JP2002290755A - Gray regulation method in image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily perform regulation by lessening uncomfortable feeling of a gray patch comprising CMY and K mono-color gray. SOLUTION: In the CMY gray regulation method for judging the density of an image from an image forming device by human eyes and performing the regulation density of the image forming device, gray regulation is performed by comparing the patch comprising CMYK and the CMY patch. Then, an amount of K of the CMYK patch is variable and the amount of K is K of regulated density.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, such as a copying machine, a facsimile, and a printer, which is characterized by gamma correction of engine output.

[0002]

2. Description of the Related Art In an image forming apparatus such as a color printer, the color density of a print deviates from a reference value due to a change over time or the like, so that color correction is required. Therefore, various color correction methods have conventionally been adopted.

For example, a color sample sheet included in advance with a product is compared with a printout of a test pattern stored in the printer, and a method of determining a correction amount of density is performed. A method of reading the density of a figure printed on paper, calculating the difference between the color of the drawn figure and the actual color, and correcting the density curve,
Prepare a template with the standard density printed in advance, print the paper with all the selectable densities printed on the printer where you want to correct the density curve, and print the paper with the same density as the template. It is known that the density curve is corrected by selecting from among them.

The density value of print data sent from a host to an image forming apparatus such as a printer is designated by a numerical value from 0 to 255 which is usually expressed by 8 bits per color. On the other hand, a process called γ conversion is performed so that the density in the print result becomes a desired density. When the density is represented by 8 bits, the gamma conversion is performed for an output value of 0 to 255 for an input value of 0 to 255
Is obtained using a conversion table stored in a memory in the controller. In a graph with the same scale for both the horizontal axis and the vertical axis, if the horizontal axis is an input value and the vertical axis is an output value, if the input / output characteristics of the printer engine are represented by a straight line rising 45 degrees to the right Then, the input value = the output value, and the process of γ conversion becomes unnecessary. However, the input / output characteristics of the printer engine do not usually have the above-mentioned linear characteristics, and the process of γ conversion is indispensable for obtaining an appropriate image by the printer.

[0005] In addition, even in the case of printer engines of the same model, input / output characteristics usually differ due to individual differences. The input / output characteristics change with time and also depending on the environment in which the printer is placed. Therefore, it is necessary to rewrite the contents of the conversion table used for the γ conversion according to the change in the input / output characteristics. In general, if the contents of the γ conversion table are represented as a curve when the contents of the γ conversion table are represented in a graph in which the input value and the output value are respectively taken on the horizontal axis and the vertical axis, the process of rewriting the contents of the γ conversion table is referred to as “correcting the γ curve Or the content of the corrected γ conversion table may be referred to as “corrected γ” or “corrected γ curve”.

FIG. 1 is a diagram showing an example of a conventional printer system. This system includes a host computer 1 and a printer engine 2. A printer controller 3 is provided at a stage preceding the printer engine 2. Data to be printed is specified by the host computer 1, and the printer controller 3 creates and prints image data according to the command. At this time,
The image data to be created is drawn in the frame memory according to the designated density, sent to the printer engine 2, and the printing is completed.

[0007] As shown in FIG.
PU 31, RAM 32, program ROM 33, font ROM 34, host I / F 35, and engine I / F
36, each of which is connected via a bus 37. The CPU 31 controls the entire printer controller 3 according to a program stored in the program ROM 33, a mode instruction from the panel device, and a command from the host computer 1. Program ROM 3 as described above
3 stores a control program of the printer controller 3, and the font ROM 34 stores font pattern data and the like. The RAM 32 functions as a work memory for the CPU 31 and is used as an input buffer for input data, a page buffer for print data, a memory for download fonts, and the like. Engine I / F3
Reference numeral 6 denotes a command and status with the printer engine 2,
The host I / F 35 is an interface that communicates with the host computer 1 for communicating print data.
Usually, it is a Centro I / F or RS232C, but may be connected to a host via a network such as EtherNet or LocalTalk.

Here, the density of the printer engine may be different from the density intended by the printer controller due to the surrounding environment and changes over time. In this case, for example, in a printer controller having a reading device such as a scanner device, paper output by a printer engine is read by the scanner device, and a density value (output result) as a result of the reading and a density value intended by the printer controller (output result) are read. Output expected value), and if there is a difference, the density value for performing drawing is corrected so as to absorb the difference (the above-mentioned γ correction), so that the printed matter is the result intended by the printer controller, that is, the host computer. Gives the intended result.

In an image forming apparatus having no reading device such as a scanner device, as shown in FIG. 3, a printing result is output dark or light by human eyes without using a reading device such as a scanner. The same effect can be obtained by judging whether the printing has been performed and inputting it to the printer controller 3. In this case, unlike a reading device such as a scanner, it is difficult for the human eyes to determine the density. Therefore, the density value can be easily determined through the eyes of the human 4 using a sheet called an adjustment sheet 5 to support the density. To do. In the adjustment sheet 5, for a density to be adjusted, a predetermined density range including a reference density pattern (B in FIG. 4) and a peripheral density including the density is used as a pattern ( 4) are output side by side, and the density is compared by selecting a number having the same density, and the density value (output result) indicated by this number (number attached to A in FIG. 4) and the controller The gamma correction is derived from the intended density value (expected output value), and the gamma correction is reflected at the time of drawing to perform drawing, thereby obtaining a desired density result. An example of such processing is described in Japanese Patent Application No. 11-314395 filed by the present applicant.

As a reference density pattern, a pattern which is not affected by a change with time or machine difference is used. For example, to create a density of 50% of the maximum density of the printer engine 2, a checkerboard pattern as shown in FIG. 5 may be used, but the dots constituting the pattern are one pixel (dot) of the printer engine 2. Then, since it is affected by the output characteristics of the printer engine 2, a stable 50% density cannot be created. Therefore, a pattern that is not affected by the above-described effect can be created by using a checkerboard pattern (FIG. 6) having several dots.

By performing such processing, the output characteristics, that is, the density can be adjusted even by a printer controller having no reading device.

On the other hand, in the case of a color printer, it is necessary to adjust the density of colors other than black, such as cyan, magenta, and yellow. In the example of FIG. 7 shown in the specification of Japanese Patent Application No. 11-314395 described above, the above-described density adjustment is performed for magenta and black, and gray of cyan and magenta yellow in which the composition ratio of cyan and yellow is changed. Patch (part B in FIG. 7) and black base (A in FIG. 7)
) Is adjusted to adjust the four colors.

[0013]

However, in many cases,
The CMY mixed-colored grays have a hue, and the user receives a slightly different impression when comparing with the K single-colored gray.
It turned out that it was difficult to select one patch.

The present invention has been made in view of the above points,
An object of the present invention is to reduce the sense of incongruity between a gray patch composed of CMY and K single-color gray, and to facilitate adjustment.

[0015]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method for determining the density of an image output from an image forming apparatus with human eyes and adjusting the density of the image forming apparatus.
The MY gray adjustment method is characterized in that gray adjustment is performed by comparing a CMYK patch and a CMY patch.

In this case, the amount of K of the CMYK patch is made variable, and the amount of K is adjusted to the adjusted concentration of K. Furthermore, it is preferable that the K gray patch is mixed with CMY mixed color gray to give a tint, and the color tone of the CMY patch is made inconspicuous to perform gray adjustment.

[0017]

Embodiments of the present invention will be described below.

The operation of a printer using four colors of CMYK using the above-mentioned gray adjustment patch (FIG. 7) will be described.

If it is attempted to adjust the CMY at a density of 25%, the K density (density at A in FIG. 7) of the gray adjustment sheet in FIG. 7 is 25%, and the density of each CMY (FIG. (The density of the portion B) is 25% (A in FIG. 8).

In FIG. 7, the C patch (FIG. 7A)
CMY mixed color patches with different composition ratios of Y and Y (FIG. 7B)
Are displayed, and the user obtains the desired C and Y composition ratio by selecting a patch that blends with the K gray background. In this case, the CMY mixed color gray has a tint and cannot be dissolved with the K gray background.

Therefore, in the present embodiment, the K gray patches (portion A in FIG. 7) are mixed with CMY mixed gray to give a color to make the color of the CMY patch inconspicuous (B in FIG. 8). The density value of CMY to be mixed is determined by the magnitude of the color of CMY mixed color gray and the density to be adjusted (25 in the above example).
%) And the color distribution of toner and ink, it is expected that the target is determined at the time of design and the density of CMY in which the color is not noticeable is experimentally found.

If the density is not uniquely determined, but can be set from a panel or the like so that the density can be varied within an experimentally determined range at the time of adjustment, and the user can set at the time of adjustment, The adjustment can be performed at a density that is easy for the user to see.

Also, if the density of the CMY to be mixed is not gray-adjusted, the CM to be adjusted is not adjusted.
The adjustment value of Y also shifts. By making the CMY concentration mixed with the CMY concentration adjusted by the conventional method,
Avoid this.

The above is the operation for determining the four-color density adjustment value using the CMYK mixed-color gray. However, the reflection of the actually determined density on the gamma is the same as in the case of the single color, so that the gamma correction calculation is performed as follows. By doing so, the density correction can be reflected.

FIG. 9 shows an example of the input / output characteristics of the printer. This example shows that the density fluctuation of the printer engine tends to be output at a lower density in a low density part and a higher density in a high density. It is also known that the change over time of the printer indicates that the gain of the lower density becomes smaller and the gain of the higher density part becomes larger as shown in FIG.

FIG. 11 is a diagram showing a linear brightness characteristic used by the printer system, that is, a desirable output characteristic (target γ). A correction is made to match this characteristic with the input / output characteristic of the printer shown in FIG. . The result of this is the correction γ shown in FIG. When the printer input / output characteristics change as shown in FIG. 10 due to a change with time, γ correction is performed to obtain the printer input / output characteristics shown in FIG. Looking at the input / output characteristics of the printer, as shown in FIG. 9, since the gain of the target is originally low in the low density portion, the degree of change becomes more severe. Conversely, the degree of change is lower at medium and high densities than at low density parts, so the degree of change is not as great as at low density parts. Therefore, in the present invention, FIG. 13 and FIG.
As shown in (2), different correction points are selected for the low-density part and the medium-high density, and the low-density part indicated by A is corrected as the correction point 1,
B is separately corrected as the correction point 2 of the intermediate density portion. In other words, the correction point 1 is the point C shown in FIG.
Take between. The correction point 2 is the point C and the upper limit of the density 25.
Take between 5. At this time, the point C can be obtained from the graph because it is a place close to the changing point of the quadratic curve of the input / output characteristics of the printer.

In the present invention, as described above, the densities at these correction points are stored in advance as color sample test turns, and color correction test data is created and output based on the test turns. , Or the user performs an operation of obtaining a corrected density value by comparing the values.

FIG. 15 shows the read values at the correction points 1 and 2, that is, the deviation between the current density of the printer and the correction value, and the respective read values have deviations from the correction values indicated by arrows. It indicates that. The user inputs the correction values at the respective correction points, and obtains the correction γ in FIG. 16 from the correction values at the correction points 1 and 2 in the controller.

FIGS. 16 and 17 show the correction γ obtained in this way. FIG. 16 shows the correction points connected by straight lines, and FIG. 17 shows, for example, a Bezier curve or a spline curve. Complementary curves are shown by such curves, and correction γ similar to the correction γ shown in FIG. 13 can be obtained.

As described above, by setting two correction points, for example, a low density part and a middle and high density part, although the number of correction points is small, the correction points are set in areas corresponding to the characteristics of the input / output characteristics of the printer. By selecting, sufficient correction is possible. In the case of a color printer, since the characteristics of the engine differ depending on the color, the correction γ can be similarly provided for each color. The correction γ can be obtained by setting the correction point for each color in the same manner as described above. As in the case of the color mode, the tone processing (dithering) is different even in a drawing mode such as a character / photo, so that the engine characteristics after the tone processing are different as shown in FIG. In this case as well, it can be dealt with by appropriately increasing the number of correction points.
Furthermore, it is also possible to separately obtain, for example, 4 × 2 = 8 correction γs for the color mode (CMYK) and the drawing mode (character / photograph).

A density pattern composed of a plurality of density portions obtained by equally dividing the density between the highest density and the lowest density in color printing and a reference density portion is formed, and the density pattern is printed on the same sheet. For each step of correcting the input / output characteristics of the image forming apparatus based on the density correction values obtained, a program for executing the steps is, for example, FD or C
It can be recorded on a recording medium such as a D-ROM. For example, by mounting it on the host computer 1 of FIG. 1 and downloading it, the printer controller 3 can be controlled from the host computer 1 through the host I / F, and the above-described steps in the color correction method can be executed.

[0032]

As described above, according to the first to fourth aspects of the present invention, when the density adjustment is performed by human eyes, C
It is possible to reduce the sense of incongruity between the MY gray patch and the K single color gray, and to perform color adjustment more easily and more accurately.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a conventionally implemented printer system.

FIG. 2 is a block diagram showing the printer system of FIG. 1 in further detail.

FIG. 3 is a diagram for explaining a procedure in a case where density adjustment is performed by human eyes.

FIG. 4 is a diagram illustrating an example of a density correction sheet.

FIG. 5 is a diagram showing a pattern when the density is 50%.

FIG. 6 is a diagram showing a checkered pattern when the density is 50%.

FIG. 7 is a diagram illustrating a gray adjustment performed when density is adjusted by performing density adjustment with magenta and black, and comparing a gray patch composed of cyan and magenta yellow with a changed composition ratio of cyan and yellow with a black base to adjust the density. FIG. 4 is a diagram illustrating an example of a patch.

FIG. 8 is an enlarged view showing a main part of FIG. 7;

FIG. 9 is a diagram illustrating input / output characteristics of a printer engine.

FIG. 10 is a diagram showing input / output characteristics after the change with time.

FIG. 11 is a diagram showing target corrected input / output characteristics.

FIG. 12 is a diagram showing input / output characteristics after correction.

FIG. 13 is a diagram showing corrected input / output characteristics after a change over time.

FIG. 14 is a partially enlarged view of FIG.

FIG. 15 shows a read value, a correction value, and a correction γ in FIG.
FIG.

FIG. 16 is a diagram illustrating a method of creating a correction γ (corrected input / output characteristics).

FIG. 17 is a diagram illustrating a method of creating a correction γ.

FIG. 18 is a diagram illustrating dither characteristics after a print mode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Host computer 2 Printer engine 3 Printer controller 4 Human (user) 5 Adjustment sheet

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5B057 CA01 CA08 CA12 CB01 CB08 CB12 CC01 CE17 5C077 LL04 LL12 LL19 MM27 MP08 PP15 PP33 5C079 HB02 HB03 LA12 LA23 LB01 MA10 NA03 NA21 NA27 NA29 PA01 PA02 PA03

Claims (4)

[Claims] An image forming apparatus that determines the density of an image output from an image forming apparatus with human eyes and adjusts the density of the image forming apparatus.
A gray adjustment method for an image forming apparatus, wherein a gray adjustment is performed by comparing a CMYK patch with a CMY patch. 2. The gray adjustment method according to claim 1, wherein the amount of K of the CMYK patches is variable. 3. The gray adjustment method for an image forming apparatus according to claim 2, wherein the amount of K is set to K of an adjusted density. 4. The image forming apparatus according to claim 1, wherein a color adjustment is performed by mixing a CMY mixed color gray with a K gray patch to make the color of the CMY patch inconspicuous. Gray adjustment method.