” means a color that can be separated into two chromatic primary color components. When the chromatic secondary color ink is used, the color reproduction range can be expanded. However, conventionally, when such chromatic primary color ink and chromatic secondary color ink are available, image graininess and ink saving caused by chromatic secondary color ink dots are reduced. In fact, the fact that separation processing is taken into consideration has not been devised.

The present invention is for solving the above-described conventional problems, and is caused by dots of chromatic secondary color ink when chromatic primary color ink and chromatic secondary color ink can be used. An object is to perform printing in consideration of image graininess and ink saving.

  In order to solve at least a part of the above problems, a color separation method according to the present invention is a color separation method for determining an ink amount of each ink in order to reproduce an arbitrary color using a plurality of colors of ink on a print medium. The method includes: (a) a plurality of chromatic primary color inks that can reproduce achromatic colors when used in combination with each other, and a hue of each of the plurality of chromatic primary color inks. A step of setting an ink set including at least one different chromatic secondary color ink; and (b) a color reproduced on the print medium according to any one input color is called a reproduction color, and the reproduction A combination of each ink amount of the ink set for reproducing the color on the printing medium is called a color separation ink amount set, and a color represented by using each ink amount of the plurality of chromatic primary color inks as a reference vector Space is primary Determining a plurality of reproduction colors to be reproduced on the print medium in accordance with a plurality of input colors in the primary color space, and (c) reproducing the plurality of reproduction colors. A plurality of color separation ink amount sets for determining the actual ink amount of the chromatic secondary color ink with respect to the maximum ink amount of the chromatic secondary color ink determined according to the reproduction color. The ratio is called a secondary color ink usage rate, and the hue of the reproduced color is reproduced by a combination of one chromatic primary color ink and one chromatic secondary color ink. When the chromatic primary color ink is referred to as a primary color component ink and the one chromatic secondary color ink is referred to as a secondary color component ink, the step (c) includes the steps (c1) A process for obtaining a brightness parameter value correlated with the brightness of the reproduced color; (C2) The lightness parameter value is in a first high lightness range that is the brightest partial range, the primary color component ink and the secondary color component ink are the same, and the lightness parameter value is Of the two reproduction colors that are the same, the first reproduction color whose hue is relatively close to the primary color component ink and the second reproduction color whose hue is relatively close to the secondary color component ink, The chromatic secondary color included in the color separation ink amount set so that the secondary color ink usage rate of the second reproduction color is smaller than the secondary color ink usage rate of the first reproduction color. And a step of determining an ink amount of the ink.

  According to this color separation method, in a bright image area, the secondary color ink usage rate in an area where the hue is relatively close to chromatic secondary color ink is 2 in the area where the hue is relatively close to chromatic primary color ink. The ink amount of the chromatic secondary color ink is determined so as to be smaller than the secondary color ink usage rate. Therefore, since the secondary color ink usage rate is small in the region where the hue is relatively close to the chromatic secondary color ink, the chromatic secondary color ink is suppressed from being noticeable and the graininess of the image is improved. Can do. Further, in the region where the hue is relatively close to the chromatic primary color ink, the secondary color ink usage rate is increased, and the ink amount of the plurality of chromatic primary color inks is reduced, thereby saving the ink usage amount. can do.

  In the color separation method, the predetermined maximum ink amount of the chromatic secondary color ink is an ink amount when the chromatic secondary color ink is used to the maximum extent within a range in which the reproduced color can be reproduced. Preferably there is.

  In this way, the maximum ink amount can be easily set according to the reproduced color.

  In each of the color separation methods, when the plurality of chromatic primary color inks include a cyan ink, a magenta ink, and a yellow ink, the step (c2) includes the step of sharing the first and second reproduction colors. When the primary color component ink is cyan ink or magenta ink, the secondary color ink usage rate of the second reproduction color is smaller than the secondary color ink usage rate of the first reproduction color. Thus, it is preferable to determine the ink amount of the chromatic secondary color ink included in the color separation ink amount set.

  In this way, the ink amount of the cyan ink or magenta ink can be increased by reducing the secondary color ink usage rate. When the dots of the cyan ink and the magenta ink can make the dots of the chromatic secondary color ink less noticeable than the dots of the yellow ink of the same ink amount, these ink amounts increase, It is possible to effectively suppress the dots of the chromatic secondary color ink from being noticeable.

  In each of the color separation methods, in step (c2), the ink amount of the chromatic secondary color ink included in the color separation ink amount set is larger than the change rate of the lightness parameter value in the direction of lightening. It is preferably determined so that the ink amount decreases at a rate.

  By doing so, the ink amount of the chromatic secondary color ink is adjusted so as to decrease at a change rate larger than the change rate of the brightness parameter value, so that the chromatic secondary color ink is suppressed from being noticeable in a bright region. In addition, the graininess of the image can be improved.

  In each of the color separation methods, in the step (c2), the method of reducing the ink amount of the chromatic secondary color ink with respect to the change in the lightness parameter value is less than the method of reducing the ink amount of the chromatic primary color ink. It is preferable that the ink amount of the chromatic secondary color ink is adjusted so as to be larger.

  In this way, the amount of chromatic secondary color ink in the bright image area can be effectively reduced, so that the chromatic secondary color ink is suppressed from conspicuous in the bright area, and the graininess of the image is reduced. Improvements can be made.

  In each of the above color separation methods, it is preferable that in the step (c2), the amount of ink of the chromatic secondary color ink is adjusted so as to decrease more greatly than a decrease in proportion to the lightness parameter value.

  By doing this, the ink amount of the chromatic secondary color ink can be adjusted to a value smaller than the value proportional to the lightness parameter value, so that the chromatic secondary color ink is suppressed from being noticeable in a bright region, The graininess of the image can be improved.

  In each of the color separation methods, in the step (c2), when the lightness parameter value is in a predetermined range that is the brightest part, the actual ink amount of the chromatic secondary color ink is the reproduced color. A virtual ink amount of the chromatic secondary color ink included in the color separation ink amount set to be reproduced, which is obtained by adjusting the ink amount of each ink so that the total value of each ink amount is minimized. It is preferable to adjust so as to be smaller than the virtual ink amount of the chromatic secondary color ink included in the plate ink amount set.

  By doing so, the amount of chromatic secondary color ink is smaller than the amount of ink of the color separation ink amount set that minimizes the total amount of ink, so that chromatic secondary color ink is conspicuous in a bright region. It is possible to suppress and improve the granularity of the image.

  In each of the color separation methods, in the step (c2), a virtual ink amount of the chromatic secondary color ink included in the color separation ink amount set for reproducing the reproduction color, wherein the ink amount of each ink is The actual ink amount of the chromatic secondary color ink with respect to the virtual ink amount of the chromatic secondary color ink included in the color separation ink amount set obtained by adjusting so that the total value of the ink amounts is minimized. It is preferable that the ratio is adjusted so as to monotonously decrease with respect to a change in the brightness parameter value in a bright direction.

  By doing so, the ratio of the ink amount of the chromatic secondary color ink to the ink amount of the color separation ink amount set that minimizes the total ink amount is reduced in the bright region, and the chromatic secondary color ink is conspicuous. Can be suppressed.

  In each of the color separation methods, in the step (c2), the ink amount of the chromatic secondary color ink is in a first range in which the lightness is the brightest part of the lightness parameter value range. It is preferable to adjust so that it may become zero.

  By doing so, the ink amount of the chromatic secondary color ink is adjusted so as to become zero in the first range, which is the brightest partial range in the range of the brightness parameter value. It is possible to suppress the chromatic secondary color ink from being conspicuous in the region and improve the granularity of the image.

  In each of the color separation methods, it is preferable that the lightness parameter value is a maximum ink amount when the chromatic secondary color ink is used to the maximum extent within a range where the reproduced color can be reproduced.

  In this way, the brightness parameter value can be easily obtained.

  In each of the color separation methods, the step (c2) includes a step (c2-1) of determining a reference ink amount of the chromatic secondary color ink determined according to the reproduction color according to a predetermined condition set in advance. (C2-2) determining a reference ink amount of each ink of the ink set required for reproducing the reproduced color together with the reference ink amount of the chromatic secondary color ink A step of determining an amount set; and (c2-3) a plurality of reference ink amounts excluding a reference ink amount of the chromatic secondary color ink among a plurality of reference ink amounts included in the reference ink amount set (C2-4) when the lightness parameter value is substantially the same, the smaller the residual ink amount parameter value, the smaller the secondary color ink usage rate. Kunar so on, and determining the ink amount of the spot color inks contained in the separation ink amount set preferably contains.

  In this way, since the ink amount of the chromatic secondary color ink is determined so that the usage rate of the secondary color ink becomes smaller as the residual ink amount parameter value becomes smaller, when the residual ink amount is small, chromatic 2 By reducing the next color ink, the graininess of the image can be improved.

  In each of the color separation methods, the maximum ink amount when the chromatic secondary color ink is used to the maximum extent within the reproducible color range is used as the reference ink amount of the chromatic secondary color ink. It is preferable.

  By doing so, it is possible to easily obtain the reference ink amount of the secondary color ink.

  In each of the color separation methods, the remaining ink amount parameter value is set in advance for each of a plurality of reference ink amounts excluding the reference ink amount of the chromatic secondary color ink corresponding to each ink of the ink set. It is preferable to use a total value obtained by multiplying each of the obtained coefficients.

  In this way, a residual ink amount parameter value corresponding to the characteristics of each ink can be obtained.

  In each of the color separation methods, it is preferable that the coefficient is set to be larger as the reflection density of the ink dot of the corresponding ink is higher.

  By doing so, it is possible to obtain a residual ink amount parameter value in consideration of the difference in reflection density of the ink dots of each ink.

  In each of the color separation methods, it is preferable that the coefficient is set to be larger as the difference in color appearance between the corresponding ink color and the chromatic secondary color ink is smaller.

  By doing this, it is possible to obtain a residual ink amount parameter value that takes into account the difference in color appearance of each ink with the chromatic secondary color ink.

  In each of the color separation methods, the step (c2-4) includes (c2-4-1) a candidate ink amount of the chromatic secondary color ink based on the lightness parameter value and the residual ink amount parameter value. And (c2-4-2) determining the candidate ink amount of the chromatic primary color ink required for reproducing the reproduced color together with the candidate ink amount of the chromatic secondary color ink A step of determining a candidate ink amount set; and (c2-4-3) an ink duty limit that limits the upper limit value of the ink amount that the candidate ink amount set can use per unit area of the print medium. If it is within the range, the candidate ink amount set is directly adopted as the color separation ink amount set, while if the candidate ink amount set exceeds the ink duty limit, And determining the separation ink quantity set by modifying the candidate ink amount set so as to satisfy the ink duty limit, it will be preferable to include.

  By doing so, the ink amount of the chromatic secondary color ink can be easily adjusted. Further, since the color separation ink amount set can be determined so as to satisfy the ink duty limit, it is possible to prevent the printing medium from undulating.

  In each of the color separation methods, the ink set includes first and second chromatic secondary color inks, and in the step (c1), for each of the first and second chromatic secondary color inks. The brightness parameter value is calculated independently, and in the steps (c2-1), (c2-2), and (c2-3), the first and second chromatic secondary color inks are calculated. A reference ink amount set and the residual ink amount parameter value are independently determined, and in the step (c2-4-1), the lightness parameter value for each of the first and second chromatic secondary color inks is determined. And the residual ink amount parameter value, the candidate ink amounts of the first and second chromatic secondary color inks are respectively determined, and the candidate ink amount set is determined in the step (c2-4-3). Ink duty system In the case of a two-dimensional color space defined by the ink amounts of the first and second chromatic secondary color inks, the first and second chromatic secondary color inks A color coordinate point defined by the color separation ink amount is within a range satisfying the ink duty limit, and a color coordinate point defined by the candidate ink amount of the first and second chromatic secondary color inks It is preferable that the color separation ink amount set is determined so as to exist at a position close to the ink.

  By doing so, the color separation ink amount set can be determined so as to satisfy the ink duty limit, and therefore it is possible to suppress the undulation of the print medium.

  In each of the color separation methods, when the candidate ink amount set exceeds the ink duty limit in the step (c2-4-3), the two-dimensional data relating to the first and second chromatic secondary color inks. In the color space, color coordinate points defined by the color separation ink amounts of the first and second chromatic secondary color inks are within a range satisfying the ink duty limit, and the first and second chromatic secondary inks are present. It is preferable that the color separation ink amount set is determined so that a ratio of color separation ink amounts of the chromatic secondary color ink is equal to a ratio of candidate ink amounts of the first and second chromatic secondary color inks.

  By doing so, the graininess can be improved more appropriately.

  In each of the color separation methods, the step (b) includes (b1) when the chromatic color at the outermost shell position in the primary color space is called the outermost shell chromatic color, Corresponding outermost shell color separation ink amount set, the outermost shell color separation ink amount that can be reproduced by the ink set and reproduces an extended chromatic color having a higher saturation than the outermost shell chromatic color A step of determining a set; and (b2) each of the plurality of input colors in the primary color space based on a relationship between the outermost shell chromatic color and the outermost shell color separation ink amount set. Determining the plurality of reproduction colors, wherein the step (b1) sets an upper limit value of an ink amount that can be used per unit area of the print medium as an ink duty limit, and the expansion The chromatic color is the outermost color in the primary color space. The outermost shell color separation ink amount set for determining the color represented by a longer extended chromatic color vector having the same direction as the outermost shell chromatic color vector representing the chromatic color and reproducing the extended chromatic color And determining the extended chromatic color and the outermost shell color separation ink amount set under the following conditions: (i) the outermost shell color separation ink amount set is within the ink duty limit It is preferable to be carried out so as to satisfy certain conditions.

  By doing this, the outermost shell color separation ink amount so as to reproduce an extended chromatic color having a higher saturation than the outermost shell chromatic color having the highest saturation that can be reproduced only with the chromatic primary color ink. Since the set is determined, it is possible to perform color separation processing considering expansion of the color reproduction range. In addition, since the ink amount is limited by the ink duty limit, it is possible to perform the color separation process according to the characteristics of the print medium.

  In each of the color separation methods, the extended chromatic color and the outermost shell color separation ink amount set are further determined by the following condition: (ii) the length of the extended chromatic color vector within a range reproducible by the ink set. It is preferable to be carried out so as to satisfy

  By doing so, it is possible to perform color separation processing that effectively uses the color reproduction range that can be reproduced by the ink set.

  In each of the color separation methods, the extended chromatic color and the outermost shell color separation ink amount set are further determined by the following condition: (iii) the outermost shell color separation ink for reproducing the extended chromatic color It is preferable to carry out so as to satisfy that the total amount of ink in the amount set is minimized.

  By doing so, the amount of ink used can be saved.

  In each of the color separation methods, the reproduction color is set to an outermost shell color separation ink amount set for an outermost shell chromatic color having the same vector direction as the input color in the primary color space, and a vector length of the input color. It is preferable that the color be reproduced by a temporary color separation ink amount set obtained by multiplying the ratio with the vector length of the outermost shell chromatic color.

  By doing so, it is possible to easily set the reproduction color associated with the input color.

  In each of the above color separation methods, it is preferable that the chromatic secondary color ink contains a color material different from the plurality of chromatic primary color inks.

  By doing so, color reproducibility can be improved.

  In each of the above color separation methods, the chromatic secondary color ink is obtained when the hue that can be reproduced by the chromatic secondary color ink is reproduced by a color mixture of the plurality of chromatic primary color inks. It is preferable that it is possible to reproduce a higher saturation than that which can be reproduced by mixing the next color inks.

  By doing so, it is possible to reproduce a color having a saturation greater than or equal to the saturation that can be reproduced only with the chromatic primary color ink.

  In each of the color separation methods, the ink set includes first and second chromatic secondary color inks having different hues, and the chromatic secondary color ink is used as the plurality of chromatic primary color inks. The amount of each of the plurality of chromatic primary color inks relative to the amount of ink of the chromatic secondary color ink when reproducing substantially the same hue and saturation by substituting the combination of For each of the first and second chromatic secondary color inks, the first chromatic secondary color when the two primary inks having the largest value among the replacement ink amounts are the primary color inks. It is preferable that one of the two principal component primary color inks of the ink and one of the two principal component primary color inks of the second chromatic secondary color ink are different inks.

  In this way, the color reproduction range can be further expanded.

