JP2003198865A - Calibration method - Google Patents

Abstract

(57) [Problem] To provide a calibration method that has good gradation properties over the entire density and that can perform accurate adjustment. A calibration method for correcting a density variation of an image output device for forming a color image using four color materials of CMYK, wherein a single-color patch is provided on a reference chart prepared in advance by the image output device. Is printed, and the density adjustment value is determined based on the comparison result between the reference density and the single color patch. In the calibration method, after selecting the single color patch, highlight and shadow are adjusted using the density adjustment value of one point adjusted Outputs two types of monochromatic gradation to the image output device 101
, And a gamma curve is determined by selecting a single-color gradation with the optimum gradation from among them.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color printer,
The present invention relates to a calibration method in an image output device such as a color copying machine.

[0002]

2. Description of the Related Art Japanese Unexamined Patent Publication No. 09-321999 relates to a calibration method for correcting density fluctuations of an image output device for forming a color image using four color materials of CMYK.
The publication discloses a technique for correcting color conversion data by comparing a printed balance chart with a reference reference chart and selecting patches that are visually the same color.

Japanese Patent Laid-Open No. 10-6562 discloses that
A technique for performing calibration by comparing a printed test chart with a reference chart for each of CMYK highlight, middle, and shadow and selecting patches of the same density is disclosed.

[0004]

In the image output device, the quality of the output image may be different even if the same image is output due to changes in the internal mechanism of the device over time. . In order to solve this problem, it was necessary to calibrate the device.
Conventionally, various methods have been proposed as described above, in which a test chart is printed out from an image output device, compared with a reference chart prepared in advance, and the data is registered to perform calibration.

However, in many of these conventional methods, adjustment is made by a single color patch or the like, and the overall density characteristic value is estimated from the density characteristic value at one point or several points of density, and the density is estimated from the estimated value. Many of them determine the overall adjustment value. Therefore, although the density adjustment value can be accurately determined for a certain part of the density, there have been cases in which the gradation of the entire density cannot be adjusted well.

The present invention has been made in view of these problems, and it is an object of the present invention to provide a calibration system which has good gradation over the entire density and which can be adjusted with high accuracy.

[0007]

In order to achieve the above object, the invention according to claim 1 is a calibration system for correcting density fluctuation of an image output device for forming a color image using color materials of four colors of CMYK. In a calibration method in which a monochrome patch is printed by an image output device on a reference chart prepared in advance and the density adjustment value is determined based on the comparison result of the reference density and the monochrome patch, the adjustment is performed after the monochrome patch is selected. Using the adjusted value of the density at one point, highlight and shadow 2
Output a single color gradation from the image output device,
The most main feature is the calibration method that determines the gamma curve by selecting a monochromatic gradation with the optimum gradation from among them.

According to a second aspect of the present invention, in the calibration method according to the first aspect, when selecting a monochromatic gradation, the monochromatic gradation is printed by an image output device on a reference chart on which the standard gradation is printed. The main feature is a calibration method that makes selections and adjustments while making a comparison.

According to a third aspect of the present invention, in the calibration method according to the first aspect, when selecting a single color patch, density adjustment is performed for each color and two or more density values,
A main feature of the gradation method is a calibration method that uses the adjustment values, prints three or more single-color gradations for each color, and selects from among them to perform density adjustment.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a conceptual diagram of processing until obtaining a density characteristic value in this calibration method, and FIG.
Is a conceptual diagram of the process until the gamma curve is determined, FIG. 3 is a flowchart showing the control contents of the present invention, FIG. 4 is a diagram showing one patch reference density, and FIG. 5 is a gamma curve corresponding to FIG. 6 is a diagram showing two patch reference densities, FIG. 7 is a diagram showing a gamma curve corresponding to FIG. 6, and FIG. 8 is a conceptual diagram showing an example of outputting a reference chart instead of the test chart of FIG. Is.

CMYK4 colors to be calibrated (Cyan, Magenta, Yellow, Blac
An outline of the image output apparatus 101 that forms a color image using the color material of k) and the present calibration method will be described.

In the present invention, a monochrome patch is printed on the reference chart 102 prepared in advance (printed reference chart 103), the comparison with the reference density around the patch is visually performed, and the result is displayed on the image output device 101. By registering, the density characteristic value at a certain density is obtained (FIG. 1).

After that, various gamma curves are created for each of the highlight part and the shadow part based on the adjustment result, and the test chart 2 is prepared by using the gamma curves.
By outputting the gradation of each color such as 01, highlight, and shadow, visually selecting the gradation number that seems to have the best gradation and density, and registering that number, the gamma curve Make a decision (Figure 2).

A large flow of processing in the calibration method of the present invention is shown in FIG. In this calibration method, the reference chart 102 is set in advance.
Is prepared. The reference chart 102 is shown in FIG.
As described above, each CMYK is printed with a density that is a reference for a certain point in a form in which only that part is blank so that several patches can be printed.

In this method, first, a patch is printed by the image output device 101 on a blank portion on the reference chart 102 (301). The patches here are printed by slightly changing the densities above and below each of CMYK. Next, using the peripheral portion of the patch that has been printed in advance as a reference density, the reference density and the density of the patch are visually compared to select a patch that seems to have the same density (302). Then, the patch numbers selected for CMYK are registered in the image output apparatus 101 (30
3).

According to this registration method, only the density characteristic of a certain density is known, but here, the density characteristics of other portions are estimated from the density characteristic of that one point. A gamma curve is created based on the estimated value so that the density characteristics are as specified. However, in consideration of various cases, several kinds of gamma curves are created for each of the highlight part and the shadow part as shown in FIG. (305).

Then, using these gamma curves, the test chart 20 in which gradations are printed for each highlight portion and shadow portion of each color
1 is output (306). Output test chart 2
Of the gradations for each color 01 and each density, those that are considered to be optimum gradations such as gradation and density are selected (307), and the number is registered in the image output device 101 (308). The gamma curve of each color is determined by the number registered here (309). As an example, when the numbers selected and registered in 307 and 308 are "2" in the highlight part and "4" in the shadow part, the bold curve in FIG. 5 is used as the gamma curve for the entire density. I will decide.

Further, instead of printing the test chart 201 at 306, the reference chart 80 of FIG.
A method of outputting 2 may be used. In this case, the reference chart 801 in which the reference gradations for each color and each density are printed in advance is used.

In this reference chart 801, blanks are arranged so that gradations can be printed, and gradations are printed by the image output device 101 in the blanks, and the reference chart 8
02 is output. Using this reference chart 802, the optimum gradation is selected while comparing with the reference gradation, and the gamma curve is determined by registering it in the image output device.

Up to this point, the density has been divided into two parts, the highlight part and the shadow part, and the density adjustment has been performed for each, but the density may be divided into three or more. In that case, a plurality of reference densities are used to perform a plurality of patch selections, rather than a single patch selection based on one reference density for each color in the first patch selection. Also,
In that case, as the test chart 201, three or more gradation groups are printed for each color, and each gradation is selected from the gradation group.

An example of creating a gamma curve in that case is as shown in FIGS. In FIG. 6 and FIG. 7, there are two single-color patch selections for each color, and regarding gradation, the highlight portion, the middle portion, and the shadow portion are three.
It shows how to create a gamma curve in the case of splitting.

[0022]

As described above, in the calibration method according to the first aspect, since it is possible to select the gradation for each density such as the highlight part and the shadow part, it is possible to select the gradation according to the density characteristic of each density. The density can be adjusted, and the density can be adjusted with high accuracy over the entire density.

In the calibration method according to the second aspect, since the gradation can be selected while comparing it with the reference gradation, it is possible for the user to easily select the gradation with high accuracy. So, you can do a simple calibration.

In the calibration method according to the third aspect, gradation selection is performed at various densities, so an optimum adjustment value can be determined for each density, and high-precision density adjustment can be performed.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a process for obtaining a density characteristic value in the present calibration method.

FIG. 2 is a conceptual diagram of processing up to determination of a gamma curve.

FIG. 3 is a flowchart showing the control content of the present invention.

FIG. 4 is a diagram showing one patch reference density.

5 is a diagram showing a gamma curve corresponding to FIG. 4. FIG.

FIG. 6 is a diagram showing two patch reference densities.

7 is a diagram showing a gamma curve corresponding to FIG.

8 is a conceptual diagram showing an example of outputting a reference chart instead of the test chart of FIG.

[Explanation of symbols]

101 image output device 102 reference chart 103 Printed reference chart

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Claims (3)

[Claims] 1. A calibration method for correcting density fluctuations of an image output device for forming a color image using CMYK four color materials, wherein a monochrome patch is printed on the reference chart prepared in advance by the image output device. Then, in the calibration method in which the density adjustment value is determined based on the comparison result of the reference density and the single color patch, after the single color patch is selected, the adjusted adjustment value of the density at one point is used to select the highlight and shadow portions 2. A calibration method characterized in that a gamma curve is determined by outputting a single color gradation of a type from an image output device and selecting a single color gradation having the optimum gradation from the output. 2. The calibration method according to claim 1, wherein, when selecting a monochromatic gradation, the monochromatic gradation is printed by an image output device on a reference chart on which the standard gradation is printed, and selected while comparing with the standard gradation. ,
A calibration method characterized by making adjustments. 3. The calibration method according to claim 1, wherein when a single color patch is selected, density adjustment is performed for two or more density values for each color, and the adjustment value is used for gradation selection, and three or more colors for each color are selected. A calibration method characterized by adjusting the density by printing a single-color gradation and selecting from among them.