JP3243397B2 - Color image processing equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention outputs the color image data by the color image output device such as a color plotter, relates to a color image processing apparatus such as a color copier, in particular, it is related to the gray balance correction in this type of device <br/>

[0002]

2. Description of the Related Art When a color image read by an image input device such as an image scanner is reproduced as a hard copy by a color image output device such as a color plotter, gamma correction (conversion) for bringing the output image closer to the input image is performed. I do.

[0003] The output characteristics of a color image output device such as a color plotter fluctuate due to the deterioration over time of the toner and the photoreceptor. Conventionally, in response to such a change in color tone due to aging, the color tone of the output image is corrected manually or automatically by correcting the γ curve of each color (the relationship between input image data and output image data). Has been adjusted.

[0004] As a technique for automatically correcting the γ curve, a test pattern is built in a color copier or the like.
If necessary, output this built-in test pattern, read the output image with an image scanner or the like, compare the read image data with the test pattern, and based on the result, select the optimal curve from among multiple γ curves. Is known (JP-A-2-266765).

[0005]

However, when the output characteristics of the color image output device change with time, or when the γ curve is changed manually or automatically, the gray balance may be lost.

An object of the present invention is to provide a color image processing apparatus such as a color copier or a color facsimile apparatus for outputting color image data by a color image output apparatus.
An object of the present invention is to prevent the gray balance from being lost due to a change over time of a color image output device or a correction of a γ curve.

[0007]

According to the present invention, there is provided a color image processing device for outputting color image data by a color image output device, wherein a gray balance condition prepared in advance for the color image output device is stored; Gray balance correction means for performing signal level correction for satisfying the gray balance condition with respect to the input signal of the color image output device is provided. Further, by measuring the output characteristics of each color toner of the color image output device, for each single color other than the reference single color,
The output characteristic curve of the single color, gray balance condition and reference
Means for creating or correcting a gray balance correction curve based on the output characteristic curve of a single color is provided, and the signal level correction is performed by the gray balance correction means in accordance with the created or corrected gray balance correction curve. ( Claim 3 ).

The gray balance condition is stored as data associated with the print density of each single color toner of the color image output apparatus. The gray balance condition data is stored as relative value data with respect to one reference single color. The stored signal level is corrected only for each single color other than the reference single color ( claim 2 ).

[0009]

According to the input signal level correction of the color image output device, the apparent output characteristics of the color image output device can be gray-balanced over substantially the entire density range. Even when the density is raised or lowered by correction, the gray balance of the output image is unlikely to be lost.

If the gray balance condition is stored as data associated with the print density of each single color toner, the gray balance can be easily obtained without considering the influence of the three-color superposition.

In this case, by setting the data of the gray balance condition as relative value data based on one color (for example, cyan), the memory capacity for storing the gray balance can be reduced, and the reference color can be reduced. Since there is no need to perform signal level correction, the configuration of the means for signal level correction is simplified. Further, since it is not necessary to create or modify the gray level correction curve for the reference color, the curve creation / modification process is simplified accordingly. Also,
The gray level correction curve is stored, for example, as a table structure, but requires less memory.

Since the output characteristics of each color toner of the color image output device are measured and a gray balance correction curve is created or corrected, even if the output characteristics of each color image output device vary, Even if the output characteristics change, the gray balance correction curve is optimized and appropriate signal level correction is performed, so that an output image with a good gray balance can be obtained.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an overall configuration of a color copier according to an embodiment of the present invention. 1 Te at <br/>, 100 is an image input device such as an image scanner for reading by decomposing the image of the document to RGB3 primary colors, RGB
The data signal is input to the image processing unit 102.

