JPH01194666A - Variable power circuit for color picture processor - Google Patents

Abstract

PURPOSE:To enhance the reproducibility of a color picture by applying variable power processing to color code data as well together with concentration data. CONSTITUTION:A color code, which is color-ghost corrected, in addition to the concentration data are supplied to a variable power circuit 70, and the variably multiplied concentration data and the color code are respectively supplied to a multilevel circuit 80. Thus, by interpolating the color code data according to a variable power rate, the color in a boundary part is also correctly expansion/reduction-processed. Consequently, when a threshold is determined at every color, since the multilevel operation is attained by the color code corresponding to the concentration data after the variably multiplying processing, the variably multiplying processing is attained by the optimum threshold.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a variable magnification circuit suitable for application to an image processing apparatus such as a color copying machine that records on plain paper.

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

Such color copying machines are capable of performing various image processing such as scaling processing and partial color conversion processing.

An example of a color image processing apparatus that records images by performing various types of image processing is shown in FIG. 5 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 cutoff of the dichroic mirror 4 can be approximately 540 to 600 nm.

The color separated images of red R and cyan cy are supplied to an image reading means, for example, a CCD 6.7, and an image K (number g) of only the red component R and cyan component cy is output from each image reading means, for example, a CCD 6.7.

The images No. 43 R and Cy are supplied to the A/D converter 10.11 and converted into a digital signal having a predetermined number of pits, in this example 6 pits. Shading correction is performed simultaneously with A/D conversion. 12 and 13 indicate shading correction circuits.

The digital image signal subjected to the shading correction is extracted by the effective area extraction circuit 15 for only the signal corresponding to the maximum original size, and is supplied to the color discrimination circuit 20 at the next stage. When the maximum document width to be handled is 84 size, size i2+'fB4 generated by the timing signal generating means 170 of the system is used as the gate signal.

Here, if the shading-corrected digital image signals are VR and VC, respectively, these image body 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, blue, and black.

That is, no matter what color the original is, each pixel is assigned to one of red, blue, or black. When this process is performed, each part of the document can be 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).
It consists of

The data for each color signal is stored in a color discrimination conversion table (map) in a ROM, for example.

FIG. 6 shows an example of this color discrimination map.

The color-discriminated image data is transferred to a color image processing step.

First, the light is supplied to the next stage color ghost correction port 1130, and color ghosts in the main scanning direction (horizontal scanning direction) and the sub-scanning direction (drum rotation direction) are corrected.

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

FIG. 7 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. 8A to 8C, red and blue 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 and the resolution (MTF)
is 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. 9 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 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, use a convolution filter that uses 3x3 pixel image data as the resolution correction circuit. Can be done.

FIG. 10 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 is a mode in which an area surrounded by 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. 11, 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, an area extraction circuit 60 is provided to detect the color marker area on the document and supply the area 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. 12, 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 command 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 during 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, sampling data in the sub-scanning direction is thinned out, resulting in a reduction process; on the other hand, if the scanning speed is made slower, an enlargement process is performed.

The density data subjected to the enlargement/reduction processing is sent to the multi-value conversion circuit 80.
At , multivalue processing is performed. For example, by using four threshold values, 6-bit density data can be converted into 5 values.

Threshold data is set manually or automatically.

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

The histogram creation circuit 100 creates a density histogram as shown in FIG. 13 from certain captured image data, and calculates optimal threshold data for the image based on the created density histogram.

Create a density histogram for each color, calculate threshold data for each color from the density histogram obtained from each color,
Multi-value processing may be performed using different threshold data for each color.

The 3-pit configuration multi-value data subjected to multi-value processing is supplied to the driver 140 via the interface circuit 130.

The driver 140 can modulate 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 laser 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.

In other words, the transfer drum used in conventional color image formation cannot be used. In order to downsize the device, three types of blue, red and black are placed on the OPC photoreceptor (drum) for image formation.
The color image is developed by rotating the drum three times, and transfer is performed once after development to transfer it to recording paper such as plain paper.

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.

180 is a timing signal generation circuit for obtaining scaling timing.

[Problems to be Solved by the Invention] In the above-described configuration, when an input color image is enlarged or reduced based on external specifications, the data to be scaled is color-discriminated as described above. The color code is not subject to scaling processing.

Therefore, there is a drawback that an optimal color threshold cannot be selected, especially when adjacent images have different colors.

This is because the color code corresponds to the original image data before being scaled.

Therefore, this invention solves these problems with a simple structure, and by subjecting the color code to the processing of scaling, it is possible to select the optimal color threshold even when changing the scaling. This paper proposes a variable magnification circuit that can improve image quality.

