JPH0344271A - Color picture processing unit - Google Patents

Abstract

PURPOSE:To attain high quality picture processing suitable for each picture by applying color reproduction processing in which background color elimination ratio is increased when a picture is discriminated to be a character picture and applying color reproduction processing in which background color elimination ratio is decreased when a picture is discriminated to be a gradation picture. CONSTITUTION:A color reproducing means 17 is provided with a color reproduction section 17A with a high background color elimination ratio and a color reproduction section 17B with a low background color elimination ratio and uses selectively either the color reproduction section 17A with a high background color elimination ratio or the color reproduction section 17B with a low background color elimination ratio depending on the result of discrimination of a mixed picture discrimination means 21. Then the color reproduction processing suitable for the kind of the picture is applied by selecting either of the color reproduction tables based on the result of discrimination of the mixed picture discrimination means 21.

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, and more specifically, to a color image processing device suitable for a digital copying machine, and more specifically to a color image processing device that has excellent image reproducibility in both character and gradation images. The present invention relates to an image processing device.

(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 storage 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 manually generated image.

For example, when the human 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 image is reproduced by converting human image information into binary data at a certain fixed level. In the case of a printer capable of multi-value recording according to density, character images can be reproduced clearly by controlling the reproduction with emphasis on white and black output.

On the other hand, when the input image has so-called gradation, such as a photographic image, reproduction of intermediate tones becomes important, which is different from when the purpose of processing is mainly 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 pitch is 16 dat/am and the number of mesh lines is 13311 ne/1 nch, the number of mesh lines is quite close to the sampling pitch.

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 when pseudo-intermediate representation such as a dither method is used, the frequency of appearance only decreases and does 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 the operator himself 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 human 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 gray scale images'' (IEICE Journal VOL,
J67-B No. 7 (1984) pl).

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 incorporated, such as the technique described in Japanese Patent Laid-Open No. 104372/1982.

(Issue 8 to be solved by the invention) Among the above-mentioned discrimination means, a discrimination method for discriminating 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 ways to do this. According to this 111 alternative method, if a misclassification is made, all of the blocks will be processed incorrectly, which may seriously degrade the 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.

In particular, when reproducing a gradation image in full color, it is difficult to faithfully reproduce subtle color tones and colors close to achromatic colors to the original image. Furthermore, if emphasis is placed on reproducing color gradation images, there is a drawback that characters become difficult to read when reproduced with a full-color copying machine.

The present invention has been made in view of the above-mentioned problems, and its purpose is to perform high-quality color image processing that is suitable for the characteristics of each character image, three-gradation image, and character image. There are several ways to implement an image processing device.

(Means for Solving the Problems) The present invention to solve the above-mentioned problems includes a color reproduction means that converts a primary color image signal obtained by scanning a document into a color signal for image recording and removes an undercolor; A color image processing device comprising mixed image discrimination means for discriminating a document image into a gradation image and a character image, the color reproduction means having a color reproduction section with a high undercolor removal ratio and a color reproduction section with a low undercolor removal ratio. a reproduction section, and configured to selectively use either the color reproduction section with a high undercolor removal ratio or the color reproduction section with a low undercolor removal ratio according to the determination result of the mixed image determination means. It is characterized by:

(Operation) In the color image processing apparatus of the present invention, one of the color reproduction tables is selected based on the determination result of the mixed image determination means, and color reproduction processing suitable for the type of image is executed.

(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 a document, 2 and 3 are dichroic mirrors for resolving the image information (optical image) of the document into R, G, and B optical images, 4, 5°6 are R,
CCDs 7 and 8.9 photoelectrically convert the G and B optical images to obtain primary color image signals; A/D converters A/D convert the R, G and B primary color image signals to generate digital image signals; /D converter, 10.11.12 are R, G, respectively
A shading correction circuit corrects the shading of the B digital image signal, 13, 14, and 15 a gate circuit that extracts only the effective width from the R, G, and B digital image signals, and 16 a R, G, and B digital image signal. 17 is a density conversion circuit that performs density conversion of R, G,
This is a color reproduction section for converting (color reproduction) a B digital image signal into Y (yellow), 1M (magenta), C (cyan), and K (black) color signals for image recording. This color reproduction section 17 has two independent color reproduction tables (
It has a high UCR color reproduction table 17A and a low UCR color reproduction table 17B), and only one of them is selected and color reproduction processing is executed by an image discrimination signal from a discrimination circuit 21, which will be described later. 18 is a selector that selectively passes Y, M, C, and K digital color signals (density data) from the color reproduction section 17 in accordance with image formation;
One is a multi-value conversion circuit that performs multi-value processing on the digital color signal and converts it into multi-value data, and 20 is a multi-value conversion circuit that receives the multi-value data.
, M.

