JP2006211220A - Color image processing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color matching system capable of eliminating the occurrence of blurring in a DARK part so as to attain better color reproduction. <P>SOLUTION: An image processing apparatus including: a profile generating means for generating a profile corresponding to a device: a profile storage means for storing the generated profile; and a color matching processing means for applying color matching to image data, generates an inverse gamma 2.2 LUT, furthermore a profile corresponding to the device mounted with an LUT subjected to color space compression by taking into the gamma 2.2 account, and carries out color matching by using the generated profile. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention belongs to a gamma curve design method for reducing information loss in a dark part due to color space compression when calculating a LUT of a printer profile in a color management system.

  As described in Japanese Patent Application Laid-Open No. 07-222009, the color management system is composed of a CMM (Color Management Module) and a device profile, and corresponds to a profile corresponding to a source device before conversion and a destination device after conversion. Using the profile, color conversion processing is performed to perform color matching of the input / output images.

  The former profile is called a source profile, and the latter profile is called a destination profile.

  For example, in the color conversion process shown in FIG. 1, a process of converting from a scanner color space (scanner RGB) or a monitor color space (monitor RGB) to a printer color space (printer CMYK) is performed.

  In this case, the source device is the scanner 101 or the monitor 102, the scanner or monitor profile is the source profile 103, the destination device is the printer 106, and the printer profile is the destination profile 104.

  The source profile 103 and the destination profile 104 include device-dependent data and relational data for converting between device-independent color spaces such as XYZ and L * a * b * color systems defined by the CIE. Stored. The source profile 103 stores the gamma value 103A and conversion matrix 103B of each device, and the destination profile 104 stores the conversion LUT 104B of the printer 106.

  In general, as described in Japanese Patent Laid-Open No. 09-181908, in the embodiment of the color management system, override information is added to a device profile based on an ICC (Inter Color Consortium) format as shown in FIG. 1, and color conversion processing is performed. Can do.

  The CMM 105 obtains information from the source profile and the destination profile, and realizes color matching by using a device-independent color space.

  However, in the conventional destination profile, the output corresponding to the input having the gamma value 103A of the source profile is stored as the conversion LUT 104B, and there is little information in the Dark part, resulting in the output image being crushed. .

  FIG. 2 shows an outline of a conventional color matching processing design. Here, a block diagram and a graph of processing for converting from the monitor color space (monitor RGB) A to the printer color space (printer CMYK) C are shown. In this case, the monitor profile is the source profile 201 and the printer profile is the destination profile 202. A indicates input luminance RGB, B indicates data after gamma conversion of the monitor profile 201, and C indicates output CMYK values after gamma conversion of the printer profile 202. Here, black circles 207 on the lines A to C are grid points of the input luminance A. On the graph, the conversion curve 203 when the monitor gamma is 2.2, the conversion curve 204 when the monitor gamma is 1.3, the difference 205 between the data obtained by converting the data of the grid point 207 with the conversion curve with the conversion curve, Further, an output luminance difference 206 of data converted by the printer gamma linear line is shown.

As shown in FIG. 2, when the input luminance grid point 207 is converted into the converted data B by the monitor profile, a luminance difference 205 appears. Further, after conversion by the printer profile, a difference 206 occurs in the output luminance, and the grid point interval of the information in the Dark portion is changed by the monitor gamma. The higher the monitor gamma value is, the narrower the grid point interval in the Dark portion becomes, and the amount of information is reduced when designing the conversion LUT for the printer profile, so that the Dark portion is crushed in the output luminance value C.
Japanese Patent Application Laid-Open No. 07-222009 Japanese Patent Laid-Open No. 09-181908

  In the conventional method, as described in Japanese Patent Application Laid-Open No. 09-181908, the destination profile is designed by performing color space compression as a linear output with respect to the input with gamma inputted in the source profile, and stored in the destination profile. It was. For this reason, there is less information in the Dark part when designing the color space compression LUT, and the final output gradation and color reproduction are not sufficiently expressed.

  In order to solve the above-described problems of the conventional method, the present invention adds the inverse gamma 2.2LUT 104A as override information to the destination profile 104 of FIG. The color space compression considering the above is performed to regenerate the conversion LUT and store it in the destination profile. An object of the present invention is to provide a color matching system that uses the destination profile to eliminate the collapse of the dark portion and enables better color reproduction.

  In order to achieve the above object, in the present invention, profile creation means for creating a profile corresponding to a device, profile storage means for storing the created profile, and color matching processing means for performing color matching on image data are provided. In the image processing apparatus, an inverse gamma 2.2 LUT is generated, and a profile corresponding to the device mounted with the LUT subjected to color space compression in consideration of gamma 2.2 is created, and the created profile is used. Perform color matching.

  As described above, according to the present invention, when creating a color space compression LUT in consideration of a gamma value, the amount of information in the Dark portion is increased, and highly accurate calculation can be performed in the Dark portion. Further, by creating a profile by the above method and performing color matching, the collapse of the Dark portion after CMS processing is improved, and better color reproduction becomes possible.

(Embodiment 1)
Hereinafter, an example of a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 3 shows a system configuration according to an embodiment of the present invention. As shown in FIG. 3, the system according to this embodiment includes a PC main body 1, a monitor 2, and a printer 3. The figure shows a case where the colors displayed on the monitor are reproduced so that they appear to be the same color when printed by a printer.

  The PC main body 1 is provided with a CPU, VRAM, and the like necessary for monitor display and image processing. The utility 11 and the OS are used as work for the OS 11 that provides basic functions necessary for the operation of software such as application software, and color matching processing. A RAM 12, an image data storage unit 13 for storing image image data, a monitor driver 14 for controlling display data when displayed on the monitor 2, a printer driver 15 for connecting the printer 3 and the PC main body, and color matching processing. The module CMM 16, utility software 4 for creating a profile to which an inverse gamma 2.2 LUT is added by calculation, the monitor profile storage unit 17 storing the monitor profile of the monitor 2, and the printer profile of the printer 3 are stored To be And a printer profile storage unit 18. In addition, the utility software 4 includes an inverse gamma 2.2 LUT calculation unit 1A that generates an inverse gamma 2.2 LUT, and a color space compression LUT calculation unit that calculates a LUT obtained by performing color space compression on data considering the inverse gamma 2.2. 1B has a profile creation unit 1C that creates profile data from the calculated inverse gamma 2.2 LUT and color space compression LUT.

  FIG. 4 shows an outline of the color matching process design in an example of the embodiment in which the inverse gamma LUT is implemented. Here, a block diagram and a graph of processing for converting from the monitor color space (monitor RGB) A to the printer color space (printer CMYK) C are shown.

  In this case, the monitor profile becomes the source profile 401 and the printer profile becomes the destination profile 402. A is input luminance RGB, B is data after gamma conversion of the monitor profile 401, B 'is data after inverse gamma conversion of the printer profile 402, and C is an output CMYK value after gamma conversion of the printer profile 402. Yes. Here, black circles 407 on the lines A to B ′ are grid points of the input luminance A, and white circles are data after printer gamma conversion. Further, black circles 408 on the lines B to C are grid points of the output CMYK.

  Also, on the graph, the conversion curve 403 when the monitor gamma is 2.2, the data of the grid point 407 is converted by the conversion curve by the conversion curve, and the data converted by the printer gamma linear line 404 is the white circle grid point 409. Further, data converted by the LUT 406 designed with a printer gamma linear line is indicated by black dot lattice points 408. On the other hand, the conversion curve 403 when the monitor gamma is 2.2, the data of the grid point 407 is converted by the conversion curve by the conversion curve, the data converted by the printer inverse gamma curve 405 is the grid point 410 of the white circle, and the printer gamma 2 The data converted by the LUT 407 designed with a .2 curve is indicated by black dot lattice points 408.

  Although there is no difference in the output luminance difference grid point data 408 due to the difference in the printer gamma conversion curve, the data after the printer gamma conversion appears in the white circle grid points on the lines A to B ′. Yes. Conventionally, the dark portion is designed with information up to the lattice point 409. However, by adopting the inverse gamma transformation curve, the amount of information is increased as in the lattice point 410. In this way, the color space compression LUT is designed and the data is converted in a state where the information of the Dark portion is increased, so that the collapse of the Dark portion is further eliminated.

  FIG. 5 shows a conventional arithmetic processing block diagram 501 and an arithmetic processing block diagram 502 of the present invention. A conventional arithmetic processing block diagram 501 shows color matching processing when an sRGB monitor profile is selected as the source profile 503 and a printer profile is selected as the destination profile 505. Here, only the gamma value is noted and mentioned. First, the gamma value 2.2 of the source profile sRGB monitor profile 503 is applied to the input sRGB value. Then, in the conventional arithmetic processing block diagram 501, a conversion LUT 506 to an output devRGB that is designed to be linear after that is calculated, and a destination profile 505 is created by storing the LUT 506. In the arithmetic processing block diagram 502 of the present invention, the input sRGB value is multiplied by the gamma value 2.2 of the source profile sRGB monitor profile 504, and then the inverse gamma 2.2 LUT 508 is multiplied so that the gamma is linear at 2.2. A conversion LUT 509 to devRGB designed for color space compression is calculated. A profile is created by storing the inverse gamma 2.2 LUT 508 and the conversion LUT 509.

  FIG. 6 shows a flowchart of the present embodiment. Here, the case where the color displayed on the monitor is reproduced so as to look the same color under each environment when printed by a printer is shown. An example will be described in which sRGB is selected as the monitor profile, an inverse gamma 2.2 LUT and a color space compression LUT are generated, mounted in the profile, and output.

  In S101, the PC main body 1 is operated, the inverse gamma 2.2 is calculated by the calculation unit 1A using the utility software 4, and the inverse gamma 2.2 LUT to be stored in the profile is generated. In S102, a color space compression calculation considering the gamma value 2.2 is performed by the calculation unit 1B, and an LUT stored in the profile is generated. In S103, the inverse gamma 2.2 LUT generated in S101 and the LUT generated in S102 are stored in the profile by the profile creation unit 1C to generate a printer profile. In step S104, the printer profile generated in step S103 is stored in the printer profile storage unit 18. In S 105, each profile is obtained from the printer profile storage unit 18 and the monitor profile storage unit 17 and set in the CMM 16. In S 106, the image is read from the image data storage unit 20 and set in the CMM 16. In S106, color matching is performed on the image by the CMM 16. The image matched in S107 is output to the printer 3.

  By performing the processing as described above, even if the gamma value of the monitor on which the user actually creates and uses an image is high, it is possible to improve the color reproducibility by increasing the amount of information in the Dark portion. .

(Other embodiments)
The present invention is not limited to the embodiments described above, and the flow and the like can be changed without departing from the spirit of the present invention.

The conceptual diagram of a color management system. Overview of conventional color matching processing design. The structure of the Example of this invention. The outline | summary of the color matching process design in an example of an Example. The block diagram of the Example of this invention. The flowchart of an Example.

Claims (1)

  A color matching processing means for performing color matching on image data, an arithmetic means for generating an inverse gamma LUT, an arithmetic means for generating an LUT corresponding to a device, and a profile corresponding to the device from the two LUTs An image processing apparatus comprising: a profile creating unit configured to perform color matching using the created profile.

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