JPH01194678A - Color image processor - Google Patents

Abstract

PURPOSE:To prevent an image quality from being deteriorated such that a character in a color marker is made patchy, thin and by changing the processing contents of color distinguishment when a part color converting mode is selected. CONSTITUTION:Plural tables for color distinguishment are prepared at a color distinguishing means 20 and they are selected in accordance with a processing mode. At the time of a part color converting mode, a color distinguishing map to expand a black detecting area is selected. For that reason, even when a part of the outline of an image is decided as a color marker by the color marker, it can be detected and separated as an outline part approximately corresponding to an original image as a result.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a color image processing device suitable for application to an image processing device such as a PPC color copying machine, particularly having a color discrimination processing function and a partial color conversion function. The present invention relates to a color image processing device.

[Background of the Invention] In a cocolor image processing device, such as a color copying machine using a laser beam, a color original is separated into a plurality of colors to obtain color image information, and a color image is recorded based on this color image information. That's what I do.

In such a color copying machine, a color image is separated into a plurality of color separation images, and these are roughly separated into their density data and color codes indicating their color information, and the separated image data ( ia degree data and color code data), various image processing such as scaling processing and partial color conversion processing can be performed.

An example of a color image processing apparatus that records images by performing various types of image processing is shown in FIG. 4 and subsequent figures.

Color image information (optical image) of a subject 2 such as a document passes through an optical system 3 and is separated into two color-separated images by a dichroic mirror 4. In this example, the image is separated into a color-separated image of red R and a color-separated image of cyan Cy. Therefore, the dichroic mirror 4 used has a cutoff of about 540 to 600 nm.

The color separation images of red R and cyan Cy are supplied to an image reading means, for example, a CCD 6.7, and image signals of only the red component R and cyan component cy can be output from each image reading means, for example.

By supplying the image signals R and Cy to the A/D converters 10 and 11, they can be converted into digital signals of a predetermined number of bits, 6 bits in this example. Shading correction is performed simultaneously with A/D conversion. 12.13 shows a shading correction circuit.

The digital image signal subjected to the shading correction is extracted by the effective area extraction circuit 15 only for the signal corresponding to the maximum document size width, and is supplied to the next stage color discrimination circuit 2O. When the maximum document width to be handled is 84 size, the size signal B4 generated by the timing signal generating means 170 of the system is used as the gate signal.

Here, if the digital image signals subjected to shedding correction are VR and VC, respectively, these image signals VR.

VC is supplied to a color discrimination circuit 20 and separated into a plurality of color signals.

In this example, a case is illustrated in which the signal is configured to be separated into three color signals: red, helmet, and black.

That is, no matter what color the original is, each pixel is assigned to one of red, helmet, or black. When this process is performed, each part of the document is recognized as a red, blue, or black color part.

In addition, if these red, blue, and black are other colors, roughly 4
This color discrimination processing also includes the determination of a color or more.

Each color-discriminated color signal is divided into color code data (2-bit data) indicating its color information and its density data (6-bit data).
bit data).

Data for each of these color signals may be stored in a color discrimination conversion table (map) in a ROM, for example.

FIG. 5 shows an example of this color discrimination map.

The image data that has undergone color discrimination is transferred to a color image processing step.

First, it is supplied to the next-stage color ghost correction circuit 130, where color ghosts in the main scanning direction (horizontal scanning direction) and sub-scanning direction (drum rotation direction) are corrected.

This is because unnecessary color ghosts occur during color discrimination, especially around black characters.

FIG. 6 shows an example of appearance of color ghosts.

The figure shows the color ghost that appears after color discrimination is performed by capturing an image of the kanji character "sexuality" written in black.

As you can see from this example, as a color ghost,
As shown in FIGS. 7A to 7C, red and helmet appear at the edge of the black line, black appears at the edge of the blue line, and black appears at the edge of the red line.

It is clear that color ghosts appear differently in other color combinations.

This color ghost correction circuit is a circuit for correcting such color ghosts as much as possible.

Color ghost processing applies only to color code data.

In addition to color ghost correction, image processing includes resolution correction, partial color conversion processing, scaling processing, multi-value processing, and the like.

First, the image data (color code data and density data) after color ghost correction is sent to the subsequent resolution correction circuit 40.
At , the density data is processed to determine its resolution (MT
F) can be corrected.

Deterioration of resolution includes deformation of the beam shape of the laser beam, deterioration of the development characteristics of toner onto the photoreceptor drum, and the like. Of these, the optical system and its travel system directly affect resolution deterioration.

FIG. 8 shows MTF values (before correction) in the main scanning direction and the sub-scanning direction when the optical system is driven. This characteristic is 2~16d
These are the measured values when scanning a black and white pattern with a spatial frequency up to ots/mm.

The MTF in this case was defined and used as MTF=(W-BK)/(W+BK)(%). Here, W is a white signal No. 48, and BK is a black signal.

The deterioration of MTF is more significant in the sub-scanning direction. To make the same amount of correction, the amount of correction in the sub-scanning direction should be 2 times that of the main-scanning direction.
It should be set to ~4 times.

In order to correct the main and sub-scanning directions to the same degree while not degrading the reproducibility of fine line areas, a convolution filter that uses 3 x 3 pixel image data is used as the resolution correction circuit. can do.

FIG. 9 shows the correction results when using the convolution filter.

The resolution-corrected density data and color code data are each supplied to a color data selector 50, and when the partial color conversion mode is selected, the image area is recorded in a specific color.

This partial color conversion mode refers to a mode in which an area surrounded by or filled out with a marker (color marker) on a black and white document is recorded in the color of the color marker.

For example, as shown in FIG. 10, in this mode, an area a surrounded by a blue color marker is recorded in blue.

To do this, it is necessary to detect the color marker and extract its area.

For this reason, a region extraction circuit 60 is provided to detect the color marker region on the document and supply the region signal to the data selector 50.

The region extraction circuit 60 outputs region signals QR and QB corresponding to the color marker region, as shown in FIG. 11, for example.

In addition to these signals, the data selector 50 also includes a scan code signal BBR indicating which color is currently being copied.
and partial color conversion signal CC are supplied, respectively.

This is a multi-color copying machine that can record multiple specific colors.One color is developed for each rotation of the photoreceptor drum, and after all colors have been developed, a transfer separation process is performed. In the case of a type that records a color image by doing this, the scan code signal indicates which color is currently being developed.

Therefore, when a blue color marker is detected, the corresponding color data can be output at the end of the blue copy sequence and when the area signal is obtained.
Images within the blue color marker can be recorded in blue.

When not performing partial color conversion processing, density data is output only when the color code data matches the scan code signal. That is, during the red copy sequence, while the red color code is being obtained, the corresponding density data is selectively output.

The image data output from the color data selector 50 (
The density data) is subjected to enlargement/reduction processing in a scaling circuit 70.

Enlargement/reduction processing is performed by interpolating the density data in the main scanning direction, and by controlling the scanning speed in the sub-scanning direction (rotation direction of the photosensitive drum).

If the scanning speed is increased, the sampling data in the sub-scanning direction will be thinned out, resulting in a reduction process; on the other hand, if the scanning speed is made slower, the process will be an enlargement process.

In this example, the color code data is also enlarged/reduced at the same time.

The density data subjected to the enlargement/reduction processing is sent to the multi-value conversion circuit 80.
, multi-value processing is performed. For example, by using four threshold values, 6-bit density data is quinarized.

Threshold data is set manually or automatically.

A histogram creation circuit 100 is provided to automatically determine threshold data.

In the histogram creation step 'I@100, a density histogram as shown in FIG. 12 is created from certain captured image data, and optimal threshold data for the image is calculated based on the created density histogram.

A density pistogram may be created for each color, and multi-value processing may be performed for each color using threshold data calculated based on the density pistogram.

The 3-bit multi-value data that has been subjected to multi-value processing is supplied to the driver 140 via the interface circuit 130.

The driver 140 modulates the laser beam in accordance with the multilevel data. In this example, PWM modulation is performed.

The driver 140 may be built into the multi-value conversion circuit 80.

Output device 150 by a PWM modulated laser beam
A photoreceptor drum installed in the photoreceptor drum is used for development.

As the output device 150, a rape recording device or the like can be used.

As the developing device, an electrophotographic color copying machine is used. In this example, two-component non-contact jumping development and reversal development are employed.

That is, the transfer drum used in conventional color image formation is not used. In order to downsize the device, three-color images of blue, red, and black are developed on an OPC photoreceptor (drum) for image formation in three rotations of the drum, and transferred once after development to print on plain paper. I try to transfer it to recording paper such as.

The various image processing commands and image processing timings described above are all controlled by the CPU 160.

170 is a processing timing signal generation circuit for obtaining various processing timings, which includes a clock CLK, horizontal and vertical synchronization signals HV in the main scanning direction and sub-scanning direction obtained from the output device 150 side, V
An index signal IDX indicating the start of laser beam scanning is supplied to the V-coat.

Reference numeral 180 denotes a timing signal generation circuit for changing the zooming timing.

[Problems to be Solved by the Invention] By the way, in the above-described configuration, when various types of image processing are selected, especially when selecting the partial color conversion mode, the following inconvenient problems arise.

That is, in the partial color conversion mode, especially when a specific area (indicated by a dashed line) is filled in with a color marker as shown in FIG. A problem occurs.

This is based on the following reasons.

For example, when there are red or blue color markers around a black character, and the edge of the black character is recognized as a red or blue color marker, this overlapped part may be recognized as a red or blue color marker. Since it is recognized as a color marker, the actual image area is narrowed accordingly.

This is because the color marker is for area detection and the color marker portion is not recorded.

As a result, the edges of the image become blurred or thin.

