JP3784673B2 - Color conversion definition correction method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention uses a color conversion definition comprising a combination of a profile of a target device that outputs an image based on image data and a profile of a proofer that outputs an image based on the image data, and converts the image data for the target device into an image for the proofer. The present invention relates to a color conversion definition correction method for correcting a color conversion definition when converting to data and outputting a proof image based on the converted image data.
[0002]
[Prior art]
Conventionally, when printing a color image using a printing machine, before printing, a color printer or the like is used to create a proof image that resembles the color of the image printed by the printing machine as much as possible. It has been made. When creating a proof image with a printer, color reproduction characteristics (print profile) describing the relationship between the image data and the color of the actual printed material, corresponding to the printing machine that is about to print, and the printer Knowing the color reproduction characteristics (printer profile) describing the relationship between the image data and the color of the image that is actually printed, create a color conversion definition consisting of the combination of these print profile and printer profile. The image data for printing is converted into image data for printer based on the color conversion definition, and a proof image is created based on the converted image data for printer. By doing so, it is possible to create a proof image whose color matches that of the actual printed matter.
[0003]
In order to obtain an image in which colors are matched as described above, it is necessary to accurately obtain the color reproduction characteristics (profile) of an output device such as a printing press or a printer. In obtaining this color reproduction characteristic (profile), image data corresponding to a color chart in which color patches are arranged is created, a color chart is output by an output device based on the image data, and the color chart is spectroscopically measured. The color of the output device is determined by associating the coordinates of the colorimetric color space obtained in this way with a colorimeter and the coordinates of the color space (device color space) in which the image data is represented. Desired.
[0004]
[Problems to be solved by the invention]
However, the color reproduction characteristics (profiles) of output devices such as printing presses and printers are carefully determined in this way, and image data is converted based on the color conversion definition that is a combination of these color reproduction characteristics (profiles). However, due to various errors and fluctuation factors, a phenomenon occurs in which the color between the printed material and the proof image is slightly different.
[0005]
In this way, there are cases where it is unclear how and how to modify those profiles and color conversion definitions in order to correctly match the slightly different colors, and it is possible to know where and how to modify them. Even so, it is extremely difficult to manually correct it.
[0006]
In view of the above circumstances, the present invention defines the color conversion definition when image data representing an image output by a target device such as a printing press is converted into image data for a proofer and a proof image is output by a proofer such as a printer. It is an object of the present invention to provide a color conversion definition correcting method that can easily and accurately correct the above.
[0007]
[Means for Solving the Problems]
The color conversion definition correcting method of the present invention that achieves the above object provides a coordinate value in a target color space of a target device that outputs an image based on target image data defined by coordinate values in a predetermined target device color space. The proofer color space of a proofer that outputs an image based on a target profile that represents the correspondence between the coordinate values in the device-independent colorimetric color space and the coordinate values in a predetermined proofer color space The target defined by the coordinate values in the target device color space based on the color conversion definition comprising the combination of the above coordinate values and the proofer profile representing the correspondence between the coordinate values in the device-independent colorimetric color space. The image data is converted into proof image data defined by the coordinate values in the proofer color space, and the proof is displayed. When outputting the proof image based on the proof image data by using the Subwoofer, the color conversion definition correction method for correcting the color conversion definition,
The target profile outputs a color chart using the target device based on first chart data representing a color chart in which a plurality of color patches are arranged, which are defined by coordinate values in the target device color space. First color measurement data defined by the coordinate values in the color measurement color space by measuring the color patches constituting the color chart obtained in the first chart output process. It was created through a first chart colorimetric process to obtain,
A plurality of colors including at least a part of color patches defined by coordinate values different from the coordinate values of the plurality of color patches constituting the color chart represented by the first chart data on the target device color space A patch addition process for creating patch addition chart data by adding arbitrary coordinate values defining a color patch to predetermined second chart data representing a color chart in which patches are arranged;
Second color in which a plurality of color patches constituting the color chart when the color chart is output by the target device based on the patch addition chart data created in the patch addition process are defined by coordinate values in the colorimetric color space A second colorimetric data acquisition process for obtaining colorimetric data;
The patch addition chart data defined by the coordinate values in the target device color space is converted into the third chart data defined by the coordinate values in the proofer color space by using the color conversion definition, and the first chart data is converted. A third chart output process for causing the proofer to output a color chart based on the chart data of 3;
Third colorimetric data for obtaining third colorimetric data defined by coordinate values in a colorimetric color space, in which a plurality of color patches constituting the color chart output in the third chart output process are measured. Acquisition process,
Definition correction for correcting the color conversion definition based on the second color measurement data obtained in the second color measurement data acquisition process and the third color measurement data obtained in the third color measurement data acquisition process And a process.
