JP4027137B2 - Image processing method and image processing apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image processing method and an image processing apparatus that perform color conversion processing using a profile.
[0002]
[Prior art]
In applications and device drivers that operate on personal computers and the like, especially software that handles images, color conversion processing for converting image data from one color space to another is often performed.
[0003]
For example, when printing RGB image data input to a personal computer with a printer, the image data is converted from an RGB color space to a CMYK color space composed of cyan, magenta, yellow, and black. Is called.
[0004]
When such RGB → CMYK conversion is performed, a method of performing the color conversion process in two stages is known. Hereinafter, the two-stage color conversion process will be described.
[0005]
In this two-stage color conversion process, the latter process performs color space conversion that matches the input characteristics of the printer, that is, the output device, such as the RGB color space to the CMYK color space, and the former process uses, for example, an arbitrary input color space. Performs conversion to a predetermined color space such as RGB color space.
[0006]
FIG. 3 is a diagram showing an outline of the conventional two-stage color conversion process. Generally, the RGB color space to which the input image data belongs is often a standardized monitor color space such as sRGB. Therefore, in the first stage processing, conversion from the monitor RGB color space such as sRGB to the device RGB color space (Mon.RGB → Dev.RGB) is performed. Here, the device RGB color space is a device-dependent color space designed to represent the entire color gamut by a device such as a printer. In the subsequent processing, conversion from device RGB to CMYK or the like (Dev.RGB → CMYK) into a color space suitable for the printing characteristics of the output device is performed and converted to output image data.
[0007]
When two-stage color conversion as shown in FIG. 3 is performed, it is necessary to refer to the profile for the previous conversion from the monitor RGB to the device RGB and the profile for the subsequent conversion from the device RGB to CMYK. Such a color conversion profile is often preinstalled in a printer main body, a printer driver that controls the printer, or application software that controls the printer.
[0008]
Here, for example, if the input color space is fixed to sRGB or the like, the two-step conversion can be defined as one conversion in advance, so that the profiles to be used can be combined into one. In this case, as shown in FIG. 4, it is possible to convert from a monitor RGB color space to a color space such as CMYK (Mon.RGB → CMYK) by performing color conversion processing once.
[0009]
In this way, when the input color space is fixed, such as standardized sRGB, color conversion processing using one profile as shown in FIG. 4 is possible. However, conversion from any color space may be desired. For example, a case where the user desires color conversion reflecting the color space characteristics of the scanner for the image data read by the scanner.
[0010]
In order to cope with such color conversion processing from an arbitrary color space, color conversion processing as shown in FIG. 5 is required. According to FIG. 5, first, image data in an arbitrary input color space is converted into a device RGB color space. At this time, an input profile (Source Profile: Source Profile) representing the characteristics of the input color space that is the conversion source and an output profile (Destination Profile: Dest.Profile, in this case, device RGB) representing the color space characteristics after conversion. Conversion using two profiles (profiles describing characteristics). This input profile and output profile are connected in a color space such as CIE XYZ or CIE L * a * b *. Next, as in the case of FIG. 3, conversion from device RGB to a color space suitable for printing such as CMYK (Dev.RGB → CMYK) is performed.
[0011]
By performing color conversion using two profiles of an input profile and an output profile as shown in FIG. 5, it is possible to perform color conversion combining arbitrary input / output color spaces.
[0012]
There is a standard advocated by the ICC (International Color Consortium) as a profile format that is widely used to perform such color conversion with a high degree of freedom, and is commonly called an ICC profile. By specifying an input profile and an output profile in the ICC profile format and using a color conversion module (CMM) compliant with the ICC profile, color conversion in an arbitrary color space can be performed.
[0013]
[Problems to be solved by the invention]
Generally, in an output device such as an ink jet printer, the characteristics of the output color space change depending on the media and the printing method. Here, the medium refers to an output medium such as paper or film, and generally has a characteristic such that a coated medium or the like has a wide color reproduction range and a plain paper or the like has a narrow color reproduction range. The printing method represents a driving method for a print head. In many cases, several types of modes such as “fast”, “standard”, and “pretty” are prepared as the driving method. For example, the “fast” mode setting has a short print time but a narrow color reproduction range, the “clean” mode setting has a slow print time but a wide color reproduction range, and the “standard” mode setting has intermediate characteristics. ing.
