JPH0346868A - Color image processor - Google Patents

Abstract

PURPOSE:To enable image processing of high-definition suitable to the kind of an image by discriminating a mixed image of a character image and a gradational image with primary color image signals and performing color reproduction processing differently between the character image and gradational image according to the decision result. CONSTITUTION:A digital image signal after density conversion is supplied to a decision circuit 21 constituting a mixed image discriminating means, its image discrimination output is supplied to a color reproduction part 17 and color reproduction tables for the character image and gradational image are used selectively according to the image contents. The color reproduction table for the character image is stored with such data that importance is attached to the clear reproduction of characters, etc., and colors which are fine and thin coloring and an achromatic color are reproduced forcibly in black and white and the color reproduction table for the gradational image is stored with such data that importance is attached to the faithful reproduction of an original image and the colors which are thin and thick coloring and close to the achromatic color are represented as they are as much as possible. Therefore, even if the character image and gradational images are both present on the same document, the image output quality is maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a color image processing device suitable for a digital copying machine. The present invention relates to a color image processing device that has excellent performance and is easy to connect with external equipment.

(Background of the Invention) Generally, in an electrophotographic digital copying machine,
The image information (original image) of the original is divided into micropixels of approximately several tens of microns, the electric signal (image signal) corresponding to the density of each pixel is converted into a digital signal, and the digital image signal is processed internally. After conversion, the image is output to a recording device such as a laser, and a copy image is obtained through an electrophotographic process.

In such digital copying apparatuses, internal signal processing is often changed depending on the type of input image.

For example, when the input image is a so-called general document such as a book or a letter, the density of the characters and the color level of the background are not so important, and it is desired that the characters be reproduced sharply.

Therefore, in the case of a printer whose output is only binary (on and off), the input image information is binarized at a certain fixed level to reproduce the image. In the case of a printer capable of multi-value recording according to density, character images can be reproduced clearly by controlling the reproduction time and black output with emphasis.

On the other hand, when the input image has so-called gradation, such as a photographic image, reproduction of intermediate tones is important, and the purpose of processing is different from when the input image is centered on text.

For example, in the case of a binary printer, a pseudo halftone image is formed using a known method such as a dither method or a density matrix method, and the image is reproduced using the output. Even in the case of multilevel printers, the output characteristics are often designed to emphasize the reproduction of halftones.

Furthermore, especially in these processes, halftone drawings often used in newspapers and the like require special processing. A halftone drawing is made up of many dots, and when viewed microscopically, it does not have any midtone areas and resembles a letter drawing.

However, since the original purpose of halftone drawings is to reproduce pseudo-halftones using dots of different sizes, it is often easier to see the output if it is reproduced as a gradation image similar to that of a photographic image. Furthermore, a certain number of lines among halftone dots is very close to the sampling pitch used in the image reading system and writing system of digital copying devices that are currently widely used.

For example, when the sampling pinch is 16 dat/mm, the number of mesh lines is quite close to the sampling pitch when the number of mesh lines is 1331 ine/1 nch.

Under such conditions, an aliasing error occurs in sampling, which appears as a so-called moiré image, resulting in a significant deterioration in image quality. Moiré appears particularly clearly when the original image is binarized, but even if pseudo-intermediate representations such as dithering are used, the frequency of appearance will only decrease and will not disappear completely.

As a countermeasure to this problem, it is possible to reduce the high frequency components of the original image to reduce interference with the sampling pitch. Specifically, it is sufficient to perform smoothing using surrounding pixels.

As described above, by switching the coefficients for image processing and multi-value conversion according to the characteristics of each image, the output image can be maintained in high quality. Normally, these switching is performed by an operator or the like by switching the processing mode depending on the document.

However, when copying a document such as a pamphlet that has different features such as text and photos in one image,
If text and image processing is set, the reproducibility of photographic parts will be lost, making it impossible to obtain a copy that is satisfactory for both parties. Therefore, the overall copy quality is not good.

To solve this problem, it is sufficient to determine whether the input image information is a character image or a gradation image, and to switch the processing based on the determination result.

Conventionally, the so-called block-by-block discrimination method, which divides the original image into several small blocks and switches processing based on the discrimination results for each block, has been used as a means of discriminating whether it is a character image or a gradation image. "Binarization processing method for manuscripts containing a mixture of value images and grayscale images" (IEICE Journal ■0[,
1f37-B No. 7 (1,984) pp.

781-788) and a so-called pixel-by-pixel discrimination method in which processing is performed on a pixel-by-pixel basis even if information on surrounding pixels is taken in. There is.

(Problem to be Solved by the Invention) Among the above-mentioned discrimination methods, a discrimination method that discriminates each block includes, for example, examining the dispersion of density within the block of interest, and if the dispersion is large, determining that it is a character stroke. There are methods. According to this discrimination method, if an incorrect discrimination is made, all of the blocks will be processed incorrectly, resulting in a severe deterioration in quality.

Furthermore, in general, block-by-block discrimination requires more memory to temporarily store image data than pixel-by-pixel discrimination, is expensive, and has the disadvantage that its signal processing is also complicated.

On the other hand, although the pixel-by-pixel discrimination method has advantages such as fewer side effects of misclassification and requires relatively less memory, this method is difficult to distinguish between clearly printed characters and photographs. It was something.

Therefore, no process has yet been proposed that automatically distinguishes even characters with shading, such as halftone drawings and general handwritten characters, and applies optimal image processing to each character.

An image reading device equipped with this type of image processing device (
There was no system that took into consideration the transmission and reception of data when connecting a scanner) with an external printer, external computer for image processing, etc.

The present invention has been made in view of the above-mentioned problems, and its purpose is to accurately discriminate between character and one-gradation images, and to perform high-quality color image processing suitable for the characteristics of each image. The present invention is intended to realize a color image processing device that can be easily connected to an external image processing device and processed by the external image processing device.

(Means for Solving the Problems) The present invention solves the above-mentioned problems by using a color reproduction table for generating color signals and color codes for image recording from primary color image signals obtained by scanning a document. A color reproduction means is provided for both gradation image and gradation image, and performs color reproduction using one of the color reproduction tables based on a discrimination signal given from the outside, and a color reproduction means is provided for both gradation image and gradation image of the original image for each primary color image signal. and a mixed image discriminating means for discriminating between characters and images, and an interface means for outputting the color code and color signal from the color reproduction means and the discrimination result from the mixed image discriminating means to the outside. It is something to do.

(Function) In the color image processing device of the present invention, mixed image discrimination is performed using primary color image signals. Then, based on this determination result, the character image color reproduction table or the gradation image color reproduction table is selectively used to execute color reproduction processing. The color reproduction processing results and mixed image discrimination results are output to the outside.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of the present invention. The outline of the color image processing apparatus will be explained with reference to FIG.

In this figure, 1 is the original, 2 and 3 are dichroic mirrors for separating the image information (optical image) of the original into R, G, and B optical images, and 4.5° and 6 are R, respectively.
, G, and B optical images to obtain primary color image signals; A
/D converter, 10.11.12 are R, G, respectively
A shading correction circuit for correcting the shading of the digital image signal of B, 1B and 14.15 are R, respectively.
, G, and B digital image signals, 16 is a density conversion circuit that converts the density of R, G, and B digital image signals, and 17 is a density conversion circuit that converts R, G, and B digital image signals into Y. , M.

This is a color reproduction section for converting (color reproduction) into C and K color signals for image recording and outputting a color code indicating the type of chromatic color or achromatic color. The color reproduction section 17 has a plurality of independent color reproduction tables therein, and one of them is selected according to an image discrimination signal from the outside to perform color reproduction processing. That is, the color reproduction unit 17 sets color reproduction tables for character images and gradation images as Y, M,
C.

Each K has one. 18 is Y from the color reproduction section 17;

a selector for selectively passing the M, C, digital color signals in accordance with image formation; 19 a multi-value conversion circuit for performing multi-value processing on the digital color signals and converting them into multi-value data; 2;
0 is an interface unit that outputs digital color signals, color codes, and mixed image discrimination results to the outside. 21 is discrimination of character image and 1 gradation image from G image signal (mixed image discrimination)
A discriminating circuit 22 receives the multilevel data and determines Y,
M.

This printer unit (image output device) outputs a color image as a hard copy by sequentially overlapping toner images of each color. Incidentally, the part surrounded by the broken line in FIG. 1 is the part constituting the scanner.

The operation of the apparatus of this embodiment will be explained below.

Color image information (optical image) of original document 1 is separated into three color separated images (optical images) by two dichroic mirrors 2 and 3. In this example, the image is separated into a red R color separation image, a green G color separation image, and a blue B color separation image. Therefore, the cutoff wavelength of dichroic mirror 2 is 450 to 520
A dichroic mirror 3 having a cutoff wavelength of 550 to 620 nm is used. As a result, the green component becomes the transmitted light, the blue component becomes the first reflected light, and the red component becomes the second reflected light.

The color separated images of red R1, green G, and blue B are supplied to image reading means, for example, CCD sensors 4, 5.6, and primary color image signals of only the red component R1, the green component G, and the blue component B are output from each of them. .

Primary color image signals R, G, and B are sent to A/D converters 7 and 8°9.
A predetermined number of bits, in this example 8
It is converted into a bit digital image signal. And A
Shading correction is performed simultaneously with /D conversion.

The shading-corrected digital image signal is processed by gate circuits 13, 14, and 15 to extract only the signal bones of the width of the maximum document size, and then subjected to density conversion in accordance with human visual characteristics. When the maximum document width to be handled is A3 size, the gate signal is used as a size signal generated by a timing signal generating means (not shown) of the system.

Here, if the density-converted R, G, and B digital image signals are VR, VG, and VB, respectively, these digital image signals VR, VG, and VB are supplied to the color reproduction section 17 and used for the printer unit 20. It is converted into Y, M, and C color signals.

In this example, the recording colors for image formation in the printer unit 22 are Y (yellow) and 1M (magenta).

A case is illustrated in which the colors are C (cyan) and K (black).

The color reproduction unit 17 is a color reproduction table (lookup table) configured in ROM, and includes a character image color reproduction table suitable for processing character images and a gradation image suitable for processing gradation images. A color reproduction table is provided for each of Y, M, and C. That is, in this embodiment, the color reproduction section 17 (R
The storage area of OM) is divided into two blocks, and each block contains data for color reproduction, Y, M,
C.

It is stored for each K.

The color reproduction table for text and drawings focuses on clearly reproducing text, etc., and stores data that forces delicate pale hues and colors close to achromatic colors to be expressed in white/black. This is a reproduction table.

In addition, the color reproduction table for gradation painting is a color reproduction table that stores data that focuses on faithfully reproducing the original image, and expresses subtle pale hues and colors close to achromatic colors as much as possible. .

Selection of these color reproduction tables is based on an image discrimination signal from the discrimination circuit 21. That is, the image discrimination signal is given as the most significant bit of the address of the ROM forming the color reproduction table, and thereby the color reproduction table for gradation images and character images is switched. That is, when a character image and a gradation image are mixed in one document image, the color reproduction table selected by the image discrimination signal performs color reproduction processing suitable for each image. This color reproduction process uses digital image signals VR2VG and VB as input,
It outputs Y, M, C, and K color signals (degree data). The one-color reproduction process for generating the image discrimination signal will be described later.

Y generated by color reproduction processing in this way.

The respective density data for M and C are supplied to the selector 18. A scan code (a color code for forming a toner image in the printer unit 20) is given to the selector 18 by a CPU (not shown), and density data according to this scan code is sequentially and selectively passed through. Then, this density data is subjected to multi-value processing in the printer unit 22 so as to be suitable for image formation. The multi-value data for which multi-value processing has been completed in this manner is supplied to the printer unit 22, where image formation is performed. In this printer unit 22, toner images of four colors Y, M, and C are sequentially superimposed, so image reading to color reproduction is also performed four times.

Further, the digital image signal after density conversion is supplied to a discrimination circuit 21 constituting a mixed side discrimination means.

The image discrimination output thus obtained (in this example, 1 and cut data) is supplied to the color reproduction section 17. That is, the above-mentioned color reproduction table for character images and gradation images is selectively used according to the image content based on the image discrimination output.

In other words, when it is determined that it is a character stroke, the determination signal is
0'' and the character image color reproduction table in the color reproduction section 17 is selected, and when it is determined that it is a gradation image, the determination signal becomes ``1'' and the gradation image in the color reproduction section 17 is selected. The color reproduction table used for this purpose will be selected.

Therefore, even if character images and gradation images coexist on the same document, the image output quality is maintained because character image processing and gradation image processing are selected respectively.

Furthermore, digital color signals (6 bits each), color code (2 bits), and image discrimination output (1 bit) for Y, M, and C are supplied to the interface section 20 and output to the outside as parallel data. . Note that the data output to the outside includes timing signals, synchronization signals, etc., which are not shown.

Therefore, in normal operation, an image is formed on the document read by the scanner inside the dashed line using the printer unit 22 that is integrated with the scanner, but if necessary, an external printer and image processing are performed via the interface unit 20. It may also be connected to a computer etc. In this case, the signal output to the outside includes an image discrimination signal in addition to the color code and color signal (density signal). different processes).

Here, the discrimination circuit 21 will be explained in detail.

The above-mentioned discrimination circuit 21 is composed of first and second discrimination means 30 and 40, as shown in FIG.

That is, the first discrimination means 30 is a means for roughly discriminating an input image into a character image and a gradation image to obtain a first image discrimination output. On the other hand, the second discriminating means 40 to which the first image discriminating output is supplied re-discriminating the image discriminating output of the gradation image included in the first image discriminating output that corresponds to the character image in particular. This is means for obtaining a second image discrimination output related to the image and the gradation image.

Here, the first determining means 30 will be explained in detail.

The first determining means 30 uses a low-pass filter 31 for the pixel of interest and a low-pass output for the pixel of interest to a reference value RE.
It is comprised of a comparator 32 that compares with F, and a level determination circuit 33 that further determines the level of the comparison and output regarding the pixel of interest.

The purpose of the low-pass filter 31 is to reduce the high frequency components of the input image signal, thereby making it possible to roughly distinguish between character images and gradation images.

When the high frequency components of the input image information are reduced, when the input image is a photographic image or a halftone line drawing, the density of the pixel of interest is dispersed to each point, so that every pixel exhibits a certain density Na or higher.

As an example of a halftone image, as shown in FIG. 3(A), the difference in density between dots and non-dots clearly appears.

When this is passed through a low-pass filter 31 to reduce high-frequency components, a signal corresponding to the repeating pitch of the mesh pattern (a signal approximating a sine wave) is generated at a DC level Na' above a certain level Na, as shown in FIG. ) are obtained by superimposing them.

On the other hand, even when characters and line drawings are passed through the low-pass filter 31, since they have many background parts, regions with a density lower than that of Na remain.

Therefore, the comparator 32 determines the density of the pixel of interest using a reference value REF having a predetermined level that is less than or equal to Na.

This reference value REF needs to be set to a value that is considerably lower than the threshold value used when binarizing character strokes and slightly higher than the background level. This is because if it is too low, it becomes indistinguishable from the background (ground) texture level, and if it is too high, when the halftone line drawing is filtered and dispersed, there will be some that are lower than this reference value REF, resulting in erroneous classification.

Therefore, it is preferable to set the reference position REF after detecting the background level in combination with a so-called automatic density adjustment function that determines the background level from the prior reading and viewing of the original.

In the case of a photographic image or halftone line side, the comparison output is "1",
In the case of character drawings or line drawings, it is "0".

Next, in the level determination circuit 33, the comparison output obtained from the comparator 32 is re-determined.

In this re-judgment process, a check window of a certain size is set up around the pixel of interest, and the pixel of interest is determined only when all pixels existing within the window are equal to or greater than the above-mentioned reference value REF. It is judged as a style drawing.

Through this processing, the density is widely dispersed in the case of halftone lines, so that the image is determined as a gradation image.

On the other hand, even if character images are dispersed by the background, etc., a value lower than the reference value remains, and since a portion of the check window is covered by this portion, the pixel of interest is determined to be a character image as expected.

FIG. 4 shows an example of the low-pass filter 31, and in this example, a 3×3 convolution filter configured in a cross shape is used.

The convolution filter used as a low-pass filter is a process that returns a pixel of interest a and its surrounding pixels to the original pixel of interest by applying a certain weight c. is simply added, divided by 5, and averaged.

Therefore, the filtered output a' of the pixel of interest a is a' +1- (1,15)*Σ(C+1* a +
1).

Here, cl is 1 only for the pixel of interest and the four pixels to the left and right below, and is 0 for the other diagonal components.

Here, the reason why the low-pass filter 31 is expressed as a cross-shaped type with a weight of 1 is adopted as follows.

First, regarding the size of the filter, the larger the filter size, the more dispersed the results, and the more coarse dots can be handled. However, since the overall density level at that time gradually decreases, it becomes difficult to determine the threshold value, and misjudgment becomes more likely to occur. Additionally, as the filter size increases, hardware constraints also increase.

