JP2000078415A - Image processing system, image compressing device and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To compress/extend run length data through any suitable method regardless of data size. SOLUTION: A first storage means 1 stores the run length data. A compression means 2 extracts the run length data from the first storage means 1 for the unit of scan line and compresses the run length data through the compressing method instructed by a compressing method selecting means 4. When the size of a line buffer in an extension means 5 is larger than the data size of scan line to be the object of compression, two-dimensional(2D) compression is selected by the compressing method selecting means 4 but when the size is smaller, 1D compression is selected and reported to the compression means 2. A second storage means 3 stores compressed data provided by the compression means 2. The extension means 5 reads the compressed data out of the second storage means 3, extends them into run length data and outputs these data to a printer, for example.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pressure processing system, an image compression device, and a recording medium, and more particularly, to an image processing system in which image data is compressed by a compression device and decompressed by an expansion device, and image data is compressed. The present invention relates to an image compression device that outputs to an expansion device, and a computer-readable recording medium that stores a program that causes a computer to execute such processing.

[0002]

2. Description of the Related Art In recent years, with the improvement of image quality of printers and the like,
The amount of image data used for printing also tends to increase.

In order to process such a huge amount of image data with limited computer resources, a high-speed image data compression technique and a technique for expanding image data in real time are indispensable. Processing equipment is being developed.

[0004] Among image data handled by a printer, in particular, bitmap data has a high correlation between adjacent pixels.
Code) and a modified modified read code (MMR code). Such two-dimensional encoding can be realized using a compression / decompression processor or the like used in a facsimile machine.

[0005] However, facsimile machines are usually 3
Since it has a resolution of only about 00 dots / inch (hereinafter abbreviated as dpi), the processing capacity of the compression / expansion processor of the facsimile apparatus requires that the two-dimensional encoded compressed data of a high-speed, high-quality printer be expanded in real time. Often lacks power.

[0006] For this reason, Japanese Patent Laid-Open No. 5-41809 discloses a method for speeding up the decompression processing of two-dimensional encoded data. The present invention discloses a method of decompressing two-dimensional coded compressed data into run-length data, which is a form of one-dimensional coded compression, instead of directly expanding the bitmap. If necessary, the run-length data may be expanded to bitmap data thereafter.

By using such a method, the reference scan line (the scan line immediately before the scan line to be expanded) required for expanding the two-dimensional encoded compressed data is set to be smaller than the bit map data. Since it can be represented by a compact list of run-length data (hereinafter abbreviated as a run list), it is possible to reduce the number of accesses and thereby speed up the processing.

When the reference scan line is represented by a run list, the number of data shifts can be reduced when the two-dimensional encoded compressed data is decompressed, as compared with the case where the reference scan line is represented by bit map data. As a result, simplification of the configuration of the decompression device and speeding up of processing can be realized.

[0009]

By the way, when the decompression processing which requires real-time processing is realized by hardware,
The reference scan line is often constituted by a register or the like.

In such a case, if the bitmap data to be encoded is a complicated image with mixed black and white, a large number of runs occur in one scan line, and a finite-scale register (reference scan) is used. Lines) may not be able to fit all runs.

In such a case, there is a problem that the image decompression device cannot correctly decompress this bitmap data. The present invention has been made in view of the above-described problems, and performs compression by an appropriate method even when the number of runs generated in one scan line exceeds the number that can be stored in the run list, An object of the present invention is to provide an image processing system that can expand any run-length data.

[0012]

According to the present invention, in order to solve the above-mentioned problems, image data is compressed by a compression device.
In an image processing system that expands in an expansion device,
The compression device includes a first storage unit that stores run-length data to be processed, the size of a line buffer included in the decompression device, and the run-length data according to a data size of the run-length data. Compression method selection means for selecting the compression method, and the run-length data stored in the first storage means, using two-dimensional compression or one-dimensional compression according to the selection result of the compression method selection means. Compression means for compressing the compressed data into compressed data, wherein the decompression device stores the compressed data obtained by the compression means of the compression device;
An image processing system, comprising: decompression means for decompressing compressed data stored in the second storage means into run-length data in accordance with a compression method of the compression means of the compression device. You.

Here, the first storage means of the compression device stores run-length data to be processed. The compression method selection means, according to the size of the line buffer of the decompression device and the data size of the run-length data,
Select the run-length data compression method. The compression means compresses the run-length data stored in the first storage means into compressed data using two-dimensional compression or one-dimensional compression according to the result of the selection by the compression method selection means. The second storage means of the decompression device stores the compressed data obtained by the compression means of the compression device. The expansion unit expands the compressed data stored in the second storage unit into run-length data according to the compression method of the compression unit of the compression device.

In an image compression apparatus for compressing image data and outputting the compressed data to a decompression device, a first storage means for storing run-length data to be processed, and a line buffer provided in the decompression device. Compression method selection means for selecting a compression method of the run-length data according to a size and a data size of the run-length data; and a method for compressing the run-length data stored in the first storage means. According to the selection result of the selection means,
Compression means for compressing the data into compressed data using two-dimensional compression or one-dimensional compression.

Here, the first storage means stores run-length data to be processed. The compression method selection means selects a compression method for the run-length data according to the size of the line buffer included in the decompression device and the data size of the run-length data. The compression means compresses the run-length data stored in the first storage means into compressed data using two-dimensional compression or one-dimensional compression according to the result of the selection by the compression method selection means.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration example of a first embodiment according to the image processing system of the present invention.

As shown in FIG. 1, the image processing system includes a first storage unit 1, a compression unit 2, a second storage unit 3, a compression method selection unit 4, and a decompression unit 5. .

The first storage means 1 temporarily stores image data (image data expressed in a run-length data format) sent via a network I / F (Interface) not shown. .

The compression means 2 fetches run-length data from the first storage means 1 in units of scan lines, and compresses the run-length data by a compression method specified by a compression method selection means 4 described later.

The compression method selection means 4 is a reference scan line buffer (described later) incorporated in the decompression means 5 described later.
Is larger than the size of scan line data to be compressed (hereinafter abbreviated as line data), two-dimensional compression is selected. If smaller, one-dimensional compression is selected. The result is notified to the compression means 2.

As the two-dimensional compression, MR (Modifi
ed READ) Encoding and MMR (Modified Modified READ)
Encoding or the like can be used, and as one-dimensional compression, MH (Modified Huffman) encoding or the like can be used.

The second storage means 3 stores the compressed data obtained by the compression means 2 and, if necessary, the decompression means 5
To supply. The decompression means 5 reads the compressed data from the second storage means 3, decompresses the data into run-length data, and outputs the data to, for example, a printer. The decompression means 5 has a built-in reference scan line buffer, and when the compressed data is subjected to two-dimensional compression, the reference scan line buffer stores one line of run-length data (= line data). Is stored, and a decompression process is performed based on the stored data.

Next, a detailed configuration example of each part of the embodiment shown in FIG. 1 will be described. FIG. 2 is a block diagram showing a detailed configuration example of the compression unit 2 shown in FIG. As shown in this figure, the compression means 2 includes an encoded scan line buffer 21, a reference scan line buffer 22,
It is constituted by a compression code judging means 23.

The encoded scan line buffer 21 extracts the run length data stored in the first storage means 1 for one scan line and temporarily stores it. When performing the two-dimensional compression, the reference scan line buffer 22 reads the run-length data one line before the encoded scan line in a list format and temporarily stores it. When a compressed code corresponding to each run is generated by a compressed code determination unit 23 described later, the contents of the reference scan line buffer 22 are sequentially changed in accordance with the generated compressed code. In addition,
Since the compression process does not require much real-time processing, the reference scan line buffer 22 does not necessarily have to be implemented in hardware.

The compression code determination means 23 compresses the line data stored in the encoded scan line buffer 21 using the compression method specified by the compression method selection means 4. At this time, if the specified compression method is two-dimensional compression, the reference scan line buffer 22 is also referred to and the line data is compressed.

Next, a configuration example of the compression method selection means 4 shown in FIG. 1 will be described with reference to FIG. FIG.
3 is a block diagram showing a detailed configuration example of a compression method selection unit 4 shown in FIG. As shown in FIG.
Is composed of a run counter 41, a line buffer size storage means 42, and a compression method determination means 43.

The run counter 41 counts the number of runs included in the line data to be subjected to the compression processing, and supplies the count to the compression code determination unit 23 of the compression unit 2. That is, the run counter 41 resets the counter when new data is read into the encoded scan line buffer 21, and thereafter, the run included in the data stored in the encoded scan line buffer 21 is compressed. The counter is incremented each time it is processed. Then, when the compression processing for the data stored in the encoded scan line buffer 21 is completed, the value of the counter is supplied to the compression method determining means 43.

The line buffer size storage means 42 is connected to a reference scan line buffer 52 (described later) of the decompression means 5, and
2 is stored.

The compression method determining means 43 includes a run counter 4
The count value of 1 and the line buffer size storage means 42
, It is determined whether to use two-dimensional compression or one-dimensional compression.

Next, with reference to FIG. 4, an example of the configuration of the decompression means 5 shown in FIG. 1 will be described. FIG. 4 is a block diagram showing a detailed configuration example of the decompression means 5 shown in FIG. As shown in this figure, the decompression means 5 comprises a decoded scan line buffer 51, a reference scan line buffer 52, and decompression data determination means 53.

The decoding scan line buffer 51 takes out the compressed data stored in the second storage means 3 and temporarily stores it. Reference scan line buffer 5
2, when the compressed data is two-dimensionally compressed, the run-length data one line before the scan line to be decompressed is read in a list format and temporarily stored.

When the compressed data is expanded into run-length data by expanded data determining means 53, which will be described later, the contents of the reference scan line buffer 52 are sequentially changed accordingly.

Here, since the decompression means 5 needs to perform processing in accordance with the printing speed of a printer (not shown) to which data is output, the reference scan line buffer 52 is implemented by a register or the like. Have been. For this reason,
The run list has a fixed length, and there is an upper limit on the number of runs that can be stored.

The expanded data determination means 53 expands the data stored in the decoded scan line buffer 51 into run-length data. Note that the decompression data determination means 5
When the compressed data is subjected to the two-dimensional compression, the decompression process 3 refers to not only the contents of the decoded scan line buffer 51 but also the contents of the reference scan line buffer 52.

Next, before describing the operation of the above embodiment, MH coding, MR coding and MMR coding used in the present embodiment will be described. (1) MH encoding In MH encoding, all scan line data is one-dimensionally compressed.

As shown in FIG. 5, the compressed data corresponding to each scan line obtained by the MH encoding is composed of EOL (End Of Line) codes 70 and 73 added at the head and data codes 71 and 73 following the EOL (End Of Line) codes. 74 and 75.

Immediately after the data code 75 of the last line, R consisting of six consecutive EOL codes 76 to 81 is used.
A TC code is added. Here, the EOL code is “000”
This is a 12-bit code represented by “000000001”.

When the number of code bits in one scan line is shorter than a predetermined bit length T, a variable length "0" is filled immediately after the data code to satisfy the condition of the minimum code bit number. It is added as bit 72.

FIG. 6 is a diagram showing details of the data code shown in FIG. As shown in FIG.
This is a variable length code composed of a white run 91a indicating a white run length and a black run 91b indicating a black run length, and white runs and black runs are stored alternately.

Each scan line always starts with a white run, and thereafter, black runs and white runs are alternately arranged. When the first pixel is black, zero white pixels indicating that the length is “0” are stored.

When the run length is 63 or less, one terminating code TN is used as the data code. When the run length is 64 or more, the run length is set to 6
A makeup code MU representing a quotient divided by 4 and a terminate code TN representing a remainder of 64 run lengths are used.

FIG. 7 is a diagram showing an example of a termination code. In this example, the white or black run length is 0
The terminating code corresponding to the case of 63 is shown. For example, if the white run length is “15”, “110101” is selected as the termination code. If the black run length is “15”, “000011000” is selected as the termination code.

FIGS. 8 and 9 show examples of makeup codes. In the example of FIG. 8, make-up codes corresponding to the case where the white or black run length is 64 to 1728 are shown.

In the example of FIG. 9, a makeup code corresponding to the case where the white or black run length is 1792 to 2560 is shown. Next, MR coding will be described. (2) MR Coding In MR coding, a process of compressing one scan line one-dimensionally and then compressing one or three continuous scan lines two-dimensionally is repeated.

Here, the two-dimensional compression refers to a scan line (reference scan line) immediately before a scan line (encoded scan line) that is currently being encoded, and changes pixels between the reference scan line and the encoded scan line. (Position that changes from black to white or from white to black) is encoded.

In encoding, the following changed pixels are defined. a0: starting change pixel of the coded scan line a1: first change pixel to the right of a0 on the coded scan line a2: first change pixel to the right of a1 on the coded scan line b1: change on the reference scan line Among the pixels, a pixel to the right of a0 and a color opposite to a0 b2: the first changed pixel to the right of b1 on the reference scan line And, according to the positional relationship between these changed pixels,
And selects one of the three encoding modes shown in (1) and encodes (compresses) the target data. (A) Pass mode When b2 is on the left side of a1, the pass mode is set. In this case, it is encoded into "0001" as shown in FIG. After the encoding, a new a0 is set immediately below b2. (B) Vertical mode When the distance between a1 and b1 is within 3 pixels, the mode is the vertical mode. According to the relative distance between a1 and b1, V0, VR1, VR
2, VR3, VL1, VL2, VL3. VRn means that a1 is to the right of n pixels of b1, and VLn means that a1 is to the left of n pixels of b1. After encoding, a new a0 is set at the position of a1. (C) Horizontal mode When the distance between a1 and b1 is larger than 3 pixels, the horizontal mode is set. In the case of the horizontal mode, the distance and color between a0 and a1 and the distance and color between a1 and a2 are described in MH code after "001". After the encoding, a new a0 is set at the position of a2.

In the MR encoding, since the one-dimensional encoding and the two-dimensional encoding are mixed as described above, a tag bit is provided after the EOL code, and the subsequent scan line is
It is possible to identify whether the image is dimensionally encoded or two-dimensionally encoded.

Next, MMR coding will be described. (3) MMR coding In MMR coding, all scan lines are two-dimensionally compressed. When encoding the first scanline,
A virtual all-white line is set as a reference scan line.

After the last line of one page, two EOL codes are successively added as an RTC code, and "0" is thereafter added so that the number of bits of code data for one page becomes an 8-bit boundary. Add.

Next, the operation of the above-described first embodiment will be described. Now, it is assumed that the run-length data to be compressed is sent via a network I / F (not shown) or the like and stored in the first storage unit 1. When the data to be compressed is transferred as bitmap data, it is of course possible to convert the bitmap data into run-length data in the CPU of the host computer (not shown).

The compression means 2 reads run-length data from the first storage means 1 in units of scan lines. Then, an inquiry is made to the compression method selection means 4 about the compression method, and compression is performed by the specified method.

Next, the operation of the compression means 2 will be described. Hereinafter, a method of MR encoding run-length data will be described first, and then a detailed operation of the compression unit 2 will be described.

In the MR encoding, the one-dimensional compression using the MH encoding is referred to the tables shown in FIGS. 7 to 9, and therefore the description thereof will be omitted, and only the two-dimensional compression will be described.

FIG. 12 shows a flow of processing when the run-length data is MR-encoded, in particular, two-dimensionally compressed. When this flowchart is started, the following processing is executed. [S101] A run to be coded is read from the coded scan line. [S102] A run is read from the run list of the reference scan line. [S103] It is determined whether the mode is the pass mode. If the mode is the pass mode, the process proceeds to step S104; otherwise, the process proceeds to step S105.

Whether the mode is the pass mode can be determined by calculating the following equation. run (0)> p_run (0) + p_run (1)
.. (1) run (0)> p_run (0) + p_run (1) +
p_run (2) (2) where run (n) is an encoded scan line.
Length of the (n + 1) th run to be encoded, p_run
(N) is the (n +) of the run list of the reference scan line.
1) Indicates the length of the run.

Equation (1) corresponds to the case where the leading run color of the encoded scan line and the reference scan line have the same color, and equation (2) corresponds to the case where the colors are different. In any case, if these expressions are "true", the path mode is set, and if "false", the path mode is not set. [S104]
The code indicating the pass mode is output as compressed data.
[S105] It is determined whether or not the mode is the vertical mode. If the mode is the vertical mode, the process proceeds to step S106; otherwise, the process proceeds to step S107.

Whether or not the mode is the vertical mode can be determined by calculating the following equation. || represents an absolute value. | P_run (0) -run (0) | ≦ 3 (3) | p_run (0) + p_run (1) -run (0)
| ≦ 3 (4) Here, equation (3) corresponds to the case where the colors of the first run of the encoded scan line and the reference scan line are the same,
Equation (4) corresponds to a different case.

In each case, if these expressions are "true", the mode is the vertical mode, and if "false", the mode is not the vertical mode but the horizontal mode. [S106] A code corresponding to the vertical mode is output as compressed data. [S107] The code indicating the horizontal mode and the MH codes of the two runs following the code are output as compressed data. [S108] The encoded scan line is updated.

That is, in the case of the pass mode, the value of the run length of the first run is corrected. In the vertical mode, the first run is deleted. In the horizontal mode, the first two runs are deleted. [S109] The run list of the reference scan line is updated according to the encoded scan line.

That is, the run of the reference scan line corresponding to the length of the run deleted from the encoded scan line is deleted from the run list or the run length is reduced. For example, if the length of the run deleted from the encoded scan line is 5, and the run length of the run in the run list of the reference scan line is 3,5 from the beginning, the run of run length 3 is deleted and the run length is deleted. Run 5 is changed to run length 3.

The flow of the process for MR compression of run-length data, particularly for two-dimensional compression, has been described above. next,
The operation of the compression means 2 will be described in detail.

FIG. 13 is a flowchart for explaining an example of the processing of the compression means 2. When this flowchart is started, the following processing is executed. [S201] The compression unit 2 retrieves one line of run-length data to be compressed from the first storage unit 1 and stores it in the encoded scan line buffer 21. [S202] The compression unit 2 inquires of the compression method selection unit 4 about the compression method of the next scan line. If the specified compression method is two-dimensional compression, the process proceeds to S203. If it is one-dimensional compression, the process proceeds to S206. [S203] The compression unit 2 extracts the first run from the encoded scan line buffer 21 and transfers it to the compression code determination unit 23. [S204] The compressed code determination unit 23 encodes the run into an MR code by the processing described with reference to FIG. Then, the generated compressed data is stored in the second storage unit 3. Also, the reference scan line buffer 22
Update your run list to match the compressed run. [S205] The compression code determination unit 23 determines whether the run to be compressed next is EOL. If the run is not EOL, the process returns to step S203. If the run is EOL, the process proceeds to S209. [S206] The compression unit 2 extracts the first run from the encoded scan line buffer 21 and transfers it to the compression code determination unit 23. [S207] The compressed code determination unit 23 performs MH encoding, which is one-dimensional encoding, with reference to the tables shown in FIGS. 7 to 9, and stores the generated compressed data in the second storage unit 3. . [S208] The compression code determination means 23 determines whether or not the run to be compressed next is EOL.
06, and if it is EOL, the process proceeds to S209. [S209] The compression code determination unit 23 determines whether or not the scan line to be compressed still exists. If the scan line does not exist, the process ends. Otherwise, the process returns to step S201.

At this time, the contents of the coded scan line buffer 21 are copied to the reference scan line buffer 22, and new run length data is fetched from the first storage means for one line and stored in the coded scan line buffer 21. Is done. Thereafter, the same processing is repeated.

Next, the operation of the compression method selection means 4 will be described. FIG. 14 is a flowchart illustrating an example of a process performed by the compression method selection unit 4. When this flowchart is started, the following processing is executed. [S301] The compression method selection unit 4 determines whether or not the compression unit 2 has notified that the run has been compressed. If so, the process proceeds to step S302; otherwise, the process returns to step S301. . [S302] The compression method selection unit 4 sets the counter value to 1
Only increment. [S303] The compression method selection means 4 determines that the compression means 2 is EO.
It is determined whether or not L has been detected. If EOL has been detected, the process proceeds to step S304; otherwise, the process returns to step S301. [S304] The compression method selection unit 4 determines whether the value of the counter is equal to or smaller than the size of the reference scan line buffer. If the value of the counter is equal to or smaller than the size of the reference scan line buffer, the process proceeds to step S305. Otherwise, the process proceeds to step S306. [S305] The compression method selection unit 4 instructs the compression unit 2 to compress the next scan line by two-dimensional compression.

That is, when the value of the counter is equal to or smaller than the size of the reference scan line buffer, the reference scan line buffer 22 is compressed when the next scan line is compressed.
Means that all runs can be entered, so that two-dimensional compression is possible. Therefore, the compression method selection unit 4 instructs the compression unit 2 to compress the next scan line by, for example, MR encoding or MRR encoding. [S306] The compression method selection unit 4 instructs the compression unit 2 to compress the next scan line one-dimensionally.

That is, if the value of the counter exceeds the size of the reference scan line buffer, it means that when the next scan line is compressed, not all the runs can fit in the reference scan line buffer 22. Compression cannot be performed. Therefore, the compression method selecting means 4
Instructs the compression unit 2 to perform, for example, MH encoding on the next scan line. [S307] The compression method selection unit 4 resets the value of the counter.

The above processing is executed each time new data is stored in the encoded scan line buffer 21. Next, the operation of the decompression means 5 will be described. The decompression means 5 is a general processing circuit for decompressing the compressed data compressed by MR encoding into run-length data. Here, the expansion of the one-dimensionally compressed data in the MR encoding is performed by referring to the tables of FIGS. 7 to 9, and therefore the description thereof will be omitted, and only the expansion of the two-dimensionally compressed data will be described.

FIG. 15 is a flow chart for explaining an example of the processing when the expansion means 5 expands the two-dimensionally compressed data. When this flowchart is started, the following processing is executed. [S401] The decompressed data determination unit 53 reads a run from the reference scan line buffer 52. [S402] The decompressed data determination unit 53 cuts out the MR code from the decoded scan line buffer 52. [S403] The decompressed data determination unit 53 determines in step S4
In step 02, run-length data is output according to the extracted MR code.

That is, run-length data is output according to the MR code as follows. Here, run is the run length of the output run. (1) Pass mode run = p_run (0) + p_run (1) ...
(5) run = p_run (0) + p_run (1) + p_r
un (2) (6) Expression (5) corresponds to the case where the color of the run to be output next and the color of the first run of the reference scan line buffer 52 are the same. 6) corresponds to a different case. (2) Vertical mode run = p_run (0) + dist (7) run = p_run (0) + p_run (1) + dis
t (8) Equation (7) corresponds to the case where the color of the run to be output next and the color of the first run of the reference scan line buffer are the same, and Equation (8) corresponds to the case where the color is different ing. Note that "di
As “st”, a numerical value corresponding to the MR code is used with reference to FIG. (3) Horizontal mode Since the two MR codes following the code indicating the horizontal mode are run-length data, they are expanded and output. [S404] The decompressed data determination unit 53 updates the run list in the reference scan line buffer 52 according to the decoded scan line.

That is, the following processing is executed according to the MR code. (1) Pass Mode If the output run color is the same as the first run color of the reference scan line buffer 52, the first two runs are deleted from the run list of the reference scan line buffer 52. On the other hand, if the colors of the runs are different, the first three runs are deleted from the run list. (2) Vertical mode (VL) When the output run color and the head run color of the reference scan line buffer 52 are the same, the head run length of the reference scan line buffer 52 is changed to the absolute value of dist. . On the other hand, if the colors of the runs are different, the first run of the reference scan line buffer 52 is deleted, and the run length of the second run is changed to the absolute value of dist. (3) Vertical Mode (V0) When the output run color is the same as the head run color of the reference scan line buffer 52, the head run of the reference scan line buffer 52 is deleted. On the other hand, if the colors of the runs are different, the first and second run lengths are changed to the absolute value of dist. (4) Vertical mode (VR) When the output run color is the same as the first run color of the reference scan line buffer 52, the first run of the reference scan line buffer 52 is deleted and the second run is deleted. The run length is reduced by the absolute value of dist. On the other hand, if the run colors are different, the reference scan line buffer 52
Is deleted, and the run length of the third run is reduced by the absolute value of dist. (5) Horizontal mode The total length of the two output runs is deleted or changed from the run list of the reference scan line buffer 52. That is, if the run length of the output run is 7,3 and the run length of the run list of the reference scan line is 3, 4, 5 from the beginning, the runs of run lengths 3, 4 are deleted, and the run length of 5 Is changed to 2.

As described above, the compression means 2 inquires the compression method selection means 4 for the compression method for each scan line, and performs one-dimensional compression if the reference scan line buffer 22 does not have all the runs. 2 if all runs can be stored in the reference scan line buffer 22
Since the dimensional compression is performed, the reference scan line buffer 52
Can prevent the occurrence of data decoding error due to overflow.

Further, since data which does not overflow in the reference scan line buffer 52 is subjected to two-dimensional compression with high encoding efficiency, it is possible to prevent decoding errors from occurring and to increase encoding efficiency. Become.

Next, a configuration example of the second embodiment of the present invention will be described. FIG. 17 is a block diagram showing a configuration example of the second embodiment of the present invention. In this figure, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and the description thereof will be omitted as appropriate.

In the embodiment shown in FIG. 17, the compression means 2 is replaced by a compression means 200 and the compression method selection means 4 is built in the compression means 200, as compared with the case of FIG. . Other configurations are the same as those in FIG.

The compression means 200 reads run-length data from the first storage means, selects a compression method for each run, and compresses each run by an optimal compression method. The specified compression method is two-dimensional compression such as MR coding or MMR coding, or one-dimensional compression such as horizontal mode of MR coding. The compressed data is stored in the second storage means 3.

FIG. 18 is a block diagram showing a detailed configuration example of the compression means 200. In this figure, FIG.
The same reference numerals are given to the portions corresponding to the case of the above, and the description thereof will be omitted. In the embodiment shown in FIG. 18, compared with the case of FIG. 2, the compressed code determining means 23 is replaced by a compressed code determining means 203, and a compression method selecting means 400 is newly added.

The compression code determination means 203 compresses the run using the compression method specified by the compression method selection means 400. In the first embodiment, the compression means 2
Compression method selection means 4 prior to compression of one scan line
Although the second embodiment inquires about the compression method, the second embodiment is configured to inquire the compression method selection means 400 prior to the compression of each run constituting the scan line.

Therefore, since the compression code determination means 203 and the compression method selection means 400 always operate in cooperation with each other,
In the second embodiment, the configuration is such that the compression method selection means 400 is incorporated in the compression means 200.

The compression method selection means 400 includes an encoding scan line buffer 21 and a reference scan line buffer 22.
, A run compression method is selected, and the selected compression method is notified to the compression code determination means 203.

Next, the operation of the above embodiment will be described. Hereinafter, first, an outline of the operation of the second embodiment of the present invention will be described, and then a detailed operation will be described.

In the embodiment shown in FIG.
In the case of 00, when the number of runs of one scan line exceeds the size of the reference scan line buffer 22, two-dimensional compression is performed on the runs that can be accommodated in the reference scan line buffer 22, using MR coding. Is subjected to one-dimensional compression using the horizontal mode of MR encoding.

As a result, when the number (size) of runs of one scan line exceeds the size of the reference scan line buffer 22, two-dimensional compression and one
Compressed data by dimensional compression will be mixed.
By making the dimensional compression a horizontal mode of MR coding,
Decompression processing can be performed without changing the decompression means 5.

Next, a detailed operation of the above embodiment will be described with reference to FIG. FIG. 19 is a flowchart illustrating an example of a process performed by the compression unit 200 according to the embodiment illustrated in FIG. When this flowchart is started, the following processing is executed. [S501] The compression unit 200 extracts one line of run-length data to be compressed from the first storage unit 1 and stores it in the encoded scan line buffer 21. [S502] The compression unit 200 extracts a predetermined run from the encoded scan line buffer 21 and transfers it to the compression code determination unit 203. [S503] The compression code determination unit 203 makes an inquiry to the compression method selection unit 400, and proceeds to step S504 if the method of compressing the run acquired in step S502 is two-dimensional compression, otherwise, proceeds to step S504. Proceed to step S506. [S504] The compression code determination unit 203 determines in step S
At step 502, MR encoding is performed on the run acquired.

That is, the compressed code judging means 203
The run is encoded into an MR code according to the process shown in (1). Then, the generated compressed data is stored in the second storage unit 3. Further, the run list of the reference scan line buffer 22 is updated in accordance with the encoded run. [S505] The compression code determination unit 203 determines whether the next run to be compressed is an EOL. If the next run to be compressed is an EOL, the process proceeds to step S509.
Otherwise, the process returns to step S502. [S506] The compression code determination unit 203 determines in step S
The run obtained at 502 is encoded using the horizontal mode of MR encoding. That is, the compressed code determination means 20
Numeral 3 encodes the currently held run and the run stored in the encoded scan line buffer 21 in the horizontal mode, and stores them in the second storage means 3. Further, the run list of the reference scan line buffer 22 is updated according to the encoded run.

The horizontal mode is a mode in which encoding is performed without using the reference scan line buffer 22 (encoding is performed without using a relative relationship with the immediately preceding scan line), and is one-dimensional encoding. It can be said that there is. Therefore, by compressing data using this horizontal mode, it is possible to prevent data from being corrupted due to overflow of the reference scan line buffer 52 during decompression. [S507] The compression code determination unit 203 determines whether or not the run to be encoded next is an EOL.
If it is not L, the process proceeds to S508; otherwise, the process proceeds to step S509. [S508] The compression code determination unit 203 extracts the next run from the encoded scan line buffer 21, and proceeds to step S506. [S509] The compression code determination unit 203 determines whether or not a scan line to be coded still exists. If the scan line does not exist, the process ends. Otherwise, the process returns to step S501.

At this time, the contents of the coded scan line buffer 21 are copied to the reference scan line buffer 22, and new run length data is fetched from the first storage means by the coded scan line buffer 21 for one line. Stored. Thereafter, the same processing is repeated.

Next, a specific operation of the above embodiment will be described. FIG. 20 is a diagram illustrating an example of run-length data to be compressed. That is, FIG.
FIG. 2 is an example of reference scan line data.
0 (B) is an example of encoded scan line data to be compressed. In this example, a rectangle whose inside is filled with black indicates a black pixel, and a blank rectangle indicates a white pixel. Bn and Wn above the pixels are run-length data, and indicate that n black pixels (B) or white pixels (W) are continuous. Actual data is represented as a run list which is a list format of run length data.

When data input from the network I / F or the like is bitmap data, it is of course possible to convert the bitmap data into run-length data in the CPU of the host computer (not shown).

In the following, the data size of one scan line is first set to the reference scan line buffer 52 for simplicity.
Next, the case where the data size of one scan line exceeds the size of the reference scan line buffer 52 will be described. (1) When the data size of one scan line is equal to or smaller than the size of the reference scan line buffer 52.

FIGS. 21 to 23 are views showing the states of the reference scan line, the encoded scan line, and the MR encoded data in the compression process. (A) The initial state. Since the first run of the encoded scan line is one white pixel (hereinafter abbreviated as W1) and the first run of the reference scan line is W2, VL1 is obtained as MR encoded data (FIG. 10, FIG. 10).
11). Then, the coded W1 is deleted from the coded scan line run list, and the run list of the reference scan line is corrected according to the coded scan line (W2 is corrected to W1). As a result, FIG.
1 (B). (B) The first run of the coded scan line is black 4 pixels (hereinafter abbreviated as B4), the first run of the reference scan line is W1, and the second run is B2. VR1 is obtained as encoded data. Then, the coded B4 is deleted from the run list of the coded scan line, and the run list of the reference scan line is corrected according to the coded scan line (first and second W1, B2). And remove the third W
2 to W1). As a result, the state shown in FIG. (C) Since the first run of the encoded scan line is W4, the first run of the reference scan line is W1, and the second run is B2, PAS is obtained as MR encoded data. Then, the first W4 of the encoded scan line is corrected to W1, and the first and second W1 and B2 of the reference scan line are deleted. As a result, the state shown in FIG. (D) Since the first run of the encoded scan line is W1, the first run of the reference scan line is W2, and the second run is B2, VL1 is obtained as MR encoded data. Then, the first W1 of the encoded scan line is deleted, and the first W2 of the reference scan line is corrected to W1. As a result, FIG.
State. (E) The first run of the encoded scan line is B3, the first run of the reference scan line is W1, and the second run is B2, so V0 is obtained as MR encoded data. Then, the first B3 of the encoded scan line is deleted, and the first and second W1 and B2 of the reference scan line are deleted. As a result, FIG.
The state shown in FIG. (F) Since the first run of the encoded scan line is W1, the first run of the reference scan line is W5, and the second run is B1, the HOR, W1, and B3 are MR encoded data. Get. Then, the first and second W1 and B3 of the encoded scan line are deleted, and the first W5 of the reference scan line is corrected to W1. As a result, the state shown in FIG. (G) The first run of the encoded scan line is W1, the first run of the reference scan line is W1, and the second run is B1, so V0 is obtained as MR encoded data. Then, the first W1 of the encoded scan line is deleted, and the first W1 of the reference scan line is deleted. As a result, the state shown in FIG. (H) Since both the leading run of the encoded scan line and the reference scan line are B1, V0 is obtained as MR encoded data. Then, the first B1 of the encoded scan line and the reference scan line is deleted. As a result, the state shown in FIG. (I) The state in which the compression processing has been completed, and the data shown in the figure is obtained as MR encoded data.

With the above processing, compressed data is obtained. Next, referring to FIGS. 24 to 26, the compressed data (compressed data when the data size of one scan line is equal to or smaller than the size of the reference scan line buffer 52) compressed as described above is expanded. The processing will be described.

FIGS. 24 to 26 show the states of the reference scan line, the decoded scan line, and the decompressed data in the decompression process. (A) The initial state. Here, the decoded scan line is MR-encoded data, and the decompressed data is run-length data to be decoded. In this example, the leading data of the decoded scan line is VL1, and the leading run of the reference scan line is W2, so that W1 is obtained as decompressed data. And the decrypted VL1
From the list of decoded scanlines, and replace the first W2 in the run list of the reference scanline with W1
To fix. As a result, the state shown in FIG. (B) Since the head data of the decoded scan line is VR1, the head run of the reference scan line is W1, and the second run is B2, B4 is obtained as decompressed data. Then, the decrypted VR
1 from the list of decrypted scanlines, and
The first and second W1 and B2 of the run list of the reference scan line are deleted, and the third W2 is corrected to W1. As a result, the state shown in FIG. (C) The leading data of the decoded scan line is PAS, the leading run of the reference scan line is W1, and the second run is B2, so that W3 is obtained as decompressed data. Then, the decoded PAS is deleted from the decoded scan line list, and the first and second Ws in the reference scan line run list are deleted.
1 and B2 are deleted. As a result, the state shown in FIG. (D) The leading data of the decoded scan line is VL1, the leading run of the reference scan line is W2, and the second run is B2, so that W1 is obtained as decompressed data. Note that the color of the decompressed data is shown in FIG.
24 (C) is because the data decoded in FIG. 24 (C) is a PAS, and W1 is the same as that in FIG.
W4 is added to W3 obtained by decoding in (C). Then, the decoded VL1 is deleted from the decoded scanline list, and the first W2 in the reference scanline run list is corrected to W1. As a result, the state shown in FIG. (E) The leading data of the decoded scan line is V0, and the leading run of the reference scan line is W1, so that B3 is obtained as decompressed data. Then, the decrypted V0 is deleted from the decoded scan line list, and the first V0 in the reference scan line run list is deleted.
The second and second W1, B2 are deleted. As a result, the state shown in FIG. (F) The first to third data of the decoded scan line are HOR, W1, and B3, and since the first run of the reference scan line is W5, W1 and B3 are obtained as decompressed data. . Then, the decrypted H
OR, W1, and B3 are deleted from the list of decoded scan lines, and the first in the run list of the reference scan line is deleted.
Correct the fifth W5 to W1. As a result, FIG.
The state shown in FIG. (G) The leading data of the decoded scan line is V0, and the leading run of the reference scan line is W1, so that W1 is obtained as decompressed data. Then, the decrypted V0 is deleted from the decoded scan line list, and the first V0 in the reference scan line run list is deleted.
Delete the first W1. As a result, the state shown in FIG. (H) Since the leading data of the decoded scan line is V0 and the leading run of the reference scan line is B1, B1 is obtained as decompressed data. Then, the decrypted V0 is deleted from the decoded scan line list, and the first V0 in the reference scan line run list is deleted.
Delete the first B1. As a result, the state shown in FIG. (I) A state in which the decompression processing has been completed, and data shown in the figure is obtained as decompression data.

By the above processing, decompressed data is obtained. Next, processing when the data size of one scan line exceeds the size of the reference scan line buffer 52 will be described. (2) When Data Size of One Scan Line Exceeds Size of Reference Scan Line Buffer 52 FIGS. 27 and 28 show states of the reference scan line, the encoded scan line, and the MR encoded data in the compression process. It is. In this example, it is assumed that the reference scan line buffer can store only four runs.

Note that, in this figure, (A) to (C) are the same as in the above-described case, and therefore description thereof will be omitted as appropriate. (A) The initial state. The difference from FIG. 21A is that the reference scan line buffer can store only four runs. In this example, VL1 is obtained as MR encoded data, W1 is deleted from the run list of the encoded scan line, and W2 at the head of the run list of the reference scan line is corrected to W1. As a result, FIG.
7 (B). (B) VR1 is obtained as MR encoded data, B4 is deleted from the head of the run list of the encoded scan line, and the first and second W1, B2 of the run list of the reference scan line are deleted. Then, the third W2 is corrected to W1. As a result, the state shown in FIG. (C) PAS is obtained as MR encoded data, the first W4 of the encoded scan line is corrected to W1, and the first and second W1 and B2 of the reference scan line are deleted. As a result, the state shown in FIG. (D) Since there is no run in the reference scan line, the compression method selection unit 400 notifies the compression code determination unit 203 to perform encoding using the horizontal mode of MR. As a result, the compressed code determination unit 203 encodes the first run W1 and the second run B3 of the encoded scan line in the horizontal mode, and obtains HOR, W1, and B3. Then, the first and second W1 and B3 of the encoded scan line are deleted. As a result, the state shown in FIG. (E) Similarly, the encoding process is performed in the horizontal mode, and the runs W1, B3, and W remaining on the encoded scan line are performed.
1, B1 are encoded and HOR, W1, B3, HOR,
W1 and B1 are obtained. Then, the encoding of the encoded scan line is completed. As a result, the state shown in FIG. (F) The state in which the compression processing has been completed, and the data shown in the figure is obtained as compressed data.

With the above processing, compressed data is obtained. Next, a process of decompressing the compressed data obtained by the above process will be described.

FIGS. 29 and 30 show a reference scan line, a decoding scan line, and
FIG. 6 is a diagram illustrating a state of decompressed data. Also in this example, it is assumed that the reference scan line buffer can store only four runs. (A) The initial state. The difference from FIG. 24A is that the reference scan line buffer can store only four runs, and that the data of the decoded scan line is obtained by the above-described processing (the processing shown in FIGS. 27 and 28). That is two points. In this example,
Since the leading data of the decoded scan line is VL1 and the leading run of the reference scan line is W2,
W1 is obtained as decompressed data. And the decrypted VL
1 from the list of decrypted scanlines, and
The first W2 in the run list of the reference scan line is W
Modify to 1. As a result, the state shown in FIG. (B) Since the head data of the decoded scan line is VR1, the head run of the reference scan line is W1, and the second run is B2, B4 is obtained as decompressed data. Then, the decoded VR1 is deleted from the list of the decoded scan lines, and the first and second Ws in the run list of the reference scan line are deleted.
1 and B2 are deleted, and the third W2 is corrected to W1.
As a result, the state shown in FIG. (C) The leading data of the decoded scan line is PAS, the leading run of the reference scan line is W1, and the second run is B2, so that W3 is obtained as decompressed data. Then, the decoded PAS is deleted from the list of the decoded scan lines, and the first and second W1, B in the run list of the reference scan line are deleted.
Delete 2. As a result, the state shown in FIG. (D) Although there is no run in the reference scan line, the MR encoded data of the decoded scan line is HOR, so the decompressed data determination unit 53 performs decoding without referring to the reference scan line and performs decompression. W1 and B as data
Get 3. Note that W1 is equal to W as in the case of FIG.
3 and W4. Then, the decoded HOR, W1, and B3 are deleted from the decoded scan line. As a result, the state shown in FIG. (E) Similarly, no run exists in the reference scan line, but the MR encoded data of the decoded scan line is HOR
Therefore, the decompressed data determination unit 53 performs decoding without referring to the reference scan line, and outputs W
1 and B1 are obtained. And from the decrypted scanline,
The decrypted HOR, W1, and B1 are deleted. As a result, the state shown in FIG. (F) The state in which the decompression process has been completed, and the data shown in the figure is obtained as decompression data.

According to the above processing, it is possible to perform compression and decompression processing even on line data exceeding the size of the reference scan line buffer. By the way, although different compressed data are generated in FIGS. 22 to 23 and FIGS. 27 to 28, FIGS.
It is clear that the data decoded by the decompression processing shown in FIGS. 29 to 30 is the same run-length data.

As described above, in the embodiment shown in FIG. 17, the compression method is examined on a run-by-run basis, and run data that fits in the reference scan line buffer 22 is subjected to MR encoding, which is two-dimensional compression, For other data, compression is performed using the horizontal mode of MR coding, which is one-dimensional compression. Therefore, two-dimensional compression with high coding efficiency is used for the compressible range. Since one-dimensional compression is used for the other parts, it is possible to increase the coding efficiency as compared with the first embodiment.

In the above description, MR encoding is used as the two-dimensional compression processing of the compression means 1.
It is also possible to use MR coding. This MMR encoding is different only in that only a portion corresponding to two-dimensional compression in MR encoding is executed, and therefore a detailed description thereof is omitted.

The above processing functions can be realized by a computer. In that case, the processing contents of the functions that the image processing system and the image compression device should have are:
The program is described in a program recorded on a computer-readable recording medium, and the above processing is realized by the computer by executing the program on the computer. Examples of the computer-readable recording medium include a magnetic recording device and a semiconductor memory.

For distribution to the market, a CD-ROM
(Compact Disk Read Only Memory) or a program stored in a portable recording medium such as a floppy disk and distributed, or stored in a storage device of a computer connected via a network and transferred to another computer via the network You can also. When the program is executed by the computer, the program may be stored in a hard disk device or the like in the computer, loaded into the main memory, and executed.

[0102]

According to the present invention, image data is compressed by a compression device,
In an image processing system that expands in an expansion device,
The compression device stores the run-length data to be processed, selects a compression method for the run-length data according to the line buffer size of the decompression device and the data size of the run-length data, and stores the selected compression method. The run-length data is compressed into compressed data using two-dimensional compression or one-dimensional compression according to the selection result of the compression method, and the decompression device stores the compressed data obtained by the compression device and stores the stored data. Since the compressed data is expanded to the run-length data according to the compression method of the compression device, the run-length data can be compressed and expanded by an appropriate method regardless of the data size.

In an image compression apparatus for compressing image data and outputting the compressed data to a decompression device, run-length data to be processed is stored, and the line buffer size of the decompression device and the run-length data of the run-length data are stored. A run-length data compression method is selected according to the data size, and the stored run-length data is compressed into compressed data using two-dimensional compression or one-dimensional compression according to the selection result of the compression method. As a result, the run-length data can be compressed by an appropriate method regardless of the data size.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration example of a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a detailed configuration example of a compression unit illustrated in FIG. 1;

FIG. 3 is a block diagram illustrating a detailed configuration example of a compression method selection unit illustrated in FIG. 1;

FIG. 4 is a block diagram illustrating a detailed configuration example of a decompression unit illustrated in FIG. 1;

FIG. 5 is a diagram showing an example of a format of MH encoded data.

FIG. 6 is a diagram showing details of a data code shown in FIG. 5;

FIG. 7 is a diagram showing a terminating code of MH coding.

FIG. 8 is a diagram showing a makeup code for MH coding.

FIG. 9 is a diagram showing a makeup code for MH coding.

10A is a diagram showing a pass mode of MR coding, FIG. 10B is a diagram showing a vertical mode of MR coding, and FIG. It is a figure showing a horizontal mode.

FIG. 11 is a diagram showing a conversion code for MR encoding.

FIG. 12 is a diagram showing a case where run-length data is MR-coded into 2
9 is a flowchart illustrating an example of a process when performing dimensional compression.

