JP2000307867A - Device and method for image processing and computer- readable recording medium with image processing program recorded thereon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce mosquito noise due to JPEG compression, using a simple processing. SOLUTION: This image processor separates and extracts only the character part data from image data obtained by reading an original image (S5), binarizes them (S6) and stores them in a memory (S7) in the case of copying an original in which the character parts and design parts are mixed, and also performs JPEG compression of another design parts (S8), stores them in a memory (S9), performs JPEG expansion (S10) and subsequently, combines the design part data with the binarized character part data (S11) and output them (S16).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus and method capable of reducing image quality degradation called mosquito noise generated when JPEG compression is performed on image data in which, for example, a character portion and a picture portion are mixed, and an image processing method. The present invention relates to a computer-readable recording medium on which a processing program is recorded.

[0002]

2. Description of the Related Art As a method for compressing image data (particularly, a color still image), JPEG compression using DCT (Discrete Cosine Transform) is widely used at present. However, JP
In EG compression, JPEG
When the high frequency components of DCT used for compression are roughly quantized,
It is known that the elimination of high-frequency components during quantization causes image quality deterioration called mosquito noise to occur in images and edge portions (portions where pixel values change rapidly) containing high-frequency components. Therefore, in an image forming system using JPEG compression, for example, in a copying machine or a system in which a document read by a scanner is printed by a printer, when copying a document in which a character portion and a picture portion are mixed, data is Since a high-frequency component is included, mosquito noise is generated in a character portion where the pixel value changes rapidly, and an output image in which the image quality of the character portion is deteriorated is sometimes obtained.

[0003] As a conventional method for removing mosquito noise, for example, area separation data of a character portion is held before compression, and a character area is corrected based on the area separation data after decompression of compressed data. There is known a mosquito noise removing device (see Japanese Patent Application Laid-Open No. 5-294018).

[0004]

However, in the above-described mosquito noise removing method, since a character portion is corrected based on the segmentation data, a relatively complicated process such as correction of image data is separately performed. However, there is a certain limit to speeding up processing and cost reduction for improving image quality.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has an image processing apparatus and method capable of reducing mosquito noise by simple processing, and a computer-readable recording medium storing an image processing program. The purpose is to provide.

[0006]

The above object of the present invention is achieved by the following means.

(1) An image processing apparatus according to the present invention comprises a detecting means for detecting an edge part of image data, and a separating means for separating the image data into an edge part and a non-edge part based on a detection result of the detecting means. JPEG processing means for performing JPEG processing on the image data of the non-edge part separated by the separation means; and the image data of the edge part separated by the separation means and the JPEG processing after being separated by the separation means. Synthesizing means for synthesizing the non-edge image data JPEG-processed by the JPEG processing means.

(2) Further, the image processing apparatus further includes a gradation reduction processing means for performing a gradation reduction processing for reducing the number of gradations on the image data of the edge part separated by the separation means. The image data of the edge part subjected to the gradation reduction processing by the gradation reduction processing means is combined with the image data of the non-edge part subjected to the JPEG processing by the JPEG processing means.

(3) The gradation reduction processing means has a binarization processing section for binarizing the image data, and a first memory section for storing the binarized image data.

(4) The gradation reduction processing means includes a reversible compression section for reversibly compressing the image data subjected to the gradation reduction processing, and a reversible decompression section for reversibly expanding the image data after the gradation reduction processing which has been subjected to the gradation reduction processing. And the first memory stores the image data that has been subjected to the gradation loss processing that has been losslessly compressed.

(5) The JPEG processing means includes a JPEG compression unit for JPEG-compressing the image data, a second memory unit for storing the JPEG-compressed image data, and a JPEG compression unit for storing the image data taken out from the second memory unit. Extending J
And a PEG extension unit.

(6) In the image processing method according to the present invention, a step of detecting an edge portion of the image data, a step of separating the image data into an edge portion and a non-edge portion based on a detection result of the edge portion, Performing a JPEG process on the separated non-edge image data; and combining the separated edge image data and the non-edge image data subjected to the JPEG process after the separation. Features.

(7) In the computer readable recording medium according to the present invention, a procedure for detecting an edge portion of image data and separating the image data into an edge portion and a non-edge portion based on a detection result of the edge portion. A procedure for performing JPEG processing on the image data of the separated non-edge portion;
And a procedure for synthesizing the image data of the non-edge portion subjected to the PEG processing.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a configuration diagram showing an example of an image forming system to which the present invention is applied.

In this image forming system, a scanner 1 for reading a document and a printer 2 for printing are connected, and a document image read by the scanner 1 is output by the connected printer 2. It can be used like a copying machine. The original image is read by the color CCD of the scanner 1 and output as 8-bit RGB image data. This image data is transferred to the printer 2 after various processes such as RGB → YMCK color conversion in the image processing unit of the scanner 1.

The image forming system to which the present invention is applied is not limited to the above. For example, image data created by a personal computer or a workstation,
Alternatively, a system may be used in which image data from a digital device other than a scanner (for example, a digital camera or a digital video camera) is transferred from the device to a printer and printed. Further, the present invention can be applied to the copying machine itself.

FIG. 2 is a block diagram showing a detailed configuration of the image forming system of FIG.

The scanner 1 has a reading unit 101 provided with a color CCD and an A / D conversion unit, an operation panel 102 to which a user's instruction is input, and a control board 103. The control board 103 includes a reading unit 101
, A memory 105 for temporarily storing read image data, and a backup RAM 106 for storing set image processing parameters.
, A memory control unit 107 for controlling the memory 105 and the backup RAM 106, an image processing unit 108 for performing various image processing, a panel control unit 109 for controlling the operation panel 102, and a video interface (I / F) 110, a video interface control unit 111 for controlling the F / F) 110, and a CPU 112 for comprehensively controlling the entire scanner 1. The reading unit 101 and the control board 103 are connected by SCSI, and the operation panel 102 and the control board 103 are connected by a dedicated interface. The image data subjected to the image processing is transferred to the printer 2 via the video interface 110.

The printer 2 includes a video interface (I / F) 201 and a non-video interface (I / F) 202 that can communicate with the scanner 1, and a printer engine 203 that outputs (prints) image data received by the video interface 201. And a CPU 204 that comprehensively controls the entire printer 2. Printer engine 20
3 forms a color image by forming an image corresponding to each color of yellow (Y), magenta (M), cyan (C), and black (K) on one surface and synthesizing an image of four colors.

FIG. 3 is a block diagram showing an example of image processing in the image processing section 108 of FIG.

The RGB 8-bit image data read by the reading unit 101 and A / D converted and output are temporarily stored in a memory 105 of a control board 103 (not shown). Is read out at the timing of
Is input to In the image processing unit 108, the input RG
For B image data, LOG conversion, UCR / B
P processing and color correction are performed. That is, the LOG conversion unit 113
Then, a process of converting the luminance data of the RGB image data into density data is performed.
The undercolor removal of the GB image data and the processing of black generation (black amount calculation) are performed, and the color correction unit 115 performs processing of converting the RGB image data into YMC data which is a printing color.

The contents of the image processing are not limited to these. For example, scaling processing, smoothing (suppression of moiré), and MTF correction (sharpening of characters / line drawings)
Γ correction (linearization of recording density) in accordance with the output characteristics of the printer 2 may be performed. The contents of the image processing performed by the image processing unit 108 are as follows.
It can be arbitrarily selected as appropriate from the above various image processing.

According to the present invention, in order to reduce mosquito noise generated in a character portion when a document or the like in which a character portion and a picture portion are mixed using JPEG compression is used, the mosquito noise includes an image including a high frequency component. Focusing on the tendency to occur at edges and edges (where the pixel value changes rapidly), a character portion with a sudden change in pixel value and a character portion with a large gradation change and a picture with a gentle gradation and a small gradation change The JPEG compression is performed only on the picture portion, and the text portion and the picture portion are image-combined after JPEG decompression.

FIG. 4 is a block diagram showing the entire system configuration for mosquito noise reduction processing according to one embodiment of the present invention.

An image of a document in which a character portion and a picture portion are mixed is read by a color CCD 116 and sent to an A / D converter 117 as analog image data, where it is converted into multi-valued digital image data. Color CCD 11
6 and the A / D conversion unit 117
1 included.

Digital image data (hereinafter simply referred to as “image data”) output from the A / D converter 117 is
As described above, the memory 1 of the control board 103
05 (not shown), the image processing unit 10
8 and to the area determining unit 118.
The image processing section 108 performs the above-described image processing (see FIG. 3). On the other hand, the area determination unit 118 performs a process of determining a character portion and a picture portion. This determination processing is performed using a method of, for example, setting a character portion if pixels determined to be edges continue beyond a predetermined threshold value.

The character / picture separating section 119 separates the image data processed by the image processing section 108 into a character section and a picture section by using the discrimination result of the area discriminating section 118. (Hereinafter referred to as "character portion data") and image data of only the picture portion (hereinafter referred to as "picture portion data").

More specifically, as shown in FIG. 5, in the character / pattern separation section 119, the input image 131 after the image processing is performed by using the determination result of the area determination section 118 as an image of only a character portion ( This is separated into a character portion data 132 and an image (picture portion data) 133 having only a picture portion. At this time, in the image 132 including only the character portion, the density value 0 is substituted for the pixel where the picture exists. Similarly, in the image 133 including only the picture portion, the density value 0 is assigned to the pixel where the character exists.

The character part data is binarized by the binarization processing section 120 and the binarized data is stored in the memory 121. That is, JPEG compression is not performed on character portion data.

On the other hand, as for the picture portion data, JPEG
JPEG compression is performed by the compression unit 122, and the compressed data is stored in the memory 123. In the JPEG decompression unit 124,
The picture data extracted from the memory 123 is JPEG
It is extended.

In the character / pattern synthesizing unit 125, the image data after the JPEG decompression by the JPEG decompression unit 124 and the character data extracted from the memory 121 are image-combined.

More specifically, as shown in FIG. 6, in the character / pattern synthesizing unit 125, an image (character part data) 134 of only the binarized character part and an image only of the pattern part after the JPEG expansion are performed. (Picture part data) 135 and a composite image 136 is created. At this time, the images are combined by, for example, adding the image 134 having only the character portion and the image 135 having only the picture portion.

The image data synthesized by the character / picture synthesizing unit 125 is subjected to screening processing by the screening processing unit 126 and sent to the printer 2. The image data sent to the printer 2 is YMCK data (see FIG. 3).

In this embodiment, the binarization process is performed on the character part data after separation, but the present invention is not limited to this. Multi-value processing may be used as long as the number of gradations is reduced.

In order to further reduce the memory capacity, the character portion data may be stored in the memory 207 after performing appropriate reversible compression after binarization or multi-level conversion. . In this case, a reversible decompression unit for reversibly decompressing the data retrieved from the memory 207 is required.

In the present embodiment, after the image-processed image data is separated into a character portion and a pattern portion by the character / pattern separation section 119, the image data is converted into any of the character portion data, the pattern portion data, and the composite image. Although no image processing is performed, the character / picture separation unit 119 is not limited to this.
After the input image is separated into a character portion and a pattern portion by (5), another image processing may be performed on the character portion data, the pattern portion data, the composite image, or a combination thereof.

FIG. 7 is a flowchart showing the procedure of the copy operation in the system of FIG.

When the copying of the document is started, the scanning operation by the reading unit 101 of the scanner 1 is started, and the image of the document is read by the color CCD 116 and A / D
The conversion unit 117 converts the image data into multi-valued digital image data (S1), and sends the image data to the image processing unit 108 and also to the area determination unit 118.

The image processing unit 108 performs the above-described image processing on the input image data (see FIG. 3).
2) On the other hand, the area discriminating section 118 performs an area discriminating process between the character portion and the picture portion on the input image data (S3). This area determination processing is executed by using a method of determining a character portion if pixels determined to be edges continue beyond a predetermined threshold value, as described above. The image data subjected to the image processing in step 2 and the result of the area discrimination processing in step 3 are both sent to the character / pattern separation unit 119.

The character / pattern separating section 119 first determines whether or not the original is a mixed original of a character portion and a pattern portion based on the result of the area discrimination processing in step 3 (S4). (S4: YES) The process proceeds to step 5, and if not a mixed document (S4: NO), the process proceeds to step 11.

If the document is a mixed document (S4: YE
S) In step 5, the image data subjected to the image processing in step 2 is separated into character portion data and picture portion data using the area determination processing result in step 3 (see FIG. 5).

The character part data separated in step 5 is subjected to the binarization processing by the binarization processing section 120 (S6), and the data after the binarization processing is temporarily stored in the memory 121 (S7). ).

On the other hand, the picture data separated in step 5 is also JPEG compressed by the JPEG compression section 122.
After compression (S8), the JPEG-compressed data is temporarily stored in the memory 123 (S9).
At 24, JPEG-compressed data extracted from the memory 123 is JPEG-decompressed (S10).

Thereafter, the character / pattern synthesizing unit 125 combines the binarized character portion data extracted from the memory 121 and the picture portion data JPEG decompressed by the JPEG decompression unit 124 in step 10 into one image data. The images are combined (see FIG. 6) (S11), and the process proceeds to step 15.

If the document is not a mixed document (S4: N
O), the image data after the image processing in step 2 is JPEG-compressed by the JPEG compression unit 122 as it is (S
12) After temporarily storing the JPEG-compressed data in the memory 123 (S13), the JPEG decompression unit 124 JPEG-decompresses the JPEG-compressed data extracted from the memory 123 (S14), and proceeds to step 15.

In step 15, the screening processing unit 126 performs a screening process on the received image data. The image data after the screening process is
It is sent to the printer 2 and printed out from the printer 2 (S16).

In this embodiment, if the original is not a mixture of a character portion and a pattern portion, the image data after image processing is directly JPEG-compressed regardless of whether the original is a character-only document or a document-only document. However, as in the case of a mixed document, if the document is a text-only document, the image data (text-portion data) after image processing is duplicated. Perform value processing, etc. (S6 to S
7), if the original is only a picture portion, JPEG compression or the like may be performed on the image data after the image processing (picture portion data) (S8 to S10).

Therefore, according to the present embodiment, when copying an original having both a character portion and a picture portion, only the character portion data is separated from the image data obtained by scanning, extracted, binarized, and stored in the memory. Along with
Other picture part data is JPEG-compressed and stored in a memory, and after JPEG decompression, the picture part data and binarized character part data are combined and output (printed).
In other words, before performing JPEG compression, a portion (edge portion or character portion) where the pixel density value changes rapidly is removed from the image data to be JPEG-compressed, and a portion where mosquito noise is unlikely to be generated even when JPEG compression is performed. JPEG compression is performed only on non-edge parts or picture parts, and then both parts are combined and output (printed). This reduces mosquito noise that has conventionally occurred in character parts due to JPEG compression. Thus, a high-quality image can be obtained. Moreover, in that case, a relatively simple operation such as separating the character part and the picture part and performing separate processing and recombining them is sufficient, and a relatively complicated operation such as correction of image data as in the past. Is not required, so that processing for improving image quality can be speeded up and cost can be reduced.

Further, by separating the character portion and the picture portion, the portion where the pixel value changes rapidly in the image data (picture portion data) to be JPEG-compressed is reduced. The compression ratio can be increased.

Further, when character part data is binarized, the data can be represented by one bit of 0 or 1, so that the memory capacity can be reduced accordingly.

The mosquito noise reduction processing in the scanner 1 is performed by the CPU 112 executing a predetermined program describing the processing procedure of FIG. 7, and the predetermined program is stored in a computer-readable recording medium (for example, , Floppy disk and CD-RO
M etc.). Further, the predetermined program may be provided, for example, as application software that executes the above-described processes independently, or may be incorporated in scanner software as one function of the scanner. The same applies to the case where the scanner output is image-processed on a personal computer and output to a printer.

[0053]

As described above, according to the present invention,
Before performing JPEG compression, edge parts where mosquito noise is likely to be generated by JPEG compression are removed from the image data to be JPEG compressed, and only the remaining non-edge image data where mosquito noise is unlikely to be generated even when JPEG compression is performed. After JPEG compression, the image data of the edge part and the non-edge part are combined and output.
With simple processing, mosquito noise that has conventionally occurred due to JPEG compression can be reduced, and a high-quality image can be obtained. Also, by separating the edge portion from the non-edge portion, the portion where the pixel value changes rapidly in the non-edge portion image data to be JPEG-compressed is reduced.
The compression ratio of G compression can be increased.

Further, when the gradation reduction processing is performed on the image data of the separated edge portion, the data can be expressed by the number of bits lower than the number of gradations of the original image. Can be reduced.

At this time, when the binarization processing is performed as the gradation reduction processing, the data can be represented by one bit of 0 or 1, so that the memory capacity can be further reduced.

When reversible compression is performed on the image data of the edge part subjected to the gradation reduction processing, the memory capacity can be further reduced as compared with the case where only the gradation reduction processing is performed. .

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating an example of an image forming system to which the present invention is applied.

FIG. 2 is a block diagram illustrating a detailed configuration of the image forming system of FIG. 1;

FIG. 3 is a block diagram illustrating an example of image processing in an image processing unit in FIG. 2;

FIG. 4 is a block diagram showing an entire system configuration for mosquito noise reduction processing according to an embodiment of the present invention.

FIG. 5 is an explanatory diagram of processing contents of a character / pattern separation unit in FIG. 4;

FIG. 6 is an explanatory diagram of processing contents of a character / picture combining unit of FIG. 4;

FIG. 7 is a flowchart illustrating a procedure of a copy operation in the system of FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... scanner, 2 ... printer, 118 ... area discrimination part (detection means), 119 ... character / picture separation part (separation means), 120 ... binarization processing part (tone reduction processing means), 121 ... memory (floor Adjustment processing means, first memory section), 122: JPEG compression section (JPEG processing means), 123: memory (JPEG processing means, second memory section), 124: JPEG decompression section (JPEG processing means), 125: characters / Picture synthesis section (synthesis means).

Continued on the front page F term (reference) 5C077 LL02 MP07 MP08 PP23 PP27 PP28 PP32 PP33 PP38 PP43 PP47 PQ22 RR02 RR21 TT02 TT06 5C078 AA09 BA21 CA21 DA01 DA02 DB06 9A001 EE04 HH27 HH28

Claims (7)

[Claims] A detecting unit that detects an edge of the image data; a separating unit that separates the image data into an edge portion and a non-edge portion based on a detection result of the detecting unit; JPEG processing means for performing JPEG processing on non-edge image data; non-edge image data separated by the separation means and non-edge JPEG processed by the JPEG processing means after being separated by the separation means And a synthesizing unit for synthesizing the image data of the section. 2. The image processing apparatus according to claim 1, further comprising: a gradation reduction processing unit configured to perform a process of reducing the number of gradations on the image data of the edge part separated by the separation unit. 2. The image processing apparatus according to claim 1, wherein the image data of the edge part subjected to the gradation reduction processing is combined with the image data of the non-edge part subjected to the JPEG processing by the JPEG processing means. 3. The image processing apparatus according to claim 2, wherein the gradation reduction processing unit includes a binarization processing unit that binarizes the image data, and a first memory unit that stores the binarized image data. Item 3. The image processing device according to Item 2. 4. A reversible compression section for reversibly compressing image data subjected to gradation reduction processing, and a reversible expansion section for reversibly expanding image data after gradation reduction processing which has been subjected to gradation reduction processing. The image processing apparatus according to claim 2, further comprising: a first memory that stores the image data that has been subjected to the gradation reduction processing that has been losslessly compressed. 5. The JPEG processing means includes: a JPEG compression unit for JPEG-compressing image data; a second memory unit for storing JPEG-compressed image data; and a JPEG decompression unit for extracting image data extracted from the second memory unit. JPE to do
The image processing apparatus according to claim 1, further comprising a G decompression unit. 6. A step of detecting an edge portion of the image data, a step of separating the image data into an edge portion and a non-edge portion based on a detection result of the edge portion, An image processing method comprising: performing a JPEG process on the image data; and combining the separated image data of the edge portion and the image data of the non-edge portion subjected to the JPEG process after the separation. 7. A procedure for detecting an edge portion of image data, a procedure for separating image data into an edge portion and a non-edge portion based on a detection result of the edge portion, A computer for storing an image processing program for causing a computer to execute a JPEG process on the image, a procedure for combining the separated edge image data with the non-edge image data subjected to the JPEG process after the separation, and A readable recording medium.