JP2002314821A - Image compression method, image expansion method, image compression device, and image expansion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the amount of scanner image data or printer image data which are used. SOLUTION: This image compression method comprises an image dividing process of dividing the inputted image data into a plurality of image blocks corresponding to the structure of the image pattern, a comparison process of comparing the divided image blocks with image blocks which have been previously stored, a symbol generating process of producing a comparison result as a symbol, a symbol dividing process of dividing the produced symbol into a plurality of compression blocks, and a compression process of forming the symbol that is divided into a plurality of compression blocks into code words by compression.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image compression method, an image expansion method, an image compression apparatus and an image expansion apparatus, and more particularly to an image processed by a computer, an image read by a scanner or the like, and output to a printer. The present invention relates to a compression method and an expansion method for compressing an image.

[0002]

2. Description of the Related Art In recent years, as the resolution of laser printers and scanners has been improved, the amount of data for transferring or storing output or input images has been steadily increasing. For this reason, image compression techniques for the purpose of improving communication efficiency, reducing storage area, and the like have been receiving attention. Image compression technology includes
There are lossy compression and lossless compression. Lossy compression is a technique for compressing using visual lossless, that is, a method in which the loss cannot be recognized by the human eye. On the other hand, lossless compression faithfully encodes digital information, and is often used in document files, executable formats, and the like. Image compression finds redundant parts of image data, and converts redundant parts having a high frequency of occurrence into simple expressions. This reduces the size of the image data. In order to find this redundant part, there is one that uses run length or frequency conversion.

[0003] The run length symbolizes and encodes the number of appearances of data having the same value.
In the case of a binary image where black is set to 1, “0000111”
Image data such as “0011” is converted as “4322.” The converted run-length value is further compressed using Huffman coding, etc. The frequency conversion is divided into blocks. The image data is subjected to frequency conversion, and high frequency components are cut out (quantized). The reduced amount of data is further compressed using Huffman coding or the like. However, the human perception system utilizes the property that it is difficult to recognize high frequency components, and JPEG is a typical example.

[0004]

The run length is often used for a binary image, and the frequency conversion represented by JPEG is used for a multi-valued color image. When these compression methods are applied to a printed image, an image obtained by scanning a printed image, or an image immediately before printing in a printing device such as a laser printer, the compression ratio may be lower than that of a general binary image or a natural image. Are known. Unlike displays, prints and print images basically have to be expressed in two ways, with or without pigments or toners.Therefore, gradations are based on the amount of pigments or toners per unit area. Expressing the key. In order to obtain this print image from general image data, a dither mask as shown in FIG. 24 is often used. In the case of a color image, the dither pattern differs for each color component so that the pigment or toner does not overlap each other. Data in a binary converted image (hereinafter referred to as a dither image) using each of the CMYK color space dither masks as shown in FIG. 25 often undergo black and white alternation in a small section. And a method of reducing the number of low-frequency components makes it difficult to find a redundant portion of a dither image.

The present invention has been made to solve these problems, and an image compression method, an image expansion method, an image compression apparatus, and an image expansion apparatus capable of reducing the amount of data used for a scanner image or a printer image. The purpose is to provide.

[0006]

According to the present invention, there is provided an image compression method for dividing input image data into a plurality of blocks in accordance with the structure of the image pattern. A dividing step, a comparing step of comparing the plurality of divided block images with a block image in a list stored in advance, a symbol generating step of generating a comparison result as a symbol, It is characterized in that it has a symbol dividing step of dividing the symbols into a plurality of compression blocks and a compression step of compressing the symbols divided into the plurality of compressed blocks to form a codeword. Therefore, the amount of data used for the scanner image and the printer image can be reduced.

In the image dividing step, by changing the size and the pattern of the image block to be divided for each component of the image, the data usage of the scanner image or the printer image can be reduced.

Further, in the image dividing step, by dividing a plurality of image blocks of different sizes, it is possible to reduce the data usage of a scanner image or a printer image.

Further, since a plurality of lists are prepared, the amount of data used for scanner images and printer images can be reduced.

Further, a list for each image block size is prepared as a list to be compared with a plurality of image blocks of different sizes, the lists corresponding to the image block sizes are compared, and the comparison result is formed as a symbol.
The data usage of the scanner image and the printer image can be reduced.

Also, a plurality of image patterns are prepared in advance as a list, the image patterns in the list are compared with the image blocks in the comparing step, and the most similar result is used as a symbol in the symbol generating step, thereby obtaining a scanner image. And the amount of data used for printer images can be reduced.

Further, when the number of image patterns is made smaller than the number of the list, and the image blocks to be compared in the comparing step are significantly different from the prepared image patterns, the image blocks to be compared in the comparing step are registered in a list, and the code words are registered. , It is possible to reduce the amount of data used for scanner images and printer images.

In the compression step, the most similar image pattern is searched from the list, the difference from the image block to be compressed is compressed, and the compressed difference data is added to the code word, thereby obtaining the scanner image. And the amount of data used for printer images can be reduced.

Further, in the compression step, the difference between the image pattern registered in the previous list and the image block to be compressed is compressed, and the compressed difference data is added to the code word, so that the scanner image or the printer image is compressed. Data usage can be reduced.

It is preferable to use a run-length coding method, an arithmetic coding method, a Huffman coding method or a Lempel-Zieb coding method as the compression.

Further, the patterns stored in the list are compressed, and it is preferable that the compressed patterns are expanded and compared at the time of comparison in the comparing step.

An image compression apparatus according to another aspect of the present invention comprises:
An image dividing unit that divides input image data into a plurality of blocks according to the structure of the image pattern, and a comparison that compares the divided block images with block images in a list stored in advance. Means, a symbol generation means for generating a result of the comparison as a symbol, a symbol division means for dividing the generated symbol into a plurality of compression blocks, and a codeword for compressing the symbol divided into a plurality of compression blocks to form a codeword. Compression means for forming.

Further, the compression means performs block sort conversion on the divided blocks and performs lossless compression on the converted symbols, thereby reducing the amount of data used for scanner images and printer images.

The compression means compresses the converted symbols by a run-length encoding method and further performs lossless compression, so that the amount of data used in a scanner image or a printer image can be reduced.

Further, it is preferable to use a run-length encoding method, an arithmetic encoding method, a Huffman encoding method, or a Lempel-Zieb encoding method as the lossless compression.

Further, the patterns stored in the list are compressed, and it is preferable that the compressed pattern is expanded and compared at the time of comparison by the comparing means.

Further, according to the image decompression method of another invention, the compressed code word is returned to the symbol before the compression means is applied, and the decompressed symbol is formed into a block image corresponding to the symbol. A plurality of block images are combined based on the division method used by the image division means. Therefore, the amount of data used for the scanner image and the printer image can be reduced.

Also, an image decompression device as another invention is
Decompression means for returning the compressed codeword to the symbol before applying the compression means, block image formation means for forming the decompressed symbol into a block image corresponding to the symbol,
Block image combining means for combining a plurality of block images based on a division method using the formed block image by the image division means. Therefore, the amount of data used for the scanner image and the printer image can be reduced.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An image compression method according to the present invention comprises the steps of: dividing input image data into a plurality of blocks in accordance with the structure of the image pattern; A comparison step of comparing with a block image in a list stored in advance, a symbol generation step of generating a comparison result as a symbol, and a symbol division step of dividing the generated symbol into a plurality of compression blocks; Compressing a symbol divided into a plurality of compressed blocks to form a codeword.

[0025]

FIG. 1 is a block diagram showing the configuration of an image compression apparatus according to the present invention. In the figure, an image compression apparatus of the present invention includes an image dividing unit 101 for dividing input image data into any of a plurality of block methods according to the structure of the image pattern, A comparing unit 103 for comparing with a block image previously stored in the list storage unit 102; a symbol generating unit 104 for generating a comparison result as a symbol; and a symbol division for dividing the generated symbol into a plurality of compression blocks. Means 105 and a compressing means 106 for compressing the symbols divided into a plurality of compressed blocks to form a codeword.

Next, the operation of the image compression apparatus of the present invention will be described with reference to the operation flow shown in FIG. First, image data immediately before scanning or printing is stored in the image dividing unit 10.
In step S101, the image data is divided into small blocks using the characteristic that can be divided into small blocks having similar characteristics as shown in FIG. The scanning order of the block images is, for example, as shown in FIG. In the example of FIG.
2-3, and then scan i-
Scan ii-iii ... Another example is shown in FIG.
In this figure, scanning is performed with image blocks of two sizes. The scanning order is 1-2-3.
bc ... are scanned. The divided images are sent to the symbol dividing means 105 as symbols by using an index of an image pattern in a list of similar or identical shapes obtained by pattern matching or simple comparison using the list by the symbol generating means 104 (step S10).
2). The generated symbol is divided into a plurality of symbols by the symbol dividing unit 105, and is further compressed by the compressing unit 106 to generate a codeword (step S103). The generated codeword is used for storage and transfer.

FIG. 3 is a block diagram showing the structure of an image decompression device according to another invention. In the figure, an image decompression device according to the present invention includes a decompression device 201 for returning a code word compressed by the image compression device of FIG. 1 to a symbol before applying the compression device 106 of FIG. Image forming means 20 for forming a block image corresponding to
2 and the formed block image is divided into image dividing means 1 shown in FIG.
And a block image combining unit 203 for combining a plurality of block images based on the division method used in step S01.

Next, the operation of the image decompression apparatus of the present invention will be described with reference to the operation flow shown in FIG. First, when the codeword is expanded, the symbol is returned to the symbol by the expansion unit 201 and sent to the block image generation unit 202 (step S2).
01). The block image generation unit 202 generates a block image of the transmitted symbol by using the reverse operation of the symbol generation unit 104 in FIG. 1 (step S20).
2). The reverse operation is to extract a pattern image from the list storage unit 102 in FIG. 1 using a symbol as an index, and use it as a block image. The generated block images are combined by the block image combining unit 203 by placing the sent image blocks according to the image block scanning procedure performed by the image dividing unit 101 in FIG. 1 (step S203).

FIGS. 8 to 11 are block diagrams showing respective structural examples of the symbol generating means in the image compression apparatus of the present invention. In FIG. 8, the input block image is compared with the pattern image in the list storage unit 12 by the comparison unit 11, and when the comparison value is within the allowable range, the index of the pattern image is generated as a symbol. Here, if there is no pattern in the allowable range in the list storage unit 12, it is registered in the list storage unit 12. 9, a plurality of types of lists are stored in a list storage unit 12 as a list to be compared with a block image, and the input block image is compared with the plurality of types of lists in the list storage unit 12 by a comparison unit 11. . In FIG. 10, a block image as it is or a compressed block image is used as a pattern image in the list storage unit 12 to be registered in the list storage unit 12. If the pattern in the list storage unit 12 is a compressed pattern, or if the comparison unit 11 cannot handle the compressed pattern, the pattern is expanded by the expansion unit 13 and then compared. When the comparing means 11 performs the comparison using the compressed data, it is sufficient as it is. FIG.
In the above, when a pattern that is not in the list storage means 12 is registered in the list, it is necessary to add the pattern to the code word. At this time, a compressed image pattern may be used, or the image pattern may be used as it is. As a method of determining the allowable range of the pattern and the block image in the list, there are a simple comparison that compares whether all pixels have the same value, a method that uses the bias of the density and the pixel, and a method that simply uses the integration of the density. Such a method may be used.

FIGS. 12 to 14 are block diagrams showing examples of the structure of the compression means in the image compression apparatus of the present invention. In FIG. 12, an input symbol is converted by a compression means 13 into a run length code, a Huffman code, an arithmetic code and an LZ code.
It is encoded with a code. In FIG. 13, a block sort conversion unit 15 may be used as a pre-process of this encoding. Further, in FIG. 14, the block sort conversion means 15 and the MTF conversion means 16 are used together as preprocessing for encoding. As a compression unit when using block sort conversion, a run length may be used as a compression unit, and a Huffman code or an arithmetic code may be used. May be used. The compression means 13 may be further subdivided. The compressed block is generated as a codeword. When a code word is registered in the list, a code word is generated by combining the code word with information indicating the number or size registered in the list.

Next, FIG. 15 to FIG. 17 are block diagrams showing respective structural examples of the expansion means in the image expansion apparatus of another invention. In FIG. 15, when there is a code word registered in the list, the input code word is divided into a list registration code word and a symbol code word, and the symbol code word is expanded by the same expansion means as that performed by the compression means. , Are sent to the subsequent stage as symbols. Like the compression means, the decompression means includes run length, Huffman code, arithmetic code and LZ code. 13 and 14, the decompression means includes a decompression means as a pre-stage as shown in FIG. 16 and FIG. 17, and an MTF inverse conversion means and a block reverse sort in a post-stage. There is a conversion means. The decompressed symbols are sent to block combining means to generate an image.

FIG. 21 is a diagram showing the arrangement order of block image generation. When generating the original image from the block image, in the scan order used by the block image combining means,
Each block image is arranged.

FIG. 22 is a histogram of a dither image. FIG. 23 is a diagram illustrating an example of how to determine the size when the size of the block image is not given. First,
The horizontal and vertical histograms of a small section larger than the predicted block size are obtained. FIG. 22 shows an example of a histogram in the horizontal direction. From this histogram, it is estimated that each peak has the center of the block image. And
As shown in FIG. 23, several representative two points are selected from the horizontal direction and the vertical direction. The difference between the centers of these two representative points is determined in the horizontal direction and the vertical direction, and the larger difference is divided into two. In FIG. 23, since the difference in the vertical direction is large, the vertical direction is divided into two, and the value is α. From these two divisions, a block image is obtained as shown in FIG. When actually obtaining, find several pairs of representative points,
By using the average, it is possible to obtain a more accurate size.

It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications and substitutions can be made within the scope of the claims.

[0035]

As described above, according to the image compression method of the present invention, an image dividing step of dividing input image data into a plurality of blocks according to the structure of the image pattern, Comparing the generated block image with a block image in a list stored in advance, a symbol generating step of generating a result of the comparison as a symbol, and dividing the generated symbol into a plurality of compression blocks. And a compression step of compressing the symbols divided into a plurality of compression blocks to form a codeword. Therefore, the amount of data used for the scanner image and the printer image can be reduced.

Further, in the image dividing step, by changing the size and the pattern of the image block to be divided for each component of the image, it is possible to reduce the amount of data used for the scanner image and the printer image. Further, in the image dividing step, by dividing a plurality of image blocks of different sizes, the amount of data used for the scanner image or the printer image can be reduced.

Since a plurality of lists are prepared, the amount of data used for scanner images and printer images can be reduced.

Further, a list for each image block size is prepared as a list to be compared with a plurality of image blocks of different sizes, the lists corresponding to the image block sizes are compared, and the comparison result is formed as a symbol.
The data usage of the scanner image and the printer image can be reduced.

Also, by preparing a plurality of image patterns as a list in advance, comparing the image patterns in the list with the image blocks in the comparison step, and using the most similar result as a symbol in the symbol generation step, the scanner image And the amount of data used for printer images can be reduced.

Further, when the number of image patterns is smaller than the number of the list, and the image blocks to be compared in the comparing step are significantly different from the prepared image patterns, the image blocks to be compared in the comparing step are registered in the list and the code words are registered. , It is possible to reduce the amount of data used for scanner images and printer images.

In the compression step, the most similar image pattern is searched for from the list, the difference from the image block to be compressed is compressed, and the compressed difference data is added to the code word to obtain the scanner image. And the amount of data used for printer images can be reduced.

Further, in the compression step, the difference between the image pattern registered in the previous list and the image block to be compressed is compressed, and the compressed difference data is added to the code word, so that the scanner image or the printer image is compressed. Data usage can be reduced.

As the compression, it is preferable to use a run-length encoding method, an arithmetic encoding method, a Huffman encoding method or a Lempel-Zieb encoding method.

Further, the patterns stored in the list are compressed, and in the comparison in the comparing step, it is preferable that the compressed patterns are expanded and compared.

An image compression apparatus according to another aspect of the present invention comprises:
An image dividing unit that divides input image data into a plurality of blocks according to the structure of the image pattern, and a comparison that compares the divided block images with block images in a list stored in advance. Means, a symbol generation means for generating a result of the comparison as a symbol, a symbol division means for dividing the generated symbol into a plurality of compression blocks, and a codeword for compressing the symbol divided into a plurality of compression blocks to form a codeword. Compression means for forming.

Further, the compression means performs block sort conversion on the divided blocks and performs lossless compression on the converted symbols, thereby reducing the amount of data used in the scanner image or the printer image.

The compressing means compresses the converted symbols by the run-length encoding method and further performs lossless compression, thereby reducing the amount of data used for scanner images and printer images.

Further, as the lossless compression, it is preferable to use a run-length encoding method, an arithmetic encoding method, a Huffman encoding method or a Lempel-Zieb encoding method.

Also, the patterns stored in the list are compressed, and it is preferable that the compressed patterns are expanded and compared at the time of comparison by the comparing means.

Further, according to the image decompression method as another invention, the compressed code word is returned to the symbol before the compression means is applied, and the decompressed symbol is formed into a block image corresponding to the symbol. A plurality of block images are combined based on the division method used by the image division means. Therefore, the amount of data used for the scanner image and the printer image can be reduced.

An image decompression device as another invention is
Decompression means for returning the compressed codeword to the symbol before applying the compression means, block image formation means for forming the decompressed symbol into a block image corresponding to the symbol,
Block image combining means for combining a plurality of block images based on a division method using the formed block image by the image division means. Therefore, the amount of data used for the scanner image and the printer image can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an image compression device according to the present invention.

FIG. 2 is a flowchart showing the operation of the image compression device of the present invention.

FIG. 3 is a block diagram illustrating a configuration of an image decompression device according to the present invention.

FIG. 4 is a flowchart showing the operation of the image decompression device of the present invention.

FIG. 5 is a diagram showing a color dither mask that is divided into blocks.

FIG. 6 is a diagram illustrating an example of a scanning state in a block image.

FIG. 7 is a diagram showing another example of a state of scanning in a block image.

FIG. 8 is a block diagram illustrating a configuration example of a symbol generation unit in the image compression device of the present invention.

FIG. 9 is a block diagram illustrating a configuration example of a symbol generation unit in the image compression device of the present invention.

FIG. 10 is a block diagram illustrating a configuration example of a symbol generation unit in the image compression device of the present invention.

FIG. 11 is a block diagram illustrating a configuration example of a symbol generation unit in the image compression device of the present invention.

FIG. 12 is a block diagram illustrating a configuration example of a compression unit in the image compression device of the present invention.

FIG. 13 is a block diagram illustrating a configuration example of a compression unit in the image compression device of the present invention.

FIG. 14 is a block diagram illustrating a configuration example of a compression unit in the image compression device of the present invention.

FIG. 15 is a block diagram showing a configuration example of a decompression means in an image decompression device of another invention.

FIG. 16 is a block diagram illustrating a configuration example of a decompression unit in an image decompression device according to another invention.

FIG. 17 is a block diagram showing a configuration example of a decompression means in an image decompression device according to another invention.

FIG. 18 is a block diagram illustrating a configuration example of a block image generation unit.

FIG. 19 is a block diagram illustrating a configuration example of a block image generation unit.

FIG. 20 is a block diagram illustrating a configuration example of a block image generation unit.

FIG. 21 is a diagram illustrating an arrangement order of block image generation.

FIG. 22 is a histogram of a dither image.

FIG. 23 is a diagram illustrating an example of how to determine a size when a size of a block image is not given;

FIG. 24 is a diagram showing a dither mask.

FIG. 25 is a diagram showing a color dither mask.

[Explanation of symbols]

101: image division means, 102; list storage means, 10
3; comparison means, 104; symbol generation means, 105; symbol division means, 106; compression means, 201; expansion means, 202; block image generation means, 203;

Claims (18)

[Claims] An image dividing step of dividing input image data into a plurality of blocks according to the structure of the image pattern, and a step of dividing a plurality of divided block images into blocks in a list stored in advance. A comparison step of comparing the image with an image, a symbol generation step of generating a comparison result as a symbol, a symbol division step of dividing the generated symbol into a plurality of compression blocks, and a symbol division step of dividing the generated symbol into a plurality of compression blocks. A compression step of compressing to form a codeword. 2. The image compression method according to claim 1, wherein in the image dividing step, the size and pattern of an image block to be divided are changed for each component of the image. 3. The image compression method according to claim 1, wherein in the image dividing step, a plurality of image blocks having different sizes are divided. 4. The image compression method according to claim 1, wherein a plurality of types of said list are prepared. 5. A method for preparing the list for each image block size as a list to be compared with a plurality of image blocks of different sizes, comparing the list corresponding to the image block size, and forming a comparison result as a symbol. Item 5. The image compression method according to any one of Items 1 to 4. 6. A plurality of image patterns are prepared in advance as the list, the image pattern in the list is compared with the image blocks in the comparing step, and the most similar result in the symbol generating step is determined by the symbol 2. The image compression method according to claim 1, wherein the image compression method is used. 7. The method according to claim 1, wherein the number of the image patterns is smaller than the number of the list, and the image blocks to be compared in the comparing step are significantly different from the prepared image patterns. 7 and added to the code word.
The image compression method as described above. 8. The compression step of searching for a most similar image pattern from the list, compressing a difference from an image block to be compressed, and adding compressed difference data to the codeword. 2. The image compression method according to 1. 9. The image according to claim 1, wherein in the compression step, a difference between an image pattern registered in a previous list and an image block to be compressed is compressed, and the compressed difference data is added to the codeword. Compression method. 10. The compression method includes a run-length encoding method,
The image compression method according to claim 1, wherein an arithmetic coding method, a Huffman coding method, or a Lempel-Zieb coding method is used. 11. The image according to claim 1, wherein the pattern stored in the list is compressed, and the compressed pattern is expanded and compared at the time of comparison in the comparing step. Compression method. 12. An image dividing means for dividing input image data into a plurality of blocks according to a structure of the image pattern, and a block in a list in which a plurality of divided block images are stored in advance. Comparing means for comparing the image with the image; symbol generating means for generating a result of the comparison as a symbol; symbol dividing means for dividing the generated symbol into a plurality of compression blocks; and symbol dividing means for dividing the symbol divided into a plurality of compressed blocks. Compression means for compressing to form a code word. 13. The image compression apparatus according to claim 12, wherein the compression unit performs block sort conversion on the divided blocks and performs lossless compression on the converted symbols. 14. The image compression apparatus according to claim 12, wherein said compression means compresses the converted symbols by a run-length encoding method and further performs lossless compression. 15. The image compression apparatus according to claim 12, wherein the lossless compression uses a run-length encoding method, an arithmetic encoding method, a Huffman encoding method, or a Lempel-Zieb encoding method. 16. The pattern stored in the list is compressed, and when the comparison is performed by the comparing means, the compressed pattern is expanded and compared.
The image compression device according to any one of the above. 17. A compressed code word is returned to a symbol before being subjected to compression means, a decompressed symbol is formed into a block image corresponding to the symbol, and the formed block image is divided by the image division means. An image decompression method comprising combining a plurality of block images based on the method. 18. A decompression unit for returning a compressed code word to a symbol before the compression unit is applied, a block image forming unit for forming a decompressed symbol into a block image corresponding to the symbol, and a formed block image And a block image combining unit that combines a plurality of block images based on a dividing method used in the image dividing unit.