JPH11136521A - Picture data processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a picture data processor of high compression efficiency, which page-divides the pictures of separated areas for respective types and uses a compression method fitted for the picture type of the divided pages. SOLUTION: In a first host computer, a first wavelet conversion part 201 frequency-converts picture data of eight bits in a bit map. In a sub-band encoding of wavelet conversion, multiplex resolution expression is realized and only one hierarchy is processed for separation. An image area separation part 202 executes an image separation processing on a character (edge) area and a pattern area by using the obtained high frequency component of one hierarchy. The separated area is divided into the page 402 of only the character area and the page 403 of only the pattern area and they are compressed by a compression system fitted to the types of the pictures of the divided pages.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention separates a character (edge) area and a picture area by using a coefficient obtained by decomposing image data on a host computer into a plurality of frequency bands. And an image data processing apparatus for performing data compression processing.

[0002]

2. Description of the Related Art DCT is used as a compression method for image data.
Generally, a method of converting image data into frequency components by orthogonal transform such as (Discret Cosine Transform) and quantizing the transform coefficients is used. This DCT is a frequency conversion method having excellent compression performance, but causes image degradation such as block distortion and mosquito noise in low bit data. On the other hand, such a problem is solved by a multi-resolution conversion in which conversion bases overlap as in a wavelet (Wavelet) conversion.

[0003] DCT or wavelet transform is a conversion method suitable for compressing continuous tone images such as photographic images. However, for images such as character images in which steep luminance conversion is dense, compression is performed. Efficiency cannot be increased. For such an image, a higher compression efficiency can be obtained with a simpler conversion method. Therefore, the method of selecting the conversion method according to the type of image has been conventionally performed,
There is no appropriate method for an image in which a photograph and text are mixed in one page.

On the other hand, when transferring image data such as an Internet facsimile, the image data read from the scanner on the transmitting side is separated into a character (edge) area and a picture area, and the image data is compressed for each type of the separated area. When the data is encoded and transferred by changing the method, on the receiving side, the character data to be confirmed first is restored and displayed on the monitor at a high speed, and the image data is thereafter sequentially displayed from above the document. Therefore, in the case of data of a mixed image of characters and pictures, it is necessary to wait until an image including an intermediate image area is slowly displayed from the information, although it is desired to obtain only character information quickly.

On the other hand, as an apparatus of this type, for example, an "image coding apparatus" disclosed in Japanese Patent Laid-Open No. 5-75875 is disclosed.
And an "image coding apparatus" disclosed in Japanese Patent Application Laid-Open No. 7-87327. These conventional inventions are configured so as to increase the compression efficiency by judging a character part and a photograph part and changing a quantization step according to each area.

[0006]

By the way, in general, when frequency-decomposing image data, if coefficients generated by performing uniform conversion without separating one image and compressing the generated data are compressed, each of the characters and the picture is decomposed. The compression efficiency is not very good because there are mixed coefficients having characteristics.

Therefore, the present invention intends to increase the compression efficiency by dividing the pages into regions, and a first object of the present invention is to separate the pages according to the types of images in the separated regions, Another object of the present invention is to provide an image data processing apparatus having high compression efficiency by changing a page compression method and using a compression method suitable for an image type.

[0008] A second object is to divide a page according to the type of image in the separated area, compress each page, transfer the code data of the page of the character area first, and transfer the data. An object of the present invention is to provide an image data processing device capable of displaying data.

Further, a third object is to divide a page according to the type of image in the separated area, compress each page, and receive only necessary data of a character area or a picture area. To provide a simple image data processing device.

[0010]

In order to achieve the above object, a first means is an image data processing apparatus provided with an image data compression means for compressing original image data.
A decomposing means for decomposing the original image data into a plurality of frequency bands, an image area separating means for separating an image area into an edge area and a picture area based on the frequency band decomposed by the decomposing means, and It is characterized by comprising a page dividing means for dividing a page into each divided area, and a control means for compressing each page divided by the page dividing means by a compression method corresponding to the divided area.

The second means is characterized in that the control means in the first means transfers the compressed data from the page in the edge area.

The third means is characterized in that the control means in the first means restores the compressed data only in a necessary area.

[0013]

An embodiment of the present invention will be described below with reference to the drawings.

First, as this embodiment, data processing in data transfer between two host computers as shown in FIG. 1 will be described. When two host computers 1 and 2 are connected on a network via an interface cable 3 as shown in FIG. 1, it is assumed that the first host computer 1 compresses bitmap image data. At this time, the first
In the host computer 1, the first wavelet transform unit 201 performs frequency decomposition on 8-bit image data of a bitmap as shown in FIG. In sub-band coding such as wavelet transform, multi-resolution expression is possible. Here, first, processing is performed only on one layer for separation. Next, the image area separating unit 202 performs image area separation processing on the character (edge) area and the picture area using the obtained one-layer high-frequency components. Further, the separated area is further divided into two pages, a page 402 having only a character area and a page 403 having only a picture area, and each page is compressed by a compression method suitable for the type of the divided image.

For example, the page 402 in which the character areas are collected is used to convert the frequency-resolved coefficients into the inverse wavelet transform unit 2.
03, the wavelet is inversely transformed, the density of the picture area is set to 0, the binarization processing unit 204 executes binarization of white / black with a preset threshold value, for example, 128, and the Huffman encoding unit 205 executes Huffman encoding. Encode and compress. On the other hand, the page 403 in which the picture data is collected is subjected to multi-resolution decomposition for the LL component shown later in FIG. 3 by the second wavelet transform unit 206 as preprocessing, and further to QM processing in the entropy encoding unit 207.
Compression by performing entropy coding such as -coder; By performing such processing, more efficient coding is performed for each area than when one image is compressed as it is, and the compression efficiency of the entire image can be increased.

In the image area separating unit 202, when the wavelet transform is applied, it is decomposed into four kinds of frequency components as shown in FIG. LL is a low frequency component, and LH, HL, and HH are high frequency components. The image area is separated using this high frequency component. That is, the wavelet transform for the two-dimensional image data is performed by first applying a low-pass filter and a high-pass filter in the horizontal direction of the original image, and then performing the same processing in the vertical direction.
H, a diagonal high band HH, and a low band LL, which are divided into four frequency bands.

In the image area, the character area is composed of an edge portion having a large gradation difference and a solid white or black portion. In the case of an edge, a large absolute value occurs in the high frequency component.
In the solid portion, the high frequency component has a value of 0. Using these characteristics, the image data is divided into four pixel blocks. As a result of the separation work, the determination result is different from the determination result of the surrounding blocks, and an isolated block occurs. In such a case, expansion processing is performed to change the area type to the same as the surrounding block.

For example, when there is an original image 401 shown on the left side of FIG. 4, when the first wavelet transform unit 201 performs wavelet transform and the image area separation unit 202 performs image area separation, as shown on the right side of FIG. The character page 402 and the picture page 403 are separated. In this figure, it seems that the bitmap data of the original image remains as it is, but in fact, it is decomposed into coefficients and separated on the coefficients.

In the data compressed by the first host computer 1 in this way, the code stream is arranged with the code of the character page 402 at the top as shown in FIG. The code data thus arranged is received by the second host computer 2. The data received by the second host computer 2 is displayed as shown in FIG. That is, first, character data is displayed (601), and thereafter, the picture portion is progressively displayed from LL4 (602). When all the data is gradually received and inversely converted, the resolution is increased and the image is completely restored. (603).

In addition, the second host computer 2 receives a code stream as shown in FIG. 5 from the first host computer 1. At this time, at the beginning of the code stream created as shown in FIG. 7, the head address CDAD of the character page and the head address I of the picture page are set.
DAD is specified. Second host computer 2
When it is desired to receive only character information, for example, by selecting "character" from an operation button on the screen, only the character code is decoded and displayed on the screen.

[0021]

As described above, a decomposing means for decomposing original image data into a plurality of frequency bands, and an image area for separating an image area into an edge area and a picture area based on the frequency bands decomposed by the decomposing means. A separating unit, a page dividing unit that divides the page by each area separated by the image area separating unit, and a control unit that compresses each page divided by the page dividing unit by a compression method corresponding to the region that has been separated. According to the first aspect of the present invention, the image is separated into an edge area and a picture area by the image area separating means,
Since pages are divided for each area by the page dividing means and compression is performed by a compression method according to the image of the area for each page, compression efficiency can be increased.

According to the second aspect of the present invention, since the compressed data is transferred from the page in the edge area, the receiving side first receives the data from the edge area, so that the character information can be obtained quickly.

Further, according to the third aspect of the present invention, the compressed data is restored only in a necessary area, and the receiving side needs only an area in the compressed and transferred data, that is, a character (edge). 3) Since only one of the area and the picture area is restored, the restoration of necessary information is not delayed by unnecessary information, and waste can be reduced and processing can be performed efficiently.

[Brief description of the drawings]

FIG. 1 is a diagram showing a connection state of two host computers according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a processing procedure of the present invention.

FIG. 3 is a diagram illustrating a wavelet transform.

FIG. 4 is a diagram showing a state where a document is separated into a page in a character (edge) area and a page in a picture area.

FIG. 5 is an explanatory diagram showing a code stream when areas are separated as shown in FIG. 4;

FIG. 6 is an explanatory diagram showing a display state when the code stream in FIG. 5 is restored.

FIG. 7 is an explanatory diagram showing a code stream transmitted when only characters or pictures are displayed on the receiving side.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st host computer 2 2nd host computer 3 Interface cable 201 1st wavelet transformation part 202 Image area separation part 203 Wavelet inverse transformation part 204 Binarization processing part 205 Huffman coding part 206 Second wavelet transformation part 207 Entropy encoder 401 Original image 402 Text page 403 Picture page

Continuing from the front page (72) Inventor Hiroyuki Shibaki 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Atsuga Matsuura 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company In Ricoh (72) Inventor Hiroshi Ishii Ricoh Co., Ltd. 1-3-6 Nakamagome, Ota-ku, Tokyo

Claims (3)

[Claims] 1. An image data processing apparatus having image data compression means for compressing original image data, comprising: decomposition means for decomposing the original image data into a plurality of frequency bands; An image area separating unit that separates an image area into an edge area and a picture area based on the image area; a page dividing unit that divides the page into each area separated by the image area separating unit; An image data processing apparatus, comprising: control means for performing compression by a compression method corresponding to a region separated into regions. 2. The image data processing apparatus according to claim 1, wherein the control unit transfers the compressed data from a page in the edge area. 3. The image data processing apparatus according to claim 1, wherein the control unit restores the compressed data only in a necessary area.