JP2001186356A - Picture compression device, picture compresion method and computer readable storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To compress input picture data of an object with high compressibility and to prevent deterioration of picture quality due to compression. SOLUTION: An image area separation part 103 separates picture data which corresponds to an original picture read by a scanner 101 and is outputted from an input picture processing part 102 into picture data of the object of a character, a graphic, a photograph and a bit map, judges the block of a pixel or a picture area where picture deterioration by compression is assumed to be severe based on data showing the attributes of the separated objects. When a data compression part 107 compresses data, the compression of low compressibility and high quality is applied to the pixel or the block whose picture deterioration is judged to be severe as the result of judgement. The compression of high compressibility and low quality is applied to the pixel or block except for the said pixel or block.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image compression apparatus, an image compression method, and a computer-readable storage medium, for example, a color image copying machine that reads a color original image recorded on a recording medium and generates a copy image thereof. And a computer-readable storage medium.

[0002]

2. Description of the Related Art Conventionally, a so-called color image copying machine shown in FIG. 6 is known as an image processing apparatus for reading a color original image recorded on a recording medium such as paper and generating a copy image thereof. .

In FIG. 6, reference numeral 601 denotes an image scanner unit which reads a document and performs digital signal processing on a read signal of the document. Reference numeral 602 denotes a printer unit, which prints an image corresponding to the original image read by the image scanner unit 601 on recording paper in full color.

In the image scanner unit 601, reference numeral 600 denotes a mirror pressure plate, and an original 604 on an original platen glass (hereinafter, platen) 603 is irradiated with a lamp 605. Then, the reflected light from the document 604 is
6,607,608, and by the lens 609,
An image is formed on a three-line solid-state image sensor (hereinafter referred to as CCD) 610, and three color image signals of red (R), green (G), and blue (B) as full-color information corresponding to the image are subjected to signal processing. It is sent to the unit 611. At this time, the entire surface of the original is, for example, 400 dpi in both the main scanning and the sub-scanning.
(dots / inch) resolution, lamp 605 and mirror 60
6 is a predetermined speed V, and mirrors 607 and 608 are speed 1 /
Scanning (sub-scanning) is performed by moving the line sensor 610 in the direction perpendicular to the electrical scanning (main scanning) direction of the line sensor 610 by a mechanism (not shown) at 2v.

[0005] In a signal processing unit 611, the image signal output from the line sensor 610 is electrically processed and decomposed into components of magenta (M), cyan (C), yellow (Y), and black (Bk). The digital image data of each color component is sent to the printer unit 602. At this time, for each document scan by the image scanner unit 601, one of the color components of M, C, Y, and Bk is sent to the printer unit 602, and the target is scanned by the document scan four times in total. One scan of the color document image is completed.

The M, C, Y, and Bk image data transferred from the image scanner unit 601 are sent to a laser driver 612, and the laser driver 612 modulates and drives a semiconductor laser 613 according to the input image data. . The laser light output from the semiconductor laser 613 is transmitted to the polygon mirror 614 and the f-θ lens 61.
5. Scan the surface of the photosensitive drum 617 via the mirror 616, so that the surface of the photosensitive drum 617 has a predetermined resolution (for example, in both the main scanning direction and the sub-scanning direction as in the case of reading by the image scanner unit 601). An electrostatic latent image is written at 400 dpi (dots / inch).

Reference numeral 618 denotes a rotary developing unit, which includes a magenta developing unit 619, a cyan developing unit 620, and a yellow developing unit 62.
1. The black developing section 622 includes four developing sections that sequentially contact the photosensitive drum 617,
The electrostatic development formed on the photosensitive drum 617 is developed with toner of each color. A transfer drum 623 wraps recording paper supplied from a paper cassette 624 or 625 around the transfer drum 623, and transfers an image developed on the photosensitive drum for recording.

The recording paper on which the toner images of the four colors M, C, Y, and Bk are sequentially transferred in the above-described procedure passes through a fixing unit 626 for fixing the toner images by heat treatment, and thereafter, the original of the color image original is removed. The sheet is discharged to a tray as a copy image.

[0009]

As described above, FIG.
In the general color image copying machine shown in FIG. 1, R, G, B image signals output from the line sensor 610 are 1
The image data is converted into M, C, Y, and Bk digital image data by the signal processing unit 611 on a pixel-by-pixel basis, and the digital image data is sequentially transferred to the printer unit 602. A copy image is formed based on the digital image data to be copied.

That is, in the above-described general color image copying machine, basically, the operation in the image scanner unit 601 for reading a document and the operation in the printer unit 602 for recording a copied image need to be synchronized. In such an apparatus configuration, for example, if the heater of the fixing unit 626 in the printer unit 602 is not sufficiently heated, the printer unit 60
2 is in the standby state, the document reading operation by the image scanner unit 601 cannot be started.

In the general color image copying machine shown in FIG. 6, an image is formed by the printer unit 602 at a certain timing in one of the four developing units M, C, Y and Bk. In the image scanner unit 601, it is necessary to repeat the reading of the color document image four times. For example, the developing unit of each color needs to repeat the same image forming process. In the case of copying a plurality of sets, it is necessary to perform an operation of reading one document image a plurality of times for each copy output, and this operation must be performed for each of the plurality of document images. Is a problem.

However, the above-described original image reading operation does not necessarily have to be performed four times in succession, and digitized image data of a color image signal obtained in one reading operation is temporarily stored in a hard disk or a memory. It is stored in a storage device, and the stored image data is stored in M,
An apparatus configuration in which reading is performed in synchronization with the image forming process of each color of C, Y, and Bk can be considered.

According to such an apparatus configuration, it is not necessary to synchronize the reading operation of the image scanner unit with the printing operation of the printer unit. Since only one reading operation is required for the original image, the image can be efficiently copied. In addition, by editing the image data of the plurality of read original images, the order of pages can be changed or the partial image can be replaced. , And secondary use of the combined output and the like can be realized.

However, since the storage capacity of a storage device such as a memory is limited from the viewpoint of cost, when reading a large number of document images, a situation arises in which image data of the document images cannot be stored. However, this is not a realistic device configuration.

Therefore, when the image data of a plurality of original images read as described above is used secondarily, for example, during rotation processing or spooling when outputting a plurality of sets, J
PEG (Joint Photographic Experts Group) and JBIG
(Joint Bi-level Image Group) or the like, there is a method of storing image data that has been subjected to general compression processing to reduce the memory capacity required for storage.

However, in the case of JPEG, if a control parameter for realizing a low-quality, high-compression-rate compressed image is selected in the compression process, an image in which the density of a character or the like contained in the compressed image greatly changes is selected. Since noise called mosquito noise occurs around the portion, the quality of the compressed image is degraded. Also, if high quality, low compression rate parameters are selected during the compression process, mosquito noise appearing around characters such as those described above is reduced,
Since the compression ratio is low, the capacity of image data does not decrease so much. As a result, the number of images that can be stored in the storage device is limited, and depending on the storage device, data that can be processed within a predetermined time due to access speed. Since the amount is limited and problems such as a reduction in the operation efficiency of the color copying machine as a whole are assumed, optimal compression cannot be performed by using only one compression method.

In general, in a compression method called Lossless compression such as the LZ method (R), the compression ratio may not be increased depending on the state of a document image. Thus, the above-mentioned problem occurs in the data size.

In the compression method called Lossy compression, for example, in a compression method such as JPEG in which the compression ratio can be switched in accordance with a parameter to be set, the quality of a compressed image with a high compression ratio is greatly deteriorated, and In a compressed image having a compression ratio, the above-described problem regarding the data size occurs.

Accordingly, the present invention provides an image compression apparatus, an image compression method, and a computer-readable storage medium that achieve both high-compression compression of input image data to be compressed and prevention of image quality deterioration due to the compression. With the goal.

[0020]

In order to achieve the above object, an image compression apparatus according to the present invention has the following configuration.

That is, image area separating means for separating input image data into a plurality of types of image areas and generating attribute information representing the attributes of the image areas, and each image area separated by the image area separating means. Irreversible method (for example, JPEG compression method) for image data corresponding to
Image compression means for performing image compression processing, and when the image compression processing is performed by the image compression means, the image area to be compressed is any one of a character area, a graphic area, and a photographic area, When the determination is made based on the attribute information generated by the separation means, a compression parameter capable of realizing a high-quality compressed image with a low compression ratio is selected as compared with the case where it is determined that the area is the other area. To
Control means for controlling the image compression means.

Further, for example, the image compressing means may compress the attribute information generated by the image area separating means by image compression processing of a reversible compression method (for example, JBIG compression method).

Further, for example, the image compression means has a low compression rate at the time of image compression but hardly causes image deterioration, and a high compression rate as compared with the first image compression means. A second image compression unit that has a large image reduction, and wherein the control unit determines that the image region to be compressed is a character region, a graphic region, or a photograph region based on the attribute information generated by the image region separation unit. The image compression is performed such that the first image compression unit is selected when it is determined to be any one of the above, and the second image compression unit is selected when it is determined that the region is the other area. The means should be controlled.

Alternatively, in order to achieve the above object, an image compression method according to the present invention has the following configuration.

That is, an image area separating step of separating input image data into a plurality of types of image areas and generating attribute information representing attributes of the image areas, and each image area separated in the image area separating step. The image data corresponding to
Whether it is a text area, graphic area, or photo area,
When the determination is made based on the attribute information generated in the image area separation step, a compression parameter that can realize a high-quality compressed image with a low compression ratio is used as compared with the case where the area is determined to be another area. Irreversible method (for example, JPE
(G compression method).

For example, in the image compression step,
The attribute information generated in the image area separation step may be compressed by a reversible compression (for example, JBIG compression) image compression process.

In the image compression step, for example,
Based on the attribute information generated in the image area separation step,
When it is determined that the image area to be compressed is any of a character area, a graphic area, and a photograph area, image compression is performed by the first image compression method which has a low compression ratio but hardly causes image deterioration in image compression. If it is determined that the area is the other area, it is preferable to perform image compression by a second image compression method which has a higher compression ratio than that of the first image compression method but has a large image reduction.

Further, the present invention is characterized by a computer-readable storage medium storing a program code for realizing the above-described image compression apparatus and image compression method by a computer.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image processing apparatus according to the present invention will be described in detail with reference to the drawings.

[First Embodiment] FIG. 1 is a block diagram showing the configuration of an image processing apparatus according to the first embodiment.

Referring to FIG. 1, a document image to be copied is optically read while placed on a document table glass (not shown) of the scanner 101. This scanner 101
Are the same as RGB for the line sensor 610 in the case of FIG.
After reading the original image in pixel units by the three-line CCD and digitizing the read image signal,
Transfer to the input image processing unit 102. Input image processing unit 10
In step 2, known image processing such as shading correction, CCD line-to-line correction, and color correction is performed on the color image data input from the scanner 101.

The image area separation processing section 103 converts the features such as a photographic area, a character area, and a halftone area included in the original image into the general color image data output from the input image processing section 102. Image area separation processing is performed to detect each pixel by a technique and generate attribute flag data representing the attribute of each image area.

That is, in the image area separation processing in the image area separation processing unit 103, features included in the read original image are extracted in order to perform optimal image processing according to the characteristics of the image included in the read original image. Then, an identifier (hereinafter, attribute flag data) indicating the attribute of the extracted image area is generated.

For example, in a general original image, various image areas such as a continuous-tone full-color photograph area, a black-only character area, and a stencil printing area such as newspaper printing are mixed. Often. If such an original image is processed and output according to the same image processing procedure, the output image generally cannot often have a desirable image quality.

Accordingly, in the present embodiment, the features (attributes) of the image included in the original image read by the scanner 101 are detected using the color image data input from the input image processing unit 102, and the detection is performed. Generate attribute flag data for identifying the result. The attribute flag data includes a compression process performed by a data compression unit 107 described later, a data decompression unit 110 that decompresses the compressed image data, and an output image processing unit that converts the decompressed image data into an output format of the printer 115. Each is used at 114 (details will be described later).

<Operation of Image Area Separation Processing Unit> The specific operation of the image area separation processing unit 103 will be described with reference to FIG.

FIG. 2 is a diagram for explaining the operation of the image area separation processing unit 103 in the first embodiment.

In the figure, reference numeral 201 denotes an example of a document image in which a plurality of types of image areas are mixed as described above, and a silver halide photographic area 20 is included in one document image.
2, the black character area 203, the halftone print area 204, and the color graphic area 205 are mixed.

The scanner 101 shown in FIG. 1 reads the original image shown in FIG. 2 by using the three-line CCD, thereby obtaining color image data (R, R) of the original image.
G, B) are output to the image area separation processing unit 103.
The RGB color image data includes different features depending on each image region of the document image illustrated in FIG.

FIG. 3 shows an image signal output from a G (green) line CCD when the original image shown in FIG. 2 is read, and a CCD arranged on the line CCD.
It is a diagram showing the relationship between the pixel position, the horizontal axis represents the pixel position in the CCD array direction, the vertical axis represents the output signal value of the CCD,
The higher the vertical axis, the closer to white (bright) pixels.

In the figure, 302, 303, 304,
Reference numeral 305 denotes a G (green) signal value (image data) value when each of the image regions 202 to 205 included in the document image illustrated in FIG. 2 is read, and is characteristic of those image regions. Represents the characteristics that appear in.

The characteristics of each of these areas will be described with reference to FIG. 3. In the case of the G signal value 302 relating to the photographic area 202, the change depending on the pixel position is relatively gradual, and the output between the pixels separated at a short distance is obtained. In the case of the signal difference 312, the value is relatively small. In the G signal value 303 relating to the black character area 203, since a black character is written on a white background, the plot of the signal value has a characteristic that changes abruptly from the white background portion 313 to the character portion 323.

The G signal value 3 for the halftone dot area 204
In the case of No. 04, since the dot area 204 is composed of a white background and a halftone dot printed thereon, a G signal value 314 representing the white background and a G signal value 324 representing the halftone dot are provided.
And white pixels and black pixels are repeated at a high frequency. Then, in the case of the G signal value 305 relating to the graph area 205, the G signal value 305 at the pixel position 315 corresponding to the graphic edge portion of the graph area 205
The signal value sharply decreases, and the pixel position 316 corresponding to the colored portion inside the graph area has a characteristic that the G signal value having a substantially constant medium level continues.

In order to determine these attributes, for each of the plurality of types of image areas described above, the image data is read out based on the read signal values (in this embodiment, green image data as an example). What is necessary is just to determine the feature included in the area. In order to realize the feature judgment,
The amount of change in the image signal of another pixel near the target pixel (that is, the pixel to be processed among the plurality of read pixels) or a general image area feature extraction method, or
The integrated value of the change amount in a predetermined section, the luminance value (whether a white background or a colored background) of a pixel (peripheral pixel) located around the target pixel, and the change of the image signal from white to black in the predetermined section May be determined based on the number of times.

FIG. 4 is a view showing an example of an attribute flag generated for the original image shown in FIG.
As an identifier (attribute flag data) indicating an attribute, three types of flags, a character flag, a graphic (graph) flag, and a halftone dot flag, are generated in accordance with the example of FIG. 2, but are limited to these flags. Not necessarily.

FIG. 4A shows a character flag. Pixels represented by black in the figure are pixels having a character attribute, and the character flag = 1 is set for those pixels. The character flag = 0 is set for the pixels in the white area.

FIG. 4 (b) shows a graphic flag.
1 is set, and the picture flag = 0 is set for the pixels in the other white areas.

Similarly, FIG. 4C shows a halftone flag. The halftone flag = 1 is set to the pixels constituting the halftone area, and the halftone flag is set to the pixels in the other white areas. = 0
Is set.

However, for the photographic area 202 shown in FIG. 2, none of the above attribute determinations apply, so that the above three types of flags are all "0" and cannot be represented in FIG.

That is, the attribute flag data of various image areas included in the original image illustrated in FIG. 2 is arranged as follows.

(1) Photo area 202: (character flag) =
(Figure flag) = (halftone flag) = 0, (2) black character area 203: (character flag) = 1, (graphic flag) = (halftone flag) = 0, (3) halftone area 204: (character (Flag) = (graphic flag) = 0, (dot flag) = 1, (4) graph area 205: (character flag) = (dot flag) = 0, (graphic flag) = 1, <input image processing unit Operation of 104> After the attribute determination of the original image in the image area separation processing section 103 described above is performed for each pixel constituting the original image, the image area separation processing is further performed in the second input image processing section 104. The RGB image data input via the unit 103 is subjected to predetermined image processing described below in accordance with the image attributes (attribute flag data) determined by the image area separation processing unit 103. Is done. Specifically, the input image processing unit 104 performs the following optimal spatial filter processing for each image area.

For example, for the character area 203, the sharpness of the characters included in the character area is enhanced by enhancing the high frequency components of the image.

The halftone dot region 204 is subjected to a so-called low-pass filter process to remove a moiré component peculiar to a digital image.

Then, the photograph area 202 and the graph area 2
In contrast to the character region 05, the harmonic components are not emphasized as much as the character region, and the low-frequency components are not emphasized as much as the halftone dot region. Realizing the perfect gradation reproduction.

Switching of the image processing for each image area in the input image processing section 104 is performed by the image area separation processing section 103.
May be performed in units of pixels in accordance with the attribute flag data generated in.

<Storing of Compressed Data> The three types of attribute flag data set by the image area separation processing unit 103 are temporarily stored in the flag memory 106.
The image data subjected to various types of image processing by the input image processing unit 104 is temporarily stored in the image memory 105. At this time, the image data stored in the image memory 105 and the attribute flag data stored in the flag memory 106 include the entire page of the document image or a partial image of a predetermined size of one page. The minutes are stored.

The temporarily stored image data and its attribute flag data are encoded in the image memory 105 and the flag memory 1 in order to reduce the redundancy contained in the data string and encode the data.
06 and read out in association with each other in pixel units, and input to the data compression unit 107.

The compression / decompression control unit 111 includes the data compression unit 1
07 and the data decompression process by the data decompression unit 110 are controlled. Hereinafter, the data compression unit 107 and the data decompression unit 11 by the compression / decompression control unit 111
The specific control of 0 will be described.

<Operation of Data Compression Unit 107> The data compression unit 107 selects a desired parameter from a plurality of types of parameters stored in advance in a lookup table (LUT) (not shown) of the compression / decompression control unit 111. Possible
Alternatively, a plurality of different compression methods are provided, and the compression method is configured to be switchable to a desired compression method (a method of selecting parameters and a specific method of switching the compression method will be described later). .

That is, image data input to the data compression unit 107 is compressed for each object in order to perform high-efficiency compression processing in which image deterioration is not noticeable in consideration of human visual characteristics. An irreversible compression process such as JPEG compression described later is performed while using different rates. In addition, a lossless compression method such as JBIG compression is applied to attribute flag data input to the data compression unit 107 in order to prevent loss or change of attribute information.

The compressed image data (compressed image data) output from the data compression unit 107 is stored in the storage device 1.
08 and sequentially stored in the storage device 108.
Preferably, a high-speed storage device such as a semiconductor storage device is used as the storage device 108.

As described above, the storage device 108 stores the image data and the attribute flag data which have been subjected to the compression processing by different methods, and the information such as the factors used for the compression, the compression ratio, and the allocated code amount of each block. Is stored for each page of the document image. The stored data may be written to the auxiliary storage device 109 which is a storage medium such as a hard disk capable of storing a large amount of data although the recording speed is slightly slower than that of the semiconductor storage device. Auxiliary storage device 1
09 can be used to efficiently accumulate a large number of document images.

<Object Switching Procedure of Image Data Compression Method and Compression Procedure of Attribute Flag Data> Here, the object switching procedure of the image data compression method in the data compression section 107 and the compression procedure of attribute flag data will be described in detail. Will be described.

As described above with reference to FIG. 4, in the present embodiment, the image area separation processing unit 103 converts the input image of one original image into a character flag, A flag and a halftone flag are generated. However, as described above, the photograph area 2
02 does not apply to these three types of attribute flag data, so that all the attribute flag data for the photographic area are set to “0”, thereby determining that the object area is a photographic image. it can.

As described above, when image data and attribute flag data are input from the image memory 105 and the flag memory 106 in association with each other on a pixel-by-pixel basis, the data compression unit 107 generates a JPEG-format compressed image. At this time, the data compressing unit 107 selects a compression parameter to be used from an LUT (not shown) based on the input attribute flag data, so that an object such as a character area or a graphic (graph) area can be obtained. The compression method is switched for each area.

In this LUT, a plurality of control parameters such as a parameter for realizing a high-quality compressed image with a low compression ratio and a parameter for realizing a low-quality compressed image with a high compression ratio are stored in advance. An optimum parameter is selected from the parameters according to the attribute flag data.

That is, when the object area is a halftone area, even if the image quality is slightly deteriorated, it is inconspicuous.
Even if a parameter that results in a low-quality image is adopted, generally, there is little problem. Therefore, in the case of a dot area, a compressed image with a high compression rate is generated by adopting a parameter for realizing a low-quality compressed image with a high compression rate. As a result, the data size after compression is reduced, and the memory capacity required for storage can be reduced.

On the other hand, when the object area is a character area, a graph area, or a photograph area, a parameter for realizing a high-quality compressed image with a low compression ratio is selected. As a result, it is possible to reduce the occurrence of mosquito noise, which is a problem when a parameter for realizing a low-quality compressed image with a high compression ratio for a character area, a graph area, and a photograph area is selected. In addition, in general, in a portion other than the bitmap object, there are many background portions where nothing is drawn, and even if the compression ratio is low, a high compression ratio may be secured in the background portion because the same signal continues. high.

For example, of the three types of attribute flag data, the pixels for which the halftone flag shown in FIG. 4C is set to "1" are halftone areas generated from halftone objects. Therefore, a parameter for realizing a low-quality compressed image with a high compression ratio is selected, and for a pixel for which “0” is set, the position where the pixel exists is:
Since it can be determined that the object is any one of a character area, a graph area, a photograph area, and a background part of a document image, a high-quality compressed image with a low compression ratio is realized for such an image area. Select the parameter to be used.

The parameters used for compressing the character area, the graph area, and the photograph area may be the same or different.

In the present embodiment, the method of image compression is not completely reversible, but is a method of Lo
Although JPEG compression, which is a type of ssy compression processing, is used, instead of parameters for realizing high-quality, low-compression-rate compressed images of JPEG, completely lossless Lossless compression such as LZ compression (C) is used. To use the JPEG high compression rate and low quality Lossy compression processing as it is, two compression / decompression circuits are provided, and one of the compression / decompression circuits is
The selection may be made based on the attribute flag data.

<Reading of Image Data> Storage Device 108
Alternatively, the image data and the attribute flag data stored in the auxiliary storage device 109 are read out by the printer 115 for output. The data decompression unit 110 includes the data compression unit 10
7, information such as a factor, a compression ratio, and an allocated code amount of each block used for compressing the image data and the attribute flag data when compressed in step 7 are received. In accordance with the operation timing of the printer engine, image data and attribute flag data compressed by different methods as described above are decompressed by a decompression method (in this embodiment, JPEG
(Compression and JBIG compression). The decompressed image data and attribute flag data are stored in the image memory 1
12 and the flag memory 113.

<Output of Image Data> The decompressed image data and attribute flag data temporarily stored in the image memory 112 and the flag memory 113 are transferred to the output image processing unit 114 when they reach a predetermined size.

<Operation of Output Image Processing Unit 114> The output image processing unit 114 performs general image processing on input RGB image data, that is, luminance-density conversion, RGB
After performing processing such as color space conversion from to CMYK, gamma correction, and binarization processing, the image data is transferred to the printer 115.

The printer 115 drives a laser mechanism (not shown) according to the input CMYK multi-valued image data.
A visible image is formed on a recording sheet in the same procedure as in FIG. 6 described above, and output after fixing by heat treatment.

Here, the attribute flag data stored in the flag memory 113 is used for switching image processing in the output image processing unit 114. That is, in the image processing in the output image processing unit 114, the RGB is converted to the CMY
The image quality of the output image is improved by using different coefficients for converting the photographic area, the graph area, and the halftone dot area, and for converting the character area to the coefficients used for color space conversion to K. be able to. More specifically, for example, for a pixel constituting a character area (that is, a character flag = 1), a conversion coefficient (that is, C or C when image data is achromatic) so that a black character can be reproduced only with black toner. M,
Y is 0), and the other pixels included in the photographic region, the graph region, and the halftone dot region are achromatic, even if C, M, and Y are 0. Instead, a coefficient that can reproduce deep black may be used.

In the present embodiment, the image quality of the output image is improved by switching the contents of the binarization processing in accordance with the attribute flag data also in the binarization processing. More specifically, C, M, Y, and K multi-valued image data are converted to 0 or 1 using well-known error diffusion processing or dither processing.
In this case, the sharpness of the output image is prioritized in the character area and the graph area, so the error diffusion processing is applied, and in the photographic area and the halftone area, the gradation is emphasized. So apply dithering.

Hereinafter, the configuration of the output image processing section 114 will be described with reference to FIG.

FIG. 5 is a block diagram showing a configuration example of the output image processing section 114 in the first embodiment.

In the figure, RGB color image data read from the image memory 112 is input in parallel to two color space conversion circuits 501 and 502, and is independently converted into CMYK multi-value image data. . The outputs of the color space conversion circuits 501 and 502 are output to the flag memory 11
Either one is selected by the selector 503 in accordance with the attribute flag data output from the third. As a specific selection operation, for example, a conversion coefficient for a character area is set in the color space conversion circuit 501 in advance, and the color space conversion circuit 5
In the case where the coefficient of the other area is set in advance to 02, when the character flag = 1 is output as the attribute flag data output from the flag memory 113, the selector 503 outputs the output of the color space conversion circuit 501. Is selected and the character flag = 0 is output, the selector 503 selects the output of the color space conversion circuit 502.

In FIG. 5, the output of the selector 503 is input to two gamma correction circuits 504 and 505 in parallel. Then, the output of the gamma correction circuit 504 is converted into a binary CMYK signal by an error diffusion binarization processing unit 506 and then input to a selector 508. The output of the gamma correction circuit 505 is output to the dither processing binarization circuit 50.
7, after being converted into binary CMYK signals, the selector 5
08 is input.

In the selector 508, the flag memory 113
Error diffusion 2 according to the attribute flag data output from
The output of either the binarization processing unit 506 or the dither processing binarization circuit 507 is selected. That is, in the present embodiment, since the error diffusion processing is selected for the character area and the graph area, the output of the error diffusion binarization processing unit 506 is performed when the attribute flag data is character flag = 1 or graphic flag = 1. Is selected, and the output of the dither processing binarization circuit 507 is selected for other image parts.

According to the above-described embodiment, for each of the text, graphic, photo, and bitmap objects included in the original image, a pixel or a block of an image area which is assumed to have severe image degradation is used as attribute flag data. Based on the result of the determination, the pixels or blocks determined to have severe image degradation are subjected to low-compression and high-quality compression processing, and the other pixels or blocks are subjected to high-compression. It is possible to perform high-speed and low-quality compression processing, and to achieve both high-compression-rate compression of input image data to be compressed and prevention of image quality deterioration due to the compression.

In the first embodiment, when the attribute flag data is compressed, a reversible compression method such as JBIG compression is employed. However, the present invention is not limited to this device configuration. Since the original data amount is much smaller than that of the image data, the compression processing may not be performed if possible due to the memory capacity of the storage device 108.

The attribute flag data employs a lossless compression method to prevent loss of information.
Further, the storage capacity of the memory can be saved.

[Second Embodiment] In the first embodiment described above, an example is shown in FIG. 4 in which the image area separation processing unit 103 sets the image compression method in accordance with the object area. By using the three types of attribute flag data of the character flag, the graphic flag, and the halftone flag, it is possible to correspond to an object area (each image area of a photograph, a character, a graph, and a halftone dot) according to the attribute flag data. The compression method is selected for each pixel to be processed. However, the present invention is not limited to this configuration. When the same compression parameter is used for each of image regions other than the halftone dot region, the first embodiment is used. The switching of the compression method based on the three types of attribute flag data need not be performed. Hereinafter, a specific method thereof will be described.

In the second embodiment, as in the first embodiment, the image area separation processing is performed on the image to be compressed, thereby obtaining three types of attribute flag data for each object area. .

Next, in the present embodiment, a parameter for a halftone area (that is, a compression parameter for realizing a low-quality image with a high compression ratio) is used for the entire image data of one image to be compressed. The first compression image data obtained as a result is stored in the storage device 108. Furthermore, the first compression is performed on the entire image data to be compressed using a parameter different from the parameter for the halftone dot area (that is, a compression parameter that realizes a high-quality image at a low compression rate). A compression process is performed in the same method as the compression method used when obtaining the image data, and the resulting second compressed image data is stored in the storage device 108.

Then, the first and second compressed image data stored in the storage device 108 are expanded by the data expansion unit 110, and the first and second compressed image data are referred to by the three types of attribute flag data obtained earlier at this time. From the composite image data based on the compressed image data, the image data corresponding to the halftone area is cut out, and from the composite image data based on the second compressed image data, the image data corresponding to the image area other than the halftone area is cut out. Is cut out, and the cut out image areas are combined with one image data, and then stored in the image memory 112.

According to the second embodiment which performs such processing, it is possible to achieve both high compression rate compression of input image data to be compressed and prevention of image quality deterioration due to the compression.

[0091]

[Other Embodiments] Even if the present invention is applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), an apparatus (for example, a copying machine) Machine, facsimile machine, etc.).

Further, an object of the present invention is to supply a storage medium (or a recording medium) on which a program code of software for realizing the functions of the above-described embodiments is recorded to a system or an apparatus, and to provide a computer (a computer) of the system or the apparatus. Alternatively, it is needless to say that the present invention can also be achieved by a CPU or an MPU) reading and executing the program code stored in the storage medium. In this case, the program code itself read from the storage medium implements the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention. Also,
When the computer executes the readout program code, not only the functions of the above-described embodiments are realized, but also the operating system (OS) running on the computer based on the instructions of the program code.
And the like perform part or all of actual processing, and the processing realizes the functions of the above-described embodiments.

Further, after the program code read from the storage medium is written into the memory provided in the function expansion card inserted into the computer or the function expansion unit connected to the computer, the program code is read based on the instruction of the program code. This also includes the case where the CPU or the like provided in the function expansion card or function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

[0094]

As described above, according to the present invention,
An image compression apparatus, an image compression method, and a computer-readable storage medium that achieve both high-compression compression of input image data to be compressed and prevention of image quality deterioration due to the compression are realized.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an image processing apparatus according to a first embodiment.

FIG. 2 is an image area separation processing unit 103 according to the first embodiment.
It is a figure explaining operation of.

FIG. 3 illustrates a case where a document image illustrated in FIG. 2 is read;
FIG. 4 is a diagram illustrating a relationship between an image signal output from a G (green) line CCD and a pixel position of a CCD disposed on the line CCD.

FIG. 4 is a diagram illustrating an example of an attribute flag generated for the document image illustrated in FIG. 2;

FIG. 5 is an output image processing unit 114 according to the first embodiment.
FIG. 3 is a block diagram illustrating a configuration example of FIG.

FIG. 6 is a diagram illustrating a configuration of a general color image copying machine.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5C059 KK01 MA00 PP01 PP15 SS20 SS28 TA17 TB18 TC01 TD11 UA02 UA05 UA38 UA39 5C078 AA06 AA09 BA21 BA42 CA02

Claims (14)

[Claims] 1. An image area separating means for separating input image data into a plurality of types of image areas and generating attribute information representing attributes of the image areas, and each image area separated by the image area separating means. Image compression means for performing irreversible image compression processing on the image data corresponding to the image data; and when the image compression processing is performed by the image compression means, the image area to be compressed includes a character area, a graphic area, and a photograph. When it is determined based on the attribute information generated by the image area separating means that the area is one of the areas, compared with the case where it is determined that the area is the other area, high-quality compression with a low compression ratio is performed. Control means for controlling the image compression means so that a compression parameter capable of realizing an image is selected. 2. The image compression processing of the irreversible method is performed by JP
2. The image compression apparatus according to claim 1, wherein the image compression method is an EG compression method. 3. The image compression apparatus according to claim 1, wherein the image compression unit compresses the attribute information generated by the image area separation unit by a reversible compression type image compression process. 4. The image compression process of the reversible method is a JBI
4. The image compression apparatus according to claim 3, wherein the compression method is a G compression method. 5. The image compression means has a low compression rate when compressing an image, but has a high compression rate as compared with the first image compression means, which hardly causes image degradation. And a second image compression unit having a large image reduction, wherein the control unit determines whether the image region to be compressed is a character region, a graphic region, or a photograph region based on the attribute information generated by the image region separation unit. The image compression means such that the first image compression means is selected when it is determined to be any one of them, and the second image compression means is selected when it is determined to be any other area. The image compression apparatus according to claim 1, wherein 6. The image compression apparatus according to claim 1, further comprising image expansion means for expanding the compressed image data generated by said image compression means. 7. The image compression apparatus according to claim 6, further comprising image recording means for recording an image on a recording medium based on the image data decompressed by said image decompression means. 8. An image area separating step of separating input image data into a plurality of types of image areas and generating attribute information representing attributes of the image areas; and each of the image areas separated in the image area separating step. When it is determined based on the attribute information generated in the image area separating step that the image data corresponding to is one of a character area, a graphic area, and a photograph area, the image data is determined to be other area. An image compression step of performing an irreversible image compression process using a compression parameter capable of realizing a high-quality compressed image with a low compression ratio as compared with the conventional method. 9. The image compression processing of the irreversible method is performed by JP
9. The image compression method according to claim 8, wherein the image compression method is an EG compression method. 10. The image compression step, wherein the attribute information generated in the image area separation step is compressed by a reversible compression type image compression process.
The image compression method as described above. 11. The image compression process of the reversible method is a JB
The image compression method according to claim 10, wherein the compression method is an IG compression method. 12. In the image compression step, based on attribute information generated in the image area separation step,
When it is determined that the image area to be compressed is any of a character area, a graphic area, and a photograph area, image compression is performed by the first image compression method which has a low compression ratio but hardly causes image deterioration in image compression. When it is determined that the area is the other area, the image compression is performed by a second image compression method which has a higher compression ratio than that of the first image compression method but has a large image reduction. Item 9. The image compression method according to Item 8. 13. A computer-readable storage medium storing a program code for operating a computer as the image compression apparatus according to claim 1. Description: 14. A computer-readable storage medium storing a program code capable of realizing the image compression method according to claim 8 by a computer.