JP2001144982A - Calibration method for color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a calibration method for a color image forming device by which fluctuation in coloring or a gray level appearing in an output image can be suppressed even in the case that a secular stage change takes place in an internal device of the color image forming device. SOLUTION: In the calibration method to correct fluctuation in a gray level of the color image forming device using 4 color materials consisting of CMYK to provide an output of a color image, comparison is conducted between a gray level of each patch on a test chart regarding at least one color among CMY three colors and color K outputted from the color image forming device and a gray level of a reference patch for each color on a reference chart prepared in advance, and the gray level data of the patch on the test chart found to be coincident through the comparison is used to adjust the gray level regarding at least the one color among the CMY three colors and the color K, and gray patches with gray level coincident with the gray level of the remaining colors in the 3 CMY colors are selected from each of a plurality of gray balance charts and the gray level data of the selected gray patches are used to adjust the gray balance thereby adjusting the gray level of the remaining colors.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an improvement of a color image forming apparatus such as a color printer for forming a full-color image using four CMYK toners, and more particularly to a calibration for appropriately adjusting the density of each color. The present invention relates to an improved method and an image forming apparatus using the calibration method.

[0002]

2. Description of the Related Art In a color image forming apparatus, since the state of the internal mechanism of the apparatus changes over time, even when the same image is output, both outputs are output between the initial stage and after the lapse of time. There may be a difference in image density. In the color image forming apparatus, it is necessary to perform the calibration after a predetermined period in order to solve the problem that the density of the output image is changed due to the state change over time or the like.
As a calibration method in a conventional color image forming apparatus, a test chart consisting of a patch group output with a very small change in density from the image forming apparatus is printed out, and the test chart is compared with a reference chart prepared in advance. Various methods have been proposed for performing calibration by selecting patches having a well-balanced density from the test chart and registering the density data of the patches. As a calibration method in a conventional color image forming apparatus, for example, Japanese Patent Application Laid-Open No. 9-321999 (color conversion accuracy correction method) discloses a CMY patch output from a color image forming apparatus with a very small change in density. Is compared with a reference reference chart prepared in advance, a patch that visually matches the reference reference chart is selected from the balance chart, and the color conversion data is corrected based on the density of the selected patch. A calibration method is disclosed. Japanese Patent Application Laid-Open No. 10-6562 (Calibration adjustment method for color printer)
Compare the test chart consisting of four color patches consisting of CMYK, which are output with a small amount of change in three levels of highlight, middle, and shadow, and the output test chart and a reference chart prepared in advance. Then, from among the test charts that output patches having the same density as the reference chart, CMY is selected based on the density of the selected patch.
A calibration method for performing adjustment for each color of K is disclosed.

[0003]

SUMMARY OF THE INVENTION
In the calibration method of the invention disclosed in Japanese Patent Application Laid-Open No. 9-321999, since it is necessary to select a completely color-matched one including the density, it is necessary to visually select a patch that is the same color as the reference reference chart. Calibration becomes difficult and difficult to adjust. In addition, JP 10
In the invention disclosed in -6562 publication, highlight, middle,
Since the adjustment based on the result of comparing the three levels of shadow density is performed for each color of CMYK, CMYK
In some cases, the balance between the images may be lost, and the hue in the output image from the color image forming apparatus may change. Also, C
In MYK, there is a color (for example, “Y”) for which it is difficult to recognize the density difference at the time of adjustment. In the invention in the above publication, the color for which the density difference is difficult to recognize is the same as other colors. Adjustments are made using a single color. For this reason, there is a problem in that the adjustment accuracy of such a color that is difficult to adjust is deteriorated, and the color cannot be adjusted with high accuracy. The present invention has been made in order to solve the conventional problems as described above, and even when the state of the internal mechanism of the color image forming apparatus changes over time or the like, a change in the hue or density appearing in the output image. It is another object of the present invention to provide a calibration method in a color image forming apparatus that can easily and accurately perform density adjustment for each of CMYK colors for an operator.

[0004]

According to a first aspect of the present invention, there is provided a calibration method for a color image forming apparatus, comprising the steps of outputting a color image using four color materials of CMYK. A calibration method for correcting a density variation of a color image forming apparatus, comprising:
For at least one of the three colors MY and K, the density of each patch on the test chart for at least one of the three colors CMY and K output from the color image forming apparatus, and on the reference chart prepared in advance. The density is adjusted using the density data of the patch on the test chart, which is matched by comparing the density of the reference patch for each color with the density of the reference patch. Selecting a gray patch having a matching density from each of the plurality of gray balance chart groups, and adjusting the gray balance by using the density data of the selected gray patch to adjust the density of the remaining color. It is characterized by. The present invention of claim 2 is the invention of claim 1
In the calibration method in the color image forming apparatus described in the above, the gray balance adjustment is performed by selecting a patch having the best gray balance from a plurality of gray balance chart groups and adjusting the gray balance. . The third aspect of the present invention is the first aspect.
In the calibration method in the color image forming apparatus described in the above, the adjustment of the gray balance is performed using a gray balance chart in an arbitrary density range. The present invention of claim 4 is the invention of claim 3
In the calibration method in the color image forming apparatus described in the above, the density adjustment using the reference patch for each color on the reference chart is a result of comparison with patches on a plurality of types of test charts output from the color image forming apparatus It is characterized by being performed using. According to a fifth aspect of the present invention, there is provided a color image forming apparatus which performs the calibration method in the color image forming apparatus according to the first to fourth aspects.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on illustrated embodiments. FIG. 1 is a flowchart illustrating a schematic process of a calibration method in a color image forming apparatus according to an embodiment of the present invention. In this embodiment,
Cyan, magenta, yellow, black (hereinafter, each is C,
C, M, Y, and K). In order to correct the density fluctuation of a color image forming apparatus that outputs a color image using four color materials composed of four colors of CMYK, CMYK is roughly classified into two steps. Adjust the density of each color (Cyan, Magenta, Yellow, Black). As shown in the flowchart of FIG. 1, in the calibration method in the color image forming apparatus according to the present embodiment, as a first step, M and K are set on a test chart of M and K output from the color image forming apparatus. The density of each patch is compared with the density of a reference patch prepared in advance in a reference chart to adjust the density (step S101). Next, as a procedure of the second stage, the color image forming apparatus is used for C and Y. The density adjustment is performed by adjusting the gray balance by selecting a gray patch having a density equal to the density of C and Y output from the plurality of gray balance chart groups (step S10).
2) In step S102, the gray balance was adjusted using the density data of M which had already been adjusted in density in step S101 as fixed values.

Next, more detailed processing of this embodiment will be described. FIG. 2 is a flowchart of a calibration method in the color image forming apparatus showing the processing of the flowchart of FIG. 1 in more detail. When a calibration instruction is input from the operator of the color image forming apparatus, the test chart 301 shown in FIG. 3 is output in order to adjust M and K as the first-stage procedure (step S201). ). In the test chart 301 shown in FIG. 3A, a plurality of patches in which the densities of M and K are changed are output arranged in a vertical direction (vertical), and seven patches are arranged in each column of M and K. Are arranged and output such that the concentration gradually decreases from top to bottom. In each column, the density intervals between vertically adjacent patches are all the same. In the present embodiment, two sets of each column of M and K are arranged side by side, and the set on the left side is group A and the group on the right side is group B.
In the group A and the group B, the density interval between vertically adjacent patches is
It is shifted by 1/2 density interval. For example, from the top, the density values of the patches of the group A on the left are “54%, 50%, 46%”.
%, 42%, 38%, 34%, 30% ”, the density of each patch of the right side B group is“ 56%,
An image is formed at a value of 52%, 48%, 44%, 40%, 36%, 32% ".

Next, in the present embodiment, using the reference chart 302 of FIG.
By comparing the reference patches on the reference chart 302 visually, a patch having the closest density is selected from the test chart 301 (step S20).
2). Then, the density value (xx%) described beside the selected patch is registered in the storage unit of the image forming apparatus (step S203). When registering a numerical value, a patch having a density closest to the reference patch of the reference chart is selected from each of the groups A and B, and a density value corresponding to the patch is registered. However, when the density is adjusted by the color image forming apparatus, a value obtained by calculating the average value of the density from the density value of each group is determined as the adjustment value. This is because the error is reduced by calculating the average value of the densities of both groups, and the density unit that can be selected and adjusted is reduced. In this embodiment, the density adjustment for M and K can be performed by this operation. Further, in the above-described registration method, only the density characteristics of the density of one point from each column of the test chart 301 can be obtained for M or K, but in the present embodiment, the density characteristic of one point of M or K is obtained. From the density characteristics, the density characteristics of an arbitrary portion other than the one point are estimated. Then, density adjustment is performed based on the estimated value so that the output has the specified density characteristic. The density adjustment is generally corrected using a gamma table. In the actual adjustment, a gamma table corresponding to the number of the patch selected from the test chart 301 is prepared, and the adjustment is performed by comparing using the gamma table. In addition to the adjustment using the gamma table, the density adjustment can also be performed by adjusting the developing bias and the LD light amount. Further, the correction using the gamma table, the developing bias, and the adjustment of the LD light amount can be performed. Any combination may be performed.

Next, as a procedure of the second stage, the density characteristics for C and Y are obtained by using the adjusted values of the density characteristics of M and K obtained as described above as fixed values. First, the test chart 401 shown in FIG. 4 is output using the density characteristics of M obtained in steps S201 to S203, which is the first stage procedure (step S204).
On the test chart 401 shown in FIG. 4, four types of gray balance charts from chart A to chart D are printed. In each of the charts A to D of the test chart 401, five patches in which the density of C is gradually increased from left to right are arranged in rows on the left and right. In the column, five patches in which the density of Y is changed so as to gradually increase from the upper side to the lower side are lined up and down. The patches formed on each of the charts A to D have the density characteristic of M as a fixed value, and change the respective densities of C and Y, for which the density characteristics are not determined, by using only the combination of CMY. Create a gray patch. In addition, the density intervals between adjacent patches vertically or horizontally are all the same. The background portion around each patch is colored in gray (achromatic color) created using only K so that the operator can easily adjust the gray balance. In each of the four types of charts from Chart A to Chart D, the patches with the best gray balance in the default state between the grays produced only by K arranged around them are arranged in the center, and the upper and lower patches are arranged. , Cyan (C: Cya)
n), the change rate of the density of yellow (Y: Yellow) changes. In addition, magenta (M: Mage) for which density characteristics are obtained
Since nta) is a reference for adjusting the densities of C and Y, the density does not fluctuate and is a fixed value.

[0009] In all four types of charts A to D,
The density intervals between adjacent patches in each chart are set to be the same. However, the density of patches at the same position in the charts is slightly different for each of the charts A to D. The amount of the different density is half the density interval between adjacent patches in the chart. For example, comparing the densities of patches at the same position in the charts A and B (positions 3 in the vertical and horizontal directions), the patch of the chart B has a density interval on the side where the density of the C is higher than the patch of the chart A. Is shifted by half the amount of The patch of the chart C is shifted by half the density interval to the side where the density of Y is higher than the patch of the chart A. Further, the patch of the chart D is shifted by half the density interval to the side where the densities of both C and Y are higher than the patch of the chart A. For example, the density difference between adjacent patches in charts A to D is “4” [%], and the density of the patch at the center of chart A is (C: 5).
0, M: 50, Y: 50) [%], the patch of the chart B at the same center position is (C: 52, M: 50,
Y: 50) [%], the patch of the chart C at the same center position is (C: 50, M: 50, Y: 52) [%], and the patch of the chart D at the same center position is (C: 52, M). : 5
0, Y: 52) [%]. This test chart 40
In No. 1, since achromatic gray created only by K is arranged in the background portion around each patch, the gray balance can be easily adjusted. Can be compared based on the background K1 gray.

Next, chart A of test chart 401
Are selected for each of the patches from (D) to (D) (step S205), and the four types of numerical values indicating the densities described on the vertical (Y) and horizontal (C) columns of each selected patch are imaged. By registering in the forming apparatus (step S206), the density adjustment for C and Y is performed. In the present embodiment, the gray-balanced points on each of the charts A to D can be calculated from the numbers assigned to the four types of patches registered in the image forming apparatus. By calculating the values, the density adjustment values for C and Y are determined. In the adjustment by the calibration method according to the present embodiment, since the density characteristics of the reference color (M) are obtained in advance by the procedure of the first stage, the patches having the gray balance on the test chart 401 are obtained. The density characteristic of the other color (C, Y) at the density of M can be obtained from the ratio of M in. Then, from the density characteristics of one patch on the test chart 401 in which the gray balance has been obtained, the density characteristics of a density portion other than the one patch portion are estimated, and C and Y are estimated using the density characteristics. Adjust the density. That is, for M and K,
The density of the reference patch prepared for each color on the reference chart prepared in advance is compared with the density of each patch on the test chart for M and K output from the color image forming apparatus. For each of C and Y, a gray patch having a density that matches the C and Y densities output from the color image forming apparatus is selected from each of the plurality of gray balance chart groups, and the selected gray is selected. By adjusting the gray balance using the density data of the patch, the density adjustment of the remaining color is performed. As described above, the calibration method of the present embodiment described above has a result of selecting from a plurality of gray balance charts as compared with a method of performing density adjustment by performing gray balance adjustment using one type of conventional chart. Since the adjustment value of the color (for example, Y) that is difficult to adjust can be determined using the density value of the balanced patch, the density adjustment error can be reduced, and the gray balance itself can be adjusted. The gray balance can be stabilized by reducing the minimum density unit.

As the adjustment of the gray balance used in the procedure of the second stage of the present embodiment, a method of registering only one point of a patch which is considered to have the best gray balance among the four types of charts is used. Can be used. In this case, the most balanced patch can be selected from a plurality of gray balance charts as compared with the conventional method of adjusting the gray balance using one type of gray balance chart. The density can be easily adjusted with a finer adjustment unit. Further, in the present embodiment, the density of the gray patch for which the gray balance is adjusted can be adjusted for an arbitrary value. For example, as shown in FIG. 5, three types of density groups, highlight, middle, and shadow, are sorted in descending order of density, and test charts 501, 502 for adjustment as shown in FIG. 503 is output from the color image forming apparatus, and the gray balance adjustment is performed for each of the three types of density groups. The gray balance can be adjusted for the density value of. In the above description, the density adjustment of M and K is performed in the procedure of the first stage of the present embodiment of step S101, and the density of the remaining C and Y is adjusted in the procedure of the second stage of the present embodiment of step S102. Although the method has been described, it is also possible to use a method of adjusting the densities of C and K in step S101 and adjusting the densities of M and Y in step S102. Also, a method of adjusting the density of three colors of CMYK in step S101 and adjusting the density of the remaining one color in step S102 can be used. In this case, the densities of C, M, and K are adjusted in step S101, and the density of Y is adjusted in step S102 using gray balance adjustment in the same manner as described above.

Further, in the calibration method in the color image forming apparatus of the present embodiment, two types of reference patches M and K are used as the reference chart 302 used in the first stage procedure, and the MK output from the color image forming apparatus is used. The result of comparison with a plurality of patch groups on the test chart 301 for each is used. Thereby, the reference chart 302 and the test chart 3
In the adjustment by comparison with 01, the density adjustment value is determined comprehensively from a plurality of results, so that stable density adjustment with few errors can be performed. Further, in the calibration method in the color image forming apparatus of the present embodiment, a printed matter can be used as a reference chart used in the procedure of the first stage. A normal reference chart needs to be created with toners having the same toner characteristics so that density comparison can be performed accurately. However, in the calibration method of the present embodiment, since the adjustment using the gray balance is the main adjustment as described above, the adjustment based on the comparison with the reference chart does not require as high accuracy as the conventional method. For this reason, in the present embodiment, a printed material that can obtain a stable output even when mass-produced and can reduce the cost can be used as the reference chart.

[0013]

As described above, according to the first aspect of the present invention, since the adjustment value can be determined comprehensively from a plurality of results by adjusting the gray balance in the procedure of the second stage, the error is small and the gray balance is reduced. Can be adjusted stably. According to the second aspect of the present invention, a well-balanced patch can be selected from a plurality of gray balance charts, so that adjustment in fine adjustment units can be easily performed. According to the third aspect of the present invention, since the gray balance at an arbitrary density value can be adjusted, the hue of the entire density can be stabilized. According to the present invention, since the density adjustment value is comprehensively determined from a plurality of results by adjustment based on comparison with the reference chart, stable density adjustment with less error can be performed. According to the fifth aspect of the present invention, the color image forming apparatus is provided with a configuration for performing the calibration method according to the first to fourth aspects. Even if such a situation occurs, it is possible to provide a color image forming apparatus capable of suppressing a change in color tone or density appearing in an output image, and enabling the operator to easily and accurately perform density adjustment for each of CMYK colors.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating a schematic process of a calibration method in a color image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a flowchart of a calibration method in the color image forming apparatus showing the processing of the flowchart of FIG. 1 in further detail;

3A is a test chart, and FIG. 3B is a reference chart.

FIG. 4 is a test chart for adjustment.

FIG. 5 is a test chart divided into three types of density groups, highlight, middle, and shadow, in descending order of density.

[Explanation of symbols]

301, 401, 501 to 503: test chart, 302: reference chart

Claims (5)

[Claims] 1. A calibration method for correcting a density fluctuation of a color image forming apparatus that outputs a color image using four color materials of CMYK, wherein at least one of the three CMY colors and K is provided. ,
The density of each patch on the test chart for at least one of the three colors CMY and K output from the color image forming apparatus is compared with the density of the reference patch for each color on the reference chart prepared in advance. Density adjustment is performed using the density data of the patches on the test chart that match with each other, and for the remaining colors of the three colors of CMY, a gray patch having a density matching the density of the color is assigned to a plurality of gray balance chart groups. Wherein the density adjustment of the remaining color is performed by adjusting the gray balance using the density data of the selected gray patch. 2. The calibration method for a color image forming apparatus according to claim 1, wherein in the gray balance adjustment, a patch having the best gray balance is selected from a plurality of gray balance chart groups. A calibration method in the color image forming apparatus, wherein the calibration is performed. 3. The color image forming apparatus according to claim 1, wherein the gray balance is adjusted using a gray balance chart in an arbitrary density range. Calibration method in the device. 4. The calibration method according to claim 3, wherein the density adjustment using a reference patch for each color on the reference chart is performed using a plurality of types of test charts output from the color image forming apparatus. A calibration method in a color image forming apparatus, wherein the calibration is performed using a result obtained by comparing the patch with an upper patch. 5. A color image forming apparatus comprising a configuration for performing the calibration method according to claim 1. Description: