JP2007282056A - Color reproducing apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color reproducing apparatus for reproducing a metallic color while keeping a sense of luster without using a particular color. <P>SOLUTION: In simulating the metallic color, a color distribution database 25 is referred to, and a color of each pixel in a region of the metallic color is extracted from the color distribution at random. The color extracted for each pixel is set to the color of the pixel. As a result, the region of the metallic color is not painted by one color but by a plurality of colors with a distribution (range) on a color space. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a color reproduction device and a color reproduction method for reproducing a metallic color.

  In the provision of a printing service, a publishing service, etc., when performing a printing operation using a printing machine, it is common to perform color proofing using a simulation device before the main printing by the printing machine. As a simulation device (color reproduction device), a proof printing machine, an electrophotographic or ink jet printer for PC, a PC monitor, or the like is used. Conventionally, a color reproduction device described in Patent Document 1 is known.

  Here, the color calibration is performed with reference to output results (printer output, monitor output, etc.) output by the simulation device. Therefore, it is desirable that the color reproduced in the output result matches the color expressed by the printing machine in the main printing. For this reason, there is a need for a technique for accurately simulating (color reproduction) various colors expressed by a printing machine used for the main printing in the color space of a simulation device.

  In general, a printing machine expresses various colors by subtractive color mixture of four color materials including cyan (C), magenta (M), yellow (Y), and black (K). These four colors are called “process colors”.

  A simulation device used for color calibration reproduces each color expressed by subtractive color mixing of process colors using color management technology. That is, the simulation device absorbs a difference in color reproduction characteristics between devices (between a printing press and a simulation device) using a profile that is a database in which the characteristics of the device are described. Thereby, it is possible to accurately reproduce various colors expressed by subtractive color mixing of process colors.

  However, in a printing machine, in addition to the above process colors, colors may be expressed using color materials other than process colors called special color inks. This is because, firstly, there are colors that are difficult to reproduce by subtractive color mixing using process colors, and secondly, the cost of printing may be reduced by using special color inks. In particular, in printing by a printing machine, glossy special color inks such as gold and silver are often used for logos and advertisement titles. Such a glossy color is called a metallic color.

Here, in order to reproduce such special color ink on a simulation device, application of the above-described color management technology will be examined. When the user inputs the name of the special color ink according to the user interface used in this technique, a value on the color space that specifies the color of the special color ink is read out. A value on the color space is stored in advance in a storage medium, and a value on a device-independent color space such as L * a * b is read. Thereafter, the read value is converted into a value on a device-dependent color space such as a CMYK value. When the converted value is output to the simulation device, color reproduction corresponding to the special color ink is realized on the simulation device.
Japanese Patent Laid-Open No. 11-313216

  However, the conventional color reproduction device has the following problems. That is, as a simulation device, an electrophotographic printer is used for color proofing of main printing, but has only CMYK color materials and cannot handle special colors. For this reason, it has been difficult to reproduce a glossy feeling like a metallic color.

  This is thought to be because the metallic color has more irregular reflection than the normal color when reflecting ambient light, so it does not seem to have one color (spectral distribution) but appears as multiple colors. (See FIG. 5). In the conventional printer, since one spot color is converted into only one color, it is impossible to obtain such a glossy feeling.

  Accordingly, an object of the present invention is to provide a color reproduction device and a color reproduction method for reproducing a metallic color while maintaining a glossy feeling without using a special color.

  In order to achieve the above object, a color reproduction device of the present invention is a color reproduction device that reproduces a metallic color, and becomes a region of the metallic color from a color distribution of the metallic color in a device-independent color space. A color selection unit that selects a color for each predetermined pixel; and a color conversion unit that converts the value of each selected color into a value in a device-dependent color space, and on the converted device-dependent color space Based on the value, the metallic color is reproduced with a plurality of colors used in the device.

  The color reproduction method of the present invention is a color reproduction method for reproducing a metallic color, and selects a color for each predetermined pixel that is a region of the metallic color from the color distribution of the metallic color in a device-independent color space. A color selection step; a color conversion step for converting the value of each selected color into a value in a device-dependent color space; and a value in the converted device-dependent color space. And a color reproduction step for reproducing the metallic color with a plurality of colors.

  According to the color reproduction device of the first aspect of the present invention, the metallic color region is not painted with one color, but is painted with a plurality of colors having a distribution in the color space. As a result, the metallic color can be reproduced while maintaining the gloss without using a special color.

  According to the color reproduction device of the second aspect, the color reproducibility of the metallic color can be improved. According to the color reproduction device of the third aspect, it is possible to increase the number of metallic colors that can be reproduced. According to the color reproduction device of the fourth aspect, the color distribution of the metallic color can be easily generated.

  According to the color reproduction device according to the fifth and sixth aspects, data that seems to be noise can be automatically deleted. For example, it is possible to avoid the possibility of reading a color different from the original color due to the influence of dust generated by using a scanner.

  According to the color reproduction device of the seventh aspect, it is possible to compress a data amount that tends to be enormous.

  According to the color reproduction device of the eighth aspect, even a printing device having only a color material such as CMYK can reproduce a metallic color without using a special color ink.

  Embodiments of a color reproduction device and a color reproduction method of the present invention will be described with reference to the drawings. The color reproduction apparatus according to the present embodiment is applied to a color reproduction system including a scanner, a simulation device, and an information processing apparatus. In this embodiment, an electrophotographic color laser printer is used as the simulation device.

  FIG. 1 is a diagram showing an overall configuration of a color reproduction system according to an embodiment. This color reproduction system includes a scanner 5, a simulation device 10, and an information processing apparatus 15. The information processing apparatus 15 has a functional configuration including a DTP application 21, a RIP system 22, a metallic color generation module 23, a color distribution generation module 27, a color conversion engine 24, and a color distribution DB 25.

  FIG. 2 is a diagram illustrating a hardware configuration of the information processing apparatus 15. The information processing apparatus 15 includes a general-purpose PC having a known CPU 31, ROM 32, RAM 33, storage memory 35, user interface (operation unit) 36, and the like connected via a bus 37. In this embodiment, the RIP system 22 that expands data from the DTP application 21 into printable bitmap data is connected to the bus 37 as dedicated hardware.

  The storage memory 35 stores a DTP application 21, a color conversion engine 24, and a color distribution database (DB) 25. The storage memory 35 stores software such as a color distribution database generation processing program and a color generation processing program which will be described later. The CPU 31 once reads these programs into the RAM 33 and executes them, thereby realizing the functions of the metallic color generation module 23 and the metallic color color distribution creation module 27 described above.

  A RIP (Raster Image Processor) system 22 extracts a metallic color portion from data input from the DTP application 21. The name of the metallic color of the extracted part and the number of pixels to be output are calculated and output to the metallic color generation module 23. In addition, the device-independent values for several pixels given from the metallic color generation module 23 are color-converted to device-dependent values using the color conversion engine 24, respectively. The color conversion engine 24 has an ICC profile indicating the color characteristics of the device (scanner, simulation device). The RIP system 22 outputs the color-converted value to the simulation device 10. The simulation device 10 outputs an image based on the input device-dependent value. In this embodiment, a CIEL * a * b * (hereinafter referred to as Lab) space is used as the device-independent color space.

  The metallic color generation module 23 generates device-independent values for several pixels on the basis of the metallic color name (spot color name) and the color distribution database 25 input from the RIP system 22, and sends them to the RIP system 22. Returns the result.

  When creating the color distribution database 25, the metallic color color distribution creating module 27 performs processing such as noise removal and data number reduction on the metallic color distribution data (data group) obtained from the scanner 5. Then, the processed color distribution data is stored in the color distribution database 25.

  FIG. 3 is a diagram showing a configuration of a color laser printer as a simulation device. The color laser printer 10 has a photosensitive drum 71 as an image carrier, and forms an image by electrophotography. The photosensitive drum 71 is rotationally driven in the direction of arrow a in the figure, and the surface thereof is uniformly charged by a primary charger (charging roller) 82 during the rotation process.

  Further, the exposure device (laser scanner) 73 emits laser light corresponding to the yellow image pattern as the first color, and an electrostatic latent image of the first color is formed on the surface of the photosensitive drum 1. The laser light is generated according to the laser output signal.

  The latent image formed on the photosensitive drum 71 by the laser light is developed by the developing device 74y containing yellow toner facing the photosensitive drum 71 as the photosensitive drum 71 rotates, and is visualized as a yellow toner image. The developing devices 74y, 74m, 74c, and 74k are supported by a rotary support (rotary drum) 75, and a predetermined developing device rotates and moves to a position facing the photosensitive drum 71 prior to development. The toner image obtained by the development is transferred (primary transfer) to the surface of an intermediate transfer belt (belt-shaped intermediate transfer member) 76 rotating in the direction of arrow b at substantially the same speed as the photosensitive drum 71. This primary transfer is performed by a primary transfer bias applied to the primary transfer roller 77a inside the intermediate transfer belt 76. On the other hand, untransferred toner remaining on the photosensitive drum 71 is removed by the blade 78 (cleaning).

  The process including such charging, exposure, development, and primary transfer is performed for each color of magenta, cyan, and black after yellow. As a result, a color image obtained by superimposing toner images of four colors of yellow, magenta, cyan, and black is obtained on the intermediate transfer belt 76.

  The four color toner images superimposed on the intermediate transfer belt 76 are collectively transferred to the surface of the transfer material sent to the intermediate transfer belt 76 at a predetermined timing by the pickup roller 79 (secondary transfer). This secondary transfer is performed by a secondary transfer bias applied to the secondary transfer roller 77b inside the intermediate transfer belt 76. The transfer material onto which the four color toner images have been transferred is sent to the fixing device 81 by the transport belt 80. In the fixing device 81, the heated and pressurized toner is melted and fixed to the transfer material, and a final full-color image is obtained.

  The scanner 5 reads a color chart of a metallic color desired to be simulated or a photograph taken of the metallic color placed on the platen glass and converts it into RGB data which is a color space unique to the device. This amount of data is proportional to the number of pixels read by the scanner. For example, when a color chart of 1 inch square is read at a resolution of 200 dpi, the data amount corresponds to 40000 pixels.

  The operation of the color reproduction system having the above configuration will be described. FIG. 4 is a flowchart showing a color distribution creation processing procedure by the metallic color distribution creation module 27 for creating a color distribution database. As described above, this processing program is stored in the storage memory 35, and is once read into the RAM 33 and executed by the CPU 31. First, the name of the target metallic color (spot color name) input from the operator via the user interface (operation unit) 36 is acquired (step S1). Further, the operator scans a metallic color chart or photograph of the target set on the platen glass (not shown) of the scanner 5 and reads the data (step S2).

  In the obtained scanned image, the RGB value of each pixel in the metallic color region is converted into a Lab value using the color conversion engine 24 (step S3). The color conversion at this time is performed by a method similar to the conventional method, such as color conversion by an ICC profile indicating the device characteristics of the scanner. Each Lab value thus obtained indicates what color distribution the target metallic color has. FIG. 5 is a graph showing the gold color distribution in the Lab space. FIG. 4A shows the color distribution on the ab plane, and FIG. 4B shows the color distribution on the Lb plane. Thereafter, the color distribution is converted into a database and stored in the color distribution database 25 (step S4). Then, this process is complete | finished.

  Here, a method for creating a color distribution database will be described. The Lab data obtained in step S3 has the following problems. First, the data captured by the scanner may include data due to the influence of dust or the like, and may contain noise. Second, since the number of pixels is the number of Lab data as it is, the amount of data is often enormous.

  Therefore, in order to avoid the first problem, an average value and a standard deviation are obtained for each of the L direction, the a direction, and the b direction of the Lab data group. Using these average values and standard deviation, data far from the clustered data group that seems to be noise in the Lab space is deleted.

  This will be specifically described with reference to the drawings. FIG. 6 is a diagram showing a color distribution of a blue-green metallic color in the Lab space. In the drawing, a point (data) group 51 indicates a color distribution of a blue-green metallic color in the Lab space. The rectangular parallelepiped 55 surrounding the point group is centered on the average value of the point group 51, and the lengths of the sides in the L, a, and b directions are each 8 times the standard deviation of the L, a, and b components. It is set. When deleting data that seems to be noise, data outside the rectangular parallelepiped 55 is regarded as noise and deleted from the data group 51. Thus, the rectangular parallelepiped 55 is treated as a threshold value. Note that the size of the rectangular parallelepiped giving the threshold value can be arbitrarily set based on statistical data such as a variance value in addition to the standard deviation. Instead of a rectangular parallelepiped, an ellipsoid having a standard deviation or the like as a radius parameter may be used. As a result, it is possible to avoid the possibility of reading a color different from the original color due to the influence of dust or the like generated by using the scanner.

