JP2003338940A - Apparatus for creating information, method for creating n-dimensional information conversion table, and apparatus for forming image - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize color conversion of color image information in signal processing system in the input side broader color gamut compared with that in the output side color gamut, so as to be of the highest color saturation. <P>SOLUTION: An information processing means 44 for converting the color image information of a scanner 30 and the color image information of a printer 50 into color data Lab which can be represented in the L*-C* coordinate system, and a control unit 45 for controlling the creation of a 3DLUT 61 based on the color data Lab converted by the means 44 are comprised. The unit 45 compares the input side color gamut which is the color gamut of the scanner 30, with the output side color gamut which is the color gamut of the printer 50 in order to make a judgment in the L*-C* coordinate system, based on the color data converted by the information processing means 44. When the input side color gamut is judged to be larger than the output side color gamut, the color gamut of the scanner 30 is compressed so that the color difference between the color data Lab of the scanner 30 and the color data Lab of the printer 50 is minimized. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a three-dimensional color conversion table to convert color image information of an RGB signal processing system into YMC.
A color facsimile that converts a color image information of a K signal processing system to form a color image, a color printer, a color copying machine, and an information creating apparatus and an n-dimensional information conversion table creating method suitable for application to a composite machine of these. And an image forming apparatus.

[0002]

2. Description of the Related Art In recent years, a tandem type color printer, a copying machine, a composite machine of these, and the like are often used. In these color image forming apparatuses, an exposure unit, a developing unit, a photosensitive drum for yellow (Y), magenta (M), cyan (C), and black (K) colors, an intermediate transfer belt, and a fixing unit are provided. I have it.

For example, the exposure means for Y color draws an electrostatic latent image on the photosensitive drum based on arbitrary image information. In the developing device, toner for Y color is attached to the electrostatic latent image drawn on the photosensitive drum to form a color toner image. The photoconductor drum transfers the toner image to the intermediate transfer belt. Similar processing is performed for other M, C, and K colors. The color toner image transferred to the intermediate transfer belt is transferred to a sheet and then fixed by a fixing device.

By the way, according to this type of color image forming apparatus, an image processing section for color-converting the image information of the RGB signal processing system into the image information of the YMCK signal processing system is often incorporated. This is because the image forming unit operates based on the image information of the YMCK signal processing system. A three-dimensional color conversion table is used in the image processing unit to speed up the color conversion process.

FIG. 11 shows a conventional image forming apparatus 300.
3 is a block diagram showing a configuration example of FIG. In the image forming apparatus 300 as shown in FIG. 11, the image signals R, G, B input from the scanner 30 are converted into a three-dimensional color conversion table (hereinafter referred to as 3D color conversion table).
(Referred to as DLUT), and converted into C, M, Y, K values. The CMYK signals based on these values are sent to the printer 5
It is output to 0. This 3DLUT is a table in which C, M, Y, and K values are stored in three-dimensional color three-dimensional coordinates of R, G, and B.

Regarding this 3D LUT, technical publications (Japanese Patent No. 2895086), Japanese Laid-Open Patent Publication (Kokai) No. 6-242523, and "Po-Cieh Hun" are available.
g, ”Colorimetric calibration in electric imaging d
evices using a look-up-table model and interpolati
ons, “Journal of Electric Imaging, 2-1, pp53-61”
It is created by a method like.

FIG. 12 is a flow chart showing an example of creating a 3DLUT according to a conventional example. FIG. 13 is a representational example of a scanner color gamut, a printer color gamut, and a color data input Lab in the L ^* -C ^* coordinate system, and FIG. 14 is an image diagram showing a calculation example of a compression point p1 ′ on the printer color gamut surface. is there. In the L ^* -C ^* coordinate system shown in FIGS. 13 and 14, the vertical axis is the lightness L ^* coordinate and the horizontal axis is the saturation C ^* coordinate. The same applies to FIGS. 15 and 16 below.

For example, in step E1 of the flow chart shown in FIG. 12, modeling processing of the four-color printer 50 is performed. At this time, a color patch in which the K, C, M, and Y color values are quantized is prepared, and the KCMY signal based on this is output to the four-color printer 50.

The printer 50 prints a color patch image based on the KCMY signal. This printed image is measured with a colorimeter. L ^* , a ^* , obtained from this colorimeter
The b ^* value and the K, C, M, Y values are associated with each other, and these are tabulated to prepare color data Lab (Lab → CM).
YK table).

Then, in step E2, modeling processing of the scanner 30 is performed. At this time, the scanner 30 scans the color document to obtain RGB signals. The color patch of this document is measured with a colorimeter (not shown). The measured values L ^* , a ^* , b ^* values and R obtained by scanning the original,
The G and B colors are associated with each other, and these are tabulated to prepare color data (color signal) Lab (RGB → Lab table).

After that, in step E3, the R, G, B values necessary for creating the 3DLUT are sequentially set in a computer or the like. Then, the process proceeds to step E4, and it is determined whether the output side color gamut is inside or outside the input side color gamut. At this time, the K, C, M, and Y values (color image information) of the scanner 30 are converted into color data Lab using the RGB → Lab table and expressed in the L ^* -C ^* coordinate system, and the printer 50 is used.
R, G, and B values (color image information) are converted into color data Lab by the RGB → Lab table and expressed in the L ^* -C ^* coordinate system.

Then, it is searched whether the L ^* , a ^* , b ^* values based on the R, G, B values on the scanner 30 side are in the KCMY signal on the printer 50 side. At this time, the input side color gamut which is the color gamut of the scanner 30 and the output side color gamut which is the color gamut of the printer 50 expressed in the L ^* -C ^* coordinate system are compared (color gamut inside / outside determination). This gamut inside / outside determination is performed by using the RGB → Lab table (scanner gamut) as shown in FIG.
ab → CMYK table (color gamut of printer 50) L ^*
-C ^* coordinate (plane) system. C is calculated as follows.

[0013]

[Equation 4]

In FIG. 13, for example, color data La
When b is input, the center is set within the color gamut of the printer 50 (center Lab), and the center Lab and the input L of color data are entered.
A combination of a straight line connecting the input points p1 of ab and the surface of the color gamut of the printer 50 is sequentially searched, Search 1, Search 2,
Search 3 ... Search.

Actually, as shown in FIG. 14, there are three pieces of color data Lab on the color gamut surface. The input point is p1, the center is p2, and the three points forming a triangle on the color gamut surface are p3, p4, and p5.
Then, it can be expressed as follows: p1-p2 = a (p3-p2) + b (p4-p2) + c (p5-p2) (1), and the conditions of a, b, c are a
When ≧ 0, b ≧ 0, c ≧ 0, a + b + c ≧ 1 are satisfied,
It can be determined that it is out of the color gamut, and conversely, a ≧ 0, b ≧ 0, c ≧ 0, a
When + b + c <1, it is determined that the output side gamut is inside the input side gamut gamut.

When it is determined in step E4 that the input side color gamut is wider than the output side color gamut (outside the color gamut), the process proceeds to step E5 to compress the color gamut of the scanner 30. In this compression processing, the input point p1 is compressed within the color gamut of the printer 50 toward the compression center set on the lightness L ^* coordinate axis. If the compression point is p1 ', equation (4),
That is, the compression point p1 'is calculated by p1' = a '(p3-p2) + b' (p4-p2) + c '(p5-p2) + p2 (4). Operators a ', b',
c'is calculated by the equation (5). a '= a / (a + b + c) b' = b / (a + b + c) c '= c / (a + b + c) (5) By calculating in this way, the input point p1 is shown in FIG. It is compressed to the grid point p1 '.

Then, in step E4, it is determined that the color gamut is within the color gamut.
If the color data Lab is printed in step E5,
When compressed within the color gamut of the data 50, the process proceeds to step E6.
It Here, the compressed color data Lab is L^*, A^*, B^*
If the value is L^*, A^*, B^*The four grid points surrounding the
It From the C, M, Y, and K values of these four grid points, L^*, A^*, B
^*C, M, Y, K values corresponding to
Be done.