For this reason, in this example, the size is set to 3×3, taking into consideration hardware constraints.

The reason why the filter shape is made into a cross shape will be explained with reference to FIG.

In this figure, the center portion is a mesh dot, and the diagonal lines are a mesh pattern. Also, a collection of small dots is the minimum unit of reading.

Generally, in the case of the mesh line side, the mesh lines are often arranged in a 45 degree direction. In the case of the cross-shaped filter shown in FIG. 5(A), the filtering result spreads nicely into a diamond shape along the mesh structure as shown in FIG. 5(CB). Therefore, no matter which pixel the window is placed on, there is no extremely low part.
As expected, it is determined to be on the mesh line side.

On the other hand, if a filter that disperses in an X-shape (the 6th
If Figure 6(A)) is used, as shown in Figure 6(B), when the mesh lines are fine, the density in a certain area will be averaged to the dots of the adjacent mesh line, and the density will be quite high. On the other hand, the filter action does not reach the valleys of the X-shape, so the density in these valleys remains low.

Therefore, if a part of the window falls over this valley, this part falls below the reference value, and the pixel of interest is incorrectly determined to be not a gradation image. This can occur regardless of the shape of the window.

From the above, it can be seen that a cross shape is appropriate for the filter shape.

Further, in order to distribute the dots evenly, it is desirable that the coefficients of each filter are all 1 (ie, equal).

It is expected that this low-pass filter 31- will be able to effectively disperse even the mesh lines, which are actually quite coarse.

In addition, if the mesh line is too coarse or the dots are extremely small (
In other words, if the image is thin (thin), the filter will not be able to cover it and there is a possibility that it will be mistakenly identified as a text area.

Since the dots that can cause such misjudgment are always independent minute dots, if necessary, an independent dot detection circuit can be provided as post-processing after the low-pass filter 31, thereby further improving the mesh rain detection ability.

This post-processing involves, for example, checking the surrounding pixels of a pixel that has been determined to be black, and if they are all white, determining that they are independent dots.
Means such as halftone drawing processing can be employed.

The filter mentioned here has a 3 x 3 cross shape in order to maximize the effect with the minimum amount of hardware, but it is important that it has enough resolution to resolve the difference between the density after dispersion by the filter and the background density For example, a filter with a larger structure can also be used.

In that case, mesh line dots can be smoothed more efficiently than when the size is 3×3. In this case, in order to achieve more uniform smoothing, a cross-shaped filter is used that extends from the pixel of interest by n pixels (n is an integer of 1 or more) in the vertical and horizontal directions, and the total number of filters is 4n+
A filter having a structure that returns an average value of one pixel to the pixel of interest is preferable.

Here, a specific example of the low-pass filter 31 will be explained with reference to FIG.

A digital image signal is sent to a cascade-connected latch circuit 31a for IH (H indicates a horizontal scanning period).

31b, and the original digital image signal and 1H and 2
The digital image signal delayed by H is sent to the amplifier 31c;
3 line memory 31 via 31 d, 31 e
f at the same time.

Among the digital image signals for 3 lines obtained from the 3-line memory 31f, the digital image signal of the n-1 line is processed by a pair of latch circuits 31g with a delay time τ of 1 pixel.
, 31h and then supplied to the adder 31n.

Similarly, n-line digital image signals are sent to the adder 31 by passing through three latch circuits 31i, 31j, and 31k, respectively.
n. Then, the digital image signal obtained on the n+1 line is sent to a pair of latch circuits 31jh and 31m.
The signal is then supplied to the adder 31n.

In this way, by using a plurality of latch circuits, all the digital image signals of each pixel shown in FIG. 6 can be obtained simultaneously. The fully added digital image signals are reduced to 115 by the coefficient unit 31o at the subsequent stage. Coefficient unit 3
As 1o, RoM or the like can be used.

Next, the level determination circuit 33 will be explained. As the level determination circuit 33, a cross-shaped 7×7 check window is used as shown in FIG. This window extends by three pixels in each of the vertical and horizontal directions, and if all 12 pixels in total including the pixel of interest all are larger (darker) than the above-mentioned reference value REF, the pixel of interest is determined to be a gradation image.

The reason why the window size is set to 7×7 will be explained with reference to FIG.

Generally, characters and line drawings often run parallel to the paper surface (that is, parallel to main scanning or sub-scanning). At this time, if the outline of the boundary is not clearly processed as a character part, it will become blurred and difficult to see if it is subjected to gradation processing, for example.

As shown in the figure, if the area starts from the n-th pixel,
Due to the action of the low-pass filter 31, the density is dispersed up to n-1 pixels. If the window size is 7.times.7, and the arm of the window is up to n-2 pixels, there will be a portion lower than the reference value, and the pixel of interest will be determined to be a character image.

In other words, up to n+1 pixel rows are determined to be character parts. That is, in a boundary portion (outline portion), up to two pixels inside the boundary portion are reliably determined to be character portions.

Due to the effect of this window, a clear image can be obtained without blurring the outline at the border.

As is clear from the description of FIG. 9, the window size used in the level determination circuit 33 is preferably larger than the window size of the low-pass filter 31. If the size of the low-pass filter 31 is assumed to extend by n pixels in the vertical and horizontal directions, the window for level determination has a structure in which an integer m is larger than n and extends by m pixels in the upper, lower, left and right directions.

FIG. 10 shows a specific configuration example of the level determination circuit 33.

Since the level determination circuit 33 also has a window configuration, it is basically the same as the filter configuration shown in FIG. However, since the input to the level determination circuit 33 is the determination output of the low-pass filter 31, it is a 1-bit signal indicating whether it is a character image or a gradation image.

However, the window used in the level judgment circuit 33 is 7
Since the size is 7×7, it is necessary to delay by 7 lines and 7 pixels. Therefore, the number of latch circuits used for IH delay and one pixel delay increases accordingly.

33a to 33f are latch circuits for IH delay;
g is a memory for 7 lines. and 33h to 33j
, 33r to 33t are latch circuits for delaying by four pixels.

Although these latch circuits each consist of four latch circuits connected in series, they are shown as one latch circuit for convenience in the drawings. 33 to 33q indicate latch circuits for one pixel.

These seven lines of digital image signals are each delayed by a predetermined pixel by a plurality of latch circuits, and
By deriving the output from each predetermined position, digital image signals of each pixel corresponding to the window shown in FIG. 8 can be obtained simultaneously in time.

Therefore, when the corresponding digital image signals are logically multiplied in the AND circuit 33u, an image discrimination output in which the pixel of interest becomes "1" is obtained at the output terminal only when the density level of all the pixels is equal to or higher than the reference value.

In this way, in the first discriminating means 30, the character stroke group,
A first image discrimination output corresponding to both the photographic image and the halftone line group is obtained.

By the way, under certain conditions, a character image may be recognized as a character image or as a gradation image. .

For example, as shown in FIG. 11 (A), when the input image is the character image "Sono", if this is passed through the low-pass filter 31, it will be output as shown in FIG. 11 (B,). . In other words, it can be seen that when a character becomes smaller than a certain level, the inside of the character becomes considerably blurred due to the action of the low-pass filter.

At this time, if there is a pixel of interest inside the character, and all of the pixels in its vicinity exceed the reference density due to this filter effect, the pixel of interest will be processed as a pixel of a gradation image. As a result, even if an image is recognized as a character image as shown in FIG. 12, for example, there are parts inside the character that are erroneously determined to be gradation images.

In this way, the inside of a small character may be misidentified as a gradation image, and as a result, the quality of the character may deteriorate significantly.

Here, since the part of the real halftone line side and photographic image that is judged to be a gradation image occupies a certain area, it is actually not possible for such gradation images to be scattered in a partial area. Not in. In other words, when a discrimination result in which gradation images are scattered for a very small area is obtained, there are actually no gradation images for each small area, so the discrimination result is can be determined to be a misjudgment.

Therefore, as shown in FIG. 2, a second determining means 40 is provided. This second discrimination means 40 re-discriminates the image as a gradation image included in the above-mentioned character image or a character image.

In order to re-recognize a gradation image included in a character image as a character image, it is sufficient to check the gradation plane discrimination area (and determine whether it occupies a certain size).

To do this, image data of a certain area for the pixel of interest is stored in memory 1. Then, the table or area of the closed area of the gradation image discrimination part can be calculated.

In principle, it is necessary to store image data in both the main scanning direction and the sub-scanning direction in order to execute this discrimination process, but in the example described below, due to hardware constraints, it is not possible to implement it only in the main scanning direction. There is.

As a result, it is sufficient that the memory has a maximum capacity of one bit indicating whether the image is a character image or a gradation image and one line of memory. Furthermore, experiments have revealed that the correction effect is sufficient even with only main scanning.

FIG. 13 shows a second discriminating means 40 that achieves such processing.
An example is shown below.

The first image discrimination output output from the first discrimination means 30 is supplied to the input terminal.

As mentioned above, the first image discrimination output is rlJ when it is a gradation image.
The output is rOJ when it is a character stroke.

The length of the gradation image of the first image discrimination output is counted by a counter 40a. Therefore, the counter 40a is set at "1" and reset at "0", and is counted up in synchronization with the dot clock CK. The counter output a is compared in a comparator 40b with a reference value associated with reference length (FIG. 14A).

L is preferably about 2 mm.

The pulse comparison output that exceeds the reference value S becomes "1", and at this time a single control pulse p is output from the pulse generating means 40d (FIG. 14(B)).

On the other hand, the dot clock CK is also supplied to the address counter 40e to form a horizontal address, and the address data is latched in the latch circuit 40f.

The latch pulse is formed based on the rising edge of the first image discrimination output.

40g indicates this rising edge detection circuit.

One of the address data of the address counter 40e and the rising address data latched by the latch circuit 40f is selected by the address selector 40h by the control pulse p. In this example, it is assumed that the latched address data is selected when the control pulse p is obtained. Address data selected by address selector 40h is supplied to first line memory 40i.

A control pulse p is supplied to the first line memory 40i as a write enable pulse. Therefore, when the control pulse p is obtained, data "1" at a predetermined level is written at the latched address in synchronization with the rising point 0 of the first image discrimination output.

On the other hand, in the second line memory 40j, the first image discrimination output is written to the address obtained from the address counter 40e in synchronization with the dot clock CK (see FIG. 14).
C)).

Data is read from the line memories 40i and 40j as shown in FIG. That is, in the next first line, data is simultaneously read from the line memories 40i and 40j (FIGS. 15(A) to 15(C)).

The output of the line memory 40i passes through a NAND circuit 40k
It is supplied to the set terminal S of the 8-type flip-flop 4On. Similarly, each output of the line memories 40i and 40j is supplied to an input negation type NAND circuit 401), and the output is further passed through a NAND circuit 40m to a flip-flop 401).
It is supplied to the reset terminal R that is turned on.

As a result, a second image discrimination output as shown in FIG. 15(D) is obtained at the output terminal 400.

When the second discrimination means 40 is configured in this way, as shown in FIG. 12, even when a gradation image is recognized in the first image discrimination output, its length in the main scanning direction is a predetermined length L. Only when this is the case, an image discrimination output "1" indicating a gradation image can be set as the final image discrimination output.

Therefore, if the length is less than the predetermined length, even if it is determined to be a gradation image, it will ultimately be re-identified as a character image (FIG. 15).

As a result of this configuration, it becomes possible to discriminate and process input documents with precision and efficiency that could not be obtained in the past.

In addition, even character information with low contrast, such as handwritten characters, can be clearly determined to be a character part because it is compared with background background information, and misidentification within characters is eliminated, so the input image can be correctly determined and processed.

In the above example, the judgment was made by evaluating only the length of both gradation parts, but in the same way, a correction circuit that judges an extremely short character part as a misclassification is also installed, and the judgment results can be used in practice. You can modify it to get closer.

Next, an example of a mechanism of a digital copying apparatus to which the image processing apparatus of this embodiment is applied will be described with reference to FIG. 16.

Here, the description will be made assuming that the copying machine uses a color dry development method. In this example, two-component non-contact development and reversal development are employed. That is, the transfer drum used in conventional color image formation is not used, and the images are superimposed on the electrophotographic photosensitive drum that forms the image. Also,
In the example below, in order to reduce the size of the device, yellow Y, magenta M
.

An example will be described in which a four-color image of cyan C and black is developed by rotating the drum four times, and after development, transfer is performed once and transferred to recording paper such as plain paper.

The document reading section A is driven by turning on a copy button (not shown) on the operation section of the copying machine.

The original 101 on the original table 128 is then optically scanned by the optical system.

This optical system includes a carriage 132 provided with a light source 129 such as a halogen lamp, a reflecting mirror 131, and a movable mirror unit 1 provided with mirrors 133 and 133'.
Consists of 34.

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

Optical information (image information) obtained by irradiating the original 101 with the light source 129 is transmitted to the reflecting mirror 131. Mirror 133,1
33' to an optical information conversion unit 137.

A standard white plate is provided on the back side of the left end of the document table (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 CCD 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 13 lenses, and separated into blue optical information and yellow optical information by the dichroic mirror 102 provided in the prism 140 described above. Furthermore, dichroic mirror 103
The yellow optical information is color-separated into red optical information and green optical information.

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 a signal processing system, recording image signals of each color are output to the writing section B.

As described above, the signal processing system includes various signal processing circuits such as an A/D converter, a color reproduction table, and a multi-value processing section.

The writing section B (printer unit 22) has a deflector 141. As this deflector 141, in addition to a galvanometer mirror, a rotating polygon mirror, or the like, a deflector made of an optical deflector using crystal or the like may be used.

The laser beam modulated by the color signal passes through this deflector 14.
1 for deflection scanning.

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 member 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 replenishment for the developing unit is done by the CPU for system control.
A toner replenishing means (not shown) is controlled based on a command signal from a toner replenishing means (not shown), so that toner is replenished when necessary. 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. .

Then, by using a developing device 144 containing magenta toner, this is developed to form a magenta toner image.

Needless to say, 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 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 monochrome 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.

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 power source, 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 digital copying machine, but the present invention is not limited to this. That is, it goes without saying that it can be connected to various types of devices that process character images and gradation images.

Further, in the above-described embodiment, image discrimination was performed for G, but the present invention is not limited to this.

For example, it is also possible to perform image discrimination using all of R, G, and B, and then supply the images to the color reproduction section 17 and the interface section 20 after taking a majority vote.

Furthermore, all the image discrimination results of R, G, and B are sent to the color reproduction section 17.
It is also possible to supply it to the interface section 20.

(Effects of the Invention) As described in detail above, in the present invention, images of mixed surfaces in which character images (achromatic color character images, chromatic color character images) and gradation images are mixed are discriminated using primary color image signals. Based on this result, different color reproduction processing is performed for character images and gradation images. That is, when it is determined that the image is a character image, color reproduction processing is performed that emphasizes the background and character colors, and when it is determined that it is a gradation image, color reproduction processing is performed that emphasizes intermediate gradations.

Since the image discrimination results are also output when outputting the color reproduction processing results to the outside, it becomes easy to perform further image processing with external equipment.

Therefore, it is possible to perform high-quality image processing suitable for each type of image, and it is also possible to use a color image processing device that can be easily connected to and processed by an external image processing device. It can be realized.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing the electrical configuration of an embodiment of the present invention;
Fig. 2 is a block diagram showing the configuration of the discrimination circuit, Fig. 3 is an explanatory diagram for explaining the operation of the low-pass filter, Fig. 4 is a block diagram showing the structure of the low-pass filter, and Figs. 5 and 6 are An explanatory diagram explaining the characteristics of the low-pass filter, FIG. 7 is a configuration diagram showing the electrical configuration of the low-pass filter, FIG. 8 is a configuration diagram showing the configuration of the level determination circuit, and FIG. 9 explains the characteristics of the level determination circuit. 10 is a configuration diagram showing the electrical configuration of the level determination circuit, FIG. 1-1 is an explanatory diagram of the filter effect, FIG. A configuration diagram showing the configuration of the second determining means,
14 and 15 are explanatory diagrams of the operation of the second determining means, and FIG. 16 is a configuration diagram showing the mechanical configuration of a copying machine to which the color image processing apparatus of this embodiment is applied. 1... Original 2.3... Dichroic mirror 4.5.6... CCD 7, 8. 9... A/D converter 10.11.12... Shading correction circuit 13.
14.15... Gate 16... Density conversion circuit 17... Color reproduction section 8.
...Selector O...Interface section 1-...Discrimination circuit 2...Printer unit i.19...Multi-value processing section

Claims (1)

[Scope of Claims] A color reproduction table for generating color signals and color codes for image recording from primary color image signals obtained by scanning a document is provided for both character images and gradation images; a color reproduction means for performing color reproduction using one of the color reproduction tables according to a discrimination signal given from the color reproduction table; a mixed image discrimination means for discriminating the original image into a gradation image and a character image for each primary color image signal; A color image processing apparatus comprising: an interface means for outputting a color code and a color signal from the color reproduction means and a discrimination result from the mixed image discrimination means to the outside.