JP2557479B2 - Color image processor - Google Patents

Description

The present invention relates to a color image processing apparatus suitable for application to an image processing apparatus such as a color copying machine for plain paper recording, and particularly to a color image having a partial color conversion function. The present invention relates to a color image processing device in which the contents of a color ghost correction process are changed in a region designation process.

BACKGROUND OF THE INVENTION In a color image processing apparatus, for example, 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 the color image information. I am trying to do it.

In such a color copying machine, various image processing such as variable magnification processing and partial color conversion processing can be performed.

The partial color conversion process refers to an image editing process in which image information inside or outside a designated area can be recorded in, for example, a color used for area designation.

It is performed by the normal color marker that specifies the area. For example,
When the area a is designated by the blue marker as shown in FIG. 10A, the image included in the area a is recorded in the same color as that used for the area designation, that is, blue in this example (FIG. 10B).

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

In order to achieve such partial color conversion processing, it is necessary to detect each color for area designation such as a color marker and each of the areas. For that purpose, for example, as shown in FIG. 11, the marker signals BP and RP are detected from the color markers formed across each scanning line (n, n + 1, etc.), and the area signals QB ′ are detected from these. , QR ′ is formed.

Based on these marker signals BP, RP and the area signals QB ', QR', the image of the designated area is extracted and recorded, and the recording processing as shown in FIG. 10B is achieved. .

By the way, there is a color image processing apparatus having such a partial color conversion processing function, which has a color ghost correction function.

The color ghost is an unnecessary color signal generated when discriminating an image signal into a plurality of color signals.

That is, at the time of color discrimination, unnecessary color ghosts (color ghosts) are generated particularly around black characters.

 Figure 12 shows an example of the appearance of a color ghost.

This figure shows a color ghost appearing after color discrimination by capturing an image of a black character "sex".

As can be seen from this example, as shown in FIGS. 13A to 13C, the color ghost has red and blue at the edge of the black line, black at the edge of the blue line, and black at the edge of the blue line. Black appears at the edge.

The appearance of color ghosts is different in other color combinations.

In order to reduce such a color ghost and improve the recording image quality, a color ghost correction unit is usually provided.

[Problems to be Solved by the Invention] By the way, when a partial color conversion mode for correcting a color ghost by using such a color ghost correction means is selected, the image information of the document is erroneously determined to be a color ghost. It may end up.

In particular, as shown in FIG. 14 using a color marker, when a specific area is filled in and only that area is recorded, the contours 31 and 32 of the image in the color marker are blurred.

 It is based on the following reasons.

For example, when there are red or blue markers around a black character and it is recognized as an edge part of a black character or a red or blue color marker, this overlapping part is It is not recognized as an image required for recording.

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

Therefore, the edge portion of the image becomes faint or thin.

Especially, since the color ghost correction has a function of correcting the red or blue color ghost appearing around the black character as described above, the area around the black character is converted into
Color conversion processing will not be performed correctly.

In view of the above, the present invention proposes a color image processing apparatus which solves such a problem simply by changing the correction content of the color ghost at the time of specific image processing and avoids image deterioration. To do.

[Means for Solving the Problems] In order to solve the above-mentioned problems, in the present invention,
In a color image processing apparatus for image-processing this color image information based on the color image information converted into an electric signal, a color discriminating means for color image information, a color ghost correcting means, and a document color to be read. Is provided with image processing means for performing the specified partial color conversion processing according to different color information, and when the partial color conversion processing of the specified area is executed, the correction content of the color ghost correction means is changed. It is characterized by that.

[Operation] The color ghost correction means 300 stores data for color ghost correction used in the normal recording mode. In addition to this, when the partial color conversion mode is selected, data in which a part of the data used for color ghost correction is changed is stored.

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

When the partial color conversion mode is selected and the pattern is as shown in FIG. 13, the data which is not subjected to the color ghost correction processing is referred to as shown in FIG.

In this way, if the data for color ghost correction to be used is selected according to the operation mode, the correction processing is not performed, so that the contour of the image is not blurred or fine. Therefore, even if a fine line such as a ruled line is filled with a color marker, the ruled line is reproduced as it is.

[Example] Next, a case where an example of the color image processing apparatus according to the present invention is applied to the color image processing apparatus of the above-mentioned color copying machine will be described in detail with reference to FIG.

FIG. 1 shows an example of a color image processing apparatus 1 according to the present invention. Color image information (optical image) of a subject 2 such as a document is separated into two color separated images by a dichroic mirror 4 via an optical system 3. It

In this example, the color separation image of red R and the color separation image of cyan Cy are separated. Therefore, the cutoff wavelength of the dichroic mirror 4 is about 540 to 600 nm.

