JPH02288671A - Color picture processor - Google Patents

Abstract

PURPOSE:To improve the color reproducibility of low saturation in a color gradation picture with a simple constitution by setting an intermediate color area in the case of the separation of a chromatic color and an achromatic color and giving the chromatic color and the achromatic color to the intermediate color area in the case of color ghost correction. CONSTITUTION:The subject processor is constituted of a density conversion section 1, a color code generating section 2, a color reproduction section 3, a selector 4, a color ghost correction section 5, a gate 6, a filter processing section 7, a magnification processing section 8, and a printer unit 9. Then a color code of the chromatic color, the achromatic color and an intermediate color belonging to the intermediate area between the chromatic color and the achromatic color is generated and the color code of the intermediate color code is changed into the color code of the chromatic color and the achromatic color. Thus, the color reproducibility of low saturation in the color gradation picture is improved with the simple constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a color image processing device, and more specifically,
The present invention relates to a color image processing device that can effectively remove color ghosts and has excellent low chroma color reproducibility.

(Background of the invention) Red R1 Green G for color images such as character drawings and photographic images.

It is divided into blue B and optically read, and this is yellow Y.

There is a color image processing device that converts (color reproduction or color correction) into recording colors such as magenta M, cyan C1 and black, and records on recording paper using an electrophotographic color output device based on this. .

FIG. 8 is an explanatory diagram showing the state of color discrimination (chromatic color/achromatic color discrimination) in the color image processing apparatus as described above. In the cube shown, the front side in the horizontal direction is R
The concentration is The vertical direction is the density of B, and the depth direction is the density of G. Therefore, the lower left front, where the R, G, and B densities are all zero, is white, and the upper right back, where all the densities are maximum, is black. Therefore, the area connecting white and black corresponds to an achromatic color (gray) area, and the other areas correspond to chromatic color areas.

By the way, there are the following conflicting problems regarding the setting of this achromatic color area.

■Color ghost (
In order to reduce unnecessary colors (generated at the edges of black characters), it is necessary to make the achromatic color area as wide as possible.

- On the color gradation side, in order to accurately reproduce colors with low saturation (for example, chromatic colors such as brown, dark blue, and purple), it is necessary to make the achromatic color region as narrow as possible.

(Problems to be Solved by the Invention) Due to the above-mentioned conflicting demands, in reality, a compromise has been made by setting an achromatic color range within a range that does not dissatisfy both parties.

However, when reproducing black character images, color ghosts occurred especially around thin black lines, making it impossible to obtain satisfactory results.

On the other hand, the color reproduction of low saturation on the color gradation side was not satisfactory. In other words, since the achromatic color area has a certain width as described above, low chroma areas are reproduced as black.

The present invention has been made in view of the above-mentioned problems, and its purpose is to improve the color reproducibility of low saturation on the color gradation side and to eliminate color ghosts of black characters with a simple configuration. An object of the present invention is to realize a color image processing device that can reduce the amount of noise.

(Means for Solving the Problems) The present invention to solve the above problems generates a color code that distinguishes each pixel in a document into a chromatic color and an achromatic color, and performs color ghost correction using this color code. A color image processing device that performs image processing generates color codes for chromatic colors, achromatic colors, and intermediate colors that belong to the intermediate region between chromatic colors and achromatic colors, and also converts the color code of intermediate colors into chromatic colors or chromatic colors when performing color ghost correction. The feature is that the color code is changed to an achromatic color code.

(effect) In the color image processing device of the present invention, chromatic colors.

Achromatic and neutral color codes are changed to chromatic or achromatic color codes when color ghost correction is executed.

(Example) Examples of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing the structure of an embodiment of the present invention.

In the figure, reference numeral 1 denotes a density conversion unit that converts 8-bit digital data each of R2O and B provided from the outside into 6.6.5-bit data. 2 is the density conversion section 1
This is a color code generation unit that receives R, G, and B data from the computer, discriminates between white/black/chromatic colors/intermediate colors, and outputs a color code. 3 receives R, G, B data,
Y, M.