  In order to avoid the second problem, a three-dimensional convex hull is generated using a data group from which noise data has been deleted, and only necessary data is left. FIG. 7 is a diagram showing a three-dimensional convex hull of the data group 51 of FIG. The three-dimensional convex hull 58 is a solid that includes a data group (point group) on the color space, and is configured by connecting the outermost points. The total number of data in FIG. 6 is 16,000 or more, but the number of data used in the three-dimensional convex hull in FIG. 7 is 50. Therefore, in this case, the data can be compressed to about 0.3%. A data group forming the three-dimensional convex hull 58 is stored in the color distribution database 25 in association with the input spot color name. As a result, the amount of data can be greatly reduced.

  FIG. 8 is a flowchart showing a color generation processing procedure by the metallic color generation module 23 that generates color values using the color distribution database 25. This processing program is stored in the storage memory 35, and is once read by the CPU 31 into the RAM 33 and executed. When data generated by the DTP application 21 is output to the simulation device 10, data including a metallic color is sent from the DTP application 21 to the RIP system 22 in advance.

  First, the metallic color name (spot color name) and the number of pixels input from the RIP system 22 to be simulated are acquired (step S11). Based on the acquired spot color name, a three-dimensional convex hull (color distribution) of a metallic color to be simulated is acquired from the color distribution database 25 (step S12).

  Points (Lab values) are extracted randomly (randomly) from the acquired three-dimensional convex hull (color distribution) (step S13), and the extracted Lab values are output (step S14). Thereafter, it is determined whether or not the number of extracted Lab values has reached the number of input pixels (step S15). If it has reached, the process is terminated. On the other hand, if not reached, the process returns to step S13 and the same process is repeated until the number of pixels is reached.

  FIG. 9 is a diagram showing a simulation result of a golden metallic color. FIG. 4A shows the simulation result of this embodiment. FIG. 5B shows a simulation result by only color conversion using a conventional ICC profile. FIG. 10 is an enlarged view showing a part of the simulation result of FIG. FIG. 10A corresponds to FIG. 9A, and FIG. 10B corresponds to FIG. 9B. In FIG. 10, each quadrangle divided into a square represents a pixel. In the simulation results of the present embodiment, colors with different Lab values are expressed for each pixel (in FIG. 10A, the Lab values are different by changing the pattern in each square). On the other hand, conventionally, colors of the same Lab value are expressed in all pixels (see FIG. 10B). As described above, in the metallic color according to the simulation of the present embodiment, a different color (Lab value) is arranged for each pixel, so that the metallic color is reproduced while maintaining the gloss (see FIG. 9A). ).

  As described above, in the color reproduction system according to the present embodiment, the following operations are performed when a metallic color simulation is performed. With reference to the color distribution database 25, the color of each pixel in the region that becomes the metallic color is extracted from the color distribution by an arbitrary method (for example, random). Then, the color extracted for each pixel is set as the color of the pixel. As a result, the metallic color region is not painted with one color, but is painted with a plurality of colors having a distribution (range) in the color space. As a result, it is possible to reproduce a metallic color while maintaining a glossy feeling without using a special color ink.

  The present invention is not limited to the configuration of the above-described embodiment, and any configuration can be used as long as the functions shown in the claims or the functions of the configuration of the present embodiment can be achieved. Is also applicable.

  For example, in the above-described embodiment, an arbitrary point included in the color distribution is extracted by referring to the color distribution database for each pixel. However, it may be extracted for each predetermined pixel (for example, a plurality of pixels). . In the above embodiment, the extraction is performed randomly, but the extraction may be performed according to a predetermined rule. For example, you may make it repeat the operation | movement which extracts a point in order toward the outer side from the center vicinity of color distribution. Or you may make it extract along each direction in order of L, a, and b.

  In the above embodiment, the Lab space is used as the device-independent color space, but other device-independent color spaces (for example, Luv space, Jch space, etc.) may be used. In the above embodiment, the RIP system is configured by dedicated hardware, but may be configured by software.

  In the above embodiment, an electrophotographic color laser printer having a CMYK ink color is used as the simulation device. The printing method is not limited to the electrophotographic method, and may be various printing methods such as an inkjet method, a thermal transfer method, a thermal method, an electrostatic method, and a discharge destruction method. Further, the simulation device is not limited to a printing apparatus, and may be a display apparatus using RGB signals.

  In this embodiment, as a color reproduction system, a case where a color laser printer and a scanner device are connected to a general-purpose PC is shown. The color reproduction system may be configured by a multifunction peripheral (MFP) having a color reproduction processing function and printing, copying, and scanner functions.

  The object of the present invention is also achieved by the following. That is, a storage medium storing software program codes for realizing the functions of the above-described embodiments is supplied to the system or apparatus. The computer (or CPU, MPU, etc.) of the system or apparatus reads out and executes the program code stored in the storage medium.

  In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments. The program code and a storage medium storing the program code constitute the present invention.

  Further, for example, a floppy (registered trademark) disk, a hard disk, a magneto-optical disk, a CD-ROM, a CD-R, or a CD-RW can be used as a storage medium for supplying the program code. Further, an optical disc such as a DVD-ROM, a DVD-RAM, a DVD-RW, a DVD + RW, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used. Alternatively, the program code may be downloaded via a network.

  Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also the following cases are included. That is, based on the instruction of the program code, an OS (operating system) running on the computer performs part or all of the actual processing. The case where the functions of the above-described embodiments are realized by such processing is also included.

  Further, the program code read from the storage medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer. Thereafter, based on an instruction of the program code, a CPU or the like provided with the extension function in the extension board or the extension unit performs part or all of the actual processing. The case where the functions of the above-described embodiments are realized by such processing is also included.

It is a figure which shows the whole structure of the color reproduction system in embodiment. 2 is a diagram illustrating a hardware configuration of an information processing device 15. FIG. It is a figure which shows the structure of the color laser printer as a simulation device. It is a flowchart which shows the color distribution creation process procedure by the metallic color color distribution creation module 27 which creates a color distribution database. It is a graph which shows the color distribution of the gold color in Lab space. It is a figure which shows the color distribution of the blue-green type metallic color in Lab space. It is a figure which shows the three-dimensional convex hull of the data group 51 of FIG. 5 is a flowchart showing a color generation processing procedure by a metallic color generation module 23 that generates color values using a color distribution database 25; It is a figure which shows the simulation result of a golden metallic color. It is a figure which expands and shows a part of simulation result of FIG.

Explanation of symbols

5 Scanner 10 Simulation device (color laser printer)
15 Information processing device 22 RIP system 23 Metallic color generation module 25 Color distribution database (DB)
27 Metallic color distribution generation module

Claims (11)

A color reproduction device that reproduces a metallic color,
Color selection means for selecting a color for each predetermined pixel that is a region of the metallic color from the color distribution of the metallic color in a device-independent color space;
Color conversion means for converting the value of each selected color into a value on a device-dependent color space;
A color reproduction apparatus that reproduces the metallic color with a plurality of colors used in the device based on the converted value in the device-dependent color space.   The color reproduction device according to claim 1, wherein the color selection unit randomly selects a color included in the color distribution for each predetermined pixel.   2. The color reproduction apparatus according to claim 1, further comprising color distribution generation means for generating a color distribution of the metallic color in the device-independent color space. Comprising reading means for reading a metallic color expressed on the object;
The color reproduction device according to claim 3, wherein the color distribution generation unit generates a color distribution of the read metallic color. Based on statistical data of the read metallic color data group, the data deletion means for deleting predetermined data from the data group,
5. The color reproduction apparatus according to claim 4, wherein the color distribution generation unit generates the color distribution from a metallic color data group from which the data has been deleted.   6. The color reproduction device according to claim 5, wherein the data deleting unit deletes data out of a predetermined range centered on the average value by using an average value and a standard deviation of the metallic color data group. . Three-dimensional convex hull creation means for creating a three-dimensional convex hull representing the color distribution of the read metallic color;
Database creation means for registering the data forming the created three-dimensional convex hull in a database;
5. The color reproduction device according to claim 4, wherein the color distribution generation unit generates the color distribution using data forming a three-dimensional convex hull registered in the database.   The color reproduction apparatus according to claim 1, wherein the device is a printing apparatus, and reproduces the metallic color with a plurality of ink colors used in the printing apparatus. A color reproduction method for reproducing a metallic color,
A color selection step of selecting a color for each predetermined pixel that is a region of the metallic color from the color distribution of the metallic color in a device-independent color space;
A color conversion step of converting the value of each selected color into a value on a device-dependent color space;
And a color reproduction step of reproducing the metallic color with a plurality of colors used in the device on the basis of the converted value in the device-dependent color space.   A program having computer-readable program code for realizing the color reproduction device according to claim 1.   A storage medium storing the program according to claim 10.

Images