[0014]
In this way, general output devices have unique color space characteristics for each combination of media and printing method, so to convert input RGB data to CMYK data for printing, see Fig. 3. The Mon.RGB → Dev.RGB profile and Dev.RGB → CMYK profile shown in FIG. 4 and the Mon.RGB → CMYK profile shown in FIG. 4 need to be created for the number of combinations of media and printing methods. For example, if there are 10 types of media supported by a printer and 3 types of printing methods are prepared, 30 types of profiles need to be prepared.
[0015]
Although there are many profiles that should be prepared in advance, output device providers (manufacturers, etc.) such as printers create them with their own standards, hold them in their own formats, and are automatically selected. There is little burden on the user side.
[0016]
In addition, even in a system that performs arbitrary color matching using an ICC profile as shown in Fig. 5, since the output profile depends on the device RGB, it is necessary to prepare as many output profiles as there are combinations of media and printing methods. was there.
[0017]
As described above, according to the method shown in FIG. 5, there is an advantage that color matching can be performed in a state where the output color space of the device determined by the media and the printing method is maximally utilized. there were,
・ Profile developers had to create ICC profiles for several minutes (in many cases, dozens of combinations) of media and printing methods, which required a lot of labor.
[0018]
-Since the ICC profile is provided as an individual file, when a user arbitrarily selects a profile, it is complicated to specify an appropriate ICC profile from several tens of types of files.
[0019]
-Depending on the OS, there may be an upper limit on the number of files that can be installed by an installer such as a printer driver, and not all ICC profiles could fit in the printer driver.
[0020]
Therefore, a color conversion method as shown in FIG. 6 is known as a method for reducing the number of output profiles when performing color matching using an ICC profile. According to FIG. 6, the input ICC profile is arbitrary as in the case of FIG. 5, but color conversion is performed using a fixed output ICC profile (for example, a standardized sRGB monitor profile), and thereafter As in the case of FIG. 4, the monitor RGB → CMYK conversion is performed. According to this method, once the input color space is normalized to the monitor RGB color space, a profile (Mon.RGB → CMYK) prepared in advance when not using the ICC profile can be used. it can.
[0021]
As described above, according to the method shown in FIG. 6, it is not necessary to prepare different ICC profiles depending on the media and the printing method, and only one output profile is required.
[0022]
However, according to the method shown in FIG. 6, although the number of output ICC profiles can be limited regardless of the media and printing method, the color space is limited to the monitor RGB in the middle of color conversion, so the color reproduction capability of the device is reduced. I couldn't make the most of it.
[0023]
The present invention has been made to solve the above problems individually or collectively, and provides an image processing method and an image processing apparatus capable of performing high-quality color conversion while limiting the number of profiles. The purpose is to do.
[0024]
[Means for Solving the Problems]
As a technique for achieving the above object, the image processing method of the present invention includes the following steps.
[0025]
That is, the input image data, an image processing method for performing color conversion processing of multiple stages using a profile, determining an input profile and an output profile in ICC profile used in the color conversion in the first stage The input profile is determined based on the input profile information embedded in the input image data, and a printer profile or a common monitor profile corresponding to the media and printing conditions is determined as the output profile. A first determining step; a determining step for determining a type of device to be color-converted based on Profile / Device Class signature information in an ICC header of the determined output profile ; and the determined color conversion target based on the type of device to be, a subsequent stage of the first stage A second determining step of determining a conversion profile to CMYK used for color conversion in a given second stage, the input image data, by the input profile and an output profile determined in the first determining step The first stage color conversion using the configured ICC profile is performed, and the image data after the color conversion in the first stage is converted to the CMYK determined in the second determination step. And a color conversion step for performing the color conversion in the second stage using a profile .
[0026]
According to a preferred embodiment of the present invention, in the second determining step, when the type of device to be color-converted is for a monitor , the conversion profile to the CMYK is uniquely determined. Is preferred .
[0027]
Another aspect of the present invention relates to an image processing apparatus that performs multi-stage color conversion processing using a profile for input image data, and includes a combination of each of a plurality of input profiles and output profiles. a plurality of ICC profiles, a holding means for holding a conversion profile to multiple CMYK, based on the input profile information embedded in the input image data, from a plurality of input profile held in the holding means An input profile in an ICC profile used for color conversion in the first stage is determined, and a printer profile or a common monitor profile corresponding to the media and printing conditions is set as an output profile in the ICC profile in the holding unit. A first decision to determine from a plurality of retained output profiles Means for determining the type of device to be color-converted based on Profile / Device Class signature information in the ICC header of the determined output profile, and for the determined device to be color-converted A second CMYK conversion profile used for color conversion in the second stage, which is the latter stage of the first stage, is determined from a plurality of CMYK conversion profiles held in the holding unit based on the type. A first stage color conversion using an ICC profile composed of an input profile and an output profile determined by the first determination unit for the input image data; to the image data after the color conversion at step performs color conversion of the second step using the conversion profile to the second of the CMYK determined by the determining means And having a conversion means.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment according to the present invention will be described in detail with reference to the drawings.
[0029]
<First Embodiment>
FIG. 1 is a flowchart showing an image processing procedure in the present embodiment. FIG. 2 is a block diagram of an image processing apparatus that executes the processing shown in the flowchart of FIG.
[0030]
In FIG. 2, 1 is a CPU that controls the entire apparatus, 2 is a display such as a CRT that displays an image, 3 is a keyboard for inputting various instruction data of an operator, 4 is a ROM that stores a processing program, etc. , 5 is a RAM that temporarily stores various processing results, data, and programs, 6 is a storage device such as a hard disk drive (HDD) that stores image data and image processing programs, and 7 is a communication line with an external device. A communication interface for communication via a computer, 8 is a pointing device such as a mouse as an auxiliary input means, 9 is an external device for controlling so-called removable media such as a floppy disk drive, magneto-optical disk drive, CD-ROM, CD-R, etc. A storage device 20 is a printer connected via the communication line 10. These components are connected to each other by a bus 11.
[0031]
The image processing apparatus having the configuration shown in FIG. 2 loads program code for executing the processing shown in the flowchart of FIG. 1 into the RAM 5 from the storage device 6, the ROM 4, the external storage device 9, and the like. It is held in the storage area 500. Then, the CPU 1 starts executing the program code recorded in the program storage area 500. At this time, the program code has a code of a step for realizing the image processing method in the present embodiment.
[0032]
Next, image processing based on the program code of this embodiment will be described in detail with reference to FIG.
[0033]
In this embodiment, processing for converting input image data in an arbitrary color space to RGB color space is performed based on the ICC profile, and further, processing for converting from the RGB color space to a CMYK color space that matches the characteristics of the printer 20 Is performed based on a pre-designed profile. Then, after performing such two-stage color conversion processing, the printer 20 obtains a printed matter based on the image data.
[0034]
The image processing apparatus according to the present embodiment is characterized in that a plurality of profiles are held in advance, and optimal color matching is possible by selecting an appropriate profile at the time of color conversion. A plurality of profiles prepared in advance are held in any of ROM 5, RAM 5, storage device 6, and external storage device 9.
[0035]
First, in step S101, a medium to be output by the printer 20 is selected. As a method for selecting media, for example, there is a method in which the user uses the keyboard 3 or the pointing device 8 to select based on the GUI displayed on the display 2. Further, the result of determining the output medium by the printer 20 may be transmitted to the CPU 1 via the communication line 10 and the communication interface 7.
[0036]
In step S102, the printing method (print head driving method, halftoning method, etc.) for the printer 20 is set. In this printing method, it is preferable that a predetermined value is set as a default value, and can be changed using the keyboard 3 or the pointing device 8 when the user desires to change it.
[0037]
In step S103, an ICC profile is selected. That is, the output profile is selected from the input profile and the output profile used in the previous stage of the two-stage color conversion. This profile selection may be designed so that the software automatically selects according to the media and printing conditions, or the user can arbitrarily select from a pull-down menu in the GUI. In the initial state, it is preferable that the software automatically selects a profile and makes an arbitrary selection only when the user intends.
[0038]
Note that the input profile used in the previous color conversion can also be specified in various forms. For example, it may be specified by the OS or application, or an input profile may be embedded in the image data. Further, the user may arbitrarily specify the input profile. As described above, various methods can be considered as an input profile designation method. In the present embodiment, description will be made assuming that input profile information embedded in image data is used.
[0039]
When the selection of the ICC profile is completed, profile type information acquisition is performed in step S104. That is, the information recorded in the output profile selected in step S103 is read.
[0040]
In general, in an ICC profile, an area called “Profile / Device Class signature” is secured in the header part, and in this area, whether a device to be color-converted is an input device such as a scanner, a monitor or the like. A code indicating whether it is a display device or an output device such as a printer is stored. In step S104, the header information recorded in such an ICC profile is read.
[0041]
In step S105, a profile used in the subsequent stage of the two-stage color conversion is determined based on the information acquired in step S104.
[0042]
For example, if the information acquired in step S104 indicates that the profile type is for monitor, a profile for converting from monitor RGB to CMYK is selected as a subsequent profile. That is, the subsequent color conversion processing (Mon.RGB → CMYK) shown in FIG. 6 is selected.
[0043]
On the other hand, if the profile type indicates that for a printer, a profile for converting from device RGB to CMYK is selected. That is, the subsequent color conversion processing (Dev.RGB → CMYK) shown in FIG. 5 is selected.
[0044]
In either case, it is necessary to select a profile that matches the media and printing method set in steps S101 and S102.
[0045]
When the preceding and subsequent color conversion profiles are determined by the above processing, the image data to be processed is read from the storage device 6 or the like in step S106. In step S107, the read image data is subjected to two-stage color conversion based on the profile set as described above. That is, the input image data in an arbitrary color space is converted into the RGB color space by the previous color conversion process using the ICC profile, and then the subsequent color conversion process using the automatically determined profile. , Converted to data in the CMYK color space for the printer 20.
[0046]
In step S108, the image data converted into the CMYK color space in step S107 is transmitted to the printer 20 via the communication interface 7 and the communication line 10. As a result, the image that has been subjected to the optimum color conversion is output from the printer 20 while maintaining the original color, and the process ends.
[0047]
As described above, according to the present embodiment, the latter profile can be optimized by selecting the latter profile based on the first profile type.
[0048]
As a result, regardless of whether the previous profile is a fixed monitor color space or a device-dependent color space adapted to the media and printing conditions, the optimal profile is always selected as the subsequent profile. Appropriate color matching can be performed.
[0049]
Therefore, there is no need to prepare output ICC profiles for all types of processing conditions (for example, media and printing method), and high-quality matching is realized only for some high-quality media and printing conditions. The output ICC profile is provided, and a common monitor profile may be designated for other processing conditions. In this way, high-quality color conversion is performed under printing conditions where high-quality output is desired, and standard color matching using a common ICC profile is performed under other conditions.
[0050]
As a result, high-quality color conversion is possible even if the number of ICC profiles to be prepared in advance is reduced. In addition, since the number of profiles to be selected is small, the user operation load related to ICC profile selection is reduced.
[0051]
Even when the present embodiment is implemented as a printer driver, it is possible to install all ICC profiles by limiting the number of ICC profiles.
[0052]
<Modification>
In the apparatus configuration shown in FIG. 2 above, program codes for executing the respective means forming the present invention are stored in the RAM 5, ROM 5, storage device 6, external storage device 9 and the like, thereby realizing the present invention. A processing device can be configured. At this time, each execution step of the program code constitutes a profile selection unit, a profile type acquisition unit, a subsequent profile determination unit, and a color conversion unit.
[0053]
In addition, the image processing to which the present invention is applied is implemented by implementing all or part of the above means by a dedicated processing circuit such as DSP or ASIC, instead of a general-purpose computer system as shown in FIG. It goes without saying that the device can be configured.
[0054]
[Other Embodiments]
Note that the present invention can be applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, and a printer), and a device (for example, a copying machine and a facsimile device) including a single device. You may apply to.
Another object of the present invention is to supply a storage medium storing software program codes for realizing the functions of the above-described embodiments to a system or apparatus, and the computer (or CPU or MPU) of the system or apparatus stores the storage medium. Needless to say, this can also be achieved by reading and executing the program code stored in.
[0055]
In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention.
[0056]
As a storage medium for supplying the program code, for example, a floppy disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.
[0057]
In addition, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an OS (operating system) running on the computer based on the instruction of the program code. It goes without saying that a part of the actual processing is performed and the functions of the above-described embodiments are realized by the processing.
[0058]
Further, after the program code read from the storage medium is written to a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. It goes without saying that the CPU or the like provided in the board or the function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.
[0059]
【The invention's effect】
As described above, according to the present invention, it is possible to perform high-quality color conversion while limiting the number of profiles.
[Brief description of the drawings]
FIG. 1 is a flowchart showing image processing in an embodiment according to the present invention.
FIG. 2 is a block diagram illustrating a configuration of an image processing apparatus in which the present exemplary embodiment is implemented.
FIG. 3 is a diagram showing an outline of color conversion from a monitor RGB color space to a CMYK color space via a device RGB color space;
FIG. 4 is a diagram showing an outline of direct color conversion from a monitor RGB color space to a CMYK color space.
FIG. 5 is a diagram illustrating an outline of color conversion from an arbitrary input color space to a CMYK color space via a device RGB color space;
FIG. 6 is a diagram illustrating an outline of color conversion from an arbitrary input color space to a CMYK color space via a monitor RGB color space.
[Explanation of symbols]
1 CPU
2 display
3 Keyboard
4 ROM
5 RAM
6 Storage device
7 Communication interface
8 Pointing device
9 External storage device
10 Communication line
11 Bus
20 Printer

Claims (6)

An image processing method for performing multi-stage color conversion processing using a profile for input image data,
Determining an input profile and an output profile in an ICC profile used for color conversion in a first stage, wherein the input profile is determined based on input profile information embedded in the input image data, and a medium and print A first determination step of determining a printer profile or a common monitor profile according to conditions as the output profile ;
Based on Profile / Device Class signature information in the ICC header of the determined output profile, a determination step of determining the type of device to be color converted ,
A second determination step of determining a conversion profile to CMYK used for color conversion in a second stage, which is a subsequent stage of the first stage, based on the determined type of device to be converted ;
The first stage color conversion is performed on the input image data using an ICC profile composed of the input profile and the output profile determined in the first determination step, and the color in the first stage is determined. A color conversion step of performing color conversion in the second stage using the conversion profile to the CMYK determined in the second determination step on the converted image data ;
An image processing method comprising: 2. The image processing according to claim 1, wherein, in the second determining step, if the type of device to be color-converted is for a monitor , a conversion profile to the CMYK is uniquely determined. Method. An image processing apparatus that performs multi-stage color conversion processing using a profile for input image data,
Holding means for holding a plurality of ICC profiles configured by a combination of each of a plurality of input profiles and output profiles, and a plurality of conversion profiles to CMYK ;
Based on input profile information embedded in the input image data, an input profile in an ICC profile used for color conversion in the first stage is determined from a plurality of input profiles held in the holding unit, and a medium and a print First determining means for determining a printer profile or a common monitor profile as an output profile in the ICC profile from a plurality of output profiles held in the holding means ;
Based on Profile / Device Class signature information in the determined ICC header of the output profile, a discriminating means for discriminating the type of device to be subjected to color conversion ,
A plurality of conversion profiles to CMYK used for color conversion in the second stage, which is a subsequent stage of the first stage, are held in the holding unit based on the determined type of device to be converted. Second determining means for determining from a conversion profile of CMYK to
The first stage color conversion is performed on the input image data using an ICC profile composed of the input profile and the output profile determined by the first determination unit, and the color in the first stage is determined. Color conversion means for performing color conversion in the second stage using the conversion profile to CMYK determined by the second determination means on the converted image data ;
An image processing apparatus comprising: 4. The image processing apparatus according to claim 3, wherein the second determination unit uniquely determines a conversion profile to the CMYK when a device type to be color-converted is for a monitor. 5. . A program for causing a computer to execute the image processing method according to claim 1 . A computer-readable storage medium storing the program according to claim 5 .

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