JP2002211015A - Method for dividing print using multicolor ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately divide print using color inks containing a plurality of dyes out of three primary color dyes. SOLUTION: In order to reproduce a color with inks of light cyan, light magenta, black and yellow in addition to three primary colors of cyan, magenta and yellow, the quantity of each color ink is determined as follows. Dark yellow ink is an yellow ink having a lowered lightness and substantially contains the components of cyan and magenta. A reproduction color being subjected to print division is represented by the gray level of C, M and Y and exists in a color solid of CMY. At a point where a line extending through the origin and the reproduction color intersects the shell surface of the color solid, quantities of respective color inks are determined simultaneously including dark yellow using linear programming. On the shell surface, conditions for using individual inks are set while taking account of granularity. Print of reproduction color is divided by multiplying the print division results on the shell surface proportionally.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color separation method for determining the amount of ink of each color when colors are reproduced by mixing multi-color inks.

[0002]

2. Description of the Related Art In an ink jet printer capable of printing a color image, an ink of each color is ejected to form dots to print an image, and various colors are expressed by mixing colors of these inks. The ink jet printer is provided with cyan (C), magenta (M), and yellow (Y) inks corresponding to the three primary colors in order to express multiple colors. The amount of ink is determined in consideration of the amount of dye contained in the ink of each of these colors according to the color to be reproduced.
The relationship between the color and the amount of ink is stored in advance as a look-up table (LUT: Look Up Table), and during printing, the amount of each color ink of each pixel is determined according to the LUT. The inkjet printer realizes multi-color printing by forming dots at a recording rate corresponding to the amount of ink. When the original image data is represented by red (R), green (G), and blue (B) gradation values, the R, G, and B color systems are changed to C, M, and Y color systems by the LUT. And the ink amount of each color is determined.

In the present specification, a process for determining the amount of ink of each color used at the time of printing for color reproduction is referred to as a color separation process.
Conventionally, separation processing has been performed so as to secure the amounts of cyan (C), magenta (M), and yellow (Y) pigments necessary for color reproduction. If black ink is provided in addition to the three primary colors, Under Color Removal
In l), the amount of black ink is determined, and the amount of each color is determined so as to express the remaining color components. In recent years, cyan (C) and magenta (M) have low concentrations of light cyan (LC) and light magenta (LM).
There are also printers that use. For such printers, the range of ink amount allowed for each print medium (hereinafter, referred to as
Separation processing is performed by replacing part of cyan (C) and magenta (M) with light cyan (LC) and light magenta (LM) so as to reduce graininess in “duty limitation”. Had been done.

[0004]

The conventional color separation process cannot fully utilize the advantages of a chromatic ink containing a plurality of dyes among the three primary colors. Since two or more pigments of the three primary colors are mixed in the chromatic ink, the amount of ink used can be reduced by appropriately replacing a part of the three primary inks with the chromatic ink. As a result, it is possible to increase the amount of the three primary colors that can be used under the duty limitation, and to extend the color reproduction range, particularly the saturation. However, in the conventional color separation processing, since the ink amounts of the three primary colors are determined under the duty limit, the color reproduction range cannot be expected to be expanded even if replacement with chromatic ink is performed thereafter.

[0005] In the conventional separation processing, light cyan (LC),
There is also a problem that the replacement process with light ink such as light magenta (LM) becomes complicated. When a plurality of light inks are provided, various combinations of the usage amounts of the three primary color inks and the light ink for expressing a certain color are possible. In the conventional color separation processing, the processing of selecting an optimal combination from among these various combinations in consideration of the granularity and the amount of ink used for each color to be reproduced was very complicated.

The present invention has been made in order to solve these problems, and has as its first object to provide a color separation process that can make use of the advantages of chromatic color inks.
The second is to facilitate the setting of the amount of light ink used.
The purpose of. Accordingly, it is an object to facilitate and optimize the color separation processing for printing using various kinds of inks having different hues and densities in addition to the three primary color inks serving as the reference.

[0007]

Means for Solving the Problems and the Function / Effect The first color separation process of the present invention restricts the duty in the case where three reference color inks and chromatic color inks capable of expressing black by mixing colors are included. The ink amounts of the reference color ink and the chromatic ink required for color reproduction are set at the same time within a range that satisfies the conditions.

The reference color inks include, for example, inks corresponding to the three primary colors of cyan (C), magenta (M), and yellow (Y). It is not necessary that the three types of reference color inks strictly match the three primary colors, and slight deviations do not matter. A chromatic color ink is an ink containing a dye contained in two or more types of reference color inks. In order to obtain the amount of the dye contained in a unit volume with the reference color ink, the total volume must be equal to the unit volume. More than ink. Because it is a chromatic color ink, gray containing two or more dyes in equal amounts,
Does not include black ink. The duty limit is a value corresponding to the upper limit of the amount of ink that can be used per unit area of a print medium used for color reproduction.

According to the present invention, the color separation process can be performed based on the ink amount reduction effect obtained by replacing a part of the reference color ink with the chromatic color ink. Therefore, the advantage of the chromatic color ink, that is, the expansion of the color reproduction range can be realized.

Simultaneously, the setting means that the ink amounts of the reference color ink and the chromatic color ink are determined while mutually considering the ink amounts of the reference color ink and the chromatic color ink under the ink duty limitation. Various modes are possible for the calculation process up to the determination of the ink amount. For example, the amounts of both inks may be set using a method such as so-called linear programming. Further, by repeatedly performing the setting of the ink amount of the reference color ink and the replacement of the reference color ink with the chromatic color ink within a range that satisfies the duty limit, the ink amounts of the two may be successively and approximately set. .

