JP2898042B2 - Color image processing equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image processing apparatus for performing image processing by separating a color read signal into achromatic colors and chromatic colors.

[Background of the Invention] A color image such as a character image or a photographic image is optically read by being divided into red R, green G, and blue B, and converted into recording colors such as yellow Y, magenta M, cyan C, and black K. There is a color image processing apparatus that performs (color reproduction or color correction) and records on a recording sheet using an electrophotographic color output device.

FIG. 6 shows a state in which a chromatic color and an achromatic color are determined in the above-described color image processing apparatus.

In the cube shown in the figure, 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, the point where the concentrations of R, G, and B are all zero (lower left front) is white,
The point at which all become the maximum (upper right corner) is black. In this case, an area (shown by a broken-line cylinder) connecting the white point and the black point corresponds to an achromatic area, and the other area corresponds to a chromatic area.

By the way, when setting this achromatic area,
There are conflicting requirements, such as:

To reduce color ghosts (unnecessary colors that occur at the edges of black characters) in black characters due to pixel shifts between the R, G, and B of the CCD sensor and lens aberrations, achromatic regions Must be set as wide as possible.

In the case of a color gradation image, it is necessary to set an achromatic region as narrow as possible in order to accurately reproduce a low-saturation color (eg, brown, dark blue, purple, etc.).

[Problems to be Solved by the Invention] Therefore, in the related art, an achromatic region is set at a compromise between these conflicting requirements.

Therefore, for example, color reproduction in a low chroma portion of a color gradation image has not been satisfactory. In other words, since the achromatic region cannot be set so narrow, the low-saturation part of the color gradation image is classified into achromatic colors and the image processing corresponding to the achromatic color is performed, and this low-saturation part is reproduced as an achromatic color. Was inconvenient.

Also, for example, the reproduction of a black character image was not satisfactory. That is, since the achromatic region cannot be set so wide, the character edge portion is classified into chromatic colors, and image processing corresponding to the chromatic color is performed, and there is a problem that a color ghost occurs in the character edge portion.

SUMMARY OF THE INVENTION It is an object of the present invention to improve color reproduction in a low chroma portion of a color gradation image and reproduction of a black character image.

[Means for Solving the Problems] The present invention provides a color reproducing unit that generates chromatic image processing data corresponding to a plurality of recording colors from a color reading signal,
A color image processing apparatus having a single color reproduction unit that generates data for achromatic image processing from a color read signal, wherein the color read signal is color-coded into intermediate colors and chromatic colors, and codes of the intermediate colors and chromatic colors are respectively processed. First color classifying means for generating, image discriminating means for discriminating the type of image from the color reading signal, and intermediate colors classified by the first color discriminating means according to the discrimination result of the image discriminating means are achromatic and chromatic. A second color classifying means for generating achromatic and chromatic color codes respectively, and a color reproducing unit when the codes generated by the first and second color classifying means are chromatic color codes. Image processing switching means for selecting and outputting the selected data, and selecting and outputting the data created by the single color reproduction unit when the code is an achromatic color code. It is.

[Operation] The image discriminating means detects, for example, a density gradient of the image. When the density gradient is larger than a predetermined value, the image discriminating unit determines that the image is a black character image. The intermediate color is classified into an achromatic color when determined as a black character image, and a chromatic color when determined as a color gradation image.

Further, in the image processing switching means, when the code generated by the first and second color classification means is a chromatic color code, for example, data of Y, M, C created by the color reproduction section is selected. In addition to the output, if there is an achromatic code, the K data created by the single color reproduction unit is selected and output.

Therefore, the low chroma portion of the color gradation image is classified into chromatic colors except for the portion where the density gradient is large, and the image processing corresponding to the chromatic color is performed, so that the color reproduction of the low chroma portion is improved.

In addition, since the density gradient is large at the character edge portion of the black character image, it is classified into achromatic colors, image processing corresponding to the achromatic color is performed, no color ghost occurs at the character edge portion, and the character edge portion is reliably reproduced in black Therefore, the reproduction of a black character image is improved.

Embodiment An embodiment of the present invention will be described below with reference to FIG.

In the figure, red R and R from the image reading unit (not shown)
8-bit digital data of green G and blue B is input terminal 1
R, 1G, and 1B are supplied to the density converter 2. The density converter 2 converts R, G, and B 8-bit data into 6-bit data in accordance with human visual characteristics.

The R, G, B data from the density converter 2 is supplied to the color reproducer 3. In the color reproduction section 3, data of yellow Y, magenta M, cyan C, and black K for chromatic image processing is generated from the data of R, G, and B. Y, output from the color reproduction unit 3,
The stomach data of M, C and K are supplied to the selector 4.

Further, the G data from the density conversion unit 2 is supplied to the single color reproduction unit 5. In the single color reproduction section 5, black data K 'for achromatic image processing is generated from the G data. The black data K 'may be generated from R or B data, or may be generated from two or all of the colors R to B. K 'output from the single color reproduction unit 5
Is supplied to the selector 4.

The R, G, B data from the density converter 2 is supplied to the color code generator 6. This color code generator 6
In the above, intermediate colors and chromatic colors are classified according to the levels (densities) of R, G, and B data. The color code generator 6 outputs a color code indicating whether the color belongs to an intermediate color or a chromatic color.

Here, the setting of the intermediate color area and the chromatic color area is performed as described below.

That is, as shown in FIG. 2A, a cylinder having a radius r is created in the L ^* , a ^* , b ^* color system (the L ^* direction is not shown in FIG. 2), and the interior is set as an intermediate color area. At the same time, the outside is set as a chromatic color area. In this case, the interior of the cylinder is an area that can take both achromatic and chromatic colors according to the image information,
For example, r = 15.

In the color code generation unit 6, the data of R, G, B is L ^* ,
It is converted into a ^* , b ^* color system, and it is determined whether the color coordinate position is inside or outside the cylinder of radius r. And
When it is inside the cylinder, a color code indicating that it belongs to an intermediate color, for example, “01” is output, and when it is outside, a color code indicating that it belongs to a chromatic color, for example, “10” is output.

Note that the color code generation unit 6 is configured with a table formed of, for example, a ROM.

Returning to FIG. 1, the color code output from the color code generation unit 6 is supplied to a color code correction unit 7.

The G data supplied to the input terminal 1G is supplied to the image discriminating unit 8. The image discriminating unit 8 discriminates a black character image or a color gradation image from the density gradient of G. In this case, the determination may be made using all the data of R, G, and B, but the cost increases. Therefore, in this example, the determination is made using only the G data that best matches the visibility.

FIG. 3 shows pixels used for image discrimination. In the figure, X is a pixel of interest for which image determination is to be performed, V is a pixel one line before, W is a pixel one pixel before, Y is a pixel one pixel after, and Z is a pixel one line after. is there. Here, a density gradient is obtained using the density data (8 bits) of each pixel. That is, the density gradient S of the target pixel X is obtained by the following equation.

S = 2 | V−X | + | W−Y | In this manner, the S parameter of the density gradient is obtained from the peripheral pixels.

In addition to the S parameter, a parameter of S ′ = | V−X | + | W−X |... S ″ = | V−Z | + | W−Y |. Since only two pixels are used, the discrimination ability is not sufficient,
S "has a disadvantage that the memory capacity is increased because three pixels are required in the sub-scanning direction.

Therefore, in this example, an S parameter of an equation having a small memory capacity and a high discrimination ability is used.

 FIG. 4 is a diagram showing a specific configuration of the image determination unit 8.

In the figure, 21 is a register for holding data of pixel Y, 22 is a register for holding data of pixel X, 23 is a register for holding data of pixel W, 24 is a subtraction between W and Y, and an absolute value is obtained. Is a subtraction absolute value generation circuit for generating | W−Y |, and the absolute value | W−Y | from the subtraction absolute value generation circuit 24 is supplied to the adder 28.

Further, 25 is a line memory, 26 is a register holding the data of the pixel V, 27 is a subtraction between V and X, and the absolute value | V−
This is a subtraction absolute value generation circuit for generating X |. The absolute value | V−X | from the subtraction absolute value conversion circuit 27 is amplified by an amplifier 29 to be doubled and then supplied to an adder 28.

In the adder 28, the absolute value | W−Y | and 2 | V−X | are added, and the added signal | W−Y | +2 | V−X | is supplied to the comparator 30 as an S parameter. Further, the threshold value T of the density gradient is supplied to the comparator 30 from the threshold value generator 31.

In the comparator 30, the S parameter is compared with a threshold value T, and S
If> T, it indicates a black character image, for example, a high level "1" signal is output. If S≤T, it indicates a color gradation image, for example, a low level "0" signal. Is output.

Returning to FIG. 1, the image discrimination signal output from the image discrimination unit 8 is supplied to the color code correction unit 7. In the color code correction unit 7, the color code "10" indicating that the color code belongs to the chromatic color is output as it is, and the color code "01" indicating that the color code belongs to the intermediate color, among the color codes supplied from the color code generation unit 6. Is corrected by the image discrimination signal and output.

That is, when the image discrimination signal is a high-level “1” signal indicating a black character image, the color code “01” indicating an intermediate color is a color code indicating that the image belongs to an achromatic color.
For example, it is corrected to “11”. At this time, the setting of the area is
It is equivalently represented as shown in FIG. 2B.

On the other hand, when the image discrimination signal is a low-level “0” signal indicating a color gradation image, the color code “01” indicating an intermediate color is corrected to a color code “10” indicating that the image belongs to a chromatic color. Is done. At this time, the setting of the area is equivalently represented as shown in FIG. 2C.

The color code output from the color code correction unit 7 is supplied to the selector 4. The selector 4 is supplied with a scan code (a code indicating a color recorded by the printer). The selector 4 selects and outputs color data corresponding to the color being recorded by the printer based on the scan code.

In this case, Y, M, C, and K output from the color reproduction unit 3 as yellow to black data in a pixel portion having a color code “10” indicating that the color code belongs to a chromatic color.
Is output. On the other hand, in a pixel portion having a color code “11” indicating that the color code belongs to an achromatic color, zero is output as yellow to cyan data, and K is output from the single color reproduction unit 5 as black data. 'Is output.

The data output from the selector 4 is supplied to a printer unit 12 via a filter processing unit 10 for performing various filtering processes and a gradation correction unit 11, and an image is formed on a recording sheet.

As described above, in the present example, the area that is re-converted into an achromatic color and a chromatic color by post-processing is classified into an intermediate color, and the color code generation unit 6 outputs the color code “01” indicating that the area belongs to the intermediate color. . The color code “01” is corrected by the color code correction unit 7 to a color code “11” indicating that the image belongs to an achromatic color when the density gradient of the image is larger than the threshold value, and belongs to a chromatic color when the density gradient is smaller than the threshold value. Is corrected to the color code "10" indicating that When the color code output from the color code correcting section 7 is "10", the selector 4 selects the data of Y, M, C, K output from the color reproducing section 3 and selects an image corresponding to a chromatic color. Processing is performed. On the other hand, when the color code is "11", the data K 'output from the single color reproduction section 5 is selected and the image processing corresponding to the achromatic color is performed.

Therefore, according to this example, the color code “10” indicating that the image belongs to the chromatic color is output in the low chroma portion of the color gradation image except for the portion where the density gradient is large, and the image processing corresponding to the chromatic color is performed. It is. For this reason, the low chroma portion is less likely to be reproduced in an achromatic color, and the color reproducibility of the low chroma portion can be improved.

Further, since the density gradient is large at the character edge portion of the black character image, a color code “11” indicating that the character belongs to an achromatic color is output, and image processing corresponding to the achromatic color is performed. Therefore, a color ghost does not occur at the character edge portion and the character edge portion is reliably reproduced in black, and the reproducibility of a black character image can be improved.

Hereinafter, the configuration and operation of each unit of the color copying machine to which the color image processing apparatus of the present invention is applied will be described with reference to FIG. The color copier is developed using a color dry developing method. In this example, two-component non-contact development and reversal development are employed. That is, the transfer drum used in the conventional color image formation is not used, and the superposition is performed on the electrophotographic photosensitive drum for forming an image. In the following example, in order to reduce the size of the apparatus, yellow, magenta,
The four-color image of cyan and black is developed by four rotations of the drum, and the transfer is performed once after the development, so that the image is transferred to recording paper such as plain paper.

When the copy button of the color copier is turned on, the document reading unit A is driven. Then, the original 1 on the platen 128
01 is optically scanned by the optical system.

This optical system includes a carriage 132 provided with a light source 129 such as a halogen lamp and a reflection mirror 131, and a movable mirror unit 134 provided with V mirrors 133 and 133 '.

The carriage 132 and the movable mirror unit 134 are moved by a slide rail 136 by a stepping motor (not shown).
Each is driven at a predetermined speed and direction.

Optical information (image information) obtained by irradiating the light source 101 with the light source 129 is guided to the optical information conversion unit 137 via the reflection mirror 131 and the V mirrors 133 and 133 '.

A standard white plate 138 is provided on the back side of the left end of the document table 128. This is for normalizing an image signal to a white signal by optically scanning the standard white plate 138.

The optical information conversion unit 137 has a lens 139 and a prism 14.
0, two dichroic mirrors 102 and 103 and an R-CCD 104 for capturing a red color separation image, a G-CCD 105 for capturing a green color separation image, and a B-CCD 105 for capturing a blue color separation image.
It is constituted by the CCD 106.

The optical signal obtained by the optical system is condensed by the lens 139, and is color-separated into blue optical information and yellow optical information by the dichroic mirror 102 provided in the prism 140 described above. Sky, dichroic mirror 103
Thus, the yellow optical information is color-separated into red optical information and green optical information. Thus, the color optical image is decomposed by the prism 140 into three-color optical information of red R, green G, and blue B.

Each color separation image is formed on the light receiving surface of each of the CCDs 104 to 106, thereby obtaining an image signal converted into an electric signal. After the image signal is processed by the signal processing system, the recording image signal of each color is output to the writing unit B.

The signal processing system includes an A / D converter and the like in addition to the various signal processing circuits of the density conversion unit 2 to the gradation correction unit 11 shown in FIG.

The writing section B has a deflector 141. This deflector 1
As 41, a deflector including an optical deflector using quartz or the like may be used in addition to the galvanometer mirror and the rotating polygon mirror.
The laser beam modulated by the color signal is applied to the deflector 14
Deflection scanning is performed by 1.

When deflection scanning is started, beam scanning is detected by a laser beam index sensor (not shown), and beam modulation by a first color signal (for example, a yellow signal) is started. The modulated beam is applied to an image forming body (photosensitive drum) 142 to which uniform charging is given by a charger 154.
It is made to scan over.

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

This electrostatic latent image is developed by 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 power supply is applied to the developing device 143.

The toner supply of the developing device 143 is C for system control.
By controlling the toner replenishing means (not shown) based on a command signal from a PU (not shown), toner is replenished when necessary.

The above yellow toner image is the cleaning blade 147a
Is rotated in a state where the pressure contact is released, and an electrostatic latent image is formed based on a second color signal (for example, a magenta signal) as in the case of the first color signal. Then, by using the developing device 144 that contains the magenta toner, the developing device 144 is developed to form a magenta toner image.

It goes without saying that a predetermined developing bias voltage is applied to the developing device 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 formed.
As a result, a cyan toner image is formed. Further, an electrostatic latent image is formed based on the fourth color signal (black signal), and a black toner image is formed by the developing device 146 containing black toner.

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

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

As described above, as described above, in a state where AC and DC bias voltages are applied from a high-voltage power supply, each toner flies toward the image forming body 142 and is developed. An example of jumping development was shown.

In addition, toner supply to the developing units 144, 145, 146
As in the case of 43, a predetermined amount of toner is supplied based on a command signal from the CPU.

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 where the timing is synchronized with the rotation of the image forming body 142. Is done. Then, the multicolor toner image is transferred onto the recording paper P by the transfer pole 151 to which the high voltage is applied from the high voltage power supply, and is separated by the separation pole 152.

The separated recording paper P is conveyed to the fixing device 153, where a fixing process is performed to obtain a color image.

The transferred image forming member 142 is cleaned by the cleaning device 147 to prepare for the next image forming member process.

In the cleaning device 147, a predetermined DC voltage is applied to the metal roll 147b in order to easily collect the toner cleaned by the cleaning blade 147a.
The metal roll 147b is arranged on the surface of the image forming body 142 in a non-contact state. After the cleaning is completed, the cleaning blade 147a is released from the pressure contact.After the release, an auxiliary roller 147c is further provided in order to remove unnecessary toner remaining, and the auxiliary roller 147c is rotated in a direction opposite to the image forming body 142. By pressing, unnecessary toner is sufficiently cleaned and removed.

In the above-described embodiment, an example in which the color image processing apparatus of the present invention is applied to a color copying machine has been described. However, it goes without saying that the present invention can be used for various other devices.

[Effects of the Invention] As described above, according to the present invention, an area that can be achromatic and chromatic is classified into an intermediate color, and this intermediate color is further converted into an achromatic color and a chromatic color according to, for example, a density gradient of an image. The color is classified and the corresponding image processing is performed. Therefore, the low chroma portion of the color gradation image is classified into chromatic colors except for the portion where the density gradient is large, and image processing corresponding to the chromatic color is performed, so that the color reproducibility of the low chroma portion can be improved. In addition, since the density gradient is large at the character edge portion of the black character image, it is classified into achromatic colors, image processing corresponding to the achromatic color is performed, no color ghost occurs at the character edge portion, and the character edge portion is reliably reproduced in black Therefore, the reproducibility of a black character image can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram for explaining area setting, FIG. 3 is a diagram showing pixels used for image discrimination, and FIG. FIG. 5 is a diagram showing the overall configuration of a color copying machine, and FIG. 6 is a diagram for explaining a conventional color code generation. 1R, 1G, 1B Input terminal 2 Density conversion unit 3 Color reproduction unit 4 Selector 5 Single color reproduction unit 6 Color code generation unit 7 Color code correction unit 8 Image Discrimination unit 10 Filter processing unit 11 Tone correction unit 12 Printer unit

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Tetsuya Niizuma 2970 Ishikawacho, Hachioji-shi, Tokyo Konica Corporation (72) Inventor Seiichiro Hiratsuka 2970 Ishikawacho, Hachioji-shi, Tokyo Konica Corporation (56) References JP-A-2-249364 (JP, A) JP-A-2-288670 (JP, A) JP-A-2-288671 (JP, A) JP-A-2-288672 (JP, A) JP-A-2-280573 (JP, A) JP-A-1-309467 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H04N 1/46-1/64 H04N 1/40-1/409

Claims (1)

(57) [Claims] 1. A color reproducing section for generating chromatic image processing data corresponding to a plurality of recording colors from a color reading signal, and a single color reproducing section for generating achromatic image processing data from the color reading signal. A color image processing apparatus comprising: a first color classification unit that classifies the color read signal into an intermediate color and a chromatic color, and generates intermediate color and chromatic color codes, respectively; And an intermediate color classified by the first color classifying means into an achromatic color and a chromatic color in accordance with a result of the discrimination by the image determining means, and generate a code of an achromatic color and a code of a chromatic color respectively. And a code generated by the color reproduction unit when the code generated by the first and second color classification means is a chromatic color code. Selects and outputs the data, when achromatic code color image processing apparatus, characterized in that it comprises an image processing switching means for selecting and outputting data generated by the monochromatic color reproduction unit.