JPH04145726A - Data compression and restoring system - Google Patents

Abstract

PURPOSE:To improve the compression rate of data compression of an LZW code by registering plural character strings in advance in a dictionary while taking the frequency of use of character strings into account and using the dictionary so as to apply compression and decoding. CONSTITUTION:A CPU 12 based on an initial registration software 24 gives a registration number to each of one character of a font being a processing object and registers the result to a dictionary 10 initially. Moreover, registration numbers 4-12 are given to character strings consisting of 2-10 characters with high frequency of use and the result is registered initially in the dictionary 10. When the initial registration is finished, a desired input data or code data is stored in a data buffer 28 of a data memory 26 and encoding processing by an encoding software 20 or decoding processing based on a decoding software 22 is implemented. Thus, registration numbers are assigned at the initializing of the dictionary depending on number of character strings and when a character string registered is in use, the registration number is used for the compression processing to attain high compression.

Description

[Detailed description of the invention] [Summary] Sign ratio adjacent data is divided into different substrings and registered in a dictionary, and the input data is specified by the registration number of the substring that matches the maximum length among the substrings in the dictionary. LZW is a type of universal encoding that encodes code words and decodes them using a dictionary.
Regarding data compression and decompression methods using codes, the purpose is to increase the compression rate through initial registration in dictionaries. configure for initial registration.

[Field of Industrial Application] The present invention relates to a data compression and decompression method using an LZW code, which is known as an improved incremental decomposition type of universal code.

In recent years, computers have come to handle various types of data such as character codes, vector information, and single images.
The amount of data handled is also rapidly increasing. When handling large amounts of data, by compressing the amount of data by eliminating redundant parts, you can reduce storage capacity and speed up transmission.

Universal encoding has been proposed as a method that can compress various data using one method.

Here, the field of the present invention is not limited to character code compression.
Although it can be applied to a variety of data, in the following we will follow the nomenclature used in information theory, and refer to a single word unit of data as a character, and a string of arbitrary words of data. .

ZlvLem is a typical method for universal codes.
There is a pel (Jibou Lempel) code (for details, for example, Munakata j2iy-Lempel data compression method",
Information processing, VOl, 26. No, 1. ! 98
5 years (see Noko and).

In ziv-Lempel code, there are two types: ■Universal type and ■Incremental parsin type.
Two algorithms have been proposed: g).

Furthermore, as an improvement of the universal algorithm, L
There is a ZSS code (T, C, Be1l, 'Better
OPM/L Text Compression,
IEEE Trans, ellComman,,
Vol, C0M-34, NO, I2. 05C,1
986).

Moreover, as an improvement of the incremental decomposition type algorithm, L Z
There is a W (Lempe14iv-Welch) code (
T, ^, Wech,'^Technique for
Hlgb-Performance Data
C.

mp+esion'', Computer, Jun
e 1984).

Among these codes, the LZW code has come to be used for file compression in storage devices because of its high-speed processing capability and simple algorithm.

[Prior Art] A conventional LZW code encoding algorithm is shown in FIG. 8, and a decoding algorithm is shown in FIG. 9.

LZW encoding has a rewritable dictionary, divides the input character code data into different character strings, numbers these character strings in the order of appearance, and registers them in the dictionary.
The currently input character string is registered in the dictionary, represented by the number of the longest-dispersed character string, and encoded.

In the LZW encoding process shown in FIG. 8, first, in step SL (hereinafter "step" is omitted), a character string consisting of one character for each character is registered in the dictionary as an initial value, and then encoding is started. In addition, in Sl, the dictionary is searched using the input first character K to find the reference number ω, and this is added to the initial character string (p+
eliXstring).

Next, the next character K of the input data is read in 82, and after checking whether character input is completed in S3, the process proceeds to S4, and the character K read in S2 is added to the initial character string ω determined in Sl. Search whether the added character string ωK exists in the dictionary.

If the character string ωK is not in the dictionary in S4, proceed to S6 and select Sl.
The reference number ω for the character found in is the code word code (ω)
, and adds a new reference number to the character string (ωK) and registers it in the dictionary.Furthermore, replaces the input character K of 82 with the reference number ω, increments the dictionary address n, and returns to S2 for the next Read the letter K.

On the other hand, if the character string (ωK) is found in the dictionary in S4, the character string (ωK) is replaced with the reference number ω in S5, and the process returns to S2 to search for the maximum match length until the character string (ωK) cannot be found in the dictionary. Continue.

LZW encoding will be specifically explained as follows with reference to FIG. 10.11.

First, the input data INPUT in FIG. 10 is read from left to right. When you enter the first letter a, there are no matching strings in the dictionary other than the letter a, so 0UTPUT C0D
Output EI (reference number ω) as a code word. Then, let the character a be a new word initial character string ω.

Next, the second character S is input, and since =ab is not found in the dictionary in the character string ω obtained by adding this input character S to the initial character string ω, the character S 0UTPUT C0DE2 is output as a code word. Then, reference number 4 is added to the expanded character string ab and it is registered in the dictionary. The actual registration is in the form of a character string 1b as shown on the right side of FIG. The second input character becomes a new initial character string ω.

If you then input the third character a, the input character a
= ba = 2a is not in the dictionary, so the extended character string ω is obtained by adding the initial character string ω to the character string ω, so the character 0UTPUT C0DE
After outputting 2 as a code word, = ba is added to the extended character string ω.
is represented by 2a, and is registered in the dictionary with reference number 5.

The third input character a becomes the new initial character string ω.

For the fourth input character S, = ab is already registered in the dictionary as code word 4 in the extended character string ω, so the character string ωK is set as a new initial character string ω, and the fifth character C is input. and create =4c=abc in the extended character string ω. Since =abc is not registered in the dictionary for this extended character string ω,
0UTP of character string ab = 1b [IT C0DE 4 is output as a code word, and = abc is 4 in the dictionary for expanded character string ω.
Register with reference number 6 in the form of 0. This process continues in the same manner.

The decoding process shown in FIG. 9 performs the reverse operation of the encoding process shown in FIG. 8.

In the decoding shown in FIG. 9, similarly to encoding, a character string consisting of one character for each character is registered in the dictionary as an initial value, and then decoding is started.

First, read the first code (reference number) with Sl, set the current C0DE to 0LDcode, and since the first code corresponds to one of the single-character reference numbers already registered in the dictionary, the character code that matches the input code C0DH (K)
Find out and output the letter K. Note that the output characters (
K) is set to FINchar for later exception handling.

Next, go to 82, read the next code, and input it to C0DE.
Set as code. In S3, it is checked whether there is a new code, that is, whether the code input has ended, and then S3 is executed.
Proceeding to step 4, it is checked whether the code C0DE input in step S3 is defined (registered) in the dictionary. Normally, the input code word has been registered in the dictionary in the previous processing, so the process proceeds to S5 and the character string Code corresponding to the code C0DE is entered.
(ωK) is read from the dictionary, the character string K is temporarily stacked in S6, and the reference number code (ω) is added to the new C
Return to S5 again as 0DE, and this S5. The procedure in S6 is recursively repeated until the reference number ω reaches one character, and finally, the process advances to S7 and the stacked characters in S6 are L i L
Pop up and output in O (Lasj InFxst 0ut) format. At the same time, at 87, the code ω used last time is combined with the first character K of the character string restored this time (ω,
Add a new reference number to the character string expressed as K) and register it in the dictionary.

The decoding process will be explained in detail with reference to FIG. 12 as follows.

First, in Fig. 12, the first input code is 1, and the character a,
Since b and c have already been registered in the dictionary as reference numbers 1, 2, and 3 as shown in Table 2, they are replaced by the character string a with the reference number matching 1 by reference to the dictionary and output. Similarly, the next code 2 is replaced with a letter S and output. At this time, 1b (=
ab) is added with a new reference number 4 and registered in the dictionary.

The third code 4 replaces 1b with ab by searching the dictionary and outputs the character string ab. At the same time, a character string 2a (=ba), which is a combination of the previously processed code 2 and the first character a of the currently decoded character string, is added with a new reference number 5 and registered in the dictionary.

This process is repeated in the same manner.

The decoding shown in FIG. 12 involves the following exception handling.

This exception handling occurs in the decoding of the sixth input code 8. Code 8 is not defined in the dictionary at the time of decoding and cannot be decoded. In this case, a character string 5b is obtained by adding the first character of the previously decoded character string ba to the previously processed code 5, and then 2ab.

It is replaced with bab and output. Then, a reference number 8 is added to a character string 5b obtained by adding the characters of the character string just decoded to the previous code word 5 to the output word of the character string, and the result is registered in the dictionary.

This exception handling is performed at 84 and S8 in the decoding process flow in FIG.
Finally, in S7, the character string is output, a reference number is added to the new character string, and the new character string is registered in the dictionary.
It will be held in

Note that the encoding/decoding process in FIG. 8.9 is performed while creating the same dictionary.

[Problems to be Solved by the Invention] In the conventional LZW code, data that has appeared in the past is registered in a dictionary, and the registered information is used to perform compression. However, it cannot be asserted that registering all data that has appeared in the past in a dictionary is an effective dictionary registration method. For example, in the case of image data, it is known that all-white and all-black patterns appear frequently1, and if these data are registered sequentially, a high compression rate cannot be obtained unless the dictionary registration progresses to a certain extent. I have a problem where I can't.

The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a data compression and restoration method using an LZW code that can increase the compression rate through initial dictionary registration.

[Means to solve the problem] FIG. 1 is a diagram explaining the principle of the present invention.

First, the present invention divides encoded data into different sub-sequences, registers these sub-sequences in the dictionary 10, and inputs the input data using the registration number of the sub-sequence in the dictionary 10 that has the maximum length. LZ equipped with encoding means 100 for specifying and encoding
The target is a data compression method using W code.

Regarding such a data compression method, in the present invention, 1
The present invention is characterized in that a registration number is previously assigned to a set of character strings consisting of characters or more, and initial registration is made in a dictionary 10, and input data is compressed and encoded by an encoding means 100 using the dictionary 10.

Specifically, registration numbers are assigned in advance to character strings that include characters that appear frequently in the data to be compressed, and
Initial registration is 0. Also, in the data to be compressed, 1
A string of consecutive characters, such as aa, aaa, aa
A registration number is assigned in advance to aa, aaaaa, etc., and initial registration is made in the dictionary 1o.

Furthermore, the present invention divides the encoded data into different subsequences, registers these subsequences in the dictionary 10, and inputs the input data with the registration number of the subsequence in the dictionary 10 that has the maximum length. The present invention is directed to a data restoration method that includes a decoding means 200 that uses a dictionary 10 to restore a designated encoded code word to original data.

In the present invention, such a data restoration method also assigns a registration number to a set of character strings consisting of one or more characters and registers them initially in the dictionary 10. 200 to restore input data.

For this decoding as well, registration numbers are assigned in advance to character strings that include characters that appear frequently in the data to be compressed, and are initially registered in the dictionary 10.

Also, in the data to be compressed, character strings containing multiple consecutive characters, such as a a, a a a, a a
a a.

A registration number is assigned in advance to aaaaa, etc., and initial registration is made in the dictionary 10.

[Operation] According to the data compression and decompression method of the present invention having such a configuration, character strings with a high frequency of appearance, for example, character strings in which the same characters are consecutive, are registered in advance according to the number at the time of initializing the dictionary. If a registered character string λ is assigned to a number and a registered character string λ appears, high compression can be achieved by performing compression processing using the registration number.

[Embodiment] FIG. 2 is a block diagram showing an embodiment of the present invention.

In FIG. 2, 12 is a CPU as a control means, and a program memory 14 and a data memory 26 are connected to the CPU 12.

The program memory 14 contains control software 16, L
A maximum match length search software 18 that performs a maximum match length search using a ZW code, an encoding software 20 that converts an input character string to an LZW code, and a code converted to an LZW code by the encoding software 20 to the original character string. In addition to the decoding software 22 to be restored and each character to be processed, frequently used character strings λ, for example, in this embodiment, each character string λ consisting of 2 to 15 consecutive characters a is used as the character string λ. Initial registration software 24 is provided for initial registration by attaching a registration number to a character string.

On the other hand, the data memory 26 includes a data buffer 28 for storing a character string to be encoded or a code string to be decoded, and a data buffer 28 for storing a character string to be encoded or a code string to be decoded. It is equipped with a dictionary 10 that can be used while

The initial registration of the dictionary according to the present invention in the embodiment of FIG. 2 is performed as follows.

First, the CPU 12 starts the initial registration software 24 under the control of the control software 16 to perform initial registration of the dictionary 10. That is, the CPU 12 uses the initial registration software 24.
Based on this, each character in the character type to be processed is assigned a registration number (reference number) and initially registered in the dictionary 10.

To simplify the explanation, we will use a and b as processing targets.

Considering the three letters C, the reference numbers 1, 2, and 3 are added to the letter a as shown in the dictionary structure explanatory diagram of FIG.

b and c are initially registered.

In addition, in the present invention, character strings consisting of 2 to 10 consecutive characters a are used as frequently occurring character strings λ, as shown in the dictionary structure of FIG. 5, such as aa, aaa, ".
Add registration numbers 4 to 12 to aaaaaaaaaa and initially register it in the dictionary. In addition, in FIG. 5, aX2. aX3.
・Dispute・It is shown as a×10.

Once the initial registration for such dictionary 10 is completed,
Desired input data or encoded data is stored in the data buffer 28 of the data memory 26, and the encoding software 2
Encoding processing based on 0 or decoding processing based on decoding software 22 is performed.

The encoding algorithm of the LZW code according to the present invention is shown in FIG. 3, and the decoding algorithm is shown in FIG.

To explain the encoding of the LZW code shown in Figure 3 using the input characters shown in Figure 5, first, in addition to the initial registration in which character code i is registered one character at a time to dictionary address i in Sl, A character is assumed to be λ, and not only one character λ but also a plurality of character strings are registered in the dictionary according to the number of λ. For example, in the example of the dictionary structure shown in FIG. 6 which targets the characters a, b, and c, each of consecutive character strings from 1 to 10 characters a is registered.

Once the initial registration of Sl has been completed, processing for a case where a plurality of initially registered characters λ are consecutive is performed by processing in S2 to S7. That is, in S3, = λ is determined, and in S4, the λ counter indicating the number of consecutive characters λ is incremented by one, and the process is repeated until the input character K is not the character λ.
Since the th input character a is the character λ, S3 to 8
Proceed to step 4 and increment the λ counter by one. Since the next input character is not a character λ, the process advances to 85, and since the λ counter = 1 at this time, the process advances to 86, where the value of the λ counter is output as the code code C0DE (λ) = C0DE2, and in S7, the second Let the characters inputted in ``S'' be a new initial character string ω.

Next 88, S9, SLl, 812. S13 and 822 are the same as the conventional LZW encoding process shown in FIG.
The symbols in FIG. 8 are shown in parentheses.

During such LZW encoding processing, which is the same as in the conventional S, the present invention newly branches from SIO and processes 814 to S21.
Processing for the character λ with high frequency of appearance is included.

Specifically, after the second character inputted in S7 is set as the initial character string ω, the third character a is read in S8, and =λ is determined in S10 via S9, and the processing in S14 is performed. Proceed to.

In S14, the initial character string ω=b at that time is output as the code code C0DE (ω) =C0DE2, and then the λ counter is incremented by one in S15.
Read the next character at 6, then go to S19 via 318 =λ
In this case, since the character S is not λ, 32
0, code(λ) = codel is output as the code, and after resetting λ=0, the process returns to S7.

On the other hand, from the 13th input character in Figure 5, there are seven consecutive characters a as λ, so in this case, 815
By repeating the process of ~19, the count value of the λ counter λ=
7 is obtained, and in S20, code
9 will be output.

Here, in the case of a character string in which 10 or more characters a are consecutive, for example, in the case where 15 characters a are consecutive, it is expressed using a two-code code with reference number 12.7.

In addition, in the data encoding system of the present invention, if a character corresponding to λ appears during encoding processing, the character string ω up to that point is output as a code code in S14, and the character string ω is registered in the dictionary with =ωλ. will not be carried out.

Next, the decoding process according to the present invention shown in FIG. 4 will be explained.

In the decoding process of FIG. 4, 5l-S4. S8 and S
9 is provided to decode the code indicating the consecutive number of characters λ that appear frequently, and the other processing is the same as the conventional decoding processing shown in Fig. 9. indicates the correspondence relationship.

Taking as an example the case of decoding the input code shown in FIG. 7, decoding up to the 12th code is the same as the conventional decoding. However, for the code code S
4 or S9, one λ=a is output.

Regarding the 13th code code 9 in FIG. 7, it is determined in S8 that it is a λ code, and the process proceeds to S9.
By referencing the dictionary using the code code value 9, seven characters a are output.

In the above embodiment, a character string in which multiple identical characters are consecutive is taken as an example of a character string to be initially registered, but the present invention is not limited to this, and character strings that appear frequently If so, an appropriate character string may be initially registered.

[Effects of the Invention] As explained above, according to the present invention, a character string expressing a plurality of numbers is registered in advance in a dictionary in consideration of the frequency of use of the character string, and the dictionary is used to compress the string. By performing restoration, the compression rate of data compression using the LZW code can be made even higher.

[Brief explanation of drawings]

Fig. 1 is a diagram explaining the principle of the present invention; Fig. 2 is a configuration diagram of an embodiment of the present invention; Fig. 3 is a processing flow diagram of LZW code encoding according to the present invention; Fig. 4 is a diagram showing the encoding process of LZW code according to the present invention Decoding processing flow diagram; Figure 5 is an explanatory diagram of LZW code encoding according to the present invention; Figure 6
Figure 7 is an explanatory diagram of the dictionary configuration according to the present invention; Figure 7 is an explanatory diagram of LZW code restoration according to the present invention; Figure 8 is a flowchart of a conventional LZW encoding process; Figure 9 is a flowchart of a conventional LZW decoding process; Fig. 10 is an explanatory diagram of conventional LZW encoding; Fig. 11 is an explanatory diagram of a conventional dictionary configuration example; Fig. 12 is an explanatory diagram of conventional LZW encoding.
It is a decoding explanatory diagram. In the figure, 10: Dictionary 12 2 CPU 14 Niprogram memory 16: Control software 18: Maximum-growth search software 20: Encoding software 22: Decoding software 24: Initial registration software 26/data memory 28: Data buffer 100: Encoding means 200: decoding means Moku Umei's Kairi Kamei Diagram 1 Figure 2 Book's LZW Kaifang 10 Bar King! 70-mouth Fig. 8 Explanation of restoration of the ZW code according to the present invention Fig. 7 Prompt nLAW attached now Kffi Sekimeien Fig. 10 Sunhe's insulating tube 11 ηf1 Noro i1 circle Fig. 11 is the internal LZW Kffi Therefore Mingkou Figure 12

Claims (6)

[Claims] (1) Divide the encoded data into different subsequences, register the subsequences in the dictionary (10), and input the input data to the subsequence with the maximum length matching among the subsequences in the dictionary (10). In a data compression method equipped with an encoding means (100) that specifies and encodes with a registration number, a registration number is assigned in advance to a set of character strings consisting of one or more characters, and initial registration is made in the dictionary (10). Then, select the corresponding dictionary (1
0) is used to compress and encode input data by the encoding means (100). (2) In the data compression method according to claim 1, a registration number is assigned in advance to a character string including characters that appear frequently in the data to be compressed, and the character string is initially registered in the dictionary (10). data compression method. (3) The data compression method according to claim 1, characterized in that in the data to be compressed, a character string containing a plurality of consecutive characters is assigned a registration number in advance and is initially registered in the dictionary (10). Data compression method. (4) Divide the encoded data into different subsequences, register the subsequences in the dictionary (10), and input the input data to the subsequence with the maximum length matching among the subsequences in the dictionary (10). The code word specified by the registration number and encoded is stored in the dictionary (10).
decryption means (200) for restoring the original data using
In a data restoration method equipped with the dictionary (10
), and the input data is restored by the decoding means (100) using the dictionary (10). (5) In the data restoration method according to claim 1, a registration number is assigned in advance to a character string including characters that appear frequently in the data to be compressed, and the character string is initially registered in the dictionary (10). Data recovery method. (6) In the data restoration method according to claim 1, a registration number is assigned in advance to a string of consecutive single characters in the data to be compressed, and the string is initially registered in the dictionary (10). Data recovery method.