This is a color reproduction section that performs color reproduction processing to generate C and K data. 4 is a selector that selectively passes Y, M, C, and K density data from the color reproduction section 3 according to a scan code (not shown). 5 is a color ghost correction unit that performs color ghost correction and changes the color code;
Reference numeral 6 designates a gate that selectively passes density data based on a color code, 7 a filter processing unit that performs various filter processing, 8 a scaling processing unit that performs scaling processing, and 9 a printer unit that performs image recording.

The operation of this embodiment will be explained below.

The original image is read by an image reading unit (not shown), and R, G
, B is converted into 8-bit digital data. The R, G, and B digital data are then supplied to the density conversion section 1. In the density conversion section 1, the 8-bit data is converted into 6 and 6.5 data, respectively, in accordance with human visual characteristics.
Converted to bit data. The output data of the R, G, and B density conversion section 1 is applied to a color code generation section 2 and a color reproduction section 3. The color code generation unit 2 outputs a color code indicating whether each pixel belongs to white, black, achromatic color, or intermediate color, as described later, based on the level of each R, G, and B data.

FIG. 2 is an explanatory diagram showing how the color code generation section 2 generates a color code. In the cube in the figure, the front side in the horizontal direction is the density of R. The vertical direction is the density of B, and the depth direction is the density of G. Therefore, R,
The lower left front (and surrounding area) where the G and B densities are all zero is white (color code: 00), and the upper right back (and surrounding area) where all the densities are maximum is black. Here, we set a narrow achromatic color area (color code: 11) that connects white and black (achromatic color is recorded with black toner, henceforth referred to as black), and a relatively wide intermediate color area around it. (
Set the color code (Ol). The area other than this is defined as a chromatic area (color code: lO). In other words, only areas that are achromatic (black) are always set as black areas in both black character images and color gradation images.

In the case of color gradation paintings, it is a region of low saturation,
In the case of a black character image, an area where a color ghost may occur is set as an intermediate color area.

Therefore, the color code generating section 2 outputs the above-mentioned 2-bit color code (white: 00. black, 11. intermediate color: old, chromatic color: 10). This situation is CIE's L*a*
When shown in b* uniform color space, it becomes as shown in FIG. 3A.

This color code is supplied to the color ghost correction section 5. Then, the color ghost correction unit 5 changes the intermediate color code (01) to black (11) based on the color pattern.
) or chromatic color (lO). That is, if the image being processed is a color gradation image, the intermediate color code is modified to a chromatic color code to improve the reproducibility of low chroma colors (Figure 3C).
. Furthermore, if the image being processed is a black character image with color ghosts, the intermediate color code is corrected to a black color code to suppress the occurrence of color ghosts (FIG. 3B).

Next, color ghost correction in the color ghost correction section 5 will be explained. First, color ghost removal is performed using a color pattern method. This is because, like the ghost of the original black-chromatic color, the color boss color that appears is determined with respect to the original color. In the case of the color pattern method, the color of the original image can be identified by examining the appearance (pattern) of the colors of the pixel of interest and surrounding pixels to determine the color of the pixel of interest.

As an example, FIG. 4 shows a pixel of interest, a surrounding color pattern, and the determination of the color of the pixel of interest determined at that time.

In the first example, both sides of the pixel of interest are white.

Since it is black, the intermediate color of the pixel of interest is determined to be a color ghost appearing at the black edge. Therefore, in the first example, the pixel of interest is changed to black.

On the other hand, in the second example, there is no color ghost,
It is judged to be a color gradation painting. Therefore, the pixel of interest is changed to a chromatic color.

