JP4228207B2 - Color image processing method, color image processing apparatus, color image processing program, and storage medium - Google Patents

Description

  The present invention relates to a color image processing technique for converting an input color image signal into a color image recording signal such as a color printer. More specifically, the present invention relates to color image signals of four or more colors including black as black. The present invention relates to a technique for converting color image recording signals of 5 to 7 colors including special colors.

  In the printing technology, red (R), green, and yellow (Y), magenta (M), cyan (C), and black (K: K) are used to express vivid colors that cannot be reproduced by four-color process printing. Color reproduction is performed by adding special colors composed of primary inks (G) and blue (B) and fluorescent inks to the four colors of YMCK. As a color sample of a special color, a color sample of Pantone is known, and about 1000 special colors are defined.

  However, since the printing machine can print only up to 8 colors at the same time, the number of usable spot colors is very small, at most 8 colors, and there has been a request from the designer to increase the number of usable spot colors. Further, when the spot color is changed for each plate, the printing machine needs to be cleaned, so that the spot color printing has a problem that it takes a lot of man-hours at the printing site.

  Furthermore, in the printing workflow, submission of natural images has been performed by digital cameras. Since the sRGB color space, which is the color space of the digital camera, is wider than the color gamut of YMCK process color printing, there is a need to expand the color gamut of printing for the purpose of faithful reproduction.

  In response to such problems and demands, the printing technology aims to expand the color gamut by performing color reproduction with 5 to 7 colors including at least one of RGB in addition to the process colors of YMCK. A color reproduction method called HiFi color printing has been proposed. As HiFi color printing, Pantone's hexachrome printing is widely used. In addition to YMCK four colors, R color orange (O) ink and G ink are used for color reproduction, and special colors can be reproduced. It is known that about 90% can be reproduced. This color reproduction method for HiFi color printing (hereinafter referred to as “HiFi color”) has been extended to inkjet and electrophotographic color printers, and is a common color gamut expansion technique. .

  On the other hand, with the development of computer technology, network technology and color printer technology in recent years, electronically printed manuscripts are created using computers at offices and homes from prints that have been ordered from printing offices in the past. If so, desktop publishing (hereinafter referred to as “DTP”), which is output by a color printer owned in the office or at home, etc., and if it is a large number of prints, is submitted to a print shop as an electronic manuscript has become popular. It is coming. In the case of DTP, the target output device is a printing machine including a printer. Therefore, when electronic print data is created on a computer, it is generally created with an image recording signal in printing. For example, in the case of process color printing, an electronic document is expressed using four color signals of yellow, magenta, cyan, and black YMCK, and in the case of hexachrome printing, four colors of yellow, magenta, cyan, and black YMCK are used. In addition to the above, an electronic manuscript is expressed using six color signals of YMCKOG to which orange and green are added.

  Regardless of which color signal is used, black is designated by an editor who creates an electronic manuscript from different viewpoints in characters, figures, and natural images. Specifically, for the visibility of black characters and black thin lines, the characters and figures are designated with one black color regardless of the density of the characters and thin lines. In addition, the gray representation of the graphic is expressed by yellow, magenta, and cyan process black or one black color, depending on the expression intention of the editor.

  On the other hand, in a natural image, ink is generated by performing inking processing, usually called UCR or GCR (Gray Color Replacement), by photo retouching software or a scanner. At this time, inking is not performed in the low density area in order to ensure granularity and gradation, and inking is usually performed only in the high density area. Also, since the color reproducibility deteriorates when the inking amount is large, the inking rate is often set low for natural images.

  As described above, the method of designating ink differs between characters, figures, and natural images. Therefore, when the print is output, the same black amount is obtained in the input / output as intended by the editor, and the portion designated by one black color in the document is required to be output by one black color.

  In the case of printing a large number of copies, it is not necessary to perform color conversion processing on the color signal on the electronic document by printing with a color reproduction method corresponding to the color signal specified on the electronic document. However, when a small number of copies are output by a color printer, the color reproducibility of printing and the color printer is greatly different. Therefore, an input color signal of four or more colors including black of printing is recorded as an image recording including black of the color printer. Color conversion processing to convert to a signal is required.

  Here, when the color reproduction method specified in the electronic document is HiFi color printing such as hexachrome printing, the color printer also requires a color gamut equivalent to that of HiFi color printing, so five to seven colors are required. It is necessary to perform output using a color printer that reproduces colors in Therefore, it is necessary to perform color conversion processing for converting input color signals of four or more colors including black of printing into image recording signals of five to seven colors including black of the color printer. The following methods have been proposed as conventional techniques for color conversion processing for such HiFi colors.

In a color management system (hereinafter referred to as CMS) based on specifications proposed by the International Color Consortium (hereinafter referred to as ICC), which is widely spread as an industry standard, a YMCK color signal or a YMCKOG color signal serving as an input color signal. After the color signal of the device-dependent color space is converted into the color signal of the device-independent color space such as the L ^* a ^* b ^* or XYZ color space, the color that is the color signal of the device-dependent color space It is converted into image recording signals of 5 to 7 colors of the printer. By performing such conversion processing, the input color signal and the output image recording signal match in the device independent color signal, so that it is possible to guarantee colorimetric color reproduction. Typical examples of such CMS include ColorSync installed on the Mac (registered trademark) OS of Apple and ICM mounted on Windows (registered trademark) of Microsoft.

Since conversion from four or more input color signals including black into device-independent color signals is well known, color conversion processing for HiFi colors compliant with ICC can be performed in L ^* a ^* b ^* and XYZ color spaces. It is only necessary to realize conversion from device-independent color signals having three variables to image recording signals of 5 to 7 colors.

  Patent Document 1 describes an image forming apparatus that reproduces colors using seven color process inks of YMCKRGB. In this image forming apparatus, color conversion from RGB signals of an input device such as a scanner to YMCKRGB of an output device such as printing is determined by UCR of an achromatic component (black component) and a chromatic component (RGB component). A so-called Kueppers Technique is proposed. This method is a method originally proposed as a color conversion process for the HiFi color, and since the algorithm is simple, it is widely used.

Considering the application of Kueppers Technique to color conversion conforming to ICC, device-independent color signals such as L ^* a ^* b ^* color space are converted to RGB color signals by a known 3-input 3-output color conversion means. Then, by performing UCR processing of the achromatic component and the chromatic component on the RGB signal, conversion from a device independent color signal to an image recording signal of 5 to 7 colors can be realized.

However, in Kueppers Technique, color conversion processing for HiFi color compliant with ICC can be realized, but L ^* a can be obtained from a device-dependent color space such as a YMCK color signal or a YMCKOG color signal as an input color signal. ^* When converted to device-independent color signals such as ^* b ^* or XYZ color space, the black information of the input color signal is not retained, so when converted to an image recording signal of 5 to 7 colors of a color printer However, there is a problem that the black amount of the output is different from the black amount of the input color signal.

  As the color conversion process for the HiFi color, the HiFi color gamut composed of 5 to 7 colors is divided into a color gamut composed of three or four colors including black, and the divided color gamut In the same manner as in a normal three-color or four-color printer, the image recording signals of three colors or four colors in the divided color gamut are determined from the device-independent color signals, so that five to seven from the device-independent color signals are obtained. A so-called division method for converting color into an image recording signal has been proposed. For example, Patent Document 2 discloses a direct lookup for conversion processing from a device independent color signal to an image recording signal of 5 to 7 colors using a divided color gamut combining black and other two colors having similar hues. A method for determining a coefficient of a table (hereinafter referred to as a DLUT) has been proposed. For example, in Patent Document 3, a DLUT coefficient for conversion processing from a device independent color signal to an image recording signal of 5 to 7 colors is determined using a divided color gamut combining black and other three colors. A method has been proposed.

However, although the color conversion processing for HiFi color conforming to ICC can be realized even in the division method, the black information of the input color signal is not retained as in the case of Kueppers Technique, so the black amount of the output is the input amount. There is a problem that the black amount of the color signal is different.
US Pat. No. 4,812,899 Japanese Patent Laid-Open No. 2000-32284 JP-A-2001-136401

  The present invention has been made in view of the above-described circumstances, and is a color conversion process for HiFi color that converts an input color signal including four or more colors including black into an image recording signal of five to seven colors including black. An object of the present invention is to provide a color image processing method and apparatus capable of matching the black amount of printing as an input and the black amount of a color printer as an output. In addition, an object of the present invention is to provide a color image processing method and apparatus capable of outputting a portion designated by one black color in an electronic document with one black color. It is another object of the present invention to provide a program for causing a computer to execute such an image processing method and a storage medium storing such a program.

  In the present invention, the first color signal composed of four or more colors including black is converted into black and three primary colors and one such as five to seven colors obtained by adding one or three special colors to black and yellow, magenta and cyan. In a color image processing method for converting to a second color signal of 5 to 7 colors consisting of 3 or 3 special colors, a color system from the first color signal in the first conversion step or device independent color space conversion means The device independent color signal on the color coordinate is determined, the black signal of the second color signal is determined from the black signal of the first color signal by the second conversion step or the black signal correction means, and the determined device independent color signal is determined. Is converted into the three primary color signals of the second color signal by the third conversion step or the three color signal conversion means, and corresponds to the black signal of the second color signal from the determined three primary color signals of the second color signal. The component is subtracted by the fourth conversion step or the black amount subtraction means. To determine a corrected three primary color signal, determine a component corresponding to the special color signal of the second color signal from the determined corrected three primary color signal by UCR processing relating to the special color of the second color signal, and determine the first color signal from the corrected three primary color signal. The output three primary color signals of the second color signal obtained by subtracting the component corresponding to the spot color signal of the second color signal are determined by the fifth conversion step or the chromatic UCR conversion means, and the second conversion step or the black signal correction means. The determined black signal and the output three primary color signals and the spot color signal determined by the fifth conversion step or the chromatic UCR conversion means are output as the second color signal. As described above, as the color conversion processing for the HiFi color, it is possible to match the black amounts in the input / output devices by directly determining the second black signal from the black signal of the first color signal. .

  In addition to the above configuration, in the present invention, a sixth conversion step of setting a color signal other than black in the second color signal to zero when the color signal other than black in the first color signal is zero. Or it has a non-black color correction means. With such a configuration, the input / output black amount is used as a color conversion process for the HiFi color for converting the color signal of four or more colors including the input black into the image recording signal of five to seven colors including the output black. In addition, the portion designated with one black color in the electronic document can be output with one black color.

  As a process of subtracting a component corresponding to the black signal of the second color signal from the three primary color signals of the second color signal in the fourth conversion step or the black amount subtracting means, a correction three primary color signal is determined as the second process. The component corresponding to the black signal of the second color signal is determined by multiplying the black signal of the second color signal by the UCR rate, and the component corresponding to the black signal of the second color signal is determined as 3 of the second color signal. The regulation is performed below the minimum value of the primary color signal, and the corrected three primary color signal is determined by subtracting the component corresponding to the black signal of the second color signal after the regulation from the three primary color signals of the second color signal. It is a feature. With such a configuration, by adjusting the UCR rate in consideration of color reproducibility, it becomes possible to improve deterioration of color reproducibility such as saturation reduction in a high brightness portion, and the second color signal. Since the component corresponding to the black signal does not exceed the minimum value of the YMC color signal of the second color signal, it is possible to prevent saturation reduction.

  In the fifth conversion step or the chromatic UCR conversion means, the component corresponding to the special color signal of the second color signal is subtracted from the corrected three primary color signal to determine the output three primary color signal. The component corresponding to the first spot color signal is determined from the minimum value of the color combination, and the maximum value of the component corresponding to the first spot color signal is equivalent to the second spot color signal to be subtracted from the corrected three primary color signals. The component is determined, and the component corresponding to the second spot color signal is multiplied by the UCR rate to determine the spot color signal of the second color signal, and the determined spot color signal of the second color signal is corrected from the corrected three primary color signals. The output three primary color signals of the second color signal are determined by subtraction. With such a configuration, by performing UCR processing on a combination in which the chromatic component corresponding to the spot color signal has the maximum value, color reproduction is possible even if one of the corrected three primary color signals is not zero. It becomes possible to determine the spot color to be used. In addition, it is possible to reduce the amount of color materials such as toner and ink used in color printers, reducing costs, and enabling color reproduction using special colors efficiently, so that high color reproduction can be achieved. Is possible. In addition, by adjusting the UCR rate in consideration of color reproducibility, it becomes possible to improve deterioration of color reproducibility such as an increase in lightness in a low lightness portion.

  As described above, the second color signal can be five to seven colors, which are black and yellow (Y), magenta (M), and cyan (C) plus one to three special colors. At this time, the special color may be at least one of red, green, and blue. Thereby, color conversion processing of HiFi color can be realized.

As the device-independent color signal on the color system color coordinate, an L ^* a ^* b ^* color signal that is a colorimetric value can be used. As a result, colorimetric color reproduction between the input / output devices can be matched, so that highly accurate color conversion can be realized.

  A look-up table can be used as the conversion process or black signal correction means in the second conversion step. Thus, the black amount conversion process can be executed at high speed and with high accuracy.

  The color image processing method of the present invention as described above can also be configured as a color image processing program to be executed by a computer. Further, such a color image processing program can be configured by being stored in a storage medium.

According to the configuration of the present invention as described above, the device independent color signal on the color system color coordinate is determined from the first color signal including four or more colors including black, and the black signal of the first color signal is used. The black signal of the second color signal is determined, the determined device independent color signal is converted into the three color signal of the second color signal, and the second color signal is converted from the determined three color signal of the second color signal. The component corresponding to the black signal is subtracted to determine the corrected three-color signal, and the component corresponding to the special color signal of the second color signal from the corrected three-color signal is determined from the determined corrected three-color signal by UCR processing relating to the special color signal. The subtracted output three-color signal and the spot color signal are determined, and the output three-color signal, the spot color signal, and the previously determined black signal are output as the second color signal. As a result, as a color conversion process for the HiFi color, in addition to realizing colorimetric color reproduction, it is possible to match the black amount in the input / output device. In particular, when the conventional techniques Kepper's Technique and the division method are applied to color conversion conforming to ICC, L ^* a ^* b ^{* is determined} from a device-dependent color space such as a YMCK color signal or a YMCKOG color signal as an input color signal ^. Since the black information of the input color signal is not retained when converted into device-independent color signals such as the XYZ color space or the XYZ color space, the output of the color printer when it is converted into an image recording signal of 5 to 7 colors There is a problem that the black amount is different from the black amount of the input color signal. However, in the present invention, since the black signal of the second color signal used in the output device such as a color printer is directly determined from the black signal of the first color signal which is the input color signal, the black amount in the input / output device is reduced. Therefore, it is possible to obtain a print that faithfully reproduces the amount of black specified by the editor who creates the electronic manuscript.

  Further, by setting the color signal other than black in the second color signal to zero when the color signal other than black in the first color signal is zero, the portion designated by one black color in the electronic document Can be output in one black color, and it has become possible to achieve good reproduction of black characters and black thin lines.

  In addition, it is possible to provide a color image processing method and apparatus capable of realizing highly accurate color conversion by matching the colorimetric color reproduction between the input / output devices. In addition, it is possible to improve the deterioration of color reproducibility by adjusting the UCR rate in the subtraction process of the component corresponding to the black signal and the UCR process related to the spot color signal.

  Further, the color conversion parameters are determined in advance using the color image processing method or color image processing apparatus having the above-described configuration, and the color conversion is directly performed using, for example, DLUT using the parameters. can do. Thereby, not only the color conversion process can be executed at high speed, but also a conversion process with high color conversion accuracy can be realized. Further, when the present invention is realized by hardware, since the amount of calculation is small, it can be realized by simple hardware.

  According to the present invention, there are various effects as described above.

  FIG. 1 is a block diagram showing an example of a color DTP system using the color image processing apparatus of the present invention. In the figure, 11 is a document editing device, 12 is an image processing device, 13 is an image output device, 21 is an editing device communication unit, 22 is a format conversion unit, 23 is a rasterization unit, 24 is a color conversion unit, and 25 is output device communication. Part. First, a color DTP system is taken up as an example of a system to which the color image processing apparatus of the present invention is applied, and a configuration example thereof will be described.

  The color DTP system shown in FIG. 1 includes an original editing apparatus 11, an image processing apparatus 12, and an image output apparatus 13 as a whole. The manuscript editing device 11 is a device for creating an electronic print manuscript, and outputs electronic manuscript data of page description language and raster image data to the image processing device 12. Specifically, as the document editing apparatus 11, there are a case where a document is edited by various DTP applications on a general-purpose computer such as a personal computer, and a case where a document is edited by a dedicated computer.

  When a general-purpose computer is used, the electronic manuscript is edited using various DTP software. The created electronic document is converted to PostScript (registered trademark), which is a page description language, by, for example, a PostScript (registered trademark) printer driver from Adobe, and is output to the image processing apparatus 12 via a network such as Ethernet (registered trademark). The page description language for sending from the DTP personal computer to the image processing apparatus 12 is not limited to PostScript (registered trademark), and it is obvious that any page description language may be used.

  When a dedicated computer is used, an electronic manuscript can be edited by a dedicated workstation and application called Color Electric Presto System (hereinafter referred to as CEPS). The created electronic document is, for example, a raster information format such as TIFF / IT format which is a standard of raster image data or Scitex format which is widely used as electronic data for printing, and is transmitted over a network such as Ethernet (registered trademark). It is output to the image processing device 12. Of course, the raster information transmitted from the CEPS to the image processing apparatus 12 is not limited to TIFF / IT, and it is obvious that any image format may be used as long as it is raster format image data.

  As color signals for electronic manuscripts, it is common to assume a printing machine as an output device in color DTP, and so-called YMCK color signals for yellow, magenta, cyan and black are used to specify the color of the electronic manuscript. Is done. In recent years, there is a printing technology that uses five or more colors of ink called HiFi color printing, which aims to improve image quality by expanding the color gamut. In that case, red, green and blue are usually used as special colors for YMCK color signals. An electronic manuscript is expressed using color signals of 5 to 7 colors including 1 to 3 colors. In this embodiment, as a color signal on an electronic original, hexachrome printing, which is a kind of HiFi color printing, is assumed, and a YMCKOG color signal that performs color reproduction with six colors obtained by adding orange and green to a YMCK color signal is used. Will be described. However, it is obvious that any color signal may be used as long as it includes black with four or more color signals.

  The image processing apparatus 12 includes an editing apparatus communication unit 21, a format conversion unit 22, a rasterization unit 23, a color conversion unit 24, and an output device communication unit 25 as a whole, and code information input from the document editing apparatus 11. Or the raster information electronic document is converted into a format that can be output by the image output device 13 and output to the image output device 13.

  An electronic document designated by color signals such as YMCK, YMCKOG, and YMCKRGB transmitted from the document editing device 11 is received by the editing device communication unit 21 through a network such as a LAN, and transferred to the format conversion unit 22 and the rasterization unit 23. The The page description language is converted into raster format image data that can be output by the image output device 13 by the rasterizing unit 23. The raster format image data such as TIFF / IT is subjected to resolution conversion and format conversion processing in the format conversion unit 22 and converted into raster format image data that can be output by the image output device 13.

  The YMCKOG color signal transferred from the rasterizing unit 23 and the format converting unit 22 is selected from among red, green, and blue as the special colors of yellow, magenta, cyan, and black which are image recording signals of the image output device 13 by the color converting unit 24. It is converted into an image recording signal of 5 to 7 colors with at least one color added. In the following description, three specific colors of red, green, and blue are assumed as specific examples of the special colors, and converted into YMCKRGB seven-color image recording signals using red, green, and blue together with yellow, magenta, cyan, and black. To do. Of course, the special colors used are not limited to red, green and blue.

  The image recording signal color-converted by the color conversion unit 24 is transferred to the output device communication unit 25. The output device communication unit 25 accumulates the image recording signals that have undergone the processing up to the color conversion unit 24 and appropriately transfers them to the image output device 13, so that the processing speed of the image processing device 12 and the image output device 13 can be increased. Absorb the difference. Then, in the image output device 13, an image is formed on the sheet in accordance with the image recording signal of the raster format of YMCKRGB 7 colors.

  The image output device 13 may be any device as long as it records an image with five or more color signals. For example, any image output device may be used as long as it is a color image output device such as an electrophotographic color printer, printing, ink jet method, thermal transfer method, and silver salt photographic method.

  Next, the color conversion unit 24 that is a configuration that implements the color image processing apparatus of the present invention or the color image processing method of the present invention will be described. FIG. 2 is a block diagram showing a first embodiment of the color conversion unit. In the figure, 31 is a device independent color space conversion unit, 32 is a gradation correction unit, 33 is a non-black color determination unit, 34 is a three primary color signal conversion unit, 35 is a black amount subtraction unit, 36 is a chromatic UCR conversion unit, and 37 is A non-black color correcting unit 38 is an image recording signal output unit.

The YMCKOG color signal transferred from the rasterizing unit 23 and the format conversion unit 22 to the color conversion unit 24 is input to the device independent color space conversion unit 31, the gradation correction unit 32, and the non-black color determination unit 33. The device independent color space conversion unit 31 determines an L ^* a ^* b ^* color signal, which is a device independent color space, from the input YMCKOG color signal, and transfers it to the three primary color signal conversion unit 34.

  In the gradation correction unit 32, the black amount K color signal input from the rasterization unit 23 and the format conversion unit 22 is expressed by the image output device 13 with the same or substantially the same brightness as the K color signal. The black amount K ′ color signal in the image output device 13 is determined and transferred to the black amount subtracting unit 35 and the image recording signal output unit 38.

  Further, the non-black color determination unit 33 determines whether or not the input YMCOG color signals are all zero. If all are zero, the determination signal Flag is transferred to the non-black color correction unit 37.

The three primary color signal conversion unit 34 converts the L ^* a ^* b ^* color signal input from the device independent color space conversion unit 31 to a Y "M" C "color signal that is a complementary primary color signal in the image output apparatus 13. And is transferred to the black amount subtracting unit 35.

  The black amount subtracting unit 35 subtracts the component corresponding to the K ′ color signal from the Y “M” C ”color signal input from the three primary color signal converting unit 34 to correct Y ′ ″ M ′ which is the corrected three primary color signal. The “C ′” color signal is determined and transferred to the chromatic UCR converter 36. In general, in this step, the black amount is often generated by UCR, but in the present invention, the input black amount is used. The black amount K ′ color signal is directly obtained from the K color signal by the gradation correction unit 32, and the black amount is not generated here, and conversely, the black amount K ′ color signal obtained by the gradation correction unit 32 is obtained. It is used to correct the Y "M" C "color signal and determine the Y '' 'M' '' C '' 'color signal, which is greatly different from the conventional color processing.

  The chromatic UCR conversion unit 36 outputs three colors from the Y ′ ″ M ′ ″ C ′ ″ color signal input from the black amount subtraction unit 35 by UCR processing related to the R′G′B ′ color signal which is a special color signal. The Y′M′C ′ color signal as the signal and the R′G′B ′ color signal as the special color signal are determined and transferred to the non-black color correction unit 37.

  When the determination signal Flag is input from the non-black color determination unit 33, the non-black color correction unit 37 transfers the Y′M′C ′ color signal and the R′G′B ′ color signal as zero to the image recording signal unit 38. . When the determination signal Flag is not input, the Y′M′C ′ color signal and the R′G′B ′ color signal received from the chromatic UCR conversion unit 36 are transferred to the image recording signal unit 38.

  The image recording signal output unit 38 outputs the Y′M′C′R′G′B ′ color signal input from the non-black color correction unit 37 and the K ′ color signal input from the gradation correction unit 32 to the output device communication unit. 25. Thereby, the color conversion processing in the color conversion unit 24 is completed.

  Next, processing in each unit will be specifically described. First, as the device-independent color space conversion unit 31, a matrix operation type color conversion circuit, a direct lookup table type color conversion circuit, or a neural network type color conversion circuit widely used as a color conversion circuit is used. Is possible. In this specific example, a 6-input 3-output neural network type color conversion circuit is used.

The color conversion parameter of the device independent color space conversion unit 31 can be determined by the following method. First, a patch of printed matter is output for any combination of YMCKOG color signals of hexachrome printing input from the document editing device 11, and the colorimetric value (L ^* a ^* b ^* ) is measured with a commercially available colorimeter. Then, the colorimetric value (L ^* a ^* b ^* ) of printing corresponding to the input YMCKOG color signal is obtained, and the conversion characteristic of the colorimetric value (L ^* a ^* b ^* ) with respect to the input data (YMCKOG) is modeled. . High-order polynomials and neural networks are used for such models. In this specific example, the neural network was trained in the combination of YMCKOG data and L ^* a ^* b ^* data, and the color characteristics of the input hexachrome printing were modeled. As the device independent color space conversion unit 31, the obtained neural network may be used as it is.

  As a neural network used in this specific example, for example, the document “High-precision color conversion by flexible UCR -High-precision printer model by neural network-”, Kazumasa Murai, Japan Hard Copy '94 papers, pp. Learning can be performed by the back pro vacation method using the neural network shown in 181-184. The image recording signal in this document is YMCK 4 colors, but by increasing the number of cells in the first layer from 4 to 6 in the neural network, the image recording signal is used as a color conversion model for the HiFi color of 6 colors. It is possible. Of course, a neural network is used as the color conversion model, and other polynomial models and conversion table type color conversion models can also be applied.

Further, as a combination of the image recording signals YMCKOG used for modeling the color characteristics of hexachrome printing, for example, 5 × 5 × 5 × 5 × 5 × 5 = 15625 in which the dot area ratio of each color is 25%. The combination of patches can be output by a printing machine, colorimetric, and the patch and colorimetric value can be used in pairs. Color measurement can be performed, for example, by using X-Rite 938, which is a colorimeter manufactured by X-Rite, as a colorimeter, and measuring conditions are D50 and measuring L ^* a ^* b ^* of a two-degree field of view. . An arbitrary number of color patches can be used for measurement, but as many patches as possible are desirable in order to improve the accuracy of the color conversion model. As the color system used for the measurement, the L ^* a ^* b ^* color system which is a uniform color space is used here, but other color systems such as an XYZ color system may be used. However, a uniform color space is preferred because color differences are evaluated when learning a neural network.

  Furthermore, the device-independent color space conversion unit 31 is not limited to hexachrome printing consisting of six YMCKOG color signals, and is configured to input four or more color signals including black. Obviously you can do that. As color signals of four or more colors including black used for printing, process color printing consisting of four commonly used YMCK color signals, and HiFi color consisting of seven YMCK colors plus red, green and blue There is printing. Even color signals of four or more colors can be converted into the device-independent color space by the same method as described above. For example, when 7 color signals are input, a 7-input 3-output neural network may be applied to the device independent color space conversion unit 31.

Next, the tone correction unit 32 uses a one-dimensional look-up table, and the K color signal of one black ink to be input has a lightness equivalent to the K color signal of the black color in the output device 13. 'Can be converted to a color signal. As a method for creating the look-up table, for the printing and image output device 13, the dot area ratio is quantized to 8 bits, and the lightness L ^* when each dot area ratio is changed from 0 to 255 is measured. The value of the output black amount K ′ having the same lightness may be obtained from the lightness L ^* at the time of the input black amount K and set to the value of the lookup table.

  Here, a one-dimensional lookup table is used as the gradation correction unit 32 in order to correct the gradation of the input / output black amount with high speed and high accuracy. Anything can be used. In addition, when using a lookup table, it is clear that the number of quantization divisions is not limited to 8 bits. Further, here, the conversion characteristic of the tone correction unit 32 is set so that the blackness lightness between the input / output devices matches, but the conversion characteristic is set so as to match the blackness density between the input / output devices. May be. In addition, it is desirable to match the lightness and density of the black amount in the input / output device. However, the conversion characteristics may be set so that the lightness and density are almost equal even if they are not completely matched.

Next, the three primary color signal conversion unit 34 converts the L ^* a ^* b ^* color signal obtained from the device independent color space conversion unit 31 into Y "M" C "color which is the three primary colors of the complementary color system in the image output device 13. A known color conversion processing method typified by CMS based on specifications proposed by the ICC is used as the three-input three-output color conversion from the colorimetric values to the three primary colors of the complementary color system. For example, conversion from an L ^* a ^* b ^* color signal to a Y "M" C "color signal can be performed using a three-dimensional direct lookup table.

As an example of the three primary color signal conversion unit 34, a three-dimensional DLUT can be used. For example, a value obtained by dividing each axis of the input L ^* a ^* b ^* color signal into 16 is used as an input address, and interpolation calculation is performed by three-dimensional cube interpolation from the values of a plurality of grid points obtained based on the input address. Thus, it is possible to use a three-dimensional DLUT that calculates Y "M" C "color signals which are the three primary colors of the complementary color system in the image output apparatus 13. Of course, the interpolation method is not limited to the cubic interpolation method, and is well known. Other interpolation methods such as triangular prism interpolation and tetrahedral interpolation may be applied, and it is clear that the number of divisions for each axis of input is not limited to 16 divisions.

The color conversion parameters of the three-dimensional direct lookup table in the three primary color signal conversion unit 34 can be determined by the following method. First, similarly to the case where the color conversion parameter of the device independent color space conversion unit 31 is determined, a color patch for an arbitrary combination of Y′M′C ′ color signals of the image output device 13 is output, and the colorimetric value ( L ^* a ^* b ^* ) is measured with a commercially available colorimeter, and the colorimetric values (L ^* a ^* b ^* ) of the image output device 13 corresponding to the Y'M'C 'color signal as the input color signal are obtained. Then, the conversion characteristic of the colorimetric value (L ^* a ^* b ^* ) with respect to the input data (Y′M′C ′) is modeled. This modeling can model the color characteristics of the image output device 13 using a neural network, similarly to the case where the color conversion parameter of the device independent color space conversion unit 31 is determined. Of course, a neural network is used as the color conversion model, and other polynomial models and conversion table type color conversion models can also be applied.

As a combination of the image recording signals Y′M′C ′ used for modeling the color characteristics of the image output apparatus, for example, 11 × 11 × 11 = 1331 patches each having a dot area ratio of 10%. The combination can be obtained by outputting the combination with the image output device 13 and measuring the color. As in the case of the device-independent color space conversion unit 31, the color measurement conditions are X-Rite 938, which is a colorimeter manufactured by X-Rite, as the colorimeter, and the measurement conditions are D50 and L ^{* of} 2 degree visual field ^. a ^* b ^* was used. An arbitrary number of color patches can be used for measurement, but as many patches as possible are desirable in order to improve the accuracy of the color conversion model. As the color system used for the measurement, the L ^* a ^* b ^* color system which is a uniform color space is used here, but other color systems such as an XYZ color system may be used. However, a uniform color space is preferred because color differences are evaluated when learning a neural network.

