JPH0758967A - Digital color image reproduction device - Google Patents

Abstract

(57) [Abstract] [Purpose] It is an object to provide a high-quality digital color image reproducing apparatus which does not cause reproduction with wrong character color, blurring, and character loss. [Arrangement] In a digital color image reproducing apparatus for reading a document a plurality of times with R, G, B digital image signals and digitally recording it with Y, M, C, K inks, A digital color image reproducing apparatus comprising: an image feature determination device for determination; a storage device for storing all or a part of the determination result; and an image processing device for performing image processing based on the determination result.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to digital image processing,
In particular, the present invention relates to a digital color image reproducing apparatus which stores a result of determining a feature of an image and performs image processing based on the determination result.

[0002]

2. Description of the Related Art Some conventional digital color copying machines obtain reproduced images by using four color inks, C, M, Y, and K. However, when reproducing black characters on a white background with four colors, if the gray balance is disturbed or there is misregistration, coloring or blurring occurs and the image quality deteriorates. Therefore, in order to reproduce the black characters on the white background with high image quality, it is necessary to reproduce the black characters with a single black color. Therefore, a method is adopted in which an image area separation process is performed to separate the black characters on the white background from other color characters or patterns and to reproduce in a single black color.

By the way, a color copying machine is provided with four photoconductor drums, and a system for obtaining a reproduced image by simultaneously forming C, M, Y, and K plates for each scan once, and a system (4-drum system),
It is equipped with one photoconductor drum, and it is C sequentially in four scans.
The two main methods are a method (one-drum method) in which M, Y, and K (regardless of order) plates are formed and sequentially transferred to a transfer medium to obtain a reproduced image. In the 4-drum system, the document is scanned only once, so if there is an erroneous separation in which black characters are not separated as black characters, that part is reproduced in 4 colors, and coloring or blurring occurs, but it is almost nonexistent. It is reproduced in a color close to the coloring, and the abnormality at the time of erroneous separation is not so noticeable. On the other hand, in the one-drum system, the document is scanned four times to form the C, M, Y, and K plates.

Generally, the scanned and digitized image signal does not output exactly the same signal every four times, and the signal varies. Therefore, the same result cannot be obtained in the image area determination for each scan. That is, since the black character determination is performed for each scan, a portion having a black character may or may not be determined as a black character for each scan due to variation. For example, when generating the C and K plates, it is not judged as black characters,
When it is determined that the characters are black when printing on the Y and M plates, the Y and M inks are not ejected. Further, although the C ink subjected to the pattern treatment is ejected, the K ink may not be ejected because the K generation amount is small at the time of the pattern treatment. Then, only C ink will be struck at that location. Further, when it is determined that the character is black in the Y, M, and C plates and is determined to be the pattern in the K plate, the character disappears. Since erroneous separation is likely to occur at the same place, abnormalities in erroneous separation, such as characters that should be reproduced in black characters being reproduced as colored characters or disappearing, are noticeable and the image quality is significantly degraded. Furthermore, not only the erroneous separation of characters but also the areas other than the characters are erroneously separated from the characters, and there are areas that are determined as isolated points. This is also a major factor causing deterioration of image quality.

[0005]

As described above, in any of the above methods, a character that should be reproduced as a black character is reproduced as a colored character, a blur is generated, or the character disappears. Image quality is significantly degraded. The present invention stores the determination result of separation in a storage device, forms an image using only the determination result, further removes isolated points of the determination result stored in the storage device, and mistakes an area other than a character as a character. It is an object of the present invention to provide a high-quality digital color image reproducing device in which the separation is reduced and the image quality of the area other than the character is improved.

[0006]

According to a first aspect of the present invention, an original is read a plurality of times by R, G, B digital image signals and digitally recorded by Y, M, C, K inks. In the digital color image reproducing apparatus, the image feature determining apparatus for determining the characteristics of the image, the storage device for storing all or a part of the determination result, and the image processing are performed based on the determination result.

According to a second aspect of the present invention, there is provided an image feature determining apparatus according to the first aspect.
One was used as a means for separately determining the halftone dot area and the other area.

According to a third aspect of the present invention, there is provided an image feature determining apparatus according to the first aspect.
One was a means to determine the character area and other areas separately.

According to a fourth aspect of the invention, the image feature determining means 1 is
One was used as the color determination means.

According to the fifth aspect of the invention, one of the image processes is the filter process.

According to the sixth aspect of the invention, one of the image processes is the undercolor removal process.

In the invention of claim 7, one of the image processes is dithering.

According to the eighth aspect of the invention, the original is read a plurality of times by R, G, and B digital image signals, and Y,
In a digital color image reproducing apparatus for digitally recording with M, C, and K inks, an image feature determining device for determining image features, a storage device for storing all or a part of the determination result, and a determination result And an image processing device that performs image processing based on the above, and a result determined by the image feature determination means at the time of the first reading is stored in the storage device.
In the subsequent reading, the image processing is performed by using the determination result stored in the storage device in the first reading.

According to the ninth aspect of the present invention, the original is read a plurality of times by R, G, B digital image signals, and Y, M,
In a digital color image reproducing device for digitally recording with C and K inks, an image feature judging device for judging a feature of an image, a storage device for storing all or a part of the judgment result, and a judgment result based on the judgment result. When a plurality of sheets of the same original are reproduced in succession with the image processing apparatus that performs image processing, the result determined by the image feature determination means at the time of the first read is stored in the storage means, and the second and subsequent final At the time of reading, image processing is performed using the determination result stored in the storage unit at the time of the first reading.

According to the tenth aspect of the present invention, the original is read a plurality of times by digital image signals of R, G, B, and Y,
In a digital color image reproducing apparatus for digitally recording with M, C, and K inks, an image characteristic determining apparatus for determining image characteristics, a storage apparatus for storing all or a part of determination results, and a storage apparatus The information operating device for operating the information stored in the image processing device, the image processing device for performing image processing based on the determination result, and the result determined by the image feature determining means at the time of the first reading is stored in the storing means and stored. A correction is added to the determination result, and the image processing is performed using the corrected determination result during the second and subsequent final readings.

[0016]

According to the first aspect of the present invention, the original is read a plurality of times by the R, G, B digital image signals, and the Y,
In a digital color image reproducing apparatus that digitally records with M, C, and K inks, the characteristics of the image are judged,
It is possible to store all or part of the determination result and perform image processing based on the determination result.

According to the second aspect of the invention, it is possible to separately determine the halftone dot area and other areas.

According to the third aspect of the invention, it is possible to determine whether the character area and the other area are separated.

According to the invention of claim 4, it is possible to make a color judgment.

According to the invention of claim 5, it becomes possible to perform the filtering process.

According to the sixth aspect of the invention, the undercolor removal processing can be performed.

According to the invention of claim 7, dither processing can be performed.

In the eighth aspect of the invention, the result determined by the feature determining means at the first reading is stored in the storage means, and the result is stored in the storing means at the first reading at the second and subsequent readings. Image processing can be performed using the determination result.

In a ninth aspect of the present invention, when a plurality of identical originals are continuously reproduced, the result determined by the image feature determining means at the first reading is stored in the storing means, and the second and subsequent readings are performed. At the time of reading, it is possible to perform image processing using the determination result stored in the storage unit at the time of the first reading.

According to a tenth aspect of the present invention, the result determined by the image feature determination means at the first reading is stored in the storage means, the stored determination result is corrected, and the second and subsequent final readings are performed. Sometimes it is possible to perform image processing using the corrected determination result.

Examples of the present invention will be described below. The present invention accumulates the judgment results of separation, and is capable of forming a high-quality image using only the judgment result.
Further, by removing the isolated points of the determination result stored in the storage device, the area other than the character is not erroneously separated from the character, and the image quality of the area 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, B digital signals input from the image input device 1 are converted into density data by the LOG conversion circuit 2. The converted data is input to the halftone dot separation circuit 3, the character separation circuit 4, the color separation circuit 5 and the filter circuit 6. The output of the halftone dot separation circuit 3 is output to the filter circuit 6 and simultaneously written to the storage device 8 during the first scanning. The output of the character separation circuit 4 is output to the filter circuit 6 and the UCR circuit 10 at the same time as the first scanning, and is simultaneously written to the storage device 8. Color separation circuit 13
Is output to the UCR circuit 10 and written to the storage device 8 at the same time during the first scanning. Here, the storage device 8 writes and reads the results obtained by the halftone 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, and U
The CR circuit 10 is a circuit for generating new density data C, M, Y. The multiplexer 7 switches the signals input from the halftone dot separation circuit 3, the character separation circuit 4, the color separation circuit 5, and the storage device 8 to the multiplexer 7 to the filter circuit 6, the UCR circuit 10, and the dither circuit 11. The recording device 12 is a device that finally records the image information that has been dithered by the dither circuit 11.

With respect to the first aspect of the invention, the process until the input image data is recorded by the recording device 12 will be sequentially described. Linear reflectance R, G, B input from the image input device 1
The digital signal is converted into density data by the LOG conversion circuit 2. This density data is input to the halftone dot separation circuit 3, the character separation circuit 4, and the color separation circuit 5.

The halftone dot separation circuit 3 is a circuit for determining whether or not the pixel of interest is a halftone dot. The determination algorithm for this halftone dot separation is, for example, "Journal 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 has different characteristics of density change in each of the color halftone dot area, the black and white halftone dot area, and the character area, that is, the density change of the color halftone dot area and the black and white halftone dot area is the density change of the character area. Focusing on the point that is significantly different from the above, the detection of a peak pixel, the detection of a halftone dot area, and the correction of the halftone dot area are performed to separate the halftone dot areas.

The detection of the peak pixel is performed by, for example, (1) "3 ×
The density level L of the center pixel in the pixel block of 3 pixels
Detects whether the density 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 pair of pixels existing diagonally across the center pixel are | 2 for all four pairs.
XL-a-b |> TH (TH is a fixed threshold) is detected. When (1) and (2) are simultaneously satisfied, the central pixel is detected as a peak pixel. " Next, detection of a halftone dot region is performed, for example, in (3) “4 blocks each including 4 × 4 pixels, if two or more blocks containing peak pixels exist, the block of interest is halftone-dotted. It is determined as a point candidate area, and the other areas are determined as non-halftone dot candidate areas. " After determining the halftone dot / non-halftone dot candidate regions, correction is performed using the result of the halftone dot region detection in (3). Specifically, if four or more of the nine blocks centering on the target block are halftone dot candidates, the target block is set as a halftone dot region, and if not, the target block is set as a non-halftone dot region.

The output of the halftone dot separation circuit 3 is the multiplexer 7 according to the result of the halftone dot separation circuit 3 during the first scanning.
While switching to the filter circuit 6 by, the data is simultaneously written in the memory device 8. The output of the halftone dot separation circuit 3 is ignored during the second and subsequent scans.

The character separation circuit 4 is a circuit for determining whether or not the pixel of interest is a character on a white background. As the determination algorithm for this halftone dot separation, for example, the above-mentioned “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 64 levels of input image data, and then uses 3 types of fixed thresholds.
Perform valuation. Next, the continuity of black pixels and white pixels is detected, and if at least one black continuous pixel and one white continuous pixel are present in the AND section, the block of interest is defined as an edge area, and otherwise the non-edge area is defined. judge. The above is the outline of this algorithm. Thus, in combination with the aforementioned halftone dot separation algorithm, in other words, from the results of both halftone dot area detection and edge area detection,
That is, the non-halftone dot area detected by the halftone dot area and the area determined as the edge area by the edge area detection are character areas, and the other areas are determined as the picture area (halftone dot area, photograph area), and thus the halftone dot area is determined. 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 same time as the first scanning, and simultaneously written to the storage device 8. The output of the character separation circuit 4 is ignored during the second and subsequent scans. Based on this separation result, switching of the above-mentioned filter processing, switching of UCR processing,
Switch output dither.

The color separation circuit is a circuit for determining whether or not the pixel of interest is a black pixel. For the density-converted image data, b = max (| cm−, | m−y |, | y−c |) is calculated, and if the value obtained by this formula is less than a certain value, the pixel Are determined to be black pixels. 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, it 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
Written in. The output of this circuit is ignored during the second and subsequent scans.

The storage device 8 is a circuit for writing and reading the results obtained by the halftone dot separation circuit 3, the character separation circuit 4, and the color separation circuit 5. The halftone dot separation, character separation, and color separation results obtained during the first scanning (for example, K plate image formation) are saved, and during the second and subsequent scanning (for example, C, M, Y plate image formation). ), Read each separation result, and switch each image processing.

The filter circuit 6 applies a filter having different filter characteristics to the image according to the result of the image area separation. During the first scanning, the outputs of the halftone dot separation circuit 3 and the character separation circuit 4 are directly received. During the second and subsequent scans, the result of halftone dot separation and character separation read from the storage device 8 is received. Pixels that are determined to be halftone dots by halftone dot separation are smoothed, and pixels that are determined to be characters based on the character separation result are edge-emphasized. Weak edge enhancement is applied to pixels determined to be in other areas. Examples of each filter are shown in FIGS. 2 (a), 2 (b) and 2 (c).

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

The UCR circuit 10 uses the density data c ', m',
A black component is generated from the minimum value of the signal of y ′, the black component is subtracted from the original density data, and new density data c, m, y
Is a circuit for generating. 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 it is a black pixel,
k = min (c ', m', y '), c = 0, m = 0, y
= 0. At the first scanning, the outputs of the character separation circuit 4 and the color separation circuit 5 are directly received. During the second and subsequent scans, the results of the character separation circuit 4 and the color separation circuit 5 read from the storage device 8 are received.

The recording device 12 is a device for performing dither processing on the recording signal obtained from the UCR circuit 10 to form an image, transferring the image to a transfer medium, and recording 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 set to 1 × 1, and otherwise the matrix is set to 2 × 2.

When a plurality of the same originals are continuously reproduced, the result determined by the image feature determining device is stored in the storage device during the first reading, and the first reading is performed during the second and subsequent final readings. Sometimes, image processing may be performed using the determination result stored in the storage device.

Next, the second embodiment will be described focusing on the points different from the first embodiment. The second embodiment is shown in FIG. The difference from the first embodiment is that an information operating device 13 for operating information in the 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 the information stored in the storage device. The determination result of the image feature determined by the image feature determination device during the first reading is stored in the storage device, and the stored determination result is corrected. At 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 regarded as a portion other than the character and is corrected. The state before and after this correction is shown in FIG.
Shown in (a) and (b). The isolated area determined to be a character is subjected to isolated point removal processing, so that the area other than the character is less likely to be erroneously separated from the character, and the image quality of the area other than the character is improved. Although the embodiment of the present invention has been described above, the present invention is not limited to the above example, and the original is read a plurality of times by R, G, and B digital image signals,
It can be widely applied to a digital color image reproducing apparatus for digitally recording with Y, M, C and K inks.

[0044]

According to the first aspect of the present invention, the unique feature determination result can be used for each scan, and the deterioration of the image quality due to the different feature determination result in each scan can be prevented.

According to the inventions of claims 2, 3, and 4, halftone dots,
By separating the characters and others, it becomes possible to perform optimal processing on each area, and by using only the single separation result, it is possible to avoid a significant deterioration in image quality even if it is erroneously separated. .

According to the fifth, sixth and seventh inventions, the halftone dot,
Optimal filtering, undercolor removal processing, and dither processing can be performed on the character and other areas, and at the same time, a black character can be reproduced in a black single color.

According to the invention of claim 8, only one characteristic judgment result can be used for each scanning, and it is possible to prevent the deterioration of the image quality due to the different characteristic judgment result in each scanning.

According to the invention of claim 9, the unique image feature determination result can be used for reproducing a plurality of the same document,
An image with stable quality can be obtained by suppressing variations in image quality due to different image feature determination results for each sheet.

According to the tenth aspect of the invention, the isolated point removal processing is performed on the isolated area determined to be a character, so that the area other than the character is less likely to be erroneously separated from the character, and the image quality of the area other than the character is reduced. Can be improved.

[0050]

[Brief description of 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 isolated points are removed.

[0050]

[Explanation of symbols]

 1 Image Input Device 2 LOG Conversion Circuit 3 Halftone 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 Operating Device

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical indication H04N 1/46 4226-5C H04N 1/46 Z

Claims (10)

[Claims] 1. A digital color image reproducing apparatus for reading an original a plurality of times with R, G, B digital image signals and digitally recording it with Y, M, C, K inks. An image feature determination device for determining features,
A digital color image reproducing device comprising a storage device for storing all or part of the determination result and an image processing device for performing image processing based on the determination result. 2. The digital color image reproducing apparatus according to claim 1, wherein one of the image feature determining devices is a halftone dot separating circuit for separately determining a halftone dot region and other regions. 3. A digital color image reproducing apparatus according to claim 1, wherein one of the image feature judging apparatuses is a character separating circuit for judging separately a character area and other areas. 4. The digital color image reproducing device according to claim 1, wherein one of the image feature determining devices is a color separation circuit. 5. The digital color image reproducing apparatus according to claim 1, wherein one of the image processes is a filter process. 6. The digital color image reproducing apparatus according to claim 1, wherein one of the image processes is an undercolor removing process. 7. The digital color image reproducing apparatus according to claim 1, wherein one of the image processes is a dither process. 8. A digital color image reproducing apparatus for reading an original a plurality of times with R, G, B digital image signals and digitally recording it with Y, M, C, K inks. An image feature determination device for determining features,
A storage device that stores all or part of the determination result; an image processing device that performs image processing based on the determination result; a storage device that stores the result determined by the image feature determination device during the first reading; A digital color image reproducing device comprising an image processing device that performs image processing using the determination result stored in the storage device during the first and second readings. 9. A digital color image reproducing apparatus for reading an original document by R, G, B digital image signals a plurality of times and digitally recording it with Y, M, C, K inks. An image feature determination device for determining features,
A storage device that stores all or part of the determination result, an image processing device that performs image processing based on the determination result, and the image feature determination device at the time of the first read when reproducing a plurality of the same original document continuously. A digital color image reproduction characterized in that the result of the determination made in step 2 is stored in the storage device, and image processing is performed using the determination result stored in the storage device at the time of the first read during the second and subsequent final reads. apparatus. 10. A characteristic of an image in a digital color image reproducing apparatus in which an original is read a plurality of times by R, G, B digital image signals and digitally recorded by Y, M, C, K inks. And an image feature determining device, a storage unit that stores all or a part of the determination result, a unit that operates information stored in the storage unit, and an image processing device that performs image processing based on the determination result. Then, the result determined by the image feature determination device during the first reading is stored in the storage device, the stored determination result is corrected, and the corrected determination result is used during the second and subsequent final readings. A digital color image reproducing device characterized in that image processing is performed by using a digital color image reproducing device.