JPH01194671A - Picture processor - Google Patents

Abstract

PURPOSE:To simplify the circuit constitution of a periphery by softly switching a threshold data source in accordance with mode selection. CONSTITUTION:In an operation part to call a threshold selecting mode, when an EE mode is released, it is shifted to a threshold selecting routine by a manual, a fixed threshold is selected, and the selected threshold data are set as the threshold for a multi-value circuit 80. When the EE mode is selected by the operating mode, the pre-scanning is executed for concentration histogram preparation and the concentration data of a processing area are collected. When the pre-scanning is completed, optimum threshold data are calculated for a color based on the collected concentration data, sent to the multi-value circuit 80 and based on this, the concentration data are multi-value-processed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an image processing apparatus that can be applied to a plain paper recording color copying machine and the like, and particularly to an image processing apparatus that can perform automatic or manual multi-value conversion.

[Background of the Invention] In an image processing device, such as a color copying machine using a laser beam, a latent image of a predetermined object is formed on a photoreceptor drum by modulating the laser beam based on final image information. However, in this case, it is necessary to create binary or multivalued image data for laser beam modulation.

Recently, beams have been modulated using multivalued image data in order to display halftones.

An example of a color image processing apparatus that records images by performing such multivalue processing is shown in FIG. 3 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 red R color separation image and a cyan cy color separation image. Therefore, the dichroic mirror 4 used has a cutoff of about 540 to 600 nm.

The red R and cyan Cy color separated images are supplied to image reading means, for example, CCDs 6 and 7, from which image signals of only the red component R and cyan component Cy can be output.

The image signals R and cy are supplied to an A/D converter 10.11, where they are converted into digital signals having a predetermined number of bits, in this example 6 bits. Shading correction can be done at the same time as A/D conversion. Reference numerals 12 and 13 indicate shading correction circuits.

The shading-corrected digital image No. 18 is passed through the effective area extraction circuit 15 to extract only the signal corresponding to the maximum original size width, and is supplied to the color discrimination circuit 20 at the next stage.

When the maximum document width to be handled is 84 size, the gate signal is generated by the timing signal generation circuit 170 of the system.
The size signal B4 generated in is used.

Here, if the shading-corrected digital image signals 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, blue, 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 and t data) indicating its color information and density data (6 and 6), respectively.
It consists of pit data).

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

FIG. 4 shows an example of this color discrimination map.

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

First, the signal is supplied to the next-stage color ghost correction circuit 30, 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. 5 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. 6A to 6C, 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 is applicable 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 after color ghost correction (color to 5 dot density data) is processed by the resolution correction circuit 4 at the subsequent stage.
0, the density data is processed to obtain its resolution (M
TF) 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. Among these, the ones that directly affect the deterioration of resolution are the optical reading system for the document and the traveling system for the optical reading system.

FIG. 7 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
This is the total value 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. 8 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. 9, in this mode, the area a surrounded by the helmet 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 6o 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. 10, 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 can be supplied.

This is a multi-color copying machine that can record multiple specific colors. One color is developed each time the photoreceptor drum rotates, and once all colors have been developed, one transfer is performed. In a type of printer that records a color image by performing separation processing, the scan code signal BBR 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 in partial color conversion processing, only when the color code data matches the scan code signal! The revenge data is output. That is, at the end of the red copy sequence, the corresponding density data is selectively output while the red color code is being obtained.

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

Enlarging/reducing processing interpolates the height data in the main scanning direction, and
This is done by controlling the scanning speed.

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.

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.

The threshold data can be set manually or automatically as described later.

The 3-bit multi-value data subjected to the multi-value processing is supplied to the driver 140 via the interface circuit m130.

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.

A photosensitive drum provided in the output device 150 is developed by the PWM modulated optical signal.

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.

That is, the transfer drum used in conventional color image formation is not used. In order to downsize the device, three OPC photoreceptors (drums) for image formation, blue, red, and black, are installed in L.
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.

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 can be supplied to the V-coat.

[Problems to be Solved by the Invention] By the way, in the above-described configuration, when density data is multivalued, when a threshold value for multivalued data is automatically set,
Both cases of manual setting are possible.

Therefore, as shown in FIG. 3, in addition to an automatic threshold determination circuit (EE circuit) 163 to which density data is supplied, a threshold value table (ROM configuration) 164 in which pre-calculated threshold values are tabulated is provided.

One of the respective threshold data is selected by the selection circuit 165. This selection is made by a mode select signal obtained when specified on the operating section side.

The density data is multivalued based on the selected threshold value data.

With this configuration, the selection circuit 165 is simultaneously supplied with threshold data from the threshold table 164 in addition to the threshold data from the EE circuit 163. The configuration is such that any of these threshold data is selected by the selection circuit 165.

Therefore, there is a drawback that the circuit configuration of the selection amount 'a L 65 becomes complicated.

When the selection circuit 165 is configured with a latch circuit and the threshold value for multi-leveling is determined for each color, the number of data increases accordingly, and the number of latch circuits also increases accordingly. .

