JPH0695726B2 - Image data compression device - Google Patents

Description

DETAILED DESCRIPTION [Overview] In systems such as image processing devices and facsimiles, 2
Regarding a data compression device used for communication transmission of value image information and file storage, an object is to provide a high-speed data compression device for binary image information suitable for a computer that processes in byte units. The binary image data stored in the means is read in byte units, and for each byte data, one byte is all "0" or all "1" white / black runs, pre-registered specific patterns, and other A predetermined combination of a white / black run, a specific pattern, and a non-specific pattern exists between the pattern determining means for determining which of the non-specific patterns and the sequential byte data read from the input memory means. It is discriminated whether or not it is determined and a predetermined coding mode is set according to the result, and a white / black run and a specific pattern are discriminated by the pattern discrimination means. Or a non-specific pattern, each comprising a counter means for counting the number of consecutive bytes, and an encoding means. The encoding means has the encoding mode set by the mode discriminating means and the consecutive bytes counted by the counter means. It has a configuration in which a predetermined encoding format is selected based on the number and encoding is performed.

[Industrial application field]

The present invention relates to a data compression device used for communication transmission of binary image information and file storage in a system such as an image processing device and a facsimile.

The image information data compression method is the international standard MH method, MR
There are methods, MMR methods, etc., but these all handle image information in 1-bit (pixel) units.

On the other hand, since a general-purpose computer basically handles data in byte (8 bits) units, it is not suitable for bit-unit processing, and data compression of binary image information is performed using a general-purpose computer. In this case, since the number of steps is enormous because the bit shift instruction is frequently used, the processing time becomes extremely long as compared with the method using the dedicated circuit, and improvement is required.

[Conventional technology]

The MR method and MMR method, which are often used in conventional binary image data compression, are two-dimensional encoding methods, and encode not only the line to be encoded but also the correlation with the previous line. It is a thing. Since this encoding process is divided into various modes depending on the arrangement of the data on the previous line, it is necessary to perform mode discrimination and processing for each mode in bit units.

Conventionally, in order to execute this processing at high speed, a dedicated complex circuit was used.

[Problems to be solved by the invention]

The conventional two-dimensional data compression method of binary image information has a problem that high-speed processing cannot be performed if a general-purpose computer of byte processing type is used.

It is an object of the present invention to provide a high-speed data compression device for binary image information, which is suitable for a computer that processes in byte units.

[Means for solving problems]

The present invention provides an image data compression apparatus having a byte-unit coding algorithm that can be efficiently processed by a byte-processing type general-purpose computer.

Therefore, according to the present invention, a line to be encoded is divided into byte units, and a run in which all bits in the byte data are “0” or all bits are “1”, or a pattern that is registered in advance,
Alternatively, the coding mode is determined by determining whether it is other than that, the coding algorithm is applied according to the type of the coding mode and the continuous byte length, and the data is coded in a different byte data format for each mode. It is for compression.

FIG. 1 is an explanatory view of the principle of the present invention.

In the figure, 1 is an input memory unit, which temporarily holds the binary image data to be encoded.

Reference numeral 2 denotes a pattern discriminating unit, which reads out binary image data for each line from the input memory 1 in byte units, and the content of each byte data is stored in a specific pattern (“0”, “1”). Combination), all 1-byte “0” (white run) or all “1” (black run), and other (non-specific pattern).

The specific pattern registered in advance is a plurality of types selected from patterns having a high appearance frequency.

Reference numeral 3 denotes a mode discriminator, and the pattern discriminator 2 checks the continuous state of successive bytes based on the content of the discriminated byte data. Then, the type of a constant continuous state such as continuous white / black rambite or a combination of white / black rambite and a specific pattern byte is discriminated, and an encoding mode corresponding to each is set.

Reference numeral 4 denotes a counter, which counts the continuous number (byte length) of byte data having the same result determined by the pattern determination unit 2.

Reference numeral 5 denotes an encoding unit that uses the encoding mode set by the mode determination unit 3 for byte data and the number of consecutive bytes of the same mode counted by the counter 4 to generate a code by an encoding algorithm according to the mode. I do.

[Action]

FIG. 2 schematically shows a process of data compression and data decompression of image information to which the present invention is applied.

In the data compression process, the original image information in the binary image data format is pattern-determined and mode-determined by the configuration shown in FIG. 1, and is encoded in byte units according to the encoding algorithm for each mode to obtain a compressed image. Converted to information.

This compressed image information is transmitted or stored in a file,
Data restoration processing is performed on the user side.

The process of data decompression is the reverse process of the data compression process,
The mode discrimination and the code-pattern conversion are performed, and the compressed image information is restored to the restored image information based on the coding algorithm used in the data compression.

The operation of the present invention will be described with reference to FIG.

FIG. 3 exemplifies the coding method according to the present invention for three coding modes.

The example of FIG. 3 (a) is an encoding mode (referred to as R mode) when only white / black run lengths exist, and a plurality of consecutive bytes in the input image data are all "1" bits or " When it is 0 "bit, these are converted into the output code format of 1 byte length shown in the figure. The output code format of this white / black run length mode has a type indicating whether it is a white run (continuous "0" bits) or a black run (continuous "1" bits), and
A length indicating the number of continuous bytes is set.

The example of FIG. 3 (b) is an encoding mode (referred to as RC mode) when white / black run bytes are continuous with bytes having a specific pattern registered in advance. The output code format in this mode has a length of 1 byte, and the length of white / black runs (the number of consecutive bytes), the run types of white and black, and a pattern code for identifying a specific pattern are set.

The example in Fig. 3 (c) is the encoding mode (called the PC mode) when the byte with other non-specific pattern continues in the byte with the registered specific pattern. Takes the output code format. A mode identification code and a pattern code of a specific pattern are set in the first byte, and a byte having a non-specific pattern is set as it is in the second byte.

In addition, an encoding mode that targets only bytes having a specific pattern, an encoding mode that targets only bytes having a non-specific pattern, and the like are provided.

The output code format corresponding to each encoding mode is different, but the length is specified in byte units of 1 byte or multiple bytes. Further, the mode type can be identified by a plurality of bits at the head of each output code format.

As described above, according to the present invention, it is possible to particularly effectively perform data compression on a series of bytes having a plurality of types of specific patterns that frequently appear.

〔Example〕

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

FIG. 4 and FIG. 4 show types of coding modes and respective output code formats in the embodiment.

Is an R mode and applies to a sequence of one or more bytes with white / black run lengths. The 2nd byte is added as an extension area when 32 bytes or more that have the R mode are consecutively displayed in the 5-bit length area in the 1st byte.

Is an RC mode and is applied to a byte with a specific pattern that is registered in advance and a byte with a white / black run length in succession. The specific pattern is indicated by a 4-bit pattern code.

Is in PC mode and applies when bytes with a specific pattern are followed by bytes with a non-specific pattern. The second and subsequent bytes indicate a non-specific pattern.

Is in 1C mode, 1 byte with a specific pattern
Applies to individual cases.

Is an NC mode and is applied when N bytes (N = 3 to 18) having a specific pattern (which may be different) are continuous. The second and subsequent bytes indicate the sequence of pattern codes of each specific pattern.

Is in P mode and applies to sequences of bytes with non-specific patterns. The second and subsequent bytes indicate a non-specific pattern.

FIG. 5 is an explanatory diagram of a pattern code table which gives correspondence between registered specific patterns and pattern codes used in the embodiment of the present invention. In the example shown, 2 ⁸ =
Of the 256 patterns, the 16 types of specific patterns with the highest probability of occurrence are registered in association with the 4-bit pattern code.

When any of the specific patterns registered in this pattern code table is detected in the input byte data, it is converted into the corresponding pattern code and encoded according to the corresponding encoding mode.

FIG. 6 is a block diagram of a data compression apparatus according to an embodiment of the present invention.

An input memory 11 stores binary image data of original image information.

Reference numeral 12 is a pattern discriminating unit, which reads binary image data in byte units, and all bits of the byte are "1" or "0".
Alternatively, it is determined whether it is a specific pattern registered in advance in a pattern code table 13 described later or a non-specific pattern other than that.

Reference numeral 13 is a pattern code table in which the contents of the pattern code table shown in FIG. 5 are set.

A continuous byte number counter 13a counts the number of consecutive bytes (length) when the content of the input byte is "0" only, "1" only, or a non-specific pattern.

Reference numeral 14 is a flag portion. In the R mode (Fig. 4) when the input byte contents are only "0" (white run) and "1" (black run), the flag "0" (white run) is used. ), “01” (black run), and P for non-specific pattern bytes
The flag "1111" is set in the mode (FIG. 4).

Reference numeral 15 is a pattern code continuous counter, which counts the number of continuous pattern codes (length) when the content of the input byte is one of the specific patterns.

Reference numeral 16 is a mode discriminating unit, and only a specific pattern byte is
Alternatively, it is possible to determine whether each byte of a specific pattern is continuous with a white / black run byte and whether each byte of a specific pattern is continuous with a non-specific pattern, and 1C is set as each encoding mode.
The mode (Fig. 4), NC mode (Fig. 4), RC mode (Fig. 4) and PC mode (Fig. 4) are determined.

Reference numeral 17 is a pattern code portion, and the pattern discrimination portion 16 sets the pattern code of the specific pattern discriminated by the pattern discrimination portion 12.

Reference numeral 18 is a flag portion, and flags “1101”, “1110”, “100/101”, “1100” corresponding to each mode of 1C, NC, RC and PC are set.

An output register 19 is used to assemble and generate a code.

20 is an extended output register, and the continuous byte number counter 13
Used to assemble and generate extension bytes when the count value of a exceeds 32.

An output memory 21 stores encoded compressed image information.

FIG. 7 is a flow chart showing the control procedure of the data compression apparatus shown in FIG. The operation will be described below according to the procedure.

(1): The pattern discriminating unit 12 reads the image data in the input memory 11 byte by byte, and the pattern code table
Check if it matches any of the specific patterns registered in 13. If there is a match, it is converted into a pattern code and (7) is executed, but if there is no match, (2) is executed.

(2): Check whether the input byte is a white run (all "0"), a black run (all "1"), or a non-specific pattern. In the former case, (3) is executed, and in the latter case, (5) is executed.

(3): In the case of white / black run bytes, the continuous byte number counter 13a counts the number of continuous bytes.

(4): The R mode flag "00/01" is set in the flag section 14 and encoding is performed in the R mode.

(5): In the case of non-specific pattern bytes, the continuous byte number counter 13a counts the number of continuous bytes.

(6): A P-mode flag "1111" is set in the flag unit 14 to perform encoding in the P mode.

(7): If the content of the input byte is a specific pattern in (1), the pattern code consecutive number counter 15 counts the consecutive number C.

(8): If C = 1, execute (12), otherwise (C
For (2), execute (9).

(9): If C = 2, execute (10), otherwise (C
For (3), execute (11).

(10): "1100" is set in the flag unit 18 and encoding is performed in the 1C mode.

(11): "1110" is set in the flag unit 18 and encoding is performed in NC mode.

(12): Check whether the next input byte is a non-specific pattern. If it is a byte of non-specific pattern, execute (13), otherwise execute (14).

(13): "1101" is set in the flag unit 18 and encoding is performed in the PC mode.

(14): It is checked whether the next input byte is a white / black run with a continuous number of 1. If it is a white / black run, execute (15). If it is a white / black run with the number of continuations of 2, execute (16).

(15): "100" is set in the flag part 18 and encoding is performed in the RC mode when 1-byte white / black runs are continuous.

(16): "101" is set in the flag portion 18 and encoding is performed in the RC mode when a 2-byte white / black run is continuous.

When the value of the continuous byte counter 13a exceeds 32, the extension bit in the flag unit 14 is set to "1". At this time, the value of the continuous byte counter 13a is
It is set for both the output register 19 and the extended output register 20.

FIG. 8 shows an example of original image information to be compressed,
For simplification, the size of 10 × 16 pixels is shown.

This original image information is read in byte units for each successive line, analyzed, the corresponding encoding mode is determined, and encoded.

FIG. 9 shows the division of coding modes when the control procedure of FIG. 7 is applied to the original image information of FIG. As shown, the R mode, NC mode, P mode, 1C mode, and RC mode are sequentially coded.

FIG. 10 shows output data as a result of encoding according to the encoding mode shown in FIG. The original 20 bytes of data are compressed into 16 bytes of data.

FIG. 11 is a block diagram of a data decompression device that can be used in combination with the data compression device of the embodiment of the present invention.

In the figure, reference numeral 22 is an input memory, in which data-compressed image information is stored.

Reference numeral 23 is a code discriminating unit, which controls a process of analyzing and restoring the code of the input byte data.

A pattern code table 24 gives a specific pattern corresponding to the pattern code contained in the input byte.

A memory writing unit 25 writes the restored data in the memory under the control of the code discriminating unit 23.

Reference numeral 26 is an output memory in which the restored data is stored in byte units and is output to the device used.

The encoded (compressed) data stored in the input memory 22 is read in byte units, and the code determination unit 23 determines the encoding mode. The following operation is performed according to each mode.

In the R mode, one byte of all "0" or one byte of "1" is written from the memory writing unit 25 to the output memory 26 by the byte length specified by the length.
High-speed processing is possible by simultaneously writing this memory to multiple bytes. Here, the extension bit is "1"
In the case of (with extension), the next byte is also used to write to the output memory 26 by the specified length (the number of bytes).

In the RC mode, first, referring to the pattern code table 24, the specific pattern designated by the pattern code is
Write to the output memory 26 via the memory writing unit 25, and further write a 1-byte or 2-byte white run or black run via the memory writing unit 25.

In the PC mode, the pattern code table 24 is referred to, the specific pattern designated by the pattern code is written to the output memory 26 via the memory writing unit 25, and the subsequent non-specific pattern is directly written to the output memory 26. Write.

In the 1C mode, the pattern code table 24 is referred to, the specific pattern designated by the pattern code is written to the output memory 26 via the memory writing unit 25, and the process proceeds.

In the NC mode, the continuous length N is read, and the specified specific pattern is read via the memory writing unit 25 by referring to the pattern code table 24 with each N consecutive continuous pattern codes in units of 4 bits. , Write to output memory 26.

In the P mode, the subsequent pattern of the length length is read and written in the output memory 26.

〔The invention's effect〕

Since the encoding algorithm for data compression according to the present invention is based on byte-unit processing, it is possible to efficiently perform data compression using an ordinary general-purpose computer, and to use a dedicated circuit like the conventional one. A relatively high-speed system can be realized economically regardless of the special compression device used.

In a specific example, a compression ratio of about 30% could be obtained with a 400 x 400 dot newspaper headline character pattern.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of the principle of the present invention, FIG. 2 is an explanatory diagram of a data compression and data decompression process according to the present invention, FIG. 3 is an explanatory diagram of an encoding example showing the operation of the present invention, and FIGS. FIG. 11 shows an embodiment of the present invention, FIG. 4 is an explanatory diagram of coding mode types and output code formats, FIG. 5 is an explanatory diagram of a pattern code table, FIG. 6 is a configuration diagram of a data compression device, 7th
FIG. 8 is a flow chart of the control procedure of the data compression device, FIG. 8 is an explanatory diagram of an example of original image information, FIG. 9 is an explanatory diagram of coding mode divisions, and FIG. 10 is an explanatory diagram of an example of output data. , FIG. 11 is a block diagram of a data restoration device. In FIG. 1, 1 is an input memory unit, 2 is a pattern discrimination unit, 3 is a mode discrimination unit, 4 is a counter, and 5 is an encoding unit.

Claims (1)

[Claims] 1. An input memory means (1) for accumulating binary image data, and binary image data accumulated in the input memory means (1) are read in byte units, and for each byte data, all 1 byte A pattern discriminating means (2) for discriminating between "0" or all "1" white / black runs, a specific pattern registered in advance, and other non-specific patterns, and an input memory means (1). ) Determines whether or not there is a predetermined combination of white / black runs, a specific pattern, and a non-specific pattern between the sequential byte data read from), and the mode determination that sets the predetermined encoding mode based on the result A means (3), a counter means (4) for counting the number of continuous bytes for each of the white / black run, the specific pattern or the non-specific pattern judged by the pattern judging means (2); The encoding means (5) includes a coding means (5), and the coding means (5) performs predetermined coding based on the coding mode set by the mode discrimination means (3) and the number of consecutive bytes counted by the counter means (4). An image data compression device characterized by selecting a format and performing encoding.