JPH0779415B2 - Decompression method of compressed data - Google Patents

Description

The present invention relates to a method for decompressing and decoding compressed data, and more particularly to a method for cutting out or reducing compressed data to combine them.

[Conventional technology]

An MH (Modified Huffman) coding method is a method of compressing and coding the band when transmitting black and white binary image data. This method divides the run length, which is the continuous number of the same pixels from 0 to 1728 for 1728 pixels of one scanning line, into groups of 64, and indicates the group code (hereinafter referred to as group code) and the group This is shown in combination with a code indicating the length of the run (hereinafter referred to as a run code). As a result, the number of codes becomes 64 + 1728/64 = 91, and the number of codes decreases.

FIG. 4 is a diagram showing an example of encoding by the MH encoding method shown on page 70 of "Image signal processing for FAX, OA" issued by Nikkan Kogyo Shimbun.

In FIG. 4, reference numeral 21 denotes image data for one row (one line) to be encoded, in which 19 pixels of white are continuous and 66 pixels of black and 135 pixels of white are continuous. Also 22 M
H-encoded compressed data is shown, and a line delimiter is shown between this line and a previous line (not shown), and an EOL (End Of Line) code (00 ... 01) used for synchronization detection at the time of decoding is inserted. There is. White 19 run length is “0001100”, black 66 run length is 64+
Group code “00000011” divided into 2 and corresponding to black 64
It is encoded by a combination of the run code "11" corresponding to 11 "and black 2, the white 135 run length is divided into 128 + 7, and the group code" 10010 "corresponding to white 128 and the run code" 11 corresponding to white 7
It is encoded in combination with 11 ".

When the encoded image data is displayed on an output device such as a CRT, the display size may be smaller than the image data, and partial image data or reduced image data may be required.

FIG. 5 is a flowchart of a conventional decoding method that decodes encoded compressed data to obtain reduced image data. MH
The encoding method focuses on one row of image data, assumes a specific functional relationship with respect to its run length in which black or white pixels are arranged consecutively, and replaces it with a systematic codeword. is there.

Decoding of this encoded compressed data detects the MH encoded group code and run code (S1), then EOL
It is determined whether or not the code is detected (S2), and if the EOL code is not detected, the delimiter is identified to develop into a run-length black or white pixel corresponding to the code for decoding (S2).
3). When the EOL code is detected, step 3 is skipped. Next, it is judged whether or not the decoding of all the lines of the image data is completed (S4), and if not completed, the step 1
Then, the process is continued until the decoding of all lines is completed.

Further, when partial image data or reduced image data is required, clipping or reduction processing of that portion of the decoded image data is performed (S5). In the case of performing image data processing such as cutout processing and reduction processing, it is necessary to perform processing after decoding the encoded compressed data over all lines of the image data in the conventional method.

[Problems to be Solved by the Invention]

When such a conventional decoding method is used, since processing such as reduction and cutout processing is performed after decoding over all lines, the processing speed up to display is slow and the memory capacity used is small. There was a problem of getting bigger.

The present invention has been made in order to solve the above-mentioned problems, and in the case of performing reduction or clipping processing, for each compressed data of one line of image data, in the data column of the data of the next line. Decoding the compressed data into image data over all lines by providing address information regarding the position and skipping to the line to be decoded using the processing information of the image data and the address information when decoding the compressed data In addition to eliminating the need, it is possible to quickly access the compressed data to be decoded to shorten the time for decoding into image data and the processing of image data, reduce the number of decoded image data, and store it. It is an object of the present invention to provide a decoding method of compressed data that can reduce the capacity of the.

[Means for Solving the Problems]

The decoding method of the compressed data according to the present invention is a decoding method of compressed data for performing decoding from a compressed data string having coded data obtained by compressing and coding image data row by row For each compressed data string corresponding to each row of image data, address information regarding the position of the compressed data row of the next row is provided, and one row of encoded data is processed based on preset processing information regarding processing of image data. The image data is decoded according to the information, and the coded data of the row to be decoded next is selected based on the processing information and the address information.

[Action]

In the present invention, when the reduction processing is performed, decoding is performed in the row direction (main scanning direction) based on the processing information according to the reduction ratio, and the direction intersecting it (sub scanning direction) is converted into address information and processing information. Based on this, the line to be decoded is skipped and the encoded data of that line is decoded. When performing the cutting processing, the row direction is decoded based on the processing information according to the cutting range, and the intersecting direction is selected by selecting the encoded data of the row in the cutting range based on the address information and the processing information. Decryption is performed.

〔Example〕

The present invention will be described below with reference to the drawings showing an embodiment thereof.

FIG. 1 is a block diagram showing a configuration of a decoding device used for carrying out a method for decoding compressed data according to the present invention, and FIG. 2 is a schematic structural diagram of compressed data. The case of the reduction processing will be described here. In the figure, 5 is a CPU, which performs decoding and processing of compressed data. The CPU 5 accesses the main storage device 4, performs predetermined reduction processing on the compressed data stored therein, and decodes it. Main memory 4
Is a compressed data section 1 for storing encoded compressed data
And a reduction table unit 2 that stores reduction information for reducing and decoding compressed data in the row direction according to a preset reduction ratio, and an image data unit 3 that stores decoded image data. There is.

The compressed data is the address information A of the next line as shown in FIG.
Encoded data ED compressed into D and MH codes and an EOL code indicating the end of a row are arranged in this order in columns for each row of image data.

As the address information AD, for example, the data such as the data length of the encoded data ED of the own row is recorded, and the position in the data row of the address information AD of the next row is known and it is possible to skip there. Become. That is, it becomes possible to read the next address information by skipping the encoded data ED of the row that does not need to be decoded.

When the reduction in the direction intersecting the row direction (sub-scanning direction) is not performed, the skip is irrelevant, and the encoded data is read from the compressed data unit 1 and decoded in the order of the data string. On the other hand, when performing the reduction in the direction intersecting the row direction, it is not necessary to read the compressed data of the row that does not need decoding. In this case, the line indicated by the chain double-dashed line in FIG. 2 is decoded, and the address information of the compressed data of the line marked with * is read next, and the compressed data of the next line is read according to this address information. Skip to the address information of (shown by a solid arrow). In the example of FIG. 2, the next line is also skipped, and the compressed data string of the next line is skipped according to the address information marked with **. That is, when the address information does not exist in this way, the coded data of the unnecessary row is sequentially read and decoded, which is not necessary in the present invention.

Next, the operation of the method of the present invention by the decoding device configured as described above will be described.

FIG. 3 is a flowchart showing the reduction decoding operation performed by the CPU. Based on the address information AD of the compressed data and the reduction information of the reduction table unit 2, the first row is skipped to the row in which the encoded data ED to be decoded is stored (S51). Then, the encoded data ED is taken out (S5
2), it is determined whether it is an EOL code (S53), and if it is not an EOL code, it is decoded, and the number of pixels of the reduced image data in the row direction is calculated based on the reduction information stored in the reduction table unit 2. Get (S54). Next, in order to correspond to the reduction ratio also in the direction intersecting with it, the compressed data is skipped to the line to be coded based on the reduction information and the address information (S55). If skip 53 and EOL code, step 56
Proceed to.

The above processing is performed until the requested number of lines based on the reduction information is completed, and reduced image data can be obtained.

In this embodiment, the case where the reduction processing is performed has been described as an example. However, when performing the partial processing for partially cutting out, a cutting table unit storing cutting information that specifies the cutting range is provided, and the cutout data of The number of pixels in the row direction is obtained, and in the direction intersecting with this, the encoded data of the row in the cutout range may be selected and decoded based on the cutout information and the address information.

In the case of further enlargement, an enlargement table unit is provided to obtain the number of pixels in the row direction of the enlarged data, and the pixels in the direction intersecting with it may be repeatedly decoded according to the magnification. Enlargement processing can be performed.

Further, in this embodiment, the MH coding method has been described as an example of the coding method, but the present invention is not limited to this, and it goes without saying that the present invention can be applied to the case of decoding other compression codes.

〔The invention's effect〕

As described above, according to the present invention, when decoding and processing compressed data, address information is added to the compressed data and the row to be decoded is selected by the address information and the processing information. Therefore, it is not always necessary to decode all rows, and the time for decoding and processing image data is reduced. Further, the process of skipping useless data can be easily performed by using the address information. Further, it has an excellent effect such that the capacity of the memory for storing the decrypted data can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a decoding device used for carrying out the method for decoding compressed data according to the present invention, FIG. 2 is a schematic structural diagram of compressed data, and FIG. 3 is a flowchart showing the operation of reduction processing. FIG. 4 is a diagram showing an example of MH encoding, and FIG. 5 is a flowchart showing the operation of a conventional decoding method. 1 ... Compressed data portion, 2 ... Reduction table portion, AD ... Address information, ED ... Encoded data In the drawings, the same reference numerals indicate the same or corresponding portions.

Claims (1)

[Claims] 1. A method of decoding a compressed data sequence having compressed data obtained by compressing and coding image data row by row into an image data stream and processing the compressed data stream, which corresponds to each row of image data. Address information relating to the position of the compressed data row of the next row is provided for each compressed data row, and one line of encoded data is converted into image data according to the processing information based on the preset processing information regarding the processing of the image data. The method for decoding compressed data is characterized in that the encoded data of the row to be decoded next is selected based on the processing information and the address information.