JPH01264847A - Color image processing apparatus - Google Patents

Abstract

PURPOSE:To regenerate a high quality image by preventing the turbidity of a color character or the deterioration in the reproduction of a black character, by detecting not only the hue of an original image but also the edge part thereof and controlling an edge signal on the basis of a hue signal. CONSTITUTION:A gamma converter 209 converts the edge signal from an edge detection circuit 208 non-linearily and a mixer 206 judges whether a pixel during scanning is an edge part, on the basis of the edge emphasis signal from the gamma converter 209. As a result, when said pixel is the edge part and the judge signal from a hue detection circuit 210 is '1', the edge emphasis signal is added to the smoothing signal from a smoothing circuit 205 to be outputted. When the judge signal from the hue detection circuit 210 is '0', both of the edge emphasis signal and the smoothing signal are outputted as '0'. Therefore, a c-signal being an unnecessary color component is erased in a red character and a y-signal being a necessary color component is emphasized and all of color components other than a k-signal are erased in a black character to emphasize the k-signal.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is used in digital color copying machines, facsimile machines, etc. that read the original image of a document with a solid-state image sensor (CCD) and reproduce the image with a laser printer or the like. The present invention relates to a color image processing device, and particularly relates to a color image processing device that can realize highly accurate image reproduction with relatively simple hardware.

[Conventional technology]

Magazines and transaction documents contain a mixture of binary images such as characters and halftone images such as photographs and prints.

Edges are detected in documents with images with different characteristics, and edge enhancement processing is performed on the edges.
Other parts are generated using intermediate generation methods such as dithering (hereinafter referred to as
Method A) is known (Japanese Unexamined Patent Publication No. 1571-1988).
No. 67). FIG. 18 shows the configuration of this method A, which includes an edge detector a, an edge enhancer and a smoother C. The edge detector a obtains an edge signal by binarizing the input signal, outputs this edge signal to a gamma converter e, performs nonlinear processing thereon, and outputs the edge signal to a mixer d. The mixer d mixes the edge emphasis signal and the smoothing signal using the edge signal from the gamma converter e and outputs the mixed signal to the recording device.

On the other hand, a method (hereinafter referred to as method B) of identifying areas with different properties and performing predetermined processing based on identification information is also known (Japanese Patent Laid-Open No. 58-3374). This method B is a method in which the maximum and minimum grayscale values within a block are determined, and the density gradient of the document is detected based on the difference between these values to identify whether it is a binary image or a halftone image.

Furthermore, as shown in FIG. 19, a processing means r having a binarization circuit, a multiplexer (MUX), and a dither processing circuit for each input signal of r, g, and b, and each input signal r
, g, and b to generate a new composite signal of one color, an edge detection circuit that performs edge detection on this composite signal, and an identification circuit i that performs region identification. A device (hereinafter referred to as C device) has also been developed.

[Problem to be solved by the invention]

However, method A has the problem that color characters are reproduced in a muddy state, and black characters are not reproduced as completely black and are affected by color shift.

The former originally occurs to emphasize color components unnecessary for color characters together with necessary color components, and the latter also occurs to emphasize color components other than the black component.

On the other hand, method B cannot be applied to color image data for the following reasons. That is, in color image data, there are many color separation signals, and it is necessary to repeat or perform a number of edge detection processes and area identification processes in parallel to the number of color separation i-words, which increases the hardware scale. death,
This is because the processing speed becomes slower.

Furthermore, in the C device shown in FIG. 19, color signals r, g, b
Because the primary color characters of C, M, and Y, which are complementary colors, do not have sufficient contrast, edge detection is difficult and the quality of the characters deteriorates.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a color image processing apparatus that prevents muddiness of color characters and deterioration of reproduction of black characters, and reproduces high-quality images using relatively simple hardware.

[Means to solve the problem]

In order to achieve the above-mentioned objects, the present invention provides a color image processing device that detects the hue of an original image, detects the edge portion of the original image, and controls the edge signal based on the hue signal.

That is, the present invention provides an apparatus that separates and reads an original image into a plurality of color signals, performs image processing on these color signals, and records the images.
It is characterized by having the following means.

(1) Hue detection means This is means for detecting the hue of the original image. Hue detection is performed by comparing input color signals of at least three colors with a darkness value for each color.

The hue signal obtained by comparison is then used to control the edge signal.

(2) Edge detection means This is means for detecting edge portions of the original image.

The edge detection means has a filter of a predetermined matrix size, and detects an edge portion by filtering the input color signal. Then, the detected edge signal is output.

(3) Means for controlling the edge signal based on the hue signal obtained by the hue detection means This control selects the color material necessary for image reproduction from the hue signal and emphasizes only the necessary color components or This is done by erasing the necessary color components. Further, this is performed by selecting a complementary color or a signal that has the maximum contrast with respect to the obtained hue signal.

[Operation] With the above configuration, necessary color components are emphasized, unnecessary color components are erased, or contrast is emphasized,
The reproduced image becomes clearer.

[Example] Hereinafter, an example of the present invention will be specifically described with reference to the drawings.

FIG. 1 is a sectional view showing the configuration of a digital color copier to which the present invention is applied, and includes an image input device 1, an image processing device 20, an image output device 30, and a control device 60. . The image input device l includes a lamp 2 that irradiates light onto an original on a transparent original platen 50, a reflective mirror 3.4 arranged with reflective surfaces facing each other to reflect light from the original, and a mirror 3.4 that reflects light from the original. It includes a lens 5 that focuses reflected light, and a guichroic prism 10 that guides this focused light to a solid-state image sensor 6. The solid-state image sensor 6 simultaneously separates the received light into R (red), G (green), and B (blue) signals and reads them. The image processing device 20 performs predetermined image processing such as color correction processing, filtering processing, density conversion processing, editing processing, and halftone generation processing on the R, G, and B signals obtained by the image input device 1, as will be described later. teRSG
The complementary colors of SB are C (cyan), m (magenta), and y (
Yellow) and k (black) image data are output to the image output device 30 as 1-bit binary data. The image output device 30 receives c, m, y,
It has a laser oscillator 31 that oscillates a light beam modulated according to binary image data, a lens 32 that focuses the light beam, and a rotating polygon mirror 33 that diffuses the focused light beam in the scanning direction. are doing. Here, the rotating polygon mirror 33
is driven by a scanner motor 33a and rotates at a constant speed, and scans the laser beam perpendicularly to the rotational direction of the photosensitive drum 34. Around the photosensitive drum 34 are a cyan developer 38a, a magenta developer 38b, and a yellow developer 38.
c, a black developing device 38d, a charging corotron 37, and a cleaner 39 for removing toner remaining on the photosensitive drum 34 after transfer. These developing devices 38a, 3
8b, 38C, 38d, charging trocolon 37, and cleaner 39 are controlled by a control device 60, which will be described later.

Further, the transfer drum 35 is attached to the transfer portion 34a of the photosensitive drum 34.
are arranged, and the recording paper is fed between them from the paper feed tray 36.

A transport belt 40 receives the transferred recording paper, and a fixing device 41 is provided downstream of the transport belt 40.

The control device 60 includes an input interface 60a into which sensor signals from various sensors in the copying machine and console signals from a console that issues scanning commands are input, and a ROM 60b in which a processing program for the input signals input to the human power interface 60a is stored. , a CPU 60c that performs predetermined processing based on the program in the ROM 60b, a RAM 60d that stores data, etc., a control signal to the developing devices 38a, 38b, 38c, 38d of the image output device 30, the charging trolley 37, the cleaner 39, etc. It has an output interface 60e that outputs.

FIG. 2 is a block diagram of the image processing device 20, which includes a color correction row 201, an undercolor removal circuit 202, a selector circuit 203, a 4-line puffer memory 204, a smoothing circuit 205, a mixer 206, Tone adjustment circuit 207, edge detection circuit 208, and gamma converter 2
09, a hue detection circuit 210, and a delay circuit 211. The color correction circuit 201 extracts unnecessary absorption components of the complementary colors C (cyan), M (magenta), and Y (yellow) from the BSG and R signals that are separated and read by the image input device 1. remove. Undercolor removal circuit 202
generates y, m, and c data regarding these color materials, and also generates high-density K (
(black) Separately generate data to enhance reproduction or texture. The selector circuit 203 receives a developed color signal representing the color of the coloring material being developed, and selects only one system of signals from the y, m, and c signals based on this developed color signal. In this way, the under color removal circuit 202 and the selector circuit 203
The reason for providing this at the pre-processing stage is to separate processing that requires computation between signals of different colors from spatial processing for the same color and white, and to perform processing that requires a large number of signals for computation as early as possible. This is to reduce the number of necessary signals to one at an early stage, thereby reducing the hardware scale. As a result, when the same document is scanned four times by the image input device 1, the same processing is repeated for the signals up to the undercolor removal circuit 202 all four times.
Since only one system of signals is selected by the selector circuit 203, calculations between different color signals are not required in the processing after the selector circuit 203. Therefore, after the undercolor removal circuit 202, data can be selected and processed in y, m, and c according to the original image of the image output device 30. 4-line buffer memory 204 outputs the signal selected by selector circuit 203 to smoothing circuit 205 and edge detection circuit 208 without delay. The smoothing circuit 205 filters and averages the input signal. This removes noise, halftone dots, etc. On the other hand, the edge detection circuit 20 filters out components corresponding to noise and halftone dots in the input signal, extracts only frequency components corresponding to edges in the image, and uses it as an edge signal. FIG. 3(a) shows an example of a filter coefficient matrix with a matrix size of 5×5 used in the smoothing circuit 205. Further, FIG. 3 [Ex.] shows an example of a filter coefficient matrix with a matrix size of 5×5 used in the edge detection circuit 208. In addition, the frequency characteristics of the filter of the smoothing circuit 205 are shown in the characteristic curve a in FIG.
The frequency characteristics of the No. 08 filter are shown in the same characteristic curve isb.

The gamma converter 209 nonlinearly converts the edge signal from the edge detection circuit 208, and the mixer 206 mixes this nonlinearly converted signal with the smoothing signal averaged by the smoothing circuit 205 at an appropriate ratio to adjust the tone. Output to circuit 207. By this mixture, it is possible to reproduce the graininess and smoothness of the midtone part and the sharpness of the edge part. The present invention includes a hue detection circuit 210 in addition to the above configuration. The hue detection circuit 210 detects the hue of image information, determines which coloring material is required among the Y, M, and C coloring materials used for development, and sends the delay circuit 21
A determination signal is output to the gamma converter 209 via 1.

For this reason, the hue detection circuit 210 is provided between the undercolor removal circuit 202 and the gamma converter 209.

FIG. 5 is a block diagram showing the configuration of the hue detection circuit 210, which includes four comparators 21 to which the y signal, m signal, and C signal from the undercolor removal circuit 209 are input, respectively.
01, and a ROM 2102 into which the signals from these comparators 2101 and the developed color signal (d signal) are input. Comparator 2101 uses a predetermined fixed threshold t
By comparing y, tm, tc, and tk with the y signal, m signal, C signal, and k signal from the under color removal circuit 202,
Value. The ROM 2102 stores 2 data from each comparator 2101.
The input address is a 6-bit combination of the value signal and the 2-bit developed color signal representing the color of the color material being developed.
Based on these signals, it is determined whether or not the developing color material is necessary for the detected hue, and the result is output. An example of the detection table used to detect the hue of this ROM 2102 is shown in the sixth section.
As shown in the figure. In the same figure, W (white), y, ml
The columns r, , gXb, . . . indicate signals binarized by the comparator 2101, and the columns Y, M, C, . . . indicate developed color signals. For the hue detected from this detection table, a determination signal of "1" is sent in the case of a necessary developing colorant, and a determination signal of "0" in the case of an unnecessary developing colorant is sent to the gamma through the delay circuit 211. Output to converter 209. Note that the delay circuit 2
11 is a smoothing circuit 205 and an edge detection circuit 208
This is provided to adjust the timing with the filtering process. If the input determination signal is "1", the gamma converter 209 determines that the color is a necessary color and performs a predetermined conversion process. FIG. 7(a) shows the conversion process of the gamma converter 209 when the determination signal is "1".
This edge-enhanced signal is output by performing one of the following processes. On the other hand, if the input determination signal is "0", it is determined that the color is unnecessary and the edge emphasis signal is output as 0. FIG. 7(b) shows the output state of the signal in this case. A mixer 2 to which the signal of this gamma converter 209 is input
In 06, only the necessary color components are emphasized when it is "1", and when it is "0"
In this case, do not emphasize unnecessary components.

Therefore, the difference between the necessary color component and the unnecessary color component becomes large, and the development of the edge portion becomes clear.

FIG. 8 is a graph explaining the above processing when a red character is input.

The undercolor removal circuit 202 obtains component data as shown in FIG. Here, red-based characters generally have high saturation due to the Y signal and m signal, and have low saturation with the C signal, which is a complementary color, resulting in color muddiness. In other words, the red letters are Y,
While the M coloring material is a necessary color, the C coloring material is an unnecessary color. If the hue detection circuit 210 is not provided, the gamma conversion shown in FIG. 7(a) is applied to all signals regardless of hue, so the y and m signals, which are necessary colors for red characters, are emphasized. At the same time, C, which is an unnecessary color,
The signal is also emphasized at the same rate. As a result, the saturation of the characters to be developed decreases, and the colored characters become embellished.

On the other hand, in this embodiment including the hue detection circuit 210, the y signal and the m signal become "1" according to the detection table shown in FIG. 6, so these are emphasized and the C signal becomes "1".
This emphasis is not performed because the result is "O". Therefore, the same figure (
As shown in C), since only the necessary color components are emphasized, the reproducibility of characters is improved without causing a decrease in saturation. Also,
(d) is a case in which unnecessary color components are removed, and is realized by an embodiment described later.

FIG. 9 shows the processing when a black character is input. Same figure (
a) is data after processing by the undercolor removal circuit 202; Figure (b) shows processing data when the hue detection circuit 210 is not included, and since all color components are emphasized at the same rate, thick characters not only cause deterioration due to poor transfer, but also cause the output color to deteriorate. Reproducibility deteriorates because color edges occur due to misalignment between plates. On the other hand, in this embodiment, only the k component is emphasized, as shown in FIG. FIG. 3(d) shows the case of an embodiment described later.

FIG. 10 shows another embodiment of the present invention, in which the hue detection circuit 2
The hue detection circuit 210 and the mixer 206 are connected so that the 10 signals are directly input to the mixer 206. An edge detection signal from an edge detection circuit 208 is input to the mixer 206 via a gamma converter 209. In such a structure, the mixer 206 uses the edge emphasis signal from the gamma converter 209 to determine whether the pixel being scanned is an edge portion. As a result, if it is an edge portion and the determination signal from the hue detection circuit 210 is "1", the edge emphasis signal is added to the smoothing signal from the smoothing circuit 205 and output. On the other hand, the hue detection circuit 21
If the determination signal from 0 is "0", both the edge emphasis signal and the smoothing signal are output as O. Therefore, only necessary color components are emphasized, and unnecessary color components are completely erased. FIG. 8(d) and FIG. 9(d) show the processing according to this embodiment. Figure 8 (d) for red characters
), the C signal, which is an unnecessary color component, is erased, while the Y signal, which is a necessary color component, is emphasized. On the other hand, for black characters, all color components other than the signal are erased and the k signal is emphasized, as shown in FIG. 9(d). Therefore, the reproducibility of color characters and black characters is improved. In particular, in the case of black characters, the reproducibility is good.

In addition, in this embodiment, the gamma converter 2 is used except for the edge portion.
Since the edge emphasis signal is output as "0" in step 09, only the smoothing signal is output from the mixer 206, and the halftone portion is smoothly reproduced.

In addition, the matrix size, coefficient matrix and frequency characteristics of the filter in the above embodiment, the conversion process of the gamma converter,
The detection table of the hue detection circuit can be changed as appropriate depending on the application.

FIG. 11 is a block diagram of still another embodiment of the present invention, which is applied, for example, to a color copying machine having the system configuration shown in FIG. 12. In FIG. 12, the image input device 1 separates the original image into three signals, R, G, and B, and reads the original image at a resolution of, for example, 16 dots/mm. The image memory 70 has a memory for storing original image information of 8 bits per pixel for one page of A3 paper for each of R, G, and B. A control device 60 performs signal control of the entire device. The image output device 30 uses powder toner of 75M, C,
For example, development is performed on recording paper at a resolution of 400 do't/1 nch.

The image input device 1, the control device 60, and the image output device 30 can have the same configuration as shown in FIG. 1, so the explanation thereof will be omitted. As shown in FIG. 11, the image processing device 20 includes a processing means 80 and a hue detection means 2.
0o. The processing means 80 includes a binarization circuit 81 that binarizes each of the color signals r, g, and b separated by the image input device 1, and a multiplexer ( MUX) 82 and a dither processing circuit 83 for performing dither processing, one of which is provided for each color signal. In such a processing means 80, each of the r, g, and b signals from the image input device l is stored directly or in the image memory 70, and then
, ■ are branched into two routes.

In path (3), the rSg and b signals are input to the binarization circuit 81, where they are compared with a predetermined fixed darkness value and binarized into either O or 255, which is the maximum value of 8 bits, depending on the magnitude relationship. This binary signal is input to MUX82! On the other hand, in path (2), the rsgsk) signal is input to each MUX 82 as multi-value data. Each MUX 82 selects either binary data or multi-value data based on the determination result of an area identification circuit 215, which will be described later. For example, if the original image information is a character area, the binary data of the path ■ is selected, and if it is a halftone area, the multivalued data of the path ■ is selected. The dither processing circuit 83 performs dither processing on such selected data to reproduce each of the character area and the halftone area with high quality. The hue detection means 200 includes a hue detection circuit 212 and a multiplexer (MUX) 213.
, an edge detection circuit 214 , and an area identification circuit 215 . The hue detection circuit 212 detects the hue of each of the r, g, and b signals. MUX213 detects r, g,
The edge detection circuit 214 selects one of the b signals.
Output to. As shown in FIG. 13, the hue detection circuit 212 has a comparator 2121 corresponding to each color signal rlg and b, and the comparator 2121 compares each color signal with predetermined specific thresholds t1, 2, and t3. Compare and detect the hue. The comparator 2121 receives the detected r', g', b'
A table is stored that selects one signal among r and g'-b that has the maximum complementary color or contrast to the signal. FIG. 14 shows an example of this table, and input signals r', g', b' are input to W, C, M, B, Y, G, R.
It is designed to be divided into eight colors. Based on this table, the correction signal (r, g, b) of the hue data detected by the hue detection circuit 212 as shown in the bottom tank is selected, and the MUX 213 selects one of the selected r, g, b signals. One signal is output to the edge detection circuit 214.

Edge detection circuit 214 detects edge components based on the selected color signal.

FIG. 15 is a frequency characteristic diagram of a band-pass filter used in the edge detection circuit 214. By using a filter with such frequency characteristics, there is no influence from halftone dot components of 133 lines or more. Figure 16 shows an example of the coefficient matrix of this filter, and the matrix size is 7x7.
And, it is point symmetrical about the center point. The area identification circuit 215 compares the edge signal e obtained through the filtering process in the edge detection circuit 214 with a preset threshold t to identify whether the area is a character area or a halftone area. Therefore, the area identification circuit 215
As shown in FIG. 7, a comparison circuit 2151 is provided, and the comparison circuit 2151 performs area identification based on the following equation (1).

e≧t −−−−−−−−−−− (1) In this equation (1), if e≧, it is determined to be a character area, and if eat, it is determined to be a halftone area. Then, in the case of a character area, a command is issued to cause the MUX 82 of the processing means 80 to select the binary threshold signal of path (■), and in the case of a halftone area, to select the multivalue signal of path (■), and these signals are subjected to dither processing. A circuit 83 performs dither processing. Therefore, in this embodiment, the hue detection circuit 212 identifies the hue of the human signal and MUX2
Since 13 uses the signal that can obtain the highest contrast among R, G, and B as the color signal, it is possible to detect edges with high accuracy even for input signals such as colored characters, and it is possible to produce high-quality images. Can be recorded.

〔Effect of the invention〕

As explained above, since the present invention controls the edge signal of the edge/edge detection means based on the hue of the original image detected by the hue detection means, it is possible to prevent muddiness of colored characters and deterioration of reproduction of black characters. Moreover, high-quality image reproduction can be performed using simple hardware.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a digital color copying machine to which the present invention is applied, FIG. 2 is a block diagram showing an embodiment of the present invention, and FIGS. 3(a) and 3(b) are smoothing circuits and edges. Figure 4 is a diagram showing the coefficient matrix of the filter used in the detection circuit; Figure 4 is a characteristic diagram showing the frequency characteristics of the filter used in the smoothing circuit and edge detection circuit; Figure 5 is a block diagram showing the hue detection circuit; Figure 6 is a diagram showing a detection table for hue detection, Figure 7 (a) is a characteristic diagram showing the processing of the gamma converter, Figure 8 is a diagram showing the processing for red characters, and Figure 9 is a diagram showing the processing of the gamma converter. A diagram showing processing for black characters, FIG. 10 is a block diagram showing another embodiment of the present invention,
FIG. 11 is a block diagram showing yet another embodiment;
Figure 11 is a block diagram showing a color copying machine to which Figure 11 is applied, Figure 13 is a block diagram showing its hue detection circuit, Figure 14 is a diagram showing its control table, and Figure 15 is an edge detection circuit. FIG. 16 is a diagram showing the coefficient matrix of the filter of the edge detection circuit, FIG. 17 is a block diagram showing the configuration of the edge detection circuit,
FIG. 18 is a block diagram showing a conventional device, and FIG. 19 is a block diagram showing another conventional device. Explanation of symbols 1...-1111 Image input device 2--1--Lamp 3.4----------Reflection mirror 5-- ----------Lens 6...-1--1 Solid-state image sensor 10-1--Dichroic prism 20-------1 Image processing device 30---
-----------One image output device 31---------・-・・
-Laser oscillator 32-・-1111---Lens 3
3・-・-・-Rotating polygon mirror 3 t----------
-1 Photosensitive drum 35------Transfer drum 36--Paper feed tray 38 a-----1-
--Cyan developer 38 b--m=----Magenta developer 38 c--Yellow developer 38 d---Black developer 39- −−−−−−−−−−Cleaner 40・−・−−−−−−−−Transport belt 41
−m=−−・−−−Constant mounting 50−・−−−
---One developing table 60 --------- control section
70−・−・−・−Image memory 80−−−−−・−
-Processing means 81--Binarization circuit 82--Multiplexer 83-
−・−−−−−11−Dither processing circuit 200−−−−−
-----1.Hue detection means 201--------
---Color correction circuit 202-------Under color removal circuit 203------Selector circuit 204
-----------4 line buffer memory 205--
--- Smoothing circuit 206 --- Mixer 207 ------ Adjustment circuit 208
・----1------ Edge detection circuit 209----
-----------Gamma converter 210------
-One hue detection circuit 211---One delay circuit 212------One hue detection circuit 213---
-----------Multiplexer 214------
------One edge detection circuit 215------
-One area identification circuit 2101.2121------
--One comparator 3rd animal (0)
(b) Fig. 4 97 station 3Ij-Save Fig. 5 Briny angle oligochromatic it No. 6 Fig. 7 (?fu no Hi, , CX +g: $ 7%
/) t, IS Fig. 8 y m c k Fig. 9 mck 1/732 Fig. 15

Claims (3)

[Claims] (1) A color image processing device that separates and reads an original image into a plurality of color signals, performs image processing on the read color signals, and records the image, comprising: a hue detection means for detecting the hue of the original image; A color image processing device comprising: edge detection means for detecting an edge portion and outputting an edge signal; and control means for controlling the edge signal based on the hue signal obtained by the hue detection means. (2) The color image processing apparatus according to claim 1, wherein the control means performs control to emphasize necessary color components. (3) The color image processing apparatus according to claim 1, wherein the control means emphasizes necessary color components and removes unnecessary color components.