This printer unit (image output device) outputs a color image as a hard copy by sequentially overlapping toner images of each color. 21 receives the density-converted digital image signal, performs mixed image discrimination, and sends the color reproduction unit 1
This is a discrimination circuit that supplies an image discrimination signal to 7.

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

Color image information (optical image) of the original 1 is separated into three color separated images by two dichroic mirrors 2 and 3. In this example, the image is separated into a red R color angle q image, a green G color separated image, and a blue B color separated image.

Therefore, the cutoff wavelength of the dichroic mirror 2 is about 450 to 520 nm, and the cutoff wavelength of the dichroic mirror 3 is about 550 to 620 nm. As a result, the green component becomes 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 R2, green component G, and blue component B are output from each image reading means, for example, CCD sensors 4, 5.6. .

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 needles having the width of the maximum document size, and then subjected to density conversion in accordance with human visual characteristics. Then, it is supplied to the color reproduction section 17 at the next stage. When the maximum document width to be handled is A3 size, the size signal A3 generated by timing signal generation means (not shown) of the system is used as the gate signal.

Here, if the shading-corrected R, G, and B digital image signals are VR, VG, and VB, respectively, these digital image signals VR, VC, and VB are
7 for the printer unit 20, Y, M,
It is converted into C and K color signals.

In this example, the colors of image formation in the printer unit 20 are Y (yellow), 7M (magenta), C (cyan), and K.
(black).

The color reproduction unit 17 is a color reproduction table (lookup table) configured with ROM, and is a color reproduction table (hereinafter referred to as a high U color reproduction table) with a high undercolor removal ratio suitable for processing character images.
CR color reproduction table) and a color reproduction table with a low undercolor removal ratio suitable for processing gradation images (hereinafter referred to as low UC color reproduction table)
R color reproduction table) is provided for each of Y, M, and C.

In this embodiment, the storage area of the color reproduction section 17 (ROM) is divided into two blocks, and each block stores Y and M data for color reproduction.

C, is stored for each.

That is, the high UCR color reproduction table 17A is
Undercolor removal processing that processes the R ratio and replaces most of the density levels common to Y, M, and C with black density (
This is a lookup table configured to execute UCR) at the same time as color reproduction. As a result, the amount of black toner used increases, white and black are clearly reproduced, and characters and the like are clearly reproduced. In addition, subtle pale hues and colors that are close to achromatic colors are forcibly expressed in white/black.

Further, the low UCR color reproduction table 17B is a lookup table configured to perform under color removal processing with a low UCR ratio at the same time as color reproduction.

As a result, less toner is used for black, and Y.

The amount of M and C toners used increases, and subtle pale hues and colors close to achromatic colors are expressed as is.

Note that the difference in UCR ratio between the two color reproduction tables is relative, and is not strictly defined by an absolute value. Therefore, it is possible that the UCR% of the low UCR color reproduction table 17B is 0%.

That is, this embodiment is characterized in that the UCR ratios are changed in a plurality of color reproduction tables and are used by switching.

Selection between these two types of color reproduction tables is based on an external image discrimination signal. That is, the image discrimination signal outputs the color reproduction section 17 to II! It is given as the most significant bit of the address of the ROM to be read. If character images and gradation images 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 VR, VG, and VB as input, and reproduces Y, M, and C.

It outputs a K color signal (density data).

Generation of this image discrimination signal will be described later.

Y generated by color reproduction processing in this way.

The M, C, and Ka degree data are supplied to the selector 18.

A rescan code (a color code for forming a toner image in the printer unit 20) is given to this 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 20 so as to be suitable for image formation. The multi-value data for which multi-value processing has been completed in this way is supplied to the printer unit 20, and image formation is performed. This printer unit 2
0, since toner images of four colors Y, M, and C are sequentially superimposed, image reading to color reproduction is also performed four times.

Further, the image signal is supplied to a discrimination circuit 21 constituting the mixed image discrimination means shown in FIG.
'11 separate output (in this example, 1-bit data) is supplied to the color reproduction section 17 as a control signal (image discrimination signal). That is, the above-mentioned high UCR and low UCR color reproduction tables are selectively used according to the image content based on this image discrimination output.

That is, when it is determined that it is a character image, the image discrimination output becomes "0" and the high UCR color reproduction table 17A in the color reproduction section 17 is selected, and when it is determined that it is on the gradation side, the image discrimination output becomes "0". becomes "1" and the low U in the color reproduction section 17
The CR color reproduction table 17B will be selected.

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

Here, the discrimination circuit 21, which is a characteristic part of this embodiment, will be explained in detail with reference to FIG. The above-mentioned discrimination circuit 21 is composed of a first discrimination means 30 and a second discrimination means 40.

That is, the first discriminating means 30 is a means for roughly discriminating a human image into a character image and a gradation side to obtain a first image discriminating output. On the other hand, the second discriminating means 40 to which the first image discriminating output is supplied rediscriminates the image discriminating output on the gradation side 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 gradation side. In addition, in this image discrimination,
All the results for each of R, G, and B may be supplied to the color reproduction section 17, or the results for R, G, and B may be supplied to the color reproduction section 17 after taking a majority vote.

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

As shown in FIG. 2, the first determining means 30 includes a low-pass filter 31 for the pixel of interest, a comparator 32 for comparing the low-pass output for the pixel of interest with a reference value REF, and a level for further determining the level of the comparison output for the pixel of interest. It is composed of a judgment circuit 33.

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 the gradation side.

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. If it is too low, it will become indistinguishable from the background (ground) background level, and if it is too high, when the halftone line drawing is filtered and dispersed, there will be some that fall below this reference value REF, causing an error? This is because +J is separated.

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

In the case of photographs and halftone drawings, 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.

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

On the other hand, even if character images are dispersed such as the background, a value lower than the base wall value remains, and since part of the check window covers 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 the pixel of interest a and its surrounding pixels to the original pixel of interest by applying a certain weight C1.In this example, the pixel of interest and the pixels above, below, left, and right are In addition to the net value, it is divided by 5 and averaged.

Therefore, the filtered output a' 1 of the pixel of interest a1 is a' ++-(115)*Σ(C++* a ++).

Here, C1 is 1 only for the pixel of interest and four pixels on the upper, lower, left, and right sides, and is O for the other diagonal components.

Here, the reason why a cross-shaped type with a weight of 1 is adopted as the low-pass filter 31 is 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 errors are 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 FIG. 5(B), the center portion is a mesh line dot, and the diagonal lines are a mesh line pattern. Also, a collection of small dots is the minimum unit of reading.

Generally, in the case of halftone drawings, halftone lines are often arranged in a 45 degree direction. In the case of the cross-shaped filter shown in FIG. 5(A), the result of filtering spreads nicely into a rhombus shape along the mesh structure as shown in the figure. Therefore, no matter which pixel the window falls on, there is no extremely low part, and the window is divided into t and II as expected.

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 as the shape of the filter.

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 fill ladder 31 will effectively disperse even a fairly coarse halftone image.

In addition, please note that very coarse meshwork and extremely small dots (
In other words, if the image is thin (thin), there remains a possibility that it will be misidentified as a character part that is within the range of the filter.

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 processing can be adopted.

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 40 +
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 IH and 2
The digital image signal delayed by H is sent to the amplifier 31c, '3
It is simultaneously supplied to the 3-line memory 31f via 1d and 31e.

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 supplied to an adder 31n through three latch circuits 31i, 3], j, and 31k, respectively. Then, the digital image signal obtained on the n+1 line is transmitted through a pair of latch circuits 31g 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 175 by the coefficient unit 31o at the subsequent stage. Coefficient unit 3
As 1o, a 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 top, bottom, right and left, and if all 12 pixels in total including the pixel of interest a1 are larger (a) 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 it will be determined that the pixel of interest is 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 top, bottom, left and right directions, the window for level determination has a structure extending by m pixels in the top, bottom, left and right, where m is an integer larger than n.

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 human 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 number of windows 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 IH delay lengths and one-pixel delay latch circuits used increases accordingly.

33a to 33f are IH delay delay length latch circuits;
g is a memory for 7 lines. And 33h ~33
j, 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 ANDed 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 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 stroke may be recognized as a character stroke or may be recognized as a gradation side.

For example, as shown in FIG. 11(A), when the character image "Sono" is a human image, when this is passed through the low-pass filter 31, the image is 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 if all the pixels in its vicinity exceed the reference density due to this filter effect, the pixel of interest will be processed as a pixel on the gradation side. 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 on the gradation side.

In this way, the inside of a small character may be erroneously determined as being on the gradation side, and as a result, the quality of the character may deteriorate significantly.

Here, it is important to note that true halftone drawings and photographic drawings are on the gradation side.
Since the section to be cut occupies a certain area, such gradation side does not actually appear in the partial section. In other words, when a discrimination result in which gradation sides are scattered in a very small area is obtained, there are actually no gradation sides for each small area, so
It can be determined that the determination result is an erroneous determination.

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

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

To do this, image data of a certain area for the pixel of interest may be stored in memory, and a table or area of the closed area of the gradation side discrimination portion may 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 it is a character stroke or a gradation side, 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 "1" when it is on the 'gradation side.
", and the output is "0" 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, this 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 related to the reference length L (FIG. 14(A)).

L is preferably about 2raI11.

The pulse comparison output that exceeds the reference value S becomes "1", and at this time the pulse generating means 40d outputs the It- control pulse p (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 output of the first image 111.

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 40t passes through a NAND circuit 40k to R
It is supplied to the set terminal S of the type 3 flip-flop 40n. Similarly, each output of the line memories 40i and 40j is supplied to a NAND circuit 4ON of a non-human power type, and the output is further passed through a NAND circuit 40m to a flip-flop 40.
n's reset terminal R.

As a result, a second image discrimination output as shown in FIG. 15(D) is obtained at the output terminal 40o.

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, manual manuscripts can be identified and processed with precision and efficiency not previously possible. Furthermore, halftone drawings, which have been considered difficult in the past, can now be distinguished as gradation drawings by using the low-pass filter 31 and window processing for level determination.

In addition, 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 erroneous determination within characters is eliminated, so human images can be correctly identified and processed.

Note that in the above example, only the lengths of both gradation parts were evaluated to determine the length, but a correction circuit that similarly judges extremely short character parts as misclassifications is also provided, so that the classification 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
．． 133', it is led 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 104 that captures an image.

The optical signal obtained by the optical system is collected by the lens 139, 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 COD, 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 converter.

The writing section B (printer unit 20) 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 body 142.

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

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

Toner 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 developer 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 single-color toner image can be formed.

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

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] 47b 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 pressed. 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 the present invention can be applied to various devices that process character images and gradation images.

(Effects of the Invention) As explained in detail above, in the present invention, a mixed image in which a character image (including a character image with a light color) and a gradation image are mixed is classified by tll based on the image discrimination result, and the character Color reproduction processing is now performed with undercolor removal at different ratios for images and gradation images. In other words, if it is determined to be a text image, is it considered to be a 1-gradation image with color reproduction processing with a high undercolor removal ratio? , +
In the case of + cutoff, color reproduction processing is performed with a lower undercolor removal ratio. As a result, optimal image processing can be performed for both character and one-tone images. Therefore, it is possible to realize a color image processing apparatus that can perform high-quality image processing suitable for each image.

[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 mixed image discrimination section, 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 The figure is an explanatory diagram explaining the characteristics of a low-pass filter.
The figure is a configuration diagram showing the electrical configuration of the low-pass filter.
Figure 9 is a block diagram showing the configuration of the level judgment circuit, Figure 9 is an explanatory diagram explaining the characteristics of the level judgment circuit, Figure 10 is a block diagram showing the electrical configuration of the level judgment circuit, and Figure 11 is a diagram showing the filter effect. Is the explanatory diagram, Figure 12, an image? An explanatory diagram for explaining the results of +1, FIG. 13 is a configuration diagram showing the configuration of the second discriminating means, FIGS. 14 and 15 are explanatory diagrams of the operation of the second discriminating means, and FIG. 16 is a diagram for explaining the operation of the second discriminating means. 1 is a configuration diagram showing the mechanical configuration of a copying machine to which a color image processing device is applied. 1... Original 2.3... Dichroic mirror 4.5.6... CCD 7.8.9... A/D converter 10.1: l, 12... Shading correction circuit 13
．． 14, 1.5... Gate 16... Density conversion circuit 17... Color reproduction section 17
A...High UCR color reproduction table 17B...Low UCR color reproduction table

Claims (1)

[Scope of Claims] Color reproduction means for converting primary color image signals obtained by scanning a document into color signals for image recording and removing undercolor; and discriminating a document image into a gradation image and a character image. A color image processing device having a mixed image discriminating means, wherein the color reproducing means includes a color reproducing section with a high undercolor removal ratio and a color reproducing section with a low undercolor removal ratio, A color image processing apparatus characterized in that, depending on the result, either the color reproduction section having a high undercolor removal ratio or the color reproduction section having a low undercolor removal ratio is selectively used.