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. One-dimensional and two-dimensional systems are considered as color patterns, but if the number of colors is N1 and the surrounding pixels including the pixel of interest are M, then the number of color patterns is NM. Therefore, it is also possible to use a two-dimensional pattern, but in this case the number of M will suddenly increase. In other words, in a two-dimensional pattern, the number of peripheral pixels in each dimension (main scanning direction/sub scanning direction) cannot be increased, but the number of patterns increases.

FIG. 5 shows the relationship between pattern size and number of color patterns.

In this example, the size is 1×7 in one dimension (that is, N
-4, M-7) color patterns are 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, IX7 is selected, but if the degree of color ghost appearance is small, IX7 is selected.
It is also possible to use smaller sized color patterns, such as X5. Color ghosts of up to 1 pixel can be removed with a color pattern of size I×5, and color ghosts of up to 2 pixels can be removed with a color pattern of size 1×7.

When using color patterns of size 1x7, the number of color patterns is 4'-16384. In the present invention, the color code is input as a ROM address. In the example color pattern, White White White Medium Yes Black
Black (peripheral pixels) (Pixel of interest) (Peripheral pixels) The color code pattern is white: White: White: Medium: Yes: Black: Black 00:00:
00:01:10:11:11, and the address will be 006F C hexadecimal (using the above pattern as is).

Furthermore, data for converting the target pixel from an intermediate color to black is stored at this address destination. Similarly, data for converting intermediate colors to chromatic colors and from chromatic colors to black is also stored. Therefore, by storing data that instructs whether to convert or not using any 1×7 pattern as an address, a LUT for color ghost correction can be created.

In reality, a 1x7 pattern requires a 14-bit address line, and a bipolar ROM with a 14-bit address and 2-bit color code output is sufficient, but a high-speed ROM with this capacity is It is not widely available on the market and is expensive.

If a high-speed ROM (large capacity) is available, color patterns can be stored in the same ROM. LUT may be performed by using four ROMs and switching the ROMs depending on the color of the first pixel.

Examples of high-capacity, high-speed bipolar ROM include Fuji Renso M87143/7144.

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.

FIG. 6 is a block diagram showing an example of the color ghost correction circuit 5 and its peripheral parts. Color ghost processing is performed in the main scanning direction (horizontal scanning direction) and the sub-scanning direction (vertical scanning direction).

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 correction ROM is first sequentially supplied to a shift register 57 having a 7-bit configuration and parallelized for ghost correction in the main scanning direction.

This parallel color code data for seven pixels is supplied to a ROM 58 for horizontal ghost detection, and ghost detection processing and color code correction processing (intermediate color - chromatic color, achromatic color) are performed for each pixel.

An example of how the ROM 58 is used is as described above.

The serially processed color code data is supplied to the line memory section 59.

The line memory section 59 is provided to remove color ghosts in the vertical direction using seven lines of image data. The register group 60 includes registers 60a to 60a corresponding to the line memories 59a to 59g, respectively.
60g is provided.

The color code data for 7 line memories synchronized in the line memory section 59 is supplied to a ROM 61 for removing vertical ghosts in the next stage, where vertical color ghosts are detected and applied to the gate 6.

The density data input to the selector 62 is Y, M, C, or K, depending on the recording color signal (scan code). If it is Y, M or C, ROM61
Density data is output from the gate 6 only when the color code output from the gate 6 is a chromatic color. Furthermore, when the recording color signal is K, density data is output from the gate 6 only when the color code is achromatic.

This embodiment has the advantage that it is possible to correct not only chromatic color ghosts occurring at the edges of black characters, but also achromatic color ghosts occurring at the edges of chromatic characters. Furthermore, since intermediate color codes are used in addition to chromatic and achromatic color codes, color ghost correction is accurate. Therefore, it is possible to improve the accuracy of color ghost correction without impairing the gradation characteristics of a color gradation image.

Then, the printer unit 9 performs filter processing.

Image formation is performed according to the type of document using the density signal that has been subjected to gradation correction and scaling processing.

