JP2008228231A - Image processing unit and color processing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To cancel or reduce the difference between a color taste reproduced by a basic color material and that reproduced by a light color material, or a combination of the basic color material and the light color material. <P>SOLUTION: A color conversion processing section 102 performs color conversion processing to the color signal of the basic color material. A color separation processing section 103 performs color separation to the color signal subjected to the color conversion processing to generate a color signal of the basic color material and that of the light color one. An image formation section 105 forms an image, based on the color signal. A color conversion table section 107 allows the image formation section 105 to form a first color patch using the basic color material based on a color signal for color patches, allows the color separation processing section 103 to perform the color separation to the color signal for color patches, and allows the image formation section 105 to form a second color patch, using the basic color material and the light color material. The color conversion table 107 inputs the colorimetry values of the first and second color patches and creates a color conversion table used for color conversion processing by the color conversion processing section 102, based on the difference in the colorimetry values. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to image formation using a basic color material and a light color material.

  Graininess is an important factor that affects the image quality of printed images.

  As an improvement method using a color material that effectively reduces graininess, it is known to use a color material that is lighter than a color material (basic color material) that is normally used. For example, in an electrophotographic image forming apparatus, for cyan (C) and magenta (M) toner, a toner having a lower density is used in addition to a toner having a normal density. By using this light color material to the maximum in the low density part of the image such as a highlight part, the graininess can be greatly reduced.

  However, the hues of the same color for high-density color materials (dark color materials) and low-density color materials (light color materials) are different, so the colors of the printed image reproduced in six colors were reproduced in four colors. There is a problem different from the color of the printed image.

It is conceivable to deal with this problem by color matching. However, in order to color-separate CMYK four-color image data into six colorant colors including light colorant colors, for example, if a 6-dimensional lookup table with 7 grids is created, 7 ⁶ = 117,649 A color patch is required. Assuming that 15 × 25 = 375 color patches are printed on A4 size recording paper, 117649/375 = 314 color charts are required. It is not easy to measure a number of color patches from a number of color charts and create a lookup table for color matching.

JP 2005-045349

  An object of the present invention is to eliminate or reduce the difference in color reproduced by a basic color material and the color reproduced by a light color material or a combination of a basic color material and a light color material.

  The present invention has the following configuration as one means for achieving the above object.

  An image processing apparatus according to the present invention includes a color conversion unit that performs color conversion processing on a color signal of a basic color material, color-separating the color signal subjected to the color conversion processing, and a color signal of the basic color material and a light color material A color separation means for generating a color signal, a forming means for forming an image based on the color signal, and a first color patch using the basic color material for the forming means based on a color signal for a color patch. Generating means for causing the color separation means to color-separate the color signal for the color patch and forming the second color patch using the basic color material and the light color material on the formation means. And a creation means for inputting colorimetric values of the first and second color patches and creating a color conversion table used by the color conversion means for color conversion processing based on a difference between the colorimetric values. It is characterized by having.

  The color processing method according to the present invention includes a color conversion unit that performs color conversion processing on a color signal of a basic color material, color-separates the color signal subjected to the color conversion processing, and outputs a color signal of the basic color material and a light color material. A color separation method for generating a color signal, and a color processing method for an image processing apparatus having a forming unit for forming an image based on the color signal, wherein the forming unit includes the color signal for a color patch. The first color patch using the basic color material is formed, the color signal for the color patch is color-separated by the color separation means, and the basic color material and the light color material are used for the formation means. Two color patches are formed, colorimetric values of the first and second color patches are input, and the color conversion means is based on a difference between the input colorimetric values of the first and second color patches. Color conversion table used for color conversion processing Characterized in that it created.

  According to the present invention, it is possible to eliminate or reduce the difference between the color tone reproduced by the basic color material and the color tone reproduced by the light color material or the combination of the basic color material and the light color material.

  Hereinafter, color processing according to an embodiment of the present invention will be described in detail with reference to the drawings. In the following, an example in which the color processing of the present invention is applied to an electrophotographic printer will be described. However, the color processing described below can also be applied to an inkjet method, a sublimation printer, and the like.

[Device configuration]
FIG. 1 is a block diagram illustrating an example of an image processing configuration of an electrophotographic printer, and FIG. 2 is a diagram illustrating a hardware connection example.

  The controller 204 separates image data input from the computer 203 into device CMYK data of the printer 205. For example, if the input image data is sRGB data corresponding to the color gamut of the monitor 202, color processing (color gamut mapping) that matches the color reproduction of the monitor 202 and the color reproduction of the printer 205 is performed, and then the basic color of the device is obtained. Color separation into corresponding CMYK data. If the input image data is CMYK data, color processing (color gamut mapping) that matches the color reproduction of the target printing apparatus and the color reproduction of the printer 205 is performed and converted to device CMYK data.

  The color conversion processing unit 102 of the printer 205 performs an interpolation operation based on the color conversion table of the color conversion table unit 107, and converts the input color signal C1M1Y1K1 into a C2M2Y2K2 signal. The color separation processing unit 103 performs an interpolation operation based on the color separation table of the color separation table unit 108, and color-separates the C2M2Y2K2 signal into color signals corresponding to six color materials obtained by adding a light color material to a basic color material. , C3M3Y3K3Lc3Lm3 signal is generated.

  The halftone processing unit 104 converts the multi-valued C3M3Y3K3Lc3Lm3 signal (for example, 256 gradations for each color) into data of the number of gradations (for example, each color has two, three, and four gradations) that can be processed by the image forming unit 104. At that time, continuous tone is expressed by pseudo halftone processing (dither processing, error diffusion processing, etc.). An image forming unit 105, which is an electrophotographic printer engine, outputs a printed matter 106 on which an image represented by C4M4Y4K4Lc4Lm4 data input from the halftone processing unit 104 is formed.

  The color conversion table unit 107 creates a color conversion table used by the color conversion processing unit 102. The color separation table unit 108 creates a color separation table used by the color separation processing unit 103. To create the color conversion table and the color separation table, the printer 205 prints a chart 206 including a plurality of color patches. The computer 203 controls the colorimeter 201 to measure each color patch of the chart 206, and inputs the measurement result to the color conversion table unit 107 and the color separation table unit 108 via the controller 204. Done.

[Create color conversion table]
FIG. 3 is a flowchart showing a method for creating a color conversion table by the color conversion table unit 107.

  The color conversion table creation unit 107 stores CMYK data of color patches that cover a color gamut that can be reproduced by the printer 205. When the computer 203 issues an instruction to create a color conversion table, the color conversion processing unit 102 and the color separation processing unit 103 set the through-pass state, and supply CMYK data of the color patch to the color conversion processing unit 102 (S301). ). The printer 205 outputs a (first) color patch formed of CMYK four-color color materials as a chart 206 (hereinafter, a four-color chart).

  Next, the color conversion table creation unit 107 sets only the color conversion processing unit 102 to the through-pass state, and supplies the CMYK data of the color patch to the color conversion processing unit 102 (S302). The printer 205 outputs a (second) color patch formed of CMYKLcLm six color materials as a chart 206 (hereinafter, six color chart).

  The operator places the four-color chart and the six-color chart on the reading surface of the colorimeter 201 in order, and instructs the reading of the color information of each color patch of the chart 206 via the computer 203. In accordance with this instruction, the colorimeter 201 outputs a colorimetric value (Lab value) to the computer 203. The computer 203 outputs the colorimetric value input from the colorimeter 201. The color conversion table creation unit 107 receives the colorimetric values output from the computer 203 (S303).

  Next, the color conversion table creation unit 107 predicts Lab values at each grid point of the CMYK grid having a predetermined number of grids from the colorimetric values of the input four-color chart using, for example, a Cellular Neugebauer color prediction formula. (S304). Similarly, the Lab value at each grid point of the CMYK grid having the above-mentioned grid number is predicted from the colorimetric values of the input six-color chart using, for example, the Cellular Neugebauer color prediction formula (S305). Hereinafter, these lattices are referred to as a four-color lattice and a six-color lattice. The number of grids is set according to the conversion accuracy of the color conversion table. Further, in order to reduce the trouble of color measurement of the color patch, the number of grids for setting the CMYK value of the color patch for the chart 206 is smaller than the number of grids of the four-color grid. For this reason, it is necessary to predict the Lab value.

  The Lab value of the grid point (C, M, Y, K) of the four-color grid and the Lab value of the same grid point (C, M, Y, K) of the six-color grid are CMYK four for the same CMYK input value. This represents the difference between the color and the color that is reproduced when printing with 6 colors of CMYKLcLm. Therefore, the color conversion table creation unit 107 calculates the CMYK value when the Lab value of the grid point P6 having the six-color grid is moved to the Lab value of the corresponding grid point P4 of the four-color grid, and the grid point P6 and the surroundings. The process of interpolating from the grid points (six-color grid points) is repeated (S306). As a result, when CMYK values of grid points (corresponding to C1M1Y1K1) are printed in six colors, the color indicating the relationship between the converted values C2M2Y2K2 (CMYK values of interpolation results) that reproduce the same color as when four colors were printed A conversion table can be obtained (S307).

  The color conversion processing unit 102 performs color conversion processing using the color conversion table created in this way. Therefore, it is possible to eliminate or reduce the difference between the colors of the print image reproduced with six colors and the color of the print image reproduced with four colors, which are caused by the hue difference between the dark color material and the light color material. At this time, unlike the above-described creation of the color matching look-up table, it is only necessary to form two charts 206, a four-color chart and a six-color chart, and measure the color.

  The color processing according to the second embodiment of the present invention will be described below. Note that the same reference numerals in the second embodiment denote the same parts as in the first embodiment, and a detailed description thereof will be omitted.

  In the conversion table created by the method of Example 1, the color of the print image reproduced in six colors and the color of the print image reproduced in four colors are different due to the hue difference between the dark color material and the light color material. The problem can be solved or at least reduced. However, the color of the primary color that can be expressed by a single color of the basic color material and the color area that can be reproduced by the secondary color by mixing the two colors of the basic color material are mixed with the colors of other basic color materials. Degradation of color area (color turbidity) occurs.

  The primary color is the color on each axis in CMYK space. The secondary color is the color on the surface sandwiched between the axes in the CMYK space. Therefore, at the grid points on each axis of the CMYK grid and the grid points on the plane sandwiched by each axis, if the interpolation calculation (S306) in Example 1 is not performed, the CMYK values of those grid points are mixed with other colors. Will not be invited.

  FIG. 4 is a flowchart showing a method of creating a color conversion table of the second embodiment by the color conversion table unit 107.

  The color conversion table unit 107 performs the same processing as in the first embodiment from step S301 to S305. Then, one grid point of the six-color grid is selected (S311), and among the CMYK values of the grid point, three values are zero (grid points on the axis corresponding to the primary color), and two values are zero ( It is determined whether or not it is a lattice point on the boundary surface of the lattice (S312). The boundary surface of the grid is the CM plane between the C and M axes corresponding to the secondary color, the MY plane between the M and Y axes, the YC plane between the Y and C axes, the K axis and another axis These are the KC, KM, and KY surfaces that are sandwiched.

  The color conversion table unit 107 selects the CMYK value when the Lab value of the selected grid point whose three or two of the CMYK values are not zero is moved to the Lab value of the grid point of the corresponding four-color grid. Interpolation is performed from the grid points and the grid points of the surrounding six-color grid (S313). Also. If three or two of the CMYK values of the selected grid point are zero, the interpolation calculation value (C2M2Y2K2) of the selected grid point is set to the CMYK value (C1M1Y1K1) of the selected grid point without performing the interpolation calculation. (S314).

  Next, the color conversion table unit 107 determines whether or not the processing of steps S311 to S314 has been performed for all grid points of the six-color grid (S315), and if not completed, returns the processing to step S311. If completed, a color conversion table is created as in the first embodiment (S307).

  The color conversion processing unit 102 performs color conversion processing using the color conversion table created in this way. Therefore, in addition to the same effects as in Example 1, the primary color that can be expressed by the basic color material alone, and the color area that can be reproduced by the secondary color by mixing two colors of the basic color material, etc. This will not lead to the mixing of the colors of the basic color materials.

[Other embodiments]
Note that the present invention can be applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, and a printer), and a device (for example, a copying machine and a facsimile device) including a single device. You may apply to.

  Another object of the present invention is to supply a storage medium storing a computer program for realizing the functions of the above embodiments to a system or apparatus, and the computer (CPU or MPU) of the system or apparatus executes the computer program. But it is achieved. In this case, the software itself read from the storage medium realizes the functions of the above embodiments, and the storage medium storing the computer program constitutes the present invention.

  Further, the above functions are not only realized by the execution of the computer program. That is, it includes a case where an operating system (OS) or the like running on the computer performs part or all of the actual processing according to an instruction of the computer program, thereby realizing the above functions.

  The computer program may be written in a function expansion card connected to the computer or a memory of the unit. That is, the case where the above functions are realized by the CPU or the CPU of the unit performing part or all of the actual processing in accordance with the instruction of the computer program.

  When the present invention is applied to the storage medium, the storage medium stores a computer program corresponding to the flowchart described above.

A block diagram showing an example of an image processing configuration of an electrophotographic printer; Figure showing an example of hardware connection Flowchart showing a method for creating a color conversion table of Example 1, 10 is a flowchart illustrating a method for creating a color conversion table according to the second embodiment.

Claims (6)

Color conversion means for performing color conversion processing on the color signal of the basic color material;
Color separation means for color-separating the color signal subjected to the color conversion processing to generate a color signal of the basic color material and a color signal of a light color material;
Forming means for forming an image based on the color signal;
Based on the color signal for the color patch, the forming unit forms the first color patch using the basic color material, and the color signal for the color patch is color-separated by the color separation unit, Patch generating means for forming a second color patch using the basic color material and the light color material in the forming means;
Creating a color conversion table for inputting colorimetric values of the first and second color patches and generating a color conversion table used by the color conversion unit for color conversion based on a difference between the colorimetric values; An image processing apparatus.   The creating means predicts the Lab value of each grid point of the CMYK grid from the colorimetric values of the first and second color patches, and the grid point predicted from the colorimetric values of the second color patch The Lab value of the first color patch predicted from the colorimetric value of the first color patch, the interpolation means for interpolating the CMYK value when moved to the Lab value of the corresponding grid point, and the CMYK value of the grid point 2. The image processing apparatus according to claim 1, further comprising a table creation unit that creates a conversion table indicating a relationship between the CMYK values subjected to the interpolation calculation.   The interpolation means sets the CMYK value of the grid point to the CMYK value after the interpolation calculation without performing the interpolation calculation for the grid point on each axis of the CMYK grid and the grid point of the surface sandwiched by each axis. 3. The image processing apparatus according to claim 2, wherein Color conversion means for performing color conversion processing on the color signal of the basic color material, color separation means for color-separating the color signal subjected to the color conversion processing to generate the color signal of the basic color material and the color signal of the light color material, And a color processing method of an image processing apparatus having a forming means for forming an image based on the color signal,
Based on color signals for color patches, the forming means forms a first color patch using the basic color material,
The color signal for the color patch is color-separated by the color separation means, and the forming means is caused to form a second color patch using the basic color material and the light color material,
Enter the colorimetric values of the first and second color patches,
A color processing method comprising: creating a color conversion table used by the color conversion means for color conversion processing based on a difference between the input colorimetric values of the first and second color patches.   5. A computer program for controlling the image processing apparatus to execute the color processing according to claim 4.   6. A computer-readable storage medium in which the computer program according to claim 5 is recorded.

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