  In each of the above color separation methods, the ink set includes black ink, and in the step (b), the black component is removed by performing undercolor removal processing of the black ink on the input color. Preferably, the method includes a step of obtaining a corrected input color composed of a primary color component, and the reproduction color is determined according to the corrected input color.

  In this way, the color reproduction range can be further expanded.

  The present invention can be realized in various forms. For example, an image data conversion method and apparatus, a printing method and a printing apparatus, and a color conversion lookup table creation method and apparatus using the color separation method described above. It can be realized in the form of a computer program for realizing the functions of these methods or apparatuses, a recording medium recording the computer program, a data signal including the computer program and embodied in a carrier wave, and the like.

Next, embodiments of the present invention will be described in the following order based on examples.
A. Device configuration:
B. First embodiment of separation processing:
C. Second embodiment of separation processing:
D. Example of final color separation ink amount set calculation processing:
E. Third embodiment of separation processing:
F. Variation of ink set:
G. Variations:

A. Device configuration:
FIG. 1 is a block diagram showing the configuration of a printing system as an embodiment of the present invention. This printing system includes a computer 90 as an image data processing apparatus and a color printer 20 as a printing unit. The printer 20 and the computer 90 can be referred to as a “printing apparatus” in a broad sense.

  In the computer 90, an application program 95 operates under a predetermined operating system. A video driver 91 and a printer driver 96 are incorporated in the operating system, and print data PD to be transferred to the printer 20 is output from the application program 95 via these drivers. The application program 95 that performs image retouching or the like performs desired processing on the image to be processed, and displays an image on the CRT 21 via the video driver 91.

  When the application program 95 issues a print command, the printer driver 96 of the computer 90 receives the image data from the application program 95 and converts it into print data PD to be supplied to the printer 20. In the example shown in FIG. 1, the printer driver 96 includes a resolution conversion module 97, a color conversion module 98, a halftone module 99, a rasterizer 100, and a color conversion lookup table LUT. Yes.

  The resolution conversion module 97 serves to convert the resolution (that is, the number of pixels per unit length) of the color image data formed by the application program 95 into the print resolution. The image data thus converted in resolution is still image information composed of three color components of RGB. The color conversion module 98 refers to the color conversion lookup table LUT, and converts RGB image data (input color image data) for each pixel into multi-tone data (first gradation data) that can be used by the printer 20. 2 color image data).

  The color-converted multi-gradation data has, for example, 256 gradation values. The halftone module 99 performs so-called halftone processing to generate halftone image data. The halftone image data is rearranged in the order of data to be transferred to the printer 20 by the rasterizer 100, and output as final print data PD. The print data PD includes raster data indicating the dot recording state during each main scan and data indicating the sub-scan feed amount.

  The printer driver 96 corresponds to a program for realizing a function for generating the print data PD. A program for realizing the function of the printer driver 96 is supplied in a form recorded on a computer-readable recording medium. Such recording media include flexible disks, CD-ROMs, magneto-optical disks, IC cards, ROM cartridges, punch cards, printed matter on which codes such as bar codes are printed, computer internal storage devices (such as RAM and ROM). A variety of computer-readable media such as a memory) and an external storage device can be used.

  FIG. 2 is a schematic configuration diagram of the printer 20. The printer 20 includes a sub-scan feed mechanism that transports the printing paper PP in the sub-scan direction by the paper feed motor 22, and a main scan feed mechanism that reciprocates the carriage 30 in the axial direction (main scan direction) of the platen 26 by the carriage motor 24. A head drive mechanism that drives the print head unit 60 mounted on the carriage 30 to control ink ejection and dot formation, the paper feed motor 22, the carriage motor 24, the print head unit 60, and the operation panel 32. And a control circuit 40 that manages the exchange of the above signals. The control circuit 40 is connected to the computer 90 via the connector 56.

  The sub-scan feed mechanism that transports the printing paper PP includes a gear train (not shown) that transmits the rotation of the paper feed motor 22 to the platen 26 and a paper transport roller (not shown). Further, the main scanning feed mechanism for reciprocating the carriage 30 has an endless drive belt 36 between the carriage motor 24 and a slide shaft 34 that is installed in parallel with the axis of the platen 26 and slidably holds the carriage 30. And a position sensor 39 for detecting the origin position of the carriage 30.

  FIG. 3 is a block diagram showing the configuration of the printer 20 with the control circuit 40 as the center. The control circuit 40 is configured as an arithmetic and logic circuit including a CPU 41, a programmable ROM (PROM) 43, a RAM 44, and a character generator (CG) 45 that stores a dot matrix of characters. The control circuit 40 further includes an I / F dedicated circuit 50 dedicated to interface with an external motor and the like, and a head that is connected to the I / F dedicated circuit 50 and drives the print head unit 60 to eject ink. A drive circuit 52 and a motor drive circuit 54 for driving the paper feed motor 22 and the carriage motor 24 are provided. The I / F dedicated circuit 50 incorporates a parallel interface circuit and can receive print data PD supplied from the computer 90 via the connector 56. The circuit built in the I / F dedicated circuit 50 is not limited to the parallel interface circuit, but can be determined in consideration of the ease of connection with the computer 90, such as a universal serial bus interface circuit, and the communication speed. The printer 20 executes printing according to the print data PD. The RAM 44 functions as a buffer memory for temporarily storing raster data.

  The print head unit 60 has a print head 28 and can be mounted with an ink cartridge. The print head unit 60 is attached to and detached from the printer 20 as one component. That is, when the print head 28 is to be replaced, the print head unit 60 is replaced.

  FIG. 4 is an explanatory diagram showing the nozzle arrangement on the lower surface of the print head 28. On the lower surface of the print head 28, a nozzle group for ejecting cyan ink C, a nozzle group for ejecting magenta ink M, a nozzle group for ejecting black ink K, and red ink R are ejected. For this purpose, a nozzle group for ejecting the violet ink V, and a nozzle group for ejecting the yellow ink Y are formed. In this embodiment, it is possible to use an ink set composed of six inks C, M, Y, R, V, and K. In the example of FIG. 4, the plurality of nozzles Nz of one nozzle group are arranged on a straight line along the sub-scanning direction SS, but may be arranged in a staggered manner.

  FIG. 5A is an explanatory diagram showing ink components of each color ink of CMYRVK in the ink set. The ink of each color is a mixed solution in which appropriate amounts of a coloring material composed of various dyes or pigments for imparting a desired color, ethylene glycol for viscosity adjustment, and the like are added based on ion-exchanged water. The type of color material is indicated by the color index (C.I.) of the color material.

  Cyan ink C, magenta ink M, and yellow ink Y can be used in combination with each other to reproduce gray (achromatic color) and correspond to chromatic primary color ink. The red ink R and the violet ink V are inks whose hues are different from any of the chromatic primary color inks (CMY), and correspond to chromatic secondary color inks. The red ink R has a hue between the yellow ink Y and the magenta ink M, and the violet ink V has a hue between the magenta ink M and the cyan ink C.

  The mixed color of the chromatic primary color inks C, M, and Y can reproduce the same hue and saturation as the respective colors of the chromatic secondary color inks R and V. Here, the chromatic primary color ink when each ink amount of the mixed color of the chromatic primary color ink with respect to the ink amount of the chromatic secondary color ink, that is, the ink amount of the chromatic secondary color ink is 1. Each of the mixed color ink amounts is referred to as a replacement ink amount. At this time, it is possible to reproduce substantially the same color even if the CMY inks and the RV inks are replaced based on the replacement ink amount.

  FIGS. 5B and 5C show the experimental results of measuring the replacement ink amount using the ink set shown in FIG. This experimental result was obtained by measuring and comparing the color patches obtained by mixing the chromatic primary color inks C, M, and Y with the color patches of the chromatic secondary color inks R and V. is there. FIG. 5B shows the replacement ink amount with respect to the red ink R, and the replacement ink amount of each color of CMY is described with the codes wCR, wMR, and wYR in order. FIG. 5C shows the replacement ink amount with respect to the violet ink V, and the replacement ink amount of each color of CMY is described with the symbols wCV, wMV, and wYV in order. The total value of each replacement ink amount is written in the right column of each table.

  Thus, the replacement ink amounts of the chromatic secondary color inks R and V are such that two of the three ink amounts are larger than zero, and one ink amount is zero. That is, the chromatic secondary color inks R and V can be decomposed into two chromatic primary color components. In the ink set shown in FIG. 5, it is possible to replace the chromatic primary color ink mixture with a chromatic secondary color ink whose amount is smaller than the total value of the respective ink amounts. As a result, by actively using chromatic secondary color ink, it is possible to reproduce substantially the same hue and saturation with a smaller amount of ink. Further, it is possible to reproduce higher brightness by reducing the ink amount. Furthermore, by using a chromatic secondary color ink having an ink amount comparable to the mixed color of the chromatic primary color ink, higher saturation can be reproduced. Therefore, even when a limit (ink duty limit) is imposed on the total amount of ink to be used (details will be described later), by using chromatic secondary color ink, it is possible to mix chromatic primary color inks. It is possible to reproduce a saturation higher than the saturation that can be reproduced. Thus, by using the chromatic primary color ink and the chromatic secondary color ink, it is possible to reproduce a wider range of colors than the range that can be reproduced with only the chromatic primary color ink.

  The two chromatic secondary color inks R and V are inks having different hues. Furthermore, the primary component primary color inks of these inks R and V, that is, the two inks having the largest value among the replacement ink amounts of the respective CMY colors are different from each other. In the example of FIG. 5, the primary color inks of red ink R are magenta ink M and yellow ink Y. The primary color inks of the violet ink V are cyan ink C and magenta ink M. In this example, the yellow ink Y and the cyan ink C are different. As a result, the two chromatic secondary color inks R and V can extend the color reproduction range of regions having different hues. Therefore, a wider color reproduction range can be reproduced as compared with the case where chromatic secondary color inks having similar hues are used.

  Further, in the ink set shown in FIG. 5A, the chromatic secondary color inks R and V contain a color material different from the chromatic primary color inks C, M, and Y. Therefore, by using the chromatic secondary color ink instead of the mixed color of the chromatic primary color inks C, M, and Y, the reproducibility of the hue close to that of the chromatic secondary color ink can be improved.

  In the printer 20 having the hardware configuration described above, the carriage 30 is reciprocated by the carriage motor 24 while the paper PP is being conveyed by the paper feed motor 22, and at the same time, the piezo elements of the print head 28 are driven. Are ejected to form ink dots to form a multi-color / multi-tone image on the paper PP.

B. First embodiment of separation processing:
B1. To create a color conversion lookup table:
FIG. 6 is a flowchart showing a color reproduction processing procedure in this embodiment. In steps S10 to S70, a color conversion lookup table LUT (FIG. 1) for color reproduction is created.

  First, in step S10, one combination of a print medium and an ink set used for printing is selected. In a normal printer, it is assumed that one print medium selected by the user from a plurality of types of print media (plain paper, glossy paper, matte paper, etc.) is used. In some types of printers, the ink set to be used may be selected from a plurality of types of ink sets (for example, a dye ink set and a pigment ink set). The color reproducibility of the printed material depends on the printing medium and the ink set. Therefore, in this embodiment, the processing of steps S10 to S60 is executed for each combination of the print medium and the ink set, and a color conversion lookup table LUT suitable for the combination is created. Note that the type of print medium and the type of ink set that are assumed to be used in the printer 20 are normally displayed on a screen (not shown) for setting print conditions of the printer driver 96.

  In step S20, a color separation process for converting the primary color gradation value set represented by the primary color system to the second gradation value set represented by the reproduction color system is executed. The primary color system is a color system represented by the amount of each color ink of the chromatic primary color inks CMY, and the reproduction color system is a color system represented by the ink amount of each color ink used during printing. It is a system. This primary color gradation value set is composed of a plurality of chromatic primary color inks C, M, and Y. The ink amount of each of the chromatic primary color inks C, M, and Y is in the range from the minimum value (zero) to the maximum value (ink amount when reproducing the solid area), for example, 256 of 0 to 255. It is a value expressed in gradation. In this embodiment, the solid area is reproduced by ejecting ink to all pixels. Therefore, the ink amount when reproducing such a solid region can be set to 100%.

  In step S20, first, a plurality of primary color gradation value sets are prepared. The ink amounts of the chromatic primary color inks C, M, and Y in the plurality of primary color gradation value sets are preferably distributed over the entire range (0% to 100%) that can be taken. It is particularly preferable that the distribution is uniform throughout. As such a plurality of ink amount values, for example, 11 values of “0, 25, 50, 75, 100, 125, 150, 175, 200, 225, 255” can be used. Note that the change in the appearance of the reproduced color with respect to the change in the gradation value of each ink amount may differ depending on the gradation value of each ink. In such a case, it is preferable to prepare the ink amount of each ink at a finer interval in a gradation value range where the change in color appearance is larger. By doing so, it is possible to create a color conversion lookup table LUT that finely corresponds to changes in the apparent color.

  Next, the plurality of primary color gradation value sets are converted into a second gradation value set expressed in the reproduction color system. The reproduction color system is a color system represented by each ink amount of the ink set used at the time of printing, for example, each color ink amount of the chromatic primary color ink CMY and the chromatic secondary color ink RV. The second gradation value set is a value expressing the range of the minimum value (0%) to the maximum value (100%) that can be taken with respect to the ink amount of each color of CMYRV, for example, with 256 gradations from 0 to 255. is there. Details of the color separation process from the primary color system to the reproduction color system will be described later.

  In step S30, a plurality of types of color patches corresponding to a plurality of primary color gradation value sets are created. FIG. 7 is an explanatory diagram illustrating an example of a color patch created in the present embodiment. The vertical axis represents the tone value of magenta ink M in the primary color tone value set prepared in step S20 described above, and the horizontal axis represents the tone value of yellow ink Y. Each color patch is reproduced with each ink amount of the ink set obtained by converting each gradation value according to the color separation process of step S20. The example of FIG. 7 shows a case where the gradation value of cyan ink C in the primary color gradation value set is set to zero. Actually, a plurality of types of color patches corresponding to a plurality of gradation values of cyan ink C are created, but the illustration is omitted. Thus, in step S30, a plurality of types of color patches corresponding to the plurality of primary color gradation value sets prepared in step S20 described above are created.

  In step S40 (FIG. 6), the color measurement of the plurality of color patches created in step 30 is performed using a colorimeter. The data obtained as a result of the color measurement is data expressed in a color system that does not depend on a device such as a printer or a monitor, for example, an L * a * b * color system or an XYZ color system. In this way, in step S40, by performing colorimetry of each color patch, “correspondence between primary color / device independent color system” between the primary color system and the device independent color system. Can be determined. As a result of the color measurement, it is also possible to confirm the color range that can be reproduced by the printer 20 in the device-independent color system.

  In step S50, the correspondence between the arbitrary first color system and the primary color system is based on the “correspondence between the primary color / device-independent color system” obtained in step S40 described above. To set. The first color system is a color system of input color image data of the color conversion lookup table LUT, and for example, an sRGB color system can be used. Such “first color system / device-independent color system” correspondence between the first color system and the device-independent color system is set in advance. Therefore, by using this “first color system / device-independent color system correspondence” and the “primary color / device-independent color system correspondence” obtained in step S40, A correspondence relationship between one color system and the primary color system can be set. Note that there may be a portion where the color reproduction range in the first color system and the color reproduction range of the printer do not overlap each other. In such a case, it is preferable to use the entire color area effectively by appropriately setting the corresponding relationship of enlargement / reduction.

  Thus, the first correspondence between the first color system and the primary color system (step S50) and the second correspondence between the primary color system and the reproduction color system (step S20). Is set, a color conversion lookup table LUT (FIG. 1) for reproducing the set correspondence is created in step S60. The color conversion lookup table LUT in the present embodiment receives RGB image data and outputs multi-tone image data for the six ink colors shown in FIG. Therefore, when the color conversion lookup table LUT is created, first, a primary color gradation value set expressed in CMY corresponding to the gradation values of the RGB image data is calculated. Next, a second gradation value set corresponding to the primary color gradation value set, that is, the ink amount of each ink is determined according to a color separation process described later. A correspondence relationship in which the value of the RGB image data is input and the ink amount of each ink is output is stored in the lookup table LUT.

  In step S70 of FIG. 6, it is determined whether or not the processing in steps S10 to S60 has been completed for all combinations of print media and ink sets that are assumed to be used in the printer 20. If all the processes are not completed, the processes of steps S10 to S60 are repeated. If completed, the process proceeds to the next step S80.