[0008]
When a phenomenon occurs in which the colors between the printed matter and the proof image are slightly different, there are often colors in which the difference is particularly worrisome.
[0009]
According to the color reproduction characteristic correction method of the present invention, it is possible to easily and accurately correct the color conversion definition by adding a patch corresponding to such a particularly interesting color to the color chart in the patch addition process. it can.
[0010]
Here, in the color reproduction characteristic correcting method of the present invention, the second colorimetric data acquisition process and the third chart output process use the color chart represented by the first chart data as the patch additional chart data. It is preferable that patch additional chart data representing a color chart in which a number of color patches smaller than the number of color patches constituting the color chart is employed is employed.
[0011]
For correction, it is not necessary to use as many color patches as when the profile was first created, a smaller number of color patches is sufficient, and correction can be achieved by reducing the number of color patches. It can be carried out efficiently in a short time.
[0012]
Further, in the color reproduction characteristic correcting method of the present invention, the second colorimetric data acquisition process and the third chart output process include the patch additional chart data as the patch additional chart data, and the third chart for proofers. Patch additional chart data is adopted so that when it is converted to data, a plurality of color patches constituting the color chart represented by the third chart data all become color patches in the color reproduction region reproduced by the proofer. It is preferable that this process be performed.
[0013]
If the third chart data converted from the additional patch chart data contains patch data that deviates from the color reproduction characteristics of the proofer, if it is corrected forcibly as it is, it will be distorted instead of being corrected correctly. There is a risk of it. On the other hand, when the third chart data is within the color reproduction characteristic of the proofer, there is no such a risk and correct correction is performed.
[0014]
In the color reproduction characteristic correction method of the present invention, the definition correction step obtains differential colorimetric data representing a difference between the second colorimetric data and the third colorimetric data, and the difference colorimetric data is obtained as the difference colorimetric data. It may be a process of correcting the color conversion definition based on the above.
[0015]
The purpose of correction is to eliminate the difference between the second color measurement data and the third color measurement data, and accurate correction is performed by obtaining the difference measurement data and correcting the color conversion definition based on the difference measurement data. Is called.
[0016]
In the color reproduction characteristic correction method of the present invention, the definition correction process further includes:
A first correction process for correcting the color conversion definition for a relatively wide range;
The color conversion definition corrected in the first definition correction process is further compared based on a data portion corresponding to the color patch represented by the coordinate value added in the patch addition process in the second colorimetric data. It is preferable that the process includes a second correction process for correcting a narrow range.
[0017]
After correcting the color conversion definition as a whole in the first correction process, in the second correction process, correct correction is performed by further correcting the vicinity of the color desired to be corrected.
[0018]
Furthermore, in the color reproduction characteristic correction method of the present invention, the definition correction process is preferably a process of correcting a target profile out of a target profile and a proofer profile constituting a color conversion definition.
[0019]
It is unclear whether the second color measurement data and the third color measurement data do not match the target profile or the proofer profile, but if the proofer profile is corrected, As a result, when a proof image of another target device is output using the proofer, the color is shifted. On the other hand, by correcting the target profile, this proofer can be shared as a proofer for a plurality of target devices.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0021]
FIG. 1 is an overall configuration diagram of a printing and proof image creation system to which an embodiment of the present invention is applied.
[0022]
The color scanner 10 reads a document image 11 and generates color-separated image data of four colors of CMYK representing the read document image 11. The CMYK image data is input to the workstation 20. In the workstation 20, electronic plate collection based on the input image data is performed by the operator, and image data representing an image for printing is generated. The image data for printing is input to the film printer 30 when printing is performed, and the film printer 30 creates the CMYK plate originals for printing corresponding to the input image data.
[0023]
A printing plate is created from the printing film original plate, and the created printing plate is mounted on the printing machine 40. Ink is applied to the printing plate mounted on the printing machine 40, and the applied ink is transferred onto a printing sheet to form a printed image 41 on the sheet.