As described above, in this embodiment, the color code is
It is divided into black/white/intermediate color, and the intermediate color is divided into black or chromatic color in the color ghost correction section. Therefore, the color reproducibility of low chroma is improved, and the accuracy of color ghost correction is also improved.

Next, the t1 configuration and operation of each part of a color copying machine to which the color image processing apparatus of this embodiment is applied will be explained with reference to FIG. Note that this color copying machine uses color dry development (♀ method). In this example, two-component non-contact development and reversal development are adopted. In other words, the transfer drum used in conventional color image formation is not used, but is superimposed on the electrophotographic photoreceptor drum that forms the image.In addition, in the following example, in order to reduce the size of the apparatus, yellow , magenta,
A four-color image of cyan and black is developed with four rotations of the drum,
After development, transfer is performed once to transfer onto recording paper such as plain paper.

By turning on the copy button of the color copying machine, the original reading section A is driven. And the manuscript table 128
An original 101 is optically scanned by an optical system.

This optical system uses a light source such as a halogen lamp at 129° and 130°.
and a carriage 132 provided with a reflective mirror 131.
It is composed of a movable mirror unit 134 provided with V mirrors 133 and 133'.

The carriage 132 and the movable unit 134 are caused to travel on a slide rail 136 at predetermined speeds and directions, respectively, by a stepping motor 135.

Optical information (image information) obtained by irradiating the original 101 with the light sources 129 and 130 is transmitted to the reflecting mirror 131 and the mirror 1.
33.133', the optical information conversion unit 13
Guided by 7.

A standard white plate is provided on the back side of the left end of the platen glass 128. This is because the image signal is normalized to a white signal by optically scanning the standard white plate.

The optical information conversion unit 137 includes a lens 139, a prism 140, two dichroic mirrors 102 and 103, a C0D 104 for capturing a red color-separated image, a CCD 105 for capturing a green color-separated image, and a blue color-separated image. It is composed of a CCD 106 to be imaged.

The optical signals obtained by the optical system are collected by the lens 139, and the dichroic mirror 102 provided in the prism 140 described above converts the blue optical information and the yellow optical information.
The yellow optical information is separated into red optical information and green optical information by the dichroic mirror 103.

In this way, the color optical image is decomposed by the prism 140 into three-color optical information of red, R, green, and blue.

Each color separation image is formed on the light receiving surface of each CCD, thereby obtaining an image signal converted into an electrical signal.

After the image signal is processed by the signal processing system, each color signal is output to the writing section B.

The signal processing system includes various signal processing circuits such as the density converter 1 to the variable magnification processor 9 shown in FIG. 1, as well as an A/D converter and the like.

The writing section has a deflector 141. As this deflector 141, in addition to a galvanometer mirror, a rotating polygon mirror, etc.
A deflector consisting of an optical deflector using crystal or the like may be used. The laser beam modulated by the color signal is deflected and scanned by this deflector 141.

When deflection scanning is started, beam scanning is detected by a laser beam index sensor (not shown), and beam modulation using a first color signal (for example, a yellow signal) is started. The modulated beam is applied to an image forming member (photosensitive drum) 1 which is charged with a negative charge by a charger 154.
42 is scanned.

Here, the main scanning by the laser beam and the image forming body 142 are performed.
Due to the sub-scanning caused by the rotation of the image forming member 142, an electrostatic latent image corresponding to the first color signal is formed on the image forming body 142.

This electrostatic latent image is transferred to a developing device 14 containing yellow toner.
3 to form a yellow toner image.

Note that a predetermined developing bias voltage from a high voltage source is applied to this developing device.

Toner is supplied to the developing device 143 when necessary by controlling a toner replenishing means (not shown) based on a command signal from a system control CPU (not shown). . The yellow toner image described above is rotated with the cleaning blade 147a released from pressure, and an electrostatic latent image is formed based on a second color signal (for example, a magenta signal) in the same manner as in the case of the first color signal. .The developing device 1 contains magenta toner.
44, this is developed to form a magenta toner image.

Needless to say, a predetermined developing bias voltage is applied to the developing unit 144 from a high voltage power supply.

Similarly, an electrostatic latent image is formed based on the third color signal (cyan signal), and a developing device 145 containing cyan toner is provided.
A cyan toner image is formed. Further, an electrostatic latent image is formed based on the fourth color signal (black signal), and is developed in the same manner as the previous time using the developing device 146 filled with black toner.

Therefore, multicolor toner images are formed on the image forming body 142 in an overlapping manner.

Although the formation of a four-color multicolor toner image has been described here, it goes without saying that a two-color or single-color toner image can be formed.

As described above, the development process is a so-called two-component non-contact process in which each toner is caused to fly toward the image forming body 142 while AC and DC bias voltages from a high-voltage power source are applied. An example of development is shown.

Furthermore, toner replenishment to the developing units 144, 145, and 146 is performed based on a command signal from the CPU, as described above, with a predetermined amount of toner.

On the other hand, the recording paper P fed from the paper feeding device 148 via the feed roll 149 and the timing roll 150 is conveyed onto the surface of the image forming body 142 in a state in which the timing is synchronized with the rotation of the image forming body 142. Ru. Then, the multicolor toner image is transferred onto the recording paper P by the transfer pole 151 to which a high voltage is applied from the high voltage ms, and the separation pole 152
separated by

The separated recording paper P is conveyed to the fixing device 153, where it undergoes a fixing process and a color image is obtained.

The image forming body 142 after the transfer is transferred to a cleaning device 147
is cleaned and prepared for the next imaging process.

In the cleaning device 147, a predetermined DC voltage is applied to the metal roll 147b in order to facilitate recovery of the toner cleaned by the cleaning blade 147a. This metal roll 147b is placed on the surface of the image forming body 142 in a non-contact state. cleaning blade 1
47a is released from pressure bonding after cleaning is completed, but in order to release unnecessary toner that is left behind at the time of release, an auxiliary roller 147C is further provided, and this auxiliary roller 147c is rotated in the opposite direction to the image forming body 142 and is pressed against the image forming member 142. As a result, unnecessary toner is sufficiently cleaned and removed.

In the above description, the color image processing apparatus of this embodiment is applied to a color copying machine, but it goes without saying that the color image processing apparatus of the present invention can be used for various other types of equipment.

(Effects of the Invention) As described above in detail, in the present invention, an intermediate color area is set when classifying chromatic colors and achromatic colors, and this intermediate color area is divided into chromatic colors or achromatic colors during color ghost correction. did.

Therefore, with a simple configuration, it is possible to realize a color image processing device that can improve low saturation color reproducibility on the color gradation side and reduce color ghosts of black characters.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram showing the configuration of an embodiment of the present invention, Fig. 2 is an explanatory diagram illustrating how color codes are generated, Fig. 3 is an explanatory diagram showing how colors are divided, and Fig. 4 is a color code FIG. 5 is an explanatory diagram showing the relationship between the pattern size and the number of patterns for color ghost correction. FIG. FIG. 7 is a block diagram showing the overall configuration of a color copying machine, and FIG. 8 is an explanatory diagram showing the state of conventional color code generation. 1... Density conversion section 2... Color code generation section 3. ...Color reproduction section 4...Selector 5...
・Color ghost correction section 6...Gate 7...Filter processing section 8
... Magnification processing section 9 ... Printer unit

Claims (1)

[Scope of Claim] A color image processing device that generates a color code that distinguishes each pixel in a document into a chromatic color and an achromatic color, and uses this color code to perform image processing including color ghost correction. The system is configured to generate color codes for chromatic colors, achromatic colors, and intermediate colors that belong to the intermediate region between chromatic colors and achromatic colors, and to change the color code for intermediate colors to chromatic or achromatic color codes when color ghost correction is executed. A color image processing device featuring: