JP2011239428A - Image processing device and its data conversion method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processing device which converts a colored original image data into a color-material color image data corresponding to a plurality of color-material colors used for printing and outputs the converted image data to a printer for printing, and automatically conducts printing in the plural color-material colors suitable for a kind of a sheet selected by a user for use for printing.SOLUTION: A type of a sheet selected by a user is input from a sheet type input section 410. A parameter setting section 411 prepares a plurality of color conversion tables 408 corresponding to a plurality of types of sheets respectively, and selects among those a table corresponding to the input type of the sheet so as to set to a color conversion processing section 403. The processing section 403 performs the color conversion processing using the set table for R'G'B' data which is RGB data of the original image data input from an input section 401 subjected to color matching processing in a processing section 402, and performs conversion into the color-material color image data such as CMYK data or CMYKcm data.

Description

  The present invention relates to an image processing apparatus that converts color original image data into color material color image data corresponding to the colors of a plurality of color materials (ink, toner, etc.) used for printing, and outputs the data to a printer for printing. The present invention relates to a color data conversion method.

  There is a print system including a color printer and an image processing apparatus such as a personal computer that performs color printing on the color printer. In this system, a printer driver of an image processing apparatus converts color original image data into color material color image data corresponding to a plurality of color material colors used for printing, and outputs the data to a printer for printing. The original image data is, for example, R (red), G (green), and B (blue) image data (hereinafter referred to as RGB data). This is converted into color material color image data (hereinafter referred to as CMYK data) corresponding to, for example, C (cyan), M (magenta), Y (yellow), and K (black) as color material colors and output. Alternatively, for example, it is converted into color material color image data (hereinafter referred to as CMYKcm data) corresponding to C, M, Y, K, c (low density cyan), m (low density magenta) and output. Alternatively, for example, it is converted into color material color image data (hereinafter referred to as CMYKcmRGB data) corresponding to C, M, Y, K, c, m, R, G, and B and output.

  On the other hand, color printers in recent years have a wide range of uses and can print on various types of paper (media). For example, business documents are printed using plain paper, natural images such as photographs using glossy paper, and drawing documents are printed using CAD or the like using tracing paper. Further, POP / flyers are printed on coated paper, and art works such as CG / monochrome photographs are printed on art paper.

  A configuration of a printer that performs an optimal printing process corresponding to each of the types of paper is described in, for example, Patent Document 1 below. In this configuration, when the user selects a paper type to be printed on the printer setting screen, the central processing unit recognizes the paper type, and for example, it is determined as plain paper, glossy paper, coated paper, or OHP. The Then, the printing process of the printer suitable for the determined paper type is automatically selected.

JP-A-8-297553

  A plurality of colorant colors required for printing are different for each of the above-described various types of paper. For example, natural image printing on glossy paper requires a wide color reproduction range and no graininess. To achieve this, special color materials such as R, G, and B are increased, or c and m For example, it is necessary to make the binary dots inconspicuous with a low-density color material. On the other hand, in monochrome photo printing on art paper, the stability of gray balance is the first requirement, so it is desirable to refrain from using chromatic color materials in order to reduce the effects of instability of each color material. Further, when printing a drawing document on tracing paper, it is required that each thin line is printed clearly. For this reason, even in color printing, it is necessary to use a minimum of color materials so that fine lines are not thickened due to dot gain as a result of using various color materials in the same place.

  On the other hand, as described above, a configuration in which a printing process suitable for the type of paper selected by the user with a printer is automatically performed is disclosed in Patent Document 1 and the like. However, there is no known configuration that automatically performs printing with a plurality of colorant colors suitable for the selected paper type (suitable for that type of use).

  The present invention has been made in view of such circumstances. SUMMARY OF THE INVENTION An object of the present invention is an image processing apparatus that converts color original image data into color material color image data corresponding to a plurality of color material colors used for printing, and outputs the data to a printer for printing. The object is to automatically perform printing with a plurality of colorant colors suitable for the type.

  The present invention is an image processing apparatus for converting color original image data into ink color image data corresponding to a plurality of ink colors used for printing, and when the paper used for printing is glossy paper The conversion using at least the basic color ink and the special color ink is performed, and when the paper used for printing is plain paper, at least the basic color ink is used, and the special color ink is not used. An image processing apparatus that performs conversion.

  Further, the present invention is a data conversion method for converting color original image data into ink color image data corresponding to a plurality of ink colors used for printing, and when the paper used for printing is glossy paper, The conversion is performed so that at least the basic color ink and the special color ink are used, and when the paper used for printing is plain paper, at least the basic color ink is used and the special color ink is not used. This is a data conversion method characterized by

  According to the present invention, when the user selects and inputs one of a plurality of types of paper to be used for printing, the original image data is changed to a plurality of color material colors depending on the input paper type. The corresponding color material color image data is converted, output to a printer, and printed. This allows you to automatically print with multiple colorant colors that are appropriate for the type of paper selected for printing by the user, and color printing depending on the type of paper used for that printing. Can be done appropriately.

1 is a block diagram illustrating a hardware configuration of an image forming system including an image processing apparatus and a printer according to an embodiment of the present invention. It is a block diagram which shows the software structure of the image processing apparatus of an Example. FIG. 2 is a block diagram illustrating an outline of an internal configuration of a printer driver of the image processing apparatus. FIG. 3 is a block diagram illustrating details of a configuration of a printer correction processing unit of the printer driver. It is a table | surface figure which shows the correspondence of the kind of paper used for printing in an Example, and a color material. FIG. 6 is a flowchart illustrating a flow of an operation of selecting and setting each table used for image processing according to an input of a paper type used for printing by a user in the embodiment. It is explanatory drawing which shows the difference of the color reproduction space of a printer, and the color reproduction space of a display apparatus. It is explanatory drawing which shows notionally the monitor gamut compression to a saturation (S) direction in SV plane.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In an image processing apparatus according to an embodiment described below, RGB data as color original image data is converted into color material color image data, which is output to a printer for color printing. The color material (ink or toner) that can be used by the printer is a total of nine colors: C, M, Y, K, c, m, R, G, and B. The low concentrations of c and m are used for the purpose of reducing graininess and improving gradation. R, G, and B are special color materials, and are used for the purpose of extending the color reproduction range. Three types of paper (recording medium) used for printing are assumed to be plain paper, coated paper, and glossy paper in order to simplify the explanation.

  When the user selects plain paper as the type of paper used for printing, the image processing apparatus performs color conversion processing for converting RGB data into CMYK data. In addition, when coated paper is selected, color conversion processing for converting RGB data into CMYKcm data is performed. Further, when glossy paper is selected, color conversion processing for converting RGB data into CMYKcmRGB data is performed. Therefore, when the selected paper is plain paper, C, M, Y, K color materials are used, and when the selected paper is coated paper, C, M, Y, K, c, m color materials are used. In the case of paper, printing is performed using C, M, Y, K, c, m, R, G, and B color materials. FIG. 5 shows the correspondence between the type of paper and the color material used. The three types of color conversion processing corresponding to each of the three types of paper are performed using an N-dimensional lookup table (hereinafter referred to as LUT). That is, three LUTs for performing each of the three types of color conversion processing are prepared, and color conversion processing is performed by selecting and using one of the three LUTs according to the selected paper type. . Note that the color conversion process may be performed by matrix calculation.

  FIG. 1 is a block diagram illustrating an example of a hardware configuration of an image forming (printing) system including an image processing apparatus and a printer (color printer) according to an embodiment.

  The image processing apparatus 100 is a personal computer or the like. The CPU 101 is a central processing unit that integrally controls each unit of the image processing apparatus 100 by executing programs such as an OS (operating system), application programs, and device drivers. The RAM 102 is a memory used as a work area for the CPU 101. The ROM 103 is a memory for storing fixed data such as a boot program such as BIOS. An HDD (Hard Disk Drive) 104 is used to store image data such as a test pattern image in addition to computer programs such as an OS, application programs, and various driver programs. The communication I / F (interface) 105 is a USB, IEEE 1394, wired LAN, wireless LAN, or the like, and is an interface for performing data communication with an external device. The display I / F 106 transmits image information and the like to the display device 109 connected to the outside or the inside, and controls the display.

  The operation unit 107 includes an input device such as a pointing device or a key input device. The printer 108 is an image forming apparatus that forms (prints) an image on a sheet by an inkjet method, a laser beam method, or the like. The display device 109 is a liquid crystal display for displaying an image.

  FIG. 2 shows an example of the software configuration of the image processing apparatus 100. In the image processing apparatus 100, various application programs 202 operate under the control and management of the OS 201. Also, an operation unit driver 207 that drives and controls the operation unit 107, a printer driver 208 that controls the printer 108 and transmits image data to the printer 108 to perform printing, and a display that controls the display device 209 to perform display. The device driver 209 operates.