[0024]
A series of operations in which a film original plate is prepared by the film printer 30, a printing plate is further prepared, mounted on the printing machine 40, ink is applied to the printing plate, and printing is performed on paper is a large-scale operation. Cost too. For this reason, before the actual printing operation is performed, the proof image 61 is created by the printer 60 as described below, and the finished confirmation of the printed image 41 is performed in advance.
[0025]
In creating a proof image, image data created by electronic plate collection on the workstation 20 is input to the personal computer 80. Here, the image data input to the personal computer 80 is description language data described in so-called PDL (Page Description Language). In the personal computer 80, the image data is developed into a bitmap by a so-called RIP (Raster Image Processor). The converted CMYK four-color image data. The CMYK four-color image data is substantially the same as the image data for printing input to the film printer 30.
[0026]
The CMYK four-color printing image data is converted into CMYK four-color image data suitable for the printer 60 by referring to the color conversion definition having the LUT (Look Up Table) format inside the personal computer 80. . The printer 60 receives CMYK four-color image data for the printer, and the printer 60 creates a proof image 61 based on the input CMYK four-color image data for the printer.
[0027]
Here, the degree of color matching between the image 41 obtained by printing by the printing machine 40 and the proof image obtained by the printer 60 is determined by the color conversion definition in the personal computer 80.
[0028]
Further, FIG. 1 shows only one printing machine, but there may be a plurality of printing machines, or even a single printing machine may have a plurality of different printing conditions. Often, the color conversion definition is created according to each of a plurality of printing conditions including differences in printing presses. The spectrocolorimeter 70 and the personal computer 80 shown in FIG. 1 are related to the creation of the color conversion definition.
[0029]
By creating a proof image and confirming the proof image in this way, the finishing of printing can be confirmed in advance.
[0030]
Here, the feature of the printing and proof image creation system shown in FIG. 1 as an embodiment of the present invention relates to the processing contents executed in the personal computer 80. First, the personal computer will be described below. 80 will be described.
[0031]
2 is an external perspective view of the spectrocolorimeter 70 and the personal computer 80 shown as blocks in FIG. 1, and FIG. 3 is a hardware configuration diagram of the personal computer 80. As shown in FIG. FIG. 4 is a schematic diagram of a color chart.
[0032]
2 is mounted with a color chart 90 in which a plurality of color patches are arranged as shown in FIG. 4, and a plurality of color patches 91a, 91b, Colorimetric values (here, XYZ values) are measured for each of. Colorimetric data representing the colorimetric values of the respective color patches obtained by measurement with the spectrocolorimeter 70 is input to the personal computer 80 via the cable 92.
[0033]
The color chart 90 is created by printing on the printing machine 40 shown as one block in FIG. 1 or by printing output on the printer 60. The personal computer 80 is configured by each of the color charts 90 constituting the color chart 90. The color data (coordinates in the device color space; each value of CMYK) corresponding to the color patch is known, and this personal computer 80 obtains the color data of each color patch of the color chart 90 and the spectrocolorimeter 70. A print profile and a printer profile are created based on the measured color measurement data. A detailed description of this point will be given later. Here, the hardware configuration of the personal computer 80 will be described next.
[0034]
The personal computer 80 has a main body device 81, an image display device 82 that displays an image on a display screen 82a in accordance with an instruction from the main body device 81, and a main body device 81 according to key operations. A keyboard 84 for inputting information and a mouse 84 for inputting an instruction corresponding to, for example, an icon or the like displayed at that position by designating an arbitrary position on the display screen 82a are provided. The main body device 81 has a floppy (registered trademark) disk loading port 81a for loading a floppy (registered trademark) disk and a CD-ROM loading port 81b for loading a CD-ROM.
[0035]
As shown in FIG. 3, the main body 81 includes a CPU 811 that executes various programs, a main memory 812 that reads programs stored in the hard disk device 813 and develops them for execution by the CPU 811, and various programs. And a hard disk device 813 in which data and data are stored, a floppy (registered trademark) disk 100 is loaded, an FD drive 814 that accesses the loaded floppy (registered trademark) disk 100, and a CD-ROM 110 are loaded and loaded. A CD-ROM drive 815 for accessing the CD-ROM 110 and a spectrocolorimeter 70 (see FIGS. 1 and 2) are connected, and an I / O interface 816 for receiving colorimetric data from the spectrocolorimeter 70 is incorporated. These various elements and the image display device 8 shown in FIG. , A keyboard 83, a mouse 84 are connected to each other via a bus 85.