Therefore, color conversion processing will not be performed correctly on the image information inside or outside the partial color conversion spot color marker9.

Therefore, the present invention proposes a color image processing device that solves these problems with a simple structure and that allows color conversion processing to be performed correctly even during specific image processing. .

[Technical means for solving the problem] In order to solve the above-mentioned problems, the present invention provides a color image processing system that performs image processing on color image information converted into an electrical signal. The image processing device is provided with a color discrimination means for color image information and other image processing means such as a color ghost correction means, and the processing content of color discrimination is changed according to the processing content of the other image processing means. It is special that this has been done.

Another feature of the image processing means is that when the partial color conversion process is fully selected, the content of the color discrimination process is changed.

[Function] In this configuration, when specific image processing is selected,
That is, when the partial color conversion mode is selected, the content of color discrimination processing is changed.

In other words, a plurality of different color discrimination maps are prepared, and in partial color conversion mode, a map with an enlarged black area is selected.

As a result, even if the edge portion is recognized as a color marker, the edge portion of the image will not become blurred or thin.

[Embodiment] Next, an example of the present invention applied to the above-mentioned color image processing apparatus will be described in detail with reference to FIG. 1 and subsequent figures.

In this invention as well, the color image processing apparatus 1 as shown in FIG. 4 is used, so the same parts are given the same reference numerals and the explanation thereof will be omitted.

FIG. 1 is a system diagram showing an example of a color image processing apparatus 1 according to the present invention, in which the processing contents of the color discrimination means 20 are changed based on instructions from the CPU 160.

Therefore, the color discrimination means 20 is provided with a plurality of color discrimination tables, which are selected according to the processing mode.

Specifically, in addition to the color discrimination map shown in FIG.
A color discrimination map as shown in the figure is ready.

The color discrimination map shown in FIG. 2 differs from that shown in FIG. 5 in that the black detection area has been enlarged.

Therefore, except in a specific image processing mode, the normal color discrimination map shown in FIG. 5 is selected, and color discrimination is performed based on this table.

On the other hand, in a specific image processing mode, ie, partial color conversion mode, the color discrimination map shown in FIG. 2 is selected.

At this time, the black detection area is enlarged compared to the map normally used, so even if a part of the outline of the image is determined as a color marker, the result is that it almost corresponds to the original image. The detected amount la will be removed as a contour part.

When a map such as the one shown in FIG. 3 is used as a color discrimination map, the black detection area will be roughly expanded. At the same time, in this case, it becomes possible to copy red and black or blue and black.

In the embodiment, the color ghost correction circuit 30 is also controlled at the same time as changing the processing content of the color discrimination means 20.

As shown in Figure 6, even if a color appears due to a color ghost, if it matches the color of the color marker, the ghost part will be corrected and removed, causing the edges of the image to become even fainter or thinner. This is because there is a possibility that it will be repeated.

Therefore, when the partial color conversion mode is selected on the operation unit, color ghost correction processing in the main scanning direction and the sub-scanning direction is prohibited based on a command from the CPU 160.

Since the data subject to color ghost correction is only color code data, the color code after color discrimination is supplied to the color data selector 50 as is. Of course,
The density data can also be corrected as is! Supplied to I40.

In an image processing mode other than partial color conversion, a normal processing mode, that is, color ghost correction processing is executed.

[Effects of the Invention] As explained above, according to the configuration of the present invention, when a specific image processing mode, that is, a partial color conversion mode is selected, the processing content of color discrimination is changed. The characters in the marker become blurred or thin.
This has the practical benefit of effectively preventing image quality from deteriorating.

Therefore, the present invention is extremely suitable for application to the above-mentioned color image processing apparatus.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an example of a color image processing device according to the present invention, FIGS. 2 and 3 are diagrams showing other examples of color discrimination maps, and FIG. 4 is used to explain the invention. A system diagram of the color image processing device, FIG. 5 is a color discrimination map diagram, FIGS. 6 and 7 are illustrations of color ghosts, FIGS. 8 and 9 are illustrations of resolution correction, and FIGS. FIG. 11 is an explanatory diagram of partial color conversion, FIG. 12 is a diagram of a density histogram, and FIG. 13 is an explanatory diagram of partial color conversion processing. 1... Color image processing device 20... Color discrimination circuit 30... Color ghost correction circuit 40... Resolution correction circuit 50... Color data selector 6o... Area extraction circuit 70... Magnification change Circuit 80...Multi-value conversion circuit 100...Histogram creation circuit 150...Output device 160...CPU

Claims (2)

[Claims] (1) A color image processing device that performs image processing on color image information converted into an electrical signal, which includes color discrimination means for the color image information and other components such as color ghost correction means. 2. A color image processing apparatus, comprising: an image processing means, wherein the processing content of the color discrimination is changed according to the processing content of the other image processing means. (2) The color image processing apparatus according to claim 1, wherein when partial color conversion processing is selected as the other image processing means, the content of color discrimination processing is changed.