  In step S80, the created plural types of color conversion lookup tables LUT are incorporated in the printer driver 96 (FIG. 1). The printer driver 96 is a computer program for causing the computer 90 to realize a function of creating print data PD supplied to the printer 20. The color conversion lookup table LUT is installed in the computer 90 together with the printer driver 96 as data referred to by the printer driver 96. The printer driver 96 in which the color conversion lookup table LUT is incorporated is usually supplied by the printer 20 manufacturer.

  In step S <b> 90 of FIG. 6, the user executes printing using the printer 20. At this time, a look-up table suitable for the combination of the print medium and ink set used for actual printing is selected from the color conversion look-up table LUT for all combinations of the print medium and ink set, and printing is executed. Is done. A set of a print medium and an ink set used for actual printing is selected by a user on a screen (not shown) for setting print conditions of the printer driver 96.

B2. Details of separation processing in the first embodiment:
FIG. 8 is a flowchart showing the processing procedure of the color separation process. In this color separation processing, conversion processing from the primary color system to the reproduction color system is executed. In step S500 in FIG. 8, an ink set including chromatic primary color inks C, M, and Y and chromatic secondary color inks R and V is set as usable ink.

  In step S510, a temporary color separation ink amount set I (Cp, Mp, Yp, Rp, Vp) for reproducing a reproduction color corresponding to the input color I (Ci, Mi, Yi) on the print medium is calculated. . In the first embodiment, the input color I (Ci, Mi, Yi) matches the reproduced color. There can be an infinite number of color separation ink amount sets for obtaining an arbitrary reproduction color. Therefore, the provisional color separation ink amount set is determined by providing specific conditions. For example, in this embodiment, the provisional color separation ink amount set P (Cp, Mp, Yp, Rp, Vp) is determined so that the total ink amount is minimized.

  As described with reference to FIG. 5, the color component of the chromatic secondary color ink can be separated into the color components of the two chromatic primary color inks. Accordingly, the total ink amount decreases as the amount of chromatic secondary color ink increases. In addition, the provisional color separation ink amount set P of the present embodiment is uniquely determined because the total ink amount is the smallest among the color separation ink amount sets that can reproduce the same reproduction color as the input color I. Is done. However, as can be understood from other examples described later, the provisional color separation ink amount set P can be determined according to other conditions.

  In step S520, a final color separation ink amount set O (Co, Mo, Yo, Ro, Vo) is determined based on the provisional color separation ink amount set P (Cp, Mp, Yp, Rp, Vp). (Details will be described later). In step S530, it is determined whether or not the processing in steps S510 and S520 has been completed for all reproduction colors required to create the lookup table. Then, the processes in steps S510 and S520 are repeated until the processes for all reproduced colors are completed.

  FIG. 9 is a flowchart showing a detailed procedure of step S520. In step S600, residual ink amounts RES_R and RES_V corresponding to the two chromatic secondary color inks R and V from the provisional color separation ink amount set P are determined. The remaining ink amount is a total value of the ink amounts of inks other than the chromatic secondary color ink. In the next step S610, candidate ink amounts Rtmp and Vtmp for the two chromatic secondary color inks R and V are determined using the remaining ink amounts RES_R and RES_V.

  10A to 10E are explanatory diagrams for explaining the relationship between the usage rate of the chromatic secondary color ink and the ink amount of the other ink. In the examples of FIGS. 10A to 10E, for the sake of simplicity, two types of chromatic primary color ink, cyan ink C and magenta ink M, can be used. It is assumed that one type of violet ink V can be used as the ink.

  FIG. 10A is an explanatory diagram showing the range of hues that can be reproduced using cyan ink C and magenta ink M. FIG. The violet ink V has a hue between the cyan ink C and the magenta ink M. FIG. 10A shows two colors ColA and ColB. The two colors ColA and ColB have a hue between the violet ink V and the cyan ink C. The color ColA is a color having a hue close to the violet ink V. The color ColB is a color obtained by adjusting the hue of the color ColA so as to be closer to the cyan ink C.

  FIG. 10B shows an example of the ink amounts of the three inks C, M, and V for reproducing the color ColA. Since the color ColA has a hue close to that of the violet ink V, it can be reproduced by using a large amount of the violet ink V. Further, since the color ColA has a hue between the violet ink V and the cyan ink C, it can be reproduced by using the cyan ink C. In the example of FIG. 10B, the cyan ink C is 2, the magenta ink M is 0, and the violet ink V is 20. Here, the ink amount of each color of CMV can take a value in the range of 0-100. The ink amount = 0 means that the ink amount is zero, and the ink amount = 100 means the ink amount when reproducing the solid area.

  Violet ink V is characterized by higher saturation and density than cyan ink C and magenta ink M. Therefore, in a bright region, if the violet ink V is positively used as shown in FIG. 10B, the ink dots are likely to stand out, and the graininess may not be sufficiently improved.

  FIG. 10C shows another example of the ink amounts of the three inks C, M, and V for reproducing the color ColA. The difference from the example of FIG. 10B is that the amount of violet ink V is small and the amount of cyan ink C and magenta ink M is large. Specifically, cyan ink C is 11, magenta ink M is 9, and violet ink V is 11.

  Here, it is assumed that an equal amount of mixed colors of the cyan ink C and the magenta ink M can reproduce substantially the same hue and saturation as the equivalent amount of the violet ink V. That is, the replacement ink amount for the violet ink V is cyan ink C = 1 and magenta ink M = 1. In the example of FIG. 10C, based on the ink amount of FIG. 10B, the violet ink V with the ink amount = 9 is changed into the cyan ink C with the ink amount = 9 and the magenta ink M with the ink amount = 9. This is a combination of ink amounts obtained by replacement. Therefore, the example of FIG. 10C can reproduce the same color ColA as the example of FIG. Note that there can be countless combinations of ink amounts obtained by replacing the ink amount according to the replacement ink amount. Among these combinations, the example of FIG. 10B shows a combination in which the ink amount of the violet ink V is maximized.

  By the way, if the ink amount of the violet ink V is reduced as shown in FIG. 10C, the ink amounts of the other inks C and M are increased, so that the ink dots of the violet ink V can be made inconspicuous. Here, it is assumed that if the total value of the ink amounts of the other inks C and M is greater than or equal to twice the ink amount of the violet ink V, the ink dots of the violet ink V are less noticeable. Then, as shown in FIG. 10C, if the usage rate of the ink amount of the violet ink V (in this example, the ratio of the ink amount to the maximum value) is set to 55% (= 11/20), the graininess Can be improved.

  FIG. 10D shows an example of the ink amounts of the three inks C, M, and V for reproducing the color ColB. Since the color ColB has a hue close to that of the cyan ink C compared to the color ColA, even when the violet ink V is actively used, the cyan ink C is relatively used. In the example of FIG. 4D, the cyan ink C is 10, the magenta ink M is 0, and the violet ink V is 15. This example shows a combination in which the ink amount of the violet ink V is maximized, as in FIG.

  In the example of FIG. 10D, the total ink amount (10) of inks other than the violet ink V is smaller than the double value (30) of the violet ink V ink amount. Accordingly, in a bright region, the ink dots of the violet ink V are easily noticeable, and there is a possibility that the graininess cannot be sufficiently improved.

  FIG. 10E shows another example of the ink amounts of the three inks C, M, and V for reproducing the color ColB. The difference from the example of FIG. 10D is that the amount of violet ink V is small and the amount of cyan ink C and magenta ink M is large. Specifically, the cyan ink C is 15, the magenta ink M is 5, and the violet ink V is 10. These ink amounts are obtained by replacing the violet ink V with the ink amount = 5 with the cyan ink C with the ink amount = 5 and the magenta ink M with the ink amount = 5 based on the ink amount in FIG. This is a combination of the obtained ink amounts.

  In the example of FIG. 10E, the total value (20) of the ink amounts of the inks C and M other than the violet ink V is approximately twice the ink amount (10) of the violet ink V. Therefore, regarding the color ColB, if the usage rate of the ink amount of the violet ink V is 67% (= 10/15), the graininess can be improved.

  As described above, regarding the color ColA whose hue is relatively close to the chromatic secondary color ink, if the chromatic secondary color ink is actively used for reproduction, the ink amount of the other ink becomes small. Therefore, in order to improve the graininess, it is preferable to reduce the usage rate of the chromatic secondary color ink. On the other hand, for the color ColB whose hue is relatively close to the chromatic primary color ink, even if the chromatic secondary color ink is actively used for reproduction, the ink amount of the other ink is maintained at a relatively large value. The Therefore, the graininess can be improved even when the usage rate of the chromatic secondary color ink is set to a relatively large value. Also, if the usage rate of chromatic secondary color ink is set to a relatively large value, the total value of all ink amounts can be reduced compared to when the usage rate is set to a small value, thus saving ink. can do.

  By the way, the relationship between the usage rate and hue of the chromatic secondary color ink can be considered by replacing it with the relationship between the usage rate of the chromatic secondary color ink and the ink amount of ink other than the chromatic secondary color ink. . As shown in FIGS. 10A to 10E, when the hue is relatively close to the chromatic primary color ink, even if the ink amount of the chromatic secondary color ink is increased, the ink amounts of the other inks are compared. Is maintained at a large value. On the other hand, when the hue is relatively close to the chromatic secondary color ink, increasing the ink amount of the chromatic secondary color ink makes the ink amounts of the other inks relatively small. Therefore, if the usage rate of the chromatic secondary color ink is increased when the ink amount of the other ink is large, and the usage rate of the chromatic secondary color ink is decreased when the ink amount of the other ink is small, The graininess can be improved appropriately according to the hue.

  The relationship between the usage rate of the chromatic secondary color ink described above and the ink amount of the other ink can be considered in the same manner even when the number of ink types is increased. Also in this case, it is preferable that the usage rate of the chromatic secondary color ink when the ink amount of the other ink is small is smaller than the usage rate when the ink amount of the other ink is large. In this way, it is possible to improve graininess in a bright area and save ink.

  In step S600 of FIG. 9, residual ink amounts RES_R and RES_V corresponding to the chromatic secondary color inks R and V are calculated. In this embodiment, the remaining ink amounts RES_R and RES_V are expressed by the following equations using the respective ink amounts included in the temporary color separation ink amount set P calculated in step S510 of FIG.

  In the formula, Cp, Mp, Yp, Rp, and Vp are ink amounts of the respective inks included in the provisional color separation ink amount set P. The residual ink amount RES_R corresponding to the red ink R is a total value of the ink amounts of the inks other than the red ink R. The residual ink amount RES_V corresponding to the violet ink V is a total value of the ink amounts of the respective inks other than the violet ink V.

  Next, in step S610, candidate ink amounts Rtmp and Vtmp for the chromatic secondary color inks R and V are determined from the remaining ink amounts RES_R and RES_V and the provisional color separation ink set P. FIG. 11A shows a graph for obtaining the candidate ink amount Rtmp from the provisional color separation ink amount Rp of the red ink R. The graph L10 is a graph corresponding to a relatively large residual ink amount RES_R10, and the graph L20 is a graph corresponding to a relatively small residual ink amount RES_R20. For example, the graph L10 corresponds to the cases of FIGS. 10D and 10E, and the graph L20 corresponds to the cases of FIGS. 10B and 10C.

  Hereinafter, the relationship between the candidate ink amount Rtmp and the provisional color separation ink amount Rp will be described using the graph L10 as an example. In the first range R1 where the provisional color separation ink amount Rp reaches the first value Rs10 from zero, the candidate ink amount Rtmp is set to zero. Further, the candidate ink amount Rtmp increases linearly from zero in the second range R2 in which the provisional color separation ink amount Rp reaches the second value Re10 from the first value Rs10. However, in the second range R2, the candidate ink amount Rtmp is maintained at a value smaller than the provisional color separation ink amount Rp. In the third range R3 in which the temporary color separation ink amount Rp is equal to or greater than the second value Re10, the candidate ink amount Rtmp is set to a value equal to the temporary color separation ink amount Rp.

  Also for the graph L20 corresponding to the relatively small residual ink amount RES_R20, the candidate ink amount Rtmp is set according to the first value Rs20 and the second value Re20 as in the graph L10. However, the first value Rs20 is set to a value larger than the first value Rs10 of the graph L10, and the second value Re20 is also set to a value larger than the second value Re10 of the graph L10. Therefore, when the provisional color separation ink amount Rp has the same value, a relatively large candidate ink amount Rtmp can be obtained when the residual ink amount RES_R is relatively large.

  FIG. 11B is a graph showing a ratio k of the candidate ink amount Rtmp to the provisional color separation ink amount Rp. The ratio k10 corresponding to the residual ink amount RES_R10 will be described as an example. As can be understood from this graph, the ratio k10 is zero in the first range R1, and the ratio k10 is monotonically from zero to 1 in the second range R2. It has increased. In the third range R3, the ratio k10 is 1 and constant.

  Regarding the ratio k20 corresponding to the remaining ink amount RES_R20, the way of changing the ratio k20 in each of the first to third ranges R201 to R203 is the same as the way of changing the ratio k10. When the provisional color separation ink amount Rp is the same value, a relatively large ratio k can be obtained when the residual ink amount RES_R is relatively large.

  Hereinafter, the reason why the change method of the candidate ink amount Rtmp with respect to the change of the provisional color separation ink amount Rp is set as shown in FIGS. 11A and 11B will be described using the graph L10 as an example. When the provisional color separation ink amount Rp is small, an image reproduced with the reproduced color is often a so-called highlight area (high brightness area) image. Incidentally, the chromatic secondary color inks R and V are characterized in that their saturation and density are higher than those of the chromatic primary color ink. Since the dots of the chromatic secondary color ink have high saturation and density, they are easily noticeable in the highlight area and may deteriorate the graininess of the image. Therefore, it is preferable that the amount of chromatic secondary color ink is small in the highlight region. Further, when the ink amount of the chromatic secondary color ink is decreased, the ink amount of the chromatic primary color ink is increased, so that the total number of ink dots is increased. Also from this point, the graininess of the image can be improved by reducing the ink amount of the chromatic secondary color ink in the highlight region. Therefore, in the first range R1 in FIG. 11A, the ink amount Rtmp of the chromatic secondary color ink is set to zero so that the dots of the chromatic secondary color ink are not formed in the highlight region. ing. In this way, the graininess of the image in the highlight area can be greatly improved.

  On the other hand, in the third range R3 where the provisional color separation ink amount Rp is large, it is preferable to increase the saturation of the image by increasing the ink amount of the chromatic secondary color ink as much as possible. Therefore, in this range R3, the provisional color separation ink amount Rp is set as the candidate ink amount Rtmp as it is. In the second range R2, the candidate ink amount Rtmp is linearly increased so that the candidate ink amount Rtmp changes smoothly without changing stepwise in the three ranges R1 to R3. Note that the candidate ink amount Rtmp may be changed in a curved line instead of linearly. In general, it is preferable to change the candidate ink amount Rtmp so as to continuously and monotonously increase.

  Note that the provisional color separation ink amount Rp of red ink for a certain reproduction color means the density of the red ink component of the reproduction color, and therefore this ink amount Ro is considered as an index indicating the lightness of the red ink component. Can do. Further, when the provisional color separation ink amount Rp of red ink relating to a certain reproduction color is large, the lightness of the reproduction color tends to be low. Therefore, the provisional color separation ink amount Rp can be considered as a lightness parameter value correlated with the lightness of the reproduced color.

  On the other hand, the reason why the change in the candidate ink amount Rtmp relative to the change in the residual ink amount RES_R is set as shown in FIGS. 11A and 11B is as follows. When the residual ink amount RES_R is small, the hue of the reproduced color is often close to chromatic secondary color ink. When such a reproduced color is reproduced by actively using chromatic secondary color ink, the ink amount of the plurality of chromatic primary color inks is reduced, so that the total number of ink dots is reduced. As a result, the ink dots of the chromatic secondary color ink become conspicuous in a bright region, and there is a possibility that the graininess of the image is deteriorated. On the other hand, when the residual ink amount RES_R is large, the hue of the reproduced color is often far from the chromatic secondary color ink. Even if such a reproduced color is reproduced by actively using chromatic secondary color ink, the amount of chromatic primary color ink is relatively large compared to when the residual ink amount RES_R is small. Maintained. As a result, since the total number of ink dots does not become an extremely small value, ink can be saved without deteriorating the graininess of the image. Therefore, in FIGS. 11A and 11B, even when the lightness parameter value Rp is the same, a larger ratio k can be obtained when the residual ink amount RES_R is large. By doing so, it is possible to improve graininess and save ink.

  In this embodiment, the remaining ink amount RES_R is calculated based on the provisional color separation ink amount Rp. Therefore, when the candidate ink amount Rtmp determined based on the residual ink amount RES_R becomes larger than the provisional color separation ink amount Rp, the ink amount of the chromatic primary color ink becomes smaller than the intended value, and the granularity in the bright region May worsen sex. Therefore, in the examples of FIGS. 11A and 11B, the candidate ink amount Rtmp is set to a value that does not exceed the provisional color separation ink amount Rp. By doing so, it is possible to improve graininess and save ink. The ratio k shown in FIG. 11B can be considered to correspond to the secondary color ink usage rate in the present invention.

  In addition, the secondary color ink usage rate k may be a constant value in a part of the range where the value of the residual ink amount RES_R can be obtained regardless of the change of the residual ink amount RES_R. For example, in the example of FIG. 11B, when the lightness parameter value Rp = Re10, the secondary color ink usage rate k is a constant value 1 even if the residual ink amount RES_R is larger than RES_R10. At this time, the hue of the reproduced color is within a partial range close to the chromatic primary color ink determined according to the residual ink amount RES_R in the bright region. When the lightness parameter value Rp = RS20, the secondary color ink usage rate is a constant value 0 even if the residual ink amount RES_R is smaller than RES_R20. At this time, the hue of the reproduced color is within a partial range close to the chromatic secondary color ink determined according to the residual ink amount RES_R in the bright region. As described above, the secondary color ink usage rate k is determined by improving the graininess and saving ink. As a result, depending on the value of the lightness parameter value Rp, the secondary color ink usage rate k may be reproduced. There may be a constant value in a part of the hue range. In this way, if the secondary color ink usage rate k is a variable value based on the hue, that is, the residual ink amount RES_R, in at least a part of the hue range, the improvement in graininess and the ink are achieved. Savings.

  Further, in this embodiment, when the lightness parameter value Rp is equal to or less than a first value (R1 and R201 in FIGS. 11A and 11B) determined according to the residual ink amount RES_R, the secondary color ink usage rate. k is set to zero. Here, it is preferable that the first value when the residual ink amount RES_R is the maximum value in a range in which the value can take a value be equal to or greater than zero (hereinafter referred to as a first high brightness reference value). In this way, when the brightness parameter value Rp is in the brightest partial range smaller than the first high brightness reference value, the secondary ink is used regardless of the residual ink amount RES_R, that is, the hue of the reproduced color. The rate k is set to zero. As a result, it is possible to suppress the chromatic secondary color ink from being noticeable in a bright region, and to improve the graininess of the image. Such a first high brightness reference value is preferably a bright range of 5% or less when the range in which the brightness parameter value can take a value is 0% (bright) to 100% (dark), A bright range of 10% or less is particularly preferable, and a bright range of 15% or less is most preferable.

  In this embodiment, when the lightness parameter value Rp is in a bright range smaller than the second high lightness reference value, the secondary color ink usage rate k is a variable value based on the hue, that is, the residual ink amount RES_R. Can be. Here, the second high lightness reference value is a second value when the residual ink amount RES_R is zero (not shown). However, as described above, in the range where the lightness parameter value Rp is smaller than the first high lightness reference value, the secondary color ink usage rate k is set to zero regardless of the residual ink amount RES_R. Thus, the secondary ink usage rate k is the residual ink in at least a part of the brightest range of the brightness parameter value Rp (in this embodiment, a range smaller than the second high brightness reference value). If the variable value is based on the amount RES_R, it is possible to improve graininess and save ink.

  Also for the violet ink V, the candidate ink amount Vtmp is determined from the provisional color separation ink amount Vp according to the same method as the red ink R.

  In step S610 of FIG. 9, the final color separation ink amount pair Ro, Vo is determined from the candidate ink amount pair Rtmp, Vtmp. This final color separation ink amount pair Ro, Vo is determined by correcting the candidate ink amount pair Rtmp, Vtmp as necessary so as to satisfy the ink duty limit. Here, the ink duty limit is a limit on the amount of ink that can be used per unit area of the print medium. The ink duty limit includes a limit for each ink, a limit for the total ink amount of two types of ink, a limit for the total ink amount of all inks, and the like.

  When executing step S610, first, candidate ink amounts of the chromatic primary color inks C, M, and Y required for reproducing a desired reproduction color are calculated together with the candidate ink amount pair Rtmp, Vtmp. The Then, it is determined whether or not this candidate ink amount set satisfies the ink duty limit.

  FIG. 12A shows an example of the allowable range RA of the ink duty limit in a two-dimensional color space defined by the chromatic secondary color inks R and V. This figure also shows an example of a coordinate point P (Rp, Vp) of a temporary color separation ink amount pair and a coordinate point Prv (Rtmp, Vtmp) of a candidate ink amount pair. The outer edge of the allowable range RA is defined not only by the boundary line determined by the duty limit of the chromatic secondary color ink alone, but also by the boundary line determined by the duty limit of other ink. For example, the lower left boundary line LRVM1 of the allowable range RA corresponds to the ink duty limit of magenta ink. As described with reference to FIG. 5, since the two chromatic secondary color inks R and V both contain a magenta component, if the ink amount of the chromatic secondary color inks R and V decreases, the magenta ink M The amount of ink increases. Therefore, in order to satisfy the duty limit of the magenta ink M, the ink amounts of the two chromatic secondary color inks R and V are required to be at the upper right of the boundary line LRVM1. As can be understood from this description, whether or not the ink duty limit is satisfied is determined in consideration of the ink amounts of all the inks constituting the ink set. However, in the following, for convenience of explanation, it is assumed that all ink duty limits are satisfied when the candidate ink amount pair Rtmp, Vtmp is within the allowable range RA.

  When the color coordinate point Prv of the candidate ink amount pair is within the allowable range RA as shown in FIG. 12A, the candidate ink amount pair Rtmp, Vtmp is directly adopted as the final color separation ink amount pair Ro, Vo. . On the other hand, as shown in FIG. 12B, when the color coordinate point Prv of the candidate ink amount pair is outside the allowable range RA, the candidate ink amount pair Rtmp, Vtmp is corrected so as to satisfy the ink duty limit. The final color separation ink amount pair Ro. Determine Vo. At this time, as the color coordinate point of the final color separation ink amount pair Ro, Vo, a point that is within the allowable range RA of the two-dimensional color space and is close to the color coordinate point Prv of the candidate ink amount pair is selected. The In the example of FIG. 12B, three points Oa, Ob, and Oc that can be selected as color coordinate points of such a final color separation ink amount pair are drawn. The first point Oa (Ro, Vo) is a point at which the ratio Rtmp: Vtmp of the candidate ink amount pair is equal to the ratio Ro: Vo of the final color separation ink amount pair. The second point Ob is a point where a straight line connecting the color coordinate point P (Rp, Vp) of the temporary color separation ink amount pair and the color coordinate point Prv of the candidate ink amount pair intersects the boundary line of the allowable range RA. It is. The third point Oc is the closest point to the color coordinate point Prv of the candidate ink amount pair within the allowable range RA.

  Any of these three points Oa, Ob, and Oc may be selected as the color coordinate point of the final color separation ink amount pair, but it is particularly preferable to select the first point Oa. This is because the candidate ink amount pair Rtmp, Vtmp is determined in accordance with the relationship of FIG. 11 as a preferable ink amount for improving the granularity of the image. Therefore, if the ratio Rtmp: Vtmp is maintained, two candidates are present. This is because it is possible to maintain a good balance that the dots of the chromatic secondary color inks are all inconspicuous and to improve the granularity of the image.

  The ink duty limit functions as a limit only when the amount of ink forming an image is large, and thus becomes a problem mainly in an image area with low brightness (that is, an image area with high density). Accordingly, the ink duty limit does not matter in the highlight area with high brightness, and the candidate ink amounts Rtmp and Vtmp set in the relationship shown in FIG. 11 are adopted as the final color separation ink amounts Ro and Vo as they are. Accordingly, the number of ink dots of the chromatic secondary color inks R and V is reduced in the highlight area, so that the graininess of the image can be improved.

  In step S630 in FIG. 9, the ink quantities Co, Mo, Yo of other inks necessary for reproducing a desired reproduction color are determined together with the final color separation ink quantity pairs Ro, Vo thus obtained. As a result, a color separation ink amount set (Co, Mo, Yo, Ro, Vo) for reproducing a desired reproduction color is determined.

  As described above, in the first embodiment, for each of the chromatic secondary color inks R and V, as the lightness parameter values (provisional color separation ink amounts) Rp and Vp are smaller, the final color separation ink amounts Ro, Since Vo is set to decrease, the number of chromatic secondary color ink dots decreases in the highlight area, and the number of chromatic primary color ink dots increases. As a result, there is an advantage that the graininess of the image in the highlight area is improved. In particular, the candidate ink amounts Rtmp and Vtmp are set to zero in the first range (the range R1 and the range R201 in the example of FIG. 11A) where the provisional color separation ink amounts Rp and Vp are relatively small. Therefore, in the highlight area, the final color separation ink amounts Ro and Vo are also set to zero, and the graininess of the image is greatly improved. However, in the first ranges R1 and R201, the candidate ink amounts Rtmp and Vtmp can be set to relatively small values other than zero.

  Further, for each of the chromatic secondary color inks R and V, as the residual ink amounts RES_R and RES_V are larger, the final secondary color ink usage rates k of the separation ink amounts Ro and Vo (FIG. 11B) are increased. Since it is set to a large value, it is possible to improve the graininess of the image in the highlight area and to save ink.

  Note that the conspicuousness of ink dots (influence on graininess) may vary depending on the type of ink. Accordingly, as shown in FIGS. 11A and 11B, the adjustment of the usage rate of the chromatic secondary color ink according to the residual ink amounts RES_R and RES_V is the same as that of the same one chromatic primary color ink. It is preferable to independently perform each of the hue ranges in which the hue can be reproduced in combination with one chromatic secondary color ink. For example, the hue between cyan ink C and violet ink V can be reproduced by a combination of cyan ink C and violet ink V. Colors within this hue range are reproduced mainly using cyan ink C and violet ink V when bright. Further, the hue between the magenta ink M and the red ink R can be reproduced by a combination of the magenta ink M and the red ink R. Colors within this hue range are reproduced mainly using magenta ink M and red ink R when bright. As described above, by independently setting the usage rate of the chromatic secondary color ink according to the combination of the types of inks used mainly, the graininess is improved according to the characteristics of each ink and the ink is saved. be able to.

C. Second embodiment of separation processing:
FIG. 13 is a flowchart showing the processing procedure of the second embodiment. In the first embodiment described above, the input color of the primary color system is used as it is as a reproduced color (a color in the reproduced color system), but in the second embodiment, the reproduced color is more colored than the input color. Assign a higher color. The reason why this is possible is that the chromatic secondary color inks R and V included in the reproduction color system can achieve higher saturation than the mixed color of the chromatic primary color inks with respect to the red color and the violet color. .

  In step S100 in FIG. 13, an ink set including chromatic primary color inks C, M, and Y and chromatic secondary color inks R and V is set as an usable ink set.

  Next, in step S110, an ink duty limit that is a limit on the amount of ink of each color in the ink set is set. This ink duty limit is set according to the type of ink or print medium (details will be described later).

  By the way, the input color represented by the primary color system is a gradation value (primary color) representing the range (0% to 100%) of the ink amount of each color of CMY expressed by 256 gradations from 0 to 255. (Tone value set). In addition, the color separation ink amount set represented by the reproduction color system uses tone values that represent the range (0% to 100%) of the ink amount of each color of CMYRV expressed by 256 tones of 0 to 255. It is expressed.

  FIGS. 14A and 14B are explanatory diagrams showing primary color spaces represented by the ink amounts of CMY colors as reference vectors. A color expressed in the primary color system is expressed as one point in a cube represented by CMY gradation values 0 to 255 in the primary color space. Further, this cube is an area where the ink amounts of the CMY colors of the chromatic primary color ink can take values. Hereinafter, this cube is referred to as a color solid, and among the six surfaces of the color solid, three surfaces facing the origin W (three surfaces surrounding K (C = M = Y = 100%)) are first. Called the seed shell. In other words, the amount of ink of at least one chromatic primary color is 100% and the amount of ink of at least one chromatic primary color ink is smaller than 100% on the first type outer shell surface. It consists of color points with values. When a straight line connecting the origin W and the point K is called an achromatic color line, the distance between one point in the primary color space and the achromatic color line can be used as an index of saturation. Further, when a point obtained by vertically projecting a point in the primary color space onto an achromatic color line is called a projection point, the distance between the origin W and the projection point can be used as an indicator of brightness. The direction from the projection point toward one point in the primary color space can be used as a hue index.

  14 (a) and 14 (b), the first type outer shell surface where Y is maximum (Y = 255) is hatched. Furthermore, one color m is written on the outer shell surface of the first type that is hatched. This color m is set as the outermost shell chromatic color m in step S120 of FIG. 14A and 14B, the outermost shell chromatic color m is set on the outer shell surface where the Y component is maximum, and the gradation values of the CMY colors are Cm and Mm in the order of CMY. Ym (Ym = 255 in this example).

  In the color separation process of the present embodiment, the color separation associated with the input color I on the line segment connecting the origin W and the outermost chromatic color m is performed by sequentially executing the processes of steps S130 to S150 described later. An ink amount set (a gradation value of each color of CMYRV in this embodiment) can be obtained. In the present embodiment, a plurality of outermost chromatic colors are prepared in order to execute color separation processing for a plurality of input colors I, and a series of processes (S130 to S150) for each outermost chromatic color. Is executed.

  In step S130 of FIG. 13, an extended chromatic color em positioned in the outer shell of the color area that can be reproduced by using the inks of the CMYRV colors of the ink set is further obtained (FIG. 14B).

  FIG. 15 is an explanatory diagram showing an outline of how the extended chromatic color em is calculated. In the example of FIG. 15, in order to simplify the description, two types of cyan ink C and magenta ink M can be used as the chromatic primary color ink, and 1 of the violet ink V as the chromatic secondary color ink. The types are assumed to be available.

  FIG. 15A is an explanatory diagram showing a primary color space. In this example, the gradation value of each color of CMV can take a value in the range of 0-100. Therefore, the input color expressed in the primary color system is expressed as one point in a square whose side is 100 in length. This square corresponds to the color solid described above. Further, in the drawing, the first type outer shell line OL1 having a square shape is indicated by a bold line. The first type outer shell line OL1 corresponds to the first type outer shell surface described above. The outermost shell chromatic color m is set on the line where C of the first type outer shell line OL1 is maximum (C = 100).

  FIG. 15B shows each color when a color that can be reproduced by using the chromatic secondary color ink V in addition to the chromatic primary color ink CM is expressed in the primary color system. The range in which the virtual ink amount can take a value is shown. Here, it is assumed that a 1: 1 color mixture of cyan ink C and magenta ink M can reproduce substantially the same hue and saturation as violet ink V of the same ink amount. That is, the replacement ink amount for the violet ink V is 1 for both the cyan ink C and the magenta ink M. For example, the color P1 in FIG. 15B is a color that can be reproduced by setting the gradation value of each color of CM to 100. Further, even if the gradation value of each color of CM is replaced with the gradation value of V, it is possible to reproduce almost the same color. For example, even if only the gradation value of V is set to 100, that is, all of the gradation values of each color of CM are replaced with the gradation value of V, almost the same color can be reproduced. Here, the gradation values obtained by replacing all the gradation values of the chromatic secondary color ink V with the gradation values of the chromatic primary color ink CM (in this example, C = 100, M = 100). Can be used as a virtual gradation value for expressing a color reproduced using each color of the CMV in a primary color space.

  Furthermore, in this example, the following restrictions are imposed on the tone value of each ink.

(Condition a) The gradation value of each ink is 80 or less.
(Condition b) The total value of the gradation values of each ink is 200 or less.

  The limitation of the gradation value by the conditions a and b can be explained as follows. That is, the print medium has a limit on the amount of ink absorbed per unit area. If an amount of ink that exceeds this limit is ejected, bleeding may occur due to ink that cannot be absorbed, or the printing medium may wave. Therefore, it is preferable to limit the amount of ink used. Such an upper limit value of the ink amount, that is, an upper limit value of the gradation value is called an ink duty limit. Also, the appropriate value for the ink duty limit may vary depending on the type of ink. In such a case, the image quality of the print image can be further improved by setting different limit values for each color. Further, as in condition b, by providing a limit value for the total value of the gradation values of each color (that is, the total value of the ink amount), an amount of ink exceeding the limit of the ink absorption amount of the print medium is ejected. Can be suppressed. Furthermore, it is also preferable to set a limit value for the total value of any two types of ink amounts, and to set a limit value for the total value of many types of ink amounts, for an area to be reproduced with a mixed color of two colors. It is also preferable to do. If these limit values are changed according to the type of the print medium, the image quality of the print image can be improved according to the type of the print medium.

  Such an ink duty limit is expressed by the gradation value of each color of usable ink CMV, but the primary color space can be obtained by using the virtual gradation value of each CM color obtained by using the replacement ink amount. Can be expressed in In the example of FIG. 15, the relationship between the CMV colors is expressed linearly in the ink duty limit, and thus is expressed as a straight line in the primary color space. Therefore, the color area that can be reproduced using the ink of each color of CMV within a range that satisfies the ink duty limit is represented by an area surrounded by a straight line corresponding to each ink duty limit. In FIG. 15B, a straight line LC indicates a straight line where C = 80. The reason for the inclination with respect to the C axis is that by using the violet ink V, the virtual gradation value of each color of the CM can be further increased. Therefore, the region satisfying C ≦ 80 is inside the straight line LC. The straight line LCV is a straight line where C + V = 160. This straight line corresponds to the restriction of C + V ≦ 160 derived from two restrictions of C ≦ 80 and V ≦ 80. A region satisfying C + V ≦ 160 is inside the straight line LCV.

  At the intersection P2 of the straight lines LC and LCV, the gradation value of C is 160 and the gradation value of M is 80. This color P2 cannot be reproduced when only the CM two-color ink is used because the C gradation value does not satisfy the ink duty limit (condition a). Here, 80 of the gradation values of each CM color are replaced with a gradation value of V. Then, the gradation value of each color of CMV, that is, the color separation ink amount becomes 80, 0, 80 in order, and the ink duty limit is satisfied. That is, the color P2 can be reproduced by using the chromatic primary color ink CM and the chromatic secondary color ink V.

  Further, FIG. 15B shows the following straight line corresponding to the ink duty limit. That is, the straight line LCMV is a straight line with C + M + V = 200, the straight line LMV is a straight line with M + V = 160, and the straight line LM is a straight line with M = 80. As a result, the color in the area A surrounded by these straight lines satisfies the ink duty limit and can be reproduced by using the chromatic secondary color ink V. In other words, if the virtual gradation value obtained by replacing the gradation value of the chromatic secondary color ink with the gradation value of the chromatic primary color ink is within the region A, the chromatic primary color ink. And chromatic secondary color ink can be used.

  The distances between these straight lines LCV, LCMV, and LMV and the origin W are values that change according to the amount of replacement ink of the chromatic secondary color ink. That is, the greater the amount of replacement ink, the greater the distance between the straight line corresponding to each ink duty limit and the origin W. As a result, the greater the amount of replacement ink, the wider the area that can be reproduced by using chromatic primary color ink and chromatic secondary color ink. Therefore, from the viewpoint of reproducible region expansion, the total value of the replacement ink amount is preferably larger than 1, and particularly preferably 1.5 or more. In the example of FIG. 15, the replacement ink amount of the violet ink V is 1 for each of the CM colors, so the total value of the replacement ink amount is 2. In the example of the ink set in FIG. 5, the replacement ink amount of the red ink R is 0.0, 0.71, and 2.86 in the order of CMY, and the total value is 3.57. The replacement ink amount of the violet ink V is 0.68, 2.89, 0.0 in the order of CMY, and the total value is 3.57. Since the total value of the replacement ink amounts of the two inks RV is 1.5 or more, a wider color reproduction range can be obtained by using these inks R and V. In addition, when the total value of the replacement ink amount of each chromatic primary color ink is larger than 1, the chromatic secondary color ink should use an ink amount equivalent to the mixed color of the chromatic primary color ink. It is possible to reproduce higher saturation. In this way, by using the chromatic primary color ink and the chromatic secondary color ink, it is possible to reproduce a wider range of colors than the area reproducible with only the chromatic primary color ink. .

  In the present specification, the outer shell in such a region that satisfies the ink duty limit is referred to as a reproduction color outer shell surface. The reproduction color outer surface is represented by a reproduction color system for each ink amount of the ink set, but the chromatic primary color ink is changed according to the replacement ink amount for each ink amount of the chromatic secondary color ink. By substituting with the amount of ink, it can be mapped into the primary color system. In the example of FIG. 15B, the outer shell line OL2 constituting the outer shell of the region A corresponds to a reproduced color outer shell surface mapped to the primary color space (hereinafter, the outer shell line OL2 is reproduced outside the reproduced color). Called shell line OL2.) Note that the condition of V ≦ 80 is satisfied within this region A, and therefore the corresponding straight line is not shown.

  In FIG. 15, the area A is hatched, and the reproduction color outer shell line OL2 is displayed thick. An extended chromatic color em is set on the reproduction color outer shell line OL2. The extended chromatic color em is a color located at the intersection of the line segment passing through the origin W and the outermost shell chromatic color m and the reproduced color outer shell line OL2. That is, the extended chromatic color em is a color represented by the longest extended chromatic color vector having the same direction as the outermost shell chromatic color vector representing the outermost shell chromatic color m in the primary color space, The outermost shell color separation ink amount set for reproducing the color em is a color within the ink duty limit.

  As described above, the extended chromatic color described above can be set in the same manner even when the number of ink types is increased. In FIG. 14B, the extended chromatic color em is shown in the primary color space based on the ink amounts of the CMY colors. The extended chromatic color em is a color obtained using the chromatic primary color inks C, M, and Y and the chromatic secondary color inks R and V.

  Here, it is assumed that virtual tone values for expressing the extended chromatic color em in the primary color space are CDem, MDem, and YDem in the order of CMY colors. In addition, the ink amounts of the color separation ink amount set (corresponding to the outermost shell color separation ink amount set) corresponding to the extended chromatic color em are Cem, Mem, Yem, Rem, and Vem in the order of CMYRV. Then, the gradation values CDem, MDem, and YDem of each virtual CMY color are expressed by the following equations using the replacement ink amounts shown in FIGS.

  In this embodiment, the extended chromatic color em is calculated so that these outermost shell color separation ink amounts Cem, Mem, Yem, Rem, and Vem satisfy the following conditions.

(Condition 1) The CMYRV color separation ink amount set satisfies the ink duty limit.

  As the ink duty limit, for example, it is possible to set a limit on the total value of all kinds of ink amounts, a limit on the amount of ink for each color alone, a limit on the amount of ink for mixing two colors, and the like.

  The limitation on the total value of all types of ink amounts is expressed by the following equation, for example.

  In the formulas, C, M, Y, R, and V are the ink amounts of the respective colors CMYRV (the same applies to other formulas described later). Duty_T is a limit value set in advance according to the type of ink or print medium.

  The limitation on the amount of ink for each color is expressed, for example, by the following equation.

  Duty_C to Duty_V are limit values set in advance for each color according to the type of ink or print medium.

  The restriction on the amount of ink when mixing two colors is expressed by the following equation, for example.

  In addition, in this restriction | limiting, although restrictions are imposed about the combination of two arbitrary inks, it has illustrated about the combination of six among them. Duty_CM to Duty_MR are limit values set in advance for each ink combination in accordance with the type of ink or print medium.

  The ink duty limit may be set for any combination of inks such as a mixed color of three colors, a mixed color of four colors, or the like.

  Each ink duty limit (condition 1) as described above can be expressed by a surface in the primary color space shown in FIG. 14 using virtual gradation values of CMY colors obtained by using the replacement ink amount. Yes (not shown). The area surrounded by these surfaces is an area that satisfies the ink duty limit. Therefore, if the virtual gradation value of each CMY color represented by the amount of each CMYRV color is within the area surrounded by these surfaces, each ink amount can satisfy the ink duty limit. It is possible to reproduce using chromatic primary color inks C, M, Y and chromatic secondary color inks R, V. In this embodiment, the mixed color of the chromatic primary color inks C, M, and Y is less than the total value of the respective ink amounts based on the replacement ink amounts shown in FIGS. It is possible to replace with chromatic secondary color inks R and V. In other words, the chromatic secondary color inks R and V can reproduce higher saturation by using an ink amount similar to the mixed color of the chromatic primary color inks C, M, and Y. As a result, by using the chromatic primary color ink CMY and the chromatic secondary color ink RV, it is possible to reproduce a wider range of colors than can be reproduced by the chromatic primary color ink CMY alone. It becomes.

  FIG. 14B shows the extended chromatic color em. The extended chromatic color em is located on the outer shell surface of the region that satisfies the ink duty limit (condition 1), that is, the reproduced color outer shell surface (not shown). The extended chromatic color em is positioned on a line segment that passes through the origin W and the outermost shell chromatic color m. That is, the extended chromatic color em is a color at a position where a line segment passing through the origin W and the outermost shell chromatic color m intersects the reproduced color outer shell surface. In other words, the extended chromatic color em is a color represented by the longest extended chromatic color vector having the same direction as the outermost shell chromatic color vector representing the outermost shell chromatic color m in the primary color space, The outermost shell color separation ink amount set for reproducing the extended chromatic color em is a color within the ink duty limit.

  Such an extended chromatic color em can be calculated using various methods. For example, a color in the primary color space is selected, a color separation ink amount set is calculated by replacing chromatic primary color ink with chromatic secondary color ink, and the color separation ink amount set is an ink duty limit ( By repeatedly executing a series of processes of determining whether or not the condition 1) is satisfied, it is possible to calculate approximately successively. Further, it can also be calculated using a so-called linear programming method based on the equations for the replacement ink amount and the ink duty limit (condition 1). In this case, a series of steps S120 to S130 (FIG. 13) are executed at a time.

  As described above, by calculating the extended chromatic color em in which the outermost shell color separation ink amount set satisfies the ink duty limit (condition 1), the outermost outer color is within the range where the image quality when printing the color is good. An extended chromatic color em having the largest gradation value located in the same direction as the shell chromatic color m can be obtained.

  In step S140 of FIG. 13, a provisional color separation ink amount set P corresponding to the input color I (FIG. 14) is calculated. In step S140, first, the outermost shell color separation ink amount set emp for the extended chromatic color em is calculated. The outermost shell color separation ink amount set emp is a value already calculated for determining whether or not the ink duty limit (condition 1) is satisfied when the extended chromatic color em is calculated in step S130 described above. is there. However, when there are many types of ink that can be used, the degree of freedom of replacement between the chromatic primary color ink and the chromatic secondary color ink increases. For this reason, as the outermost shell color separation ink amount set emp corresponding to the extended chromatic color em, a combination of a plurality of types of ink amounts may be selected within a range that satisfies the ink duty limit (condition 1). In such a case, in this embodiment, a combination having the smallest total amount of each ink amount is selected from a plurality of combinations and used as the outermost shell color separation ink amount set emp.

  Next, a temporary color separation ink amount set P is calculated based on the outermost shell color separation ink amount set. FIG. 14C is an explanatory diagram showing an outline of the relationship between the input color I and the provisional color separation ink amount set P. In this embodiment, a value calculated by multiplying the ratio of the vector length LLI indicated by the input color I and the vector length LLm indicated by the outermost shell chromatic color m by the outermost shell color separation ink amount set emp. Are used as a provisional color separation ink amount set P. At this time, the color separation ink amount set corresponding to the outermost shell chromatic color m is the outermost shell color separation ink amount set emp. The color between the origin W and the outermost shell color separation ink amount set emp can be reproduced by a specific combination of the print medium and the ink set. Therefore, it is possible to effectively use a color range that can be reproduced by a specific combination of a print medium and an ink set. Further, by calculating the provisional color separation ink amount set P so as to be proportional to the length LLI, the provisional color separation ink amount set P for the input color I can be easily calculated. In addition, the provisional color separation ink amount set P is calculated based on the linear programming method based on the relationship between the input color I and the lengths LLI and LLm, as well as the equations for the replacement ink amount and the ink duty limit (condition 1). It is also possible to directly calculate using. In this case, a series of steps S120 to S140 (FIG. 13) are executed at a time. Note that the color reproduced in the provisional color separation ink amount set P corresponds to the reproduction color associated with the input color I (color reproduced on the print medium).

  In step S150 of FIG. 13, the final color separation ink amount set O is calculated based on the provisional color separation ink amount set P. The final color separation ink amount set O is a color separation ink amount obtained by replacing the chromatic primary color ink and the chromatic secondary color ink according to the replacement ink amount based on the provisional color separation ink amount set P. Is a set. Accordingly, the color reproduced in the final color separation ink amount set O substantially matches the color reproduced in the temporary color separation ink amount set P. Here, the replacement of the chromatic primary color ink and the chromatic secondary color ink is performed in consideration of improvement in graininess and saving of ink. As the final color separation ink amount set calculation process, the above-described processing method (FIGS. 9 to 12) and various methods described later can be used.

  In this way, the final color separation ink amount set O expressed in the reproduction color system corresponding to the input color I expressed in the primary color system is calculated by sequentially executing the processes of steps S100 to S150. The The final color separation ink amount set O thus obtained can be used as the second gradation value set in step S20 of FIG.

  In step S160 of FIG. 13, it is determined whether or not a final color separation ink amount set has been calculated for all input colors. If all the final color separation ink amount set calculations have not been completed, the processes in steps S120 to S150 are repeated, and if completed, the process ends.

  In order to further shorten the time required for the color separation process, it is preferable to limit the number of outermost chromatic colors for executing a series of processes. At this time, if there is no outermost chromatic color corresponding to the input color to be subjected to color separation processing, the final color separation ink amount set of a plurality of colors close to the input color is interpolated, and the corresponding final color separation An ink amount set can be obtained. At this time, it is preferable to prepare a plurality of outermost chromatic colors in advance so that a straight line connecting the outermost chromatic color and the origin W is distributed over the entire range in the color solid. By doing so, it is possible to suppress an increase in the interpolation error of the color separation ink amount set in a specific region in the color solid.

As described above, in this embodiment, the extended chromatic color em and the outermost shell color separation ink amount set are determined by the following three conditions:
(I) The outermost shell color separation ink amount set is within the ink duty limit,
(Ii) The length of the extended chromatic color vector is the longest within the range reproducible with the ink set.
(Iii) The sum of the ink amounts of the outermost shell color separation ink amount set for reproducing the extended chromatic color em is minimized.
Running to meet. Even if not all of these conditions are satisfied, the color reproduction range can be extended if the extended chromatic color em has a higher saturation than the outermost shell chromatic color m. For example, even if the condition (ii) is not satisfied and the extended chromatic color vector is not the longest, the color reproduction range can be extended if it is configured to be longer than the outermost shell chromatic color vector.

  In order to extend the color reproduction range in a wider hue range, it is preferable that the extended chromatic color vector is longer than the outermost shell chromatic color vector in a wider hue range. Here, the range of hues in which the extended chromatic color vector can be extended is a range that changes according to the hue of usable chromatic secondary color ink. The chromatic secondary color ink can extend the color reproduction range of an area having a hue close to the hue of the ink. Therefore, by making it possible to use more kinds of chromatic secondary color inks having different hues, the extended chromatic color vector becomes longer than the outermost shell chromatic color vector in a wider hue range. Can do.

  As described above, in this embodiment, the color separation process is performed by effectively using the color range that can be reproduced using the chromatic primary color ink and the chromatic secondary color ink. Therefore, printing with an extended color reproduction range can be performed. In addition, since the separation process is based on the extended chromatic color located at the intersection of the straight line connecting the origin and the outermost chromatic color and the reproduced color outer shell surface, the number of types of ink that can be used increases However, the separation processing result can be easily obtained.

