JP2009165056A - Color gamut normalizing method of printer, and color data converting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that proper normalization cannot be performed to cause a defect in gradations if a color gamut of a print image and a color gamut of color data supplied to the printer are normalized with a black point as reference when a color value of the black point of the color gamut in the print image printed by the printer is not the darkest value. <P>SOLUTION: Whether the color value of the black point printed by the printer is the darkest value of the color gamut in the print image is discriminated, when it is the darkest, normalization is normally performed, and when it is not the darkest, a virtual black point is set in a part darker than the color value, and normalization is performed with the virtual black point as reference. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to color correspondence between devices having different color expressible ranges, and more particularly, to a technique for converting color data from an image processing apparatus having a large color expressible range into color data for printing.

  As a color system for expressing a color image by a combination of numerical values, an RGB color system using each color value of red (R), green (G), and blue (B), cyan (C), magenta (M) The CMY color system using the color values of yellow and yellow (Y) is well known. The RGB color system is used in devices that express colors by combining light emission colors or transmitted light colors, such as CRTs, liquid crystal display devices, and plasma displays. On the other hand, the CMY color system is used for photographic paper and printers. Further, an L * a * b * (hereinafter simply referred to as “Lab”) color system is also used as a color system that corresponds to human perception and does not depend on equipment.

  In order to transfer color image data between devices using different color systems, it is necessary to perform color conversion between the color systems. For example, when an image displayed on a display device of a computer is printed by a printer, conversion from the RGB color system to the CMY color system is necessary. This conversion is generally performed via the Lab color system in order to remove the device dependency.

  In addition, even in the same Lab color system, the range (color gamut or gamut) in which colors can be expressed is different between devices, so it is necessary to associate them. For example, considering the case of printing image data from an image processing apparatus such as a computer, the printing apparatus gamut (hereinafter referred to as “printer gamut”) is generally smaller than the gamut of the image processing apparatus (hereinafter referred to as “source gamut”). In order to print color data from the image processing apparatus, it is necessary to perform processing in which each color point of each gamut corresponds. For this process, standardization is performed by performing range compression so that the brightness of each other corresponds (see Patent Document 1). Note that color points on the source gamut that are still not included in the printer gamut are mapped separately in the printer gamut.

Japanese Patent No. 3583630

  In order to match the ranges of the source gamut and the printer gamut, conventionally, standardization has been performed in which lightness range compression is performed at a ratio such that the white point and the black point of each other match each other. However, a printer gamut is created by measuring a color actually printed by a printing apparatus, and its shape changes depending on a combination of ink, resolution, paper, and the like. Such changes cannot be known unless they are actually measured. In particular, in the dark part, the amount of ink increases, and there is a tendency for the shape to become very complicated due to conditions such as the degree of ink overlap. In addition, the influence of measurement error is likely to occur. For this reason, in some cases, the color value of the black spot of the printer gamut may not be the darkest of the printer gamut.

  When the color value of the black spot of the printer gamut is not the darkest, if normalization is performed based on such a black spot, appropriate standardization could not be performed, and a problem may occur in gradation. .

  SUMMARY OF THE INVENTION An object of the present invention is to solve such problems and to provide a method for standardizing gamut so as not to cause a problem in gradation and a color data conversion apparatus using such normalization. And

  The color gamut standardization method for a printing apparatus according to the present invention standardizes the color gamut (source gamut) of color data supplied to the printing apparatus corresponding to the color gamut (printer gamut) in a print image printed by the printing apparatus. In the color gamut normalization method, the color value of the black point in the print image is determined to be the darkest color in the print image, and if the color value of the black point in the print image is the darkest, the print If the color gamut of the color data is normalized by a ratio such that the white point and the black point match each other in the color gamut of the image and the color data, and if the color value of the black point in the printed image is not the darkest, the color value In addition, a virtual black spot is set in a darker area, and the color gamut of the color data is normalized so that the virtual black spot matches the black spot of the color gamut of the color data.

  The color data conversion apparatus according to the present invention is a color data conversion apparatus that converts color data from an image processing apparatus into a data format that can be printed by a printing apparatus, and that stores a color gamut in a print image printed by the printing apparatus. And a normalization processing means for referencing the color gamut stored in the storage means and normalizing the color gamut of the color data from the image processing apparatus with the stored color gamut, Means for determining whether the color value of the black point of the color gamut stored in the storage means is the darkest of the color gamut, and, if the color value is the darkest, the white point of the color data of the color gamut And means for normalizing the color gamut of the color data by a ratio such that the black point coincides with the white point and the black point of the color gamut stored in the storage means, and the color value of the black point of the color gamut stored in the storage means If it is not the darkest, it is darker than the color value. Set the virtual black spots, characterized in that the black point of the color gamut of the color data in this virtual black dots and means for normalizing the color gamut of the color data to match.

[Device configuration]
FIG. 1 is a block diagram showing an embodiment of the present invention, and shows a configuration example of a color data conversion apparatus that converts color data from an image processing apparatus into a data format of a printing apparatus.

  The color data conversion device refers to a memory 3 that stores a color gamut (printer gamut) in a print image printed by a printing device, and a printer gamut stored in the memory 3, and the color data from the image processing device A gamut normalization processing unit 2 for normalizing a color gamut (source gamut) with a printer gamut. The gamut normalization processing unit 2 stores the color value of the black spot of the printer gamut stored in the memory 3 in the gamut. A black point discriminating unit 21 for discriminating whether the color is dark or not, and when the color value is the darkest, the source gamut is such that the white point and black point of the source gamut match the white point and black point of the printer gamut, respectively. When the color value of the black point of the printer gamut is not the darkest, the normal normalization unit 22 for normalizing the image and the virtual black point in the dark part of the color value Constant and, and a virtual black point setting and normalizing unit 23 for normalizing the source gamut as black spots match the source gamut to the virtual bullets.

  The color data converter further includes a color converter 1 that converts color data of individual pixels of RGB image data input from the image processing device into Lab color system color data, a printer on a standardized source gamut, and the like. A gamut mapping processing unit 4 that performs processing for mapping points that are not included in the gamut into the slitter gamut, and conversion from the color data of the mapped Lab color system into the dot amount of ink of each color in the printing apparatus A print data generation unit 4 that performs halftone processing and literalization processing of each color and outputs the color print data to a printing apparatus is provided. In the memory 3, in addition to the source gamut, a color conversion table (look-up table LUT) in which the correspondence between the RGB color system gradation value and the Lab color system gradation value is described, the source gamut, and the printer gamut For example, data necessary for processing of each unit is stored in advance.

[Standardization of gamut]
2 and 3 are diagrams for explaining gamut normalization. FIG. 2 is an example of normalization based on the black point of a printer gamut whose black point color value is not the darkest (conventional example), and FIG. 3 is a virtual black point. An example of normalization in which is set is shown. Although not shown in the figure, the vertical direction is the L * axis, and the horizontal direction is the a * and b * axes. Here, it is assumed that the printer gamut is included in the source gamut including white spots and black spots in a state before normalization.

  Conventionally, a standardized source gamut 33 is obtained by performing range compression of lightness at a ratio such that the white dots 31 and 41 and the black dots 32 and 42 of the source gamut 30 and the printer gamut 40 match each other. It was. For this reason, as shown in FIG. 2, when the color value of the black point 32 of the printer gamut 30 is not the darkest of the printer gamut 40, proper standardization is not performed, and there is a possibility that a problem occurs in gradation. It was. Therefore, in the present invention, as shown in FIG. 3, a virtual black point 43 is set in a darker area than the color value of the black point 42 of the printer gamut 40, and normalization is performed so that the black point 32 of the source gamut matches the virtual black point 43. .

  Referring to FIG. 1 again, the black point determination unit 21 determines whether the color value of the black point 42 of the printer gamut 40 stored in the memory 3 is the darkest of the color gamut, and the color value is determined. If it is the darkest (not shown), the normalization unit 22 is instructed, and if not, the virtual black spot setting / normalization unit 23 is instructed to normalize the gamut. The normal normalization unit 22 performs normalization to compress the lightness range of the source gamut at such a ratio that the white point and black point of the source gamut match the white point and black point of the printer gamut, respectively. As shown in FIG. 3, the virtual black spot setting / standardizing unit 23 sets a virtual black spot 43 in a darker area than the color value of the black spot 42, and the source so that the black spot 32 of the source gamut 30 matches the virtual black spot 43. A standardized source gamut 34 is obtained by compressing the lightness range of the gamut 30.

  Note that the printer gamut may have a complicated shape such as irregularities other than near the black spot, but generally, there is not much problem in gradation except for the black spot. In the example of FIG. 3, a point where the extended line of the printer gamut 40 intersects is adopted as the position of the virtual black point. In general, however, the point between the intersection of the extended line and the darkest point of the printer gamut is used. Any point can be a virtual black point.

[Embodiment using computer program]
FIG. 4 is a block diagram showing an example in which the color data conversion apparatus of the present invention is implemented as a printer driver program. Although the hardware configuration is omitted in FIG. 4, the computer 50 includes a CPU, a RAM, a ROM, a hard disk, various interfaces, and the like, and under a predetermined operating system, an application program 50, a video driver program 52, a printer driver program 53, and the like. The program is operational.

  The color image processing of each program will be described. The video driver program 52 displays a color image, a video, a user interface, and the like on the display device 60 according to commands from the application program 51 and the printer driver program 53. The printer driver program 53 operates as an apparatus equivalent to the color data conversion apparatus shown in FIG. 1 by starting up the computer 50, and converts RGB image data into print data according to an instruction from the application program 51, and performs printing. Output to the device 70.

  The printer driver program 53 is basically realized by implementing the color data conversion apparatus of FIG. 1 as a program, but the resolution of the image processed by the application program 51 and the resolution of the printing apparatus 70 are generally different. A resolution conversion unit 54 that performs conversion is provided. The RGB image data whose resolution has been converted by the resolution conversion unit 54 is converted to Lab image data by the color space conversion unit 55, gamut normalization processing is performed by the gamut normalization processing unit 56, and the gamut mapping processing unit 57 A mapping process from the source gamut to the printer gamut is performed, converted into color print data for printing by the printing apparatus 70 by the print data generation unit 58, and output to the printing apparatus 70. Necessary for processing of each unit such as the color conversion table, source gamut, and printer gamut, the data is stored in a memory (not shown), and each unit can access the memory as necessary.

  FIG. 5 is a flowchart showing the flow of processing by the gamut normalization processing unit 56. The gamut normalization processing unit 56 determines whether or not the color value of the black spot of the printer gamut is the darkest of the gamut (S11), and if it is the darkest (S12), the printer gamut and the source gamut are determined. The source gamut is normalized by a ratio such that the white point and the black point coincide with each other (S13). If the color value of the black point of the source gamut is not the darkest (S13), a virtual black point is set in the dark part of the color value. (S14) The source gamut is standardized so that the black spot of the source gamut matches this virtual black spot.

1 is a block configuration diagram showing a color data conversion apparatus according to an embodiment of the present invention. The figure explaining normalization of a gamut (conventional example). The figure explaining the normalization which set the virtual black spot. 1 is a block diagram showing an example in which the present invention is implemented as a printer driver program. The flowchart which shows the flow of a normalization process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Color space conversion part 2 Gamut normalization process part 3 Memory 4 Gamut mapping process part 5 Print data generation part 21 Black point determination part 22 Normal normalization part 23 Virtual black point setting and normalization part 30 Source gamut 31 White point of source gamut 32 Source gamut black spots 33, 34 Standardized source gamut 40 Printer gamut 41 Printer gamut white spots 42 Printer gamut black spots 43 Virtual black spots 50 Computer 51 Application program 52 Video driver program 53 Printer driver program 54 Resolution converter 55 Color space Conversion unit 56 Gamut standardization processing unit 57 Mapping processing unit 58 Print data generation unit 60 Display device 70 Printing device

Claims (2)

In a color gamut standardization method for standardizing the color gamut of color data supplied to a printing apparatus corresponding to the color gamut in a print image printed by a printing apparatus,
Determining whether the color value of the black spot in the printed image is the darkest color gamut in the printed image;
When the color value of the black point in the print image is the darkest, the color gamut of the color data is in a ratio such that the white point and the black point coincide with each other in the color gamut of the print image and the color gamut of the color data. Standardize
If the color value of the black point in the printed image is not the darkest, a virtual black point is set in the dark part of the color value, and the color of the color data is set so that the black point of the color gamut of the color data matches the virtual black point. A color gamut normalization method for a printing apparatus, characterized by normalizing the gamut. In a color data conversion device that converts color data from an image processing device into a data format that can be printed by a printing device,
Storage means for storing a color gamut in a print image printed by the printing apparatus;
With reference to the color gamut stored in the storage means, and normalization processing means for normalizing the color gamut of the color data from the image processing device with the stored color gamut,
The standardization processing means is
Means for determining whether the color value of the black spot of the color gamut stored in the storage means is the darkest of the color gamut;
If the color value is the darkest, the color data has a ratio such that the white point and black point of the color gamut of the color data match the white point and black point of the color gamut stored in the storage means. Means for standardizing the color gamut;
If the color value of the black point in the color gamut stored in the storage means is not the darkest, a virtual black point is set in the dark part of the color value so that the black point of the color gamut of the color data matches the virtual black point. And a means for normalizing the color gamut of the color data.

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