JP2009004865A - Profile creation method and profile creation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To recreate a profile with a high accuracy by using a color chart with a small number of patches, correcting the entire range of correspondence between color designation and color value, and reproducing well the nonlinear characteristic existing in the correspondence. Provide a profile creation method to create.
SOLUTION: In multi-order color calibration, out of patches necessary for creating an ICC profile, create a color chart with a small number of patches consisting of a point that becomes the outer shell of the space or a point that corresponds to the middle point. To do. After the printer changes, the chart is output and measured, and the difference before and after the change of each point is calculated. From the difference, the difference at each point of the patch necessary for creating the ICC profile is estimated, and the difference is added to the colorimetric value before the change, so that the colorimetric values of all the points after the change are created. A profile is created using the colorimetric values.
[Selection] Figure 1

Description

  The present invention relates to a profile creation method for creating a profile that defines device characteristics based on correspondence of color values to a predetermined color designation.

Color matching using a profile is performed between an input device such as a scanner and an output device such as a display and a printer so that each device performs good color reproduction. The profile defines the correspondence between the coordinates of the device-dependent color space and the coordinates of the device-independent color space, and creates a profile using a color chart in which a large number of patches are arranged It has been known. FIG. 5 is a flowchart for creating a printer profile by a conventional method. First, in step b1, a color chart is output from the printer. Next, in step b2, the patch formed on the output is measured to obtain a color value. Next, in step b3, from the relationship between the color specification of the patch on the color chart and the measured color value, the device-dependent color space coordinates and the device-independent color space coordinates in the printer Is calculated and created as a profile.
Japanese Patent Laid-Open No. 10-146219 JP-A-10-203907

  There are many fluctuation factors such as fluctuation due to environment, fluctuation due to setting, fluctuation due to time, etc. in the device, and when those fluctuations occur from the state of creating the profile, the color space coordinates depending on the device and the device The correspondence with the coordinates of the independent color space also varies, and good color reproduction cannot be achieved unless the profile is recreated. In order to recreate a profile in the conventional method, it is necessary to output and measure a color chart composed of an enormous number of patches each time, which requires a lot of time and labor.

  As a means to solve this, we propose a method to reduce the time and effort required for output and measurement of the color chart by reducing the number of patches required for profile creation and supplementing the color values of the reduced patches with complementary calculation. However, the nonlinear characteristics existing in the correspondence between the color designation and the color value of the device cannot be captured, and the resulting profile has a problem in terms of accuracy.

  In addition, JP-A-10-146219 discloses a correction relationship based on the difference between the color value obtained under the reference output condition and the color value obtained from the corrected output condition, and a small number of patches under the target output condition. A method for obtaining the correspondence between the color specification and the color value under the target output condition from the measurement result has been proposed. However, in the method proposed in this publication, in order to obtain an accurate correction relationship, there are a number of conditions. It is necessary to perform color chart output and measurement, and since correction is performed only along the axis adopted as the basic scale, there is a problem in terms of accuracy in other color mixing, and the change over time, etc. It is impossible to deal with correction conditions that are difficult to control.

  Further, in Japanese Patent Laid-Open No. 10-203907, color values extracted from an original profile are deformed so as to follow the color values of a color chart corresponding to a small number of coarsely distributed coordinate points, and new color values are acquired. A method has been proposed. However, in the method proposed in this publication, since the deformation is performed only on the axis connecting the coarsely distributed coordinate points, there is a problem in terms of accuracy at a point that is not on the axis, and also on the axis. However, since three or more coordinate points are required, it is difficult to reduce patches to some extent.

  In view of the above circumstances, the present invention uses a color chart with a small number of patches in profile re-creation, corrects the entire correspondence between color designation and color value, and reproduces the non-linear characteristics existing in the correspondence well. An object of the present invention is to provide a profile creation method for creating a highly accurate profile.

  In order to achieve the above object, the present invention provides a profile creating method for creating a profile that defines device characteristics based on the correspondence of color values to a predetermined color designation, and a process of forming a first color chart and outputting it from the device Measuring a patch formed by the output and obtaining a first color value; forming a second color chart and outputting the second color chart; and measuring a patch formed by the output and measuring a second color chart. A process of obtaining a color value of the first color value, a process of obtaining a color value difference of patches having overlapping color designations of the first color value and the second color value, A process of estimating a color value difference in each patch, a process of generating a third color value by adding the estimated difference to the first color value, and device characteristics based on the third color value And creating a profile that defines.

  Here, the patch of the second color chart is one of the patches of the first color chart, which is the vertex of the solid that becomes the outermost shell when plotted in the space used for specifying the color of the patch, or Further, it includes a point on a line connecting the vertices or a point on a line connecting the points on the line.

  Further, in the process of measuring the patch on the second color chart and obtaining the second color value, the patch of the first color chart among the patches of the second color chart is used for specifying the color of the patch. A patch having the same color designation as that of the vertex of the solid that becomes the outermost shell when plotted in space, or a patch having the same color designation as that of a point on a line connecting the vertices, or further A second color value is obtained by measuring a patch having the same color designation as a point on the line connecting the points on the line.

  As described above, according to the present invention, a highly accurate profile can be created with less effort.

  Hereinafter, an embodiment according to the present invention will be described in detail with reference to the drawings.

<First embodiment>
FIG. 1 is a block diagram showing the configuration of an image forming apparatus according to the present invention. A printer 13 and a measuring machine 14 are connected to a computer 10. The computer 10 includes a central control device 11, a user interface (UI) 12, and a storage device 15. The storage device 15 stores and holds an output image 16, a measured color value 17, a difference 18, an estimated difference 19, and a profile color value 20. As the output image 16, a first color chart and a second color chart are stored and held. In this embodiment, the first color chart is a color chart used in the conventional method. In the present embodiment, cyan C, magenta M, yellow Y, and black K are used for the color designation of the printer 13.

When the patch of the second color chart a2 stored and held in the output image 16 in the present embodiment is represented by a mesh%,
(C, M, Y, K) = (c, m, y, k)
(c = {0%, 50%, 100%}, m = {0%, 50%, 100%}, y = {0%, 50%, 100%}, k = {0%, 50%, 100 %})
These points are points corresponding to the vertices of the outermost cube in the CMY space of K = 0%, 50%, and 100%, and the midpoint thereof. It is assumed that the first color chart patch includes these 81 points. Fig. 2 is a plot of a part of it in the CMY space with K = 0. The white circle is a part of the patch of the first color chart, and the black circle is a patch that exists in both the first color chart and the second color chart. Is expressed.

FIG. 3 is a flowchart showing a profile creation procedure in the present invention.
First, in step a1, it is checked whether the measured color value 17 includes the measured color value of the patch of the first color chart in the output image 16. If not, the process proceeds to step a2, and if there is, the process proceeds to step a4.

  In step a2, the first color chart in the output image 16 is output from the printer 13, and in step a3, the patch formed on the output result is measured by the measuring instrument 14 and stored in the profile color value 20 Then, the process proceeds to step a9.

  In step a4, the second color chart in the output image 16 is output from the printer 13, and in step a5, the patch formed on the output result is measured by the measuring instrument 14 and stored in the measured color value 17. .

  Next, in step a 6, the difference between the measured color value of the first color chart and the measured color value of the second color chart stored in the measured color value 17 is calculated and stored in the difference 18.

  Next, in step a7, the difference in color designation of each patch of the first color chart is estimated from the difference 18. An example of the difference estimation method will be described. First, the color specification (C1, M1, Y1, K1) of the patch for which the current difference is estimated is extracted from the patches of the first color chart. Next, the maximum K2 that satisfies K2 <K1 and the minimum K3 that satisfies K2 <K3 are determined from the patches of the second color chart. Next, eight points that surround the color designation S1 in a cubic shape are determined from the patches of black K2 in the patch of the second color chart. FIG. 4 illustrates this. In the CMY space at K = K2, the color designation (C1, M1, Y1, K2) is a double circle, and 8 of the patches of the second color chart that surround it in a cube shape. The dots are plotted with black circles, and other patches of the second color chart are plotted with white circles. Next, the difference corresponding to the color designation of the eight points is extracted from the difference 18, and the difference D1 in the color designation (C1, M1, Y1, K2) is calculated by three-dimensional linear interpolation. Similarly, the difference amount D2 at K = K3 is calculated. From the difference amounts D1 and D2, a difference D3 at K = K1 is calculated by linear interpolation. The difference D3 is an estimated value of the difference in color designation (C1, M1, Y1, K1). In the process of determining K2 and K3, if there is K2 where K1 = K2, the difference D3 can be obtained by calculating the difference D1. The above estimation method is sequentially performed on all the patches of the first color chart. In addition, there are tetrahedral interpolation performed using four points instead of the eight points.

  Next, in step a8, each difference obtained in step a7 and the measured color value of the patch of the first color chart in the corresponding measured color value 17 are added and stored in the profile color value 20.

  In step a9, a profile is created based on the profile color value 20 by the same calculation as in step b3 in the conventional profile creation method.

  By the above method, in the re-creation of the profile, correction is performed over the entire range of correspondence between color designation and color value with a color chart with a small number of patches, and the nonlinear characteristics existing in the correspondence are reproduced well. Thus, accurate profile generation can be performed.

<Second embodiment>
In the first embodiment, as the second color chart,
(C, M, Y, K) = (c, m, y, k)
(c = {0%, 100%}, m = {0%, 100%}, y = {0%, 100%}, k = {0%, 100%})
A 16-point color chart is used. Others are the same as the first embodiment, and correction can be performed with less effort by using this color chart.

<Third embodiment>
In the first embodiment, the color value of the first color chart is obtained by holding, outputting, or measuring. If there is a profile that has already been created, the color value of the first color chart is determined from that profile. The color value corresponding to each point is calculated, and the subsequent processing is executed. For the calculation, a color matching algorithm may be used.

(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), or 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.

  In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention.

  As a storage medium for supplying the program code, for example, a floppy (registered trademark) disk, hard disk, optical disk, magneto-optical disk, CD-ROM, CD-R, magnetic tape, nonvolatile memory card, ROM or the like is used. I can do it.

  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.

  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.

It is a block diagram which shows the structure of the profile creation apparatus in one Example of this invention. It is the figure which showed a part of patch in one Example of this invention on CMY space. It is a flowchart which shows the profile creation method in this invention. It is the figure which showed the concept of the difference estimation in one Example of this invention on CMY space. It is a flowchart which shows the profile creation method in a conventional system.

Explanation of symbols

10 computers
11 Central control unit
12 User interface
13 Printer
14 Measuring instrument
15 Storage device
16 Output image
17 Measurement color value
18 Difference
19 Estimated difference
20 Color value for profile

Claims (4)

  In a profile creation method for creating a profile that defines device characteristics based on correspondence of color values to a predetermined color specification, a process of forming a first color chart and outputting it from the device, and measuring a patch formed by the output A process of obtaining a first color value, a process of forming a second color chart and outputting it from the device, a process of measuring a patch formed by the output and obtaining a second color value, and the first color value A process of obtaining a difference between color values of a patch having an overlapping color designation among the color value of the second color value and a process of estimating a color value difference in each patch of the first color chart from the difference; , A step of calculating a third color value by adding the estimated difference to the first color value, and a step of creating a profile defining device characteristics based on the third color value A profile creating method characterized by comprising:   The second color chart is a patch of the first color chart, which is a vertex of a solid that is the outermost shell when plotted in a space used for specifying the color of the patch, or further, 2. The profile creation method according to claim 1, further comprising: a point on the connected line, or a point on the line connecting the points on the line.   In the process of measuring the patch on the second color chart and obtaining the second color value, the patch of the first color chart among the patches of the second color chart is set in a space used for specifying the color of the patch. A patch with the same color designation as the vertex of the solid that becomes the outermost shell when plotted, or a patch with the same color designation as a point on the line connecting the vertices, or further on the line 2. The profile creation method according to claim 1, wherein the second color value is obtained by measuring a patch having the same color designation as a point on a line connecting the points.   A profile creation apparatus for creating a profile that defines device characteristics based on correspondence of color values to a predetermined color designation, comprising: means for forming a first color chart and outputting from the device; and a patch formed by the output Means for measuring and obtaining a first color value; means for forming a second color chart and outputting from the device; means for measuring a patch formed by the output and obtaining a second color value; Means for obtaining a difference between color values of patches having overlapping color designations of the first color value and the second color value, and estimating a difference between color values in each patch of the first color chart from the difference. Means for generating a third color value by adding the estimated difference to the first color value; and means for creating a profile for defining device characteristics based on the third color value And a profile creation device.

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