[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 and a scaling means for color image information, and the color discrimination means separates the color image information into its density data and a color code indicating its color. This invention is characterized in that each of the color code and density data can be scaled by a scaling means.

[Function] In this configuration, when the scaling process is specified, not only the density data but also the color code can be scaled.

The scaling process is performed by data interpolation in the main scanning direction, and by changing the scanning speed in the sub-scanning direction.

Therefore, each of the density data and color code data is
Data addition and thinning are performed in accordance with the scaling process.

By doing this, the relationship between the density data after scaling and the color code data is 1:1, and the optimum color threshold value is selected.

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

FIG. 1 shows a specific example of a color image processing apparatus 1 to which a variable magnification circuit according to the present invention is applied, and the same parts as in FIG. 5 are given the same reference numerals, and the explanation thereof will be omitted.

In this invention, the color code that has undergone color ghost correction is supplied to the variable magnification circuit 70 together with the density data,
The scaled density data and color code are each supplied to a multi-value conversion circuit 80.

By doing this, the density data is subjected to multi-value processing based on the scaled color code.

FIG. 2 is a system diagram showing an example of a variable magnification circuit 70 according to the present invention, which includes an interpolation ROM 73 in which interpolation data for density data is stored, and a conversion ROM 75 in which color code data for interpolation is stored.

Since data interpolation is performed based on the data of adjacent pixels, a pair of cascade-connected latch circuits 71 and 72 are provided, and density data and color code data are supplied to the first stage latch circuit 71. Ru.

The respective latch outputs are then supplied to the interpolation ROM 73 as address data. Rough interpolation selection data is supplied to the interpolation ROM 73 from a terminal 74 as its address data.

The interpolation selection data is control data related to the magnification ratio in order to obtain an enlarged/reduced image that is faithful to the original image by interpolating what data at the time of scaling.

Latch output and interpolation selection data are roughly converted into ROM 7
5 is also supplied. It is assumed that the following color code data after scaling is obtained from the conversion ROM 75.

For example, as shown in FIG. 3, when the red, blue, and black fir stripes are enlarged twice, the sampling position at that time becomes the position marked with an "x" in the figure.

At that time, the color code data closer to the sampling position (indicated by the original color in the figure) is interpolated. Therefore, the color code data after conversion becomes data (color) as shown in the figure.

When it is reduced, it becomes as shown in Fig. 4.

If the color code data is also interpolated according to the scaling factor in this way, the colors at the border can also be accurately enlarged or reduced. Therefore, when determining a threshold value for each color, multi-value processing can be performed using the color code data corresponding to the density data after scaling, so that multi-value processing can be performed using the optimal threshold value.

Note that, as an example of multi-value conversion, this example illustrates a case of five-value conversion, but the number of multi-value conversion is not limited.

[Effects of the Invention] As explained above, according to the configuration of the present invention, the color code data is also subjected to the scaling process along with the density data, so that the relationship between the density data and the color code data after the scaling process is changed. The relationship is 1:1.

As a result, even if the scaling factor changes, the optimal color threshold can be selected. Therefore, it has a feature that the reproducibility of color images is good.

Therefore, the variable magnification circuit according to the present invention is extremely suitable for application to the variable magnification circuit of the color image output device as described above.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of a color image processing device according to the present invention;
Fig. 2 is a system diagram showing an example of a variable magnification circuit used for this, Fig. 3 and Fig. 4 are diagrams showing the relationship between variable magnification processing and color code data, and Fig. 5 is a diagram for explaining the present invention. A system diagram of the color image processing device provided, Figure 6 is a diagram of the color discrimination map,
Figures 7 and 8 are illustrations of color ghosts, Figures 9 and 1°0 are illustrations of resolution correction, and Figures 11 and 1 are illustrations of resolution correction.
FIG. 2 is an explanatory diagram of partial color conversion, and FIG. 13 is a diagram of a density histogram. 1... Color image processing device 20... Color discrimination circuit 30... Color ghost correction circuit 40... Resolution correction circuit 50... Color data selector 60... Area extraction circuit 70... Magnification change Circuit 73... Density data interpolation ROM 75, φ, color code conversion ROM 80... Multi-value conversion circuit 100... Pistogram creation circuit 130... Interface circuit 140... Driver 150... Output Device 160 ・ ・ ・ CPU

Claims (1)

[Claims] (1) A color image processing device configured to image-process color image information based on color image information converted into an electrical signal, further comprising a color discrimination means and a variable magnification means for the color image information, In the color discrimination means, the color image information is separated into density data thereof and a color code indicating the color, and each of the separated color code and density data is scaled by the scaling means. A variable magnification circuit for a color image processing device, characterized in that: