JP2005269184A - Data compressing process, program, data recovery method, and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a data compressing method based on an LZ77 code which can improve a compression rate, and to provide a data compressing method which time duration does not require for processing of data compression and restoration. <P>SOLUTION: The data compression method includes the steps of retrieving the maximum length coincidence sequence coincident longest to sequence to a signature sequence for encoding existing in the coded signature sequence, encoding based on the position coincident to the longest sequence and the length coincident to the length of the longest sequence, and compressing the data. The sign formed by the encoding includes a code representing the sign about the length of the represent sign in length and the coincident length of the represent sign, the sign representing the coincident position, and the sign representing the coincident length. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method of compressing data by encoding based on a match with an encoded symbol string, and in particular, it can improve a data compression rate and spend time on data compression and decompression processing. The present invention relates to a data compression method that does not cost.

  In recent years, with the development of information processing technology and the spread of networks such as the Internet, a huge amount of data has been processed and communicated. For example, it is a common practice to cause a printer to execute printing from a host computer via a network, and the processing speed of the printer is improved as needed, but the capacity of print data transmitted from the host computer to the printer is large. In some cases, the communication takes time, and the processing speed of the printer cannot be fully utilized. Therefore, a data compression and decompression technique is required for how data is compressed and transmitted and how it is restored after reception.

  Conventionally, several data compression and decompression techniques have been proposed depending on the purpose and target data. One of them is a method using an LZ77 (Ziv and Lempel (1977)) code. In this method, a symbol string before and after a symbol (data) that is currently encoded is stored in a buffer, and this buffer is referred to as a dictionary, and the longest symbol string that matches the symbol string to be encoded is stored. In the dictionary. Then, the target symbol string is encoded based on the length and position information of the searched symbol string.

  Various variations have been developed for the LZ77 system. For example, a method using an LZSS code described in Non-Patent Document 1 below is frequently used. In this method, when the length of the matching longest symbol string is smaller than a predetermined value, the original symbol is used as it is, that is, the above matching symbol string is not encoded according to the length and position. When the length of the longest symbol string to be performed is larger than a predetermined value, the above-described encoding based on the length and position of the matching symbol string is performed. Then, a flag for distinguishing both is added to the head of the code.

Further, several proposals have been made for such an LZ77 data compression method for the purpose of improving the compression ratio (for example, Patent Documents 1 and 2 below).
Japanese Patent Laid-Open No. 5-11973 JP 7-261977 A Tomohiko Uematsu, “Introduction to Document Data Compression Algorithm”, Second Edition, CQ Publishing, June 1995, p. 145-148

  However, in the above-described LZSS code, the position (hereinafter referred to as the matching position) and the length (hereinafter referred to as the matching length) of the longest matching symbol string are expressed by a fixed-length code (bit string). There was a problem that the data compression rate was not so good.

  Further, Patent Document 1 describes a method for improving the data compression rate by attaching an appearance number to a matching symbol string in the dictionary and outputting the appearance number as the matching position. However, such a method has a problem in that it takes time for the restoration process because it is necessary to obtain the appearance position of the matching symbol string by searching even when the compressed data is decoded.

  Further, in Patent Document 2, a technique for expressing the matching position and the matching length with a code that dynamically changes according to a spray tree and improving the compression ratio is shown. Because of the change, both the compression and decompression processes are complicated, and there is a problem that these processes take time.

  Therefore, an object of the present invention is to provide a data compression method based on the LZ77 code, which can improve the compression rate, and that does not take time for data compression and decompression processing.

  In order to achieve the above object, one aspect of the present invention is to search for a longest match sequence having a maximum length match with a symbol string to be encoded, existing in an encoded symbol string, and to perform the longest match. A data compression method for compressing data by performing encoding based on a match position that is a sequence existing position and a match length that is a length of the longest match sequence, wherein the code generated by the encoding is It is characterized by comprising a code representing the length of the code representing the coincidence position and the length of the code representing the coincidence length, a code representing the coincidence position, and a code representing the coincidence length. Therefore, according to the present invention, the length of the code representing the coincidence position and the code representing the coincidence length can be set to the minimum necessary length, and the data compression rate can be improved.

  Further, in the above invention, a preferable aspect thereof is that the code representing the coincidence position is obtained by removing the most significant 1 when the value representing the coincidence position is expressed in a binary system, and the coincidence length. Is a code obtained by removing the most significant 1 when the value representing the matching length is expressed in binary. Thereby, the data compression rate can be increased.

  In order to achieve the above object, another aspect of the present invention is to search for a longest matching sequence having a maximum length match with a symbol string to be encoded, existing in an encoded symbol string, and to perform the longest match. A data compression method for compressing data by encoding based on a match position that is a sequence existing position and a match length that is a length of the longest match sequence, wherein the length of the longest match sequence is a predetermined length If the value is smaller than the value, the encoding is performed with the first identification information having a predetermined length indicating that the original symbol is smaller than the predetermined value, and the length of the longest matching sequence is the predetermined value. If the value is greater than or equal to the value, the same as the first identification information indicating that the value is greater than or equal to the predetermined value, the length of the match position information indicating the match position, and the length of the match length information indicating the match length Second identification information of length, the matching position information, and the matching length And broadcasting, by and performing the coding. Therefore, according to the present invention, it is possible to perform data compression that is easy to restore and has a high compression rate.

  Furthermore, in the above-described invention, a preferable aspect thereof is that the matching position information is obtained by removing the highest-order 1 when the value representing the matching position is expressed in binary, and the matching length information is The value representing the matching length is obtained by excluding the most significant 1 when expressed in binary.

  Furthermore, in the above invention, a preferred aspect is characterized in that the first identification information and / or the second identification information is Huffman-encoded. As a result, the data compression rate can be further increased.

  In order to achieve the above object, another aspect of the present invention is to search for a longest matching sequence having a maximum length match with a symbol string to be encoded, existing in an encoded symbol string, and to perform the longest match. A data compression program that causes a computer to execute a process of encoding and compressing data based on a match position that is the position of a sequence and a match length that is the length of the longest match sequence is the length of the longest match sequence Is determined to be greater than or equal to a predetermined value, and in the first step, when it is determined that the length of the longest match sequence is not equal to or greater than the predetermined value, In the second step of performing the encoding with the first identification information of a predetermined length, which represents that the original symbol is not greater than or equal to the value, and in the first step, the length of the longest match sequence is greater than or equal to the predetermined value It is determined that there is no In this case, the length is equal to or more than the predetermined value, the length of the matching position information indicating the matching position, and the length of the matching length information indicating the matching length, and the same length as the first identification information. And causing the computer to execute a third step of performing the encoding by using second identification information, the matching position information, and the matching length information.

  In order to achieve the above object, another aspect of the present invention is to search for a longest matching sequence having a maximum length match with a symbol string to be encoded, existing in an encoded symbol string, and to perform the longest match. A data restoration method for restoring data encoded based on a match position that is a position of a sequence and a match length that is a length of the longest match sequence, wherein the data to be restored is the longest match sequence If the length of the longest matching sequence is smaller than the predetermined value, the length of the longest matching sequence is encoded with the first identification information of a predetermined length indicating that the length is smaller than the predetermined value and the original symbol. Is equal to or greater than the predetermined value, indicates that it is equal to or greater than the predetermined value, the length of the matching position information indicating the matching position, and the length of the matching length information indicating the matching length, Second identification information having the same length as one identification information, and the matching position information And the matching length information, the code corresponding to the predetermined length which is the length of the first identification information or the second identification information is interpreted, and the code is the first identification A first step for determining whether the information is information or second identification information; and if the first step determines that the identification information is first identification information, the source included in the first identification information In the second step of decoding into the symbol of the above, and in the first step, if it is determined that the second identification information, the length of the matching position information and the matching length information based on the second identification information A third step for obtaining the matching position, a fourth step for obtaining the matching position from the code for the length of the matching position information obtained in the third step, and the matching position information. Next, in the third step The fifth step for obtaining the match length from the code corresponding to the length of the match length information obtained, and decoding based on the match position and the match length obtained in the fourth and fifth steps And a sixth step of decoding using the symbol string. Therefore, according to the present invention, it is possible to easily restore the data encoded as described above.

  In order to achieve the above object, another aspect of the present invention is to search for a longest matching sequence having a maximum length match with a symbol string to be encoded, existing in an encoded symbol string, and to perform the longest match. A data restoration device that restores data encoded based on a match position that is a sequence existing position and a match length that is a length of the longest match sequence, and a symbol string storage unit that stores a decoded symbol string When the length of the longest matching sequence is smaller than a predetermined value, the first identification information having a predetermined length represents that the data to be restored is smaller than the predetermined value and the original symbol. When the length of the longest match sequence is equal to or greater than the predetermined value, the length of the match position information indicating the match position and the match length are expressed. Same as the first identification information, indicating the length of the matching length information. The predetermined length that is the length of the first identification information or the second identification information when encoded by the second identification information of the length, the matching position information, and the matching length information The code of minutes determines whether the code is first identification information or second identification information, and if it is determined to be first identification information, the first identification information includes the When the original symbol is decoded and determined to be the second identification information, the length of the matching position information and the matching length information is obtained based on the second identification information, and the second identification information is Subsequently, from the code for the length of the obtained match position information and the code for the length of the obtained match length information, the match position and the match length are obtained, and the obtained match position Based on the matching length, the symbol string stored in the symbol string storage means is used. Decoding Te, it is to include a decoding means.

  Further objects and features of the present invention will become apparent from the embodiments of the invention described below.

Embodiments of the present invention will be described below with reference to the drawings. However, such an embodiment does not limit the technical scope of the present invention. In the drawings, the same or similar elements are denoted by the same reference numerals or reference symbols.

  FIG. 1 is a configuration diagram according to an embodiment of a data compression apparatus to which the present invention is applied. FIG. 2 is a configuration diagram according to an embodiment of a data restoration apparatus to which the present invention is applied. The data compression apparatus 1 and the data decompression apparatus 2 shown in FIGS. 1 and 2 are apparatuses using the data compression method and the decompression method according to the present invention. The data compression method of the data compression apparatus 1 is based on the concept of the LZ77 code, but does not represent the coincidence position and coincidence length used for encoding with a fixed-length code (bit string) but coincides with the coincidence position. By encoding information with the length (number of bits) of the codes representing the lengths in front of those codes, and shortening the length of the codes representing the matching position and the matching length as much as possible It is intended to improve the data compression rate. In addition, the data restoration method of the data restoration device 2 easily obtains the information on the match position and the match length based on the code length information representing the match position and the match length added at the time of compression. In addition, the information is decoded into the original symbol string, and a restoration process that does not take much time is realized.

  As shown in FIG. 1, the data compression apparatus 1 is composed of an input buffer 11, an encoding unit 12, and a dictionary buffer 13, and encodes input data to compress the data capacity. Here, input data before encoding is referred to as a symbol (column). In this embodiment, each symbol, for example, “A”, “B” in the input buffer 11 of FIG. "Etc." are assumed to be 8-bit data. Further, the processed code is expressed by a bit string of “0” or “1” in binary.

  The input buffer 11 is a data buffer that sequentially receives and stores symbol strings to be encoded, and sequentially transfers the symbol strings that have been encoded to the dictionary buffer 13. The length of the input buffer 11 (L2 in FIG. 1), that is, the number of symbols that can be stored is 258 in the present embodiment. This length L2 means the maximum value of the matching length (for example, 1 in FIG. 1).

  The dictionary buffer 13 is a data buffer that sequentially receives encoded symbol strings from the input buffer 11 and stores them, and is called a so-called dictionary in the LZ77 system. The symbol string stored here is compared with the symbol string to be encoded in the input buffer 11, and the maximum length symbol string that matches the symbol string in the input buffer 11 (hereinafter referred to as the longest matching sequence). Is called). In the dictionary buffer 13, every time encoding in the encoding unit 12 is completed, the encoded symbol string is accepted, and the symbol string at the head (located on the left side in FIG. 1) is unnecessary. Will be exhaled. Further, the length of the dictionary buffer 13 (L1 in FIG. 1), that is, the number of symbols that can be stored is 16384 (16K) in the present embodiment. This length L1 means the maximum value of the distance (for example, d in FIG. 1) representing the coincidence position. In the example shown in FIG. 1, the longest matching sequence is “ABCD”, the matching length which is the length thereof is l, and the matching position is p.

  Next, the encoding unit 12 is a part that performs general control related to the input, encoding, and output of the symbol string in the data compression apparatus 1, mainly referring to the dictionary buffer 13, A process of encoding the symbol string in the input buffer 11 is executed. The encoding process performed by the encoding unit 12 is characterized, and the specific contents thereof will be described later. The encoding unit 12 may be configured by a program indicating a processing procedure, a CPU that executes processing according to the program, or may be configured by a hardware circuit.

  As shown in FIG. 2, the data decompression device 2 has the same configuration as the data compression device 1, and includes an input buffer 21, a decoding unit 22 (decoding means), and a dictionary buffer 23 (symbol string storage means). Yes. The data restoration device 2 is a device for restoring the data (code) compressed by the data compression device 1 to the original symbol string data. The input buffer 21 is a data buffer that sequentially receives and stores codes to be processed. The dictionary buffer 23 is a data buffer that sequentially receives and stores decoded symbol strings from the decoding unit 22. The symbol string stored here is referred to during the decoding process by the decoding unit 22 and is used for the decoding process. In the dictionary buffer 23, every time the processing in the decoding unit 22 is completed, the decoded symbol string is accepted, and the corresponding symbol string at the head (located on the right side in FIG. 2) is spouted as an unnecessary symbol. Further, the length (size) of the dictionary buffer 23 is the same as the length L1 of the dictionary buffer 13 of the data compression apparatus 1.

  Further, the state in the dictionary buffer 23 is the same as the state of the dictionary buffer 13 when the code to be processed in the decoding unit 22 at that time is encoded in the data compression apparatus 1. In the example shown in FIG. 1, when the symbol string “ABCD” is encoded based on the matching position p (or d) and the matching length l, when the code is decoded by the data restoration device 2. The state in the dictionary buffer 23 is as shown in FIG. That is, the symbol strings (expressed in the reverse direction in FIG. 2) are stored in the order of “ABCD” from the position p at a distance d from the left end of the dictionary buffer 23. Therefore, the decoding unit 22 can decode “ABCD” based on the matching position p (or d) acquired from the code and the matching length l.

  The decoding unit 22 is a part that performs general control related to code input, decoding, and symbol output in the data restoration device 2, and mainly refers to the code in the input buffer 21 while referring to the dictionary buffer 23. The process which decodes is performed. Specific contents of the decoding process performed by the decoding unit 22 will be described later. The decoding unit 22 may be configured by a program showing a processing procedure, a CPU that executes processing according to the program, or may be configured by a hardware circuit.

  FIG. 3 is a flowchart illustrating the contents of the process performed by the encoding unit 12 of the data compression apparatus 1. Hereinafter, based on FIG. 3, the specific content of the compression process performed by this data compression apparatus 1 is demonstrated. First, the symbol strings to be processed are sequentially read into the input buffer 11 (step S10). Next, the encoding unit 12 searches the symbol string from the head position (left end position in FIG. 1) stored in the input buffer 11 for a match with the symbol string stored in the dictionary buffer 13 (step S11). That is, the longest matching sequence described above is searched.

  Then, it is checked whether or not the length of the searched longest matching sequence (matching length) is not less than a predetermined value (step S12). For example, the predetermined number is “4”. As a result, if the match length is 3 or less (No in step S12), the encoding unit 12 does not represent the symbol at the head position of the input buffer 11 with the match position of the longest match sequence and the match length. In addition, the symbol is encoded by a method of expressing the symbol as it is in the binary system. And the code | symbol is output (step S13). Specifically, in the present embodiment, since the symbol is 8-bit data, the 8-bit data as the original symbol is represented by 9 bits, which is used as the code of the symbol.

  FIG. 4 is a diagram for explaining codes and the like generated by the data compression apparatus 1. FIG. 4A schematically shows the code generated by the data compression apparatus 1, and the diagram shown in the upper part (denoted [mismatch]) is the code output in step S13. It is. In other words, the code in the case where there is no match in the dictionary buffer 13 for a predetermined number of symbol strings from the head position of the input buffer 11 is shown. As described above, since this code originally represents 8 bits of data in 9 bits, the most significant bit is always “0”. As will be described later, when the matching length is greater than or equal to a predetermined number in step S12, the most significant bit is always “1”, so that the most significant bit is “mismatched” for a predetermined number of symbol strings. ". The subsequent 8-bit data is the original symbol itself.

  Therefore, the code is identified by the most significant bit as being “mismatched”, that is, indicating the symbol itself in the subsequent bit string. In other words, an expression that can take a value of 0 to 511 is used to express a value of 0 to 255, thereby identifying the original symbol as it is. The entire code in the case of “mismatch” including the “mismatch” and the original symbol is referred to as identification information (first identification information) in the case of “mismatch”.

  Returning to FIG. 3, when the matching length is equal to or larger than the predetermined number in Step S12 (Yes in Step S12), the encoding unit 12 sets the matching position and the matching length of the searched longest matching sequence. The number of bits (bit string length) necessary to represent is obtained (step S15). In the present embodiment, the matching position takes a value of 1 to 16384 based on the size of the dictionary buffer 13 described above. Therefore, the number of bits necessary to represent the matching position is a value of 1 to 14. Further, the matching length takes a value of 4 to 258 from the size of the input buffer 11 and the condition in step S12 described above, so the number of bits necessary to represent the matching length is a value of 1 to 8. .

Next, the encoding unit 12 “matches” in the dictionary buffer 13 with respect to the number of bits of the obtained matching position and matching length and a predetermined number of symbol strings from the head position of the input buffer 11. The code | symbol which shows that is produced | generated and output (step S16). Such a code is referred to herein as identification information (second identification information) in the case of “match”. Specifically, as an example, a value such as the following formula (1) is generated as identification information.
Identification information (in case of “match”) = 256+ (BL−1) × maximum BP + (BP−1) (1)
Where BL is the number of bits required to represent the matching length
BP: Number of bits required to represent the matching position
Maximum BP: Maximum number of bits required to represent the matching position In the present embodiment, as described above, the maximum BP has a value of 14, and BP and BL have the above values. Thus, the identification information (in the case of “match”) has a value of 256 to 367. Therefore, the identification information (in the case of “match”) is also expressed by 9 bits as a binary code. The figure shown in the lower part of FIG. 4A (described as [match]) shows a code generated and output when there is a “match” of the predetermined number of symbol strings. The 9 bits of the portion correspond to the identification information.

  As described above, since the identification information takes a value of 256 or more, it is possible to identify that there is a “match”, and to match the position and match by the value obtained by subtracting 256 from the value of the identification information. The number of bits required to represent the length is shown. In other words, the most significant bit of the code represented by 9 bits always has a value of “1”, which indicates that there is a “match”, and the lower 8 bits indicate the match position and match length. The number of bits necessary to represent

  As described above, in the code according to the present embodiment, the identification information is expressed by 9 bits both in the case of “match” and “mismatch”, depending on whether the value is 256 or more. In other words, it is possible to identify whether or not encoding is performed based on the matching position and the matching length by the most significant bit. In addition, after the identification, the lower 8 bits can be used to know the original symbol itself in the case of “mismatch”, and in the case of “match”, the matching position and the matching length that follow the identification information can be obtained. The length of the code to represent can be known.

  When the output of the identification information is completed, the encoding unit 12 outputs the matching position information indicating the matching position of the searched longest matching sequence as a code (step S17). Specifically, a lower-order bit string excluding the most significant “1” bit when the value representing the matching position is expressed in binary notation is output as matching position information. This is self-evident that the most significant bit is “1”, and is for the purpose of reducing the amount of data as much as possible. For example, when the value of the coincidence position is 9, although “1001” is obtained in the binary system, “001” is output as the coincidence position information.

  Further, if the matching position and the matching length are expressed in comparison with the case of the LZSS code expressing the fixed-length bit string, the matching position is expressed by the maximum length of 14 bits, and the MSB (Most Significant) of the bit string is expressed. Bits) obtained by removing the “0” bit continuously present from the “Bit” side and the next “1” bit are used as matching position information.

  Next, the encoding unit 12 outputs match length information indicating the match length of the longest match sequence as a code (step S18). Similarly to the match position information, the match length information is output as a match length information by subordinate bit strings excluding the most significant “1” when the value representing the match length is expressed in binary. .

  In the code illustrated in the lower part of FIG. 4A, “coincidence position information” and “coincidence length information” shown on the right side correspond to each information output in steps S17 and S18.

  As described above, when the code generation and output processing in the case of “mismatch” or “match” is completed, the symbol strings stored in the input buffer 11 and the dictionary buffer 13 are slid (step S14). ). Specifically, the symbol (sequence) generated by the code generated by the above processing and output is moved from the head portion of the input buffer 11 to the tail portion of the dictionary buffer 13. Then, a new symbol (sequence) for the movement is input to the input buffer 11, and a symbol (sequence) for the movement is discharged from the dictionary buffer 13. Note that in the case of “mismatch”, only one symbol is encoded, so there is only one symbol that moves. In the case of “match”, four or more symbols are encoded. The moving symbol is 4 or more.

  Thereafter, it is determined whether or not the compression process to be performed this time has ended (step S19). If the compression process has not ended (No in step S19), the process from step S11 described above is repeated. If it is determined that the compression process has been completed (Yes in step S19), the series of data compression processes is terminated.

  FIG. 5 is a flowchart illustrating the contents of the process performed by the decryption unit 22 of the data restoration device 2. Hereinafter, based on FIG. 5, the specific content of the restoration process performed by the data restoration apparatus 2 will be described. First, the codes to be processed are sequentially read into the input buffer 21 (step S20). Next, the decoding unit 22 reads the first 9 bits of the code, that is, identification information from the input buffer 21 and interprets the information (step S21).

  Then, it is determined whether the current processing target code is the case of “mismatch” or “match” at the time of encoding (step S22). As described above, this determination can be made based on the most significant bit of the identification information. If the most significant bit is “0”, it is determined that the case is “mismatch”, and the most significant bit is “ If it is “1”, it is determined that the case is “match”. In other words, if the value of the read identification information is 0 to 255, it is determined that the value represents the original symbol itself, and if the value of the identification information is 256 or more, this identification information follows. It is determined that the number of bits of information on the matching position and the matching length can be known.

  If it is determined that the result is “mismatch” (No in step S22), since the read identification information represents the original symbol itself, the original symbol is restored and output. (Step S23). More specifically, 9-bit identification information is output as 8 bits.

  On the other hand, if it is determined that it is a case of “match” (Yes in step S22), the number of bits of match position information and the number of bits of match length information following the identification information are obtained from the read identification information. (Step S25). Specifically, since the identification information is generated by the above-described equation (1), 256 is subtracted from the value of the read identification information, the subsequent value is divided by the maximum BP (14), and the remainder at that time matches. The number of bits of the position information is used, and the quotient at that time is the number of bits of the matching length information.

  Next, the decoding unit 22 reads, from the input buffer 21, codes corresponding to the number of bits of the obtained matching position information following the read identification information (step S26). Thereafter, the decoding unit 22 obtains the value of the coincidence position from the read coincidence position information (step S27). Specifically, a value obtained by adding a bit of “1” to the most significant bit string of the read matching position information is set as the matching position value. In other words, a value obtained by adding the value of the matching position information to the power of 2 (the number of bits of the matching position information) is set as the value of the matching position.

  Subsequently, the decoding unit 22 reads, from the input buffer 21, codes corresponding to the number of bits of the obtained match length information following the read match position information (step S28). Thereafter, the decoding unit 22 obtains a value of the matching length from the read matching length information (step S29). Specifically, a value obtained by adding 3 to the value obtained by adding the bit of “1” to the most significant bit string of the read match length information is set as the match length value. In other words, a value obtained by adding the value of the matching position information and 3 to the power of 2 (the number of bits of the matching length information) is set as the matching length value. Here, 3 is added, as described above, the value of the match length takes a value of 4 to 258, and 3 is subtracted from the value of the match length in order to express it with 8 bits at the time of encoding. This is because the values (1 to 255) are encoded.

  Next, the decoding unit 22 restores the original symbol string from the value of the obtained matching position and matching length, and outputs the restored symbol string (step S30). Specifically, a symbol string corresponding to the coincidence length of the obtained value is read from the coincidence position of the obtained value of the symbol string stored in the dictionary buffer 23, and the read symbol string is used as the original symbol string. Output.

  As described above, when the decoding process in the case of “mismatch” or “match” is completed, the codes and symbol strings stored in the input buffer 21 and the dictionary buffer 23 are slid (step S24). Specifically, the code restored by the above processing is deleted from the input buffer 21, and a new code corresponding to the code is input to the input buffer 21. Further, the symbol string restored by the above processing is added to the tail portion of the dictionary buffer 23, and the corresponding symbol string at the head portion is discharged from the dictionary buffer 13 as an unnecessary symbol.

  Thereafter, it is determined whether or not the restoration process to be performed this time has been completed (step S31). If the restoration process has not been completed (No in step S31), the process from step S21 described above is repeated. If it is determined that the restoration process has been completed (Yes in step S31), the series of data restoration processes is terminated.

  FIG. 6 is a diagram showing a specific example of processing performed by the data compression apparatus 1 and the data restoration apparatus 2. The example shown in the figure is a case where there is a “match” of the predetermined number or more of symbols at the time of data compression, the match position at that time is 300, and the match length is 22. FIG. 6A is a diagram schematically showing the matching position (300) and the matching length (22) with the maximum number of bits. FIG. 6B shows the matching position (300) and matching length (22) in binary notation with the maximum number of bits.

  When the encoding by the encoding unit 12 described above is performed on this state, a code as shown in FIG. 6C is generated and output. The left part of the code shown in the figure is the above-described identification information (in the case of “match”), and the calculation shown in the figure is performed according to the above equation (1), and the value of the identification information is 320. That is, the value of 4 obtained by subtracting 1 from the number of bits 5 (BL) necessary for binary representation of 19 obtained by subtracting 3 from 22 which is the value of the matching length is multiplied by 14 (maximum BP), The value 8 obtained by subtracting 1 from the number of bits 9 (BP) necessary for binary representation of 300, which is the value of the matching position, and 256 are added to the value, and identification information of 320 is obtained.

  Further, 8 bits in the central portion of the code shown in FIG. 6C is the coincidence position information, and the most significant “1” of the bit string expressing 300 in binary is removed. Accordingly, 8 bits obtained by removing all “0” s on the MSB side and the most significant “1” from the 14-bit representation shown in FIG. 6B are output as codes. Further, the right part of the code shown in FIG. 6C is the matching length information, and is obtained by excluding the most significant “1” of the bit string in which 19 obtained by subtracting 3 from 22 is represented in binary. ing. Therefore, 4 bits obtained by removing all “0” s on the MSB side and the most significant “1” from the 8-bit expression shown in FIG. 6B are output as codes.

  When such a code is received by the data restoration device 2 and decoded by the decoding unit 22, the identification information is interpreted and it is determined that the number of bits of the matching position information and the matching length information is 8 and 4, respectively. Is done. Then, according to the processing contents described above, as shown in FIG. 6D, first, the 8 bits after the identification information are read, and the bit “1” is added to the most significant bit. Thereby, it is determined that the value of the coincidence position is 300. Also, the 4 bits after the coincidence position information are read out, a bit of “1” is added to the most significant bit, and 3 is added, and it is determined that the coincidence length value is 22. . Thus, the decoding unit 22 extracts and outputs a predetermined symbol string from the dictionary buffer 23, and ends the decoding process for the code.

  As described above, in the data compression method and the decompression method according to the present embodiment, when there is no longest matching sequence of a predetermined length or more in the dictionary (buffer 13), a constant including the fact and the original symbol. If the longest identification sequence longer than a predetermined length exists in the dictionary, the length identification information is output as a code, and to that effect, the length of the information indicating the matching position and the length of the information indicating the matching length First, identification information having the same length as that of the above-described identification information is output, and thereafter, matching position information and matching length information are output. The coincidence position information and the coincidence length information are expressed by a bit string excluding the most significant bit when the value indicating the coincidence position and the coincidence length is displayed in binary.

  Therefore, when encoding is performed based on the matching position and the matching length, it is not necessary to always represent the information representing them with a bit string of the maximum fixed length (14 and 8 in the present embodiment), and the above identification Even if information is added, the length of the code as a whole can be shortened on average, and the data compression rate can be improved as compared with the conventional case. FIG. 4B schematically shows a code example when the LZSS code is used when the maximum value of the matching position and the matching length is the same as in the present embodiment. If there is no longest matching sequence of a predetermined length or longer in the upper dictionary (“mismatch”), “0” indicating that fact and 8 bits of the original symbol are output. If the longest matching sequence having a predetermined length or longer exists in the lower dictionary (“match”), “1” indicating that, a fixed-length match position information (14 bits), and match length information (8 bits) is output. Compared to the case of the present embodiment shown in FIG. 4A, the data length is the same in the case of “mismatch”, but in the case of “match”, the present embodiment example In the case of, the evaluation that the data length becomes shorter on average is obtained.

  Also, when restoring the code, first, the identification information of the same length is interpreted, it is determined whether the encoding based on the matching position and the matching length has been made, and the coding has been made In addition, the matching position information and the matching length information can be easily read from the identification information. Therefore, complicated processing such as search is not required at the time of decoding processing, and processing does not take time.

  Although the multiplier in the equation (1), that is, the multiplier to be applied to the number of bits of the matching length information is 14, the multiplier may be 16. As a result, the multiplication at the time of encoding and the division at the time of decoding need only be a bit shift, and the compression and decompression processes can be further accelerated. Also in this case, it is not necessary to increase the number of bits of identification information, and the amount of data does not increase.

  Further, the fixed-length identification information in this embodiment may be Huffman encoded. Thereby, the data compression rate can be further increased.

  Next, application examples of the data compression method and the decompression method according to this embodiment will be described. FIG. 7 is a schematic configuration diagram of a printing system using the data compression method and the decompression method according to the present embodiment. As shown in FIG. 7, the printing system includes a host computer 3 and a printer 4. A print request is issued from the application 31 of the host computer 3, and the printer driver 32 that receives the print request generates print data and transmits it to the printer 4. In the printer 4, the controller 41 receives the print data, performs predetermined processing, and sends the data to the engine 42. The engine 42 executes printing on a print medium based on the data.

  The printing system is a so-called host-based system and performs up to halftone processing (screen processing) on the host computer 3 side. Accordingly, as shown in FIG. 7, the printer driver 32 includes an image generation unit 33 that generates image data, a color conversion unit 34 that performs color conversion processing, a halftone processing unit 35 that performs halftone processing, and a halftone. A compression unit 36 is provided for compressing the processed print data. Note that these portions can be configured by a driver program showing the contents of each process and a CPU (control device) that executes the process according to the driver program.

  On the other hand, the print data compressed by the host computer 3 is transmitted to the controller 41 of the printer 4 and is provided with a decompression unit 43 for restoring the print data.

  The data compression apparatus 1 and the data restoration apparatus 2 according to the above-described embodiment are used for the compression unit 36 and the decompression unit 43 of the printing system configured as described above, respectively. Accordingly, the compression unit 36 encodes the print data representing the dot image after the halftone process by the method described above. The encoded print data is transmitted to the printer 4 and decoded by the method described in the decompression unit 43.

  In this printing system, the data compression method and restoration method according to this embodiment are used in this way, so that the compression rate of print data can be increased and the transmission time from the host computer 3 to the printer 4 can be shortened. . Accordingly, it is possible to follow the data transmission in the processing by the host computer 3 and the printer 4 which are increased in speed, and the throughput as the printing system can be improved. In particular, since the print data after halftone processing tends to appear repeatedly in the same way as in this application example, it can be said that the present data compression method is suitable for improving the compression rate. For the data after halftone processing, when this compression method is used so that the smaller matching value is selected when the longest matching sequence is the same, the matching position information is an average of 7-8. It has been evaluated that the coincidence length information can be expressed by 2 to 3 bits on the average, and it can be said that the average is about 19 bits for the entire code. Therefore, the data can be shortened as compared with the 23-bit code by the LZSS system (see FIG. 4).

  In addition, there is a demand that the control device (CPU) of the printer 4 does not need to be so fast as compared to the host computer 3 constituted by a personal computer or the like. If the method is used, as described above, the restoration process performed by the printer 4 is facilitated, and the request is met. In addition, in the case of print data after halftone processing, it is suitable for Huffman coding of the identification information, which can further improve the compression rate.

  The protection scope of the present invention is not limited to the above-described embodiment, but covers the invention described in the claims and equivalents thereof.

It is a block diagram concerning the example of an embodiment of a data compression device to which the present invention is applied. It is a block diagram concerning the example of an embodiment of a data restoration device to which the present invention is applied. It is the flowchart which illustrated the content of the process which the encoding part 12 performs. It is a figure for demonstrating the code | symbol etc. which are produced | generated by this data compression apparatus. It is the flowchart which illustrated the content of the process which the decoding part 22 performs. It is the figure which showed the specific example of the process which the data compression apparatus 1 and the data decompression | restoration apparatus 2 perform. It is a schematic block diagram of the printing system using this data compression method and the decompression | restoration method.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Data compression apparatus, 2 Data decompression | restoration apparatus, 3 Host computer, 4 Printer, 11 Input buffer, 12 Encoding part, 13 Dictionary buffer, 21 Input buffer, 22 Decoding part (decoding means), 23 Dictionary buffer (Symbol string storage means) ), 31 application, 32 printer driver, 33 image generation unit, 34 color conversion unit, 35 halftone processing unit, 36 compression unit, 41 controller, 42 engine, 43 decompression unit

Claims (8)

The longest matching sequence that matches the maximum length with the encoding target symbol sequence that exists in the encoded symbol sequence is searched, and the matching position that is the location of the longest matching sequence and the length of the longest matching sequence are searched. A data compression method for encoding data based on a certain matching length and compressing data,
The code generated by the encoding is
A code representing the length of the code representing the matching position and the length of the code representing the matching length;
A code representing the matching position;
A data compression method comprising: a code representing the coincidence length. In claim 1,
The sign representing the matching position is obtained by removing the highest-order 1 when the value representing the matching position is expressed in binary.
The data compression method characterized in that the code representing the matching length is obtained by removing the most significant 1 when the value representing the matching length is expressed in binary. The longest matching sequence that matches the maximum length of the encoding target symbol string that exists in the encoded symbol string is searched, and the matching position that is the position of the longest matching sequence and the length of the longest matching sequence are searched. A data compression method for encoding data based on a certain matching length and compressing data,
When the length of the longest matching sequence is smaller than a predetermined value, the encoding is performed with the first identification information having a predetermined length, representing the fact that it is smaller than the predetermined value and the original symbol,
When the length of the longest match sequence is equal to or greater than the predetermined value, the length of the match position information indicating the match position and the length of the match position information indicating the match position A data compression method, wherein the encoding is performed using second identification information having the same length as the first identification information, the matching position information, and the matching length information. In claim 3,
The matching position information is obtained by removing the highest-order 1 when a value representing the matching position is expressed in binary.
The data compression method according to claim 1, wherein the match length information is obtained by excluding the highest 1 when a value representing the match length is expressed in binary. In claim 3 or claim 4,
The data compression method, wherein the first identification information and / or the second identification information is Huffman encoded. The longest matching sequence that matches the maximum length with the encoding target symbol sequence that exists in the encoded symbol sequence is searched, and the matching position that is the location of the longest matching sequence and the length of the longest matching sequence are searched. A data compression program for causing a computer to execute a process of encoding and compressing data based on a certain matching length,
A first step of determining whether the length of the longest match sequence is equal to or greater than a predetermined value;
In the first step, when it is determined that the length of the longest matching sequence is not greater than or equal to the predetermined value, first identification information having a predetermined length indicating that the length is not equal to or greater than the predetermined value and the original symbol A second step of performing said encoding by:
In the first step, when it is determined that the length of the longest match sequence is not greater than or equal to the predetermined value, the fact that the length is equal to or greater than the predetermined value and the length of the match position information indicating the match position The encoding is performed by second identification information having the same length as the first identification information, the matching position information, and the matching length information, representing the length of the matching length information representing the matching length. A data compression program that causes the computer to execute a third step to be performed. The longest matching sequence that matches the maximum length of the encoding target symbol string that exists in the encoded symbol string is searched, and the matching position that is the position of the longest matching sequence and the length of the longest matching sequence are searched. A data restoration method for restoring encoded data based on a certain matching length,
The data to be restored is
When the length of the longest matching sequence is smaller than a predetermined value, it is encoded with first identification information of a predetermined length, representing the fact that it is smaller than the predetermined value and the original symbol,
When the length of the longest match sequence is equal to or greater than the predetermined value, the length of the match position information indicating the match position and the length of the match position information indicating the match position When encoded by second identification information having the same length as the first identification information, the matching position information, and the matching length information,
A first step of interpreting a code for the predetermined length, which is the length of the first identification information or the second identification information, and determining whether the code is the first identification information or the second identification information When,
In the first step, when it is determined as the first identification information, a second step of decoding into the original symbol included in the first identification information;
In the first step, when it is determined as the second identification information, a third step for obtaining the length of the matching position information and the matching length information based on the second identification information;
A fourth step for obtaining the coincidence position from the code for the length of the coincidence position information obtained in the third step following the second identification information;
A fifth step for obtaining the matching length from the code for the length of the matching length information obtained in the third step, following the matching position information;
A data restoration method comprising: a sixth step of decoding using a decoded symbol string based on the matching position and the matching length obtained in the fourth and fifth steps. The longest matching sequence that matches the maximum length of the encoding target symbol string that exists in the encoded symbol string is searched, and the matching position that is the position of the longest matching sequence and the length of the longest matching sequence are searched. A data restoration device for restoring data encoded based on a certain matching length,
Symbol string storage means for storing the decoded symbol string;
The data to be restored is
When the length of the longest matching sequence is smaller than a predetermined value, it is encoded with first identification information of a predetermined length, representing the fact that it is smaller than the predetermined value and the original symbol,
If the length of the longest match sequence is equal to or greater than the predetermined value, the length of the match position information indicating the match position and the length of the match position information indicating the match position When encoded by second identification information having the same length as the first identification information, the matching position information, and the matching length information,
The code for the predetermined length, which is the length of the first identification information or the second identification information, determines whether the code is the first identification information or the second identification information,
If it is determined to be the first identification information, decode to the original symbol included in the first identification information,
If it is determined to be the second identification information, the length of the matching position information and the matching length information is obtained based on the second identification information, and the obtained matching following the second identification information. From the code for the length of the position information and the code for the length of the determined match length information, determine the match position and the match length, and based on the determined match position and the match length, Decoding means for decoding using the symbol string stored in the symbol string storage means.

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