  With reference to FIGS. 1 and 2, an outline flow of operations at the time of print output will be described. When printing the output image data, first, the application program 202 makes a print output request to the OS 201. For example, the graphics data portion is composed of a graphics rendering command, and the image image data portion issues a rendering command group indicating an output image composed of an image rendering command to the OS 201.

  In response to the print output request from the application program 202, the OS 201 issues a print request and a drawing command group to the printer driver 208 corresponding to the printer 108 that performs the print output.

  The printer driver 208 processes the print request and drawing command group input from the OS 201, creates print data that can be printed by the printer 108, and transfers the print data to the printer 108. When the printer 108 is a raster printer, the printer driver 208 sequentially performs image correction processing on the drawing commands from the OS 201 and sequentially rasterizes the drawing commands on the RGB 24-bit page memory. After rasterizing all drawing commands, the RGB raster image data as the original image data, which is the content of the RGB 24-bit page memory, is converted into color material color image data that can be printed by the printer 108, for example, CMYK data. Transfer to the printer 108. The printer 108 performs color printing of the transferred color material color image data. For example, when the color material color image data is CMYK data, color printing is performed using C, M, Y, and K color materials.

  Next, processing performed by the printer driver 208 will be described with reference to FIG. FIG. 3 shows an outline of the internal configuration of the printer driver 208. The printer driver 208 includes an image correction processing unit 301 and a printer correction processing unit 302.

  The image correction processing unit 301 performs image correction processing on color information included in the drawing command group input from the OS 201. As the image correction processing, for example, RGB color information is converted into luminance / color difference signals, exposure correction processing is performed on the luminance signals, and the corrected luminance / color difference signals are inversely converted into RGB color information.

  The printer correction processing unit 302 first rasterizes a rendering command based on the RGB color information subjected to the image correction process, and generates RGB raster image data (RGB data) as original image data on the RGB 24-bit page memory. Then, in order to match the color reproduction characteristics of the RGB data with the color of the printer, color matching processing for performing color reproduction space mapping is performed on the RGB data to obtain R′G′B ′ data. Then, color conversion processing for converting R′G′B ′ data into color material color image data (CMYK data, CMYKcm data, or CMYKcmRGB data) is performed. After that, in order to correct the gradation characteristics, gamma correction processing and halftone processing are performed to generate color material color image data depending on the color reproducibility of the printer for each pixel, and the printer as printable image data Forward to.

  Details of the configuration and processing of the printer correction processing unit 302 will be described with reference to FIG. In the following, for the sake of simplicity of explanation, it is assumed that a color space usually expressed in three dimensions is schematically expressed in two dimensions (FIG. 7 and the like). The printer correction processing unit 302 is provided with the following configurations denoted by reference numerals 401 to 411.

  An image data input unit 401 inputs RGB data as original image data processed by the image correction processing unit 301.

  The color matching processing unit 402 performs color matching processing on the input RGB data and converts it into R′G′B ′ data.

  The color conversion processing unit 403 converts the R′G′B ′ data into color material color image data. That is, the data is converted into CMYK data, CMYKcm data, or CMYKcmRGB data.

The gamma correction unit 404 performs gamma correction processing on the converted color material color image data.
The halftone processing unit 405 performs halftone processing on the color material color image data that has been subjected to gamma correction processing.
An image data output unit 405 outputs halftone processed color material color image data to the printer 108.

  A paper type input unit 410 is used by the user to select and input one of a plurality of types of paper used for printing (in this embodiment, three types of plain paper, coated paper, and glossy paper). It is. Specifically, the printer driver 208 causes the display device 109 to display a print setting screen via the OS 201 and the display device driver 209, and the user can select one of the above three types of paper to be used for printing on the screen. The type is selected and input.

  The image processing parameter setting unit 411 corresponds to the paper type of the matching table 407, the color conversion table 408, and the gamma correction table 409 used by the color matching processing unit 402, the color conversion processing unit 403, and the gamma correction unit 404 for processing. Three (three types) are prepared.

  Since the color reproduction space of the printer 108, that is, the size of the so-called printer gamut differs depending on the paper type, three matching tables 407 are prepared as LUTs for each paper type. Composed.

  The color conversion table 408 includes an LUT for each paper type in order to convert R′G′B ′ data into three different color material color image data (CMYK data, CMYKcm data, or CMYKcmRGB data) for each paper type. Three are prepared. This is also configured as, for example, a 3D-LUT format by interpolation calculation.