[0036]
Here, the CD-ROM 110 stores a profile creation program for creating a profile by the personal computer 80. The CD-ROM 110 is loaded in the CD-ROM drive 815 and stored in the CD-ROM 110. The profile creation program is uploaded to the personal computer 80 and stored in the hard disk device 813.
[0037]
Next, a profile creation method in the personal computer 80 will be described.
[0038]
Here, a method for creating a print profile will be described first.
[0039]
1 generates, for example, 0%, 10%,..., 100%, for example, CMYK four-color halftone data, and the halftone data thus produced in accordance with the printing procedure described above. A color chart 90 (see FIG. 4) based on the data is created. Although the image 41 shown in FIG. 1 is not an image representing a color chart, it is assumed that the color chart 90 shown in FIG. 4 is printed instead of the image 41, and each color patch 90a, 90b constituting the color chart is printed. ,... Are measured with the spectrocolorimeter 70. By doing this, a print profile is created that represents the correspondence between the coordinate values in the color space of CMYK four colors and the coordinate values in the colorimetric color space.
[0040]
FIG. 5 is a conceptual diagram of a print profile.
[0041]
In this print profile, image data defined in CMYK (an example of a target device color space according to the present invention) is input, and the CMYK image data is defined in XYZ (an example of a colorimetric color space according to the present invention). It is converted to the image data.
[0042]
Next, a printer profile creation method will be described.
[0043]
Here, it is assumed that the printer profile has already been created by the manufacturer of the printer and delivered with the printer. Therefore, it is not necessary to create a new printer profile here, but in the following, a new printer profile will be created. In this case, the basic creation method will be described.
[0044]
This printer profile creation method is the same as the print profile creation method, except that the output device that outputs the color chart is not a printer but a printer. That is, here, the personal computer 80 shown in FIG. 1 generates halftone data of CMYK four colors, for example, 0%, 10%,... The data is sent to the printer 60, and the printer 60 prints out a color chart based on the halftone data. It should be noted that the halftone data may be sequentially changed at intervals other than 10%. However, in the following, for the convenience of explanation, it is assumed that halftone data in increments of 10% is used.
[0045]
Although the image 61 shown in FIG. 1 is not an image representing a color chart, the printer 60 replaces the image 61 with, for example, a color chart created by printing on the printing machine 40 to create a printing profile. The color chart of the same type is output, and each color patch constituting the color chart is measured by the spectrocolorimeter 70. By doing so, a printer profile representing the correspondence between the coordinate values in the CMYK four color space (an example of the proofer color space according to the present invention) and the coordinate values in the colorimetric color space (XYZ space) for the printer 60. Is built.
[0046]
FIG. 6 is a conceptual diagram of a printer profile.
[0047]
CMYK halftone data is input to the printer profile, and the CMYK halftone data is converted into XYZ colorimetric data. Here, the printer profile for converting the CMYK halftone data into XYZ colorimetric data is represented by P, and the reverse conversion, that is, the printer profile for converting the XYZ colorimetric data into CMYK halftone data is P. ^-1 It expresses.
[0048]
Here, the printer 60 is described as being a printer that outputs an image based on CMYK halftone data. However, for example, a printer that outputs an image based on RGB data is also used by the personal computer 80 in the RGB space. By generating defined data and outputting a color chart, a printer profile suitable for the printer can be created in the same manner.
[0049]
However, here, the description will be made assuming that the printer 60 that outputs an image based on the CMYK halftone data is used.
[0050]
FIG. 7 is a diagram illustrating a combined profile obtained by combining a print profile and a printer profile.
[0051]
The CMYK halftone data for printing is converted to XYZ colorimetric data by the printing profile T, and then the XYZ colorimetric data is converted to the printer profile P. ^-1 Again, but this time, it is converted to CMYK halftone data for the printer. The printer 60 can output a proof image having the same color as that of printing based on the CMYK halftone data for the printer thus generated. This print profile T and printer profile P ^-1 Is a color conversion definition for converting image data defined in the CMYK color space for printing into image data defined in the CMYK color space for printers.
[0052]
Such a color conversion definition is created by the personal computer 80 constituting the printing and proof image creation system shown in FIG. 1, and the image data described in PDL input from the workstation 20 is converted into CMYK image data. Thereafter, the CMYK image data is converted into CMYK image data for a printer using the color conversion definition, and an image based on the CMYK image data for the printer is printed out by the printer 60. A proof image for the printed image is created.
[0053]
Create a color conversion definition as described above, and use the color conversion definition to convert image data for printing input from a workstation into image data for a printer and based on the image data for the printer Even if a proof image is created, the color of the proof image does not completely match the color of the image on the printed material when the printed material is created based on the image data for printing, and there is an error. There is. As one of the causes, it has been explained that the printer profile has already been created by the manufacturer of the printer in accordance with the above procedure, but the printer profile created by the manufacturer has been delivered. The printer itself was created using the printer's original machine specified by the manufacturer, and there was a certain degree of machine difference between the printer's original machine and the delivered printer. Can be mentioned.
[0054]
However, the cause of the color mismatch of the proof image is not limited to this, but may be due to various error factors in the process of creating the print profile and other various factors.
[0055]
Therefore, a correction method for the color conversion definition when the color matching degree of the proof image is unsatisfactory and the color is to be matched with higher accuracy will be described next.
[0056]
The CD-ROM 110 shown in FIG. 2 also stores a color conversion definition correction program for correcting the color conversion definition by the personal computer 80 described above, and the color conversion definition correction program is uploaded to the personal computer 80 and stored on the hard disk. It is stored in the device 813. When the color conversion definition correction program is activated and executed, the personal computer 80 operates as a color conversion definition correction device that corrects the color conversion definition by a method described later.
[0057]
FIG. 8 is a flowchart illustrating an embodiment of a color conversion definition correction method, FIG. 9 is a diagram illustrating an example of a color chart employed in the correction, and FIG. 10 is a color added in the correction. It is a figure which shows GUI which designates the color of a patch. First, the color chart of FIG. 9 will be described.
[0058]
A color chart 90 ′ shown in FIG. 9 is a combination (grid points) of, for example, 10% of mesh% in the CMYK color space, similar to the color chart 90 used in creating the print profile shown in FIG. This is created on the basis of the halftone data, but is used in the color chart 90 used when creating the print profile shown in FIG. 4 among the 10% grid points in the CMYK color space. It is created on the basis of halftone data of a combination of halftone dots (lattice points) different from the halftone dot combination (grid points). For important colors such as skin color, sky blue, and gray, color chart data in which the density of measurement points selected from 10% grid points in the CMYK color space is increased may be adopted. preferable. Here, such data for creating the color chart 90 ′ shown in FIG. 9 is referred to as correction chart data.
[0059]
In this way, by using the color chart 90 ′ of the dot% that is different from the dot% grid point when the print profile is first created, it is combined with the time when the print profile is first created, and in the CMYK color space. The same effect as creating a profile based on color patches corresponding to more points can be expected, and a more accurate profile can be constructed.
[0060]
Further, the color chart 90 ′ created based on the correction chart data has fewer color patches constituting the color chart than the color chart 90 (FIG. 4) when the print profile is created. Since the color chart 90 'is used for correcting a profile once created, the number of color patches does not need to be as large as when a print profile is first created, and the correction can be performed by reducing the number of color patches. The amount of work and the amount of calculation for correction can be reduced.
[0061]
Further, when the correction chart data for printing representing the color chart 90 ′ is converted into correction chart data for the printer using the color conversion definition to be corrected, the correction chart data for the printer is converted. Is composed of data within the color gamut of the printer 60 (see FIG. 1) used here.
[0062]
If the correction chart data for the printer includes data outside the color gamut of the printer 60, it is difficult to process the boundary inside and outside the color gamut. If this is the case, the result may be an error rather than correction. Although there is a possibility, high-precision correction can be realized with a small amount of calculation by placing the restriction that the correction chart data in the color gamut of the printer 60 is employed as described above.
[0063]
The flowchart of FIG. 8 will be described.