Here, the color conversion model by the neural network can be expressed by the following function.
(L ^* , a ^* , b ^* ) = F (Y ″, M ″, C ″) (1)
Since the equation (1) is a non-linear function with three inputs and three outputs, the L ^* , a ^* , and b ^* color signals, which are the input addresses of the three-dimensional direct lookup table in the three primary color signal conversion unit 34, are represented in the equation (1). It is possible to obtain a colorimetrically matching Y "M" C "color signal using a known numerical solution such as Newton's method, etc. The calculated Y" M "C" color signal is three-dimensionally obtained. What is necessary is just to set to the grid point of a direct lookup table. In this way, it is possible to determine the color conversion parameters of the three primary color signal conversion unit 34 by solving the color conversion model of the image output device 13.

  Here, the YMC color space in the image output device 13 is used as the color space of the Y "M" C "color signal output from the three primary color signal conversion unit 34. However, the color conversion accuracy, the degree of utilization of the color gamut, etc. In view of this, other YMC color spaces may be used, and conversion to the RGB color space, which is the primary color of the three primary colors, may be performed instead of the YMC color space, which is the complementary primary color. .

Next, the black amount subtraction unit 35 corresponds to the K ′ color signal obtained from the gradation correction unit 32 from the Y “M” C ”color signal input from the three primary color signal conversion unit 34 as described above. Subtract the part and convert it to Y '''M''' C '''color signal.Here, Y "M" C "color is calculated by the calculation based on the following formulas (2) to (7). A process of subtracting a portion corresponding to the K ′ color signal from the signal is realized. Here, in the expression (4), since it is necessary to judge the condition, the calculation is described in C language grammar here.
Kacro = UCRAcro (K ′) × K ′ (2)
Kmin = min (Y ″, M ″, C ″) (3)
if (Kacro> Kmin) Kacro = Kmin (4)
Y ″ ′ = Y ″ −Kacro (5)
M ′ ″ = M ″ −Kacro (6)
C ″ ′ = C ″ −Kacro (7)

  Here, Kacro represents an achromatic component of the Y "M" C "color signal determined from the K 'color signal and the Y" M "C" color signal. UCR acro (K ′) is a UCR function of an achromatic component, and is a function that defines a UCR rate of an achromatic component for a K ′ color signal. Usually, in order to subtract the portion corresponding to the K ′ color signal from the Y ″ M ″ C ″ color signal, it is desirable to set UCR acro (K ′) to 100% of the constant rate. However, Kacro is set to UCR acro (K ′ ), For example, in order to improve deterioration of color reproducibility such as saturation reduction in the high lightness portion, color reproduction such as setting the UCR rate low when the K ′ color signal is in the high lightness portion. The UCR rate can be adjusted in consideration of the characteristics, and the Kacro is determined by multiplying the K ′ color signal by the UCR acro (K ′), which is the UCR rate of the achromatic component, as shown in Equation (2). be able to.

  Kmin is the minimum value of the Y "M" C "color signal and represents the achromatic component of the Y" M "C" color signal, as shown in equation (3). In the equation (4), when Kacro exceeds Kmin, by restricting to Kmin, the achromatic component subtracted from the Y "M" C "color signal does not exceed the maximum value, and the saturation decreases. It is possible to prevent the color reproducibility of the color of Y '' 'M' '' C '' 'as shown in the equations (5) to (7). It can be calculated by subtracting the achromatic component Kacro from the color signal.

  In the above example, the UCR process for subtracting the portion corresponding to the K ′ color signal from the Y ”M” C ”color signal is realized by the calculation based on the formulas (2) to (7). For the sake of simplicity, the operations of the equations (2) to (4) may be omitted, and the K ′ color signal may be directly subtracted instead of Kacro in the equations (5) to (7).

Next, the chromatic UCR conversion unit 36 calculates a special color amount R′G′B ′ color signal from the Y ′ ″ M ′ ″ C ″ ′ color signal obtained from the black amount subtraction unit 35, and Y ″. A component corresponding to the special color amount R'G'B 'color signal (chromatic component) is subtracted from the'M''C'''color signal by UCR processing to convert it into a Y'M'C' color signal. . For example, UCR processing relating to the chromatic component can be realized by calculation based on the following equations (8) to (14). Here, in the expressions (12) to (14), since it is necessary to judge the condition, the calculation is described in C language grammar here.
Rcro = min (Y ′ ″, M ′ ″) (8)
Gcro = min (Y ′ ″, C ′ ″) (9)
Bcro = min (C ′ ″, M ′ ″) (10)
Cmax = max (Rcro, Gcro, Bcro) (11)
if (Cmax == Rcro) {
R ′ = UCRr (Rcro) × Rcro
G '= 0
B '= 0
Y '= Y''' -R '
M '= M''' -R '
C '= C'''
} (12)
else if (Cmax == Gcro) {
R ′ = 0
G ′ = UCRg (Gcro) × Gcro
B '= 0
Y '= Y''' -G '
M '= M'''
C '= C''' -G '
} (13)
else (Cmax == Bcro) {
R ′ = 0
G '= 0
B ′ = UCRb (Bcro) × Bcro
Y '= Y'''
M '= M''' -B '
C '= C''' -B '
} (14)

  Here, Rcro represents a chromatic component (R ′ color signal) of the Y ′ ″ M ′ ″ color signal determined from the minimum value of the Y ″ ′ M ′ ″ color signal. Similarly, Gcro represents the chromatic component (G ′ color signal) of the Y ′ ″ C ′ ″ color signal determined from the minimum value of the Y ′ ″ C ′ ″ color signal, and Bcro represents C ′. “M ′” represents a chromatic component (C ′ color signal) of the C ′ ″ M ′ ″ color signal determined from the minimum value of the color signal.

  As UCR processing related to known chromatic components, UCR processing in Kueppers Technique shown in Patent Document 1 (US Pat. No. 4,812,899) is representative, but in UCR processing in Kueppers Technique, chromatic components are related. In the UCR process related to the achromatic component in the previous stage of the UCR process, the UCR rate is 100%. Therefore, among the Y '' 'M' '' C '' 'color signals input to the UCR process related to the chromatic component One color is zero. Therefore, in the UCR processing relating to the chromatic component, the minimum value of the two non-zero color signals of the Y ′ ″ M ′ ″ C ′ ″ color signal is calculated, thereby obtaining the special color amount R′G′B ′ color signal. It is possible to uniquely determine one of the colors, and by subtracting the determined spot color amount from the two non-zero color signals of the Y '' 'M' '' C '' 'color signal, It is possible to realize UCR processing for the chromatic component.

  However, in the present invention, since the black amount K ′ color signal input to the black amount subtracting unit 35 depends on the black amount K color signal specified on the electronic document, the UCR is obtained from the Y ”M” C ”color signal. Even if the component corresponding to the black amount K ′ color signal is subtracted under the condition that the rate is 100%, the color signal of one of the Y ′ ″ M ′ ″ C ′ ″ color signals is zero. Further, the same can be said when the UCR rate is set lower than 100% in the black amount subtracting unit 35. Therefore, it is considered that the UCR processing relating to the chromatic component known in the present invention cannot be applied. It is done.

  Therefore, in the present invention, the maximum value Cmax of the chromatic components Rcro, Gcro and Bcro is calculated from the equation (11), and the chromatic component becomes the maximum value by the arithmetic processing based on the equations (12) to (14). For the combination, a special color amount R′G′B ′ color signal is determined, and a component corresponding to the special color amount is subtracted from the Y ′ ″ M ′ ″ C ′ ″ color signal by UCR processing to obtain Y′M. The processing system was configured to perform conversion to a “C” color signal.

  In this way, by performing UCR processing for a combination in which the chromatic component has a maximum value, one of the Y ′ ″ M ′ ″ C ″ ′ color signals is not zero. It is also possible to determine the spot color used for color reproduction. In addition, the amount of color material such as toner and ink used in the image output device 13 can be reduced, and the cost can be reduced. At the same time, it is possible to achieve color reproduction that uses special colors efficiently, and it is possible to realize color reproduction with high saturation. However, in the equations (12) to (14), when Rcro, Gcro and Bcro are all equal, or when there are two chromatic components equal to Cmax, the spot colors are in the order of R ′, G ′ and B ′. Priority will be given to color reproduction. In the above example, the priority order for using the spot colors for color reproduction is set in the order of R ′, G ′, and B ′. However, the priority order is obviously not limited to this order.

  Here, UCRr (Rcro), UCRg (Gcro), and UCRb (Bcro) are UCR functions of chromatic components, and are functions that define respective UCR rates for chromatic components Rcro, Gcro, and Bcro. As shown in the equations (12) to (14), the special color amount R′G′B ′ color signal includes UCRr (Rcro), UCRg (Gcro), and UCRb, which are UCR ratios of chromatic components in Rcro, Gcro, and Bcro. It can be determined by multiplying each by (Bcro).

  Usually, in order to subtract the portion corresponding to the special color amount R′G′B ′ color signal from the Y ′ ″ M ′ ″ C ′ ″ color signal, the UCR rate is set to 100% of the constant rate. Although it is desirable, the spot color amount R′G′B ′ is controlled by the UCR function, for example, in order to improve deterioration of color reproducibility such as brightness increase in the low brightness portion, the spot color amount R′G′B. 'The UCR rate can be adjusted in consideration of color reproducibility, for example, by setting the UCR rate low when the color signal is a low brightness portion.

  Here, UCR processing for subtracting the component corresponding to the special color amount R′G′B ′ color signal from the Y ′ ″ M ′ ″ C ′ ″ color signal by the calculation based on the equations (8) to (14). However, in order to simplify the arithmetic processing, the UCR function in Expressions (12) to (14) is omitted, and Rcro, Gcro, and Bcro are directly determined as the special color amount R′G′B ′ color signal. You may do it.

  Next, the non-black color determination unit 33 determines whether or not the input YMCOG 5 color signals are simultaneously zero, and if so, the determination flag Flag is transferred to the non-black color correction unit 37. The non-black color correction unit 37 corrects all the Y′M′C′R′G′B ′ color signals obtained by the chromatic UCR conversion unit 36 to zero when the determination flag Flag is received from the non-black color determination unit 33. . As a result, black characters and black thin lines expressed with one black color in an electronic document can be expressed with one black color, and the reproducibility of black characters and black thin lines can be greatly improved. On the other hand, in the black and white portion of the input / output, Y'M'C'R'G 'even if the brightness is matched due to the difference in the color material between the printing and the image output device 13 and the difference in the image structure. Although a slight color difference is caused by correcting the B ′ color signal to zero, it is at a level that does not cause a visual problem.

  Here, the Y′M′C′R′G′B ′ color signal obtained by the chromatic UCR conversion unit 36 in the non-black color correction unit 37 is all set to zero when the determination flag Flag is received from the non-black color determination unit 33. Although the correction is made, if the accuracy of color matching in input / output is more important, the Y'M'C'R'G'B 'color signal may not be corrected. However, in order to ensure the black one-color reproduction of black characters and black thin lines, Y'M'C'R'G'B 'color signal correction processing is performed in the non-black color correction unit 37 as in the present invention. It is desirable to configure as follows.

  Finally, the Y′M′C′K′R′G′B ′ color signal, which is an image recording signal to be input to the image output device 13, is transferred to the output device communication unit 25 by the image recording signal output unit 38. The color conversion process in the conversion unit 24 is completed.

  FIG. 3 is an explanatory diagram of a comparison result of color conversion characteristics between the present invention and the prior art. In order to confirm the effectiveness of the present invention, in the case of the present invention, the case where the color conversion unit 24 is configured as in the present embodiment and the case of Kueppers Technique represented by Patent Document 1 (US Pat. No. 4,812,899). Is applied to the color conversion processing conforming to the ICC, and the case where the division method represented by Patent Document 3 (Japanese Patent Laid-Open No. 121-136401) is applied to the color conversion processing conforming to the ICC. The consistency of the amount and the reproduction of black ink were evaluated. The result is shown in FIG.

Regarding the configuration of the color conversion unit 24 other than the present invention, the conversion from the hexachrome printing YMCKOG color signal to the device-independent L ^* a ^* b ^* color signal is performed by a known 6-input 3-output DLUT based on ICC. In the case of Kuperpers Technique, conversion from an L ^* a ^* b ^* color signal to an RGB color signal is performed by a known 3-input 3-output DLUT, and the RGB color signal is converted to Y'M'C'K'R '. For the conversion to the G′B ′ color signal, the embodiment of Patent Document 1 was applied as it was. In Patent Document 1, the UCR rate is not defined, but the UCR function relating to the achromatic component and the chromatic component is considered to correspond to 100% of the constant rate. In the case of the division method, the conversion from the L ^* a ^* b ^* color signal to the Y′M′C′K′R′G′B ′ color signal is based on the input conditions of the black amount and the special color amount that are similar to those in Patent Document 1. In order to achieve this, the conditions of Max Black (representing the condition that maximizes the black amount) and max HFC (representing the condition that maximizes the special color amount) in the example of Patent Document 3 are applied as they are. Also in the present invention, the UCR function relating to the achromatic component and the chromatic component is set to 100% of a constant rate in order to set the black amount and the special color amount as input conditions similar to Patent Document 1.

  As an example of a color signal to be input, as an example of black characters and black thin lines in an electronic document, FIG. 3A shows a color conversion result when the input color signal is black (K is 100% and YMCOG is 0%). FIG. 3B shows the color conversion result when the input color signal does not have black (YMC is 50% and KOG is 0%) as an example of the high lightness portion to the medium lightness portion of the natural image in the electronic document. .

  As can be seen from FIG. 3A, in the present invention, when the input color signal is a single black color, a black K ′ signal for storing the black K signal is obtained and the non-black color determination unit 33 determines that the black color is black. Since detection and correction other than the black K ′ signal are made zero, a black amount equivalent to that of the input image can be obtained and reproduction with a single black color is possible. On the other hand, with the division method which is the prior art, it is understood that a black amount substantially equal to that of the input image can be obtained, but black monochrome reproduction is impossible. Further, with Kueppers Technique, a color conversion result almost similar to that of the present invention can be obtained, but it can be seen that there is a slight blue color signal, and reproduction with black ink is not realized completely. As described above, when the input color signal is black only in the conventional technology, it is impossible to reproduce in black, so the image quality of black characters and black thin lines deteriorates. Since reproduction is performed, black characters and black thin lines can be output with high image quality.

  Further, as can be seen from FIG. 3B, in the present invention, when there is no black in the input color signal, the state without this black is stored in the gradation correction unit 32, so that a black amount equal to the input image is obtained. And not inked. On the other hand, it can be seen that in the conventional technique Kuppers Technique and the division method, the ink amount is completely different from that of the input image, and the ink is inked. As described above, in the conventional technique, when the input color signal does not have black ink, the inking that is different from the intention of the editor is performed, and it is understood that the graininess and color reproducibility of the natural image are deteriorated. In the present invention, since such inking does not occur, image formation with high image quality is possible. For example, when the editor does not intend to use black in the input color signal, it is possible to form an image without using black in the output device.