For example, using threshold values for each of the three colors, quinarization (3
(bit), the density data consists of 6 bits, so the number of data is 3X3X6=54. Therefore, even if the latch circuit part is made common, the configuration of the selection part of the latch circuit is It becomes complicated.

Therefore, the present invention solves these problems and proposes an image processing apparatus that has a simple configuration and can perform switching processing.

[Technical means for solving the problem] In order to solve the above problems, the present invention provides an image processing device that performs image processing on image information converted into an electrical signal. The method includes a means for automatically calculating a threshold value for multilevel conversion from image information, and a means for outputting a threshold value specified from a threshold value table calculated in advance. It is characterized by the fact that one means can be selected.

[Operation] In this configuration, whether the threshold value is set automatically or manually is processed by software according to the mode selection from the outside.

When the EE mode is selected, an appropriate threshold value is calculated based on the density histogram from the histogram creation circuit 100 under the intervention of the CPU 160.

In contrast, when manual mode is selected, the CPU
160 is referenced and used as threshold data.

The threshold data used during manual operation is a fixed threshold calculated in advance, and the number of threshold data is divided into about seven levels.

[Example] Next, an example of the image processing apparatus according to the present invention, when 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, a color image processing apparatus 1 as shown in FIG. 3 is used, so a description of the same parts will be omitted.

In this invention, the creation and selection of threshold data for multi-value processing is performed by the CPU 1.60.

Therefore, a pistogram creation circuit 100 is provided, and the creation of a density histogram and the threshold value calculated for each color from the data of this density histogram are processed by the CPU 160.

Therefore, the data bus of the CPU 160 is also connected to the multi-value conversion circuit 80.

In this example, the pistogram creation circuit 100 performs optimal multi-value processing for each color, so a density histogram is also created for each color, and threshold data is calculated for each color. Therefore, color code data is also supplied to this histogram creation circuit 100 in addition to density data.

When creating a density histogram, a predetermined image area (
Density data is obtained by blisscanning a partial area of the entire image.

To bliscan a predetermined area, image data is sampled while being thinned out in the main scanning direction, and scanned at a faster scanning speed than normal in the sub-scanning direction.

Thereby, it is possible to collect density data necessary for creating a density histogram from a predetermined area without requiring any Briscan time.

Therefore, the histogram creation circuit 100 is supplied with a prescan signal PS, a signal HPS roughly indicating an area in the main scanning direction, and the like.

When manually selecting fixed threshold data, CP
A threshold data ROM provided in connection with U160 is used. This ROM is also used as a data storage RAM or a control program storage ROM attached to the CPU 160.

Note that 180 is the timing 48 used during scaling processing.
This is a timing signal generation circuit for generating signals.

Next, an example of automatic and manual selection of threshold data will be explained with reference to FIG.

When the threshold selection mode is called, the presence or absence of the EE mode is first checked (step 191).

When the EE mode is canceled in the operation unit, the process moves to a manual threshold selection routine 192, where the above-mentioned fixed threshold is selected, and the selected threshold data is set as the threshold for the multi-value circuit 80 ( step 193).

When the EE mode is selected on the operation unit, the state of the briscan is checked (step 194).

When in EE mode, to create a density histogram,
This is because it is necessary to perform blisscanning to collect density data of the processing area.

When the Briscan is completed, the process moves to a threshold processing step using EE (step 195), and optimal threshold data is calculated for each color based on the collected density data.

The calculated threshold value data is sent to the multi-value conversion circuit 80, and the density data is subjected to multi-value conversion processing based on this (step 193).

[Effects of the Invention] As described above, according to the configuration of the present invention, the threshold data source is switched by software in accordance with mode selection.

Therefore, compared to the case where a selection circuit is used to perform hardware switching, there is a practical benefit in that the peripheral circuit configuration can be simplified.

In general, even if the number of data handled related to threshold data increases, the circuit scale will not increase because it is controlled by the CPU.

Therefore, the present invention is extremely suitable for application to the color image output device as described above.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an example of an image processing device according to the present invention, FIG. 2 is a flowchart showing an example of a processing routine for selecting multiple threshold values, and FIG. 3 is a color image used to explain the invention. A system diagram of the processing device, Figure 4 is a diagram of a color discrimination map, Figures 5 and 6 are illustrations of color ghosts,
7 and 8 are explanatory diagrams of resolution correction, FIGS. 9 and 10 are explanatory diagrams of partial color conversion, and FIG. 11 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...Modification Multiplier circuit 80...Multi-level conversion circuit 100...Histogram creation circuit 130...Interface circuit 140...Driver 150...Output device 1 (30...CP tJ 170...Processing timing signal generation circuit patent applicant
Konica Co., Ltd. 1, -64 or ↑ Tsubuichiichi Figure 11 DL Input level 17 D) -1 Figure 5 Figure 6 A [3C

Claims (1)

[Claims] (1) In an image processing device configured to perform image processing on image information based on image information converted into an electrical signal, means for automatically calculating a threshold value for multi-value conversion from image information; and means for outputting a threshold specified from a calculated threshold table, the two means being selected based on the specified mode.