JPH06276103A - Method for partially extending compressed data - Google Patents

Abstract

(57) [Summary] [Purpose] Decompress only the specified range of compressed data to restore the compressed data reasonably. [Structure] When decompressing compressed data, skip to the beginning of a line of compressed data to be decompressed (step S1
S3), a predetermined code is extracted from the compressed data of the row (step S4), and the range in which the expansion of the compressed data is designated is determined from the predetermined code (step S5, etc.).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compressed data method such as an image decompression method, and more particularly to an MH (Modify) method.
The present invention relates to a method for decompressing compressed data which is used for decompressing data compressed by the d Huffman) coding method or the like to restore an image.

[0002]

2. Description of the Related Art As a conventional method of decompressing compressed data, there is a FAX algorithm described in, for example, Image Information Compression (published by Ohmsha Co., Ltd.) P28. FIG. 7 is a flowchart of a decompression process of the one-dimensional encoding method (MH numbering method) in the G3 facsimile, which is a flowchart when decompressing the compressed image data and then restoring the image data. In FIG. 7, EoL is an abbreviation for (End of Line), which is a code inserted at the end of one line of compressed data, and six EoL codes are continuously arranged at the end of the compressed data. Further, S70 and S74 of FIG. 7 are steps of MH code extraction processing for extracting one compressed data and updating the counter indicating the position of the currently extracted compressed data, and S71 is whether the extracted compressed data is an EoL code or not. This is the step of the processing for judging the EoL code to be judged. S73 is a step of restoring white bits according to the extracted compressed data, S77 is a step of restoring black bits, and S72, S75, and S76 are EoL code subtracted if there is an EoL code. Subsequently, it is a processing step of determining the EoL code for continuously checking whether or not the EoL code exists.

Next, the operation of this conventional example will be described.
In the case of the MH method, the compression code is composed of a variable-length code of 13 bits or less, and the code of white bits and the code of black bits are alternated starting from the white bit. Also, when one line of image data is completed, the EoL code is always included, and when all the data is completed, 6 EoLs are included. Therefore, in FIG. 7, the extraction unit and the restoration unit are divided into two for the white pixel and the black pixel.
It is composed as one set. First, step S7
At 0, one MH compression code is extracted, and the start position of the next compression code is stored in the counter in advance based on the length of the MH compression code. Next, in step S71,
Check whether or not the extracted code is an EoL code,
If it is a sign (YES), E again in step S72.
Check if the oL code continues. At this time, if the EoL code continues twice, it means that the compressed data is the last one, so the process ends (END), and if it is not ended, 1
It is determined that the line decompression process has ended, and the process returns to the beginning (step S70). If the extracted code is not the EoL code (NO in step S71), the white bit is actually restored by the process of step S73 according to the extracted code. Similarly, the same process is performed on the black bit (steps S75 to S77), the white bit and the black bit are sequentially restored, and this restoration process is performed by having two or more consecutive EoLs in the compressed data. Continue until you confirm.

[0004]

In the conventional method of decompressing compressed data, since all the compressed data are interpreted and all the original image data are restored in this way,
If the required data is only one part, there is a problem in that the memory used for restoring the image data is wasted and that it takes a long time to calculate the image data.

The present invention has been made in order to solve the above problems, and it takes a long time to perform an operation without wasting a memory by expanding compressed data only in a designated range. It is an object of the present invention to provide a compressed data decompression method.

[0006]

According to the method of partially decompressing compressed data according to the first aspect of the present invention, when decompressing compressed data, the compressed data is skipped to the beginning of a line of compressed data by the MH coding method. A predetermined code is extracted from the compressed data of the row, and the range in which the expansion of the compressed data is designated is determined from the predetermined code. This second
In the method of partially decompressing compressed data according to the invention of claim 1, when decompressing the compressed data, the compressed data of the preceding row of a predetermined row is stored, and the compressed data of the preceding row is compared with the compressed data of the predetermined row. While skipping to the beginning of the line of compressed data to be expanded, a predetermined code is extracted from the compressed data of that line, and the range in which the expansion of the compressed data is specified is determined from this predetermined code. . In the method for partially decompressing compressed data according to the third aspect of the present invention, when decompressing the compressed data, a predetermined code is extracted from all the compressed data in which the difference between the row and another row is encoded, and the predetermined code is extracted. When the code extraction result does not reach the beginning of the line of the compressed data, the decompression process of the compressed data is not performed.

[0007]

In the method of partially decompressing compressed data according to the first aspect of the present invention, first, the compression data encoded in the MH encoding method is skipped to the beginning of the line. Next, a predetermined code is extracted from the compressed data of the row, and the range in which the expansion of the compressed data is designated is determined from this predetermined code, so that only the designated range of the compressed data is restored. In the method for partially decompressing compressed data according to the second aspect of the present invention, first, the compressed data of the preceding row of a predetermined row of the compressed data encoded by the MR encoding method is stored, and the compressed data of the preceding row and the prescribed data are stored. While comparing the compressed data of the line, skip to the beginning of the line of the compressed data to be expanded. next,
Only a specified range of the compressed data is restored by extracting a specified code from the compressed data of the row and determining the specified range of expansion of the compressed data from the specified code. In the method of partially decompressing compressed data according to the third aspect of the present invention, first, the difference between a row of compressed data encoded by the MMR encoding method and another row is extracted. Next, when the extraction result of the predetermined code does not reach the beginning of the line of the compressed data, the decompression process of the compressed data is not performed, and only the specified range of the compressed data is restored. .

[0008]

Embodiments of the present invention will be described below with reference to the drawings. First Embodiment FIG. 1 is a flow chart for explaining a method for expanding compressed data according to a first embodiment of the present invention. In FIG. 1, S1 to S3 are preprocessing steps for skipping to the beginning of each line of compressed data. This pre-processing step is processing for skipping compressed data up to the yo_ex line when it is desired to decompress compressed data such as image data from the yo_ex line (row), and the processing of steps S1 to S3 in FIG. Equivalent to. These steps S1 to S
In No. 3, the fact that the “EoL” code is written at the end of one line of compressed data is used to change the “EoL” code to yo_.
This is done by counting ex times. S4 is MH (Mo
This is the step of the process of extracting the Hiffman (Difid Huffman) code, and this MH coding method encodes the continuous number of white and black bits of the image data. S5 is a step of determining the restoration of the MH code, S6 and S10 are steps of comparing the value of the vertical direction counter with the value of the vertical direction first bit position, and S
7 is a white bit restoration step, S9 is a restoration judgment step, and S11 is a black bit restoration step.

Next, the operation of the first embodiment will be described. First, by the pre-processing of steps S1 to S3, a counter that represents the compressed data decompression position until the number of vertical head bit positions yo_ex (vertical head coordinates) of the EoL code that skips compressed data to the vertical head is extracted ( count) is updated. Next, set the EoL code to yo
When the _ex number is detected, the conventional decompression operation is started. That is, first, by the MH code extraction processing in step S4,
The MH code is extracted, and restoration judgment is performed in step S5. If this restoration judgment result is "0", the restoration of the compressed data is skipped and the process proceeds to the next process. If the restoration judgment result is "1", the compressed data of the white bit in step S3. Is restored and the process proceeds to the next process, and if the result of the restoration judgment is "2", the process of step S6 currently being processed is terminated. In this step S6, the vertical coordinate yo
_End and the value yi of the vertical direction counter are large if the value yi of the vertical direction counter is large, the process is ended. If the value yi is small, it is determined that the process for one row is completed and the process returns to step S4. By repeating the above, the value yi of the vertical counter is y
If it becomes larger than o_end, the processing is ended. Further, the above processing is similarly performed for the black bit (step S).
9-S11).

Next, the restoration judgment processing will be described with reference to FIG. In the decompression processing in steps S5 and S9 of FIG. 1, the currently extracted bit position is compared with the range of compressed data to be decompressed, "1" is output if within the range, and "1" if outside the range. "0" is output, and if the end of one line is output, "2" is output. In this restoration judgment processing, for example, as shown in the image data of FIG. 2, xo to xo_ex and xe_ex to x from the currently expanded portion.
Since there is no need to expand the image data between ex and ye_ex, only the code decompression process is performed and the decompression process is skipped. That is, first, in step S31, it is determined whether the extracted code is an EoL code. If it is an EoL code (YES in step S31),
The value y of the vertical direction counter is judged to be the end of processing for one line
i is incremented (step S32) and "2" is output. If it is not an EoL code (N in step S31)
O), and compares the value of the horizontal first bit position xo_ex with the value of the current horizontal bit counter * pa (step S3).
3) If the value of the current horizontal bit counter is smaller (YES), "0" is output. If the value of the current horizontal bit is larger (NO in step S33), the value of the previous horizontal bit counter * (pa-1) is smaller than the partially expanded horizontal head bit position xo_ex, and The horizontal bit counter displays the horizontal output bit position xe
It is compared whether it is smaller than _ex (step S34),
If this condition is satisfied, the restored bit number bit_c is obtained by subtracting the value of the horizontal output bit position xe_ex from the value of the current horizontal bit counter * pa (step S35).
Outputs "1". Thereafter, similarly, the processes of steps S36 to S40 are sequentially performed, and if the compressed data is within the range to be decompressed, "1" is output after calculating the decompression bit number bit_c, and otherwise "0". Is output.

FIG. 4 is a flow chart for explaining the method of decompressing compressed data according to the second embodiment of the present invention. In the first embodiment, the case where the MH method is used as a base as the partial decompression method of the compressed data has been described, but in the second embodiment, the MR method (Mo
The case of application to "defined READ" will be described.
This MR method is called M for every number of times indicated by the K parameter.
A line between H compression and MH compression is a method of encoding a difference from the preceding line. Therefore, in the process of the second embodiment, step S is performed every K times.
This is largely divided into the MH decompression process of 44 and the MR decompression process of step S46. In order to examine the difference from the preceding line, the change point table for one line is created in steps S43 and S45 before decompression. In the processing of steps S44 to S48, the compression code is extracted as described in the first embodiment, and then it is determined whether the data can be restored. If it is good, the restoration is performed. However, since the MR method encodes the difference from the preceding line, it may be meaningless to start the decompression by skipping the vertical start coordinates in the preprocessing of step S42. For this reason, in order to skip to the smallest MH portion which is the closest to the vertical head coordinate, the calculation of step S41 is performed. Here, all variables in the process of step S41 are integer type.

FIG. 5 and FIG. 6 are flow charts for explaining a method of decompressing compressed data according to the third embodiment of the present invention.
In the third embodiment, the MMR coding method (Modified M
It is applied to R). The MMR method is different from the MR method in which the MH method is performed for each K parameter, and all the compressed data encode the difference from the preceding line. Therefore, in the third embodiment, the process of creating the change point table in step S51 and the process of MR decompression in step S52 are sufficient. However, as a result of extracting the code, if the vertical head coordinates have not been reached, it is necessary to skip the bit restoration process, so one additional process of steps S61 and S62 is added. The other processes of steps S31 to S40 are the same as the processes of FIG. 3 (Example 1).

[0013]

According to the first aspect of the present invention, when decompressing compressed data by the MH coding method, unnecessary decompressed data lines that are not decompressed are skipped to find a decompressed line, and Since the range of decompression from the compressed data of the row is performed by extracting a predetermined code, only the necessary data can be decompressed, the memory can be saved, and the operation time can be shortened. According to the second aspect of the present invention, when decompressing compressed data by the MR encoding method, a row of uncompressed unnecessary compressed data is skipped to find a row to be decompressed, and the compressed data of the row is further decompressed. Since the range in which the expansion is performed is performed by extracting a predetermined code, only the necessary data can be expanded, the memory can be saved, and the calculation time can be shortened. According to the third aspect of the invention, when decompressing compressed data by the MH coding method, unnecessary decompressed data lines that are not decompressed are skipped to find a decompressed line,
Further, since the range of expansion from the compressed data of the row is performed by extracting a predetermined code, only the necessary data can be expanded, the memory can be saved, and the operation time can be shortened.

[Brief description of drawings]

FIG. 1 is a flowchart illustrating a method of partially expanding compressed data according to a first embodiment of the present invention.

FIG. 2 is a diagram of image data for explaining a restoration determination process in the flowchart of FIG.

FIG. 3 is a flowchart illustrating in detail the restoration determination process of the flowchart of FIG.

FIG. 4 is a flowchart illustrating a method of partially decompressing compressed data according to a second embodiment of the present invention.

FIG. 5 is a flowchart illustrating a method of partially expanding compressed data according to a third embodiment of the present invention.

FIG. 6 is a flowchart illustrating in detail the restoration determination process of the flowchart of FIG.

FIG. 7 is a flowchart illustrating a conventional method of decompressing compressed data.

[Explanation of symbols]

 yi Vertical direction counter value * pa Current horizontal direction bit counter value * (pa-1) Previous horizontal direction bit counter value xo_ex Partially expanded horizontal direction first bit position xe_ex Horizontal direction output bit position bit_c Number of restored bits xex_dat Horizontal direction output Bit width yo_ex Vertical start bit position

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[Procedure amendment]

[Submission date] August 6, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

Claims (3)

[Claims] 1. A partial compression method of compressed data for expanding only a specified range of vertical and horizontal compressed data by the MH encoding method, which skips to the beginning of a line of compressed data to be expanded and A partial decompression method for compressed data, wherein a predetermined code is extracted from the compressed data and the range in which the expansion of the compressed data is designated is determined from the predetermined code. 2. A partial decompression method of compressed data for expanding only a specified range of vertical and horizontal compressed data by an MR encoding method, wherein compressed data of a preceding line of a predetermined line is stored, and the preceding line is stored. While comparing the compressed data of the above and the compressed data of the predetermined line, skip to the beginning of the line of the compressed data to be expanded, extract a predetermined code from the compressed data of the line, and compress the above from the predetermined code. A partial decompression method for compressed data, characterized in that the range of decompression of data is determined. 3. A partial decompression method of compressed data for decompressing only a specified range of vertical and horizontal compressed data by the MMR encoding method, wherein all compressed data obtained by encoding the difference between a row and another row. A predetermined code is extracted from the compressed data, and when the extraction result of the predetermined code does not reach the head of the line of the compressed data, the decompression process of the compressed data is not performed. Extension method.