  As described above, the color conversion unit 24 performs the above-described color conversion processing on the YMCKOG 6 color signals designated by the document editing apparatus 11, so that the input black amount and the output color printer. It is possible to match the amount of ink. Further, it is possible to output a portion designated with one black color on the electronic document with one black color.

  FIG. 4 is a block diagram showing a second embodiment of the color conversion unit. In the figure, reference numeral 39 denotes a DLUT color conversion unit. In the second embodiment of the color conversion unit 24, an example is shown in which the color conversion unit 24 is configured by a 6-input 7-output DLUT color conversion unit 39.

  The DLUT color converter 39 receives a YMCKOG color signal and outputs a Y'M'C'K'R'G'B 'color signal corresponding to the YMCKOG color signal. It consists of For example, Y′M′C′K′R which is an image recording signal of the image output device 13 by performing interpolation calculation by 6-dimensional cubic interpolation using a value obtained by dividing each axis of the input YMCKOG color signal into 8 as an input address. A 6-dimensional DLUT for calculating the 'G'B' color signal can be used. Of course, the interpolation method is not limited to the cubic interpolation method, and other methods such as triangular prism interpolation and tetrahedral interpolation may be applied as long as they are known interpolation methods. It is also clear that the number of divisions for each axis of input is not limited to eight divisions.

  Here, the color conversion unit 24 is configured by a 6-dimensional direct look-up table. However, the color conversion unit 24 is not limited to this as long as 6-input 7-output color conversion can be performed, and any known color conversion method such as a neural network may be used. For example, other color conversion methods may be applied. Further, the color signal input to the color conversion unit 24 is not limited to the YMCKOG color signal for hexachrome printing, but includes black, such as a YMCK color signal for process color printing and a YMCKRGB color signal for HiFi color printing. Obviously, it is sufficient if the color signal is more than the color. Since the number of dimensions of the DLUT color conversion unit 39 matches the number of input color signals, for example, when the input color signal is a YMCK color signal for process color printing, a four-dimensional DLUT is required. In the case of YMCKRGB color signals for HiFi color printing, it is clear that a 7-dimensional DLUT is necessary.

  FIG. 5 is a flowchart showing an example of the color conversion parameter determination process of the DLUT color conversion unit 39 in the second embodiment of the color conversion unit 24. This process is substantially the same as the process performed by each unit of the color conversion unit 24 in the first embodiment.

First, in S1, a color patch for an arbitrary combination of the hexachrome printing YMCKOG color signal and the image recording signal Y′M′C ′ of the image output device 13 is printed out by the hexachrome printing and image output device 13 to perform colorimetry. A colorimetric value L ^* a ^* b ^* at that time is measured using a meter. The combination of the YMCKOG color signal for hexachrome printing and the image recording signal Y′M′C ′ of the image output device 13 and the color measurement conditions may be the same as those in the first embodiment.

In S2, the neural network 1 and the neural network 2 which are color conversion models are trained using the data sets of YMCKOG and Y′M′C ′ and L ^* a ^* b ^* obtained in S1 as teacher data, respectively. The neural network may be the same as that used in the first implementation described above. The neural network 1 models the color conversion characteristics of the input side device when converting the device-dependent YMCKOG color signal into a device-independent L ^* a ^* b ^* color signal. The neural network 2 models the color conversion characteristics of the output side device when converting the device-independent L ^* a ^* b ^* color signal to the device-dependent Y′M′C ′ color signal.

In S <b ^{> 3} , the color measurement value L ^* a ^* b ^* for the input address value YMCKOG of the DLUT color conversion unit 39 is determined by the neural network 1.

  In S4, the black amount K ′ in the image output device 13 having a lightness equivalent to the input address value K of the DLUT color conversion unit 39 is determined by a one-dimensional lookup table. The method for determining the one-dimensional lookup table may be the same as in the first embodiment described above.

In S5, L ^* a ^* b ^* obtained in S3 is input to the neural network 2 and solved by a numerical solution method to obtain a colorimetrically matching Y "M" C "color signal.Y" M "C “The color signal can be determined using the same method as in the first embodiment.

  In S6, the Y ′ ″ M ′ ″ C ′ ″ color signal is determined by subtracting the component corresponding to the black amount K ′ obtained in S4 from the Y ″ M ″ C ″ color signal obtained in S5. The Y ′ ″ M ′ ″ C ′ ″ color signal determination method may be the same as that in the first embodiment.

  In S7, the Y'M'C'R'G'B 'color signal is determined by UCR processing corresponding to the spot color signal from the Y' '' M '' 'C' '' color signal obtained in S6. The UCR process corresponding to the spot color signal may be the same method as in the first embodiment.

  In S8, when the input address values YMCOG of the DLUT color conversion unit 39 are all zero, the Y'M'C'R'G'B 'color signal obtained in S7 is corrected to zero.

  Finally, in S9, the obtained Y′M′C′K′R′G′B ′ is set as the grid point of the DLUT color conversion unit 39, thereby determining the color conversion parameter of the DLUT color conversion unit 39. Can do.

  In this way, the color conversion parameters of the DLUT color conversion unit 39 are determined in advance. Note that what is set in the DLUT color conversion unit 39 is, for example, the value of Y′M′C′K′R′G′B ′ at a lattice point obtained by dividing each axis of the input YMCKOG color signal into eight. The YMCKOG color signal color signal that is actually input is not limited to a grid point, and an arbitrary YMCKOG color signal is input. Therefore, when performing color conversion processing, the addresses of one or more grid points are generated based on the input YMCKOG color signal, and the values of Y'M'C'K'R'G'B 'are read out. By performing the interpolation process, the Y′M′C′K′R′G′B ′ color signal corresponding to the input YMCKOG color signal is obtained.

  As described above, in the second embodiment, when the color conversion process is performed in the color conversion unit 24 as in the configuration shown in the first embodiment, the process is performed in advance without performing a process with a large amount of calculation. Since the direct color conversion is performed directly using the direct lookup table, the color conversion can be realized at a very high speed. Further, when configured with hardware, the amount of calculation is small, so that a simple configuration can be achieved.

  FIG. 6 is an explanatory diagram of an example of a computer program and a storage medium storing the computer program when the function of the color image processing apparatus or the color image processing method of the present invention is realized by the computer program. In the figure, 101 is a program, 102 is a computer, 111 is a magneto-optical disk, 112 is an optical disk, 113 is a magnetic disk, 114 is a memory, 121 is a magneto-optical disk apparatus, 122 is an optical disk apparatus, and 123 is a magnetic disk apparatus.

  The function of the color conversion unit 24 described in each of the above-described embodiments, or a part or all of the configuration of the image processing apparatus 12 other than the color conversion unit 24 illustrated in FIG. It is possible to realize. In that case, the program 101 and data used by the program can be stored in a computer-readable storage medium. A storage medium is a signal format that causes a state of change in energy such as magnetism, light, electricity, etc. according to the description of a program to a reader provided in the hardware resources of a computer. Thus, the description content of the program can be transmitted to the reading device. For example, a magneto-optical disk 111, an optical disk 112 (including a CD and a DVD), a magnetic disk 113, a memory 114 (including an IC card and a memory card), and the like. Of course, these storage media are not limited to portable types.

  By storing the program 101 in these storage media and mounting these storage media in, for example, the magneto-optical disk device 121, optical disk device 122, magnetic disk device 123, or memory slot (not shown) of the computer 102, the computer 101 The program 101 can be read to execute the function of the image processing apparatus or the image processing method of the present invention. Alternatively, a storage medium may be attached to the computer 102 in advance, and the program 101 may be transferred to the computer 102 via a network, for example, and the program 101 may be stored and executed on the storage medium.

  Of course, some functions may be configured by hardware, or all may be configured by hardware. Alternatively, it can be configured as a program including the configuration of the document editing device 11, or can be configured as one program together with the control program in the image output device 13. Furthermore, in the case of application to other purposes, integration with a program for that purpose is also possible.

It is a block diagram which shows an example of the color DTP system using the color image processing apparatus of this invention. It is a block diagram which shows 1st Embodiment of a color conversion part. It is explanatory drawing of the comparison result of the color conversion characteristic of this invention and a prior art. It is a block diagram which shows 2nd Embodiment of a color conversion part. It is a flowchart which shows an example of the determination process of the color conversion parameter of the DLUT color conversion part 39 in 2nd Embodiment of the color conversion part 24. FIG. It is explanatory drawing of an example of the storage medium which stored the computer program in the case of implement | achieving the function of the color image processing apparatus or color image processing method of this invention with a computer program, and the computer program.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Document editing apparatus, 12 ... Image processing apparatus, 13 ... Image output apparatus, 21 ... Editing apparatus communication part, 22 ... Format conversion part, 23 ... Rasterization part, 24 ... Color conversion part, 25 ... Output apparatus communication part, 31 ... device-independent color space conversion unit, 32 ... gradation correction unit, 33 ... non-black color determination unit, 34 ... three primary color signal conversion unit, 35 ... black amount subtraction unit, 36 ... chromatic UCR conversion unit, 37 ... non-black color correction unit , 38 ... Image recording signal output unit, 39 ... DLUT color conversion unit, 101 ... program, 102 ... computer, 111 ... magneto-optical disk, 112 ... optical disk, 113 ... magnetic disk, 114 ... memory, 121 ... magneto-optical disk device, 122: an optical disk device, 123: a magnetic disk device.

Claims (18)

The first color signal consisting of four or more colors including black, in black and three primary colors and a color image processing method for converting the five colors to 7 colors second color signal consisting of three color features of 1, the A first conversion step of determining a device-independent color signal on the color system color coordinate from the first color signal; and a first conversion step of determining the black signal of the second color signal from the black signal of the first color signal. and second conversion step, and a third conversion step of converting the device independent color signal into three primary color signals of the second color signals, the second color from the three primary color signals of the second color signals a fourth conversion step of determining a correction 3 primary color signals obtained by subtracting the component corresponding to the signal black signal, related to the feature of the second color signal from said correction 3 primary color signals of the second color signals UCR of (Under color Removal) the second color signal by processing The second color signals the correction 3 primary color signals from the output 3 primary color signals of the second of said by subtracting the corresponding components in the spot color signal of the color signal second color signal and determines the color signal a fifth conversion step of determining, the output 3 primary color signals and the spot color signals obtained in the second of the black signal obtained by the conversion step fifth conversion step as the second color signals A color image processing method comprising: outputting a color image; Furthermore, when the color signal other than black in the first color signal is zero, a sixth conversion step is provided in which the color signal other than black in the second color signal is set to zero and output. The color image processing method according to claim 1. In the fourth conversion step, a component corresponding to the black signal of the second color signal is determined by multiplying the black signal of the second color signal by the UCR rate, and the second color signal of the determined second color signal is determined. the components corresponding to black signal regulated below the minimum value of the three primary color signals of the second color signal, said second color signal corresponding component black signal of the second color signal after regulation the color image processing method according to claim 1 or claim 2, characterized in that to determine the correction 3 primary color signals by subtracting from the 3 primary color signals. In the fifth step of translating, determining the component corresponding to the first feature signals from 2-color minimum value of the combination of the correction 3 primary color signals, the maximum value of the component corresponding to the first feature signals determined as a component that corresponds to the second spot color signal to be subtracted from the corrected 3 primary color signals, a feature signal of the second color signal by multiplying the UCR rate component corresponding to the second spot color signals determined, claims 1 and determines the output 3 primary color signals of the second color signal by subtracting the feature signal of the second color signal from said correction 3 primary color signals 4. The color image processing method according to any one of items 3. 2. The second color signal is composed of five to seven colors obtained by adding one to three special colors to black and yellow (Y), magenta (M), and cyan (C). The color image processing method according to any one of claims 4 to 4. 6. The color image processing method according to claim 5, wherein the spot color in the second color signal is at least one of red, green, and blue. 7. The color image processing method according to claim 1, wherein the device independent color signal on the color system color coordinates is an L ^* a ^* b ^* color signal. 8. The black signal of the second color signal is determined from the black signal of the first color signal using a lookup table in the second conversion step. A color image processing method according to claim 1. The first color signal consisting of four or more colors including black, in the color image processing apparatus for converting a black and three primary colors and 1 to 5 colors to 7 colors second color signal composed of the three colors characteristic of the Device-independent color space conversion means for determining a device-independent color signal on the color system color coordinate from the first color signal, and a black signal of the second color signal from the black signal of the first color signal. a black signal correction means, and the three-color signal conversion means for converting the device independent color signal into three primary color signals of the second color signals, the second color from the three primary color signals of the second color signals a black amount subtraction means for determining a correction 3 primary color signals obtained by subtracting the component corresponding to the signal black signal, UCR relating to the characteristic of the second color signal from said correction 3 primary color signals of the second color signals wherein said second color signal and determines the JP color signal of the second color signal by processing The component corresponding positive 3 primary color signals to the feature signal of the second color signal by subtracting a chromatic UCR conversion means for determining an output 3 primary color signals of the second color signals, the black signal color image processing apparatus and outputs the output 3 primary color signals and the spot color signals obtained by the black signal obtained by the correction means and the chromatic UCR conversion means as the second color signal. In addition, when the color signal other than black in the first color signal is zero, non-black color correcting means for setting the non-black color signal in the second color signal to zero and outputting the non-black color signal is provided. The color image processing apparatus according to claim 9. The black amount subtracting means determines a component corresponding to the black signal of the second color signal by multiplying the black signal of the second color signal by a UCR rate, and determines the black color of the determined second color signal. regulating the component corresponding to the signal below the minimum value of the three primary color signals of the second color signal, a component corresponding to the black signal of the second color signal after regulation of the second color signals the color image processing apparatus according to claim 9 or claim 10, characterized in that to determine the correction 3 primary color signals by subtracting from the 3 primary color signals. The chromatic UCR conversion means, the correction 3 the corresponding components to the first feature signals from 2-color minimum value of the combination of the original color signals to determine the maximum value of the component corresponding to the first feature signals determined as a component that corresponds to the second spot color signal to be subtracted from the correction 3 primary color signals, determines the feature signal of the second color signal by multiplying the UCR rate component corresponding to the second spot color signals and, claims 9 to 11 and determines the output 3 primary color signals of the second color signal by subtracting the feature signal of the second color signal from said correction 3 primary color signals The color image processing apparatus according to any one of the above. 10. The second color signal is composed of five to seven colors obtained by adding one to three special colors to black and yellow (Y), magenta (M), and cyan (C). The color image processing apparatus according to claim 12. The color image processing apparatus according to claim 13, wherein the special color in the second color signal is at least one of red, green, and blue. The color image processing apparatus according to claim 9, wherein the device independent color signal on the color system color coordinates is an L ^* a ^* b ^* color signal. The color image processing apparatus according to any one of claims 9 to 15, wherein the black signal correcting unit is configured by a lookup table. The first color signal consisting of four or more colors including black, color to execute the process of converting to black and three primary colors and 1 to 5 colors to 7 colors second color signal composed of the three colors characteristic of the computer A color image processing program for causing a computer to execute the color image processing method according to any one of claims 1 to 8. The first color signal consisting of four or more colors including black, program for executing the process of converting to black and three primary colors and 1 to 5 colors to 7 colors second color signal composed of the three colors characteristic of the computer A computer-readable storage medium storing a program storing a program for causing a computer to execute the color image processing method according to any one of claims 1 to 8. Storage medium.

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