D. Example of final color separation ink amount set calculation processing:
D1. First embodiment of final color separation ink amount set calculation processing:
In this final color separation ink amount set calculation process, the final color separation ink amount set O is calculated using the temporary color separation ink amount set P for the input color I. The final color separation ink amount set O is calculated so as to reproduce substantially the same color as the provisional color separation ink amount set P within a range that satisfies the ink duty limit (condition 1). In order to reproduce almost the same color as the temporary color separation ink amount set P, the combination of the ink amounts obtained by replacing each ink amount of the temporary color separation ink amount set P according to the replacement ink amount is the final amount. Used as plate ink amount set O. Here, the degree of freedom of ink replacement increases as the number of usable inks increases. Therefore, there may be a plurality of combinations of ink amounts that can be used as the final color separation ink amount set O. In such a case, the final color separation ink amount set O is calculated in consideration of improvement in image granularity and ink saving.

  FIG. 16 is a flowchart illustrating a processing procedure for calculating the final color separation ink amount set according to the present exemplary embodiment. The difference from the processing shown in FIG. 9 is that the remaining ink amounts RES_R2, RES_V2 and the candidate ink amounts Rtmp, Vtmp are the maximum ink amounts Rmax, Vmax when the chromatic secondary color inks R, V are used to the maximum. It is a point that is determined based on.

  In the first step S300, the secondary color maximum color separation ink amount sets Prmax (Crmax, Mrmax, Yrmax, Rmax, 0) and Pvmax (Cvmax, Mvmax, 0) corresponding to the two chromatic secondary color inks R and V, respectively. Yvmax, 0, Vmax) is calculated. These secondary color maximum color separation ink amount sets Prmax and Pvmax are color separation ink amount sets obtained by replacing the respective ink amounts of the provisional color separation ink amount set P in accordance with the replacement ink amount.

  The ink amount Rmax of the red ink R included in the secondary color maximum color separation ink amount set Prmax corresponding to the red ink R is determined based on each ink amount of the temporary color separation ink amount set P based on the replacement ink amount. This is the maximum value that the ink amount of the red ink R can take when the ink amount is replaced. In this embodiment, the maximum ink amount Rmax is the maximum value when the ink duty limit is not taken into consideration. Therefore, the maximum value that the final color separation ink amount of the red ink R can actually take may be smaller than the maximum ink amount Rmax. Instead, a maximum value considering the ink duty limit can be used.

  As described above, even when the ink amount of the red ink R is set to the maximum value Rmax, there may be a plurality of combinations of the ink amounts of the violet ink V and the chromatic primary color inks C, M, and Y. In such a case, in this embodiment, a combination in which the ink amount of other chromatic secondary color ink (violet ink V in this embodiment) is set to zero is selected from a plurality of combinations. This is used as the next color maximum color separation ink amount set Prmax.

  The secondary color maximum color separation ink amount set Pvmax corresponding to the violet ink V is also calculated in the same manner as the secondary color maximum color separation ink amount set Prmax of the red ink R.

  In the next step S310, residual ink amounts RES_R2 and RES_V2 respectively corresponding to the chromatic secondary color inks R and V are determined from the secondary color maximum color separation ink amount sets Prmax and Pvmax. In the present embodiment, the remaining ink amounts RES_R2 and RES_V2 are expressed by the following equations using the respective ink amounts included in the secondary color maximum color separation ink amount sets Prmax and Pvmax obtained in step S300.

  In the formula, Crmax, Mrmax, and Yrmax are the ink amounts of CMY colors included in the secondary color maximum color separation ink amount set Prmax, and Cvmax, Mvmax, and Yvmax are included in the secondary color maximum color separation ink amount set Pvmax. This is the ink amount of each color of CMY. The coefficients krc, krm, kry, and kvc, kvm, kvy are coefficients set in advance corresponding to each color of CMYRV. Thus, the residual ink amount RES_R2 is a weighted total value for each ink amount other than the red ink R, and the residual ink amount RES_V2 is a weighted total value for each ink amount other than the violet ink V. Formula 1 described above is obtained by setting all the coefficients of each ink to 1. However, the remaining ink amount can be expressed by another function related to the ink amount of ink other than the corresponding chromatic secondary color ink. In general, the remaining ink amount may be a parameter value relating to the size of the ink amount other than the corresponding chromatic secondary color ink.

  These coefficients krc to kry and kvc to kvy are determined according to the influence of the chromatic secondary color ink on the conspicuousness of dots. Ink with a high reflection density of ink dots can make chromatic secondary color ink dots less noticeable with a small amount of ink. Therefore, it is preferable to set a larger coefficient for ink having a higher reflection density. In addition, it is preferable to set a large coefficient because an ink having a smaller difference in color appearance from the chromatic secondary color ink can make the dots of the chromatic secondary color ink less noticeable with a small amount of ink. .

  Here, when comparing the reflection density of the ink dots of a plurality of types of ink, it is possible to use a method of ejecting an equal amount of ink onto the same printing medium and measuring the density using a densitometer for each. it can. In addition, when comparing the appearance of colors, the same amount of ink is ejected onto the same printing medium, and each color is measured using a colorimeter, and the color difference (for example, L * A method of obtaining the color difference ΔE) in the a * b * color system can be used. As will be described later, these coefficients krc to kry and kvc to kvy can also be determined based on sensory evaluation.

  In the next step S320, candidate ink amounts Rtmp and Vtmp for chromatic secondary color inks R and V are set. FIG. 17A is a graph showing the relationship between the candidate ink amount Rtmp and the maximum ink amount Rmax. FIG. 17B is a graph showing the relationship between the ratio k of the candidate ink amount Rtmp to the maximum ink amount Rmax (corresponding to the secondary color ink usage rate in the present invention) and the maximum ink amount Rmax.

  In this embodiment, as shown in FIG. 17A, the candidate ink amount Rtmp decreases as the maximum ink amount Rmax decreases. Further, as shown in FIG. 17B, the ratio k of the candidate ink amount Rtmp to the maximum ink amount Rmax is configured to be smaller as the maximum ink amount Rmax is smaller. In this example, two values Rstart and Rend for determining the maximum ink amount Rmax are set. In the first range R11 where Rmax ≦ Rstart, Rtmp = 0 (k = 0) is set. In the third range R13 where Rend ≦ Rmax, Rtmp = Rmax (k = 1) is set. In the second range R12 where Rstart <Rmax <Rend, the candidate ink amount Rtmp is set to change linearly.

  Such a setting for the candidate ink amount Rtmp can be understood as follows. The chromatic secondary color ink can be replaced with a plurality of chromatic primary color inks. Therefore, when the chromatic secondary color ink is positively used, the ink amount of the plurality of chromatic primary color inks is reduced according to the replacement ink amount, so that the total number of ink dots recorded on the print medium is reduced. On the other hand, when the color mixture of chromatic primary color ink is positively used, the total number of ink dots increases. Such a difference in the number of ink dots that varies depending on the combination of the ink amounts is particularly that the mixed color of the chromatic primary color ink is replaced with a chromatic secondary color ink whose amount is smaller than the total value of the respective ink amounts. This is noticeable when possible. Further, the granularity (roughness of the image) of the region to be reproduced is more conspicuous as the number of ink dots is smaller. Therefore, in an area where the amount of ink, that is, the number of ink dots is smaller, increasing the number of ink dots by using a mixture of chromatic primary color inks instead of chromatic secondary color inks improves the graininess. preferable. In the example of FIG. 17, the ratio k is configured to be smaller as the maximum ink amount Rmax is smaller. Therefore, the graininess of the region to be reproduced can be improved by setting the ink amount of the red ink R to a value as small as the candidate ink amount Rtmp.

  In the example of FIG. 17, Rtmp = 0 is set in the first range R11. That is, in a particularly bright region, the candidate ink amount Rtmp is set to a value (that is, zero) that increases the number of ink dots to the maximum without using the chromatic secondary color ink. Thus, by making the ink amount of the red ink R zero, the ink dots of the red ink R can be suppressed from being noticeable.

  Here, the first value Rstart means an ink amount that makes ink dots less noticeable even when the red ink R is used if the ink amount is equal to or larger than this value. The inconspicuousness of the red ink R dots changes according to the residual ink amount RES_R2. As the residual ink amount RES_R2 is larger, the dots of the red ink R are less noticeable, so that the ink amount of the red ink R can be increased. Therefore, in this embodiment, Rstart is set based on the following expression, so that Rstart is reduced as RES_R2 is increased.

  In the equation, Crs is a preset constant. Such constants Crs and coefficients krc to kry (equation 6) for the residual ink amount RES_R2 can be set based on, for example, the following sensory evaluation. First, a gradation pattern in which the ink amount of red ink R per unit area (hereinafter referred to as index red ink amount) changes from 0 to 100% is reproduced by the color mixture of magenta ink M and yellow ink Y. Further, the ink dots of red ink R are printed at appropriate intervals in the pattern. In the range where the index red ink amount is small, the red ink R dots are easily noticeable, but in the range where the index red ink amount is large, the red ink R dots are less noticeable. Such an index red ink amount (hereinafter referred to as a first boundary red ink amount) at which dots start to become inconspicuous can be used as the constant Crs.

  Further, the coefficients krc to kry can be set as follows. A gradation pattern obtained by adding a certain amount of cyan ink C to the mixed color of magenta ink M and yellow ink Y based on the index red ink amount is reproduced. At this time, the larger the amount of cyan ink C, the smaller the first boundary red ink amount. The change in the first boundary red ink amount with respect to the change in the ink amount of the cyan ink C at this time can be used as the coefficient krc. Other coefficients krm and kry can be obtained in the same manner using a gradation pattern obtained by adding a certain amount of each ink.

  In the example of FIG. 17, Rtmp = Rmax is set in the third range R13. That is, particularly in a range where the ink amount is large, the candidate ink amount Rtmp is set to a value that actively uses the red ink R (that is, the maximum ink amount Rmax). Thus, by setting the ink amount of the red ink R to a large value, the total amount of ink to be used can be reduced. As a result, the amount of ink used can be saved, and furthermore, the printing medium can be prevented from wavy.

  Here, the second value Rend means an ink amount where the granularity due to the red ink R and the granularity due to the color mixture of other inks start to change if the ink amount is equal to or larger than this value. In dark areas and areas with high saturation, even if the ink amount of the red ink R is set to a large value, the number of red ink dots increases, so that each dot is difficult to stand out. Further, if the residual ink amount RES_R is large, the dots of the red ink R become less conspicuous, and the ink amount of the red ink R can be further increased. Therefore, in this embodiment, Rend is set based on the following equation, so that Rend is reduced as RES_R2 is increased.

  In the formula, Cre is a preset constant. Such a constant Cre can be set based on the following sensory evaluation, for example. First, a gradation pattern in which the ink amount (index red ink amount) of the red ink R per unit area is changed to 0 to 100% is reproduced by the mixed color of the magenta ink M and the yellow ink Y. Similarly, a gradation pattern in which the index red ink amount changes from 0 to 100% is reproduced using the red ink R. In a range where the amount of the index red ink is small, the gradation pattern by the mixed color has more granularity because the number of ink dots is larger. In a range where the index red ink amount is large, the number of ink dots increases in both of the two gradation patterns, so the difference in graininess becomes inconspicuous. Such a two gradation pattern is compared, and an index red ink amount (hereinafter referred to as a second boundary red ink amount) at which the graininess of the two starts to change can be used as the constant Cre.

  Further, the coefficients krc to kry for the residual ink amount RES_R2 can be set as follows. For example, when determining the coefficient krc, a certain amount of cyan ink C is added to each of the mixed color of magenta ink M and yellow ink Y based on the index red ink amount and red ink R based on the index red ink amount. Reproduce the two gradation patterns. The second boundary red ink amount when these patterns are compared decreases as the added ink amount increases. The change in the second boundary red ink amount with respect to the change in the added ink amount at this time can be used as the coefficient krc. The other coefficients krm and kry can be similarly determined.

  In this embodiment, the coefficients krc to kry, that is, the residual ink amount RES_R2 are used in common for the first and second values Rstart and Rend. When the influence of each ink C, M, Y on the first and second values Rstart, Rend is different, the remaining ink amount RES_R2 is set independently for the first and second values Rstart, Rend. It is preferable to do.

  In addition, when using an ink that has a small influence on the first and second values Rstart and Rend, that is, an ink that cannot suppress the conspicuousness of chromatic secondary color ink dots even if the amount of ink is increased. The coefficient of the ink is preferably zero. For example, when the reflection density of the yellow ink Y ink dot is thin and the conspicuousness of the red ink R dot does not change even when the ink amount is increased, the coefficient kry of the yellow ink Y is preferably set to zero. By doing so, even when the hue of the reproduced color is close to the yellow ink Y, the usage rate (ratio k) of the red ink R does not increase, so that the dots of the red ink R can be suppressed from conspicuous. Further, when the reproduction color hue is relatively close to the magenta ink M, the usage rate (ratio k) of the red ink R is set to a relatively large value, so that ink can be saved. Similarly, even when the amount of yellow ink Y is increased and the conspicuousness of dots of violet ink V does not change, the coefficient kvy can be set to zero similarly. At this time, when the hue of the reproduced color is relatively close to the cyan ink C and the magenta ink M, the usage rate of the violet ink V is set to a relatively large value, so that the ink can be saved. However, the coefficients kry and kvy can be set to relatively small values other than zero.

  As described above, by setting the first and second values Rstart and Rend, when the maximum ink amount Rmax is the same value, a relatively large usage rate k is obtained when the residual ink amount RES_R2 is relatively large. be able to. Further, the residual ink amount RES_R2 is a value determined in consideration of ink characteristics. Therefore, the graininess can be appropriately improved according to the characteristics of the ink. Further, when the residual ink amount RES_R2 is relatively large, the usage rate k is relatively large. Therefore, the ink amount of the chromatic secondary color ink is increased, and the ink amounts of the plurality of chromatic primary color inks are decreased. Can do. Therefore, ink can be saved appropriately according to the ink characteristics. In this embodiment, the usage rate k is a value calculated based on the maximum ink amount when the chromatic secondary color ink is used to the maximum. Therefore, the ink amount of the chromatic secondary color ink can be determined by effectively using the range in which the ink amount of the chromatic secondary color ink can take a value.

  The maximum ink amount Rmax can also be considered as an index value indicating the brightness of the input color I, that is, a brightness parameter value correlated with the brightness of the reproduced color. In a bright region, the amount of ink of each color that reproduces that color is reduced. Therefore, the maximum ink amount Rmax of the red ink R is also reduced. On the other hand, in a dark region, the amount of ink of each color that reproduces the color increases. Therefore, in the area where the red ink R is used, the maximum ink amount Rmax is also increased. That is, the smaller the maximum ink amount Rmax is, the brighter the area is, and the larger the maximum ink amount Rmax is, the darker the area is. Therefore, it can be considered that the candidate ink amount Rtmp and the ratio k shown in FIG. 16 are set so as to decrease as the brightness of the input color I becomes brighter.

  The candidate ink amount Rtmp is configured to continuously change over the entire range of the maximum ink amount Rmax. By doing so, it is possible to prevent the amount of ink of each color component from changing suddenly in a gradation region where the amount of ink continuously changes, and the boundary of the color component being noticeable. Note that the candidate ink amount Rtmp is not limited to a configuration that linearly changes with respect to the maximum ink amount Rmax, and may be configured to change smoothly using, for example, a curve.

  In the example of FIG. 17, the candidate ink amount Rtmp of the red ink R is calculated, but the candidate ink amount can be calculated in the same manner for other types of chromatic secondary color inks. In any case, it is preferable that the ratio of the candidate ink amount to the maximum ink amount becomes smaller as the maximum ink amount is smaller. By doing so, the number of ink dots can be increased by actively using the chromatic primary color ink instead of the chromatic secondary color ink, so that the graininess can be improved.

  At this time, it is preferable that the secondary color ink usage rate be reduced when the residual ink amount is relatively small. By doing so, it is possible to improve graininess and save ink.

  In step S330 of FIG. 16, based on the candidate ink amounts Rtmp and Vtmp of the chromatic secondary color inks R and V set in step S320 described above, the final color separation ink amounts Ro of the chromatic secondary color inks R and V are set. , Vo is calculated. As described above, the candidate ink amounts Rtmp and Vtmp are ink amounts calculated mainly in consideration of the graininess and ink saving. Therefore, a combination of ink amounts using Rtmp and Vtmp may not satisfy the ink duty limit (condition 1). Further, when the candidate ink amounts Rtmp and Vtmp are used, there are cases where the color reproduced with the provisional color separation ink amount set P obtained in step S140 of FIG. 13 cannot be reproduced. In this case, it is necessary to correct the ink amount so that the reproduced color can be achieved. In step S330, ink amounts close to the candidate ink amounts Rtmp and Vtmp are used as the final color separation ink amounts Ro and Vo within a range satisfying these restrictions.

  FIG. 18 is an explanatory diagram showing an outline of how the color coordinate point Prv (Ro, Vo) of the final color separation ink amount pair is calculated. 18A to 18D show a two-dimensional color space represented by using the ink amount of each RV color as a reference vector. The horizontal axis indicates the ink amount of the red ink R, and the vertical axis indicates the ink amount of the violet ink V. A combination of the ink amounts of the red ink R and the violet ink V is expressed as one point in the drawing.

  FIG. 18A is an explanatory diagram showing a range in which the final color separation ink amounts Ro and Vo can take values. The final color separation ink amounts Ro and Vo are set within an allowable range that satisfies the following conditions.

(Condition 1b) The final color separation ink amount of each color of CMYRV satisfies the ink duty limit.
(Condition 2b) The final color separation ink amount of each color of CMYRV is a combination of ink amounts that can be obtained by replacing the ink based on the replacement ink amount (FIG. 5) from the provisional color separation ink amount set P.
(Condition 3b) For color components whose candidate ink amount is smaller than the provisional color separation ink amount, the final color separation ink amount is set to be equal to or less than the provisional color separation ink amount.

  “Condition 1b” is the same as “Condition 1” described above. Moreover, these conditions can be represented by lines in FIG. Therefore, the allowable range can be expressed by a region surrounded by a line corresponding to each of these conditions. In the example of FIG. 18A, in order to simplify the description, it is assumed that a region surrounded by five straight lines LR to LRVM2 described below is an allowable range RA.

  The straight line LR is a straight line corresponding to the upper limit value of the red ink R. The ink amount of the red ink R can be increased by replacing each ink according to the replacement ink amount (FIG. 5). However, the upper limit value is limited by the ink duty limit of the red ink R and the maximum ink amount of the red ink R determined by the provisional color separation ink amount set P and the replacement ink amount. The straight line LR corresponds to an upper limit value that satisfies both of these restrictions.

  The straight line LV is a straight line corresponding to the upper limit value of the violet ink V. The meaning of this straight line is the same as the straight line LR described above.

  The straight line LVC is a straight line corresponding to the lower limit value of the violet ink V. The ink amount of the violet ink V can be reduced by substituting the two chromatic primary color inks C and M, but the ink amount of the chromatic primary color ink is increased instead. Accordingly, the lower limit value of the violet ink V is limited by the ink duty limit of the chromatic primary color ink. The straight line LVC corresponds to a lower limit value that satisfies this restriction.

  The straight line LRVM1 is a straight line corresponding to a lower limit value common to the two inks R and V. The ink amounts of the red ink R and the violet ink V can be reduced by substituting two chromatic primary color inks. Instead, the ink amount of the primary color ink common to these inks R and V (FIGS. 5B and 5C, magenta ink M in this example) increases. The ink amount of magenta ink M is limited by the ink duty limit of magenta ink M and the maximum ink amount of magenta ink M determined by provisional color separation ink amount set P and replacement ink amount. Therefore, the lower limit value of the ink amounts of the two inks R and V is limited to a range in which the upper limit value of the ink amount of the magenta ink M can be shared. In this limitation, the lower limits of the two inks R and V are inversely proportional to each other. The straight line LRVM1 corresponds to the lower limit values of the two inks R and V determined in this way.

  The straight line LRVM2 is a straight line corresponding to an upper limit value common to the two inks R and V. The ink amounts of the red ink R and the violet ink V can both be increased by replacing the two chromatic primary color inks. Instead, the amount of primary component primary color ink (magenta ink M) common to these inks R and V decreases. Therefore, the upper limit value of the ink amounts of the two inks R and V is limited to a range in which the maximum ink amount of the magenta ink M can be shared. In this limitation, the upper limit values of the two inks R and V are inversely proportional to each other. The straight line LRVM2 corresponds to the upper limit values of the two inks R and V determined in this way.

  Further, in the present embodiment, among the color components of the chromatic secondary color ink, for the color component whose candidate ink amount is smaller than the provisional color separation ink amount, the final color separation ink amount is equal to or less than the provisional color separation ink amount. The restriction (condition 3b) is imposed. For example, when the candidate ink amount Rtmp of the red ink R is smaller than the temporary color separation ink amount Rp, the final color separation ink amount Ro is limited to a value equal to or smaller than the temporary color separation ink amount Rp. A small candidate ink amount means that adjusting the ink amount of the color component to be small is preferable in terms of improving the graininess. Further, among the plurality of color separation ink amount sets obtained by replacing the ink amounts of the respective colors according to the replacement ink amount based on the provisional color separation ink amount set, the color separation ink having a small amount of chromatic secondary color ink Since the total number of ink dots increases as the amount is set, the graininess is less noticeable. Therefore, for a color component whose candidate ink amount is smaller than the temporary color separation ink amount, the final color separation ink amount is suppressed from being larger than the temporary color separation ink amount.

In step S330 of FIG. 16, a combination of ink amounts close to the color coordinate point Prv (Rtmp, Vtmp) of the candidate ink amount pair within the allowable range RA obtained in this way is set as the final color separation ink amounts Ro, Vo. Use. Hereinafter, the calculation of the final color separation ink amounts Ro and Vo will be described by dividing the relationship between the allowable range RA and the color coordinate point Prv (Rtmp, Vtmp) of the candidate ink amount pair into three cases.
(Case 1): The color coordinate point Prv of the candidate ink amount pair is within the allowable range RA.
(Case 2): The color coordinate point Prv of the candidate ink amount pair is outside the allowable range RA, and a straight line connecting the origin W and the color coordinate point Prv of the candidate ink amount pair passes through the allowable range RA.
(Case 3): The color coordinate point Prv of the candidate ink amount pair is outside the allowable range RA, and the straight line connecting the origin W and the color coordinate point Prv of the candidate ink amount pair does not pass within the allowable range RA.

(Case 1):
FIG. 18B shows a case where the color coordinate point Prv of the candidate ink amount pair is within the allowable range RA. In this case, the candidate ink amounts Rtmp and Vtmp are used as the final color separation ink amounts Ro and Vo as they are. By doing so, it is possible to calculate the final color separation ink amounts Ro and Vo that are preferable in terms of improvement in graininess. In the example of FIG. 18B, since the candidate ink amount Vtmp of the violet ink V is smaller than the provisional color separation ink amount Vp, the range of Vo ≦ Vp is the allowable range RA.

(Case 2):
FIG. 18C shows that the color coordinate point Prv of the candidate ink amount pair is outside the allowable range RA, and the straight line LP connecting the origin W and the color coordinate point Prv of the candidate ink amount pair is within the allowable range RA. The case where it passes is shown. In this case, the combination of the ink amounts expressed by the point Oa closer to the color coordinate point Prv of the candidate ink amount pair among the intersections of the straight line LP and the allowable range RA is the final color separation ink amount Ro. , Vo. The straight line LP is a straight line in which the ratio between the candidate ink amounts Rtmp and Vtmp is kept constant. By using such points on the straight line LP, the amount of one of the chromatic secondary color inks R and V is excessively decreased, and the amount of the other ink is not sufficiently decreased. it can. In other words, by using the points on the straight line LP, the final color separation ink amounts Ro and Vo can be obtained in consideration of the balance of influence on the graininess of each chromatic secondary color ink.

  Note that the combination of inks used as the final color separation ink amount set is not limited to the combination represented by the above point Oa. If the combination is expressed by a point within the allowable range RA and located near the color coordinate point Prv of the candidate ink amount pair, the graininess can be improved. For example, it is possible to use a combination of ink amounts expressed by an intersection Ob between the temporary color separation ink amount set P and the color coordinate point Prv of the candidate ink amount pair and the boundary of the allowable range RA. Also, a combination of ink amounts expressed by a point Oc that is a point within the allowable range RA and is closest to the color coordinate point Prv of the candidate ink amount pair can be used. In any case, the final color separation ink amount in consideration of improvement in graininess is used by using a combination of ink amounts that are within the allowable range RA and are expressed by points close to the color coordinate point Prv of the candidate ink amount pair. Ro and Vo can be calculated.

(Case 3):
In FIG. 18D, the color coordinate point Prv of the candidate ink amount pair is outside the allowable range RA, and the straight line LP connecting the origin W and the color coordinate point Prv of the candidate ink amount pair is within the allowable range RA. The case where it does not pass is shown. In this case, the point is within the allowable range RA, and is represented by a point Od that minimizes the final color separation ink amount Ro for the red ink R having the smaller value Rtmp among the candidate ink amounts Rtmp, Vtmp. A combination of the ink amounts to be used is used as the final color separation ink amounts Ro and Vo. The ink having the smallest candidate ink amount is the ink having the greatest influence on the graininess. Therefore, the graininess of the reproduced image area can be further improved by using the point Od at which the ink amount of the ink is minimized.

  The combination of inks used as the final color separation ink amount set is not limited to the combination represented by the above point Od. If the combination is expressed by a point within the allowable range RA and located near the color coordinate point Prv of the candidate ink amount pair, the graininess can be improved.

  Note that when all the candidate ink amounts Rtmp and Vtmp of the chromatic secondary color ink are zero, any combination expressed by a point within the allowable range RA and close to the origin W may be used. For example, the graininess can be improved. As such a point, for example, an intersection (not shown) between a straight line connecting the color coordinate point P and the origin W of the temporary color separation ink amount set and the boundary of the allowable range RA can be used. In addition, a point having a minimum distance from the origin W can be used.

  In step S340 in FIG. 16, the final color separation ink amount set of all inks constituting the ink set is calculated. The ink amounts calculated in step S330 are used as the final color separation ink amounts Ro and Vo of the chromatic secondary color ink. The final color separation ink amounts Co, Mo, and Yo of the chromatic primary color ink are calculated based on the provisional color separation ink amount set P and the replacement ink amount.

  As described above, the final color separation ink amount set calculation process of the present embodiment is performed in consideration of improvement in graininess. When the image area to be reproduced is bright, the ink amount of each color becomes small. At this time, since the amount of chromatic secondary color ink used is reduced and the chromatic primary color ink is actively used to increase the number of ink dots, the graininess can be improved.

  Particularly in a high lightness region, the size of each ink amount in the ink set is smaller than the ink duty limit. Therefore, a combination of a larger amount of ink satisfies the ink duty limit. As a result, when the candidate ink amounts Rtmp and Vtmp of the chromatic secondary color ink are zero, the final color separation ink amounts Ro and Vo can be zero. That is, since the color is reproduced without using the chromatic secondary color ink in a particularly bright area, it is possible to prevent the ink dots of the chromatic secondary color ink from being noticeable in such a particularly bright area. Can do.

  When the residual ink amounts RES_R2 and RES_V2 are relatively small, the chromatic secondary color inks R and V have relatively small ink amounts, and the residual ink amounts RES_R2 and RES_V2 are relatively small. When it is large, the ink amounts of the chromatic secondary color inks R and V become relatively large. Therefore, it is possible to improve graininess, save ink, and further suppress the undulation of the print medium.

  In the present embodiment, the final color separation ink amount set calculation process is performed on the candidate ink amounts Rtmp and Vtmp set independently for each of the chromatic secondary color inks, that is, the influence on the graininess of each ink. Is done according to. As a result, it is possible to appropriately improve graininess in consideration of the influence of each chromatic secondary color ink.

  Such a final color separation ink amount set calculation process can be executed in the same manner even when more types of chromatic secondary color inks are used. For example, when three chromatic secondary color inks are used, first, the candidate ink amount of each ink is calculated. Next, ink that is expressed as a point within an allowable range (represented by a solid in a color space represented by three ink amounts as a reference vector) and close to a point represented by a candidate ink amount set. The combination of amounts is used as the final color separation ink amount set for the chromatic secondary color ink. Also in this case, if the final color separation ink amount set is calculated according to the positional relationship between the straight line passing through the point represented by the candidate ink amount set and the allowable range, the influence on the graininess of each chromatic secondary color ink The final color separation ink amount set can be calculated in consideration of the balance.

  As described above, in the present embodiment, the final color separation ink amount set calculation process is performed in consideration of the improvement in graininess, so that it is possible to prevent the image from being rough in a bright region.

D2. Second embodiment of final color separation ink amount set calculation processing:
The difference from the first embodiment described above is that the candidate ink amount Rtmp is set according to the lightness L of the reproduced color. FIG. 19 is a graph showing a relationship between the ratio k of the candidate ink amount Rtmp to the maximum ink amount Rmax and the lightness L.

  As the lightness L of the reproduced color, for example, when the temporary color separation ink amount set P is expressed in the primary color space (FIG. 14), the point P is an achromatic color axis (a straight line connecting the origin W and the point K). The distance between the point projected above and the origin W can be used. At this time, the greater the distance from the origin W, the lower the brightness. Further, the maximum ink amount Rmax is the value of the ink amount of the red ink R in the combination of ink amounts that can reproduce substantially the same color as that reproduced in the provisional color separation ink amount set P. The maximum possible value can be used.

  In this embodiment, as shown in FIG. 19, the ratio k of the candidate ink amount Rtmp to the maximum ink amount Rmax is set so as to be smaller as the lightness L of the reproduced color is higher, that is, as it is brighter. The candidate ink amounts of other chromatic secondary color inks are set similarly. Therefore, in an image area where the lightness L is high and the amount of ink of each color is small, the amount of chromatic secondary color ink used is reduced, and the chromatic primary color ink is actively used to increase the number of ink dots. Therefore, the graininess can be improved.

  In the brightest range R21 where Lstart ≦ L, Rtmp = 0 is set. As a result, since the color is reproduced without using the chromatic secondary color ink in a particularly high lightness region, it is possible to suppress the conspicuous ink dots of the chromatic secondary color ink. In the darkest range R23 where L ≦ Lend, Rtmp = Rmax is set. As a result, particularly in a low lightness range, the color is reproduced by actively using the chromatic secondary color ink, so that the amount of ink used can be saved, and further, the printing medium can be prevented from undulating. be able to.

  The values Lstart and Lend for determining the magnitude of the lightness L can be set in the same manner as the Rstart and Rend in FIG. 17 described above. For example, based on the sensitivity evaluation comparing the gradation pattern of the chromatic secondary color ink reproduced so that the lightness L changes from the minimum value to the maximum value and the gradation pattern by the mixed color of the chromatic primary color ink, Can be set.

  At this time, it is preferable that the first and second values Lstart and Lend are set to larger values as the residual ink amount RES_R2 is larger. By doing so, it is possible to improve graininess and save ink. The sizes of Lstart and Lend are set independently for each of the hue ranges in which the hue can be reproduced with a combination of the same chromatic primary color ink and the same chromatic secondary color ink. Is preferred. By doing so, it is possible to appropriately improve graininess and save ink according to the hue.

  In this embodiment, for the violet ink V, the candidate ink amount Vtmp is set according to the lightness L according to the same method as that for the red ink R. Further, even when many types of chromatic secondary color ink are used, the amount of candidate ink can be set similarly.

  As the final color separation ink amount set calculation processing S150 of the color separation processing (FIG. 13) of this embodiment, the color separation shown in FIG. 8 is used instead of the various methods shown in FIGS. The method (FIGS. 9 to 12) applied to the calculation process S520 of the final color separation ink amount set of the process may be used. Similarly, the final color separation ink amount set calculation process S520 of the color separation process shown in FIG. 8 is the final of the color separation process (FIG. 13) of this embodiment instead of the method shown in FIGS. Any of various methods (FIGS. 16 to 18 and FIG. 19) applied to the color separation ink amount set calculation process S150 may be used.

E. Third embodiment of separation processing:
FIG. 20 is a flowchart showing a processing procedure of the third embodiment of the color separation processing. A difference from the above-described color separation processing embodiment of FIG. 13 is that an under color removal (UCR) process S220 using the black ink K is performed. The UCR process of this embodiment is a process for replacing a part of the gradation values of the chromatic primary color inks C, M, and Y with the gradation value of the black ink K. Since the UCR process can be realized by various known methods, detailed description thereof is omitted here.

  In step S200, an ink set including chromatic primary color inks C, M, and Y, chromatic secondary color inks R and V, and black ink K is set as a usable ink set.