  The gamma correction table 409 has three types of LUTs for each paper type because the non-linear characteristic of brightness varies depending on the paper type, and is configured as a one-dimensional LUT format for each color.

  The image processing parameter setting unit 411 selects one type of table corresponding to the type of paper input from the paper type input unit 410 from three types of tables 407, 408, and 409. These are set as tables to be used for each of the color matching processing unit 402, the color conversion processing unit 403, and the gamma correction unit 404. Each of these units 402, 403, and 404 performs respective image processing using a table set for each.

  The flow of operations related to the selection of the tables 407 to 409 corresponding to the type of paper is shown in the flowchart of FIG. In this flow of operation, first, a paper type selected from plain paper, coated paper, and glossy paper to be used for printing by the user from the paper type input unit 410 is input to the image processing parameter setting unit 411 ( Step S1).

  Next, the setting unit 411 determines the type of the input paper (step S2). If it is determined as plain paper, one type of table corresponding to plain paper is selected for each of the three types of tables 407, 408, and 409. For the color conversion table 408, a table for conversion to CMYK data is selected. Then, each of the selected plain paper tables is set as a table to be used for each process for the color matching processing unit 402, the color conversion processing unit 403, and the gamma correction unit 404 (step S3).

  If the input paper type is determined to be coated paper, one table corresponding to the coated paper is selected for each of the tables 407, 408, and 409. For the color conversion table 408, a table for conversion to CMYKcm data is selected. Then, each of the selected coated paper tables is set for the respective sections 402, 403, and 404 (step S4).

  If the input paper type is determined to be glossy paper, one table corresponding to glossy paper is selected for each of the tables 407, 408, and 409. For the color conversion table 408, a table for conversion to CMYKcmRGB data is selected. Then, each of the selected glossy paper tables is set as a table to be used for each processing in the respective sections 402, 403, and 404 (step S5).

  The color matching processing unit 402, the color conversion processing unit 403, and the gamma correction unit 404 perform color matching processing, color conversion processing, and gamma correction processing using the tables 407, 408, and 409 respectively set ( Step S6). In the color conversion processing here, according to the selection of the above table, if the input paper type is plain paper, it is converted to CMYK data, if it is coated paper, it is converted to CMYKcm data, and if it is glossy paper, it is CMYKcmRGB. Conversion to data is performed (see the correspondence table in FIG. 5).

  After these processes, the processed color material color image data is halftone processed by the halftone processing unit 405 and output from the image data output unit 406 to the printer 108, and color printing is performed by the printer 108.

Next, details of the image processing performed in the configuration of FIG. 4 will be described below.
First, the image correction processing unit 301 inputs RGB 8-bit image data (RGB data) whose brightness, contrast, and color tone are adjusted to the image data input unit 401. The RGB data input to the image data input unit 401 corresponds to the monitor color, that is, the color reproduced on the display device 109. For example, in the coordinate values of the CIE (International Lighting Commission) L * a * b * color system, which is a uniform color space, the RGB data represents the color (L_Monitor, a_Monitor, b_Monitor).

  However, as can be seen from FIG. 7, the color reproduction space of the display device 109 and the color reproduction space of the printer 108 do not coincide with each other in a uniform color space such as an L * a * b * space. As a result, an area outside the color reproduction space of the printer 108 shown in FIG. 7 and an area (shaded portion) in the color reproduction space of the display device 109 cannot be formed by the printer. More specifically, the image data expressed on the display device 109 is converted from RGB data to color material color image data by the subsequent color conversion processing unit 403, and the gradation is converted by the gamma correction unit 404. Even if the image is output from the image output unit 406 after the correction process is performed and the binarization process is performed by the halftone processing unit 405, the area cannot be formed, that is, in the color space that cannot be expressed by the printer 108. An area (shaded area) is generated.

  Therefore, on the printer 108 side, a pseudo color (L * a * b * value), that is, a display for an area (shaded portion) in the color space that can be reproduced by the display device 109 but cannot be reproduced by the printer 108. It is necessary to print by generating a pseudo color different from the color of the device 109. For this reason, the color matching processing unit 402 performs color matching processing on the RGB data input from the image data input unit 401.

<Color matching processing>
The color matching processing unit 402 compresses an area that cannot be reproduced by the printer 108 in the color reproduction space (monitor gamut) of the display device 109, thereby associating it with a point in the color reproduction space (printer gamut) of the printer 108. Process. That is, RGB 8-bit RGB data input from the image data input unit 401 is processed by the color matching processing unit 402, and R′G′B ′ 8-bit R corresponding to a point on the printer color reproduction space. Converted to 'G'B' data. This conversion is performed using a matching table (LUT) that is alternatively set by the image processing parameter setting unit 411 for the color matching processing unit 402 according to the type of paper.

  Note that the color matching processing unit 402 can perform conversion from the RGB color signal space of the display device 109 to the R′G′B ′ color signal space of the printer 108 by calculation according to the following procedure. In the following, L * a * b * space is used as the uniform color space, and cylindrical coordinates H (= atan (b / a)), S (= sqrt (a * 2 + b * 2)), V (= L *) A case where color space compression is performed on the entire space will be described. Here, atan (x) is a function for obtaining the arc tangent of x. Further, sqrt (x) is a function for obtaining √x.

  First, for example, the saturation S (= sqrt (a * × a) while maintaining the lightness L * so that the monitor RGB gamut enters the inside of the printer R′G′B ′ gamut in the L * a * b * space. * + B * × b *)) to reduce the compression. An example of this compression processing is shown in FIG.

  FIG. 8 conceptually shows gamut compression in the saturation (S) direction on the SV plane. By this process, a set of L * a * b * values in the printer gamut corresponding to the monitor RGB values is obtained. Ensure that the compressed monitor gamut fits in the printer gamut. Then, for example, L * so that the color difference ΔE (= sqrt ((L * ′ − L *) 2+ (a * ′ − a *) 2+ (b * ′ − b *) 2)) is minimized. A set of monitor (R, G, B) and printer (R ′, G ′, B ′) is determined using the a * b * value as a key. Thereby, the printer R′G′B ′ value corresponding to the monitor RGB value can be obtained.

<Color conversion processing>
The color conversion processing unit 403 converts the 8-bit R′G′B ′ data of each color converted into R′G′B ′ for the printer by the color matching processing unit 402 into each color 8 corresponding to the color material color of the printer. Convert to bit color material color image data. That is, using the color conversion table 408 that is alternatively set by the image processing parameter setting unit 411 according to the paper type input from the paper type input unit 410, each color 8-bit CMYK data, CMYKcm data, or Convert to CMYKcmRGB data.

  As the color conversion table 408, a table for conversion into CMYKcm data or a conversion into CMYKcmRGB data can be generated by replacing colors based on the table for conversion to CMYK data. For example, the value of (C, M, Y, K) = (0, 255, 255, 0) is changed to (C, M, Y, K, c, m, R, G, B) = (0, 0, 0, (0, 0, 0, 255, 0, 0). Therefore, the image processing parameter setting unit 411 stores only the table for conversion to CMYK data as the color conversion table 408, and generates a table for conversion to CMYKcm data and a table for conversion to CMYKcmRGB data. May be.

  Note that the color conversion process may be performed by an N × M-order matrix operation (color masking process) without using the color conversion table. As an example, color conversion processing from R′G′B ′ data to CMYK data by matrix calculation will be described below.

First, the density values Dr ′, Dg ′, Db ′ of R ′, G ′, B ′ are obtained by the following formula.
Dr ′ = − log (R ′ / 255)
Dg ′ = − log (G ′ / 255)
Db ′ = − log (B ′ / 255)
Next, CMY values are obtained by the following matrix calculation.

Further, the data value of K (black) is determined. There are various methods. For example, the rightmost side in the determinant is replaced with a vector [Dr′−K Dg′−K Db′−K] t obtained by subtracting the K value from each of the vector elements, and the CMY value corresponding to the ink amount is always positive. Alternatively, the K value can be determined by obtaining a masking matrix erroneously by trial chain while constraining the K value using the condition of 0.

  In addition, the color conversion process to CMYKcm data and the color conversion process to CMYKcmRGB data are performed by matrix calculation having a coefficient different from that of [Expression 1]. When performing color conversion processing by matrix calculation, the image processing parameter setting unit 411 has three sets of matrices for color conversion processing to CMYK data, color conversion processing to CMYKcm data, and color conversion processing to CMYKcmRGB data. Prepare the coefficients for calculation. Then, according to the type of paper input from the paper type input unit 410, one set of matrix calculation coefficients is selected from the three sets and set in the color conversion processing unit 403. The color conversion processing unit 403 performs color conversion processing by performing matrix calculation using a set of set coefficients.