In the present invention, when at least a part of the reference color ink includes a light reference color ink having a low pigment content per unit volume, the ink amount of the light reference color ink is set at the same time. It may be. By doing so, it is possible to extend the color reproduction range while suppressing graininess by using light ink.

Of course, the present invention is not limited to the case where the light reference color ink is simultaneously set, and at least a part of the reference color ink is replaced with the light reference color ink after the ink amounts of the reference color ink and the chromatic color ink are determined. It is also possible to adopt a method.

At this time, the reference color ink is replaced with a chromatic color ink so that the duty reference has a margin so that the light reference color ink can be used more, and then the light reference color ink is replaced with the light reference color ink. It may be.

Further, when the duty limit is exceeded by replacement with the light reference color ink, replacement of at least one of the light reference color ink or the reference color ink with the chromatic color ink, The amount of ink may be suppressed by at least one of the replacement with the reference color ink.

In the present invention, when black ink is included, prior to the setting of the reference color ink and the chromatic color ink,
It is desirable to determine the amount of black ink by performing undercolor removal processing. By expressing the remaining hues with the reference color ink and the chromatic color ink, the color reproduction range can be further extended.

In the second color separation process of the present invention, in the case where the reference color ink and at least one light reference color ink are included, each color component of the reference color ink is expressed as a reference vector. In at least one plane of the shell surface, there is set a restriction on the use of the reference color ink and the light reference color ink, and the ink amount is set in consideration of this restriction. The second separation method is applicable regardless of the presence or absence of the chromatic ink.

When the reference color ink and the light reference color ink are provided, the amounts of both inks are set in consideration of color reproducibility, granularity, and duty limit. For example, for a color having a relatively high brightness, it is preferable to use a light reference color ink rather than a reference color ink in consideration of graininess. Here, it is very difficult to individually determine the use of all the colors to be subjected to the color separation processing and to set the respective ink amounts. According to the second method, it is possible to easily perform the color separation processing by applying the condition of proper use set on the outer surface to other colors.

In this case, it is desirable to apply the restriction on the intersection of the outer shell surface with the straight line connecting the origin of the color solid and the color to be reproduced to the color to be reproduced. It is considered that the conditions on the graininess of colors on this straight line are considered to be similar. Therefore, by applying the above method, it is possible to realize almost appropriate use of all colors. It is also preferable to individually correct the separation results set by this method in consideration of the graininess.

According to the present invention, the first separation method described above,
May be realized as a separation method combining the above separation methods. In addition, the present invention can be configured as an apparatus that realizes the above-described separation method. The separation processing apparatus can be configured by preparing units for executing the respective steps of the separation processing described above in terms of software or hardware. The present invention can be configured in various forms such as a recording medium storing a program for performing separation, the program itself, and the like. Here, examples of the recording medium include a flexible disk, a CD-ROM, a magneto-optical disk, an IC card, a ROM cartridge, a punched card, a printed matter on which a code such as a barcode is printed, and a computer internal storage device (such as a RAM or a ROM). memory)
Various computer-readable media such as an external storage device and the like can be used. Further, an image processing apparatus, an image processing method, and the like that convert each gradation value of image data into ink amount data, that is, data corresponding to each color ink amount, using the correspondence generated by the above-described text plate method. Can also be configured. Of course, it is also possible to configure in the form of a program for realizing such image processing, a recording medium on which the program is recorded, and the like.

The chromatic ink described in the present invention includes:
In addition to the inks defined by the above definitions, inks defined in the following various modes can be applied.

(1) An ink whose wavelength range of light to be absorbed mainly overlaps with one reference color ink and has lower brightness than the reference color ink. As an example, there is an ink that includes one ink of the reference color ink as a main component and includes another ink having a different hue from the reference color ink. When the reference color ink is yellow, it can be prepared by adding an appropriate amount of a cyan dye or a magenta dye or a black dye. It can also be said that the lightness and chroma are lowered by adding a dye of another ink to the reference color ink. Different ink compositions may be used as long as the spectral characteristics are equivalent.

(2) The main wavelength range that absorbs light in the visible region most strongly overlaps with one reference color ink, and the value obtained by integrating the light absorptance in the visible region wavelength range is larger than that of the reference color ink. Ink. Here, the wavelength band in which light in the visible region is most strongly absorbed is a band having a wavelength of about 600 to 700 nm for cyan ink, about 500 to 600 nm for magenta ink, and about 400 to 500 nm for yellow ink. .

(3) An ink having the following spectral characteristics. (A) The characteristic wavelength range that largely absorbs light in the visible region and mainly determines the hue of the ink overlaps with one reference color ink, and (B) the light absorption in the characteristic wavelength range of the chromatic color ink The average value of the ratio is larger than or substantially the same as the average value of the light absorption ratio of the reference color ink. (C) In the visible light wavelength range excluding the characteristic wavelength range of the chromatic color ink,
An ink in which the average value of the light absorption of the chromatic color ink is larger than the average value of the light absorption of the reference color ink.

(4) The hue of the ink is in an area between the red area and the green area on the Munsell hue circle, and the ink has a lower brightness than the reference color ink in the area.

