JP3261247B2 - Image processing system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing system capable of improving image quality when performing image processing.
Particularly, the present invention relates to an image processing system suitable for a color copying machine and a color facsimile machine.

[0002]

2. Description of the Related Art As an image processing system of this type, a color original is read by a color image input means, and the read color image data is divided into a character area and a picture area by image area, and adapted to each image area. There is known an image processing apparatus that improves image quality by performing processing. As an example of such an image processing system, for example, black characters / patterns are separated, and a black character portion is erased with a high resolution and a yellow (Y) signal, a magenta (M) signal, and a cyan (C) signal. There is an image reproducing apparatus which reproduces a single color of black (K) and reproduces a picture portion with high gradation and four colors of K, Y, M and C to obtain high image quality.

As another example of the above-mentioned image processing system, a picture part separated as described above is further separated from a color character / pattern, and the color character part has a high resolution and 4 characters.
There is an image reproducing device which reproduces a color portion and reproduces a pattern portion with high gradation and four colors to obtain high image quality.
By the way, in a color copier constituted by a frame-sequential printer, in general, an image is formed by scanning four times for four colors of K, Y, M, and C, and the image is input again for each scan. I have.

[0004]

When an image is formed by four scans, the image data is slightly different for each scan. This is K, Y,
It is considered that the reason is that the same image area separation parameters are used in the four color plates of M and C. As described above, if the image area separation result is different in each plate, the image quality is deteriorated. For example, consider a specific example of “black characters”.
In the above image processing system, a black character portion is set to
When the image is separated as a pattern, high gradation processing is performed, and as a result, the image is reproduced thinly in black, resulting in a large deterioration in image quality.

On the other hand, in the above image processing system,
If black characters are separated during color printing (Y, M, C), the Y, M, and C signals are erased, and the character information itself is lost, resulting in significant image quality deterioration. there were. A conventional image processing system has been proposed in which the image quality is improved by differentiating the determination parameters between the determination of a black-and-white / color image and the determination of a black character (Japanese Patent Laid-Open No. 3-64272). Also, this is not the one in which the judgment parameter is optimized for each output plate (black plate or color plate), so that the above-described drawbacks occur. An object of the present invention is to provide an image processing system capable of reducing image quality deterioration due to subtle variations in image data for each scan as described above and obtaining high image quality.

[0006]

According to the first aspect of the present invention,
A color image reading unit for reading an original; and an image area separating unit for separating an image area of the color image data obtained from the reading unit, and a color plate and a black plate can be output in a frame sequential manner from the image region separated image data. In the image processing system, the image area separating unit includes an image area separation parameter for black plate and an image area separation parameter for color plate, and the parameters are used according to the color plate or black plate. Achieve the goal. According to a second aspect of the present invention, the image area separating means includes an edge determining unit that uses a parameter for determining an edge according to a color plate or a black plate to achieve the above object.

According to the third aspect of the present invention, the image area separating means is provided with a color determination unit that uses a parameter for determining black, chromatic, or achromatic color in accordance with a color plate or a black plate to achieve the above object. I do. According to a fourth aspect of the present invention, the image area separating means includes a halftone dot determination unit that uses a parameter for determining a halftone dot according to a color plate or a black plate to achieve the above object.

[0008]

The invention described in claim 1 has been made based on the following idea. That is, according to the first aspect of the present invention, the original is read by the color image reading means, the color image data is separated into the character area and the picture area by the image area separating means, and the image data is separated from the image data obtained by the image area separation. For example, printing data of a color plate or a black plate is sequentially obtained. Table 1 below shows the effect on image quality when the separation result is different for black characters / patterns for black printing data or color printing data when separating image areas. become.

[0009]

[Table 1]

As can be seen from Table 1, the worst case is a case where a black character is separated from a black pattern with a black pattern, and the character information is lost for the above-described reason. It can be seen that such a case can be reduced by setting an image area separation parameter from a picture at the time of color separation. Therefore, in the first aspect of the present invention, a black plate image area separation parameter and a color plate image area separation parameter are prepared, and the respective parameters are used according to the color plate or the black plate. In this case, for black characters, the possibility of separation as black characters in a black plate during a pattern / color plate is reduced, and for black characters / black characters in a black plate during a black plate.
The degree of separation as black characters during color printing is reduced. The above can be similarly applied to the three image area separation type (black character / color character / picture).

According to the second aspect of the present invention, the image area separating means has an edge judging unit for judging an edge, and the edge judging unit uses a parameter for judging an edge in accordance with a color plate or a black plate. I have. According to the third aspect of the present invention, the image area separating unit is provided with a color determination unit for determining a color, and the color determination unit includes a parameter for determining black and a parameter for determining chromatic and achromatic colors. Parameters are used for each output version. According to the fourth aspect of the present invention, the image area separating means has a halftone dot judging unit for judging a halftone dot, and the halftone dot judging unit uses a parameter for judging a halftone dot in accordance with each output version. I have.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, first to sixth embodiments of the present invention will be described in detail with reference to FIGS. <First Embodiment> FIGS. 1 to 8 are shown to explain a first embodiment of the present invention. Here, FIG. 1 is a block diagram showing the embodiment, FIG. 2 is a block diagram showing a specific example of a character detection circuit used in the embodiment, and FIG. 3 is a specific example of a white background detection circuit used in the embodiment. FIG. FIG. 4 is an explanatory diagram of the URC process, and FIGS.
FIG. 7 is a diagram showing a pattern for character detection, and FIGS. 7 and 8 are explanatory diagrams of the detection of an area near a white background. First, in FIG. 1, an image processing system 1 includes a color image reading means 2 for reading an original, an image area separating means 3 for separating the color image data obtained from the reading means 2 into a character area and a picture area. A UCR circuit 4 for performing black monochromatic processing or color processing in accordance with the image area separating means 3, a dither circuit 5 for dithering a signal from the UCR circuit 4, and an output from the dither circuit 5 A conversion circuit 6 for obtaining print data is provided, and the frame-sequential print data from the conversion circuit 6 is supplied to the color printer 7. The image area separating unit 3 includes a black area image area separation parameter and a color plane image area separation parameter, and is configured to change each of the parameters according to a color output version or a black output version. I have.

Here, the color image reading means 2 is a CCD
A document reading unit 21 including a photoelectric conversion device such as a camera;
An A / D converter 22 for converting the three-color separation signals of red (R), green (G), and blue (B) from the document reading unit 21 into, for example, an 8-bit digital signal, and the A / D converter 22
The digital signal density conversion from, Y, M, and logarithmic conversion circuit 23 for converting the Y _1, M _1, C ₁ signal representative of the amount of each ink of C, Y ₁ from the logarithmic conversion circuit 23, M ₁ , C
It is composed of a masking circuit 24 that performs color correction of the filter and ink color of the original reading unit 21 for _one signal and outputs Y ₂ , M ₂ , and C ₂ signals.

The image area separation means 3 has an image area separation parameter for black plate and an image area separation parameter for color plate, and can change each of the parameters according to each output plate. And a character detection circuit 31 for separating the image area of the character area / picture area from the Y ₂ , M ₂ , and C ₂ signals from the masking circuit 24, and Y ₂ , M ₂ , and C ₂ from the masking circuit 24. A white background detection circuit 32 for capturing a signal and detecting a pixel region having a white background in the background;
An AND circuit 33 that outputs a logical product signal of the output signals of these circuits 31 and 32 is provided.

In FIG. 2, a character detecting circuit 31 includes a binarizing circuit 311 and a black image pattern matching circuit 312.
A counting circuit 313, a binarizing circuit 314, a white image pattern matching circuit 315, a counting circuit 316,
It comprises an ND circuit 317 and a determination circuit 318. The binarization circuit 311 and the binarization circuit 314 are configured as follows in order to change the parameter for edge separation in the black plate or the color plate. That is, the binarization circuit 311 includes a first black level threshold TH1 _K used for black printing and a second black level threshold TH1 _I used for color printing, and TH1.
_K <TH1 _I is determined, and the first black level threshold value TH1 _K is used when separating edges for black printing, and the second black level threshold TH1 _I is used when separating edges for color printing.
Each _{use, Y 2, M 2, C} 2 signal is the minimum signal of the _{min (Y 2, M 2,} C 2) signal by binarizing the black / non-black with in the threshold output It is configured to be.

The black image pattern matching circuit 312
For example, when a black / non-black pattern in a 3 × 3 matrix and one of the patterns in FIG. 5 are matched with the target pixel as the center pixel, the target pixel is determined as a character black pixel, and “1” is output. It is configured to be. The counting circuit 313 counts the number of input “1” s (the number of black pixels of characters) in, for example, a 3 × 3 matrix, and outputs “1” when the count value is equal to or more than a certain value. It is configured. Further, the binarization circuit 314 includes a first white level threshold TH2 used for a black plate.
_K, and a second white level threshold value TH2 _I used for color printing, and determined so that the relationship of TH2 _K > TH2 _I is established. the level threshold TH2 _K, uses the second white level threshold TH2 _I respectively when edge separation color plate, Y _2,
M _2, C ₂ signal is the maximum signal of the max (Y _2, M _2,
C ₂ ) The signal is binarized into white / non-white using the threshold value.

The white image pattern matching circuit 315
For example, when a white / non-white pattern in a 3 × 3 matrix and one of the patterns in FIG. 6 are matched with the target pixel as a center pixel, the target pixel is determined to be a character white pixel, and “1” is output. It is configured to be. The counting circuit 316 counts the number of input “1” (the number of character white pixels) in, for example, a 3 × 3 matrix, and outputs “1” when the count value is equal to or more than a certain value. It is configured. The AND circuit 317 includes the counting circuit 31
3, and outputs a signal obtained by ANDing the output signals from 316. The determination circuit 318 determines, for example, 5
The provisional character pixels ( counting circuits 313, 3
16 when the signal obtained by ANDing the output signals from
If the number of elements is a certain number, a block having a certain size for the pixel of interest or the like is determined as a character area, and "1" is output.

In FIG. 3, a white background detection circuit 32
It comprises a white pixel detection section 321, an expansion processing section 322, and a correction processing section 323. Here, the white pixel detection unit 321
Is max, which is the maximum signal among the Y ₂ , M ₂ , and C ₂ signals.
The (Y ₂ , M ₂ , C ₂ ) signal is binarized into white / non-white pixels at a predetermined threshold value, and a secondary pattern formed by the binarized signal is compared with a predetermined pattern to form a white background. Is configured to be detected. When the white signal from the white pixel detection unit 321 reaches a predetermined value in a block of size N1 × N2 centered on the target pixel, the expansion processing unit 322 sets the target pixel or block near the temporary white background. It is configured to determine the area. The correction processing unit 323 will be described later.
Two pixels separated by a certain distance across the pixel of interest
Is located in the temporary white background vicinity area, the pixel of interest is determined to be a true white background vicinity area, and "1" is output.

The operation of the first embodiment will be described. The original is read by the original reading unit 21,
It becomes a three-color separation signal of red (R), green (G), and blue (B).
These three color separation signals of R, G and B are supplied to the A / D conversion circuit 2.
2, the signal is converted into an 8-bit digital signal.
The digital signal from the A / D conversion circuit 22 is density-converted by a logarithmic conversion circuit 23 and converted into Y ₁ , M ₁ , and C ₁ signals representing the amounts of Y, M, and C inks. The Y ₁ , M ₁ , and C ₁ signals from the logarithmic conversion circuit 23 are subjected to color correction of filters and ink colors of the document reading unit 21 by a masking circuit 24. This color correction is performed by, for example, the following equation 1.
Is executed by

[0020]

Y ₂ = K ₁₁ × Y ₁ + K ₁₂ × M ₁ + K ₁₃ × C ₁ M ₂ = K ₂₁ × Y ₁ + K ₂₂ × M ₁ + K ₂₃ × C ₁ C ₂ = K ₃₁ × Y ₁ + K ₃₂ × M ₁ + K ₃₃ × C ₁

Here, K _{11 to} K ₃₃ are values actually obtained. The Y ₂ , M ₂ , and C ₂ signals thus obtained are input to the character detection circuit 31 and the white background detection circuit 32 of the image area separation means 3 and the UCR circuit 4. In the character detection circuit 31 of the image area separating means 3, the parameters are changed between the black plate and the color plate, and the character area / character data is converted from the Y ₂ , M ₂ , and C ₂ signals.
The image area of the picture area is separated. That is, the above Y ₂ , M
_{The 2} and C ₂ signals are input to the character detection circuit 31 and the white background detection circuit 32 of the image area separation means 3.

The binarization circuit 3 of the character detection circuit 31
The Y ₂ , M ₂ , and C ₂ signals input to 11 use the first black level threshold TH1 _K for a black plate and the second black level threshold TH1 _I for a color plate. , Y ₂ ,
The minimum signal of the M ₂ and C ₂ signals, min (Y ₂ , M ₂ ,
C ₂ ) Binarize the signal into black / non-black. The signal thus binarized is supplied to the black image pattern matching circuit 31.
In 2, for example, when a black / non-black pattern in a 3 × 3 matrix and one of the patterns in FIG. 5 are matched with the target pixel as a center pixel, the target pixel is determined to be a character black pixel, and “1” is set. Output. The number of “1” (the number of character black pixels) is counted by the counting circuit 313. Then, the counting circuit 313 outputs “1” when the count value is equal to or more than a certain value.

Similarly, the Y ₂ , M ₂ , and C ₂ signals are input to the binarization circuit 314. In the binarization circuit 314, the first white level threshold T
The H2 _K, at the time of edge separation of the color plate using a second white level threshold TH2 _I respectively, a maximum signal of the Y _2, M _2, C ₂ signal max (Y _2, M _2, C ₂ ) Binarize the signal into white / non-white using the threshold value. The binarized signal is generated by the white image pattern matching circuit 315 when, for example, a white / non-white pattern in a 3 × 3 matrix and one of the patterns in FIG. The pixel is determined as a character white pixel, and "1" is output. The number of “1” (the number of character white pixels) is counted in, for example, a 3 × 3 matrix by the counting circuit 316, and “1” is output when the count value is equal to or more than a certain value. Counting circuits 313, 316
Are ANDed by the AND circuit 317. The AND circuit 317 outputs “1” when the output signals from the counting circuits 313 and 316 are both “1”.

On the other _{hand, Y 2, M 2, C} 2 signal is in the white pixel detection section _{321, max (Y 2, M} 2, C 2) signal to the white / non-white pixels in a predetermined threshold value It is binarized. The secondary pattern formed by the binarized signal is a white pixel detector 3
At 21, a white background is detected by comparing with a pattern provided in advance (for example, shown in FIG. 7). White pixel detector 32
The white background in No. 1 is detected as follows. That is, the white background is, for example, in a 5 × 5 mask shown in FIG.
Because conditions center pixel L ₃₃ is white pixels are selected by utilizing the fact that it is all the pixels.

This white signal is input to the expansion processing section 322. Then, when the white signal becomes equal to or larger than a predetermined value in a block having a size of N1 × N2 around the target pixel, the expansion processing unit 322 determines that the target pixel or the block is a temporary white background neighboring area. . The determination signal is counted by the correction processing unit 323. Correction processing unit 323
Then, as shown in FIG. 8, pixels A and B which are left and right L pixels away from the pixel of interest P are examined, and when both A and B are near a white background, the pixel of interest is determined to be a region near a white background. Outputs “1”. As described above, the output signals from the correction processing unit 323 and the determination circuit 318 are ANDed by the AND circuit 33 and input to the UCR circuit 4. Also,
The Y ₂ , M ₂ , and C ₂ signals and the AND signal from the AND circuit 33 are input to the UCR circuit 4. UCR circuit 4
Then, the Y ₃ , M ₃ , and C ₃ signals of the color ink and the K ₃ signal of the black ink are generated.

First, the UCR circuit 4 can select a first process or a second process. The first process in the UCR circuit 4 is a process of setting the Y ₃ , M ₃ , and C ₃ signals to zero and generating a K ₃ signal. For example, the Y ₂ , M 3 values shown in FIG.
_2, when the C ₂ signal is inputted, outputs a _{Y 3, M 3, C 3} , K 3 signal values as shown in Figure 4 (b). The second processing in the UCR circuit 4 is performed by min (Y ₂ ,
M ₂ , C ₂ ) 50% UCR processing, and FIG.
When the Y ₂ , M ₂ , and C ₂ signals having the values shown in FIG. 4A are input, the values of Y ₃ , M ₃ , C ₃ , and C ₃ shown in FIG.
And outputs a signal K _3.

"1" is output from the AND circuit 33 to UC.
When input to the R circuit 4, the UCR circuit 4 executes the first processing, and when “0” is input to the UCR circuit 4,
The CR circuit 4 performs a second process. The Y ₃ , M ₃ , C ₃ and K ₃ signals obtained in this way are input to the dither circuit 5. In the dither circuit 5, Y ₃ , M ₃ , C ₃
Signal, K ₃ signal is binarized and Y ₄ , bit by bit,
The signals become M ₄ , C ₄ , and K ₃ . These Y ₄ , M ₄ ,
The C ₄ and K ₃ signals are sent to the conversion circuit 6. The conversion circuit 6 obtains frame-sequential print data from these Y ₄ , M ₄ , C ₄ , and K ₃ signals. The frame-sequential data is supplied to the color printer 7 and reproduced as a color image. As described above, in the first embodiment, since the binarization circuit 311 and the binarization circuit 314 are configured as described above, the conditions for edge separation are high when the color plate is output, and when the color plate is used, the edge separation condition is reduced. Can be separated.

<Second Embodiment> In a second embodiment, the binarization circuit 311 and the binarization circuit 314 shown in FIG. 2 are configured to simply determine an edge as in the prior art. The second embodiment differs from the first embodiment in that the threshold value for edge determination in the black image pattern matching circuit 312 and the counting circuit 313 shown in FIG. 2 is changed.
That is, in the first embodiment, the black image pattern matching circuit 312 counts and corrects the density of the pixel whose primary edge has been determined by the binarization circuit 311.
In the embodiment, the following work steps are added to them. That is, the binarization circuit 311 sets the coefficient threshold of the first density to Tb _K and the coefficient threshold of the second density to Tb _K with respect to the constant threshold of the pixel density of the black level connected pixel.
When _I, by a Tb _K <Tb _I, edge condition becomes tight when the color plate, it is possible to separate from the picture when the color separations.

The white image pattern matching circuit 31
5 is that in the first embodiment, the density of the pixel that has been primarily determined as an edge by the binarization circuit 314 is counted and corrected, but in the second embodiment, Has been added. That is, the binarization circuit 314 sets the coefficient threshold of the first density to Tw _K and the coefficient threshold of the second density to Tw _I with respect to the constant threshold of the pixel density of the white level connected pixel. , Tw _K <Tw _I , the condition of the edge becomes tighter in color printing, and separation from the picture in color printing becomes possible. Note that both the binarization circuit 311, the binarization circuit 314 of the first embodiment, and the black image pattern matching circuit 312 and the white image pattern matching circuit 315 of the second embodiment may be used together.

<Third Embodiment> FIGS. 9 and 10 are views for explaining a third embodiment. FIG. 9 is a block diagram of the embodiment. FIG. 10 is an explanatory diagram of the operation of the achromatic color region detection circuit. The third embodiment shown in FIG. 9 differs from the first embodiment in the following two points, and the other configuration is exactly the same as that of the first embodiment. That is, the image area separating means 3a of the third embodiment includes a character detection circuit 31a, an achromatic color area detection circuit 35, and an AND circuit 33. Further, in the third embodiment, a binarization circuit 8 for binarizing the K ₃ signal from the UCR circuit 4 and outputting a K _4a signal, and a K ₄ signal from the dither circuit 5 or the binarization circuit K from 8
_A selection circuit 9 for selecting one of the _4a signals and _{supplying the} selected signal to the conversion circuit 6 is added.

[0030] The character detection circuit 31a is configured so as to detect the character region similarly to the character detection circuit 31a of the first embodiment from the M ₂ signal. The achromatic region detection circuit 35 prepares a threshold value T _CK for black plate and a threshold value T _CI for color plate, sets T _CK > T _CI, and sets the input Y ₂ , the maximum value Δ (Y ₂ , M ₂ , C ₂ ) of the difference between the M ₂ and C ₂ signals is determined by a threshold value according to each output plate, and “1” is set in the achromatic region, It is configured so that “0” can be output in the chromatic color area. The binarization circuit 8 can binarize the K ₃ signal with a predetermined threshold value and output it as a K _4a signal. The selection circuit 9 includes
The D circuit 33 can supply the K _4b signal to the conversion circuit 6 when the signal is “1” (black character) and the K ₄ signal from the dither circuit 5 when the signal is “0”.

The operation of the third embodiment will be described. The Y ₂ , M ₂ , and C ₂ signals from the masking circuit 24 are input to the achromatic region detection circuit 35 and the dither circuit 5. The achromatic color area detection circuit 35 first executes a chromatic color pixel detection process to find the maximum value Δ (Y ₂ , M ₂ , C ₂ ) of the difference between the Y ₂ , M ₂ , and C ₂ signals. Δ (Y
₂ , M ₂ , C ₂ )> T _C , a chromatic color is detected by using the threshold T _CK for a black plate and the threshold T _CI for a color plate. As described above, since the threshold value T _CK for the black plate is greater than the threshold value T _CI for the color plate, the separation result from the picture at the time of the color plate (in the case of the three-type image area separation type, it is determined as an edge) If it is, it will be the separation result from the color character).

Next, the achromatic color area detection circuit 35 executes a first correction process, counts the chromatic color pixels by using a mask of a predetermined size centering on the pixel of interest, and sets the count value to a predetermined value. If it is not less than the threshold value, the pixel of interest is set as a chromatic color candidate pixel. Thereafter, the achromatic region detection circuit 35
The second correction process is executed, and as shown in FIG. 10, the pixel of interest P is a chromatic color candidate pixel area, or pixels A and B separated by a fixed distance to the left and right of the pixel of interest are commonly chromatic color pixels. When the pixel is a region, the pixel of interest P or its block is output as a chromatic color region, and “0” is output.

As described above, the output from the achromatic color area detection circuit 35 and the output from the character detection circuit 31a are logically ANDed by the AND circuit 33 and input to the UCR circuit 4 and the selection circuit 9. On the other hand, the K ₃ signal output from the UCR circuit 4 is input to the dither circuit 5 and the binarization circuit 8. 2
The binarization circuit 8, with K ₃ signal with a predetermined threshold value K
_The signal is _supplied to the selection circuit 9 as a _4a signal. The selection circuit 9 selects the K _4a signal when the output from the AND circuit 33 is “1”, selects the K ₄ signal from the dither circuit 5 when the output is “0”, and converts it as a K _4b signal. 6 is entered.

<Fourth Embodiment> In the fourth embodiment, the first correction process in the achromatic color region detection circuit 35 is modified. That is, when the achromatic color region detection circuit 35 counts and corrects the density of the pixel determined as a chromatic color (or achromatic color) when the count value of the chromatic color pixel is equal to or greater than the predetermined threshold value Tn. _Is determined as T _nK > T _nI . As a result, in the case of a color plate, the condition of the achromatic color judgment becomes severe, and the separation result from the pattern (3
In the case of the seed image area separation type, if it is determined as an edge, the result is a separation result from a color character).

As another embodiment different from the above embodiments, the white background detection circuit 32 of the first embodiment is added to the image area separating means 3a of the third embodiment, and the white background detection circuit 32 of the first embodiment is added. In addition, the AND circuit 33 inputs the Y ₂ , M ₂ , and C ₂ signals and ANDs the outputs of the character detection circuit 31a, the achromatic color area detection circuit 35, and the white background detection circuit 32 with the AND circuit 33. You may make it comprise the separation means 3b.

<Fifth Embodiment> In the fifth embodiment, halftone dot judgment is added to the first to fourth embodiments in order to improve the image area separation performance. For example, in the first embodiment, when the edge determination and the color determination have a relationship as shown in Table 2 below, in the aspect [1], the character is separated from the black character, and in the aspect [2], the color character is separated from the black character. It was separated, and in the embodiment [3], it was separated from the picture.

[0037]

[Table 2]

Therefore, in the fifth embodiment, for example, by adding halftone judgment to the first embodiment, the image area separation performance is further improved. That is,
In the fifth embodiment, a halftone judgment is added to the edge judgment and the color judgment of the first embodiment, and when these have a relationship as shown in Table 3 below, in the mode [1], black characters, In the mode [2], it is determined as a color character, and in the mode [3], a pattern is determined. Thereby, the separation performance is further improved.

[0039]

[Table 3]

FIG. 11 shows the configuration of a halftone dot determination circuit used in the fifth embodiment, and the operation of this circuit is shown in FIGS.
This will be described with reference to FIG. As shown in FIG. 11, the halftone dot determination circuit includes an input image signal unit 91 and a pole point detection unit 92.
, A halftone dot area detection section 93 and an area determination signal output section 94. Note that this halftone dot determination circuit is for a monochrome image signal, and in the case of a color image, it is decomposed into, for example, Y, M, and C signals, and the halftone dot separation processing is performed using the contents of the above circuit. If the results of these signals are ANDed, for example, and the results are provided to the AND circuit 33 of the first embodiment, the determination shown in Table 3 can be performed.

An image signal in which a halftone image such as a halftone photograph and a line image such as a character are mixed is input to an input image signal unit 91.
It is raster-scanned and converted into a digital multi-tone image signal consisting of a luminance signal corresponding to the density level. In the digital image signal thus converted, at least the scan lines required for the separation process are stored in a line memory or the like by the input image signal unit 91 at least. To the digital multi-tone image signal output from the input image signal unit 91, a matrix composed of M × M pixels is sequentially applied in a pole detection unit 92. As a result, whether or not the center pixel of the matrix is an extreme point indicating the peak or valley of the density change is detected from the density relationship with the surrounding pixels. Specifically, the pole detection unit 92 performs a logical AND operation on a determination result based on the following first condition and a determination result based on the second condition.

The first condition for detecting the extreme point is as shown in FIG.
As shown in (a) (b), or concentration level of the center pixel m _o a matrix consisting of M × M pixels is greater than that of all the pixels m ₁ ~m _p concentration levels in the M × M pixel region when a small, detects the center pixel m _o as pole.
The pole detection unit 92 sets the threshold Δm _TH to the black threshold Δm _THK for the black plate, the color threshold Δm _THI for the color plate, and the black threshold under the second condition of the pole detection. Δm _THK > color threshold Δm _THI and FIG.
(A) As shown in (b), the difference between the density level of the central pixel m _O of the matrix composed of M × M pixels and the average value of the density levels of the other two pixels with the central pixel m ₀ as the center. Is the black threshold Δm _THK or the color threshold Δm
When greater than _THI, it is determined the center pixel m _o as pole concentration.

The result determined in this way is input to the halftone dot area detecting section 93. In the halftone dot area detection unit 93,
A block B of N × N pixels, for example, a block B having a size of 9 × 9 pixels as shown in FIG. 13 is divided into units, and the number of pole pixels indicating a peak and the number of pixels indicating a valley are respectively determined for each block. The block is counted, and the number of extreme pixels on the side with the larger count value is determined as the number of extreme pixels of the block. Next, the halftone dot area detecting section 93 selects the target block B ₀ shown in FIG.
The number of extreme pixels P _{0 of the} pixel and blocks B _{1 to} B _{8 K} surrounding the pixel P ₀
Center pixel or the like of the block of interest B ₀ from the relationship of the pole number of pixels P whether belonging to the halftone dot 5 area is determined.

The result determined as described above is input to the area determination signal output unit 94. The area determination signal output unit 94 determines whether each pixel is a halftone part or a line drawing part based on the result, and outputs the determination result. The determination result thus obtained may be input to, for example, the AND circuit 33 of the first embodiment. In the fifth embodiment, since the halftone dot determination circuit is configured as described above, the halftone dot determination circuit is easily determined to be a halftone dot during color printing, and a separation result from a picture can be obtained during color printing. .

<Sixth Embodiment> In the fifth embodiment, the color threshold value Δm _THI and the black threshold value Δm _THK dedicated to the color plate are determined by the pole detection unit 92 of the halftone determination circuit. It is prepared to make it easy to be judged as a halftone dot during color printing,
In the sixth embodiment, the pole detection unit 92 makes a determination based on one threshold value Δm _TH as in the prior art, changes the halftone determination parameter of the halftone region detection unit 93a of the halftone determination circuit, and A feature is that halftone dots are sometimes determined accurately. Therefore, the other configuration is exactly the same as that of the fifth embodiment. In the sixth embodiment, when the pixel density is counted and corrected by the halftone dot area detection unit 93, blocks in which the number of extreme pixels P is equal to or greater than a predetermined threshold P _TH are equal to or greater than a predetermined threshold B _TH. When it exists, the block of interest B _o is detected as a halftone dot.
And _THK, B _THK when the color version and a predetermined color threshold value B _THI
> B _THI , and the threshold value is changed for the color plate or the black plate.

According to the sixth embodiment, it is easy to judge a halftone dot at the time of color printing, and a separation result from a picture is obtained at the time of color printing. In the sixth embodiment,
Also by having independently P _TH in the black plate and the color plate in place of B _TH, the same effect may occur. As another configuration example, both the pole point detection unit 92 of the fifth embodiment and the halftone dot region detection unit 93 of the sixth embodiment may be used in combination. Further, the scope of the present invention is not limited to the above embodiments, but can be applied to various types of image area separation.
Although the above-described invention is most effective when applied to each of the edge determination, the color determination, and the halftone determination, the invention may be applied to, for example, only the edge determination.

[0047]

As described above, according to the first aspect of the present invention, in a frame sequential image reproducing system, the result of image area separation is caused by slightly different image input for each scan. Can be reduced from scan to scan, and image quality degradation can be reduced. According to the first aspect of the present invention, since the parameter is merely changed,
No additional hardware is required. According to the second aspect of the present invention, the condition of the edge becomes sharp at the time of color printing, and a separation result from the picture can be obtained at the time of color printing. Claim 3
According to the invention described above, the achromatic color determination condition becomes strong at the time of color printing, and a separation result from a picture can be obtained at the time of color printing. According to the fourth aspect of the invention, the halftone dot is easily determined at the time of color printing, and a separation result from a picture can be obtained at the time of color printing.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a block diagram showing a specific example of a character detection circuit used in the embodiment.

FIG. 3 is a block diagram showing a specific example of a white background detection circuit used in the embodiment.

FIG. 4 is an explanatory diagram of a URC process in the embodiment.

FIG. 5 is a diagram showing a pattern for character detection in the embodiment.

FIG. 6 is a diagram showing a pattern for character detection in the embodiment.

FIG. 7 is an explanatory diagram of detection of an area near a white background in the embodiment.

FIG. 8 is an explanatory diagram of detection of an area near a white background in the embodiment.

FIG. 9 is a block diagram showing the third embodiment.

FIG. 10 is an operation explanatory diagram of the achromatic color region detection circuit in the third embodiment.

FIG. 11 is a block diagram showing a configuration example of a halftone dot determination circuit used in the fifth embodiment.

FIG. 12 is an explanatory diagram showing the operation of a halftone dot determination circuit used in the fifth embodiment.

FIG. 13 is an explanatory diagram of the operation of the halftone dot determination circuit used in the fifth embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image processing system 2 Color image reading means 3 Image area separation means 4 UCR circuit 5 Dither circuit 6 Conversion circuit 7 Printer 21 Document reading part 22 A / D conversion circuit 23 Logarithmic conversion circuit 24 Masking circuit 31 Character detection circuit 32 White background detection Circuit 33 AND circuit 35 Achromatic area detection circuit 91 Input image signal section 92 Pole point detection section 93 Halftone dot area detection section 94 Area judgment signal output section 311 Binarization circuit 312 Black image pattern matching circuit 313 Counting circuit 314 Binarization circuit 315 White image pattern matching circuit 316 Counting circuit 317 AND circuit 318 Judgment circuit

Continuation of the front page (56) References JP-A-3-180371 (JP, A) JP-A-1-192281 (JP, A) JP-A-1-174452 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) H04N 1/40-1/409 H04N 1/46 H04N 1/60

Claims (4)

(57) [Claims] 1. A color image reading means for reading a document,
An image processing system comprising: an image area separating unit that separates an image area of the color image data obtained from the reading unit; and a color plate and a black plate that can be output in a plane-sequential manner from the image region separated image data. The image processing system is characterized in that the means includes a black plate image area separation parameter and a color plate image area separation parameter, and uses each of the parameters according to the color plate or black plate. 2. The image processing system according to claim 1, wherein said image area separating means includes an edge determination unit that uses a parameter for determining an edge according to a color plate or a black plate. 3. The image processing apparatus according to claim 1, wherein the image area separating unit includes a color determination unit that uses a parameter for determining black, chromatic color, or achromatic color in accordance with a color plate or a black plate. Image processing system. 4. The image processing system according to claim 1, wherein the image area separating unit includes a halftone dot determination unit that uses a parameter for determining a halftone dot according to a color plate or a black plate.