  The matrix calculation coefficients for conversion to CMYKcm data and conversion to CMYKcmRGB data can be generated from the coefficients for conversion to CMYK data.

  Accordingly, the setting unit 411 stores only one set of coefficients for conversion to CMYK data as matrix calculation coefficients for color conversion processing, and then sets one set of coefficients for conversion to CMYKcm data and CMYKcmRGB data. A set of coefficients for conversion to may be generated.

<Gamma correction processing>
The gamma correction processing unit 404 receives N color material color image data (CMYK, CMYKcm or CMYKcmRGB data) of 8 bits for each color from the color conversion processing unit 403. The gamma correction processing unit 404 converts the input N color material color image data into 8-bit N ′ color material color image data that can be processed by the subsequent halftone processing unit 405 and outputs the converted N ′ color material color image data. Further, the gamma correction processing unit 404 performs adjustment for each color material in order to compensate for nonlinear characteristics with respect to lightness. This adjustment is performed using the gamma correction table 409 that is alternatively set by the image processing parameter setting unit 411 in accordance with the paper type input from the paper type input unit 410.

<Halftone processing>
The halftone processing unit 405 converts the 8-bit N ′ color material color image data input from the gamma correction processing unit 404 into 2-bit N ″ color material color image data that can be printed by the printer 108. Perform halftone processing.

  As this halftone processing method, for example, a Bayer type 16 × 16 matrix is first applied to the input N ′ color material color image data image. Then, when the pixel value on the corresponding image is larger than the element of this matrix, “1” is set, and when the pixel value is equal to or less than the element of the matrix, “0” is set, so that each color material color of 2 bits Obtain image data. As another halftone processing method, an error diffusion method or the like can be used.

  The thus obtained 2-inch N ″ color material color image data that can be printed by the printer is sent to the printer 108, and the image is formed (printed) on the paper.

  According to the embodiment of the present invention as described above, when the user selects and inputs plain paper as the type of paper used for printing when printing, printing in C, M, Y, and K as color material colors is performed. Is done automatically. When coated paper is input, printing in C, M, Y, K, c, and m is automatically performed. When glossy paper is input, printing in C, M, Y, K, c, m, R, G, and B is automatically performed. In other words, it is possible to automatically perform printing with a plurality of colorant colors suitable for the type of paper selected by the user for printing, and color printing is appropriate according to the type of paper used for the printing. Can be done.

  In the above embodiment, for the sake of simplicity, the types of paper used for printing are limited to the above three types. However, of course, the types are not limited to the above three types. Of course, the combination of a plurality of colorant colors according to the type of paper is not limited to the above three sets.

100 Image processing apparatus 101 CPU
102 RAM
103 ROM
104 HDD
Reference Signs List 105 Communication Interface 106 Display Interface 107 Operation Unit 108 Printer 109 Display Device 201 Operating System 202 Application Program 207 Operation Unit Driver 208 Printer Driver 209 Display Device Driver 301 Image Correction Processing Unit 302 Printer Correction Processing Unit 401 Image Data Input Unit 402 Color Matching Processing unit 403 Color conversion processing unit 404 Gamma correction unit 405 Halftone processing unit 406 Image data output unit 407 Matching table 408 Color conversion table 409 Gamma correction table 410 Paper type input unit 411 Image processing parameter setting unit

Claims (5)

An image processing apparatus for converting original color image data into ink color image data corresponding to a plurality of ink colors used for printing,
When the paper used for printing is glossy paper, the conversion using at least basic color ink and special color ink is performed. When the paper used for printing is plain paper, at least the basic color ink is used. And performing the conversion so that the spot color ink is not used.   A plurality of lookup tables for performing the conversion are prepared, and the conversion is performed by selecting and using a lookup table corresponding to the type of paper to be printed among the plurality of lookup tables. The image processing apparatus according to claim 1.   The image processing apparatus according to claim 1, wherein cyan, magenta, and yellow ink are used as the basic color ink. A data conversion method for converting original color image data into ink color image data corresponding to a plurality of ink colors used for printing,
When the paper used for printing is glossy paper, the conversion using at least basic color ink and special color ink is performed. When the paper used for printing is plain paper, at least the basic color ink is used. And performing the conversion so that the special color ink is not used. 5. The data conversion method according to claim 4, wherein cyan, magenta, and yellow inks are used as the basic color inks.

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