Each color separation image of red R and cyan Cy is supplied to image reading means, for example, CCDs 6 and 7, and an image signal of only red component R and cyan component Cy is output from each.

The image signals R and Cy are supplied to the A / D converters 10 and 11 to be converted into digital signals having a predetermined number of bits, in this example, 6 bits. Shading correction is performed at the same time as A / D conversion. Reference numerals 12 and 13 denote shading correction circuits.

The shading-corrected digital image signal is extracted by the effective area extraction circuit 15 for only the signal of the maximum document size width and supplied to the color discrimination circuit 20 in the next stage. When the maximum original width to be handled is the B4 size, the size signal B4 generated by the timing signal generating means 170 of the system is used as the gate signal.

Here, assuming that the shading-corrected digital image signals are VR and VC, these image signals VR and VC are supplied to the color discrimination circuit 20 and separated into a plurality of color signals.

In this example, a case is described in which the color signals are separated into three color signals of red, blue, and black.

That is, regardless of the color of the document, the color is assigned to one of red, blue, and black for each pixel. When this process is performed, each part of the document is recognized as a part of any color of red, blue, and black.

It should be noted that the use of red, blue, and black as other colors, and the use of four or more colors, are also included in the color discrimination processing.

Each of the color-separated color signals is composed of color code data (2-bit data) indicating the color information and density data (6-bit data). As the data of each color signal, for example, the one stored in the color discrimination conversion table (map) of ROM configuration is used.

 FIG. 2 shows an example of this color discrimination map.

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

The image data subjected to color discrimination is transferred to a color image processing step.

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

This is because, as described above, unnecessary color ghosts (color ghosts) are generated particularly in the vicinity of black characters during color discrimination.

A circuit for correcting such a color ghost as much as possible is the color ghost correction means 300.
The color ghost processing is only applicable to color code data.

According to the present invention, the color ghost correction means 300 includes color ghost correction data used in the normal recording mode and color ghost correction data used in the partial color conversion mode. It is stored as a table. The details will be described later.

As image processing, in addition to color ghost correction, there are resolution correction, partial color conversion processing, scaling processing, multi-valued processing, and the like.

First, the image data (color code data and density data) after color ghost correction is processed by the resolution correction circuit in the subsequent stage.
At 40, the density data is processed to resolution (MTF)
Is corrected.

As a factor of resolution deterioration, there are problems such as an optical system, an optical traveling system, a signal processing system, and a recording system. Of these, the optical system and its traveling system directly affect the deterioration of resolution.

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 2-16 dots /
This is a measurement value when scanning a black-and-white pattern having a spatial frequency of up to 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.

MTF degradation is more pronounced in the sub-scanning direction. To make the same correction, the correction amount in the sub-scanning direction with respect to the main scanning direction is set to 2
It may be set up to 4 times.

In order to correct the main scanning direction and the sub-scanning direction to the same degree and to prevent the reproduction of the fine line from deteriorating, a convolution filter using image data of 3 × 3 pixels is used as the resolution correcting circuit. be able to.

FIG. 4 shows the correction result when the convolution filter is used.

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

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

For this reason, an area extracting circuit 60 is provided to detect the area of the color marker on the document, and the area signals QR 'and QB' (see FIG. 11) obtained from the area are supplied to the data selector 50. You.

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

A multi-color copying machine capable of recording a plurality of specific colors as a color copying machine, wherein one color is developed for each rotation of the photosensitive drum, and after all the colors are developed, transfer separation is performed. In the type in which a color image is recorded by processing, a scan code signal indicates which color is currently being developed.

Therefore, when the blue color marker is detected, the image in the blue color marker is displayed by outputting the corresponding color data in the blue copy sequence and when the area signal is obtained. It can be recorded in blue.

When the partial color conversion process is not performed, the density data is output only when the color code data matches the scan code signal. That is, in the case of the red copy sequence, the corresponding density data is selectively output while the red color code is being obtained.

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

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

If the scanning speed is increased, the sampling data in the sub-scanning direction is thinned out, which results in reduction processing. Conversely, if the scanning speed is decreased, enlargement processing is performed.

In this example, the color code data is also enlarged / reduced at the same time, and then supplied to the multi-value quantization circuit 80.

The density data that has been subjected to the enlargement / reduction processing
In, multi-value processing is performed. For example, by using four threshold values, the 6-bit density data is binarized.

 The threshold data is set manually or automatically.

To automatically determine threshold data, a histogram creation circuit 100 is provided.

The histogram creating circuit 100 creates a density histogram as shown in FIG. 5 from a certain imaged image data, and based on the created density histogram, the optimum threshold value data for the image is calculated.

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

The multi-valued data having the 3-bit structure that has been multi-valued is supplied to the driver 140 via the in-interface circuit 130.

The driver 140 modulates the laser beam according to the multi-valued data. In this example, PWM modulation is performed.

The driver 140 may be incorporated in the multilevel circuit 80.

A latent image is formed on the photoconductor drum provided in the actual device 150 by the PWM-modulated laser beam.

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 adopted.

That is, the transfer drum used in the conventional color image formation is not used. To reduce the size of the device, a three-color image of blue, red, and black is developed on the OPC photoreceptor (drum) for image formation by three rotations of the drum, and transfer is performed once after development. And transfer it to recording paper.

All of the various image processing commands and image processing timings described above are controlled by the CPU 160.

Reference numeral 170 denotes a processing timing signal generating circuit for obtaining various processing timings, including a clock CLK and horizontal and vertical synchronizing signals HV, HV, in the main scanning direction and the sub-scanning direction obtained from the output device 150 side. Index signal IDX indicating the start of VV and laser beam scanning
Etc. are supplied, and based on these signals, a timing signal for starting reading for the CCDs 6, 7 is formed.

Numeral 180 denotes a timing signal generating circuit for obtaining a variable power timing.

In the present invention, when the partial color conversion mode is selected, the dedicated color ghost correction data table stored in the color ghost correction means 300 is referred to.

That is, the color ghost correction means 300 contains correction data used in the partial color conversion mode in addition to the color ghost correction data used in the normal recording mode. Will be controlled based on.

Then, the content is demonstrated in detail. First, the color ghost correction will be described.

In this example, the color ghost is corrected by the color pattern method. This is because, as with the original black-> red, blue ghost, the original red, blue-> black ghost, the color ghost color that appears is determined with respect to the original color. Therefore, according to this color pattern method, the color of the original image can be identified by determining the color appearance (pattern) of the pixel of interest and the pixels around it in order 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 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 that appears at the black edge. In the third example as well, red is judged to be a black color ghost. Therefore, in both the first and third examples, the target pixel 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 it is.

Such a process is difficult to realize with an arithmetic circuit,
In this example, ROM is used and used in LUT (lookup table) format. As the color pattern, a one-dimensional or two-dimensional method can be considered. However, when the number of colors is N and the number of peripheral pixels including the pixel of interest is M, the size of the color pattern is N ^M.

Therefore, when a two-dimensional pattern is used, the number of Ms suddenly increases, and becomes unpractical. That is, in the case of a two-dimensional pattern, the number of peripheral pixels in each dimension (main scanning direction / sub scanning direction) cannot be large, but only the number of patterns is large. FIG. 7 shows the relationship between the size and the number of color patterns.

In this example, a one-dimensional color pattern having a size of 1 × 7 (that is, N = 4, M = 7) 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 the color ghost 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.

Although the size of 1 × 7 is selected as the color pattern size, it is also possible to use a smaller color pattern such as 1 × 5 if the degree of appearance of the color ghost is small. A color ghost of 1 pixel can be removed from a 1 × 5 color pattern, and a color ghost up to 2 pixels can be removed from a 1 × 7 color pattern.

When a 1 × 7 size color pattern is used, the color code is input as the ROM address.

For example, in the color pattern below The color code pattern is white: white: blue: blue: black: black: black 11: 11: 01: 01: 00: 00: 00, and the address is D40. The black code 00 is stored in. The LUT is executed by the above method.

Actually, a 1 × 7 pattern requires a 14-bit address line, and as a bipolar ROM, the address 14
A bit input and a color code 2-bit output are all necessary, but a high-speed ROM with such a large capacity is not on the market and is expensive. The output of 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 with the color code of the remaining six pixels. That is ROM
Output data Do, D1 of is selected when the first pixel is black,
Similarly, output data D2, D3 is blue, D4, D5 is red, D6, D7
Are selected when they are white.

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

However, even if the head pixel is the same white, the color code of the pixel of interest obtained in the selected output bits D6 and D7 is different as shown in FIG. This is because the ROM reference address differs depending on the combination of input pixels (combination of color code data).

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

On the other hand, as the color pattern obtained when the color markers are filled in as shown in FIG. 14, the appearance mode as shown in FIG. 8 can be considered.

That is, when a color marker is placed on a black thin line such as a ruled line, if this black thin line is set as a target pixel, the appearance mode of peripheral pixels for the target pixel (1-2 pixels) is as shown in FIG. Like In the figure, the color patterns of numbers 1 to 6 are for the case of using the red color marker, and the color patterns of numbers 7 to 11 are for the case of using the blue color marker.

When the color ghost process is performed in this appearance mode as in the normal case, black pixels are converted into red pixels, or black pixels are converted into blue pixels. Therefore, the ruled lines are not reproduced.

Even if the image is thick to some extent, its outline becomes thin.

Therefore, in the present invention, in the partial color conversion mode, in such a specific color pattern, even if there is a black pixel, it is not corrected. That is, even with the same color pattern, the pixels are corrected in the normal recording mode,
A dedicated conversion table is prepared for each color so as not to be corrected in the partial color conversion mode.

Which conversion table is used depends on whether the partial color conversion mode is used or not. Which table is used is selected by the signal supplied to the 13th bit of the ROM 302.

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

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

In the color ghost processing, only the color code of pixel data is targeted.

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

Here, since the input bits of the ROM 302 are up to 13 bits and the output bits are up to 8 bits, the first 2 bits are used as the selection bits as described above. Therefore, a selector 303 is provided after the ROM 302, the head bit is supplied to the selector 303, and the remaining bits (12 bits) are supplied to the ROM 302.

In the ROM 302, as described above, color ghost correction color pattern data and color pattern data used in the partial color conversion mode are stored in tabular form.

When the ghost processing ends, the latch circuit 304 latches.

On the other hand, the density data output from the color discrimination circuit 20 is the timing adjustment shift register (SR) 305 (7).
The data transfer condition is set so that the density code data is supplied to the latch circuit 306 via the bit structure) and the density data is serially transferred after the color code data.

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

The line memory unit 310 is provided to remove the color ghost in the vertical direction by using the image data of 7 lines. The line memory is used for a total of eight lines, but this shows one means of real-time processing, and of course, real-time processing is possible even for seven lines.

The color code data and the density data for eight lines are separated from each other in the gate circuit group 320 at the subsequent stage. The gate circuit group 320 is provided with gate circuits 321 to 328 corresponding to the line memories 311 to 318, respectively.

The output data of the 8-line memory synchronized in the line memory unit 310 is separated into the color code data and the 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 lines. Of the line memory of 7 required for color ghost processing
Color code data in the line memory of the book is selected.
In this case, when the line memories 311 to 317 are selected, the selected line memories are sequentially shifted at the next processing timing like the line memories 312 to 318 are selected.

Color code data for the selected and synchronized 7-line memory is used in the next vertical ghost removal RO
It is supplied to the M340 to remove the vertical color ghost.

In the vertical direction, the process is the same as in the horizontal direction.
Bit, output 8-bit ROM 340, data selector
341 is provided, and the first 2 bits are used as a signal for data selection.

In the ROM 340, as described above, the data for color ghost correction used in the normal recording mode and the data used in the partial color conversion mode are tabulated, respectively. Which table is used? Do you want to use ROM340
It is selected by the signal supplied to the 13th bit. This signal is related to the operating mode
The command signal output from is used.

 Then, 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 timing-adjusted with the color code data before being output.

[Effect 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 the data for color ghost correction used in the normal recording mode, prepare data for color ghost correction used in the partial color conversion mode and select it according to the operation mode. It is intended to be used.

By doing this, when the partial color conversion mode is selected, the pixel of interest is not changed in the case of a specific color pattern, so that the contour of the image does not become faint, thin, or disappear. .

Moreover, the color ghost correction process is executed even in such a partial color conversion mode, and the recording pixels are improved.

Therefore, the present invention is very suitable when applied to a color image processing apparatus such as the above-described color copying machine.

[Brief description of drawings]

FIG. 1 is a system diagram showing an example of a color image processing apparatus according to the present invention, FIG. 2 is a diagram of a color discrimination map, FIG. 3 and FIG.
Fig. 6 is a characteristic diagram showing MTF correction, Fig. 5 is a density histogram diagram, Fig. 6 is a diagram for explaining color ghost, and Fig. 7
The figure shows the relationship between color pattern and pattern size,
FIG. 8 is a diagram showing the relationship between the operation mode and the correction content for a specific color pattern, FIG. 9 is a system diagram of the color ghost correction means, FIG.
FIG. 12 is a diagram showing the relationship between color markers and marker signals and area signals, FIGS. 12 and 13 are explanatory diagrams of color ghosts, and FIG.
The figure is a diagram showing an example of designation of color markers. 1 ... Color image processing device 20 ... Color discrimination circuit 40 ... Resolution correction circuit 50 ... Color data selector 60 ... Region extraction circuit 70 ... Magnification circuit 80 ... Multivalued circuit 100 ... Histogram creation circuit 130 …… Interface circuit 140 …… Driver 150 …… Output device 160 …… CPU 300 …… Color ghost correction means 302, 304 …… Correction ROM

Claims (1)

(57) [Claims] 1. A color image processing apparatus for image-processing the color image information based on the color image information converted into an electric signal, comprising a color discrimination means for the color image information and a color ghost correction means. An image processing means for performing partial color conversion processing of a designated area by color information different from the original color to be read is provided, and when the partial color conversion processing of the designated area is executed, the correction of the color ghost correction means is performed. A color image processing device characterized in that the contents are changed.