This is the C, M, Y, K value for the first input R, G, B value. Then, the process proceeds to step E7, where C, M, and
The Y and K values are output to the printer 50. At this time, by combining the two tables, RGB → (Lab →)
A CMYK table, or 3DLUT, is obtained.

After that, the process proceeds to step E8 and the 3DLU
It is determined whether or not the calculation process related to T creation is completed. To continue this arithmetic processing, the process returns to step E3, and the next R, G, B values by the scanner 30 are set in the information creating system and the arithmetic processing is repeated.

FIG. 15 is an image diagram showing a compression example (part 1) of the color data Lab in the L ^* -C ^* coordinate system.
The compression example of the color data Lab shown in FIG. 15 is for a system such as monitor → printer 50. in this case,
The color gamut of the monitor 'is located outside the color gamut of the printer 50. In this example, if the values of R, G, B of the R primary color are represented by the color data Lab, [L ^* , a ^* , b ^* ] = [255,
0, 0], which coincides with the grid point that creates the 3DLUT. Therefore, the input gamut of the monitor Lab = [255,
[0,0] grid point directly outputs gamut of printer 50 to La
b can be compressed, and the reproduction can fully use the brightest color of the printer 50.

FIG. 16 is an image diagram showing a compression example (part 2) of the color data Lab in the L ^* -C ^* coordinate system.
The example of compression of the color data Lab shown in FIG.
This is the case of a system such as 0 → printer 50. In this case, the color gamut of the scanner 30 is located outside the color gamut of the printer and the color gamut of the document. In the L ^* -C ^* coordinate system, the color gamut is compressed by directing the color gamut of the original toward the compression center of the color gamut of the printer 50 by the equation (4) as described with reference to FIG.

[0022]

By the way, according to the conventional method of creating a 3DLUT, the RGB signal of the scanner and the KCMY signal of the printer 50 can be expressed in the L ^* -C ^* coordinate system (color conversion mediating coordinate system). When the 3DLUT is created based on the color data Lab after being converted into different color data Lab, a compression center is provided on the lightness L ^* coordinate axis, and this compression center is converted from the RGB signal of the scanner (input side signal processing system). The converted color data Lab is compressed so as to converge. Therefore, there are the following problems.

I. This compression method is monitor → printer 50
The problem that did not occur in those that can directly adjust the primary color point of the input system, such as the scanner (signal processing system on the input side) 30
→ It occurs in a copying machine such as the printer 50.

That is, in the case of an image forming apparatus such as a color facsimile, a color printer, a color copying machine, or a composite machine of these, the value of the R primary color of the original is monitor → printer 5
The output Lab is not always the same as the primary color point of the input system such as 0.
= [255,0,0], the output Lab
= A halfway value such as [250, 4, 3].
On the other hand, the number of grid points of the 3DLUT is, for example, about 16 ³ depending on the size of the table. Therefore, the output Lab
The reproduction of the R color of = [250,4,3] greatly depends on the reproduction of surrounding grid points.

Ii. Further, when the surrounding grid points are compressed as shown in FIG. 16, the output Lab = [25
The R color of [0, 4, 3] is not the maximum saturation of the printer 50, but is reproduced to a color of low saturation inside α, and is reproduced by the printer (signal processing system on the output side) 50. You no longer use the fullest possible vividness.

Therefore, the present invention has been made to solve the above-mentioned problems, and the color image information of the signal processing system on the input side, which has a wider color gamut on the input side than the color gamut on the output side, is stored in the color gamut on the output side. It is an object of the present invention to provide an information creating apparatus, an n-dimensional information conversion table creating method, and an image forming apparatus capable of performing color conversion so as to have the highest saturation.

[0027]

In order to solve the above-mentioned problems, an information generating apparatus according to the present invention converts color image information of an input side signal processing system into color image information of an output side signal processing system. A device for creating a dimension information conversion table, which is information for converting color image information of an input side signal processing system and color image information of an output side signal processing system into intermediary image information that can be expressed by a color conversion intermediary coordinate system. The processing means and the control device for controlling the creation of the n-dimensional information conversion table based on the intermediary image information converted by the information processing means are provided, and the control device is based on the intermediary image information converted by the information processing means. In the color conversion mediation coordinate system, the input side color gamut, which is the color gamut of the input side signal processing system, and the output side color gamut, which is the color gamut of the output side signal processing system, are compared and judged, and the output side color gamut Compared to When a force side color gamut is determined to be wide,
It is characterized in that the color gamut of the input side signal processing system is compressed so as to minimize the color difference between the input side signal processing system intermediate image information and the output side signal processing system intermediate image information. is there.

According to the information creating apparatus of the present invention, when creating an n-dimensional information conversion table for converting color image information of the input side signal processing system into color image information of the output side signal processing system, In the processing means, the color image information of the signal processing system on the input side and the color image information of the signal processing system on the output side are converted into intermediary image information that can be expressed by the color conversion intermediary coordinate system.

The control device controls the creation of the n-dimensional information conversion table based on the intermediate image information converted by the information processing means. On the premise of this, in the color conversion mediation coordinate system based on the mediation image information converted by the information processing means, the control device has a color gamut of the input side signal processing system, which is the color gamut of the input side signal processing system, and an output side signal processing system. The output gamut, which is the gamut, is compared.

When it is determined that the input side color gamut is wider than the output side color gamut, the color difference between the intermediate image information of the input side signal processing system and the intermediate side image information of the output side signal processing system is found. The color gamut of the signal processing system on the input side is compressed so as to be the minimum.

Therefore, the color image information of the signal processing system on the input side after the n-dimensional information conversion, especially the image information on the primary colors such as red, blue and green, has the highest saturation in the output color gamut. In addition, the color gamut of the signal processing system on the input side can be compressed. Thereby, an n-dimensional information conversion table capable of converting the color image information of the signal processing system on the input side, which has a wider color gamut on the input side than the color gamut on the output side, to the color image information of the signal processing system on the output side is created. be able to.

An n-dimensional information conversion table creating method according to the present invention is a method of creating an n-dimensional information conversion table for converting color image information of an input side signal processing system into color image information of an output side signal processing system. Then, the color image information of the signal processing system on the input side is converted into the intermediary image information and expressed by the color mediating coordinate system, and the color image information of the signal processing system on the output side is converted into the intermediary image information and color converted. Expressed in the intermediary coordinate system, color conversion Compares the input gamut, which is the gamut of the input signal processing system, and the output gamut, which is the gamut of the output signal processing system, represented in the intermediary coordinate system. If the input-side color gamut is wider than the output-side color gamut, the color difference between the input-side signal processing system image information and the output-side signal processing system image information should be minimized. The feature is that the color gamut of the signal processing system on the input side is compressed. It is an.

According to the n-dimensional information conversion table creating method of the present invention, the n-dimensional information conversion table for converting the color image information of the input side signal processing system into the color image information of the output side signal processing system is created. In this case, color image information of the signal processing system on the input side after the n-dimensional information conversion, especially red, blue,
The color gamut of the signal processing system on the input side can be compressed so that the image information relating to the primary color such as green has the highest saturation in the color gamut on the output side.

Therefore, the color image information of the signal processing system on the input side, which has a wider color gamut on the input side than the color gamut on the output side, especially red,
Image information relating to primary colors such as blue and green can be color-converted so as to have the highest saturation in the output side color gamut.

The image forming apparatus according to the present invention is an apparatus for forming a color image based on arbitrary color image information, wherein the color image information of the signal processing system on the input side is the color image information of the signal processing system on the output side. The storage device is provided with a storage device that stores an n-dimensional information conversion table to be converted into an image, and an image forming unit that forms a color image based on the color image information information-converted by the n-dimensional information conversion table by the storage device. The stored n-dimensional information conversion table converts the color image information of the signal processing system on the input side into the media image information in advance and expresses it in the color conversion mediating coordinate system, and also displays the color image information of the signal processing system on the output side. Input side color gamut and output side signal processing system, which are the color gamuts of the input side signal processing system expressed in the color conversion medium coordinate system when converted into the medium image information and expressed in the color conversion medium coordinate system. If it is determined by comparing the output side color gamut, which is the color gamut, and it is determined that the input side color gamut is wider than the output side color gamut, the intermediate image information of the input side signal processing system and the output side signal It is characterized in that the color gamut of the signal processing system on the input side is compressed so that the color difference due to the intermediate image information of the processing system is minimized.

According to the image forming apparatus of the present invention, when a color image is formed based on arbitrary color image information,
The storage device stores an n-dimensional information conversion table for converting color image information of the signal processing system on the input side into color image information of the signal processing system on the output side.

The n-dimensional information conversion table is created by the information creating apparatus according to the present invention, that is, the color image information of the signal processing system on the input side is converted into the intermediate image information in advance and the color conversion intermediate coordinate system is used. When the color image information of the output side signal processing system is converted into media image information and expressed in the color conversion mediation coordinate system, the color of the input side signal processing system expressed in this color conversion mediation coordinate system. The determination is made by comparing the input gamut, which is the gamut, with the output gamut, which is the gamut of the signal processing system on the output side.

When the information creating apparatus determines that the input side color gamut is wider than the output side color gamut, the intermediate image information of the input side signal processing system and the intermediate image information of the output side signal processing system. The n-dimensional information conversion table is created by compressing the color gamut of the signal processing system on the input side so as to minimize the color difference due to. On the premise of this, the image forming means forms a color image based on the color image information information-converted by the n-dimensional information conversion table by the storage device.

Therefore, the color image information of the signal processing system on the input side, which has a wider color gamut on the input side than the color gamut on the output side, especially red,
Image information relating to primary colors such as blue and green can be color-converted so as to have the highest saturation in the output side color gamut. This makes it possible to form a color image that fully utilizes the output side color gamut based on the color image information after color conversion.

[0040]

DETAILED DESCRIPTION OF THE INVENTION An information creating apparatus, an n-dimensional information conversion table creating method and an image forming apparatus according to embodiments of the present invention will be described below with reference to the drawings. (1) Embodiment FIG. 1 shows an information creating apparatus 100 as an embodiment of the present invention.
3 is a block diagram showing a configuration example of FIG. FIG. 2 is an image diagram showing an example of color three-dimensional coordinates of a 3DLUT. In this embodiment, when an n-dimensional information conversion table for converting the color image information of the signal processing system on the input side into the color image information of the signal processing system on the output side is created, an intermediate image that can be represented by the color conversion intermediate coordinate system. A control device for controlling the creation of the n-dimensional information conversion table based on the information is provided. In this control device, the input side color gamut, which is the color gamut of the input side signal processing system expressed in the color conversion mediation coordinate system, is compared with the output side color gamut, which is the color gamut of the output side signal processing system, and When it is determined that the input side color gamut is wider than the output side color gamut, the color difference between the input side signal processing system intermediate image information and the output side signal processing system intermediate image information is minimized. Compress the color gamut of the signal processing system on the input side.

As a result, the color image information of the signal processing system on the input side after the n-dimensional information conversion, particularly the image information on the primary colors such as red, blue, and green, has the highest saturation in the color gamut on the output side. In this way, the color gamut of the input side signal processing system can be compressed, and the color image information of the input side signal processing system, which has a wider input side color gamut than the output side gamut, is output to the output side signal processing system. The n-dimensional information conversion table that can be converted into the color image information is created.

The information creating apparatus 100 shown in FIG. 1 is an apparatus for creating an n-dimensional information conversion table for converting color image information of the signal processing system on the input side into color image information of the signal processing system on the output side. The information creating apparatus 100 is the information processing means 4
4, the color image information of the signal processing system on the input side and the color image information of the signal processing system on the output side are represented by a lightness L ^* -saturation C ^* coordinate system as an example of a color conversion mediating coordinate system. Saturation L ^* , red a ^* , blue b as an example of possible mediation image information
^{* It} is adapted to be converted into a value (hereinafter referred to as color data Lab). A CPU (central processing unit), a DSP (digital signal processor), a memory or the like is used for the information processing means 44.

For example, the scanner 30 is connected to the information processing means 44 for modeling the signal processing system on the input side, and serves as an example of color image information obtained by scanning (reading) a colored (color) document d. Color signals of red (R), green (G), and blue (B) (hereinafter referred to as RGB signals) are output to the information processing unit 44.

This color original is used for so-called "copying", and the color patch of this original d is measured by a colorimeter (not shown). The measured values L ^* , a ^* , b ^* values are associated with the R, G, B colors obtained by scanning the document, and color data (color signals) Lab in which these are tabulated are prepared (RGB → Lab table).

A four-color printer 50 is connected to the information processing means 44 as a color reproduction device for modeling the signal processing system on the output side, and black (K) and cyan (C), which are an example of the color image information. , And magenta (M) and yellow (Y) color signals (hereinafter referred to as KCMY signals) are output.

In this information processing means 44, K, C, M, Y
A color patch in which the color values are quantized is prepared, a KCMY signal based on this is output to the printer 50, a color patch image is printed on the paper (copy) p based on this KCMY signal, and this print image is measured with a colorimeter. taking measurement. L ^* , a ^* , b ^* values obtained from this colorimeter are associated with K, C, M, Y values, and color data Lab is prepared by tabulating these values (Lab → CMYK table).

In the information processing means 44, by combining these two tables, an RGB → (Lab →) CMYK table, that is, a three-dimensional color information conversion table as an example of an n-dimensional information conversion table (hereinafter simply referred to as 3DLUT61
Is obtained). The 3DLUT 61 constitutes a color three-dimensional coordinate system model as shown in FIG. 2, in which the X direction has R color values, the Y direction has G color values, and the Z direction has B color values.

The number of grid points of the 3DLUT 61 is, for example, about 16 ³ depending on the table size. R, G,
For each of the three-dimensional color coordinates of B color, C,
M, Y, K values are stored. In practical terms, for example, 2
3DLU with R, G, B signals of 56 gradations as addresses
The KCMY signal is read from the ROM or the like that constitutes the T61.

Regarding this 3DLUT 61, technical publications such as patent publication (patent number: 2895086), open patent publication (JP-A-6-242523), and "Po-Cieh".
Hung, ”Colorimetric calibration in electric imagin
g devices using a look-up-table model and interpol
ations, ”Journal of Electric Imaging, 2-1, pp53-6
It is created by a method such as "1".

The information processing means 44 shown in FIG.
It has an OM writing function and a blank ROM 60 is set. The 3DLUT 61 is described in the ROM 60. The ROM 60 is mounted (installed) in a color facsimile, a color printer 50, a color copying machine, or a composite machine of these, and the 3DLUT6 is generated by RGB signals output from the scanner 30 mounted in these machines.
1. Convert to C, M, Y, K values by referring to 1, and ROM 60
The CMYK signals read from the printer are output to the printer 50. Accordingly, the color image information of the RGB signal processing system can be color-converted into the color image information of the YMCK signal processing system by the three-dimensional color conversion table to form a color image.

A control device 45 is connected to the information processing means 44, and an input means 46 is connected to the control device 45. The control device 45 controls the creation of the 3DLUT 61 based on the operation information D1 obtained by the input means 46 and the color data Lab converted by the information processing means 44. A keyboard or a mouse is used as the input means 46.

The control device 45 outputs the color gamut of the scanner 30 and the output color gamut of the printer 50 in the L ^* -C ^* coordinate system based on the color data Lab converted by the information processing means 44. Judge by comparing with the side color gamut.
When it is determined that the input side color gamut is wider than the output side color gamut, the color gamut of the scanner 30 is minimized so that the color difference between the color data Lab of the scanner 30 and the color data Lab of the printer 50 is minimized. Is made to compress.

In this example, the control device 45 performs the following arithmetic processing when an input point q1 represented by arbitrary color data Lab of the scanner 30 is given in the L ^* -C ^* coordinate system. Color data La that minimizes the color difference in the L ^* -C ^* coordinate system
Let q be the vertex of the triangle on the surface of the gamut indicated by b.
2, q3, q4, the operators a, b, c, and the compression point on the color gamut surface represented by the color data Lab that minimizes the color difference of the printer 50 is q1 ', equation (1), that is, q1 The compression point q1 'is obtained by' = a (q2-q1) + b (q3-q1) + c (q4-q1) + q1 (1). This gives L ^*
In the -C ^* coordinate system, it is possible to compress the input point q1 of the scanner color gamut into the compression point q1 'of the printer color gamut (color gamut compression method).

In this example, the vertices q2, q3 and q4 of the triangle on the surface of the color gamut represented by the color data Lab having the minimum color difference in the L ^* -C ^* coordinate system are extracted as follows. With this printer 50, color data Lab [q2
l, q2a, q2b], an arbitrary grid point q2
To set arbitrary color data Lab [q
[11, q1a, q1b], the color difference between the input point q1 and the grid point q2 is expressed by the formula (2), that is,

[Equation 5] Calculate with.

Then, the control device 45 compares the color difference between the input point q1 and the grid point q2 and the color difference between the input point q1 and another grid point on the color gamut surface, and sequentially extracts the grid points having a small color difference. The processing is repeated on all the color gamut surfaces, and the top three grid points having the smallest color difference are extracted (minimum color difference mapping method).

FIG. 3 is an image diagram showing an example of representation of the color gamut of the scanner, the color gamut of the printer, and the color gamut of the original in the L ^* -C ^* coordinate system. FIG. 4 is an image diagram showing a comparative example of the compression method in the L ^* -C ^* coordinate system. In the L ^* -C ^* coordinate system shown in FIGS. 3 and 4, the vertical axis represents the lightness L ^* coordinate and the horizontal axis represents the saturation C ^* coordinate.

In this example, the color gamut of the scanner 30 is located outside the color gamut of the printer and the color gamut of the original.
In the L ^* -C ^* coordinate system, the gamut is compressed by directing the input point q1 of the scanner gamut toward the compression point q1 ′ of the printer gamut, as shown in equation (1). That is, the primary color input points of the color gamut of the scanner 30 can be compressed into the primary color output points of the color gamut of the printer 50.

The process of compressing the color gamut of the scanner 30 is such that when the RGB signal of the scanner 30 cannot be represented by the KCMY signal of the printer, the color data of the printer can be represented on the output side. This means moving the Lab. As a result, the RGB signal of the scanner 30 can be converted into the KCMY signal for the printer.

Regions I to III shown in FIG. 3 are color gamut planes that intersect each other at an angle of 90 ° with reference to the primary color point including the color data Lab in the primary color output of the color gamut of the printer 50. The color data Lab existing in each of the areas I to III is compressed into the brightest primary color of the printer 50. As a result, the R, G, B values are 2 when the color adjustment is difficult in the conventional method.
Values such as 50, 4, and 3 can also be compressed to the primary color point.

Therefore, the color data L of the primary color of the input document d
Even when ab is located between the printer color gamut and the scanner color gamut, it is possible to perform color adjustment based on the color data Lab relating to the primary color at the time of printer output.

Although the compression center is set on the lightness L ^* coordinate shown in FIGS. 3 and 4, it is used only for the inside / outside determination of the color gamut of the scanner and the color gamut of the printer in this example. In the gamut compression of the method of the present invention, the compression toward the center of compression is not performed.

In the conventional method, the color data Lab at the input point was compressed toward the center of compression, but in the method of the present invention, it is compressed so as to be orthogonal to the color gamut of the printer. This is because the grid point orthogonal to the color gamut of the printer from the input point becomes the grid point having the smallest color difference with respect to the color gamut. That is, the method of the present invention does not compress the color data Lab toward the compression center as in the conventional method, but adopts a method of compressing the color data Lab around the closest color gamut from the point of compression. Each grid point is compressed as shown in FIG.

Next, a method of creating the 3DLUT 61 according to the present invention will be described. FIG. 5 is an image diagram showing a calculation example of the compression point q1 ′ on the printer color gamut surface.
FIG. 6 is a flowchart showing an example of creating the 3DLUT 61 in the information creating apparatus 100, and FIG. 7 is a flowchart showing an example of compression processing in the controller 45.

In this embodiment, the 3DLUT for converting the RGB signal of the scanner 30 into the KCMY signal of the printer 50.
It is assumed that 61 is created. Regarding the compression of the color data Lab, when the input point q1 is set, the color difference between the input point q1 and the input point q1 is minimized, and the grid points q2, q3, q4 are sequentially extracted on the printer gamut surface as shown in FIG. It is assumed that the compression point q1 ′ is calculated by performing the above.

Using this as a condition for creating the 3DLUT 61,
In step A1 of the flowchart shown in FIG. 6, modeling processing of the four-color printer 50 is performed. At this time, the information processing unit 44 prepares a color patch in which the K, C, M, and Y color values are quantized, and the KCMY signal based on this is output to the four-color printer 50.

In this printer 50, a color patch image is printed on a sheet (copy) p based on the KCMY signal,
This printed image is measured with a colorimeter. L ^* , a ^* , b ^* values obtained from this colorimeter are associated with K, C, M, Y values, and color data Lab is prepared by tabulating these values (Lab → CMYK table).

Then, in step A2, the modeling process of the scanner 30 is performed. At this time, in the information processing means 44, for example, when the scanner 30 scans the color document d, RGB signals are output from the scanner 30 to the information processing means 44. The color patch of the original document d is measured by a colorimeter (not shown). The measured values L ^* , a ^* , b ^* values and the R, G, B colors obtained by scanning the document d are associated with each other, and color data (color signal) L is tabulated.
ab is prepared (RGB → Lab table).

Thereafter, in step A3, the control device 45 sequentially sets the R, G, and B values necessary for creating the 3DLUT 61 to the information processing means 44. Then, the process proceeds to step A4, and it is determined whether the output side color gamut is inside or outside the input side color gamut. At this time, K of the scanner 30,
The C, M, Y values (color image information) are converted into color data Lab by the RGB → Lab table and expressed in the L ^* -C ^* coordinate system, and the R, G, B values (color image information) of the printer 50 are converted. RGB → Lab table with color data Lab
Converted to and expressed in the L ^* -C ^* coordinate system.

Thereafter, it is searched whether the L ^* , a ^* , b ^* values based on the R, G, B values on the scanner 30 side are in the KCMY signal on the printer 50 side. At this time, the input side color gamut which is the color gamut of the scanner 30 and the output side color gamut which is the color gamut of the printer 50 expressed in the L ^* -C ^* coordinate system are compared (color gamut inside / outside determination). This gamut inside / outside determination is performed by the RGB → Lab table (color gamut of the scanner) as described in FIG.
And a Lab → CMYK table (color gamut of the printer 50) in the L ^* -C ^* coordinate (plane) system. C is calculated as follows.

[0070]

[Equation 6]

As described with reference to FIG. 13, for example, when the color data Lab is input, the center is set within the color gamut of the printer 50 (center Lab), and the center Lab and the color data Lab are set.
The combination of the straight line connecting the input points p1 of b and the surface of the color gamut of the printer 50 is sequentially searched for.

Actually, as shown in FIG. 14, there are three pieces of color data Lab on the color gamut surface. When the input point is p1, the center is p2, and the three surface points are p3, p4, and p5, p1-p2 = a (p3-p2) + b (p4-p2) + c (p5-p2) (1) Can be expressed as follows, and the conditions of a, b, c are a
When ≧ 0, b ≧ 0, c ≧ 0, a + b + c ≧ 1 are satisfied,
It can be determined that it is out of the color gamut, and conversely, a ≧ 0, b ≧ 0, c ≧ 0, a
When + b + c <1, it is determined that the output side gamut is inside the input side gamut gamut.

The process up to this point is the same as the conventional system. In the method of the present invention, when it is determined that the input gamut is wider than the output gamut (outside the gamut), the process proceeds to step A5 and the color data Lab of the scanner 30 and the color data Lab of the printer 50 are used. The color gamut of the scanner 30 is compressed so that the color difference is minimized. This compression processing is different from the conventional method. In the conventional method, when it is determined that the input side color gamut is wider than the output side color gamut, the scanner 3 is calculated based on the equation (4).
Although the color data Lab of 0 was compressed, as shown in FIG. 4, the compression process is not necessarily performed in the direction in which the color difference is minimized. Therefore, in the method of the present invention, the surface of the color gamut having the minimum color difference is searched again.

For example, the subroutine shown in FIG. 7 is called to set the color data Lab on the color gamut surface of the L ^* -C ^* coordinate system in step B1 of the flowchart. This is to derive three lattice points q2, q3, q4 on the color gamut surface where the color difference is the minimum in the L ^* -C * coordinate system as shown in FIG. In step B1, in the L ^* -C ^* coordinate system,
An input point q1 represented by arbitrary color data Lab of the scanner 30 is set, and the color gamut surface of the printer 50 is
First, a certain grid point q2 is set on the surface of the color gamut that minimizes the color difference. In the L ^* -C ^* coordinate system, the input point q1 is given by the controller 45.

That is, the vertices q2, q3, q4 of the triangle on the color gamut surface indicated by the color data Lab having the minimum color difference in the L ^* -C ^* coordinate system are the color data Lab [q2l on the color gamut surface of the printer 50. , Q2a, q2b] to set an arbitrary grid point q2, and the scanner 30
Arbitrary color data Lab [q1l, q1a, q1b]
Assuming that the input point q1 is represented by, the color difference between the input point q1 and the grid point q2 is calculated by the above-described equation (2) in step B2.

In step B3, the color difference between the input point q1 and the grid point q2 and the color difference between the input point q1 and another grid point on the color gamut surface are compared. If the color difference is small, the process proceeds to step B4. Data L of grid points with small color difference
Store ab in memory.

Then, in step B5, it is determined whether or not the grid points having a small color difference are sequentially extracted. If the top three grid points with the smallest color difference have not been extracted, the process returns to step B1 and the above processing is repeated. When the top three grid points with the smallest color difference are extracted, the process moves to step B6 to calculate the compression point q1 ′. At this time, L ^* -C ^*
The vertices of the triangles on the surface of the color gamut represented by the color data Lab having the minimum color difference in the coordinate system are q2, q3, q4, the operators are a, b, c, and the color data Lab having the minimum color difference of the printer 50 is shown. Assuming that the compression point on the surface of the color gamut is q1 ′, the compression point q1 ′ can be obtained by the above-mentioned equation (1). By calculating the operators a, b, and c, the point q1 ′ that minimizes the color difference is calculated. The operators a, b, and c are calculated by the equation (3). a = a '/ (a' + b '+ c') b = b '/ (a' + b '+ c') c = c '/ (a' + b '+ c') (3)

After that, the process returns to step A5 of the main flow chart shown in FIG. If it is determined that the color gamut is within the color gamut at step A4, and if the color data L is found at step A5.
When ab is compressed within the color gamut of the printer 50, the process proceeds to step A6. Here, the compressed color data Lab is L
^{If the} values are ^* ', a ^* ', b ^* ', the control unit 45 has L ^* ',
Discriminate four grid points surrounding a ^* 'and b ^* '. From the C, M, Y, and K values of these four grid points, the C, M, Y, and K values corresponding to L ^* ', a ^* ', and b ^* 'can be obtained by interpolation calculation.

This is the C, M, Y, K value for the first input R, G, B value. Then, the process proceeds to step A7, where C, M, and
The Y and K values are output to the printer 50. At this time, the information processing means 44 combines these two tables to create an RGB → (Lab →) CMYK table, that is,
A 3DLUT 61 is obtained.

Then, the process proceeds to step A8 and the 3DLU
It is determined whether or not the calculation process related to T creation is completed. To continue the calculation process, the process returns to step A3 to set the next R, G, B values by the scanner 30 in the information processing means 44 and repeat the calculation process. If this arithmetic processing is executed 16 times 16 times 16 times, for example, FIG.
It is possible to create the 3DLUT 61 including a color three-dimensional coordinate system model in which the X direction has R color values, the Y direction has G color values, and the Z direction has B color values, as shown in FIG.

As described above, according to the information creating apparatus 100 and the n-dimensional information conversion table creating method according to the embodiment of the present invention, the RGB signals of the scanner 30 are transferred to the printer 5.
In the case of creating the 3DLUT 61 for converting into the KCMY signal of 0, in the L ^* -C ^* coordinate system based on the color data Lab, the control device 45 controls the input side color gamut of the scanner 30 and the color gamut of the printer 50. An output color gamut is compared.

When it is determined that the input side color gamut is wider than the output side color gamut, the scanner is set so that the color difference between the color data Lab of the scanner 30 and the color data Lab of the printer 50 is minimized. The control device 45 controls the information processing means 44 so as to compress the color gamut of 30.

Therefore, the RGB signals of the scanner 30 after the color conversion by the 3DLUT 61, especially the RGB signals of the primary colors such as red, blue, and green, have the highest saturation in the output side color gamut. The area can be compressed.
In this example, the R, G, and B values of the R primary colors of the original are input Lab.
= [250,4,3], the color gamut of the scanner 30 is compressed so that the color difference between the color data Lab of the scanner 30 and the color data Lab of the printer 50 is minimized. , Direct printer 50
The color gamut output Lab can be compressed to Lab = [255,0,0].

As a result, the 3DLUT 61 capable of converting the RGB signal of the scanner 30 having a wider input side color gamut than the output side color gamut into the KCMY signal of the printer 50 can be created with good reproducibility. Therefore, in the copying machine system such as the scanner 30 → printer 50, the printer 50
It is possible to create the 3DLUT 61 that uses the most vivid color of, and good color reproduction can be performed.

(2) Embodiment FIG. 8 is a conceptual diagram showing a structural example of a color image forming apparatus 200 as an embodiment according to the present invention. The color image forming apparatus 100 shown in FIG. 8 constitutes an example of an image forming apparatus, and is an apparatus that forms a color image on an image transfer system by superimposing colors based on arbitrary image information. The color image forming apparatus 100 includes an image forming apparatus main body (hereinafter also simply referred to as a printer) 50 and an image reading apparatus (hereinafter simply referred to as a scanner 30) 30. Printer 5
A scanner 30 including an automatic document feeder 201 and a document image scanning exposure device 202 is installed on the upper part of 0. The original d placed on the original table of the automatic original feeding device 201 is conveyed by the conveying means, and the image of one side or both sides of the original is scanned and exposed by the optical system of the original image scanning exposure device 202, and the line image sensor CCD is exposed. Is read.

The analog signal photoelectrically converted by the line image sensor CCD is subjected to analog processing, A / D conversion, shading correction, image compression processing, and the like in an image processing unit (not shown) to become image information. afterwards,
The image information is sent to image writing units (exposure means) 3Y, 3M, 3C and 3K which are an example of an image forming unit.

The automatic document feeder 201 is provided with an automatic double-sided document conveying means. The automatic document feeder 201 is configured to continuously read the contents of a large number of documents d fed from the document table and store them in a memory such as a hard disk (electronic RDH function). This electronic RD
The H function is conveniently used when copying the contents of a large number of originals by the copying function, or when transmitting a large number of originals d by the facsimile function.

The printer 50 is called a tandem type color image forming apparatus and comprises a plurality of sets of image forming units (image forming means) 10Y, 10M, 10C and 10K.
An endless intermediate transfer belt 6 and a re-feed mechanism (Automati
c Document Unite (ADU mechanism), and a fixing device 17 for fixing a toner image. Image forming units 10Y, 10M, 10C, 10
In K, a color resist (pattern) based on the KCMY signal is formed on the intermediate transfer belt 6 for each color.

The image forming unit 10Y for forming a yellow (Y) color image includes a photosensitive drum 1 as an image forming body.
Y, and a Y-color charging unit 2Y, an exposing unit 3Y, a developing device 4Y, and a cleaning unit 8Y for the image forming body, which are arranged around the photosensitive drum 1Y. An image forming unit 10M that forms an image of magenta (M) color includes a photosensitive drum 1M as an image forming body, a charging unit 2M for M color,
It has an exposing means 3M, a developing device 4M and a cleaning means 8M for the image forming body.

The image forming unit 10C for forming a cyan (C) color image is a photosensitive drum 1C as an image forming body.
And C color charging means 2C, exposure means 3C, and developing device 4
It has a cleaning means 8C for C and the image forming body. The image forming unit 10K that forms a black (K) color image is
It has a photosensitive drum 1K as an image forming body, a charging means 2K for K color, an exposing means 3K, a developing device 4K and a cleaning means 8K for the image forming body.

Charging means 2Y, exposure means 3Y, charging means 2
M and the exposing means 3M, the charging means 2C and the exposing means 3C, and the charging means 2K and the exposing means 3K constitute a latent image forming means. Development by the developing devices 4Y, 4M, 4C, and 4K is performed by reversal development in which a developing bias in which a DC voltage having the same polarity as the toner used (negative polarity in this embodiment) is superimposed with an AC voltage is applied. . The intermediate transfer belt 6 is
It is wound by a plurality of rollers and is rotatably supported.

The outline of the image forming process will be described below. The image of each color formed by the image forming units 10Y, 10M, 10C, and 10K is a primary transfer bias (not shown) of the opposite polarity (positive in this embodiment) to the toner used. Transfer roller 7
By Y, 7M, 7C, and 7K, the color images (color image: color toner image) that are sequentially transferred (primary transfer) onto the rotating intermediate transfer belt 6 are formed. The color image is transferred from the intermediate transfer belt 6 to the paper P.

The paper P stored in the paper feed cassettes 20A, 20B and 20C is the paper feed cassettes 20A, 20B and 2C.
Paper is fed by the feed roller 21 and the paper feed roller 22A respectively provided at 0C, and the transport rollers 22B, 2
The color image is collectively transferred to one surface (front surface) of the paper P (secondary transfer) by being conveyed to the secondary transfer roller 7A via the 2C, 22D, the registration roller 23, and the like.

The sheet P on which the color image has been transferred is fixed by the fixing device 17, sandwiched by the sheet discharge rollers 24, and placed on the sheet discharge tray 25 outside the apparatus. The transfer residual toner remaining on the peripheral surfaces of the photoconductor drums 1Y, 1M, 1C and 1K after the transfer is the image forming member cleaning means 8Y, 8M and 8.
After cleaning by C and 8K, the next image forming cycle is started.

At the time of double-sided image formation, the paper P discharged from the fixing device 17 is image-formed on one side (front side).
The reversing conveyance path 27, which is a sheet re-feeding mechanism (ADU mechanism), is branched from the sheet discharge path by the branching means 26 and passes through the lower circulation paper passage 27A that constitutes the paper feeding and conveying means.
The front side and the back side are reversed by B, pass through the re-feeding conveyance section 27C, and merge at the sheet feeding roller 22D.

The reversely conveyed sheet P is conveyed again to the secondary transfer roller 7A via the registration roller 23, and a color image (color toner image) is collectively transferred onto the other side (back side) of the sheet P. . Paper P on which a color image has been transferred
Is subjected to a fixing process by the fixing device 17 (or the fixing device 17A), is sandwiched by the paper discharge rollers 24, and is placed on the paper discharge tray 25 outside the machine.

On the other hand, after the color image is transferred onto the paper P by the secondary transfer roller 7A, the intermediate transfer belt 6 obtained by separating the curvature of the paper P is the cleaning means 8 for the intermediate transfer belt.
The residual toner is removed by A. When these images are formed, the paper P is 52.3 to 63.9 kg / m.
² (1000 sheets) of thin paper or 64.0-81.4 kg
/ M ² (1000 sheets) of plain paper or 83.0 to 13
About 0.0 kg / m ² (1000 sheets) of thick paper or 150.
Use ultra-thick paper of 0 kg / m ² (1000 sheets), linear velocity of 80 to 350 mm / sec, environmental conditions of temperature of 5 to 35 ° C. and humidity of 15 to 85%. Is preferred. The thickness of the paper P (paper thickness) is about 0.05 to 0.15 mm.

A toner density sensor 11 is provided on the upstream side of the above-mentioned cleaning means 8A and on the left side of the intermediate transfer belt 6, and the image forming units 10Y and 10Y are provided.
The density of the toner image (color image) formed on the intermediate transfer belt 6 is detected from M, 10C, and 10K, and the density detection signal S
1 is generated.

A registration sensor 12 is provided side by side with the toner density sensor 11 to detect the position of the color resist formed on the intermediate transfer belt 6 and generate a position detection signal S2. The printer 50 is provided with the control device 15, and at least the registration sensor 12
The input / output of the intermediate transfer belt 6 and / or the image forming units 10Y, 10M, 10C and 10K is controlled based on the output of the.

FIG. 9 is a block diagram showing a configuration example of a control system of the color image forming apparatus 200. The color image forming apparatus 200 shown in FIG. 9 is an apparatus that forms a color image based on arbitrary color image information, and has a control device 15. A ROM 6 which is an example of a storage device is provided in the control device 15.
0 is mounted, and the 3DLUT 61 for converting the RGB signal (color image information) of the scanner 30 into the KCMY signal (color image information) of the printer 50 is stored.

The 3DLUT 61 is created by the information creating apparatus 100 described in the embodiment. For example, the RGB signal of the scanner 30 is previously set to the color data Lab.
Is converted to L ^* -C ^* coordinate system and the KCMY signal of the printer 50 is converted to color data Lab to L ^*.
-C ^* when expressed in a coordinate system, L ^* -C ^* input color gamut is the color gamut of the scanner 30, which is expressed in the coordinate system and the printer 5
When the color gamut of the scanner 30 and the color data of the printer 50 are determined by comparing with the output color gamut which is 0, it is determined that the input color gamut is wider than the output color gamut. It is created by compressing the color gamut of the scanner 30 so that the color difference due to Lab is minimized.

In addition to the ROM 60 in the control device 15, the RA
An M64, a CPU (central processing unit) 65 and the like are mounted, and the ROM 60, the RAM 64 and the CPU 65 constitute the image processing unit 40. The image processing section 40 refers to the 3DLUT 61 of the ROM 60 to perform color conversion of the RGB signal from the scanner 30 and output the KCMY signal for the printer.

A printer 50, which is an example of image forming means, is connected to the control device 15, and forms a color image based on the KCMY signal color-converted by the 3DLUT 61 by the ROM 60. Control device 1
5, a toner concentration sensor 11, a registration sensor 12, a hard disk (H
The DD) 62, the operation panel 70, the display unit 71, the paper feed cassette control unit 80, and the communication modem 90 are connected.

Next, an operation example of the color image forming apparatus 200 will be described. FIG. 10 shows a color image forming apparatus 2.
It is a flowchart which shows the operation example of 00. In this embodiment, the ROM 60 in the control device 15 is stored in the ROM 60 of the scanner 30.
3DL to convert GB signal into KCMY signal for printer
It is assumed that the UT 61 is stored. It is assumed that the number of prints is set in advance.

Under these operating conditions, the document reading process is executed using the scanner 30 in step C1 of the flowchart shown in FIG. At this time, the document d placed on the document table of the automatic document feeder 201 is transported by the transporting means, and one side or both sides of the document are scanned and exposed by the optical system of the document image scanning / exposure device 202 to obtain a line image. It is read by the sensor CCD.

The analog signal photoelectrically converted by the line image sensor CCD is subjected to analog processing, A / D conversion, shading correction, image compression processing, etc. in the image processing section 40 shown in FIG. 9 to become color image information.

Then, the process proceeds to step C2, and the color image information (RGB signal) is stored in the HDD 62. At this time, a large number of documents d fed from the above-mentioned document placing table d
The contents of the above are continuously read all at once by the automatic document feeder 201, and the color image information is sequentially stored in the HDD 62 (electronic RDH function).

Then, the process proceeds to step C3 and the HDD 6
The color image information is read from 2, and then the process proceeds to step C4 where the image processing unit 40 executes the color conversion process. In step C4, the image processing unit 40 executes color conversion processing. At this time, in the image processing unit 40, for example, color image information for one page of the original document is temporarily recorded in the RAM 64, and the CPU 60 causes the ROM 60 to read the ROM 60.
Is referred to.