The image processing unit 102 performs a specific process on the RGB data signal and a CMYK conversion from the RGB data signal.
(C: cyan, M: magenta, Y: yellow, K: black)
It is a part that performs conversion into a data signal and the like, an example of which is shown in FIG. In the example shown here, reference numeral 200 denotes a filter for filtering an RGB data signal (a low-pass filter or an MTF filter for suppressing moiré is generally used). 202 is a filter 200
Is a color conversion unit that converts the RGB data signal passed through the CMYK into a CMYK data signal. A gamma conversion unit 204 performs gamma conversion (correction) on the CMYK data signal.

In FIG. 1, reference numeral 104 denotes a gray balance unit. This gray balance unit 104
The signal level correction for obtaining the gray balance is performed for each color of CMY, and is a part newly introduced by the present invention. Reference numeral 106 denotes each CMY single color toner and K (black)
This is a color image output device that outputs a hard copy of a color image using toner.

Image input device 100, image processing unit 1
02. Since the color image output device 106 may be the same as the conventional one, the gray balance unit 104 introduced according to the present invention will be described in detail below.

FIG. 3 is a block diagram showing the configuration of the gray balance unit 104. In FIG. 3, reference numeral 304 denotes a gray balance storage device for storing gray balance conditions, and 302, a correction table creating / correcting device for creating and correcting a gray balance correction table. The correction table creation / correction device 302 can access the gray balance conditions in the gray balance storage device 304, and receives an RGB data signal from the image input device 100. The gray balance correction table created or modified here is stored in the gray balance correction device 300.
Is stored in the correction table storage unit 301. Reference numeral 306 denotes a patch generation device that generates a patch for obtaining output characteristics (indicated value VS density) of each CMY single color when creating / correcting a gray balance correction table. The gray balance correction device 300 performs level correction on the CMY color data signals input from the image processing unit 102 according to a gray balance correction curve represented by a gray balance correction table stored in a correction table storage unit 301. . As will be described later, when one color in CMY is selected as a reference, no level correction is performed on the data signal of the reference color.

Next, a process for creating a gray balance condition will be described. FIG. 4 is a flowchart showing an outline of this processing. This processing is performed not by the processing of the color copier but by using, for example, a computer system having the same type of image input device and color image output device as the color copier.

First, a CMY gray balance is obtained for each density (step 400). That is, a combination of the CMY color toner density instruction values is selected such that the color image output apparatus becomes gray when the CMY three color toners are overprinted. The gray balance may be arbitrarily set. For example, for all the toner density indication values of C, a combination of several CMY toner density indication values is output by a color image output device, and the output result is output by an image input device. The CMY combination in which the RGB color data signals are read and become the same level is regarded as a CMY combination with a gray balance.

Next, the combinations of CMY with balanced gray are divided into single colors and output separately by a color image output device (step 402). The output result is read by the image input device to measure the density of each color of CMY, and the density relationship of CMY as shown in FIG. 6 is obtained (step 404). This relationship is called a gray balance condition. Here, C is selected as the reference color, and the horizontal axis in FIG. 6 indicates the density Dc of C, and the vertical axis indicates the densities Dm and Dy of M and Y. Dc-Dm and Dc-D
y is M, which can be gray-balanced for each density of C,
It is a curve which plotted the density of Y.

The gray balance conditions thus obtained are stored in the color copier gray balance storage device 304 (step 404). At this time, the gray balance condition as shown in FIG. 6 may be stored as it is, but in this embodiment, C is selected as the reference color, the density of C is stored as it is, and the density of each of the other MY colors is stored. Is stored as a relative value (increase / decrease, ratio) with respect to the concentration of C. If the gray balance conditions are stored in such a manner, the amount of memory required for storing the gray balance conditions can be reduced.

The gray balance may be set as follows, for example. First, a color image output device outputs color patches of a plurality of density levels for each of the CMY single-color toners.
Decompose into BG and read. The output characteristics (toner indicated value VS print density) of each color toner of the color image output device are measured from the read RGB color signals. And
A plurality of patches that become gray when three-color printing is performed by the color image output device are created, and the toner density of each color at that time is created.
Three-color toner that satisfies the gray balance condition by obtaining the single-color print density corresponding to the degree indication value from the output characteristics
The combination of the indicated density values is obtained over the entire density range.