(5) An ink in which the hue of the ink includes a yellow region on the Munsell hue circle and extends from the yellow region to the boundary with the green region. For example, it is possible to use an ink whose hue is in the range of 10R to 10GY in the Munsell index and whose brightness is lower than the reference color ink in the region. The ink may have a hue ranging from 2.5YR to 7.5YR and a saturation having a Munsell index smaller than 3.5C.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to examples. A. Overview of inks subject to separation processing: Separation processing: B1. Seven-color version of outer shell value: B2. Seven-color separation of reproduced colors: B3. Replacement processing with DY: B4. Duty limit correction processing:

A. Outline of ink to be subjected to separation processing: In this embodiment, cyan (C), magenta (M), yellow (Y) reference color inks, light cyan (LC) with low cyan and magenta pigment contents, light Magenta (L
M), black (K), and dark yellow (DY) color separation processing to seven color inks will be described as an example. Dark yellow (DY) corresponds to the chromatic ink in this specification.

FIG. 1 is an explanatory diagram showing a list of ink components to be subjected to the color separation processing of this embodiment. Each color ink is
This is a mixed solution in which an appropriate amount of diethylene glycol for adjusting clay and a dye are added to an aqueous solution of Surfynol. The clay of each ink is adjusted to 3.0 (mPa · s) so as to be suitable for use in an ink jet printer. The six color inks except dark yellow (DY) contain a single type of dye suitable for each hue. The type and content of the dye are not limited to these. In the present embodiment, the dye-based ink is exemplified, but the present invention can be applied to a pigment-based ink.

[0029] Dark yellow (DY) contains a plurality of types of dyes. In the present embodiment, the composition is mainly composed of direct yellow 86, which is a dye of yellow ink, and substantially equal amounts of direct blue 199, which is a dye of cyan ink, and Acid Red 289, which is a dye of magenta ink, are added as additive dyes. . The amount of the added dye can be appropriately adjusted. A difference may be made between the two amounts. Further, a small amount of food black 2 may be added instead of or together with the additive dye. Dark Yellow (D
The dye of the yellow component used in Y) may be different from the yellow ink (Y). For example, yellow dyes such as Direct Yellow 132 and Acid Yellow 23 can be used. The dark yellow ink in this embodiment is a chromatic ink that is darker than the yellow ink, and is an ink that can express an achromatic color by being mixed with an appropriate amount of cyan ink and magenta ink. The dark yellow ink is an ink that also has the features related to the spectral characteristics variously enumerated above. Here, the ink having a hue close to yellow is used as the chromatic ink, but a chromatic ink having a hue close to cyan or magenta may be used.

B. Separation Processing: FIG. 2 is a process chart of the separation processing. The separation processing exemplified below can be executed using a computer, and FIG. 2 also corresponds to the flowchart of the separation processing.

The color separation processing is started by inputting a tone value representing a reproduced color, that is, a color to be subjected to the color separation processing (hereinafter, referred to as a "reproduced color") (step S10). In the present embodiment, the gradation values C1, M corresponding to the reference colors C, M, Y
The reproduced color is represented by 1, Y1. Each gradation value is handled by 8 bits and takes a value of 0 to 255.
If the reproduced colors are expressed in the RGB color system, the L * a * b * color system, etc., it is assumed that each of the reproduced colors has been converted to CMY gradation values prior to this step.

In this embodiment, the reproduced color is represented as one point in a cube represented by CMY gradation values 0 to 255. Hereinafter, this cube is called a color solid, and its surface is called an outer shell surface.

Next, UCR processing, that is, under color removal is performed on the reproduced color (step S12). Reproduction colors C1, M1,
This is a process for reducing components of each hue by replacing a part of Y1 with a black component. Since the UCR process can be realized by various known methods, a detailed description is omitted here. By UCR processing, the reproduction color is
It is converted into each gradation value of C2, M2, Y2, K2.

In the seven color inks to be separated, a dye is contained in a plurality of inks. Therefore, there is a degree of freedom in the combination of the ink amounts when reproducing colors. In the present embodiment, the separation process is performed using a suitable combination within the range of the degree of freedom in consideration of the duty limit of the print medium and the granularity at the time of printing. In order to facilitate such processing, in the present embodiment, a condition regarding the proper use of each ink is set on the outer shell surface, and this condition is applied to each color to be reproduced.

In order to properly use the conditions set on the outer shell surface depending on the reproduced color, in the color separation processing, the gradation values C2. Based on M2, Y2 and K2, the outer shell values C3 and M
3, Y3, and K3 are calculated (step S14).

FIG. 3 is an explanatory diagram of the outer shell value. The lower part of the figure shows the color solid represented by the CMY gradation values. The outer shell value is defined as the intersection of a straight line connecting the origin (C = 0, M = 0, Y = 0) of the color solid and the reproduced color (point P2 in the figure) with the outer shell surface. In the example of the figure, the intersection P with the outer shell surface Sy of Y = 255
3 is the outer shell value. The gradation values are set to C3, M3, and Y3 (step S14). Note that the black component is handled as K3 = K2 because it does not affect the subsequent processing.

The upper surface of FIG. 3 shows the outer shell surface Sy and outer shell value P3 in a plan view. As shown, the outer shell surface Sy is A1 to A
Nine areas are set, and a condition regarding the proper use of ink is set in each area. This condition will be described later in detail. In the example in the figure, since the outer shell value P3 exists in the area A9, the reproduction color is also subjected to the color separation by applying the condition of the area A9. In the present embodiment, seven-color separation of the outer shell value is performed once based on the conditions on the outer shell surface (step S16). C4, M4, Y4, K4, Lc4, Lm4, Dy
4 is assumed. Lc4, Lm4, and Dy4 are ink amounts corresponding to light cyan (LC), light magenta (LM), and dark yellow (DY), respectively. This result is a separation result in consideration of duty limitation, color reproducibility, and granularity. Next, the seven-color separation of the reproduced colors is executed by correcting the result on the outer shell surface thus obtained (step S1).
8). C5, M5, Y5, K5, Lc
5, Lm5, and Dy5. Details of the color separation processing on the outer shell surface and the correction processing for the reproduced color will be described later.

The method for applying the conditions on the outer shell surface to the reproduced color is not limited to this, but may take various forms. The conditions set on the outer shell surface may be applied to the reproduced colors in the vicinity. A mode in which the conditions set on a single outer shell surface are applied to all reproduced colors is also possible.

The separation result thus obtained may be output as it is. In the present embodiment, processing for further suppressing graininess is performed. The conditions applied at the time of separation of reproduced colors are set by optimizing the outer shell surface, and there is room for improvement in reproduced colors. In the present embodiment, in consideration of this point, in order to further improve the graininess, a part of the separation result is replaced with LC, LM, and DY (step S20). The replacement result is represented by C6, M6,
Y6, K6, Lc6, Lm6, and Dy6. This replacement may exceed the duty limit. If the duty limit is exceeded, LC and LM are changed to DY, C,
A process for replacing with M is performed (step S22). Thus, the final separation processing result, C7, M7, Y7, K7, L
c7, Lm7, and Dy7. This result is output (step S24), and the color separation process for one reproduced color is completed. The above processing is performed for each reproduced color in the color solid.
Execute repeatedly.

B1. Seven-color separation of outer shell value: The processing of seven-color separation of outer shell value (step S16) will be described in detail. In the present embodiment, seven-color separation is executed by obtaining the value of each ink amount by a linear programming method. The following five conditions are used for separation. (Condition 1) Condition regarding the proper use of the ink on the outer shell surface: (Condition 2) Condition regarding the ratio of the dye contained in the ink: (Condition 3) Duty limitation: (Condition 4) Optimization to minimize the total amount of ink Condition: (Condition 5) Optimization condition for maximizing the component values of C, M, and Y:

The amount of each color ink obtained by the seven-color separation is represented by C
Assuming that 4, M4, Y4, K4, Lc4, Lm4, and Dy4, the above conditions are respectively represented by the following equations.

(Condition 1) Conditions Regarding Use of Ink on Outer Shell Surface: As illustrated in FIG. 3, in this embodiment, conditions regarding use of ink on the outer shell surface are set. The condition according to the outer shell surface Sy is C = 255 (the outer shell surface Sy).
c), M = 255 (shell surface Sm), and Y = 0, C =
It is also set for five outer shell surfaces represented by 0 and M = 0. The conditions on the outer shell surfaces Sy, Sc, and Sm also affect the reproduced color inside the color solid. Conditions on the outer shell surface represented by Y = 0, C = 0, and M = 0 do not affect the reproduced color inside the color solid.

The condition of the outer shell surface Sy will be described. In this embodiment, as shown in the figure, the outer shell surface Sy has nine regions A1 to A1.
A9, conditions for selectively using dark and light inks in each area were set.

The areas A1, A2 and A3 are areas where the gradation value of C is low. From the viewpoint of graininess, it is preferable to use light cyan instead of cyan. Therefore, in these areas, the cyan ink amount C4 is limited to zero.

The areas A7, A8, and A9 are areas where the gradation value of C is high. In these areas, even if cyan is used, no remarkable deterioration in image quality due to graininess occurs. From these viewpoints, it is preferable to use cyan rather than light cyan in terms of color reproducibility and duty limitation. Therefore, in these areas, the light cyan ink amount Lc4
Is limited to zero.

In the areas A2, A4, A5, A6 and A8,
The ink amounts of cyan and light cyan are set so as to maintain continuity with adjacent areas. For example,
The cyan ink amount C4 in the area A2 is interpolated so as to be equivalent to the value set in the area A3 at 0 at the boundary with the area A1 and at the boundary with the area A3. The same applies to the light cyan ink amount Lc4. In this embodiment, linear interpolation is performed by the following method.

FIG. 4 is an explanatory diagram showing a linear interpolation method. The area A2 is shown enlarged. For convenience of explanation, area A
2 and areas A3 and A1 are defined as PY1 to PY, respectively.
It shall be called 4. At the time of performing this interpolation,
It is assumed that the cyan and light cyan ink amounts C4 and Lc4 have been determined for the respective outer shell values of the regions A1 and A3.

Consider a case where the outer shell value exists at a point P3 in the area A2. In this case, linear interpolation was performed along a parallel line to the magenta axis. The intersection between the parallel line to the magenta axis and the boundary line PY1-PY2 passing through the point P3 is defined as P31, and the intersection between the boundary line PY3-PY4 is defined as P32. The ink amount at the point P3 can be calculated by linear interpolation using the internal division ratio N: 1-N of the line segment P31-P32 and the ink amounts at the points P31 and P32. A parallel line passing through the point PY2 and a line segment PY3-
If the point of intersection with PY4 is point PY5, the outer shell value is the area PY
When it is within 1-PY2-PY5-PY4, it can be interpolated by the same method. The outer shell value is in the area PY2-P
Similarly, in the case of being within Y3-PY5, a parallel line and a line segment PY2
-Intersection with PY3 (for example, point PY6) and line segment PY3
Interpolation is performed using an intersection with -PY4 (for example, point PY7). The value of the point PY6 is obtained by interpolation of the points PY2 and PY3.

