JP2696902B2 - Color image processing equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is used in digital color copiers, facsimile machines, etc., which read an original image of an original with a solid-state image sensor (CCD) and reproduce the image with a laser printer or the like. In particular, the present invention relates to a color image processing apparatus capable of realizing high-precision image reproduction with relatively simple hardware.

[Conventional technology]

In magazines and transaction documents, binary images such as characters and halftone images such as photographs and prints are mixed. The edge part is detected for a document having an image having such a different property,
A method is known in which an edge portion is subjected to edge enhancement processing, and the other portion is subjected to intermediate generation such as dithering (hereinafter, referred to as A method) (Japanese Patent Laid-Open No. 157167/1986). FIG. 18 shows the structure of the method A, in which an edge detector a and an edge enhancer b are used.
And a smoothing device c. Edge detector a
Obtains an edge signal by binarizing an input signal, outputs the edge signal to a gamma converter e, performs nonlinear processing on the gamma converter e, and outputs the nonlinear signal to a mixer d. The mixer d mixes the edge emphasizing signal and the smoothing signal with the edge signal from the gamma converter e and outputs it to the recording device.

On the other hand, a method of identifying areas having different properties and performing a predetermined process based on the identification information (hereinafter, referred to as a B method) is also known. (JP-A-58-3374). The B method is a method of obtaining the maximum value and the minimum value of the grayscale value in a block, detecting the density gradient of the document based on the difference between them, and identifying the binary image or the halftone image.

Further, as shown in FIG. 19, a processing means f having a binarization circuit, a multiplexer (MUX), and a dither processing circuit for input signals of each color of r, g, and b;
A device including a synthesizer g that generates a new one-color synthesized signal by superimposing and averaging g and b, an edge detection circuit h that performs edge detection on the synthesized signal, and an identification circuit i that performs region identification. (Hereinafter referred to as C device) has also been developed.

[Problems to be solved by the invention]

However, the method A has a problem that the color characters are reproduced in a cloudy state and the black characters are not reproduced in perfect black and are affected by color shift. The former is originally intended to enhance a color component unnecessary for a color character together with a necessary color component, and the latter is also intended to enhance a color component other than a black component.

On the other hand, the 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 edge detection processing and area identification processing in a number proportional to the number of color separation signals or to perform the processing in parallel.
This is because the processing speed becomes slow.

Further, in the device C shown in FIG. 19, the color signals r, g, b
The primary colors of C, M, and Y, which are complementary colors of C, M, and Y, cannot be sufficiently contrasted, so that edge detection is difficult to be performed, and there is a problem that character quality is degraded.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a color image processing apparatus which prevents turbidity of color characters and deterioration of black character reproduction, and performs high-quality image reproduction with relatively simple hardware.

[Means for solving the problem]

According to a first aspect of the present invention, a plurality of color materials for processing an input color signal and recording an image based on the input color signal on a recording material are provided. A color image processing device that outputs a plurality of image signals, wherein edge detection means for detecting an edge portion from the input color signal; and, based on color information of the input color signal, the plurality of color materials. Selecting means for selecting a color component to be emphasized from the corresponding color components; and the plurality of image signals in which the color component selected by the selecting means is emphasized with respect to an edge portion detected by the edge detecting means. And a color image processing apparatus comprising:

According to a second aspect of the present invention, in order to realize the above-described object, a plurality of color materials for processing an input color signal and recording an image based on the input color signal on a recording material are provided. A color image processing device that outputs a corresponding plurality of image signals, wherein: edge detection means for detecting an edge portion from the input color signal; and the plurality of color materials based on color information of the input color signal. Selecting means for selecting a color component to be de-emphasized from the color components corresponding to the plurality of color components, and the plurality of color components selected by the selecting means for the edge portion detected by the edge detecting means. And an output unit that outputs the image signal.

Further, in order to achieve the above-mentioned object, the present invention provides a method of processing a plurality of image signals corresponding to a plurality of color materials for processing an input color signal and recording an image based on the input color signal on a recording material. A color image processing apparatus that outputs an edge part from the input color signal; and a color component corresponding to the plurality of color materials based on color information of the input color signal. Selecting means for selecting a color component to be erased, and outputting means for outputting the plurality of image signals in which the color component selected by the selecting means is erased, for an edge portion detected by the edge detecting means. And a color image processing apparatus characterized by having the following.

In the first to third features of the present invention described above, "color information of a color signal" is referred to as "hue" in the following embodiments.

〔Example〕

Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.

FIG. 1 is a cross-sectional view showing the configuration of a digital color copying machine 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 1 includes a lamp 2 for irradiating a document on a transparent document table 50 with light, reflection mirrors 3 and 4 arranged so that reflection surfaces face each other and reflecting light from the document, and a mirror 3.
And a dichroic prism 10 for guiding the converged light to the solid-state imaging device 6. The solid-state imaging device 6 separates the received light into R (red), G (green), and B (blue) signals at the same time and reads the signals. The image processing device 20 performs a color correction process on the R, G, and B signals obtained by the image input device 1 as described later,
C (cyan), m (magenta), and y (yellow), which are complementary colors of R, G, and B, by performing predetermined image processing such as filtering processing, density conversion processing, editing processing, and halftone generation processing
And k (black) image data are output to the image output device 30 as 1-bit binary data. Image output device 30
Is a laser oscillator that oscillates a light beam modulated according to c, m, y, k binary image data from the image processing device 20
It has a lens 31, a lens 32 for focusing this light beam, and a rotating polygon mirror 33 for diffusing the focused light beam in the scanning direction. Here, the rotating polygon mirror 33 is driven by the scanner motor 33a and rotates at a constant speed, and scans the laser beam perpendicularly to the rotation direction of the photosensitive drum. Photosensitive drum 34
Around the cyan developing device 38a, the magenta developing device 38b, the yellow developing device 38c, the black developing device 38d, and the charging corotron 3.
7. A cleaner 39 for removing the toner remaining on the photosensitive drum 34 after the transfer is provided. These developing units 38a, 3
8b, 38c, 38d, the charging trocolon 37 and the cleaner 39 are controlled by a control device 60 described later. Further, a transfer drum 35 is provided at a transfer section 34a of the photosensitive drum 34, and recording paper is supplied from a paper feed tray 36 to between them. Reference numeral 40 denotes a transport belt for receiving the transferred recording paper, and a fixing device 41 is provided downstream of the transport belt 40. The control device 60 is provided with an input interface 60a to which a sensor signal from various sensors in the copying machine and a console signal from a console for performing a scanning command are input.
A ROM 60b that stores a processing program for an input signal input to the input interface 60a, a CPU 60c that performs predetermined processing based on the program of the ROM 60b, a RAM 60d that stores data and the like, and the image output device 30. Developer 38
It has an output interface 60e for outputting control signals to a, 38b, 38c, 38d, charging trocolon 37, cleaner 39 and the like.

FIG. 2 is a block diagram of the image processing apparatus 20, which includes a color correction circuit 201, an under color removal circuit 202, and a selector circuit 203.
, A 4-line buffer memory 204, a smoothing circuit 205, a mixer 206, a tone adjustment circuit 207, an edge detection circuit 208, a gamma converter 209, and a hue detection circuit 210
And a delay circuit 211. The color correction circuit 201 performs unnecessary absorption of the C (cyan), M (magenta), and Y (yellow) color materials, which are complementary colors, from the B, G, and R signals read out by color separation by the image input device 1. Remove ingredients. The under color removal circuit 202 calculates y, m,
In addition to generating c data, k data is separately generated to reproduce high-density K (black) that cannot be reproduced by three color materials of Y, M, and C or to enhance the texture. Selector circuit 203
Is input with a development color signal representing the color of the color material under development, and selects only one signal from the y, m, c, and k signals based on the development color signal. The reason for providing the under-color removal circuit 202 and the selector circuit 203 in the previous stage of the processing is that the processing that requires operation between different color signals and the spatial processing in the same color are separated, and the This is because the processing with a large number of signals is executed as early as possible so that the required number of signals is unified at an early stage, thereby reducing the hardware scale. Thus, when the same document is scanned four times by the image input device 1, the same processing is repeated four times for the signals up to the under color removal circuit 202, but only one signal is selected by the selector circuit 203. In the processing after the selector circuit 203, the calculation between the different color signals becomes unnecessary. Therefore, after the under color removal circuit 202, y, m, c,
k data can be selected and processed. The four-line buffer memory 204 delays the signal selected by the selector circuit 203 to provide a smoothing circuit 205 and an edge detection circuit 2
Output to 08. The smoothing circuit 205 performs averaging by filtering the input signal. As a result, noise, halftone dots, and the like are removed. Meanwhile, the edge detection circuit
A filter 208 cuts noise and components corresponding to halftone dots of the input signal by filtering, and extracts only frequency components corresponding to edges in the image to obtain edge signals. FIG. 3A shows an example of a filter coefficient matrix having a matrix size of 5 × 5 used in the smoothing circuit 205. Also,
FIG. 3B shows an example of a 5 × 5 filter coefficient matrix used in the edge detection circuit 208. The frequency characteristic of the filter of the smoothing circuit 205 is shown in the characteristic curve a of FIG. 4, and the frequency characteristic of the filter of the edge detection circuit 208 is shown in the characteristic curve b of FIG. The gamma converter 209 non-linearly converts the edge signal from the edge detection circuit 208,
The mixer 206 mixes the non-linearly converted signal and the smoothed signal averaged by the smoothing circuit 205 at an appropriate ratio and outputs the result to the tone adjustment circuit 207. By this mixing, the graininess and smoothness of the halftone portion and the sharpness of the edge portion can be reproduced. The present invention includes a hue detection circuit 210 in addition to the above configuration. The hue detection circuit 210 detects the hue of the image information, determines which of the Y, M, C, and K color materials to be used for development is necessary, and determines a gamma converter via a delay circuit 211. The judgment signal is output to 209. Therefore, the hue detection circuit 210 is provided between the under color removal circuit 202 and the gamma converter 209.

FIG. 5 is a block diagram showing the configuration of the hue detection circuit 210. The four comparators 2101 to which the y signal, the m signal, the c signal, and the k signal from the under color removal circuit 209 are input, respectively.
And a ROM 2102 to which the signal from the comparator 2101 and the development color signal (d signal) are input. The comparator 2101 binarizes the signals by comparing predetermined fixed thresholds ty, tm, tc, and tk with the y signal, m signal, c signal, and k signal from the under color removal circuit 202, respectively. ROM2102 is each comparator 2101
, And a 2-bit development color signal representing the color of the color material under development are used as an input address, and the required development color for the hue detected from these signals is 6 bits. Judge whether the material is or not and output. FIG. 6 shows an example of a detection table used for performing hue detection in the ROM 2102. In the figure, w (white), y, m,
Each column of r, g, b, and k indicates a signal binarized by the comparator 2101, and each column of Y, M, C, and K indicates a developed color signal. A determination signal of “1” is given to the development color material necessary for the hue detected from the detection table, and a determination signal of “0” is given to the hue detected by the hue via the delay circuit 211. Output to converter 209. Note that the delay circuit 211 is provided for performing timing adjustment with the filtering process in the smoothing circuit 205 and the edge detection circuit 208. In the gamma converter 209, the input judgment signal is “1”.
In the case of, the necessary color is determined and a predetermined conversion process is performed. Seventh
FIG. 9A shows the conversion processing of the gamma converter 209 in the case of the determination signal “1”, or performs any one of the processings, and outputs this edge emphasis signal. On the other hand, when the input determination signal is “0”, it is determined that the color is unnecessary, and the edge enhancement signal is output as “0”. FIG. 7B shows the output state of the signal in this case. And this gamma converter 209
In the mixer 206 to which the signal of (1) is input, only the necessary color component is emphasized in the case of “1”, and unnecessary components are not emphasized in the case of “0”. For this reason, 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 diagram illustrating the above processing in the case where red-based characters are input by using a graph. The under color removal circuit 202 obtains component data as shown in FIG. Here, in general, the saturation of a red-based character is increased by the y signal and the m signal, and the saturation of the C signal, which is a complementary color, is low, and color turbidity occurs. That is, the red-based characters require Y and M color materials, while the C color material does not. When the hue detection circuit 210 is not provided, the gamma conversion shown in FIG. 7A is applied to all the signals regardless of the hue, so that the y signal and the m signal, which are the necessary colors of the red characters, are emphasized. At the same time, the C signal, which is an unnecessary color, is also emphasized at the same rate. For this reason, the saturation of the character to be developed is reduced, and the color character becomes cloudy. On the other hand, in the present embodiment including the hue detection circuit 210, since the y signal and the m signal become “1” according to the detection table shown in FIG. 6, these are emphasized.
Since the c signal becomes “0”, this enhancement is not performed. Therefore, as shown in FIG. 3C, only the necessary color components are emphasized, so that the reproducibility of characters is improved without lowering the saturation. (D) shows a case where unnecessary color components are removed, which is realized by an embodiment described later.

FIG. 9 shows a process when a black character is input. FIG. 7A shows data after processing by the under color removal circuit 202. FIG. 9B shows processing data when the hue detection circuit 210 is not provided. Since all the color components are emphasized at the same ratio, not only deterioration of the characters due to thickening of the characters or poor transfer occurs, but also the output color. Reproducibility is deteriorated because color edges are generated due to misregistration between plates. On the other hand, in the present embodiment, only the k component is emphasized as shown in FIG. FIG. 6D shows the case of the embodiment described later.

FIG. 10 shows another embodiment of the present invention, in which a hue detecting circuit 21 is provided.
The hue detection circuit 210 and the mixer 206 are connected so that the signal of 0 is directly input to the mixer 206. The edge detection signal from the edge detection circuit 208 is input to the mixer 206 via the gamma converter 209. In such a structure, the mixer 206 determines whether or not the pixel being scanned is an edge portion based on the edge emphasis signal from the gamma converter 209. as a result,
If it is an edge portion and the determination signal from the hue detection circuit 210 is “1”, the edge enhancement signal is added to the smoothing signal from the smoothing circuit 205 and output.
On the other hand, when the determination signal from the hue detection circuit 210 is “0”, both the edge enhancement signal and the smoothing signal are output as 0. Therefore, only the 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. In the case of red characters, as shown in FIG. 8D, the c signal, which is an unnecessary color component, is deleted, while the y signal, which is a necessary color component, is emphasized. On the other hand, in a black character, as shown in FIG. 9 (d), all the color components other than the k signal are deleted, and the k signal is emphasized. Therefore, the reproducibility of color characters and black characters is improved. In particular, in the case of black characters, the reproducibility is good. In this embodiment, since the edge emphasis signal is output as "0" by the gamma converter 209 except for the edge portion, only the smoothing signal is output from the mixer 206, and the halftone portion is smoothly reproduced.

Note that the filter matrix size, the coefficient matrix and the frequency characteristics, the conversion processing of the gamma converter, and the detection table of the hue detection circuit in the above embodiment may be appropriately determined depending on the application.
It can be changed.

FIG. 11 is a block diagram of still another embodiment of the present invention, which is applied to, for example, a color copying machine having the system configuration shown in FIG. In FIG. 12, the image input apparatus 1 converts an original image into R, G, and B images at a resolution of, for example, 16 dots / mm.
Read the signal after color separation. The image memory 70 has a memory for storing original image information of 8 bits per pixel for R, G, and B for one page of A3 paper. The control device 60 performs signal control of the entire device. The image output device 30 includes Y, M,
Using a C and K powder toner, development is performed on recording paper at a resolution of, for example, 400 dots / inch. The image input device 1, the control device 60, and the image output device 30 can have the same configurations as those shown in FIG. As shown in FIG. 11, the image processing device 20 includes a processing unit 80 and a hue detection unit 200. The processing means 80 includes a binarizing circuit 81 for binarizing each of the color signals r, g, and b separated by the image input device 1, and a multiplexer (not shown) for selecting the binarized data and the multi-valued data. MUX) 82
And a dither processing circuit 83 for performing dither processing, one for each color signal. In such a processing means 80, the r, g, and b signals from the image input device 1 are branched into two paths, either directly or after being stored in the image memory 70. In the route r,
The g and b signals are input to the binarization circuit 81, compared with a predetermined fixed threshold, and binarized to either 0 or 255 which is the maximum value of 8 bits according to the magnitude relation.
This binarized signal is input to the MUX 82. On the other hand, in the path, the r, g, and b signals are input to each MUX 82 as multi-value data. Each MUX 82 selects either binary data or multi-valued data according to the determination result of the area identification circuit 215 described later. For example, if the original image information is a character area, the binarized data of the path is selected, and if the original image information is a halftone area, multi-valued data of the path is selected. The dither processing circuit 83 performs dither processing on such selected data to obtain a character area,
High quality reproduction of each halftone area is performed. The hue detection means 200 includes a hue detection circuit 212 and a multiplexer (MUX) 213.
And an edge detection circuit 214 and an area identification circuit 215. The hue detection circuit 212 detects the hue of each of the signals r, g, and b. The MUX 213 selects one of the detected r, g, and b signals and outputs the selected signal to the edge detection circuit 214. As shown in FIG. 13, the hue detection circuit 212 has a comparator 2121 corresponding to each of the r, g, and b color signals, and the comparator 2121 converts the respective color signals into predetermined specific threshold values t ₁ , t compared to _2, t _3, to detect the hue. The comparator 2121 stores a table for selecting one of r, g, and b such that the complementary color or the contrast becomes maximum for the detected r ', g', and b 'signals. Fig. 14 shows this table.
An example is shown, and input signals r ', g', b 'are W, C, M,
B, Y, G, R, and K colors are allocated. Based on this table, the correction signals (r, g, and h) of the hue data detected by the hue detection circuit 212 as shown in the bottom column.
b) is selected, and the MUX 213 outputs any one of the selected r, g, and b signals to the edge detection circuit 214. The edge detection circuit 214 detects an edge component 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 having such a frequency characteristic, there is no influence of a halftone component of 133 lines or more. FIG. 16 shows an example of a coefficient matrix of this filter, which has a matrix size of 7 × 7 and is point-symmetric with respect to the center point. Area identification circuit
Reference numeral 215 compares the edge signal e obtained by the filtering process in the edge detection circuit 214 with a preset threshold value t to identify an area as a character area or a halftone area. Therefore, the area identification circuit 215 has a comparison circuit 2151 as shown in FIG. 17, and the comparison circuit 2151 has the following (1)
Region identification is performed based on the expression.

e ≧ t (1) In this equation (1), if e ≧ t, it is determined that the area is a character area.
If <t, it is determined that the region is a halftone region. In the case of the character area, the MUX 82 of the processing means 80 selects a binary threshold signal of the path, and in the case of the halftone area, issues a command for selecting the multi-level signal of the path. Performs dither processing. Therefore, in this embodiment, the hue detection circuit 212 identifies the hue of the input signal, and the MUX 213 determines R,
Since the signal which can obtain the most contrast among G and B is used as a color signal, high-precision edge detection is possible even for an input signal such as a color character, and a high-quality image can be recorded. .

〔The invention's effect〕

As described above, according to the color image processing apparatus of the first aspect of the present invention, a color component to be emphasized is selected based on color information of an input color signal, and a color component selected at a detected edge portion is selected. Is emphasized and the image is output, so that the reproducibility of color characters and black characters can be improved. According to the color image processing apparatus of the second aspect of the present invention, a non-emphasized color component is selected based on the color information of the input color signal, and the selected color component at the detected edge portion is deemphasized. Since the image is output in this way, the same effect as that of the first feature can be obtained. Further, according to the color image processing apparatus of the third aspect of the present invention, a color component to be erased is selected based on the color information of the input color signal, and the selected color component is erased at the detected edge portion. Since an image is output, reproducibility of black characters is particularly improved.

[Brief description of the drawings]

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 one embodiment of the present invention, and FIGS. 3 (a) and 3 (b) are smoothing circuits and edges. FIG. 4 is a diagram showing a coefficient matrix of a filter used in a detection circuit, FIG. 4 is a characteristic diagram showing frequency characteristics of a filter used in a smoothing circuit and an edge detection circuit, FIG. 5 is a block diagram showing a hue detection circuit, 6 is a diagram showing a detection table for performing hue detection, FIGS. 7 (a) and 7 (b) are characteristic diagrams showing processes of a gamma converter, FIG. 8 is a diagram showing processes for red characters, and FIG. Is 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 still another embodiment, FIG.
FIG. 13 is a block diagram showing a color copying machine to which FIG. 11 is applied, FIG. 13 is a block diagram showing a hue detection circuit thereof, and FIG.
FIG. 15 is a diagram showing a control table, FIG. 15 is a characteristic diagram showing a frequency characteristic of a filter of the edge detection circuit, FIG. 16 is a diagram showing a coefficient matrix of the filter of the edge detection circuit, and FIG. FIG. 18 is a block diagram showing a circuit configuration, FIG. 18 is a block diagram showing a conventional device, and FIG. 19 is a block diagram showing another conventional device. DESCRIPTION OF SYMBOLS 1... Image input device 2... Lamp 3 4 Reflector mirror 5 Lens 6. Solid-state image sensor 10. Dichroic prism 20. Image processing device 30. Image output device 31 laser oscillator 32 lens 33 rotating polygon mirror 34 photosensitive drum 35 transfer drum 36 paper feed tray 38a cyan developing device 38b magenta developing device 38c yellow Developing device 38d: Black developing device 39: Cleaner 40: Transport belt 41: Fixing device, 50: Developing table 60: Control unit, 70: Image memory 80: Processing means, 81: 2 Value conversion circuit 82 Multiplexer 83 Dither processing circuit 200 Hue detection means 201 Color correction circuit 202 Under color removal circuit 203 Selector circuit 204 Four-line buffer memory 205 Smoothing circuit 206 …… Mixer 207 …… Tone adjustment circuit 208 ... edge detection circuit 209 ...... gamma converter 210 ...... hue detection circuit 211 ...... delay circuit 212 ...... hue detection circuit 213 ...... multiplexer 214 ...... edge detection circuit 215 ...... area identification circuit 2101,2121 ...... comparator

Claims (3)

(57) [Claims] 1. A color image processing apparatus for processing an input color signal and outputting a plurality of image signals corresponding to a plurality of color materials for recording an image based on the input color signal on a recording material. Edge detecting means for detecting an edge portion from the input color signal; and a color component to be emphasized among color components corresponding to the plurality of color materials, based on color information of the input color signal. Selecting means for selecting, and outputting means for outputting the plurality of image signals in which the color component selected by the selecting means is emphasized for an edge portion detected by the edge detecting means. Color image processing device. 2. A color image processing apparatus for processing an input color signal and outputting a plurality of image signals corresponding to a plurality of color materials for recording an image based on the input color signal on a recording material. Edge detecting means for detecting an edge portion from the input color signal; and a color component to be de-emphasized among the color components corresponding to the plurality of color materials based on color information of the input color signal. And output means for outputting the plurality of image signals obtained by de-emphasizing the color component selected by the selection means for an edge portion detected by the edge detection means. Characteristic color image processing device. 3. A color image processing apparatus for processing an input color signal and outputting a plurality of image signals corresponding to a plurality of color materials for recording an image based on the input color signal on a recording material. Edge detecting means for detecting an edge portion from the input color signal; and selecting a color component to be deleted from the color components corresponding to the plurality of color materials based on color information of the input color signal. And output means for outputting the plurality of image signals from which the color components selected by the selection means have been deleted, for the edge portion detected by the edge detection means. Color image processing device.