JP5043511B2 - Color processing apparatus and method - Google Patents

Description

  The present invention performs color conversion processing.

  In recent years, with the spread of personal computers / workstations, desktop publishing (DTP) and CAD are widely used. Under such circumstances, a color reproduction technique for matching a color expressed on a monitor by a computer with a color reproduced on an output medium is important. For example, in DTP, a workflow is performed in which a color image is created / edited / processed on a monitor and an image is output as a product by a color printer. In this workflow, the user strongly desires that the color image on the monitor and the printer output image are perceptually matched.

  A CMS (Color Management System) is used to match colors between different devices. In the CMS, a color management module (CMM) performs color conversion processing using a profile corresponding to an input device and a profile corresponding to an output device.

  For example, as shown in FIG. 1, color conversion is performed from a monitor color space (monitor RGB) to a printer color space (printer RGB). In this case, the input device is a monitor, and the monitor profile is the input device profile. The output device is a printer, and the printer profile is an output device profile. The CMM converts the colorimetric values of the input device profile and the output device profile into a device-independent color space, and performs gamut mapping (color gamut compression) in the device-independent space.

  Conventionally, since a monitor is a self-luminous device, it generally has one set of colorimetric values, that is, one device profile in one model or setting mode. This is because, unlike a reflector, a monitor that is a self-luminous device is considered to be hardly affected by illumination in the observation environment.

However, although it is not as much as a reflective object, the appearance of the color of the monitor actually changes due to the effect of illumination. Therefore, the illumination information for observing the monitor is obtained from the sensor, and the colorimetric value of the monitor is set according to the illumination. As a result, a more accurate matching result can be obtained.
JP 2007-006039 A

  In order to correct the colorimetric value of the monitor in consideration of the influence of the illumination as described above, a sensor for acquiring the illumination information is necessary. Therefore, when the user does not have such a sensor, this is necessary. The method cannot be applied.

  Therefore, an object of the present invention is to make it possible to correct a colorimetric value of a monitor in consideration of the influence of illumination even when there is no sensor, and to realize highly accurate matching.

In order to achieve the above object, the present invention provides means for acquiring a monitor profile and a printer profile, means for acquiring illumination light information in the printer profile, and illumination light information in the printer profile. A correction unit that corrects the colorimetric value of the monitor stored in the monitor profile; and a color conversion processing unit that performs color conversion using the corrected colorimetric value of the monitor and the printer profile. And

  According to the present invention, even when there is no sensor that acquires illumination information, it is possible to realize high-accuracy matching of color appearance by correcting the colorimetric value of the monitor according to the illumination.

Example 1
First, a method for correcting monitor colorimetric values according to illumination will be described.

Since the monitor has an additive color mixture, the colorimetric value XYZ _{B-measurement} of the monitor in environment B is the colorimetric value XYZ A-monitor of the monitor _in environment A, and the black colorimetric value XYZ _{A_Bk-measurement} of the monitor _in environment A. From the colorimetric value XYZ _{B_Bk-measurement} of the monitor black in environment B, it is obtained using equation (1).
XYZ _{B-measurement} = XYZ _{A -measurement} -XYZ _{A_Bk-measurement} + XYZ _{B_Bk-measurement} (1)
Therefore, if there is a colorimetric value XYZ _{A-measurement} of the monitor in the environment A, if the black colorimetric value XYZ _{B_Bk-measurement} of the monitor in the environment B can be calculated from the illumination information of the environment B, the colorimetry of the monitor in the environment B The value XYZ _{B-measurement} can be determined.

Here, as shown in FIG. 3, the XYZ _measurement of the color of the monitor entering the human eye is based on the light XYZ _{monitor emission} emitted by the monitor itself and the light XYZ _{tube in} which the monitor tube surface reflects the illumination. _{Consists of surface reflection} .
XYZ _{B-measurement} = XYZ _{B-monitor emission} + XYZ _{B-tube surface reflection} (2)
Since this naturally holds for the colorimetric value of black on the monitor, XYZ _{B_Bk−measurement} = XYZ _{B_Bk−monitor emission} + XYZ _{B_Bk−tube surface reflection} formula (3)
It becomes. The light emitted from the monitor itself is constant as long as the setting is the same, but since the tube surface reflection component changes depending on the illumination, it is necessary to correct the colorimetric value according to the illumination. XYZ _{B_Bk-monitor emission} is obtained by _{measuring the} color of monitor black under darkness where tube reflection does not occur. Therefore, if the _tube reflection component XYZ _{B_Bk−tube reflection} can be calculated from the illumination information, the black colorimetric value XYZ _{B_Bk−measurement} of the monitor in the environment B can be calculated.

The tube surface reflection component XYZ _{B_Bk—the tube surface reflection} can be calculated from the _illumination XYZ _{B_illumination} and the tube surface reflectance R by the equation (4).
XYZ _{B_Bk- tube surface reflection} = XYZ _{B_ illumination} * R · · · formula (4)
From equations (3) and (4),
R _{= (XYZ B_Bk- measuring} -xyz _{B_Bk- monitor light emission)} / XYZ _{B_ Lighting} Equation (5)
Holds. Since the tube surface reflectance R does not depend on illumination, it is obtained in advance and written in the device profile. For example, the tube surface reflectance R is written in the private data of the device profile. In addition, the colorimetric value is given by a colorimetric value in the dark by a non-contact type colorimeter or a colorimetric value by a contact type colorimeter (eg, grid 729 colors such as RGB) to obtain the equation (3). XYZ _{B_Bk—monitor emission} is known. Since the tube surface reflectance R is also known, the colorimetric value including the tube surface reflection component under the illumination can be calculated as long as the XYZ value of the illumination can be acquired.

  Here, in this embodiment, since it is assumed that there is no sensor that acquires illumination information, the illumination information must be acquired by a method other than measurement. In this embodiment, in general, in monitor / printer matching, a monitor and a printed matter are often compared under the same illumination, and therefore the XYZ values of illumination are acquired from the observation environment information in the printer profile.

  FIG. 4 is a block diagram of the color processing apparatus according to the present embodiment. 401 is a CPU, 402 is a main memory, 403 is a SCSI interface, and 404 is a network interface. Reference numeral 405 denotes an HDD, 406 denotes a graphic accelerator, 407 denotes a color monitor, 408 denotes a USB controller, and 409 denotes a color printer. Reference numeral 410 denotes a keyboard / mouse controller, 411 denotes a keyboard, 412 denotes a mouse, 413 denotes a local area network, and 414 denotes a PCI bus.

  A digital image printer output operation in the color processing apparatus will be described.

  First, an image application, which is a program stored in the HDD 405, which is a storage medium, is activated by the CPU 401 based on an OS program that receives a user instruction. In accordance with the processing of the image application, digital image data stored in the HDD 405 is transferred to the main memory 402 via the PCI bus 414 via the SCSII / F 403 based on a command from the CPU 401. Alternatively, image data stored in a server connected to the LAN or digital image data on the Internet is transferred to the main memory 402 via the PCI bus 414 via the network I / F 404 in response to a command from the CPU 401. Hereinafter, the embodiment will be described on the assumption that the digital image data held in the main memory 402 is image data in which each RGB color signal is expressed by 8 bits without a sign. The digital image data held in the main memory 402 is transferred to the graphic accelerator 406 via the PCI bus 114 in response to a command from the CPU 401. The graphic accelerator 406 performs D / A conversion on the digital image data and transmits the digital image data to the color monitor 407 through the display cable. As a result, an image is displayed on the color monitor 407. Here, when the user instructs the image application to output the digital image held in the main memory 402 from the printer 409, the image application transfers the digital image data to the printer driver. The CPU 401 converts digital image data into CMYK digital image data based on a process flowchart described later of the printer driver, and transmits the CMYK image data to the printer 409 via the USB controller 408. As a result of the above series of operations, a CMYK image is printed by the printer 409.

Hereinafter, the printer driver operation will be described with reference to the flowchart of FIG.
First, in step S <b> 501, the transferred RGB 24-bit image data (each color signal is unsigned 8-bit image data) is stored in the main memory 402.

  In step S502, an input device profile, an output device profile, and a matching method are selected. FIG. 6 shows an example of a GUI (graphical user interface) for inputting a user instruction for selecting a profile. In FIG. 6, 601 is a drop-down combo box for selecting an input device profile, 602 is a drop-down combo box for selecting an output device profile, and 603 is a check box for selecting a matching method.

  FIG. 2 is a diagram illustrating a configuration example of a device profile. A profile is a device that describes the correspondence between the header part that describes appearance parameters, etc., the signal values of the device (RGB if it is a display), and the colorimetric values when color patches with known signal values are displayed and output And a data storage unit.

  In the appearance parameters, white tristimulus values, adaptation luminance, background luminance, and paper environmental conditions are set. The white tristimulus value is the white tristimulus value of a self-luminous device such as a monitor, and the illumination tristimulus value is used as illumination light information of the environment in which the reflective object is observed in a printer that handles the reflective object. Set.

  In step S503, it is determined whether or not to convert the colorimetric values in the device profile based on the selected combination of device profiles and the matching method. If it is determined to convert, the colorimetric value is converted.

  In step S504, a color correction LUT is created. The color correction LUT has a data structure as shown in FIG. 7 in which the correspondence between the color coordinate data of the grid point in the RGB color space and the coordinate value of the Jab color space reproduced by the grid point is described. An R / G / B value step is described at the head of the data structure, and thereafter, the J value, a value, and b value, which are output values corresponding to each grid point, are in the order of R, G, and B. Nested and described.

  In step S505, the RGB 24-bit image data is converted into Jab fixed point data based on the color correction LUT and stored in the main memory 402 again. Tetrahedral interpolation is used for the conversion.

  In step S506, the previous Jab fixed-point data is converted into CMYK 32-bit image data (CMYK color signals are unsigned 8-bit image data) in accordance with a predetermined color conversion LUT, and stored in the main memory 402 again.

  In step S507, the CMYK 32-bit image data stored in the main memory is transmitted to the printer 409 via the USB controller 408.

  Hereinafter, the colorimetric value conversion processing in step S503 will be described with reference to the flowchart of FIG.

  In step S801, the input / output device profile selected in step S502 and the matching method are acquired.

  In step S802, it is determined whether the selected combination of input / output device profiles is a monitor and a printer. If the determination result is true, the process proceeds to step S803, and if it is false, the colorimetric value conversion process is terminated.

  In step S803, it is determined whether or not the acquired matching method is in the “faithful appearance” mode. If the determination result is true, the process proceeds to step S804. If the determination result is false, the colorimetric value conversion process is terminated.

In step S804, black colorimetric value XYZ _{Bk-measurement} and tube surface reflectance R are acquired from the monitor profile.

In step S805, tristimulus XYZ _illumination is acquired as illumination light information from the printer profile.

In step S806, first, a black colorimetric value XYZ _{Bk-measurement} 'of the monitor under the current illumination is calculated using equation (6). Next, the calorimetric value data XYZ _measurement of the monitor profile is converted based on the formula (7) using the calculated XYZ _{Bk-measurement} ', and the colorimetric value of the monitor under the current illumination is calculated.
XYZ _{Bk-measurement} '= XYZ _{Bk-measurement} + XYZ _illumination * R (6)
XYZ _measurement '= XYZ _measurement -XYZ _{Bk-measurement} + XYZ _{Bk-measurement} (7)
In step S807, the converted colorimetric value data of the monitor is stored in the main memory 402.

  Hereinafter, the color correction LUT creation processing in step S504 will be described with reference to the flowchart of FIG.

  In step S901, the input / output device profile and the colorimetric value data of the monitor stored in the main memory are acquired. The colorimetric value data of the monitor stored in the main memory is the colorimetric value data stored in step S807. That is, the colorimetric value data corrected by the tristimulus values of the illumination of the printer profile. If monitor colorimetric data is not stored in the main memory, only the device profile is acquired.

  In step S902, from the acquired input / output device profile, color gamut information of the input / output device is generated in the Jab color space by forward conversion of CIECAM02 using the appearance parameter in the device profile. As an example, FIG. 10 shows color gamut information. Note that the color gamut information is expressed by a combination of a plurality of polygons.

  In step S903, gamut mapping is performed in the Jab color space using the color gamut information of the input / output devices. That is, a process for mapping the color gamut of the input device to the color gamut of the output device is performed.

  In step S904, the mapping result in step S903 is converted from a Jab value to an XYZ value by inverse conversion of CIECAM02 using the appearance parameter of the output device profile.

  In step S905, the output device profile is used to convert XYZ values to RGB values, and a color correction LUT is generated.

  Hereinafter, the color gamut information generation processing for generating color gamut information from the input / output device profile in the Jab space in step S902 will be described with reference to the flowchart of FIG.

  In step S1101, an appearance parameter in the device profile is acquired.

  In step S1102, information is acquired by selecting one measurement data. In step S1103, the measurement data selected in step S1102 is converted into a Jab value using CIECAM02 forward conversion. In step S1104, the selected data information is updated so that the next different data is selected. In step S1105, it is determined whether all data has been selected. If the determination is true, the process proceeds to step S1108, and if the determination is false, the process proceeds to step S1104.

  In step S1106, color gamut information is generated in the Jab color space from all data points converted into Jab values.

The figure which shows a color conversion process. It is a figure which shows the data structure of a device profile. It is a figure which shows the element which comprises the color appearance of a monitor. It is a block diagram which shows the system configuration | structure of the color reproduction editing apparatus of this invention. 6 is a flowchart illustrating processing of a printer driver in the color reproduction editing apparatus of the present invention. It is a figure which shows GUI for selecting a profile and a matching method. It is a figure explaining the data structure of a color correction LUT. It is a flowchart which shows the process which converts the colorimetric value data of a monitor profile according to illumination. It is a flowchart which shows the creation process of a color correction LUT. It is a figure which shows an example of color gamut information. It is a flowchart which shows the color gamut information creation process from an input device profile.

Claims (5)

Means for obtaining a monitor profile and a printer profile;
Means for obtaining illumination light information in the printer profile;
Correction means for correcting colorimetric values of the monitor stored in the monitor profile using illumination light information in the printer profile ;
A color processing apparatus comprising color conversion processing means for performing color conversion processing using the corrected colorimetric value of the monitor and the printer profile.   The color processing apparatus according to claim 1, wherein the correction unit corrects the colorimetric value of the monitor using the illumination light information, the tube surface reflectance, and the black colorimetric value of the monitor. And a selection means for selecting a matching method.
When a matching method that faithfully reproduces color appearance is selected in the selection unit, the color conversion processing unit performs the color conversion process using the corrected colorimetric value of the monitor and the printer profile,
If the matching means that faithfully reproduces the appearance of the color is not selected in the selection means, the color conversion means performs the color conversion processing using the colorimetric values stored in the monitor profile. The color processing apparatus according to claim 1, wherein the color processing apparatus is a color processing apparatus.   A program stored in a storage medium so as to be readable by a computer in order to realize the color processing apparatus according to claim 1 using the computer. Get monitor profile and printer profile
Obtaining illumination light information in the printer profile;
Using the illumination light information in the printer profile, correct the colorimetric value of the monitor stored in the monitor profile,
A color processing method comprising: performing color conversion processing using the corrected colorimetric value of the monitor and the printer profile.

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