JPH0227370A - Color picture processor - Google Patents

Abstract

PURPOSE:To avoid the deterioration of a picture by changing the data contents for correcting a color ghost at the time of a partial color conversion mode. CONSTITUTION:In a ghost eliminating ROM 340 in the vertical direction, data for correcting a color ghost which is used at the time of a regular recording mode and data which is used at the time of a partial color conversion mode are prepared so that they can be selected and used in accordance with an operation mode. According to such a constitution, when the partial color conversion mode is selected, an objective picture element is not changed at the time of a specific color pattern, therefore, it does not occur that the contour of the picture is blurred, thinned or disappears.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention is a color image processing device suitable for application to image processing means such as a plain paper recording color copying machine, and particularly a color image processing device having a partial color conversion function. The present invention relates to a color image processing device in which the content of color ghost correction processing is changed during area designation processing.

[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 various image processing such as scaling processing and partial color conversion processing.

Partial color conversion processing refers to image editing processing that allows image information inside or outside a designated area to be recorded in the color used for specifying the area, for example.

Areas are usually specified using color markers. For example, as shown in FIG.
If specified, the image included in this area a will be recorded in the same color as used for area specification, in this example blue (
Figure B).

Images in other areas may be erased or recorded as normal black and white images.

In order to achieve such partial color conversion processing, it is necessary to detect each color for specifying an area, such as a color marker, and the area. To do this, for example, as shown in FIG. 11, marker signals BP and RP are detected from color markers formed across each scanning line (n, n+1, etc.), and from these, an area signal QB= , QR= is formed.

These marker signals BP, RP and area signal QB=.

Based on the QR'', the image of the designated area is extracted and recorded, and the recording process as shown in No. 10l8 is achieved.

Incidentally, among the color image processing apparatuses having such a partial color conversion processing function, some have a color ghost correction function.

Color ghosts are unnecessary color signals that occur when an image (No. 8) is differentiated into multiple color signals.

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

FIG. 12 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. 13A to 13C, 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.

The appearance of color ghosts differs for other color combinations.

In order to reduce such color ghosts and improve recorded image quality, color ghost correction means is often provided.

[Problems to be Solved by the Invention] By the way, when color ghosts are corrected using such a color ghost correction means, the image information of the document may be mistakenly judged as a color ghost when the partial color conversion mode is selected. Sometimes it happens.

In particular, when a color marker is used to fill in a specific area and record only that area, as shown in FIG. 14, the outlines 31 and 32 of the image within the color marker become blurred.

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. is not recognized as an image necessary for recording.

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.

In particular, color ghost correction has the function of correcting the red and blue color ghosts that appear around black characters, as mentioned above, so the surroundings of black characters are converted to white, etc., and color conversion processing is not performed correctly. It turns out.

Therefore, the present invention proposes a color image processing device that solves these problems with a simple structure and avoids image deterioration by changing the color ghost correction content during specific image processing. It is something to do.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a color image processing device that performs image processing on color image information converted into an electrical signal. The image processing apparatus includes a color discrimination means for color image information, a color ghost correction means, and an image processing means for performing image processing on a specified area using color information different from the original color to be read. The present invention is characterized in that when executed, the correction contents of the color ghost correction means are changed.

[Function 1] The color ghost correction means 300 stores color ghost correction data used in the normal recording mode. In addition, when the partial color conversion mode is selected, data used for color ghost correction, partially changed data, is stored.

Therefore, in the normal recording mode, correction processing using normal color ghost correction data is performed.

When the partial color conversion mode is selected and the pattern is as shown in FIG. 13, data that is not subject to color ghost correction processing can be referenced as shown in FIG.

In this way, if the data for color ghost correction to be used is selected according to the operation mode, no correction processing is performed, so the outline of the image will not become blurred or thin. Therefore, even if a thin line such as a ruled line is filled in with a color marker, the ruled line will be reproduced as is.

[Example] Next, an example of a color image processing device according to the present invention will be described.
A case in which the present invention is applied to the color image processing apparatus of the color copying machine described above will be described in detail with reference to FIG. 1 and subsequent figures.

FIG. 1 shows an example of a color image processing device 1 according to the present invention, in which color image information (optical image) of a subject 2 such as a document is transmitted to a dichroic mirror 4 through an optical system 3.
It is separated into two color separation images.

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 wavelength 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, C0D6.7, and image signals of only the red component R and cyan component Cy can be output from each image reading means.

The image signal R, ay is supplied to an A/D converter 10.11 and is converted into a digital number 48 having a predetermined number of bits, in this example 6 bits. Shading correction is performed simultaneously with A/D conversion. Reference numerals 12 and 13 indicate shading correction circuits.

The shading-corrected digital image signal is extracted in an effective area extraction path 15 for only a signal corresponding to the maximum document 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 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.

The VC is supplied to the 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, and 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-pit data) indicating its color information and its density data (6-pit 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. 2 shows an example of this color discrimination map.

It is also possible to prepare a plurality of color discrimination conversion tables and select one of them depending on the recording mode, for example. In this case, table selection processing is executed based on instructions from a microcomputer, which will be described later.

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

First, it is supplied to the next-stage color ghost correction means 300, and color ghosts in the main scanning direction (horizontal scanning direction) and the sub-scanning direction (drum rotation direction) are corrected.

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

The color ghost correction means 300 is a circuit for correcting such color ghosts as much as possible. Note that color ghost processing applies only to color code data.

In this invention, the color ghost correction means 300 includes color ghost correction data used in the partial color conversion mode as well as color ghost correction data used in the normal recording mode. It is stored in a table.

The details will be described later.

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.
, the concentration data and evening data are processed and the resolution (MTF
) is corrected.

Factors contributing to resolution deterioration include problems with the optical system, optical travel system, signal processing system, recording system, etc. Of these, the optical system and its travel system do not directly affect resolution deterioration.

FIG. 3 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 obtained by scanning a black and white pattern with a spatial frequency up to ots/am.

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, a convolution filter that uses 3 x 3 pixel image data is used as the resolution correction circuit. can do.

FIG. 4 shows the correction results when a convolution filter is used.

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.

When performing image processing such as this partial color conversion mode, it is necessary to detect color markers written on the document and extract the area.

For this reason, a region extraction circuit 60 is provided to detect the color marker region on the document, and the region signals QR-, QB' (see FIG. 11) obtained from this are supplied to the data selector 50. Ru.

In addition to these numbers 48, the data selector 50 is supplied with a scan code signal indicating which color is currently being copied and a partial color conversion signal CC.

It is a multi-color copying machine that can record multiple specific colors, and it develops one color per rotation of the photoreceptor drum, and after all colors are developed,
In a type of printer that records a color image by performing transfer separation processing, 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.
The image within the helmet 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.

In this example, the color code data is also subjected to enlarging/reducing processing at the same time, and is then supplied to the multi-value conversion circuit 80.

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 pistogram creation circuit 100 is provided to automatically determine threshold data.

The histogram creation circuit 100 creates a density histogram as shown in FIG. 5 from certain captured image data, and calculates optimal threshold data for the image based on the created density histogram.

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

The 3-bit 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 latent image is formed on the photoreceptor drum provided on the photoreceptor drum.

As the output device 150, an electrophotographic color copying machine using a laser beam 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 60.

170 is a processing timing signal generation circuit for obtaining various processing timings, which includes a clock CLK.
horizontal and vertical synchronization No. 48 HV in the main scanning direction and sub-scanning direction obtained from the output device 150 side.
, VV and VV are supplied with an index signal IDX indicating the start of laser beam scanning, and based on these signals, a timing signal for starting reading for the CCD 6.7 is formed.

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

In the present invention, once a partial color conversion mode has been selected, a dedicated color ghost correction data table stored in the color ghost correction means 300 described above is referred to.

That is, in addition to the color ghost correction data used in the normal recording mode, the color ghost correction means 300 has built-in correction data used in the partial color conversion mode, and these data are stored in accordance with commands from the microcomputer 160. will be controlled based on.

Next, the contents will be explained in detail. First, color ghost correction will be explained.

In this example, color ghost correction is performed using a color pattern method. This is because the color ghost color that appears is determined for the original color, such as original black → red, blue ghost, original red, blue → black ghost. Therefore, according to this color pattern method, the color of the original image can be identified by examining the color appearance (pattern) of the pixel of interest and its surrounding pixels to determine the color of the pixel of interest.

As an example, FIG. 6 shows the relationship between the pixel of interest, the surrounding color pattern, and the color of the pixel of interest that can be determined at that time.

In the first example, since both sides of the pixel of interest are white and black, the blue color of the pixel of interest is determined to be a color ghost appearing at the black edge. Red in the third example is also determined to be a color ghost of black. Therefore, in both the first and third examples, the pixel of interest is changed to black.

On the other hand, in the second and fourth examples, it is not determined that a color ghost has appeared, and the color of the pixel of interest is output as is.

This type of processing is difficult to implement with an arithmetic circuit, so in this example, it is implemented in ROM and LUT (lookup table).
It is used in the format. As a color pattern, one-dimensional and two-dimensional systems are possible, but if the number of colors is N1 and the number of surrounding pixels including the pixel of interest is M, the size of the color pattern is NM.

Therefore, if a two-dimensional pattern is used, the number of M will suddenly increase, making it impractical. In other words, although a two-dimensional pattern cannot have a large number of peripheral pixels in each dimension (main scanning direction/sub scanning direction), the number of patterns increases. FIG. 7 shows the relationship between size and number of color patterns.

In this example, the size is 1×7 in one dimension (that is, N
=4. M=7) color pattern is used, and color ghost removal is performed independently in the main scanning direction and the sub-scanning direction. At this time, since there is no difference in the appearance of color ghosts in the image between the main scanning direction and the sub-scanning direction, the same color pattern is used in the main scanning direction and the sub-scanning direction in this example.

As the color pattern size, we selected a size of 1 x 7, but if the degree of color ghost appearance is small, I
It is also possible to use smaller sized color patterns such as X5. Color ghosts of up to 1 pixel can be removed in a 1×5 color pattern, and up to 2 pixels in a 1×7 color pattern.

When using a color pattern of IX7 size, the color code is input as a ROM address.

For example, in the color pattern below, the color code pattern is white: white: blue: blue: black: black: black 1111]:01:01':○O:00:00, and the address is, and this address is , a black code O is stored as shown in FIG. The LUT is executed using the above method.

In reality, a 1x7 pattern requires 14-bit address lines, and a bipolar ROM with 14-bit address input and 2-bit color code output is sufficient, but such a large-capacity, high-speed R , OM are not widely available on the market and are expensive. Further, the output of the ROM is generally 8 bits.

Therefore, in the embodiment, the output data of the ROM is selected based on the color code of the first pixel, and the LUT is performed using the color codes of the remaining six pixels. That is, the output data Do, Dl of the ROM are selected when the first pixel is black, and the output data D2. D3 is blue, D4. D5 is red, D6. D7 is selected next to white.

Therefore, for example, in the color pattern shown in FIG. 6, the beginning is white, so in this case, among the output bits of the ROM,
Bit D6. Both D7 will be selected.

However, even if the first pixel is the same white, the selected output bit D6. The color codes of the pixel of interest obtained in D7 are different as shown in FIG. This means that the ROM reference address is a combination of input pixels (a combination of color code data)
This is because it differs depending on the

When using a low-speed, large-capacity EPROM, it is also possible to transfer data to a plurality of SRAMs or the like before operation and perform color ghost correction using these SRAMs.

On the other hand, the color pattern obtained when the color markers are filled in as shown in FIG. 14 may appear as shown in FIG. 8.

In other words, when a color marker is placed on a thin black line such as a ruled line, if this thin black line is the pixel of interest, the appearance of surrounding pixels for the pixel of interest (pixels 1 to 2) is
It will look like the figure. In the figure, the color patterns numbered 1 to 6 are when a red color marker is used.
The color patterns numbered 7 to 11 are when a blue color marker is used.

If color ghost processing is performed in this manner as in the normal case, black pixels will be converted to red pixels, or black pixels will be converted to helmet pixels.

Therefore, ruled lines etc. are not reproduced.

Even if the image is somewhat thick, its outline becomes thinner.

Therefore, in the present invention, in the partial color conversion mode, when such a specific color pattern exists, no correction is made even if there are black pixels. In other words, even if the color pattern is the same, dedicated conversion tables are prepared for each pixel so that pixels are corrected in the normal printing mode and not corrected in the partial color conversion mode.

Which conversion table is used depends on whether the partial color conversion mode is selected. Which table to use is selected by a signal supplied to the 13th bit of ROM 302.

FIG. 9 shows a specific example of a color ghost correction means 300 that accomplishes such processing. Color ghost processing is performed in the main scanning direction (horizontal scanning direction) and the sub-scanning direction (vertical scanning direction, direction of rotation of the drum).

In this example, horizontal and vertical ghosts are removed using image data for 7 pixels in the horizontal direction and 7 lines in the vertical direction.

Color ghost processing applies only to color codes of image data.

Therefore, the color code read from the color discrimination circuit 20 is first supplied to the ghost correction circuit 300A in the output scanning direction.

The color code data is sequentially supplied to a 7-bit shift register (SR) 301 and parallelized. This parallel color code data (2×7 bits) for 7 pixels is supplied to a horizontal ghost removal ROM 302, and ghost removal processing is performed for each pixel.

Here, the input bits of the ROM 302 are a maximum of 13 bits,
Since up to eight output bits are used, the first two bits are used as selection bits as described above. Therefore, a selector 303 is provided after the ROM 302, and the first bit is completely supplied to the selector 303, and the remaining bits (12 bits) are supplied to the ROM 302.
supplied to

As described above, the R, OM 302 stores color pattern data for color ghost correction and color pattern data used in the partial color conversion mode, respectively, in the form of tables.

When the ghost processing is completed, the data is latched by the latch circuit 304.

On the other hand, the density data output from the color discrimination circuit 20 is transferred to a shift register (SR) 305 for timing adjustment.
Data transfer conditions are determined such that the density data is serially transferred following the color code data.

The serially processed color code data and density data are supplied to a line memory unit 310 provided in the color ghost correction circuit 300B.

The line memory unit 310 is provided to remove vertical color ghosts using seven lines of image data. Note that the line memory is used for a total of 8 lines, but this is a means of real-time processing, and of course? Real-time processing is possible even for lines.

The color code data and density data for eight lines can be separated in the subsequent gate circuit group 320. In the gate circuit group 320, gate circuits 321-328 are provided corresponding to the line memories 311-318, respectively.

The output data of the 8 line memories synchronized in the line memory section 310 is separated into color code data and density data in the gate circuit group 320, and the separated color code data is supplied to the selection circuit 330 for a total of 8 pieces of data. Among the line memories, color code data of seven line memories necessary for color ghost processing is selected. In this case, when line memories 311 to 317 are selected, line memory 3 is selected at the next processing timing.
As 12 to 318 are selected, the selected line memory is sequentially shifted.

The selected and synchronized 7-line memory worth of color code data is sent to the next vertical ghost removal ROM.
340 to remove vertical color ghosts.

The vertical direction is also processed in the same way as the horizontal direction, and the input 13
In addition to the 8-bit ROM 340, a data selector 341 is provided, and the first 2 bits are used as a data selection signal.

As mentioned above, the ROM 340 contains tables of data for color ghost correction used in the normal recording mode and data used in the partial color conversion mode, and which table is used. Whether to do so is RO
It is selected by the signal supplied to the 13th bit of M340. For this signal, a command signal output from the microcomputer 160 in relation to the operation mode is used.

Thereafter, it is latched by the latch circuit 342.

On the other hand, the density data separated by the gate circuit group 320 is directly supplied to the latch circuit 343, and is output after being timing-adjusted with the color code data.

[Effects of the Invention] As described above, according to the present invention, the data content for color ghost correction is changed in the partial color conversion mode.

In other words, in addition to data for color ghost correction used in normal recording mode, data for color ghost correction used in partial color conversion mode is prepared.
These are selectively used depending on the operation mode.

This way, when partial color conversion mode is selected,
Since the pixel of interest is not changed in the case of a specific color pattern, the outline of the image will not become blurred, thinned, or disappear.

Moreover, since color ghost correction processing is executed even in such partial color conversion mode, the recorded image quality is improved.

Therefore, the present invention is extremely suitable for application to a color image processing apparatus such as the above-mentioned color copying machine.

[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, FIG. 2 is a color discrimination map, FIGS. 3 and 4 are characteristic diagrams showing MTF correction, and FIG. 5 is a density diagram. A histogram diagram, Figure 6 is a diagram used to explain color ghosts,
FIG. 7 is a diagram showing the relationship between color patterns and pattern sizes, FIG. 8 is a diagram showing the relationship between operation modes and correction contents for a specific color pattern, FIG. 9 is a system diagram of color ghost correction means, and FIG. The figure is an explanatory diagram of partial color conversion processing, Figure 11 is a diagram showing the relationship between color markers, marker signals, and area signals, Figures 12 and 13 are diagrams explaining color ghosts, and Figure 14 is a diagram showing the relationship between color markers, marker signals, and area signals. It is a figure which shows the example of a specification.・Color image processing device ・Color discrimination circuit ・Resolution correction circuit ・Color data selector ・Region extraction circuit ・Scaling circuit ・Multi-value conversion circuit ・Histogram creation circuit ・Interface circuit ・Driver output device ・CPU 300 ・Color ghost correction means 302゜340 ・ ・Correction ROM

Claims (1)

[Claims] (1) In a color image processing device that performs image processing on color image information converted into an electrical signal, the color image information is read by a color discrimination means and a color ghost correction means. An image processing means is provided which performs image processing of a specified area using color information different from the original color to be used, and when image processing of the specified area is executed, correction contents of the color ghost correction means are changed. A color image processing device characterized by the following features: