JP2007049642A - Image processing apparatus, image processing method and table creating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively use color gamuts of an output device in gamut mapping, to excellently reproduce colors of an input device and to also guarantee color reproduction for other colors. <P>SOLUTION: It is judged whether or not a lattice point X of an object of gamut mapping is within an input estimated color gamut 1202. If it is determined that the point X is within the input estimated color gamut 1202, the lattice point is compressed into point X' of a distance OX' within a preferential color gamut 1204. If it is judged that the point X is outside the input estimated color gamut 1202, on the other hand, the point X is compressed into point X' between a boundary Pf of the preferential color gamut 1204 and an outer-most shell D of a printer color gamut 1203. Thus, the preferential color gamut is made comparatively large for colors within the input estimated color gamut 1202, so that excellent compression can be performed without incurring color crush or the like. Furthermore, areas for colors after compression are secured within the printer color gamut for colors outside the input estimated color gamut 1202, and the colors outside the input estimated color gamut can also be reproduced in a printer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image processing apparatus, an image processing method, and a table creation method, and more particularly to a table used for gamut mapping for converting a color gamut of an input device to a color gamut of an output device via a standard color space independent of the device. Is.

  In recent years, digital devices such as digital cameras and image scanners have become widespread, and digital images can be easily obtained. Also, full-color hard copy technology is rapidly developing. In particular, inkjet printing is becoming more widely used because its image quality is comparable to silver salt photography. On the other hand, networks such as the Internet are widely spread, and many users can connect various devices. In an environment where such input / output devices are diverse, the color reproduction range, for example, when a color image signal of a monitor having a certain color reproduction range is hard-copied by a printer with a narrower color reproduction range. Input / output of color image data is performed between devices having different.

  On the other hand, “color management system (hereinafter also simply referred to as“ CMS ”)” is known as a technique for reproducing the same color between different devices.

FIG. 1 is a diagram showing an outline of one configuration of this CMS, and shows a CMS using a device-independent color space. For example, when an image input device such as a camera or a scanner is connected to an image output device such as a printer or monitor, in the configuration shown in FIG. 1, conversion from a color signal of a certain device to a color signal of an output device Device-independent color space (for example, CIE-XYZ, CIE-L) based on a profile (a conversion formula that links each device color and a device-independent color space, or a conversion table in which the above conversion is created in advance as a lookup table) ^{* A *} b ^* ). Such a system has an advantage that a system having different input and output devices to be connected can be easily exchanged.

Such a device-independent color space used in CMS (hereinafter also referred to as “standard color space”) is, for example, a profile proposed by the International Color Consortium (ICC) that is widely spread as an industry standard. A CIE-XYZ color space and a CIE-L ^* a ^* b ^* color space under a D50 light source are defined as those for linking profiles. As a standard color gamut, an sRGB color space (IEC 61966-2-1) is used under the Microsoft operating system Windows (registered trademark) environment. Furthermore, in recent years, the Adobe RGB color space proposed by Adobe may be used in input devices such as high-end digital cameras. A color space having these color gamuts may be a standard color space. Through such a standard color space which is a device-independent color space, it is possible to perform color reproduction independent of a device.

  When performing color reproduction with each device in this CMS, in order to be able to reproduce colors that can be reproduced with a certain device with an output device, the gamut that absorbs the difference in the color reproduction range between those input and output devices Mapping techniques are used.

In Patent Document 1, when mapping to a device color gamut with a narrower color reproduction gamut, colors other than the device color reproduction gamut are compressed with only lightness and hue being constant, and the color of the device is compressed. a method of compressing the outermost shell of the range, the color other than the color reproduction range is described gamut mapping by a method of compression to color the color difference in the CIE-L ^* a ^* b ^* color space is minimized.

JP-A-6-225130

  However, when the gamut mapping with the standard color space interposed is realized by using the lookup table (hereinafter also referred to as LUT), the size and shape of the standard color space and the color reproduction of the input device and output device In relation to the area, it is difficult to perform mapping in two main points. As a result, there is a problem that the quality of the printed image is not sufficiently realized.

  The first problem is caused by the inclusion relationship between the size of the standard color space, the input, and the color gamut of each output device.

FIG. 2 is a diagram illustrating a case where the standard color space does not include the entire color gamut of the output device when creating an LUT as a profile for the output device. This figure shows an sRGB color space 201 as a standard color space and a color gamut 202 of an ink jet printer as an example of an output device in a CIE-L ^* a ^* b ^* color system, and an area 203 indicated by hatching Is an area where the printer color gamut is wider than the standard color space. Even if such an out-of-gamut color is input from the input device, it cannot be handled at the time via the standard color space. That is, in order to use all the color gamut of the output device effectively and maximize the color reproduction capability of the output device, it is necessary to use a standard color space including the color gamut of the output device.

  However, on the other hand, the standard color space that satisfies such conditions may be considerably wider than the color gamut that can be assumed to be actually input (hereinafter referred to as “input assumed color gamut”). Will cause problems. In this way, the standard color space tends to be wider than the assumed input color gamut because the standard color space of the standard such as the above-mentioned ICC profile is used and the LUT has a total color reproduction gamut for any output device. This is because the standard color space is determined so that it can be included.

  Here, the assumed input color gamut is as follows. For example, consider a case where the output device is an inkjet printer and the input image to be printed is a photographic image taken with a digital camera. In general, in a popular digital camera, a color signal acquired by an input sensor is converted into YCrCb data assuming compression into an sRGB color space by a predetermined process. That is, the color input from the digital camera is a color in the sRGB color space. In this case, the sRGB color space is defined as the assumed input color gamut. As described above, when an LUT is created, an input color gamut that is assumed to be input most often in a system using the LUT is determined.

When the input assumed color gamut is the sRGB color space as described above and the standard color space is, for example, the CIE-L ^* a ^* b ^* color space or the AdobeRGB color space, the standard color space is sRGB which is the assumed input color gamut. It is wider than the color space. FIG. 3 is a diagram illustrating a relationship between a CIE-L ^* a ^* b ^* color space 301, a printer color gamut 302, and an assumed input color gamut (sRGB color space) 303 as an example of a wide standard color space.

  In this figure, when the standard color space 301 defined by the LUT as the profile for the output device is converted and gamut mapped to the color gamut 302 of the output device, it is a color other than the input assumed color gamut 303, for example, the color X Also need to be compressed into the color gamut of the output device. In other words, it is necessary to perform compression that guarantees color reproduction in the output device up to colors that are unlikely to be actually input. For this reason, the color reproduction region of the color of the assumed input color gamut 303 is narrowed within the color gamut 302 of the output device. In this case, when performing photographic printing or the like in the printer, color collapse may occur or saturation may be lowered, resulting in a poor-looking print image.

  The second problem is caused by the fact that the size of the color gamut of the output device differs from the standard color space depending on the print medium used.

  In general, the color gamut of the output device varies depending on the type of print medium and the intended print quality. When the output device is an inkjet printer, the color gamut when printing on photographic paper is wide, and the color gamut when printing on plain paper is narrow. Therefore, when a standard color space that covers the color gamut of the output device is used, the color gamut of photo-dedicated paper is mapped with gradation, and the color gamut of plain paper is narrower than that. Color reproducibility differs depending on the case. That is, in the color gamut of the photo paper, there is little decrease in saturation and lightness due to mapping, and when mapping to the color gamut of plain paper, the saturation and lightness are considerably reduced. As a result, the printed image becomes dull or the contrast becomes low, and good color reproduction cannot be realized.

  The present invention has been made in order to solve the above two main problems, and the object of the present invention is to use the color gamut of the output device effectively and to change the color of the input assumed color gamut. An object of the present invention is to provide an image processing apparatus, an image processing method, and a table creation method capable of achieving good color reproduction and ensuring color reproduction for other colors.

  Therefore, in the present invention, an image processing apparatus that performs a process of converting a color in the first color reproduction range to a color in the second color reproduction range, and is input within the first color reproduction range. Means for defining a third color reproduction range of the assumed color, and within the second color reproduction range, a color reproduction range to which the color of the third color reproduction range is compressed, Means for defining a fourth color reproduction range that is smaller than the second color reproduction range; and when the color of the first color reproduction range is converted into the second color reproduction range, the third color Compression means for compressing a color in the reproduction range to a color in the fourth color reproduction range.

  An image processing method for performing a process of converting a color in the first color reproduction range to a color in the second color reproduction range, and is assumed to be input within the first color reproduction range A step of defining a third color reproduction range of the generated color, and a color reproduction range to which the color of the third color reproduction range is compressed within the second color reproduction range, A step of defining a fourth color reproduction range smaller than the second color reproduction range, and the third color reproduction range when the color of the first color reproduction range is converted into the second color reproduction range. A compression step of compressing the first color into a color in the fourth color reproduction range.

  Furthermore, it is a method for creating a table used for the process of converting the color in the first color reproduction range to the color in the second color reproduction range, and is assumed to be input within the first color reproduction range. A step of defining a third color reproduction range of the generated color, and a color reproduction range to which the color of the third color reproduction range is compressed within the second color reproduction range, A step of defining a fourth color reproduction range smaller than the second color reproduction range, and the third color reproduction range when the color of the first color reproduction range is converted into the second color reproduction range. Determining the grid point data of each grid point so as to compress the color of the color into the color of the fourth color reproduction range.

  According to the above configuration, the third color reproduction range of the color assumed to be input is defined, and the color in the range is, for example, the fourth smaller than that within the second color reproduction range of the output device. Therefore, almost all input color signals can be compressed while maintaining the conditions of gradation and colorimetric coincidence, for example. Even when a color outside the third color reproduction range is input, it is possible to compress within the second color reproduction range to a range outside the third color reproduction range.

  As a result, the color gamut of the output device can be used effectively, the color of the assumed color gamut can be reproduced well, and color reproduction can be guaranteed for other colors.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 4 is a block diagram showing a schematic configuration of an image processing system according to an embodiment of the present invention. In the figure, an image input device 401 is, for example, a digital camera or an image scanner. The image processing apparatus 402 performs predetermined image processing such as gamut mapping using an LUT described in the following embodiments in the image processing unit 404 on the image data input by the image input unit 403, and the image output unit 405 The finally obtained print data is output to the image output device 406. The image processing apparatus 402 can be a personal computer (PC). Of course, the present invention is not limited to this mode, and a part or all of the image processing apparatus may be executed by a printing apparatus such as a printer. For example, in an embodiment in which an image captured by a digital camera is directly input to a printer and printed out, an image processing apparatus is configured in the printer. The image output device 406 can be a printing device such as a printer or a monitor.

  The LUT creation described in each embodiment described later can be performed on a PC as the image processing apparatus, and the created LUT is stored in a predetermined memory such as a PC or a printer as the image processing apparatus. Can be stored and used.

  FIG. 5 is a flowchart showing an outline of processing performed in the image processing apparatus 402 shown in FIG. First, in step 501, an image is input, and in step 502, the input image is subjected to input color space conversion processing. The input color space conversion process is a process of converting a color signal in the color space of the input device into a color signal in the standard color space. Next, in step 503, in order to improve the appearance of the image, color processing / correction processing such as increasing the saturation or brightness of the input image or correcting the color is performed. In step 504, gamut mapping is performed to convert the color signal in the standard color space into the color signal in the color gamut of the output device. A device-specific color is obtained based on the color after gamut mapping. Finally, after the color separation and quantization processing in step 505, the data is output in step 506.

In each embodiment described below, an LUT used in the gamut mapping in step S504 or a method for creating the LUT will be described. In these embodiments, a system using an inkjet printer as an image output apparatus will be described. In addition, all the color spaces used in the description of each embodiment are handled in the CIE-L ^* a ^* b ^* color system. Needless to say, the present invention is not limited to the CIE-L ^* a ^* b ^* color system, and can be realized if the color space is similar to the L ^* u ^* v ^* color space.
(Embodiment 1)
The first embodiment of the present invention relates to a gamut mapping LUT that changes the method of compression into the printer color gamut, depending on the colors that are within the input expected color gamut and the colors that are outside of the color.

  FIG. 6 is a flowchart showing this LUT creation processing. FIG. 7 is a diagram schematically showing a standard color space 1201, an assumed input color gamut 1202, a color gamut 1203 of an inkjet printer, and the like defined by this LUT.

  Since the standard color space of the present embodiment desirably includes the color gamut of the output device as described above, a color space having a wider color gamut than the AdobeRGB color space (hereinafter referred to as a WideGamutRGB color space). ) Is used. In the case of the ink jet printer of the present embodiment, the assumed input color gamut includes printing an image photographed by a digital camera and printing a document as main applications. Therefore, the color gamut of the input image often falls within the sRGB color space. Therefore, in this embodiment, the assumed input color gamut is the sRGB color space.

In FIG. 6, first, the standard color space described above is set in step S601. Specifically, each grid point that defines each grid point of the LUT is set so that, for example, a combination color of RGB values exists in a standard color space represented by an L ^* a ^* b ^* color space. To do.
In step S602, an assumed input color gamut 1202, a printer color gamut 1203, and a priority color gamut 1204 described below are set. That is, for the assumed input color gamut, printer color gamut, and priority color gamut represented by the L ^* a ^* b ^* color space, data of combinations of RGB values corresponding to them is set. As shown in FIG. 7, the compression is performed in a direction along a straight line connecting a point (color) O on the lightness axis defined as a compression destination and the color X of the lattice point to be compressed. In this straight line, the range of the straight line OP is the range of the assumed input color gamut 1202, and the range of the straight line PT outside the range is outside the assumed input color gamut.

  In the setting of step S602, first, the distance OX from the point O to the point X, the distance from the point O to the intersection T with the outermost shell of the standard color space 1201, the OT, and the outermost point of the input assumed color gamut from the point O A distance OP to the intersection point P of the shells and a distance OD to the point D of the outermost shell in the color gamut of the inkjet printer are calculated. Next, a color gamut (referred to as a priority color gamut) for compressing the assumed input color gamut is set.

  Since this priority color gamut 1204 needs to be within the printer color gamut 1203, it is set to be equal to or less than the distance OD. On the other hand, colors outside the assumed input color gamut are also set within the color gamut 1203 of the printer. For this reason, in this embodiment, 80% of the distance OD is set as the priority color gamut 1204. A distance from the point O to the intersection Pf with the outermost contour of the priority color gamut 1204 is defined as OPf.

  In step S603, based on the respective color gamut data set in step S602, it is determined whether or not the grid point X to be gamut mapped is within the input assumed color gamut set above. In the following, the compression method is varied depending on whether the compression target point X is within or outside the assumed input color gamut.

  When the compression destination point to be obtained is X ′, when it is determined that the point X falls within the assumed input color gamut, the point X is compressed to the point X ′ of the distance OX ′ within the priority color gamut 1204 in step S604. . The distance OX ′ is calculated from the following compression function (1.1). That is, as is apparent from the equation and FIG. 8, this compression is performed while maintaining uniform gradation. By obtaining the point X ′ for the point X in this way, the grid point data of the grid point X is used as a combination of RGB values representing the point X ′ in the creation of the LUT.

  On the other hand, when it is determined that the point X is outside the assumed input color gamut, the distance OX ′ is calculated from the following compression function (1.2), and the boundary Pf of the priority color gamut 1204 and the outermost shell D of the printer color gamut 1203. To a point X ′ between As is apparent from the equation and FIG. 8, the image is compressed into a narrower region than the color within the assumed input color gamut. By obtaining the point X ′ for the point X in this manner, similarly, in the creation of the LUT, the lattice point data of the lattice point X is used as a combination of RGB values representing the point X ′. Here, PX is the distance between the boundary of the assumed color gamut and the grid point X, PfD is the distance between the priority color gamut and the outer shell of the color gamut of the inkjet printer, and PT is the boundary between the priority color gamut and the standard color space. Indicates the distance to the outermost shell.

  As described above, all grid points in the standard color space can be gamut-compressed into the printer color gamut. In this way, the compressed color in the printer color gamut is determined depending on whether the color to be compressed when being compressed is within or outside the assumed input color gamut. By making the compressed color area, that is, the priority color gamut relatively large, it is possible to perform good compression without causing color collapse or the like. In addition, for colors outside the assumed input color gamut, the compressed color area is secured in the printer color gamut, and colors outside the assumed input color gamut can be reproduced (without color collapse) in the printer.

(Embodiment 2)
Although the method for compressing the standard color space while maintaining the uniform gradation in the color gamut of the output device shown in the first embodiment has good gradation reproducibility, it is colorimetric for all colors. There is a demerit that a different color reproduction is produced for each output device. On the other hand, a gamut compression method that realizes colorimetric matching is known. However, when this method is used, all colors outside the printer gamut are crushed and cannot be said to have good color reproduction. There is a case.

  Therefore, in the second embodiment of the present invention, a color gamut (hereinafter referred to as a colorimetric coincidence color gamut) that reproduces a colorimetric approximation in the output device is provided, and the color of the standard color space is set. Of these, the colors within the colorimetric color gamut are reproduced so that they are approximated colorimetrically. Colors outside the colorimetric color gamut are output devices outside the outer shell of the colorimetric color gamut. In the embodiment, the image is compressed into the printer color gamut. As a result, in different types of output devices, the colors within the colorimetric matching color gamut are colorimetrically approximated, and all colors outside the colorimetric matching color gamut are not crushed, ensuring color reproduction. Can be compressed.

  FIG. 9 is a flowchart showing the LUT creation processing of this embodiment. FIG. 10 is a diagram schematically showing a standard color space 1401 defined by the LUT, an assumed input color gamut 1402, a color gamut 1403 of an inkjet printer, and a colorimetric color gamut 1404 described below. is there. In FIG. 10, the boundary point of the colorimetric matching color gamut on the straight line connecting the compression target point O and the lattice point X to be compressed is F, and the distance is OF. Other points are the same as those shown in FIG. 7 according to the first embodiment described above.

  In this embodiment, the colorimetric color gamut 1404 has a shape similar to the printer color gamut 1403 and a volume of 60%. Here, the colorimetric color gamut is similar to the color gamut of the printer, but is not necessarily similar.

  In FIG. 9, a standard color space 1401 is set in step S901, and an assumed input color gamut 1405, a printer color gamut 1403, and a colorimetric matching color gamut 1404 are set in step S902. The specific setting method is the same as that of the first embodiment described above.

In step S903, it is determined to which color gamut the grid point X to be compressed belongs for each color gamut set as described above. Specifically, the compression target grid point X is
(I) Within the colorimetric color gamut (ii) Outside the colorimetric color gamut and within the assumed input color gamut (iii) Which color gamut is outside the assumed color gamut and within the standard color space To do.

  When it is determined that the point X is located in the color gamut (i), the compression is performed according to the following compression function (2.1) in step S904. That is, mapping is performed to faithfully reproduce the input color.

  When it is determined that the point X is in the color gamut (ii), in step S905, compression is performed according to the following compression function (2.2), and when it is determined that it is in the color gamut (iii). In step S906, compression is performed according to the following compression function (2.3).

  When the compression destination point X ′ is determined as described above, the RGB value is stored as lattice point data of the lattice point X.

  FIG. 11 is a diagram illustrating the compression functions (2.1), (2.2), and (2.3). As is clear from the figure, among the colors in the standard color space, the color in the color gamut (i) is faithfully reproduced as the color as it is, and the color in the color gamut (ii) is the colorimetric color gamut. Color reproduction is performed as a color outside 1404 and in the priority color gamut 1405. Furthermore, the color in the color gamut (iii) is compressed outside the priority color gamut 1405 to a color in the printer color gamut 1403.

  As described above, in this embodiment, by defining a colorimetric coincidence color gamut in particular, the colorimetrically consistent compression of the colors in this color gamut is realized, and the colors in the other color gamuts are realized by this compression. Can be prevented from being crushed due to compression.

  In each of the embodiments described above, the compression function is a function using a one-dimensional straight line. However, the present invention is not limited to this, and a quadratic function, an exponential function, or the like can also be used. In each of the above embodiments, the method of performing compression toward a single compression destination has been described. However, the method is not particularly limited to the gamut compression method. For example, a compression method that performs compression toward the achromatic color axis while maintaining lightness, or compression that does not cause saturation inversion as will be described in detail later can be performed.

(Embodiment 3)
The third embodiment of the present invention relates to an LUT configuration for gamut mapping that solves the problem related to the difference in the shape and size of the color gamut of an output device depending on the print medium used in the output device.

  In general, the color gamut when using plain paper as a printing medium is narrower and the volume is smaller than the color gamut when using dedicated photo paper. A color gamut 1602 and a color gamut 1603 shown in FIG. 12 indicate the color gamut of the ink jet printer when printing is performed on plain paper and photo paper, respectively. In this embodiment, the WideGamutRGB color space 1601 is used as a standard color space that can include both photo-dedicated paper and plain paper, as in the above-described embodiments. For example, when a point in the standard color space such as the point 1604 is directed to the point O of the compression destination and the gradation is maintained in the color gamut of the photo-dedicated paper, the point 1605 is compressed. When the point 1604 is compressed into the plain paper color gamut, the point 1604 is compressed to the position of the point 1606. That is, when the compression is performed in the color gamut of plain paper, both saturation and lightness are reduced as compared with the case of compression in the color gamut of the dedicated photo paper.

  Therefore, an assumed input color gamut is defined according to the printer color gamut. For example, in the case of a narrow color gamut such as plain paper, the assumed input color gamut is a narrow color gamut such as an sRGB color space, and an LUT that places importance on color reproduction of colors in the sRGB color space.

  FIG. 13 is a diagram showing a standard color space 1701, an assumed input color gamut 1702, a printer color gamut 1703 using plain paper, and the like according to this embodiment. As shown in the figure, a printer color gamut 1703 made of plain paper has an area with a shape similar to that gamut and a volume of 90%, and this is designated as a priority color gamut 1704.

  For these color gamuts, the color 1705 in the standard color space is compressed to the position of the point 1707 when, for example, this point is compressed by a conventional method of maintaining gradation. On the other hand, in this embodiment, since the point 1705 is a color within the assumed input color gamut 1702, the point 1705 is compressed to the position of the point 1706 within the priority color gamut 1704. That is, according to the present embodiment, it is possible to prevent a decrease in saturation and lightness due to gamut compression and to realize good color reproduction.

  In addition, a paper having a wide color gamut, such as photo-dedicated paper, can have a color space wider than an sRGB color space such as an AdobeRGB color space as an assumed input color gamut.

  Furthermore, the size of the priority area may be determined according to the size of the printer color gamut. For example, a case will be described in which the assumed input color gamut is a wide color space such as the AdobeRGB color space in the color gamut of the plain paper and the photo paper. For example, when the priority area is narrowed in a narrow color gamut such as plain paper, the color of the assumed input color gamut that is frequently input is reproduced with a dull color with low saturation. Therefore, it is effective to make the priority area relatively large. On the contrary, since the color gamut of the photo-dedicated paper is wide, the priority area may be narrowed for the purpose of maintaining the gradation of colors outside the assumed input color gamut. This is because the decrease in saturation is lower than that of plain paper. As described above, it is effective to determine the size of each color gamut in consideration of the relationship between the size of the printer color gamut and the assumed input color gamut.

(Embodiment 4)
In each of the above-described embodiments, the priority color gamut is an equal ratio of the distance from the compression destination point to the color gamut of the output device. The method for determining the priority color gamut is not limited to this. In consideration of the characteristics of the assumed color gamut, the distance ratio may be changed for each point in the standard color space to be compressed. For example, when the input assumed color gamut is the sRGB color space, if the high chroma portion of the green is not input so much, the distance OPf between the compression destination point O of the green area and the boundary of the priority color gamut is set long. Narrow the area to compress colors outside the expected color gamut. As a result, a color gamut that reproduces a green color with low saturation, which is substantially input frequently, is widened, which is effective in achieving good gradation reproduction.

  Moreover, in the reproduction of photographs, the skin color of a person is a particularly noticeable part. Therefore, it is also effective to set the distance OPf between the compression destination point O and the priority color gamut longer in the vicinity of the flesh-colored hue. Thereby, since the skin color area in a wide range can be mapped to the priority color gamut, it is possible to prevent crushing, extreme saturation, and a decrease in brightness.

  In each of the above embodiments, the priority color gamut is defined based on the distance from the compression destination point to the color gamut of the output device, but the present invention is not limited to this. For example, a color gamut having a similar shape smaller than the color gamut of the output device is provided, and this region is set as the priority color gamut, and a straight line connecting the point to be compressed from the compression destination point O and the outermost shell of the priority color gamut intersect. A point may be searched and the distance between the point and the point O may be OPf. The color gamut indicating the priority color gamut is not limited to a shape similar to the color gamut of the output device, and the shape can be appropriately modified as long as it falls within the color gamut of the output device. Thus, if the priority color gamut is one color gamut, the priority color gamut can be easily imaged, and there is an advantage that the shape of the priority color gamut is easily deformed.

(Embodiment 5)
In each of the above embodiments, the output device is assumed to be an ink jet printer, and an example of the assumed input color gamut has been described as the sRGB color space. Here, when the output device is used only for printing images taken with a digital camera, it is also effective to set the assumed input color gamut to a color space specialized for the characteristics of the digital camera. is there. For example, since there are not many high-saturation colors such as green, which is the primary color of the sRGB color space, in a normal shooting scene, a color space in which the high-saturation part of the sRGB color space is removed may be used as the assumed input color gamut. As described above, the assumed input color gamut is not limited to the existing color space, and can be adaptively set as a color space assumed to be input.

(Other embodiments)
The compression in the above-described gamut mapping may cause inversion of gradation change such as inversion of saturation change. That is, as shown in FIG. 14, in the standard color space 601, the saturation decreases from the point P1 to the point P2, whereas these points are mapped from the point P1 ′ to the point P2 ′ of the printer color gamut 602. Saturation increases. Therefore, in a more preferred embodiment of the present invention, the color gamut is deformed so as not to cause the inversion again as described above, and then the LUT creation of the gamut mapping described in each of the above embodiments is performed.

  FIG. 15 is a diagram for explaining reversal of the saturation change in the hue angle direction. As shown in FIG. 15, the primary colors (R (red), G (green), B (blue), C (cyan), M (magenta)) between the standard color space 701 and the printer color gamut 702, respectively. , Y (yellow)) generally deviates. Now, considering the color G of the hue of green (G) and the color L whose hue angle is converted from the hue to the hue direction of C, and considering the compression mapping in the respective lightness axis directions, the point (color) G is The point (color) L is mapped to the boundary point G ′, and the point (color) L is mapped to the boundary L ′. In this case, as can be seen from the figure, the saturation change in the hue angle direction from the point G to the point L decreases, while the saturation change from the point G ′ to the point L ′ increases. Thus, the compression mapping may cause saturation or reversal of the saturation change in the hue angle direction.

  For such a problem, as a first process, “deletion” of the printer color gamut is performed.

  FIG. 16 is a diagram for explaining the deletion of the printer color gamut. As shown in FIG. 16, the hatched portion of the printer color gamut 702 is deleted. Specifically, this deletion is performed by defining a saturation conversion curve for a hue for each predetermined brightness as shown in FIG. 17 and applying it to grid point data representing a printer color gamut. That is, as shown in FIG. 17, the horizontal axis represents the hue angle of the color gamut, and R, Y, G, C, B, and M represent the primary color of the monitor color gamut or the hue thereof, respectively. The vertical axis represents the maximum saturation of the printer color gamut at each hue angle. In the present embodiment, the maximum saturation point of each primary color is plotted with a white circle and connected with a straight line as a saturation conversion curve. Then, the saturation conversion curve is applied to the respective grid data as described above, and the portion larger than the saturation value indicated by the curve is subtracted to obtain the saturation value indicated by the curve. As a result, as shown in FIG. 17, a color having a higher saturation than the line connecting the maximum saturation points of each primary color (for example, a portion indicated by hatching between hues GC) is deleted. Become. This process is performed for each predetermined brightness. As a result, the standard color space 701 is deformed so that the saturation is reduced by the amount of deletion, and the point L on the color space 701 is mapped to the point L ″. As a result, in the printer color gamut 702, the saturation in the hue angle direction is almost the same from the point G ′ to the point L ″ from the point G to the point L in the standard color space 701 (the gradation change tends to be the same). , And saturation inversion due to compression mapping does not occur.

  In the above example, the conversion definition in which the maximum saturation points in the hues of the primary colors are linearly connected is shown. For example, by using a spline curve or the like, a “continuous” color gamut can be deleted. "It can be performed.

  Next, as a second process of the present embodiment, the printer color gamut is deformed, and the color (point) of the maximum saturation of the printer color gamut is the same hue as the hue of the maximum saturation point of the monitor color gamut. Process to move to.

  As described with reference to FIG. 14, when color gamut compression is performed toward a specific point, saturation inversion often occurs. On the other hand, there is a case where “deletion” is performed so that the saturation of the printer color gamut is reduced by the first processing described above, and the saturation inversion shown in FIG. However, the saturation inversion can be reliably eliminated by performing the second processing of the present embodiment. Also, by performing this second process, the amount of deletion in the first process is reduced to prevent the printer's color gamut from becoming unnecessarily small. It can also prevent the appearance from deteriorating. As described above, how much the deletion related to the first processing is performed in relation to the deformation related to the second processing is output based on the difference in the deterioration of the appearance due to “deletion” and the change in the gradation in the hue direction. Image can be comprehensively determined and set.

  FIG. 18 is a diagram for explaining color gamut deformation according to the second processing. As shown in FIG. 18, the maximum saturation point S of the printer color gamut 1002 indicated by the broken line is changed to a point S ′ on a straight line connecting the convergence point T of the compression map and the maximum saturation point P1 of the standard color space 1001. The color gamut is changed. That is, the color gamut 1002 is transformed into a printer color gamut 1003 indicated by a solid line. As a result, when a color that is not within the printer color gamut of the standard color space 1001 is compressed and mapped toward the convergence point T, the maximum saturation color P1 in the standard color space is the maximum saturation color S ′ in the printer color gamut 1003. Is mapped. As a result, when the saturation decreases from the point P1 to the point P2 in the standard color space 1001, the saturation decreases in the same manner from the point S ′ to P2 ′ on the color gamut 1003 to which these are mapped. Does not cause inversion.

  FIG. 19 is a diagram showing the color gamut modification of the present embodiment described above. As shown in FIG. 19, in this embodiment, a modification that simply increases the brightness of each color is performed. That is, the color in the range up to the lightness Ls of the maximum saturation point S of the printer color gamut 1002 is converted into the lightness Ls ′ of the maximum saturation point S ′ of the transformed color gamut 1003 as defined above. A relatively large proportion of linear transformation is performed. Further, a color having a lightness higher than the lightness Ls is subjected to linear conversion at a smaller ratio. Of course, the conversion shown in FIG. 19 is performed not only on the boundary of the printer color gamut 1002 but also on the internal color.

(Still another embodiment)
The present invention is applied to an apparatus or a computer in a system connected to various devices so as to operate various devices so as to realize the functions of the above-described embodiments, and the embodiments shown in FIGS. Software program codes for realizing the functions are supplied, and the system or apparatus computer (CPU or MPU) is operated by operating the various devices according to the stored program. included.

  In this case, the program code of the software itself realizes the functions of the above-described embodiments, and the program code itself and means for supplying the program code to the computer, for example, the program code are stored. This storage medium constitutes the present invention.

  As a storage medium for storing the program code, for example, a floppy (registered trademark) disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

Further, by executing the program code supplied by the computer, not only the functions of the above-described embodiments are realized, but also the OS (operating system) in which the program code is running on the computer, or other application software, etc. It goes without saying that the program code is also included in the embodiment of the present invention even when the functions of the above-described embodiment are realized in cooperation with the embodiment.
Further, after the supplied program code is stored in the memory of the function expansion board of the computer or the function expansion unit connected to the computer, the CPU of the function expansion board or function storage unit based on the instruction of the program code However, it is needless to say that the present invention also includes a case where the function of the above-described embodiment is realized by performing part or all of the actual processing.

It is a figure which shows the outline | summary of one structure of a color management system. FIG. 10 is a diagram illustrating a case where a standard color space does not include the entire color gamut of an output device when creating an LUT as an output device profile. A ^{CIE-L *} a * ^{b *} color space as an example of a wide standard color space is a diagram showing the relationship between color gamut and input assumption gamut of the printer and (sRGB color space). 1 is a block diagram illustrating a schematic configuration of an image processing system according to an embodiment of the present invention. 5 is a flowchart illustrating an outline of processing performed in the image processing apparatus illustrated in FIG. 4. It is a flowchart which shows the process of LUT creation of the gamut mapping which concerns on the 1st Embodiment of this invention. It is a figure which shows typically the standard color space prescribed | regulated with the said LUT produced | generated, an input assumption color gamut, the color gamut of an inkjet printer, etc. FIG. It is a figure which shows the compression function used in 1st embodiment of this invention. It is a flowchart which shows the process of LUT creation which concerns on 2nd embodiment of this invention. It is a figure which shows typically the standard color space prescribed | regulated by the said created LUT, the input assumption color gamut, the color gamut of an inkjet printer, and also a colorimetric coincidence color gamut. It is a figure which shows the compression function used in 2nd embodiment of this invention. It is a figure explaining compression to each color gamut by plain paper and photographic exclusive paper according to a third embodiment of the present invention. It is a figure which shows the standard color space which concerns on 3rd embodiment, the input assumption color gamut, the printer color gamut by plain paper, etc. It is a figure which shows the relationship between the color gamut of the sRGB color space which a monitor has, and the color gamut of an inkjet printer. It is a figure explaining inversion of the saturation change of the hue angle direction solved by embodiment of this invention. FIG. 10 is a diagram illustrating deletion of a printer color gamut according to the embodiment of the present invention. It is a figure which shows the saturation conversion curve with respect to the hue concerning embodiment of this invention. It is a figure explaining the color gamut deformation | transformation concerning embodiment of this invention. It is a figure explaining the process which raises the brightness in the color gamut deformation | transformation concerning embodiment of this invention.

Explanation of symbols

401 Image Input Device 402 Image Processing Device 403 Image Input Unit 404 Image Processing Unit 405 Image Output Unit 406 Image Output Device

Claims (26)

An image processing apparatus that performs a process of converting a color in a first color reproduction range to a color in a second color reproduction range,
Means for defining a third color reproduction range of colors assumed to be input within the first color reproduction range;
Within the second color gamut, a fourth color gamut that is a color gamut to which the colors in the third color gamut are to be compressed and is smaller than the second color gamut is defined. Means,
Compression means for compressing the color of the third color reproduction range to the color of the fourth color reproduction range when color-converting the color of the first color reproduction range to the second color reproduction range;
An image processing apparatus comprising:   Means for defining a fifth color reproduction range smaller than the fourth color reproduction range, which is a color reproduction range for colorimetrically matching or approximating color reproduction within the second color reproduction range. And the compression means converts the color in the first color reproduction range to the color in the second color reproduction range, and the color in the fifth color reproduction range is colorimetric. The color conversion is performed so as to approximate to the color, and the color in the third color reproduction range is compressed to the color in the fourth color reproduction range outside the fifth color reproduction range. Image processing apparatus.   The image processing apparatus according to claim 1, wherein the third color reproduction range is defined based on a shape and a size of the second color reproduction range.   4. The image processing apparatus according to claim 1, wherein the third color reproduction range is defined by a size corresponding to a size of the second color reproduction range of an output device. 5. .   The image processing apparatus according to claim 1, wherein the first and second color reproduction ranges are deformed into a shape suitable for color conversion.   The image processing apparatus according to claim 1, wherein the fourth color reproduction range is determined according to a width of the second color reproduction range.   The fourth color reproduction range obtains an intersection point where a straight line connecting a compression destination point and a point to be compressed in the first color reproduction range and an outermost shell of the second color reproduction range intersect, and the compression destination The image processing device according to claim 1, wherein the image processing device is defined based on a ratio based on a distance from the point to the intersection.   The image processing apparatus according to claim 7, wherein the ratio is variable for each hue.   9. The image processing apparatus according to claim 1, wherein a part or the whole of the fourth color reproduction range has a shape similar to the second color reproduction range.   The image according to any one of claims 1 to 9, wherein the fourth color reproduction range is determined in accordance with the characteristics of the third color reproduction range within the second color reproduction range. Processing equipment.   11. The first color reproduction range is a device-independent color space, and the second color reproduction range is a color reproduction range of an output device. The image processing apparatus described.   The image processing apparatus according to claim 1, wherein the third color reproduction range is determined according to characteristics of an input device and an application. An image processing method for performing a process of converting a color in a first color reproduction range to a color in a second color reproduction range,
Defining a third color reproduction range of colors assumed to be input within the first color reproduction range;
Within the second color gamut, a fourth color gamut that is a color gamut to which the colors in the third color gamut are to be compressed and is smaller than the second color gamut is defined. Process,
A compression step of compressing the color of the third color reproduction range to the color of the fourth color reproduction range when color-converting the color of the first color reproduction range to the second color reproduction range;
An image processing method characterized by comprising:   In the second color reproduction range, a step of defining a fifth color reproduction range which is a color reproduction range for colorimetrically matching or approximating color reproduction and smaller than the fourth color reproduction range And when the color in the first color reproduction range is converted to the color in the second color reproduction range, the color in the fifth color reproduction range is colorimetric. The color conversion is performed so as to approximate to the color, and the color in the third color reproduction range is compressed to the color in the fourth color reproduction range outside the fifth color reproduction range. Image processing method.   15. The image processing method according to claim 13, wherein the third color reproduction range is defined based on the shape and size of the second color reproduction range.   The image processing method according to claim 13, wherein the third color reproduction range is defined by a size corresponding to a size of the second color reproduction range of the output device. .   17. The image processing method according to claim 13, wherein the first and second color reproduction ranges are transformed into a shape suitable for color conversion.   The image processing method according to claim 13, wherein the fourth color reproduction range is determined according to a width of the second color reproduction range.   The fourth color reproduction range obtains an intersection point where a straight line connecting a compression destination point and a point to be compressed in the first color reproduction range and an outermost shell of the second color reproduction range intersect, and the compression destination The image processing method according to claim 13, wherein the image processing method is defined based on a ratio based on a distance from the point to the intersection.   The image processing method according to claim 19, wherein the ratio is variable for each hue.   21. The image processing method according to claim 13, wherein a part or all of the fourth color reproduction range has a shape similar to the second color reproduction range.   The image according to any one of claims 13 to 21, wherein the fourth color reproduction range is determined in accordance with the characteristics of the third color reproduction range within the second color reproduction range. Processing method.   23. The device according to claim 13, wherein the first color reproduction range is a device-independent color space, and the second color reproduction range is a color reproduction range of an output device. The image processing method as described.   The image processing method according to any one of claims 13 to 23, wherein the third color reproduction range is determined according to characteristics of an input device and an application. A method for creating a table used for a process of converting a color in a first color reproduction range to a color in a second color reproduction range,
Defining a third color reproduction range of colors assumed to be input within the first color reproduction range;
Within the second color gamut, a fourth color gamut that is a color gamut to which the colors in the third color gamut are to be compressed and is smaller than the second color gamut is defined. Process,
When the color of the first color reproduction range is converted to the second color reproduction range, the color of the third color reproduction range is compressed to the color of the fourth color reproduction range. A step of determining lattice point data of lattice points;
A table creation method characterized by comprising: A program causing a computer to function as the image processing apparatus according to any one of claims 1 to 12.

Images