Color image information (RG
The B signal) is color-converted based on the 3DLUT 61 of the ROM 60. The color-converted KCMY signals for the printer for one page of the original are image writing units 3Y and 3Y.
It is sent to M, 3C and 3K.

Then, proceeding to step C5, the printer 50 prints out based on the KCMY signal. At this time, the control device 15 controls the paper feed cassette controller 80 to feed paper. For example, the paper feed cassettes 20A, 20B, 20
The paper P accommodated in C is fed by the feed roller 21 and the paper feed roller 22A, and is conveyed by the conveyance rollers 22B, 2B.
It is conveyed to the secondary transfer roller 7A via 2C, 22D, the registration roller 23 and the like.

On the other hand, the image forming unit 1 of the printer 50.
In 0Y, 10M, 10C, and 10K, electrostatic latent images are formed on the photoconductor drums 1Y, 1M, 1C, and 1K by the image writing units 3Y, 3M, 3C, and 3K based on the KCMY signal. This electrostatic latent image is applied to the developing devices 4Y, 4M, 4C,
Developed by 4K. The development at this time is performed by reversal development in which a development bias in which a DC voltage having the same polarity as the toner used (negative polarity in this embodiment) is superimposed on an AC voltage is applied.

In the image forming unit 10Y, a yellow (Y) color toner image is formed. In the image forming unit 10M, a magenta (M) color toner image is formed. In the image forming unit 10C, a cyan (C) color toner image is formed. The image forming unit 10K forms a black (K) toner image. The color toner images formed on the respective photoconductor drums 1Y, 1M, 1C and 1K are transferred as a color resist (pattern) to the intermediate transfer belt 6 (primary transfer).

The color images formed on the intermediate transfer belt 6 are collectively transferred onto one surface of the paper P (secondary transfer). The paper P on which the color image is transferred is fixed by the fixing device 17
Then, the sheet is fixed by the sheet ejection roller 24, is sandwiched by the sheet ejection rollers 24, and is placed on the sheet ejection tray 25 outside the apparatus. The transfer residual toner remaining on the peripheral surfaces of the photoconductor drums 1Y, 1M, 1C and 1K after transfer is the image forming member cleaning means 8Y, 8M, 8C and 8.
After cleaning by K, the next image forming cycle is started.

Then, in step C6, the control device 15 determines whether or not all printing has been completed. If the preset number of copies has not been completed, the process returns to step C5 to continue the printout. When the printing is completed, the image forming process is completed.

As described above, according to the color image forming apparatus 200 as the embodiment of the present invention, when the color image is formed on the basis of the arbitrary color image information, the RGB signal of the scanner 30 is stored in the ROM 60 by the printer. 50 KCMY
The 3DLUT 61 for converting into a signal is stored. Therefore, in the printer 50, the 3DLUT 61 by the ROM 60 is
It is possible to form a color image based on the KCMY signal color-converted by.

As a result, the color image information of the scanner 30, which has a wider input side color gamut than the output side color gamut, particularly red,
Image information relating to primary colors such as blue and green can be color-converted so as to have the highest saturation in the output side color gamut. Therefore, based on the color image information after color conversion, the printer 5
It is possible to form a color image that fully utilizes the 0 color gamut.

In this embodiment, the case where the RGB signals relating to the color image are supplied from the scanner 30 has been described. However, the present invention is not limited to this, and the RGB signals relating to the digital color image are received from a personal computer and the like. May be color-converted to form a color image based on the KCMY signal.

[0118]

As described above, according to the information generating apparatus of the present invention, the color image information of the input side signal processing system is converted into the color image information of the output side signal processing system.
When the dimensional information conversion table is created, a control device is provided for controlling the creation of the n-dimensional information conversion table based on the intermediary image information that can be represented by the color conversion intermediary coordinate system. The input side color gamut, which is the expressed color gamut of the input side signal processing system, is compared with the output side color gamut, which is the color gamut of the output side signal processing system, and the input side color gamut is compared with the output side gamut. When it is determined that the color gamut is wide, the color gamut of the signal processing system on the input side is minimized so that the color difference between the image information of the signal processing system on the input side and the image information of the signal processing system on the output side is minimized. It is to compress.

With this configuration, the color image information of the signal processing system on the input side after the n-dimensional information conversion, especially the image information of the primary colors such as red, blue, and green, has the highest saturation in the color gamut on the output side. The color gamut of the signal processing system on the input side can be compressed so that Therefore, an n-dimensional information conversion table capable of converting the color image information of the signal processing system on the input side having a wider color gamut on the input side to the color image information of the signal processing system on the output side is created. You can

According to the n-dimensional information conversion table creating method of the present invention, the color image information in the signal processing system on the input side is replaced with the intermediate image information to be expressed in the color conversion intermediate coordinate system, and the signal on the output side is generated. The color image information of the processing system is replaced with the intermediary image information and expressed in the color conversion intermediary coordinate system, and the input side color gamut, which is the color gamut of the input side signal processing system expressed in this color conversion intermediary coordinate system, and the output. When the input side color gamut is wide by comparing with the output side color gamut which is the color gamut of the side signal processing system, the intermediate image information of the input side signal processing system and the intermediate image information of the output side signal processing system are compared. The color gamut of the signal processing system on the input side is compressed so that the color difference due to is minimized.

With this configuration, the color image information of the signal processing system on the input side after the n-dimensional information conversion, particularly the image information of the primary colors such as red, blue, and green, has the highest saturation in the output color gamut. The color gamut of the signal processing system on the input side can be compressed so that Therefore, the color image information of the signal processing system on the input side having a wider color gamut on the input side than the color gamut on the output side, especially red,
Image information relating to primary colors such as blue and green can be color-converted so as to have the highest saturation in the output side color gamut.

According to the image forming apparatus of the present invention, when a color image is formed based on arbitrary color image information,
A storage device storing an n-dimensional information conversion table for converting color image information of the signal processing system on the input side into color image information of the signal processing system on the output side is provided with this storage device according to the information generating device of the present invention. The created n-dimensional information conversion table is stored.

With this configuration, the color image information of the signal processing system on the input side, which has a wider input side color gamut than the output side color gamut, and particularly the image information about the primary colors such as red, blue, and green, is output on the output side color gamut. It is possible to perform color conversion and the like so that the highest saturation can be obtained. Therefore, it is possible to form a color image in which the output side color gamut is fully utilized based on the color image information after color conversion.

The present invention is a color facsimile, a color printer or a color copying machine which forms a color image by color converting color image information of an RGB signal processing system into color image information of a YMCK signal processing system by a three-dimensional color conversion table. It is very suitable to be applied to these complex machines.

[Brief description of drawings]

FIG. 1 is an information creating device 100 as an embodiment of the present invention.
3 is a block diagram showing a configuration example of FIG.

FIG. 2 is an image diagram showing an example of color three-dimensional coordinates of a 3DLUT 61.

FIG. 3 is an image diagram showing a representation example of a scanner color gamut, a printer color gamut, and a document color gamut in an L ^* -C ^* coordinate system.

FIG. 4 is an image diagram showing a comparative example of compression methods in an L ^* -C ^* coordinate system.

FIG. 5 is an image diagram showing a calculation example of a compression point q1 ′ on the printer color gamut surface.

6 is a flowchart showing an example of creating a 3DLUT 61 in the information creating device 100. FIG.

FIG. 7 is a flowchart showing an example of compression processing in the control device 45.

FIG. 8 is a conceptual diagram showing a configuration example of a color image forming apparatus 200 as an embodiment according to the present invention.

9 is a block diagram showing a configuration example of a control system of the color image forming apparatus 200. FIG.

FIG. 10 is a flowchart showing an operation example in the color image forming apparatus 200.

FIG. 11 is a block diagram showing a configuration example of an image forming apparatus 300 according to a conventional example.

FIG. 12 is a flowchart showing an example of creating a 3DLUT according to a conventional example.

FIG. 13 is an image diagram showing a representation example of a scanner color gamut, a printer color gamut, and a document color gamut in the L ^* -C ^* coordinate system.

FIG. 14 is an image diagram showing a calculation example of a compression point p1 ′ on the printer color gamut surface.

FIG. 15 is an image diagram showing a compression example (No. 1) in the L ^* -C ^* coordinate system.

FIG. 16 is an image diagram showing a compression example (No. 2) in the L ^* -C ^* coordinate system.

[Explanation of symbols]

15 Control device 30 Scanner (image reading device) 40 Image processing unit 44 Information processing means 45 Control device 46 Input means 50 Printer (image forming means) 60 ROM (storage device) 61 3DLUT (n-dimensional information conversion table) 100 information creation device 200 color image forming apparatus

Continued front page    F-term (reference) 2C262 AB11 AB13 AC08 BA01 BA02                       BA09 BA10 BA17 BA19 BC01                       BC07 BC09 BC11 BC19 CA07                       CA08 CA10                 5B057 AA11 BA02 CA01 CA08 CA12                       CA16 CB01 CB08 CB12 CB16                       CC01 CE17 CE18 CH07 CH08                 5C077 LL19 MP08 PP32 PP33 PP36                       PP37 PP47 PQ12 PQ23 TT03                 5C079 HB01 HB03 HB08 HB12 LA26                       LB02 MA04 MA05 MA11 NA03                       PA02 PA03

Claims (10)

[Claims] 1. An apparatus for creating an n-dimensional information conversion table for converting color image information of an input side signal processing system into color image information of an output side signal processing system, the apparatus comprising: Information processing means for converting color image information and color image information of the output side signal processing system into mediation image information expressible in a color conversion mediation coordinate system; and based on the mediation image information converted by the information processing means. a control device for controlling creation of an n-dimensional information conversion table, wherein the control device is a color conversion intermediary coordinate system based on the intermediary image information converted by the information processing means, and the color of the signal processing system on the input side. When the input side color gamut which is the color gamut and the output side color gamut which is the color gamut of the output side signal processing system are compared and judged, and when it is judged that the input side color gamut is wider than the output side color gamut , The input An information generating apparatus for compressing the color gamut of the input side signal processing system so that the color difference between the intermediate image information of the signal processing system and the intermediate image information of the output side signal processing system is minimized. . 2. The control device, in the color conversion mediation coordinate system, is provided with an input point q1 indicated by arbitrary mediation image information of the signal processing system on the input side, and a color difference in the signal processing system on the output side. Let q2 be the vertex of the triangle on the surface of the color gamut indicated by the minimum intermediary image information.
Let q3 and q4, operators be a, b and c, and the compression point on the color gamut surface indicated by the intermediary image information that minimizes the color difference of the signal processing system on the output side be q1 ′.
That is, q1 '= a (q2-q1) + b (q3-q1) + c (q
The information creating apparatus according to claim 1, wherein the compression point q1 ′ is obtained by 4-q1) + q1. 3. The control device is configured such that the signal processing system on the output side controls the intermediate image information [q
2l, q2a, q2b], an arbitrary grid point q
2 is set, and any intermediate image information [q1 of the signal processing system on the input side is set.
[1, q1a, q1b], the color difference between the input point q1 and the grid point q2 is expressed by the following equation: And the color difference between the input point q1 and the grid point q2 and the input point q1.
And the color difference with other grid points on the surface of the color gamut, the process of sequentially extracting the grid points having a small color difference is repeated on all the color gamut surfaces, and the top three points q2 of the grid points having the smallest color difference are q3, q
4. The information creating apparatus according to claim 1, wherein 4 is extracted. 4. A method of creating an n-dimensional information conversion table for converting color image information of an input side signal processing system into color image information of an output side signal processing system, the method comprising: The color image information is converted into mediation image information and expressed in a color conversion mediation coordinate system, and the color image information of the output side signal processing system is converted into mediation image information and expressed in the color conversion mediation coordinate system, The input side color gamut, which is the color gamut of the input side signal processing system expressed in the color conversion mediation coordinate system, and the output side color gamut, which is the color gamut of the output side signal processing system, are compared, and the output When the input side color gamut is wider than the side color gamut, the input is performed so that the color difference between the input side signal processing system image information and the output side signal processing system image information is minimized. Characterized by compressing the color gamut of the signal processing system on the side A method for creating an n-dimensional information conversion table. 5. In the color conversion mediating coordinate system, an input point q1 indicated by arbitrary mediation image information of the signal processing system on the input side is given, and a medial image having a minimum color difference in the signal processing system on the output side is given. Let q2 be the vertex of the triangle on the surface of the gamut indicated by the information.
Let q3 and q4, operators be a, b and c, and the compression point on the color gamut surface indicated by the intermediary image information that minimizes the color difference of the signal processing system on the output side be q1 ′.
That is, q1 '= a (q2-q1) + b (q3-q1) + c (q
5. The n-dimensional information conversion table creating method according to claim 4, wherein the compression point q1 ′ is obtained by 4-q1) + q1. 6. The vertexes q2, q3, q4 of the triangles on the surface of the color gamut indicated by the intermediary image information having the minimum color difference in the signal processing system on the output side are transferred to the surface of the color gamut by the signal processing system on the output side. Image information [q
2l, q2a, q2b], an arbitrary grid point q
2 is set, and any intermediate image information [q1 of the signal processing system on the input side is set.
[1, q1a, q1b], the color difference between the input point q1 and the grid point q2 is expressed by the following equation: And the color difference between the input point q1 and the grid point q2 and the input point q1.
And the color difference with other grid points on the surface of the color gamut, the process of sequentially extracting the grid points with the smallest color difference is repeated on all the color gamut surfaces, and the top three grid points with the smallest color difference are extracted. 5. The n-dimensional information conversion table creating method according to claim 4, which is obtained by 7. An apparatus for forming a color image based on arbitrary color image information, the n-dimensional conversion of the color image information of the input side signal processing system into the color image information of the output side signal processing system. The storage device stores an information conversion table, and an image forming unit that forms a color image based on the color image information converted by the n-dimensional information conversion table by the storage device. The dimensional information conversion table converts the color image information of the signal processing system on the input side into mediation image information in advance and expresses it in a color conversion mediation coordinate system,
When the color image information of the signal processing system on the output side is converted into the mediation image information and expressed in the color conversion mediating coordinate system, the color gamut of the signal processing system on the input side expressed in the color conversion mediating coordinate system. When the input color gamut and the output color gamut of the output side signal processing system are compared and determined, and it is determined that the input color gamut is wider than the output color gamut, The color gamut of the signal processing system on the input side is compressed so that the color difference between the image information of the signal processing system on the input side and the image information of the signal processing system on the output side is minimized. Image forming apparatus. 8. The signal processing system on the input side is provided with a scanner for reading a colored original document and outputting color image information, and the image forming means constitutes a tandem type printer for forming a color image. The image forming apparatus according to claim 7, which is characterized in that. 9. In the color conversion mediation coordinate system, an input point q1 represented by arbitrary mediation image information based on the color image information output from the scanner is given, and the mediation image information that minimizes the color difference in the printer is used. The vertices of the triangle on the surface of the gamut shown are q2, q3, q4
And the operator is a, b, c, and the compression point on the color gamut surface indicated by the intermediary image information that minimizes the color difference of the printer is q1 ', the following equation is obtained: q1' = a (q2-q1 ) + B (q3-q1) + c (q
9. The image forming apparatus according to claim 7, wherein the compression point q1 ′ is obtained by 4-q1) + q1. 10. A vertex q of a triangle on a surface of a color gamut indicated by mediation image information having a minimum color difference in the printer.
2, q3, q4 are intermediary image information [q21, q2 on the surface of the color gamut by the printer.
a, q2b], an arbitrary grid point q2 is set, and arbitrary intermediate image information [q11, q1a,
q1b], the input point q1
The color difference between 1 and the grid point q2 is expressed by the following equation: And the color difference between the input point q1 and the grid point q2 and the input point q1.
And the color difference with other grid points on the surface of the color gamut, the process of sequentially extracting the grid points with the smallest color difference is repeated on all the color gamut surfaces, and the top three grid points with the smallest color difference are extracted. The image forming apparatus according to claim 7, wherein the image forming apparatus is obtained by