FIG. 13 is a flowchart illustrating an example of a process performed by the compression unit illustrated in FIG. 1;

FIG. 14 is a flowchart illustrating an example of a process performed by a compression method selection unit illustrated in FIG. 1;

FIG. 15 is a flowchart illustrating an example of a process when the decompression unit illustrated in FIG. 1 decompresses two-dimensionally compressed data.

FIG. 16 is a diagram showing the correspondence between MR codes and dist.

FIG. 17 is a block diagram illustrating a configuration example of a second embodiment of the present invention.

FIG. 18 is a block diagram illustrating a detailed configuration example of a compression unit illustrated in FIG. 17;

FIG. 19 is a flowchart illustrating an example of a process performed by a compression unit illustrated in FIG. 17;

20A is a diagram illustrating an example of a reference scan line, and FIG. 20B is a diagram illustrating an example of an encoded scan line.

FIG. 21 is a diagram illustrating an example of states of a reference scan line, an encoded scan line, and MR encoded data in a compression process when the data size of one scan line does not exceed the size of a reference scan line buffer.

FIG. 22 is a diagram illustrating an example of a state of a reference scan line, an encoded scan line, and MR encoded data in a compression process when the data size of one scan line does not exceed the size of a reference scan line buffer.

FIG. 23 is a diagram illustrating an example of states of a reference scan line, an encoded scan line, and MR encoded data in a compression process when the data size of one scan line does not exceed the size of a reference scan line buffer.

FIG. 24 is a diagram illustrating an example of a state of a reference scan line, a decoding scan line, and decompressed data in a decompression process when the data size of one scan line does not exceed the size of a reference scan line buffer.

FIG. 25 is a diagram illustrating an example of a state of a reference scan line, a decoded scan line, and decompressed data in a decompression process when the data size of one scan line does not exceed the size of a reference scan line buffer.

FIG. 26 is a diagram illustrating an example of a state of a reference scan line, a decoding scan line, and decompressed data in a decompression process when the data size of one scan line does not exceed the size of a reference scan line buffer.

FIG. 27 shows a reference scan line, an encoded scan line, and a compression line in the compression process when the data size of one scan line exceeds the size of the reference scan line buffer.
FIG. 4 is a diagram illustrating an example of a state of MR encoded data.

FIG. 28 illustrates a reference scan line, an encoded scan line, and a compression scan line in a compression process when the data size of one scan line exceeds the size of a reference scan line buffer.
FIG. 4 is a diagram illustrating an example of a state of MR encoded data.

FIG. 29 shows a reference scan line, a decoding scan line, and a reference scan line in a decompression process when the data size of one scan line exceeds the size of a reference scan line buffer.
FIG. 4 is a diagram illustrating an example of a state of decompressed data.

FIG. 30 shows a reference scan line, a decoding scan line, and a reference scan line in a decompression process when the data size of one scan line exceeds the size of a reference scan line buffer.
FIG. 4 is a diagram illustrating an example of a state of decompressed data.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 first storage means 2 compression means 3 second storage means 4 compression method selection means 5 decompression means 21 encoded scan line buffer 22 reference scan line buffer 23 compression code determination means 41 run counter 42 line buffer size storage means 43 compression Method determination means 51 Decoding scan line buffer 52 Reference scan line buffer 53 Decompressed data determination means

Claims (10)

[Claims] An image data is compressed by a compression device,
In the image processing system for decompressing in a decompression device, the compression device includes: first storage means for storing run-length data to be processed; a size of a line buffer included in the decompression device; Compression method selection means for selecting a compression method of the run-length data according to the size; and run-length data stored in the first storage means, according to a selection result of the compression method selection means, Compression means for compressing to compressed data using two-dimensional compression or one-dimensional compression; the decompression device; a second storage means for storing the compressed data obtained by the compression means of the compression device; Decompressing the compressed data stored in the second storage means into run-length data according to a compression method of the compression means of the compression device. An image processing system comprising: 2. The decompression means has a line buffer referred to when decompressing the two-dimensionally compressed data into run-length data. The line buffer stores one line in a list format composed of run-length data. The image processing system according to claim 1, wherein the data is stored. 3. The data size of the scan line is calculated by counting the number of runs included in each scan line of the run length data. 2. The image processing system according to 1. 4. The method according to claim 1, wherein said compression method selection means is configured to execute the second method if the size of said line buffer is larger than said data size.
2. The image processing system according to claim 1, wherein one-dimensional compression is selected, and otherwise, one-dimensional compression is selected. 5. The image processing system according to claim 4, wherein said two-dimensional compression is a modified read coding or a modified modified read coding, and said one-dimensional compression is a modified Huffman coding. 6. The compression method selection means selects two-dimensional compression for run data that fits in the line buffer out of data for one scan line, and one-dimensional compression for other run data. The image processing system according to claim 1, wherein compression is selected. 7. The image processing system according to claim 6, wherein the two-dimensional compression is a modified read coding or a modified modified read coding, and the one-dimensional compression is a horizontal mode of the modified read coding. . 8. A computer-readable recording medium storing a program for causing a computer to execute a process of decompressing image data and then decompressing the image data, the computer comprising: a first storage for storing run-length data to be processed; Means for selecting a method for compressing the run-length data according to the size of a line buffer used in a process of expanding image data and the data size of the run-length data; the first storage means Compression means for compressing the run-length data stored in the storage means into compressed data using two-dimensional compression or one-dimensional compression according to the selection result of the compression method selection means; Second storage means for storing the compressed data stored in the second storage means, A computer-readable recording medium storing a program that functions as an expansion unit that expands run-length data in accordance with a compression method of a compression unit. 9. An image compression apparatus for compressing image data and outputting the compressed data to a decompression device, wherein: first storage means for storing run-length data to be processed; Compression method selection means for selecting a compression method of the run-length data according to a size and a data size of the run-length data; and a method for compressing the run-length data stored in the first storage means. An image compression apparatus comprising: compression means for compressing compressed data using two-dimensional compression or one-dimensional compression in accordance with a selection result of the selection means. 10. A computer-readable recording medium storing a program for causing a computer to execute image compression processing for compressing image data and outputting the compressed image data to a decompression device, wherein the computer executes run-length data to be processed. First storage means for storing the run-length data according to the line buffer size of the decompression device and the data size of the run-length data; and the first storage means. A compression means for compressing the run-length data stored in the storage means into compressed data using two-dimensional compression or one-dimensional compression in accordance with the selection result of the compression method selection means. Computer readable recording medium.