JP3251101B2 - Digital color image reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention, digital image processing, in particular, stores a result of determining the characteristics of the image, the determination result based on
Dzu-out image processing a digital color image reproducing apparatus for.

[0002]

2. Description of the Related Art Some conventional digital color copying machines obtain a reproduced image using four color inks, C, M, Y and K. However, when a black character on a white background is reproduced in four colors, if the gray balance is disrupted or a misregistration occurs, coloring or bleeding occurs, and the image quality deteriorates. Therefore, in order to reproduce black characters on a white background with high image quality, it is necessary to reproduce black characters in a single black color. Therefore, a method of performing image area separation processing for separating a black character on a white background from another color character or picture and reproducing the image in a single black color is adopted.

In a color copier, four photosensitive drums are provided, and C, M, Y, and K plates are simultaneously formed in a single scan to obtain a reproduced image (four-drum system).
Equipped with one photoreceptor drum, C,
There are two main systems (one-drum system) in which M, Y, and K (in any order) plates are formed and sequentially transferred to a transfer medium to obtain a reproduced image. In the four-drum system, since the original is scanned only once, if a black character is not separated as a black character and erroneous separation occurs, the portion is reproduced in four colors, so that coloring or bleeding occurs, but there is substantially no bleeding. It is reproduced with colors close to coloring, and abnormalities at the time of erroneous separation are not so noticeable. On the other hand, in the one-drum system, the original is scanned four times to form the C, M, Y, and K plates.

In general, a scanned and digitized image signal does not output exactly the same signal four times, and the signal fluctuates. Therefore, the same result cannot be obtained in the area determination of the image for each scan. That is, since black character determination is performed for each scan, a portion having black characters may or may not be determined to be a black character for each scan due to fluctuations. For example, when the C and K plates are generated, they are not determined as black characters,
If black characters are determined during the Y and M printing, the Y and M inks are not applied. Further, although the C ink subjected to the pattern processing is ejected, the K ink may not be ejected at the time of the pattern processing because the amount of generated K is small. Then, only the C ink is applied to that location. In addition, when it is determined that the character is a black character at the time of the Y, M, and C plates and is determined that the image is a pattern at the time of the K plate, the character disappears. Since erroneous separation is likely to occur at the same place, abnormalities in erroneous separation such as characters to be reproduced as black characters are reproduced as colored characters or characters disappear, and image quality is significantly degraded. Further, there is an area where not only the character is erroneously separated but also a region other than the character is erroneously separated from the character, and the character is determined as an isolated point. This is also a major factor causing image quality degradation.

[0005]

As described above, in any of the above methods, characters to be reproduced as black characters are reproduced as colored characters, bleeding appears, or characters disappear. The image quality is significantly degraded. According to the present invention, a determination result of separation is stored in a storage device, an image is formed using only one determination result, and an isolated point of the determination result stored in the storage device is removed. It is an object of the present invention to provide a high-quality digital color image reproducing apparatus in which separation is reduced and the image quality of a region other than characters is improved.

[0006]

According to the first aspect of the present invention, an original is read a plurality of times using R, G, and B digital image signals, and digitally recorded using Y, M, C, and K color materials. In a digital color image reproducing apparatus, an image feature judging device for judging an image feature, a storage device for storing all or a part of the judgment result, and an image processing device for performing image processing based on the judgment result are successively provided. in case of reproducing a plurality of the same document, the result of judgment in the image feature judging device when one color th readout of the same document stored in said storage device, said storage device at the time of reading 2-color or subsequent the document Image processing is performed using the stored determination result.

According to the second aspect of the present invention, an original is read a plurality of times using digital image signals of R, G, and B, and Y, M, and
Digital color recording digitally with C and K color materials
In the image reproduction device, an image feature determination device that determines the feature of the image, a storage device that stores all or a part of the determination result, and a unit that operates information stored in the storage device,
Determination result and an image processing apparatus that performs image processing based stores the result of the determination in the storage device in the image feature judging device when one color th readout of the same document,
Isolation of an isolated area determined to be a character in the stored determination result
Adding the correction for processing point removal, at the time of reading 2-color subsequent the document decided to perform image processing using the corrected result of the determination.

[0008]

[Action] In the invention of claim 1, stored in a case of reproducing a plurality of the same original is continuously, the result of the determination in the image characteristic determining means when one color th readout of the same document in a storage means, the document during the two-color subsequent readout becomes possible to perform image processing using the determination result stored in the storage means.

According to the second aspect of the present invention, the same original
Storing the result of determining the image characteristic determining means when the color th read in the storage means, sentences stored in the determination result
Adding the correction for processing an isolated point removal shape and the determined isolated areas, two colors subsequent the document, it becomes possible to perform image processing using the corrected determination result at the time of the final read-out.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below. Book
In the embodiment, the determination result of separation is stored, and a high-quality image can be formed using only one determination result. In addition, by removing isolated points of the determination result stored in the storage device, erroneous separation of a region other than a character from a character is reduced, and the image quality of the region other than the character is improved.

FIG. 1 shows a schematic configuration of a color image reproducing apparatus to which the present invention is applied. The R, G, and B digital signals input from the image input device 1 are converted into density data by a LOG conversion circuit 2. The converted data is input to a dot separation circuit 3, a character separation circuit 4, a color separation circuit 5, and a filter circuit 6. The output of the halftone dot separation circuit 3 is output to the filter circuit 6 at the time of the first scanning and is simultaneously written to the storage device 8. The output of the character separation circuit 4 is output to the filter circuit 6 and the UCR circuit 10 at the time of the first scanning, and is simultaneously written to the storage device 8. Color separation circuit 13
Are output to the UCR circuit 10 at the time of the first scanning and are simultaneously written to the storage device 8. Here, the storage device 8 is for writing and reading the results obtained by the dot separation circuit 3, the character separation circuit 4, and the color separation circuit 5. The color correction circuit 9 performs color correction and black signal generation.
The CR circuit 10 is a circuit for generating new density data C, M, Y. The multiplexer 7 switches a signal input to the multiplexer 7 from the halftone dot separation circuit 3, the character separation circuit 4, the color separation circuit 5, and the storage device 8 to the filter circuit 6, the UCR circuit 10, and the dither circuit 11. The recording device 12 is a device for recording the image information finally dithered by the dither circuit 11.

First, a process until input image data is recorded by the recording device 12 will be sequentially described. The reflectance linear R, G, B digital signals input from the image input device 1 are:
The LOG conversion circuit 2 converts the data into density data. This density data is input to a halftone dot separation circuit 3, a character separation circuit 4, and a color separation circuit 5.

The dot separation circuit 3 is a circuit for determining whether or not a pixel of interest is a dot. As an algorithm for determining the halftone dot separation, for example, “Transactions of the Institute of Electronics, Information and Communication Engineers D
-II Vol. J75-D-II No. 1 page 39-47 "may be used. This separation algorithm differs in the characteristics of the density change between the color halftone area, the black and white halftone area, and the character area. That is, the density change between the color halftone area and the black and white halftone area is the density change of the character area. Focusing on a point that is significantly different from the above, a peak pixel is detected, a halftone dot region is detected, and a halftone dot region is corrected to separate a halftone dot region.

The detection of a peak pixel is performed by, for example, (1) "3 ×
The density level L of the central pixel in the pixel block of 3 pixels
Is higher or lower than the density of all pixels. "
(2) “The density level of the center pixel and the density levels a and b of the paired pixels present diagonally across the center pixel are | 2
* L-ab-> TH (TH is a fixed threshold) is detected. If (1) and (2) are simultaneously satisfied, the center pixel is detected as a peak pixel. " Next, a halftone dot area is detected. For example, (3) "If four or more blocks including a peak pixel exist in four blocks in units of 4 × 4 pixels, the target block is detected as a halftone dot." It is determined as a point candidate area, and the others are determined as non-halftone candidate areas. " After determining the halftone / non-halftone candidate area, correction is performed using the result of the halftone area detection in (3). More specifically, if four or more of the nine blocks around the target block are halftone dot candidates, the target block is set as a halftone dot region. Otherwise, the target block is set as a non-halftone dot region.

The output of the dot separating circuit 3 is supplied to the multiplexer 7 according to the separation result of the dot separating circuit 3 during the first scanning.
Is switched to the filter circuit 6 at the same time, and is simultaneously written to the storage device 8. During the second and subsequent scans, the output of the dot separation circuit 3 is ignored.

The character separation circuit 4 is a circuit for determining whether or not the target pixel is a character on a white background. As a determination algorithm of the halftone dot separation, for example, the aforementioned “Transactions of the Institute of Electronics, Information and Communication Engineers D-II Vol. J75-D-II N
o. 1 page 39-47 ". This algorithm applies edge enhancement to input image data of 64 gradations and then sets 3
Perform value conversion. Next, the continuity of the black pixel and the white pixel is detected. After that, when both the black continuous pixel and the white continuous pixel exist in the AND section, at least one block is regarded as an edge area. judge. The above is the outline of the algorithm. Thus, in combination with the above-described halftone dot separation algorithm, in other words, from the results of both halftone dot region detection and edge region detection,
That is, the area determined as a non-halftone area by the halftone area detection and the edge area determined by the edge area detection is defined as a character area, and the other areas are determined as a picture area (halftone area, photograph area). Character areas can be separated.

The output of the character separation circuit 4 is output to the filter circuit 6 and the UCR circuit 10 at the time of the first scanning, and is simultaneously written into the storage device 8. During the second and subsequent scans, the output of the character separation circuit 4 is ignored. According to the separation result, the above-described switching of the filtering process, the switching of the UCR process,
Performs output dither switching.

The color separation circuit is a circuit for determining whether or not the target pixel is a black pixel. The expression b = max (| cm |, | my |, | yc |) is calculated for the image data subjected to the density conversion, and if the value obtained by the expression is less than a certain value, the pixel is calculated. Is determined as a black pixel. If the character separation circuit 4 determines that the character is a character and the color separation circuit 5 determines that the pixel is a black pixel, the character is determined to be a black character. The output of the color separation circuit 5 is output to the UCR circuit 10 at the time of the first scanning, and at the same time, the storage device 8
Is written to. During the second and subsequent scans, the output of this circuit is ignored.

The storage device 8 is a circuit for writing and reading the results obtained by the dot separation circuit 3, character separation circuit 4, and color separation circuit 5. The results of halftone dot separation, character separation, and color separation obtained during the first scan (for example, when forming the K plate) are stored, and when the second and subsequent scans (for example, when forming the C, M, and Y plates). ), Each separation result is read out and each image processing is switched.

The filter circuit 6 applies a filter having different filter characteristics to the image according to the result of the image area separation. At the time of the first scanning, the output of the dot separation circuit 3 and the character separation circuit 4 is directly received. In the second and subsequent scans, the result of halftone separation and character separation read from the storage device 8 is received. Pixels determined to be halftone dots by halftone separation are subjected to smoothing, and pixels determined to be characters as a result of character separation are subjected to edge enhancement. Weak edge enhancement is applied to pixels determined to be in other areas. FIGS. 2A, 2B, and 2C show examples of the respective filters.

The color correction circuit 9 performs primary linear masking on the density data to perform color correction and black signal generation.

The UCR circuit 10 generates density data c ', m',
A black component is generated from the minimum value of the signal y ′, the black component is subtracted from the original density data, and new density data c, m, y
Is a circuit that generates. Normally, the following equation, k = min
(C ', m', y '), c = c'-k, m = m'-k,
Calculate with y = y'-k. If the character separation circuit 4 determines that the pixel is a character pixel and the color separation circuit 5 determines that the pixel is a black pixel,
k = min (c ′, m ′, y ′), c = 0, m = 0, y
= 0. At the time of the first scanning, the output of the character separation circuit 4 and the color separation circuit 5 is directly received. At the time of the second and subsequent scans, the result of the character separation circuit 4 and the color separation circuit 5 read from the storage device 8 is received.

The recording device 12 is a device that performs dither processing from a recording signal obtained from the UCR circuit 10, forms an image, transfers the image to a transfer medium, and records the image. Here, the matrix size of the dither matrix is changed according to the character separation result. If the pixel is determined to be a character, the matrix is 1 × 1, otherwise, the matrix is 2 × 2.

When a plurality of identical documents are successively reproduced, the result determined by the image characteristic determination device is stored in the storage device at the time of the first reading, and the first reading is performed at the time of the second reading and the final reading. The image processing may be performed using the determination result that is sometimes stored in the storage device.

Next, the second embodiment will be described focusing on the differences from the first embodiment. FIG. 3 shows a second embodiment. The difference from the first embodiment is that an information operation device 13 for operating information in a storage device is added. The devices other than the information operating device 13 may be the same devices as in the first embodiment.

The information operating device 13 is a device for correcting information stored in the storage device. The determination result of the feature of the image determined by the image feature determination device at the time of the first reading is stored in the storage device, and the stored determination result is corrected. At the time of the second and subsequent final readings, appropriate image processing is performed using the corrected determination result.

Specifically, the result of the character area determination circuit is corrected. That is, if a portion determined to be a character in 16 × 16 pixels is isolated, it is corrected by regarding it as a non-character portion. The state before and after the correction is shown in FIG.
(A) and (b) show. Since the isolated area determined to be a character is subjected to the process of removing isolated points, erroneous separation of the area other than the character from the character is reduced, and the image quality of the area other than the character is improved. Although the description of the embodiment of the present invention is as described above, the present invention is not limited to the above example, and reads an original multiple times with R, G, B digital image signals,
It can be widely applied to a digital color image reproducing apparatus that digitally records with Y, M, C, and K inks.

[0028]

According to the first aspect of the present invention, multiple copies of the same original are provided.
It is possible to use the unique image feature judgment result
Image quality due to different image feature judgment results
And a stable quality image can be obtained.

According to the second aspect of the present invention, the character is determined to be a character.
The isolated area is subjected to the process of removing isolated points.
It is less likely that areas other than
The image quality in the outer area can be improved.

[0030]

[Brief description of the drawings]

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

FIG. 2 is a diagram showing various filters.

FIG. 3 is a diagram showing a second embodiment of the present invention.

FIG. 4 is a diagram showing how an isolated point is removed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image input device 2 LOG conversion circuit 3 Halftone dot separation circuit 4 Character separation circuit 5 Color separation circuit 6 Filter circuit 7 Multiplexer 8 Storage device 9 Color correction circuit 10 UCR circuit 11 Dither circuit 12 Recording device 13 Information operation device

Continuation of front page (56) References JP-A-3-256178 (JP, A) JP-A-3-208467 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N 1 / 40-1/409 H04N 1/46 H04N 1/60

Claims (2)

(57) [Claims] 1. A digital color image reproducing apparatus which reads an original document a plurality of times using digital image signals of R, G, and B and digitally records the image using Y, M, C, and K color materials. An image feature determination device that determines a feature, a storage device that stores all or a part of the determination result, an image processing device that performs image processing based on the determination result, and a case where a plurality of the same original are continuously reproduced. the result of the determination in the image feature judging device when one color th readout of the same document stored in the storage device, the image processing at the time of reading 2-color subsequent the document by using the determination result is stored in the storage device A digital color image reproducing apparatus. 2. A digital color image reproducing apparatus for reading a document a plurality of times using R, G, and B digital image signals and digitally recording the image using Y, M, C, and K color materials. An image feature determination device that determines a feature, a storage device that stores all or part of the determination result, a unit that operates information stored in the storage device, and an image processing device that performs image processing based on the determination result. Have the same manuscript
The result of the determination in the image feature judging device when one color th read and stored in the storage device, the stored determination result is determined as a character row processing of the isolated point removal the isolated region
Cormorant correct addition, digital color image reproducing apparatus characterized by performing image processing using at the time of two-color or subsequent reading said corrected determination result of the document.