In the area A2, light magenta was interpolated along a parallel line to the magenta axis, and light cyan was interpolated along a parallel line to the cyan axis.

The interpolation method is only required to ensure continuity with an adjacent area, and is not limited to the above method. For example, since the region A2 is close to the magenta axis, both light magenta and light cyan may be interpolated along a parallel line to this axis. In a region near the cyan axis such as the region A4, interpolation is performed along a line parallel to the cyan axis. Area A5
Is divided into two equal parts, a region near the magenta axis and a region near the cyan axis, and interpolation is performed using parallel lines to the respective axes. Further, the interpolation may take the following mode. FIG. 5 is an explanatory diagram showing a modification of the interpolation method. In the modified example, interpolation is performed using points that divide the boundary line of the area at the same ratio. Consider a case where the outer shell value exists at a point P3 in the figure. A straight line passing through the point P3 and internally dividing the line segments PY1-PY2 and PY3-PY4 by N: 1-N, and the value N at that time are as follows:
Determined uniquely. The intersection of this straight line and the line segment PY1-PY2 is point P31a, and the intersection of the line segment PY3-PY4 is point P32a.

The line segment PY1-PY passing through the point P3
4. The straight line that internally divides the line segments PY2 and PY3 into M: 1-M, and the value M at that time are also uniquely determined. The intersection between this straight line and the line segment PY1-PY4 is defined as a point P33a, and the intersection between the line segment PY2-PY3 is defined as a point P34a.

In the modified example, interpolation is performed by selecting two opposing points out of the four points P31a, P32a, P33a, and P34a specified in this manner. Point P3 is a line segment P31a
-Since P32a corresponds to the point of internally dividing M: 1-M,
Interpolation can be performed using the points P31a and P32a.
Since the point P3 also corresponds to a point that internally divides the line segment P33a-P34a by N: 1-N, the point P3 may be interpolated using the points P33a and P34a. For the interpolation, various other methods can be applied. A non-linear interpolation method may be used.

For M, from the same viewpoint, the areas A1,
For A4 and A7, the magenta ink amount M4 is limited to zero. In the areas A3, A6, and A9, the light magenta ink amount Lm4 is limited to zero.

From the above, regarding the outer shell surface Sy, the region A1
The restrictions on the amount of ink in A9 are as follows. In the present embodiment, there is no restriction on the ink that is not set. Area A1 ... C4 = 0, M4 = 0; Area A2 ... C4 = 0, Lm4 is interpolated between areas A1 and A3; Area A3 ... C4 = 0, Lm4 = 0; Area A4 ... M4 = 0, Lc4 is area A1 Lc4, M4, Lm4 are interpolated between peripheral areas; Area A6 ... Lm4 = 0, Lc4 is interpolated between areas A3, A9; Area A7 ... Lc4 = 0, M4 = 0; A8 ... Lc4 = 0, Lm4 is interpolated between areas A7 and A9; Area A9 ... Lc4 = 0, Lm4 = 0;

The condition setting on the outer shell surface is not limited to this. The number of divisions of the area and the conditions in each area can be variously set.

(Condition 2) Condition relating to the ratio of the dye contained in the ink: Each color component value C3, M3, Y3 of the outer shell value
And the ratio of the respective color dyes contained in the color-separated ink is equal. This is an essential condition for reproducing the hue corresponding to the outer shell value.

Cyan, magenta and yellow dye amounts Cink
4, Mink4 and Yink4 are represented by the following equations, respectively. Cink4 = C4 + RCLC × Lc4 + RCDY × DY4; Mink4 = M4 + RMLM × Lm4 + RMDY × DY4; Yink4 = Y4 + RYDY × DY4; where RCLC ... LC cyan dye content / C cyan dye content; RCDY ... DY cyan dye content / C cyan dye content; RMLM ... LM magenta dye content / M magenta dye content; RMDY ... DY magenta dye content / M magenta dye content; RYDY ... DY yellow dye content / Y Yellow dye content;

Condition 2 is that the dye amounts Cink4, Mink4,
It is represented by the following equation using Yink4. Cink4: Mink4: Yink4 = C3: M3: Y3;

(Condition 3) Duty limit: There is a limit on the amount of ink absorbed per unit area depending on the printing medium. This restriction is called duty restriction. Separation processing needs to be performed under this restriction. The duty limit has a limit such as a primary color limit value Duty1 when ink is used alone, a secondary color limit value Duty2 when two colors are mixed, and a total limit value Dutyt.

The primary color restriction is expressed by the following equation. C4, M4, Lc4, Lm4, Dy4, K4 ≦ Duty
1, seven conditional expressions, C4 ≦ Duty1, M4 ≦ Duty1,..., Are listed for convenience only on the left side.

The secondary color restriction is expressed by the following equation. C4 + M4, C4 + Lc4... ≦ Duty2; Twenty-one values obtained by adding two color inks among the seven colors used are listed on the left side.

The total limit value Duty is expressed by the following equation. C4 + M4 + Lc4 + Lm4 + Y4 + Dy4 + K4 ≦ D
util; Depending on the print medium, restrictions on tertiary colors, quaternary colors, etc. may be further provided.

(Condition 4) Optimization condition for minimizing the total amount of ink: Since it is desirable that the amount of ink used at the time of printing be small, such a condition is provided as the optimization condition.
The total amount of ink Tink is given by the following equation. Tink = C4 + M4 + Lc4 + Lm4 + Y4 + Dy4 +
K4: Each ink amount is determined so that this value is minimized.

(Condition 5) Optimization condition for maximizing the component values of C, M, and Y: The range of colors reproducible using the ink to be separated is determined by the C range in the separation process on the outer shell surface. , M,
It is determined by the component value of Y. The larger this value is, the wider the color reproduction range that can be expressed by the separation result is. From the viewpoint of improving print image quality, it is desirable that the color reproduction range is wide, and thus such conditions are provided as optimization conditions. The C component is Cink4, the M component is Mink4, and the Y component is Yink4.
It is. Separation processing is performed so that these values become maximum.

In the present embodiment, in the method of applying the linear programming, first, values satisfying the conditions 1 to 3 and 5 are obtained, and a solution satisfying the condition 4 is obtained. However, since the black ink K4 does not affect the hue, the black ink K4 is set in advance by using the equation “K4 = K3 × Duty1 / 255” in consideration of only the duty limit. Thus, for the outer shell value, the duty limit, color reproducibility,
Separation processing in consideration of graininess is realized. The amount of each color ink is C4, M4, Lc4, Lm4, Y4, Dy4, K4
Given by

In this embodiment, the ink amounts of the seven colors are set at the same time by using the linear programming method. An ink satisfying the conditions 1 to 5 may be obtained by another method. For example, the temporary setting of each color ink, the determination as to whether or not the above-described conditions are satisfied, and the correction of the temporary setting value according to the result may be repeatedly executed to obtain a solution sequentially and approximately.

B2. Seven-color separation of reproduced colors: The processing of the seven-color separation of reproduced colors (step S18) will be described in detail. C4, M4, Lc4, Lm4, Y4, Dy obtained on the outer shell surface
4, K4 was corrected to a value corresponding to the reproduced color to obtain a separation result for the reproduced color. Correction was performed by proportional multiplication of the separation result on the outer shell surface.

The lower part of FIG. 3 shows the relationship between the shell value P3 and the reproduction color P2. Both ride on a straight line passing through the origin of the color solid. At the origin, the C, M, and Y color components are all 0, so it is assumed that a linear relationship holds for each color component, and thus the ink amount, on this straight line. According to such an assumption, the distance from the origin to the outer shell value P3,
By correcting the separation result for the outer shell value based on the ratio of the distance from the origin to the reproduction color P2, the separation result for the reproduction color P2 can be obtained. From the outer shell value P3 to Y =
The triangle O-P2-P2 is defined as P1h, the foot of the perpendicular lowered to the plane 0, and P2h, the foot of the perpendicular lowered from the reproduction color P2.
Consider a similarity between h and the triangle OP3-P1h.
The above ratio is equal to the ratio between line segment P3-P1h and line segment P2-P2h. The line segment P3-P1h has a value of 255, and the line segment P
2-P2h is Y2.

Therefore, the separation result C for the reproduction color P2
5, Lc5, M5, Lm5, Y5, and Dy5 are the separation results C4, Lc4, M4, Lm4, Y4, and Dy4 in the outer shell value.
Is multiplied by Y2 / 255, respectively. The ink amount K5 of the black ink is “K5 = K4”
And

B3. Replacement processing with DY: LC, LM, D
The process of the replacement process with Y (step S20) will be described in detail. This process is a correction process for suppressing the graininess of the color separation result of the reproduced color inside the color solid. Reproduction color P
This is a process of replacing the dye of each color obtained by the separation result of No. 2 with ink having low granularity such as LC, LM, and DY.

In order to perform this process, the dye amounts Cink5, Mink of C, M, and Y are determined based on the separation results for the reproduced color P2.
Find ink5 and Yink5. Cink5 = C5 + RCLC × Lc5 + RCDY × DY5 + K5; Mink5 = M5 + RMLM × Lm5 + RMDY × DY5 + K5; Yink5 = Y5 + RYDY × DY5 + K5 ing.

Next, the maximum value that can be replaced with dark yellow DY is calculated while maintaining this dye amount. For example, consider the case where all of the cyan dye Cink5 is replaced with dark yellow DY. At this time, the required amount of dark yellow ink is given by “Cink5 / RCDY”. Similarly,
Magenta is given by "Mink5 / RCDY" and yellow is given by "Yink5 / RCDY". If replacement with dark yellow exceeds these values, the dyes of each color become redundant. Therefore, the maximum value Dymax of the ink amount that can be replaced with the dark yellow DY is given by the following equation. Dymax = min (Cink5 / RCDY, Mink5 / RCDY, Yin
k5 / RCDY);

Since dark yellow is an ink having a low lightness, if it is replaced with the maximum value Dymax, the dark yellow dots are conspicuous, and there is a possibility that the graininess is deteriorated. Therefore, as shown below, replacement with dark yellow is performed using a function that takes into account granularity.

FIG. 6 is an explanatory diagram showing a function for correcting the ink amount in consideration of the granularity. When Dymax is the input value,
This function returns a value that can be replaced in consideration of the graininess as a correction value. As shown in the figure, if Dymax <tstart, the correction value is 0. That is, since the region is considered to be a region having relatively high lightness, replacement with dark yellow is not performed in consideration of granularity. If Dymax> tend, the correction value becomes equal to the input value. In other words, it is considered to be a region with relatively low brightness,
Replace with all colors dark yellow. tstart <Dymax <ten
In the case of d, a correction value is set by linear interpolation.

The values of tstart and tend defining the above function are
It is set by the following method. tstart is equivalent to the amount of ink in which the dark yellow dots become inconspicuous. As shown in the figure, a gradation pattern in which the amount of dark yellow ink per unit area changes from 0 to 255 is represented by L
Printing is performed with a combination of C, LM, and Y, and dark yellow dots are printed at appropriate intervals. In an area where the ink amount is low, the dots are conspicuous, but as the ink amount increases, the dots become inconspicuous. In this embodiment, the amount of ink at which the dots start to become inconspicuous is defined as tstart.

The term “tend” corresponds to the amount of ink that does not cause a significant reduction in image quality due to graininess even when dark yellow is used. As shown in the figure, two types of gradation patterns of only the combination of LC, LM, and Y and the dark yellow are printed. The graininess of the combination pattern is lower. When the amount of ink increases, the granularity of the gradation pattern of only dark yellow becomes inconspicuous, and L
The graininess becomes almost equal to the combination of C, LM, and Y. In this embodiment, the amount of ink at which the graininess of both inks is substantially equal is set to tend. By setting the function in this way, it is possible to easily perform ink replacement in consideration of graininess.

The correction amount obtained by the above function is defined as DeepDY. The ink amount Dy6 of the dark yellow Dy when this correction is performed is given by the following equation. Dy6 = DeepDY-K5; The reason why K5 is subtracted is that the color component of the black ink is taken into consideration.

Similarly, a correction amount C6 for cyan C is obtained. Assuming that all of the cyan dye Cink5 previously obtained is covered with cyan, the maximum value of the cyan ink is Cink5. Using this value, a correction amount DeepC taking into account the graininess is obtained by a function equivalent to that of FIG. This value is given by the following equation in consideration of the replacement with dark yellow. C6 = DeepC-K5-Dy6 / RCDY;

Similarly, the correction amount M for M, LC, LM, and Y
6, Lc6, Lm6, and Y6 are respectively given by the following equations. M6 = DeepM-K5-Dy6 / RMDY; Lc6 = DeepLC-K5-Dy6 / RLCDY; Lm6 = DeepLM-K5-Dy6 / RLMDY; Y6 = DeepY-K5-Dy6 / RYDY; For black ink, K6 = K5. And

With the above processing, it is possible to perform a correction on the reproduced color in consideration of the granularity. The dye amounts of C, M, and Y, which are the reference values for calculating the correction amounts of the respective inks, are obtained by separating the outer shell values in a state in which the color reproduction range is sufficiently expanded in consideration of the conditions regarding the duty limit and the granularity. This is set based on the processing. Thus, LC, L
By sufficiently considering the use of M and DY, it is possible to determine each ink amount for each reproduced color with a relatively simple correction based on the dye.

B4. Duty limit correction process: The process of the duty limit correction process (step S22) will be described in detail. The replacement processing with DY or the like described above was performed mainly in consideration of graininess. Therefore, the obtained result may not satisfy the duty limit. The duty limit correction process is a process of correcting the ink amount so as to satisfy the duty limit. If the duty limit is satisfied, this process may be skipped.

First, C6, M6, Lc6, Lm6, Y
6, DY6, K6 is the total duty limit Du
Let us consider a case where the value exceeds typ. At this time, the total amount of ink is reduced by replacing with dark yellow. The ink amount Dutyover exceeding the duty limit is given by the following equation. Dutyover = (C6 + M6 + Lc6 + Lm6 + Y6 + DY
6 + K6) -Dutyt; If the C, M, and Y inks are replaced with dark yellow,
The replacement amount is “Dutyover / (RCDY + RMDY + RYDY−
1) ". On the other hand, this replacement needs to be performed within the primary color duty limit of dark yellow. The maximum value of the replaceable amount due to the primary color restriction is “Duty1-Dy”.
6 ". Further, the substitution with dark yellow must be performed within the range of the dyes contained in cyan, magenta and yellow before substitution. If all cyan ink is replaced with dark yellow, the maximum replacement amount is "C6 / RCD
Y ”. Similarly, for magenta ink and yellow ink, the maximum replacement amount is “M6 / RMDY”,
Given as "Y6 / RYDY". Considering all of these conditions, the replacement amount Dyadd of the dark yellow is given by the following equation. Dyadd = min ｛Dutyover / (RCDY + RMDY + RYDY-
1), Duty1-Dy6, C6 / RCDY, M6 / RMDY, Y
6 / RYDY｝;

The ink amount reflecting this replacement is given by the following equation. DY6a = DY6 + Dyadd; C6a = C6-Dyadd × RCDY; M6a = M6-Dyadd × RMDY; Y6a = Y6-Dyadd × RYDY; Lc6a = Lc6; Lm6a = Lm6; K6a = K6; Not subject to. When these ink amounts satisfy the duty limit, the respective ink amounts are set to the final separation result, C7, M7, Lc.
7, Lm7, Y7, DY7, K7.

As a result of the above replacement, if the duty limit is not satisfied, a process for replacing Lc, M, and Y with DY is performed next. This processing is realized by considering the same conditions as the replacement of C, M, Y with DY. Subsequently, Lm, C, and Y are replaced with DY and Lc, Lm, and Y are replaced with DY until the duty limit is satisfied. If the duty limit is not satisfied by the above-described replacement with DY, replacement is performed from LC to C and from LM to M. In these processes, the ink amount at the time when the duty limit is satisfied is determined by the final separation result, C7, M7, Lc7, Lm.
7, Y7, DY7, and K7.

In this embodiment, replacement of ink is performed with priority on DY, and replacement with ink having a high density such as C and M is performed with priority. The replacement for satisfying the duty limit can be performed in various other orders.