  Next, in step S210, an ink duty limit that is a limit on the ink amount of each color of the ink set is set. The difference from the ink duty limit in the embodiment shown in FIG. 12 described above is that the ink amount of the black ink K is set in consideration (details will be described later).

  Next, in step S220, UCR processing is executed for the input color (for example, represented by the primary color gradation value set in step S20 in FIG. 6) that is the target of color separation processing. As a result, the input color I expressed by the gradation values Ci, Mi, Yi, and Ki of each color of CMYK is obtained. In the present embodiment, a color separation process using the extended chromatic color em is executed on the gradation values Ci, Mi, Yi of the CMY colors among these gradation values. A series of processes S230 to S270 is the same as the processes S120 to S160 of the embodiment shown in FIG. As a result, color separation ink amounts Co, Mo, Yo, Ro, and Vo for the gradation values Ci, Mi, and Yi of the CMY colors are obtained. For the black ink K, the gradation value Ki obtained as a result of the UCR process S220 is used as the color separation ink amount Ko.

  As described above, in the color separation processing of the third embodiment, the color range that can be reproduced using the black ink K in addition to the chromatic primary color ink CMY and the chromatic secondary color ink RV is effective. Separation processing used for. Therefore, it is possible to perform printing with a further expanded color reproduction range.

  In this embodiment, it is preferable to provide a limit in consideration of the ink amount of the black ink K in the above-described ink duty limit (condition 1). For example, regarding the limitation on the total value of all types of ink amounts shown in Equation 3, the total value obtained by adding the ink amount Ki of the black ink K obtained in step S220 to the ink amount of each color of CMYRV is equal to or less than Duty_T. Can be set as follows. By doing so, it is possible to suppress ejection of an amount of ink that exceeds the limit of the ink absorption amount of the print medium. Further, regarding the restriction of the ink amount when mixing a plurality of colors, the restriction can be set by using the ink amount Ki of the black ink K. It is preferable to consider the limitation of the ink amount of the black ink K when calculating the ink amount Ki in the UCR process S220.

  Further, it is preferable to add the ink amount of the black ink K to the remaining ink amount. For example, with respect to the residual ink amounts RES_R2 and RES_V2 shown in Equation 6 above, a method of adding a value obtained by multiplying the ink amount of the black ink K by a coefficient in the same manner as the chromatic primary color inks C, M and Y is used. it can. At this time, the coefficient for the black ink K can be determined in the same manner as the coefficients for the other inks. Thus, if the ink amounts of the chromatic secondary color inks R and V are determined in consideration of the ink amount of the black ink K, the graininess of the image can be improved and the ink can be further saved.

  When the color separation process of this embodiment is applied to step S20 of the color conversion lookup table creation process shown in FIG. 6, the second tone value set is the chromatic primary color ink CMY and chromatic 2 The gradation value is represented by the amount of each color ink of the next color ink RV and the black ink K. Accordingly, in step S30, a color patch reproduced using each color of CMYRVK is created.

F. Variation of ink set:
Various types of ink sets other than the ink set shown in FIG. 5 can be applied to the above-described embodiments. FIGS. 21 to 28 are explanatory diagrams showing ink components of examples of applicable ink sets. Since the components of the black ink K and the components other than the color material are the same as those in FIG. 5, the illustration is omitted. The difference from the ink set shown in FIG. 5 is that the color material type and density are partially different. As a result, these ink sets can improve the reproducibility of slightly different colors. Therefore, by selecting and using an ink set suitable for an image to be printed, a higher quality printing result can be obtained.

  21 to 26 show the replacement ink amounts of the red ink R and the violet ink V obtained by measuring the color patch. As described above, in these ink sets, the total value of the replacement ink amounts is 1.7 or more. As a result, the chromatic secondary color ink can reproduce higher saturation by using the same amount of ink as the mixed color of the chromatic primary color ink. As a result, by using the chromatic primary color ink and the chromatic secondary color ink, it is possible to reproduce a wider range of colors than the area that can be reproduced with only the chromatic primary color ink.

  Moreover, as each ink, it is not limited to the composition shown in the above-mentioned FIG. 5, FIG. 21-28, You may use the appropriate ink according to another composition. Further, the color and number of inks used are not limited to this combination. For example, only the red ink R may be used as the chromatic secondary color ink, and the chromatic secondary color ink may be used. Alternatively, a configuration using green ink or blue ink may be used. However, it is preferable to use, as the chromatic primary color ink, an ink that can reproduce an achromatic color in combination with each other, and an ink having a hue different from any of the chromatic primary color inks. By using an ink set composed of such ink, it is possible to execute a color separation process in consideration of expansion of the color reproduction range.

  As described above, in each of the above-described embodiments, the final color separation ink amount set calculation process is performed in consideration of the improvement in graininess, so that it is possible to suppress the roughness of the image in a bright region. . Further, since the ink amount of the chromatic secondary color ink is determined based on the residual ink amount, it is possible to suppress the roughening of the image in a bright region and to save ink. Further, by using the chromatic primary color ink and the chromatic secondary color ink, it is possible to perform the color separation process based on the extended chromatic color having a large gradation value. Therefore, it is possible to easily execute the color separation process considering the expansion of the color reproduction range.

  Note that the final color separation ink amount set calculation processing (for example, S520 in FIG. 8, S150 in FIG. 13, S260 in FIG. 20) is the same as the above-described processing (FIGS. 9-12, 16-18, and 19). Generally, it is a color separation ink amount set that reproduces the reproduced color, and the ink amount of the chromatic secondary color ink decreases at a rate of change larger than the rate of change in the brightness parameter value in the direction of lightening. Any processing that adjusts the amount of each ink may be used.

  The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

G. Variations:
G1. Modification 1:
In each of the embodiments described above, the hues of the inks in the usable ink set are different from each other. However, a configuration in which a plurality of types of inks having substantially the same hue and different densities may be used may be used. In this case, by using inks with different densities according to the tone value of each hue, the smaller the number of ink dots, the more noticeable graininess (roughness of the image) is improved. Easy banding (striated pattern) can be suppressed. At this time, the ink amount of each ink can be calculated using a so-called linear programming method with the above-described condition settings such as the ink duty limit and the replacement ink amount being set in consideration of the ink amounts of all the inks. Alternatively, a method may be used in which the color separation ink amount is calculated for each hue, and the obtained color separation ink amount is redistributed to a plurality of inks having substantially the same hue and different densities. Also in this case, it is preferable to provide a restriction in consideration of the ink amount of all inks in the ink duty restriction so that the final ink amount of each ink satisfies the ink duty restriction.

  In each of the above embodiments, the “ink amount” is a gradation value of each ink representing a range of 0% to 100% when the ink amount when reproducing the solid area is 100%. Means the output of the color conversion lookup table LUT. When a plurality of types of inks having substantially the same hue and different densities can be used, the color separation processing can be performed by making the total value of the color materials of the light and dark inks having the same hue correspond to the “ink amount”. it can. At this time, an appropriate color can be reproduced by distributing the obtained “ink amount” to each of the dark and light inks.

G2. Modification 2:
The present invention is also applicable to a thermal transfer printer and a drum scan printer. The present invention can be applied not only to so-called ink jet printers but also to printing apparatuses that reproduce colors by mixing a plurality of ink colors. Examples of such a printing apparatus include a facsimile machine and a copying machine.

G3. Modification 3:
Various values can be used as the brightness parameter value. In the first embodiment of the color separation process shown in FIG. 11, the provisional color separation ink amount of chromatic secondary color ink is used as the brightness parameter value. In this embodiment, the input color and the reproduction color match, and a provisional color separation ink amount set for reproducing the reproduction color is determined under the condition that the total ink amount is minimized. In the first embodiment of the final color separation ink amount set calculation process shown in FIG. 17, the maximum ink amount of chromatic secondary color ink is used as the brightness parameter value. This maximum ink amount is the maximum value of the ink amount determined from the reproduction color associated with the input color, and the ink amount that reproduces almost the same color as the provisional color separation ink amount set for reproducing the reproduction color. The maximum amount of chromatic secondary color ink in the combination. In general, any value representing the ink amount of chromatic secondary color ink determined according to a predetermined condition from an input color or reproduced color can be used as a brightness parameter value. The lightness parameter value is not limited to such a value representing the ink amount of the chromatic secondary color ink, but may be any value that correlates with the lightness of the reproduced color. For example, as in the second embodiment of the final color separation ink amount set calculation process shown in FIG. 19, the lightness of the reproduction color associated with the input color may be used as the lightness parameter value.

  The brightest first range in the lightness parameter value range in which the ink amount of the chromatic secondary color ink is adjusted to zero is 0% (lightness range in which the lightness parameter value can take a value). ) To 100% (dark), a bright range of 5% or less is preferable, a bright range of 10% or less is particularly preferable, and a bright range of 15% or less is most preferable.

G4. Modification 4:
In each of the above-described embodiments, the case where the ink amount of the chromatic secondary color ink is determined based on the residual ink amount has been described. However, it may be determined based on the parameter value correlated with the hue of the reproduced color. At this time, when the hue is relatively close to the chromatic secondary color ink, the ink amount is determined so that the usage rate of the chromatic secondary color ink is relatively large, and the hue is compared with the chromatic primary color ink. It is preferable to determine the ink amount so that the usage rate of the chromatic secondary color ink becomes relatively small when close to the target. By doing so, the graininess can be improved appropriately according to the hue, and ink can be saved. Note that various values can be used as parameter values correlated with the hue of the reproduced color. For example, a straight line connecting the origin W and the point K in the primary color space shown in FIG. 14 is called an achromatic line, and a point obtained by vertically projecting one point in the primary color space onto the achromatic line is a projected point. The direction from the projection point toward one point in the primary color space can be used as a parameter value correlated with the hue.

G5. Modification 5:
In the above embodiment, a part of the configuration realized by hardware may be replaced with software, and conversely, a part of the configuration realized by software may be replaced by hardware. For example, a part of the function of the printer driver 96 (FIG. 1) can be executed by the control circuit 40 (FIG. 3) in the printer 20.

Block diagram showing the configuration of the printing system Schematic configuration diagram of the printer 20 Block diagram showing the configuration of the printer 20 Explanatory drawing showing the nozzle arrangement on the lower surface of the print head 28 Explanatory drawing showing the ink set Flow chart showing the color reproduction processing procedure Explanatory drawing showing color patches Flow chart showing the processing procedure of separation processing Flow chart showing the processing procedure for calculating the final color separation ink amount set Explanatory drawing explaining the relationship between the secondary color ink usage rate and the ink amount of other inks Explanatory drawing showing the amount of candidate ink Explanatory drawing which shows the outline of a mode that the final color separation ink amount of chromatic secondary color ink is calculated Flow chart showing the processing procedure of separation processing Explanatory drawing showing the primary color space Explanatory drawing which shows the outline of a mode that an extended chromatic color is calculated Flow chart showing the processing procedure for calculating the final color separation ink amount set Explanatory drawing showing the amount of candidate ink Explanatory drawing which shows the outline of a mode that the final color separation ink amount of chromatic secondary color ink is calculated A graph showing the relationship between the ratio of the candidate ink amount to the maximum ink amount and the lightness Flow chart showing the processing procedure of separation processing Explanatory drawing showing another example of ink components Explanatory drawing showing another example of ink component Explanatory drawing showing another example of ink components Explanatory drawing showing another example of ink component Explanatory drawing showing another example of ink component Explanatory drawing showing another example of ink component Explanatory drawing showing another example of ink components Explanatory drawing showing another example of ink component

Explanation of symbols

20 ... Printer 21 ... CRT
DESCRIPTION OF SYMBOLS 22 ... Paper feed motor 24 ... Carriage motor 26 ... Platen 28 ... Print head 30 ... Carriage 32 ... Operation panel 34 ... Sliding shaft 36 ... Drive belt 38 ... Pulley 39 ... Position sensor 40 ... Control circuit 41 ... CPU
43 ... P-ROM
44 ... RAM
45 ... CG
DESCRIPTION OF SYMBOLS 50 ... I / F exclusive circuit 52 ... Head drive circuit 54 ... Motor drive circuit 56 ... Connector 60 ... Print head unit 90 ... Computer 91 ... Video driver 95 ... Application program 96 ... Printer driver 97 ... Resolution conversion module 98 ... Color conversion module 99 ... Halftone module 100 ... Rasterizer LUT ... Color conversion lookup table PP ... Printing paper PD ... Print data

Claims (5)

The plurality of chromatic primary color inks that can reproduce achromatic colors by being used in combination with each other and the plurality of chromatic primary color inks have different hues, and among the plurality of chromatic primary color inks A printing apparatus that prints an image on a print medium using an ink set including at least one chromatic secondary color ink having a hue reproducible by a mixed color of at least the first ink and the second ink,
  A first color having a predetermined hue between the hue of the first ink and the hue of the chromatic secondary color ink and having a predetermined lightness and a predetermined saturation is represented by the chromatic 2 Print without using the next color ink,
  A second color having a predetermined hue closer to the first ink than the first color and having the same lightness and saturation as the first color is used as the chromatic secondary color ink. Print using
  Printing device. The plurality of chromatic primary color inks that can reproduce achromatic colors by being used in combination with each other and the plurality of chromatic primary color inks have different hues, and among the plurality of chromatic primary color inks A printing apparatus that prints an image on a printing medium using an ink set including at least one chromatic secondary color ink having a hue reproducible by a mixed color of at least the first ink and the second ink,
  When printing a plurality of colors having a first hue between the hue of the first ink and the hue of the chromatic secondary color ink and having a predetermined saturation and different brightness Printing a color brighter than the first lightness without using the chromatic secondary color ink, printing a color darker than the first lightness using the chromatic secondary color ink,
  When printing a plurality of colors having a second hue closer to the first ink than the first hue and having the predetermined saturation and different brightness, the first brightness Printing a brighter color than the second lightness without using the chromatic secondary color ink, and printing a color darker than the second lightness using the chromatic secondary color ink.
  Printing device. The plurality of chromatic primary color inks that can reproduce achromatic colors by being used in combination with each other and the plurality of chromatic primary color inks have different hues, and among the plurality of chromatic primary color inks A printing apparatus that prints an image on a print medium using an ink set including at least one chromatic secondary color ink having a hue reproducible by a mixed color of at least the first ink and the second ink,
  When printing a plurality of colors having a first hue between the hue of the first ink and the hue of the chromatic secondary color ink and having a predetermined saturation and different brightness A color brighter than the first lightness is printed by decreasing the amount of the chromatic secondary color ink used in the first change as it becomes brighter, and a color darker than the first lightness is printed in the first as the lighter. The second change that is smaller than the change in the above is used to reduce the amount of chromatic secondary color ink used for printing,
  When printing a plurality of colors having a second hue closer to the first ink than the first hue and having the same saturation as the color of the first hue and different brightness A color brighter than the first lightness and brighter than the second lightness is printed by reducing the amount of the chromatic secondary color ink used in a third change as the lightness becomes brighter than the second lightness. A dark color is printed with a fourth change smaller than the third change as the brightness is reduced, and the amount of the chromatic secondary color ink used is reduced.
  Printing device. The plurality of chromatic primary color inks that can reproduce achromatic colors by being used in combination with each other and the plurality of chromatic primary color inks have different hues, and among the plurality of chromatic primary color inks A printing apparatus that prints an image on a printing medium using an ink set including at least one chromatic secondary color ink having a hue reproducible by a mixed color of at least the first ink and the second ink,
  Printing a first color having a first hue between the hue of the first ink and the hue of the chromatic secondary color ink using a first amount of the second ink;
  Printing a second color having a second hue closer to the first ink than the first color using a second amount of the second ink less than the first amount. Characteristic printing device. The plurality of chromatic primary color inks that can reproduce achromatic colors by being used in combination with each other and the plurality of chromatic primary color inks have different hues, and among the plurality of chromatic primary color inks A printing apparatus that prints an image on a print medium using an ink set including at least one chromatic secondary color ink having a hue reproducible by a mixed color of at least the first ink and the second ink,
  A first color having a first hue between the hue of the first ink and the hue of the chromatic secondary color ink; and a second color closer to the first ink than the first color When the second color having a hue is printed, the second ink is larger than the difference in ink amount of the chromatic secondary color ink between the first color and the second color. The difference in ink amount is larger,
  Printing device.

Images