Next, the operation of the color copier will be described focusing on the operation related to the gray balance unit 104.
FIG. 5 is a flowchart for explaining the operation.

First, an operation for initializing the gray balance unit 104 is performed (steps 500 and 5).
02). First, density patches of various density levels of each single color of CMY are generated by the patch generation device 306, and output by the color image output device 106 (step 500). Then, the output result of the density patch of each single color is read by the image input device 100, and the correction table creating / correcting device 302 is read.
Then, the output characteristics (indicated value VS print density) of each color of CMY of the color image output device 106 are obtained from the read result (RGB data signal), and the gray level for satisfying the gray balance condition stored in the gray balance storage device 304 is obtained. A balance correction table is created and stored in the correction table storage unit 301 of the gray balance correction device 300 (Step 502). This completes the initialization, but this is performed only once before the operation of the color copier.

The creation of the gray balance correction table (gray balance correction curve) will now be described in more detail.

By reading the output results of the density patches, the output characteristic curves ( toner
It is assumed that the density instruction value I VS density D) is obtained. This output characteristic changes over time. In FIG. 7, the horizontal axis is CMY
The toner density instruction values Ic, Im, Iy of each color, and the vertical axis is CM
The printing density of each Y color. Ic-Dc is the output characteristic curve of C, Im-Dm is the output characteristic curve of M, Iy-
Dy is an output characteristic curve of Y.

From such output characteristics and the gray balance conditions as shown in FIG. 6, a gray balance correction curve for each color can be obtained. Here, since C is selected as the reference color, a gray balance correction curve is obtained only for the two colors MY.

FIG. 8 shows an M gray balance correction curve,
9 shows a relationship between a gray balance condition and an output characteristic curve . In the first quadrant of FIG. 8, the output characteristic curve of M (FIG. 7)
Im-Dm curve) is plotted, and M is plotted in the second quadrant.
(Dc-Dm curve in FIG. 6) is plotted, and the output characteristic curve of C (Ic-Dc curve in FIG. 7) is plotted in the third quadrant. From the curves in these quadrants, an M toner density instruction value Im that achieves a gray balance with an arbitrary C toner density instruction value Ic is obtained, and when this is plotted, a curve shown in the fourth quadrant is obtained. This curve is an M gray balance correction curve based on C (Ic corresponds to an input value of Im, that is, a value before correction). In FIG. 8, three density values are shown.
Only the density values are shown.
And plot them.
By performing interpolation processing, a gray balance correction curve can be obtained.
Can be This also applies to FIG. 10, FIG. 12, FIG.
The same is true.

FIG. 9 shows an extracted gray balance correction curve of M. The horizontal axis represents M toner before correction.
Density instruction value (Im: input), vertical axis is M toner density after correction
Degree indication value (Im: output).

FIG. 10 shows the relationship between the gray balance correction curve for Y, the gray balance conditions and the output characteristics. In the first quadrant of FIG. 10, the output characteristic curve of Y (FIG. 7)
Iy-Dy curve) is plotted, and Y is plotted in the second quadrant.
Are plotted (Dc-Dy curve in FIG. 6), and the output characteristic curve of C (Ic-Dc curve in FIG. 7) is plotted in the third quadrant. From the curves in these quadrants, a Y toner density indication value Iy that can achieve a gray balance with an arbitrary C toner density indication value Ic is obtained, and when this is plotted, a curve shown in the fourth quadrant is obtained. This curve is a Y gray balance correction curve based on C (Ic corresponds to an input value of Iy, that is, a value before correction).

FIG. 11 shows the gray balance correction curve of Y extracted, and the horizontal axis represents the Y toner before correction.
-Density instruction value (Iy: input), vertical axis is Y toner after correction
This is a density instruction value (Iy: output).

A table expression of the gray balance correction curves of the respective colors MY shown in FIGS. 9 and 11 is created by the correction table creating / correcting device 302, and is stored in the correction table storage unit 301. However, since the signal level correction is not performed for the reference color C, the gray balance correction table is not created as described above.

Referring to FIG. When the above initialization is completed, normal copy processing 504 of the color copier becomes possible. The copy processing operation is as follows. A document image is read by the image input device 100, and RGB data signals are input to the image processing unit 102 (step 50).
7). In the image processing unit 102, the RGB data signal is filtered by the filter 200 and then converted by the color conversion unit 202 into a CMYK data signal.
Further, the data is subjected to γ conversion (correction) by the γ conversion unit 204 and then input to the gray balance unit 104 (step 507). In the gray balance unit 104, the gray balance correction device 300
C data signal in C data signal (C toner density indication value )
And the K data signal (K toner density indication value ) are output as they are, but the M data signal (M toner density indication value )
And the Y data signal (Y toner density indication value )
According to the corresponding gray balance correction table (gray balance correction curves shown in FIGS. 9 and 11) stored in the correction table storage unit 301, the signal level ( toner density
Is corrected and output (step 508). The YMCK data signal output from the gray balance correction device 300 is output as a hard copy by the color image output device 106 (step 509).

By correcting the signal levels of the two colors YM, an output image with a good gray balance can be obtained.
If the output image is to be made darker or lighter, if the signal level of each color component is raised or lowered as a whole by modifying the γ curve of the γ conversion, the output characteristic of the color output image device 106 has conventionally changed over time. Even if there was no, the gray balance could be lost. According to the present invention, by the signal level correction by the gray balance unit 104, the apparent output characteristics of the color image output device 106 are corrected so that the gray balance can be achieved over almost the entire density range. ,
The gray balance of the output image is unlikely to be lost. Also,
Even if the output characteristics of the color image output device 106 vary from one color copier to another, the gray balance correction table is optimized based on the actual output characteristics. The gray balance can be prevented from being lost.

However, if the output characteristics of the color image output device 106 change from the time of initialization due to a change with time, gray balance cannot be obtained. When the user wants to correct such a gray balance collapse, or periodically, manually or automatically, step 500,
By executing the process of 502, the gray balance correction table can be corrected. This correction processing is substantially the same as the processing at the time of initialization.

That is, a density patch is generated by the patch generation device 306 and output by the color image output device 106 (step 500). The output patch is read by the image input device 100, and the correction table creation / correction device 3
In step 02, the CMY output characteristics are measured, and based on the output characteristics, a gray balance correction table corrected to satisfy the gray balance condition is created, and a correction table storage unit 301 is prepared.
(Step 502).

The relationship between the change in the output characteristics and the correction of the gray balance correction curve will be described with reference to FIGS.

FIG. 12 is a view corresponding to FIG. 8, and shows a case where the output characteristic of M shown in the first quadrant has changed from the previously measured dotted curve to the solid curve. in this case,
When plotting the toner density indication value of M that satisfies the gray balance condition with respect to the arbitrary toner density indication value of C, a solid curve shown in the fourth quadrant is obtained. This solid curve is the M gray balance correction curve corrected in accordance with the current output characteristics (the dotted curve is the gray balance correction curve before correction).

FIG. 13 is a diagram corresponding to FIG.
This shows a case where the output characteristic of Y shown in the quadrant and the output characteristic of C shown in the third quadrant have changed from the previously measured dotted curve to the solid curve. Any of the toner in this case, C
-Y value for gray balance condition
When the indicated toner density value is plotted, a solid curve shown in the fourth quadrant is obtained. The solid curve is a Y gray balance correction curve corrected in accordance with the current output characteristics (the dotted curve is a gray balance correction curve before correction).

A gray balance correction table representing the corrected gray balance correction curve is created and stored in the correction table storage unit 301. Thereafter, the level correction of the M and Y data signals is performed by the gray balance correction device 300 using the corrected gray balance correction table, so that a gray-balanced output image is obtained.

[0042]

According to the present invention, the following effects can be obtained.

(1) A gray-scale condition prepared in advance for a color image output device is stored, and a color image output is performed to perform a signal level correction on the input signal of the color image output device to satisfy the gray balance condition. Since the apparent output characteristics of the device can achieve gray balance over substantially the entire density range, even if the density is raised or lowered by modifying the γ curve of the γ conversion in the previous stage, the gray balance of the output image can be adjusted. Collapse can be prevented.

(2) Since the gray balance correction curve is created or corrected by measuring the output characteristics of each color image output device for each single color toner, even if the output characteristics of each color image output device vary, Even if the output characteristics change due to deterioration with time, the gray balance correction curve is optimized and appropriate signal level correction is performed, so that an output image with good gray balance can be obtained.

(3) By storing the gray balance conditions as data associated with the print density of each single color toner, the gray balance can be easily obtained without considering the influence of the three-color superposition.

(4) By setting the data of the gray balance condition as relative value data based on one color (for example, cyan), the memory capacity for storing the gray balance can be reduced, and the reference color can be reduced. Since there is no need to perform signal level correction, the configuration of the means for signal level correction is simplified. Further, since it is not necessary to create or modify the gray level correction curve for the reference color, the curve creation / modification process is simplified accordingly. Further, the gray level correction curve is stored as, for example, a table structure, and the memory for the correction is small.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of a color copier according to one embodiment of the present invention.

FIG. 2 is a block diagram illustrating an example of an image processing unit.

FIG. 3 is a block diagram illustrating an example of a gray balance unit.

FIG. 4 is a flowchart illustrating a procedure for creating a gray balance condition.

FIG. 5 is a flowchart showing a normal operation of a color copier and a procedure for creating / correcting a gray balance correction table.

FIG. 6 is a diagram illustrating an example of a gray balance condition.

FIG. 7 is a diagram illustrating an example of output characteristics of each color toner of the color image output apparatus.

FIG. 8 is a diagram showing a relationship between an M gray balance correction curve, output characteristics, and gray balance conditions.

FIG. 9 is a diagram showing a gray balance correction curve of M.

FIG. 10 is a diagram showing a relationship between a gray balance correction curve of Y, output characteristics, and gray balance conditions.

FIG. 11 is a diagram showing a gray balance correction curve of Y.

FIG. 12 is a diagram illustrating correction of an M gray balance correction curve due to a change in M toner output characteristics.

FIG. 13 is a diagram illustrating correction of a gray balance correction curve of Y due to a change in C and M toner output characteristics.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 image input device 102 image processing unit 104 gray balance unit 106 color image output device 200 filter 202 color conversion unit 204 gamma conversion unit 300 gray balance correction device 302 correction table creation / correction device 304 gray balance storage device 306 patch generation device

Claims (3)

(57) [Claims] 1. A color image processing apparatus for outputting color image data by a color image output device, comprising: means for storing a gray balance condition prepared in advance for the color image output device; And a gray balance correction unit for performing signal level correction for satisfying the gray balance condition. 2. A color image processing apparatus according to claim 1,
Means for storing the gray balance condition
And print density of each color toner of color image output device
The attached gray balance condition is compared to one reference unit.
The gray balun is stored as relative value data for the color.
Correction means for each single color other than the reference single color.
Color image processing characterized by performing signal level correction
Equipment. 3. The color image processing apparatus according to claim 2,
Output by each color toner of the color image output device.
Measure the characteristics and check for each single color other than the reference single color.
The output characteristic curve of the single color, the gray balance condition and
Mutual input / output by reference output characteristic curve of single color
Create a gray balance correction curve based on the relationship or
Having means for making such modifications, said created or modified
The gray balance according to the gray balance correction curve
The characteristic correction means performs the signal level correction.
Color image processing device.