According to the color separation processing of the present embodiment described above, the color reproduction range can be expanded by considering the use of DY at the time of color separation processing of the outer shell value. In addition, by setting conditions regarding the proper use of C, M, LC, and LM on the outer shell surface, it is possible to realize proper use of ink in consideration of granularity. Furthermore, by indirectly applying these conditions on the outer shell surface to the reproduced color inside the color solid, the color reproduction range can be extended and expanded even in the internal separation processing.
The advantage of graininess can be easily reflected.

Although the present embodiment has exemplified the color separation processing including DY, the same technique can be applied to the color separation processing for only six color inks excluding DY. Even in such a case, it is possible to easily realize the separation processing in consideration of the graininess.

Although various embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and it goes without saying that various configurations can be adopted without departing from the spirit of the present invention. In the embodiment, only the color separation method has been exemplified, but the present invention provides an image processing apparatus and an image processing method for converting the gradation value of image data into the ink amount of each ink using the color separation method. It can also be configured.
In this case, a method of preliminarily setting the relationship between the tone value of the image data and each ink amount as a color conversion table by the color separation method of the present embodiment and performing image processing using this conversion table may be adopted. it can.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating a list of components of an ink to be subjected to a color separation process according to an embodiment.

FIG. 2 is a process chart of a plate separation process.

FIG. 3 is an explanatory diagram of an outer shell value.

FIG. 4 is an explanatory diagram showing a linear interpolation method.

FIG. 5 is an explanatory diagram showing a modification of the interpolation method.

FIG. 6 is an explanatory diagram showing a function for correcting an ink amount in consideration of graininess.

Claims (10)

[Claims] 1. A color separation method for determining an ink amount of each color in order to reproduce a color by mixing colors of a plurality of inks, wherein the ink includes three reference color inks capable of expressing black by mixing colors. And a chromatic ink containing the same amount of dye in the unit volume as the dye contained in the two or more types of the reference color inks whose total volume exceeds the unit volume, and a printing medium used in color reproduction. A color separation method comprising a setting step of simultaneously setting the ink amounts of the reference color ink and the chromatic color ink required for color reproduction within a range satisfying a duty limit corresponding to an upper limit value of an ink amount usable per unit area. 2. The color separation method according to claim 1, wherein at least a part of the reference color ink includes a light reference color ink having a low pigment content per unit volume. A color separation method for simultaneously setting the ink amount of the light reference color ink. 3. The color separation method according to claim 1, wherein at least a part of the reference color ink includes a light reference color ink having a low pigment content per unit volume, and after the setting step, A color separation method including a density replacement step of replacing at least a part of the reference color ink with the light reference color ink. 4. The color separation method according to claim 3, further comprising a step of replacing the reference color ink with the chromatic color ink before the density replacement step. 5. The color separation method according to claim 3, wherein, as a result of the shading replacement step, when the duty limit is exceeded, the chromatic color is obtained from at least one of the light reference color ink or the reference color ink. A color separation method comprising a step of suppressing an ink amount by at least one of replacement with ink and replacement of the light reference color ink with the reference color ink. 6. The color separation method according to claim 1, wherein the ink includes a black ink, and the black color ink performs undercolor removal to be reproduced before the setting step. Edition method. 7. A color separation method for determining an ink amount of each color in order to reproduce a color by mixing colors of a plurality of inks, wherein the ink includes three reference color inks capable of expressing black by mixing colors. And at least one light reference color ink having a low pigment content per unit volume, and at least one plane of a color solid outer shell surface represented by each color component of the reference color ink as a reference vector. A color separation method comprising: a setting step of setting ink amounts of the reference color ink and the light reference color ink in consideration of a set restriction on selectively using the reference color ink and the light reference color ink. 8. The color separation method according to claim 7, wherein the setting step includes setting the restriction at an intersection of an origin of the color solid, a line connecting a color to be reproduced, and the outer shell surface. A color separation method in which the above-mentioned setting is performed with respect to the color to be reproduced in consideration of the above. 9. An image processing apparatus for converting a tone value of image data into ink amount data of each color in order to reproduce a color by mixing colors of inks, the image processing device comprising: A storage unit that stores the correspondence, and a conversion processing unit that performs the conversion processing with reference to the storage unit. The ink includes three reference color inks that can express black by mixing colors, A chromatic color ink containing the same amount of dye in the unit volume as the dye contained in the two or more types of reference color inks whose total volume exceeds the unit volume is included, and the correspondence is used at the time of color reproduction. The amount of the reference color ink and the amount of the chromatic color ink required for color reproduction are simultaneously set within a range that satisfies the duty limit corresponding to the upper limit of the amount of ink that can be used per unit area of the print medium. Image processing Location. 10. An image processing program for converting a gradation value of image data into ink amount data of each color in order to reproduce a color by mixing a plurality of color inks by a computer, the program comprising: A program that causes a computer to implement a function of accessing a conversion table corresponding to the correspondence between the gradation value and the ink amount data, and a function of executing the conversion process with reference to the conversion table. Contains, in a unit volume, three reference color inks capable of expressing black by mixing colors and two or more kinds of the reference color inks having a total volume exceeding the unit volume in the same amount as the dye contained in the reference color inks. Chromatic inks are included, and the correspondence is based on a duty system corresponding to an upper limit of the amount of ink that can be used per unit area of a print medium used for color reproduction. In a range satisfying, program characterized by the ink amount of the reference color ink and chromatic color ink required for color reproduction are set at the same time.