[0064]
First, the above-described color chart 90 ′ and a color patch in which the color difference is anxious are added (step S1). Here, a GUI (Graphical User Interface) window 120 shown in FIG. 10 is opened on the image display device 82 of the personal computer 80 shown in FIG. 2, and an image 130 having a color difference is displayed in the window 120. . When the mouse pointer 135 is placed on the image 130 where the color misregistration is a concern, the halftone value 140 for printing at that position is displayed in the display field of the window 120. When the position is clicked, the halftone value 140 is added to the correction chart data.
[0065]
However, when the halftone value for printing 140 is converted into the halftone value for printer by the print profile, the halftone value for the printer is a halftone value outside the color reproduction area of the printer. The halftone value 140 for printing is prohibited from being added to the correction chart data.
[0066]
By repeating this procedure an arbitrary number of times, a series of patches 91 ″ a, 91 ″ b,... Shown in FIG. 9 is added to the color chart 90 ′.
[0067]
In the present invention, instead of specifying the halftone value by the GUI, the halftone value may be registered by using a keyboard or the like.
[0068]
FIG. 11 is a diagram showing a registration screen on which halftone values are registered using a keyboard or the like.
[0069]
The registration screen 150 is provided with input fields 151C, 151M, 151Y, and 151K for inputting the network% values of C, M, Y, and K. In these input fields 151C, 151M, 151Y, and 151K, Is entered by operating the keyboard.
[0070]
In addition, a registration button 152 and a cancel button 153 are provided on the registration screen 150. When the registration button 152 and the cancel button 153 are clicked, they are input in the input fields 151C, 151M, 151Y, and 151K. The net% value is registered or canceled.
[0071]
The registered halftone value 154a is added to the correction chart data and displayed in the halftone value list display field 154. Further, when the delete button 155 is clicked in a state where an arbitrary mesh% value 154a among the displayed mesh% values 154a is selected, the selected mesh% value 154a is deleted from the correction chart data. And is deleted from the halftone value list display field 154.
[0072]
Even when a series of halftone values 154a is registered on such a registration screen 150, a series of patches 91 ″ a, 91 ″ b,... Shown in FIG. 9 are added to the color chart 90 ′.
[0073]
Next, the color chart 90 ′ (see FIG. 9) designated by the correction chart data for printing to which the halftone value is added in this way is printed by the printing machine 40, and the color chart 90 ′ is printed. (Step S2), and as described with reference to FIG. 2, a plurality of color patches 91′a, 91′b,..., 91 ″ a, 91 ″ b,. XYZ values (X1, Y1, Z1) are measured for each (step S4). This measurement result is taken into the personal computer 80.
[0074]
Further, the correction chart data for printing is converted into correction chart data for printer based on the color conversion definition to be corrected, and is specified by the correction chart data for printing using the printer 60. The color chart is output (step S3), and the XYZ values (X2, Y2, Z2) of the respective color patches are measured in the same manner as the color chart obtained by the printing press 40 (step S5). The XYZ values (X2, Y2, Z2) are also taken into the personal computer 80.
[0075]
When the XYZ measurement data (X1, Y1, Z1) and (X2, Y2, Z2) relating to the color chart obtained by the printing press and the color chart obtained by the printer are taken into the personal computer 80, the personal computer 80 Then, the following arithmetic processing is performed.
[0076]
First, the difference between the two measurement data is obtained, and thereby the color difference between them is obtained (step S6).
[0077]
dX = X2-X1
dY = Y2-Y1
dZ = Z2-Z1 (1)
Here, (X1, Y1, Z1), (X2, Y2, Z2) representatively show the colorimetric data of each color patch of each color chart. This is done for each pair of corresponding color patches between the color chart obtained by the machine and the color chart obtained by the printer.
[0078]
Next, a colorimetric color space corresponding to each grid point of halftone 0%, 10%, 20%,..., 100% of the CMYK color space for printing by interpolation calculation based on the calculation result of the expression (1). The color differences dX, dY, dZ of each point are obtained (step S7). In this interpolation calculation, color patches (additional patches) 91 ″ a, 91 ″ b,... Added to the color chart 90 ′ shown in FIG. 9 correspond to other color patches 91′a, 91′b,. Color difference is used. This is because the color patches (addition patches) 91 ″ a, 91 ″ b,... Added to the color chart 90 ′ often do not exist on the grid points in increments of 10% and are not suitable for interpolation calculation.
[0079]
Next, as described above, the already created print profile is referred to. In this print profile, the coordinate values (CMYK values) of each grid point and the XY color space coordinate values of 0%, 10%, 20%,..., 100% for the CMYK colors on the CMYK color space. A correspondence relationship with (XYZ value) is shown, and here, for each grid point in the CMYK color space, a color difference (dX, dY, dZ) corresponding to each grid point obtained in step S7 is added (step). S8).
[0080]
X = X0-dX
Y = Y0-dY
Z = Z0−dZ (2)
Here, (X0, Y0, Z0) representatively represents each coordinate value in the XYZ color space corresponding to each grid point in the CMYK color space of the print profile before correction.
[0081]
The entire print profile is corrected by performing the above operation (2) for each grid point.
[0082]
Next, local correction based on the colorimetric data corresponding to the additional patch is applied to the print profile with respect to the surrounding network% value corresponding to the additional patch described above (step S9). That is, with respect to the grid points existing within a predetermined range near the additional patch, the correction value according to (2) above becomes a correction value based on the color difference (dX ′, dY ′, dZ ′) and the weight W in the additional patch. Replaced.
[0083]
X = X0 + W (Δ) × dX ′
Y = Y0 + W (Δ) × dY ′
Z = Z0 + W (Δ) × dZ ′ (3)
Here, W (Δ) is a weight defined as a decreasing function with respect to the distance Δ between the grid point to be corrected and the point in the CMYK color space corresponding to the additional patch.
[0084]
In addition, when one grid point receives the influence of each correction resulting from each of a plurality of additional patches in an overlapping manner, the correction having the largest weight is performed. In addition, the weight W (Δ) may be defined as a decreasing function with respect to the distance Δ on the chromaticity value section, or may be represented by another definition.
[0085]
The correction print profile is created by performing the correction (3) for each additional patch.
[0086]
According to this correction method, highly accurate correction can be performed by mechanically proceeding with the work.
[0087]
Instead of the print profile before correction, the corrected print profile created in this way is adopted, and the color conversion definition that combines this corrected print profile and the printer profile already used when performing this correction is adopted. By performing color matching, it is possible to obtain a proof image in which colors are matched with higher accuracy than before correction.
[0088]
Here, only the print profile of the printer profile and the print profile is corrected. The reason for this is that if the printer profile is corrected, this correction includes corrections related to error factors on the printing press. Therefore, when trying to use the same printer as a proofer of another printing machine (or another printing condition of the same printing machine), the other printing machine (or another printing condition of the same printing machine) This is because, when the print profile and the corrected printer profile are combined, the combined profile includes the error of the printing press used when the printer profile was corrected before, which is not appropriate. However, when the printer is used as a proofer for only one printing condition of a certain printing machine, the printer profile may be modified instead of the printing profile modification.
[0089]
Alternatively, in the present invention, neither the printing profile nor the printer profile is corrected, and the conversion definition for correction corresponding to the calculation shown in Expression (2), that is, (X0, Y0, Z0) in the XYZ color space. When creating a conversion definition for correction that converts X into (X = X0 + dX, Y = Y0 + dY, Z = Z0 + dZ) and performing color matching, the print profile, the correction conversion definition, and the printer profile are combined. The color conversion definition may be adopted.
[0090]
Any of the above aspects is also included in the “correcting color conversion definition” according to the present invention.
[0091]
In the above embodiment, the color chart is output and measured by both the printing press and the proofer based on the correction chart data. However, in the present invention, the measurement corresponding to the color chart output by the printing press is performed. The color data may be obtained by calculation according to the print profile before correction.
[0092]
【The invention's effect】
As described above, according to the present invention, the color reproduction characteristics of a proof image can be corrected easily and with high accuracy.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of a printing and proof image creation system to which an embodiment of the present invention is applied.
2 is an external perspective view of a spectrocolorimeter and a personal computer indicated by blocks in FIG.
FIG. 3 is a hardware configuration diagram of a personal computer.
FIG. 4 is a schematic diagram of a color chart.
FIG. 5 is a conceptual diagram of a print profile.
FIG. 6 is a conceptual diagram of a printer profile.
FIG. 7 is a diagram illustrating a combined profile obtained by combining a print profile and a printer profile.
FIG. 8 is a flowchart illustrating an embodiment of a color reproduction characteristic correction method.
FIG. 9 is a diagram illustrating an example of a color chart employed in correction.
FIG. 10 is a diagram illustrating a GUI for designating a color patch color to be added during correction.
FIG. 11 is a diagram showing a registration screen on which halftone values are registered using a keyboard or the like.
[Explanation of symbols]
10 Color scanner
20 workstations
30 Film printer
40 printing press
50 Personal computer
60 Printer
70 Spectral colorimeter
80 Personal computer
90,90 'color chart
91a, 91b, ... color patch
91'a, 91'b ... Color patch
91 "a, 91" b, ... Color patch
100 floppy disk
110 CD-ROM
120 GUI window
130 images
135 Mouse pointer
140 Net% value
150 Registration screen

Claims (6)

Correspondence between the coordinate values on the target color space and the coordinate values on the device-independent colorimetric color space of the target device that outputs an image based on the target image data defined by the coordinate values on the predetermined target device color space Of a proofer that outputs an image based on a target profile representing proof image data defined by coordinate values on a predetermined proofer color space, and coordinates on the proofer color space and coordinates on a device-independent colorimetric color space Target image data defined by the coordinate values in the target device color space is defined by the coordinate values in the proofer color space based on the color conversion definition consisting of the combination with the proofer profile representing the correspondence with the value. Proof image data converted into proof image data using the proofer based on the proof image data When outputting an image, the color conversion definition correction method for correcting the color conversion definitions,
The target profile outputs a color chart based on first chart data representing a color chart in which a plurality of color patches are arranged, which are defined by coordinate values in the target device color space, using the target device. First color measurement data defined by coordinate values in a color measurement color space by measuring colors of a plurality of color patches constituting the color chart obtained in the first chart output process. It was created through a first chart colorimetric process to obtain,
A plurality of colors including at least a part of color patches defined by coordinate values different from the coordinate values of the plurality of color patches constituting the color chart represented by the first chart data on the target device color space A patch addition process for creating patch additional chart data by adding an arbitrary coordinate value defining a color patch to existing second chart data representing a color chart in which patches are arranged;
A second color patch defined by coordinate values in a colorimetric color space when a color chart is output by the target device based on the patch addition chart data created in the patch addition process. A second colorimetric data acquisition process for obtaining colorimetric data;
The patch additional chart data defined by the coordinate values on the target device color space is converted into third chart data defined by the coordinate values on the proofer color space using the color conversion definition, A third chart output process for causing the proofer to output a color chart based on the third chart data;
Third colorimetric data for obtaining third colorimetric data defined by coordinate values in a colorimetric color space, in which a plurality of color patches constituting the color chart output in the third chart output process are colorimetrically measured. Acquisition process,
Definition correction for correcting the color conversion definition based on the second color measurement data obtained in the second color measurement data acquisition process and the third color measurement data obtained in the third color measurement data acquisition process And a color conversion definition correcting method characterized by comprising:   In the second colorimetric data acquisition process and the third chart output process, the patch additional chart data includes a number of color patches smaller than the number of color patches constituting the color chart represented by the first chart data. 2. The color conversion definition correcting method according to claim 1, wherein patch additional chart data representing the arranged color chart is employed.   In the second colorimetric data acquisition process and the third chart output process, the patch additional chart data is converted into the third chart data for the proofer as the patch additional chart data. 2. The process of using patch additional chart data in which a plurality of color patches constituting the color chart to be represented are all color patches in a color reproduction region reproduced by a proofer. Color conversion definition correction method.   The definition correction process is a process of obtaining difference color measurement data representing a difference between the second color measurement data and the third color measurement data, and correcting the color conversion definition based on the difference color measurement data. The color conversion definition correcting method according to claim 1. The definition correction process further includes:
A first correction process for correcting the color conversion definition for a relatively wide range;
The color conversion definition corrected in the first definition correction process is relatively based on the data portion corresponding to the color patch represented by the coordinate value added in the patch addition process in the second colorimetric data. 2. The color conversion definition correcting method according to claim 1, further comprising a second correction process for correcting a narrow range.   2. The color conversion definition correction method according to claim 1, wherein the definition correction step is a step of correcting the target profile of the target profile and the proofer profile constituting the color conversion definition.

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