JPH0969785A - Method and device for data compression - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize effective data compression in the case of taking Japanese- language text data as the compression object. SOLUTION: A correspondence list where code data of specific characters and their compressed code data correspond to each other is prepared, and it is retrieved whether character code data of one character taken out from compression object data exists in the correspondence list or not (S11 and S12). If it exists in the list as the result (S13), its compressed code data is read from the correspondence list and is outputted (S14 and S15); but if it doesn't exist there (S13), data is outputted as it is (S16 and S17).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data compression method and a data compression device used in a data processing device such as a computer that handles digital data.

[0002]

2. Description of the Related Art Conventionally, in a data processing device such as a computer that handles digital data, there is a device that compresses digital data by utilizing the difference in the appearance frequency of data in 1-byte units, such as the Huffman coding method. there were.

In addition to this, there are various methods for compressing data handled by a computer, but these basic methods have been devised in foreign countries and do not utilize the characteristics of Japanese. It was

[0004]

By the way, in Japanese sentences, hiragana, katakana, numbers, alphabets,
Many characters such as punctuation marks are seen. In the case of considering data compression for such characters, the above-mentioned method cannot perform effective data compression because it is a method of performing data compression only by the difference in appearance frequency.

Since the minimum unit of data to be compressed is 1 byte, it cannot be said to be optimal for Japanese text data based on 2 bytes. The present invention has been made in view of the above points, and an object of the present invention is to provide a data compression method and a data compression apparatus that can perform effective data compression when Japanese text data is compressed. And

[0006]

According to the present invention, a correspondence list in which code data of a specific character and its compressed code data are associated with each other is prepared, and when the data to be compressed is present in the above correspondence list. The compressed code data corresponding to the character code data is output, and when it does not exist in the correspondence list, the character code data is output as it is.

According to such a configuration, for example, hiragana,
For characters that appear frequently in Japanese text data such as katakana, numbers, alphabets, and punctuation marks,
By registering the character code data and the compressed code data in the correspondence list, it is possible to perform data compression that makes full use of the characteristics of Japanese.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a data compression apparatus according to an embodiment of the present invention. This device is a system for performing compression processing on digitized Japanese text data, and as a result, transforming it so that the number of output data is smaller than the number of input data. The memory 12 and the auxiliary storage device 13 are mainly configured.

The CPU 11 controls the entire apparatus, and here executes data compression processing. The memory 12 is, for example, a ROM or a RAM, and stores a correspondence list 12a here. Correspondence list 12a
Targets a character having a high appearance frequency in Japanese text data such as hiragana, katakana, numbers, alphabets, and punctuation marks, and associates the character code data with the compressed code data.

The auxiliary storage device 13 is, for example, a floppy disk device (FDD) or a hard disk device (H
DD), in which data to be compressed (data before compression) and data after compression are stored.

FIG. 2 is a correspondence list 12 in the embodiment.
It is a figure which shows the content of a. The correspondence list 12a stores code data of characters that appear frequently in Japanese text data such as hiragana, katakana, numbers, alphabets, and punctuation marks, and corresponding compressed code data. In this example, the character code data is 16 bits,
The compressed code is represented by 8 bits (hexadecimal).

Next, the operation of the embodiment will be described. FIG.
3 is a flowchart showing an operation of data compression processing in the same embodiment. The CPU 11 first extracts character code data for one character (2 bytes) from the compression target data stored in the auxiliary storage device 13 or the like (step S11).

Next, the CPU 11 accesses the correspondence list 12a stored in the memory 12 and searches for the extracted character code data in the correspondence list 12a (step S12).

If the character code data is present in the correspondence list 12a (Yes in step S13).
s), the compressed code data will be output. At that time, the CPU 11 outputs 1-bit information "1" indicating that the data is compressed code data (step S14),
Next, the compressed code data corresponding to the character code data is read out from the correspondence list 12a and is output (step S15).

On the other hand, if the character code data does not exist in the correspondence list 12a (No in step S13), the character code data is output without being compressed. At that time, the CPU 11 outputs 1-bit information "0" indicating that the character code data is not the compressed code data (step S16), then reads the compressed code data corresponding to the character code data from the correspondence list 12a, This is output (step S17).

Thereafter, similarly, the character code data is sequentially extracted from the data to be compressed, and the character code data is appropriately compressed while being compared with the correspondence list 12a and output (steps S18 and S19). As a result, the correspondence list 12
The character code data existing in a can be compressed and output.

Here, the above-mentioned processing will be described concretely. For example, if it is assumed in step S11 or S18 that the character code data of the katakana "A" is extracted from the compression target data, the process is S12 → S13 → S1.
4 → S15.

The 1-bit information indicating the compressed code is "1".
Then, "1" is output in step S14, and "92" (hexadecimal) is output in step S15. When the data output in steps S14 and S15 is represented by a binary number, as shown in FIG.
0 ".

Further, for example, step S11 or S18
Assuming that the character code data of the Chinese character "A" is extracted from the compression target data, the process is S12 →
The process proceeds from S13 → S16 → S17.

Assuming that the 1-bit information indicating that the code is not a compressed code is "0", "0" is output in step S16 and "3021" (hexadecimal) is output in step S17. When the data output in steps S16 and S17 is represented by a binary number, as shown in FIG.
01100000000010 ”.

In this way, when the code data of a character having a high appearance frequency is registered in advance in the correspondence list 12a in units of Japanese characters (16 bits), and the compression target data exists in the correspondence list 12a. Then, this is replaced with 8 bits and output. Thus, for example, when there is character string data such as “data handled by computer” as shown in FIG. 5, it is possible to reduce the data of 192 bits before compression to 116 bits after compression and output the data.

[0022]

As described above, according to the present invention, the character code data existing in the correspondence list is replaced with the compressed code data and is output. Therefore, for example, Japanese characters such as hiragana, katakana, numbers, alphabets and punctuation marks are used. If the character code data and the compression code data are registered in the correspondence list for the characters having a high appearance frequency in the text data, the data compression that makes the best use of the characteristics of Japanese can be performed.

In this case, basically, unlike the adaptive compression method such as the LZ method, since the data that has appeared before is not used, the data can be compressed even if the target data is short. Also, unlike the static Huffman coding, since the correspondence list is not output, the compression rate can be increased. Further, unlike the Huffman coding, there is no need for the process of calculating the appearance frequency of the data, so that the processing speed can be increased.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a data compression device according to an embodiment of the present invention.

FIG. 2 is a view showing the contents of a correspondence list in the same embodiment.

FIG. 3 is a flowchart showing an operation of data compression processing in the same embodiment.

FIG. 4 is a view for explaining the shape of a compressed code in the same embodiment.

FIG. 5 is a diagram showing a result of data compression in the same embodiment.

[Explanation of symbols]

 11 ... CPU, 12 ... Memory, 12a ... Correspondence list, 13 ... Auxiliary storage device.

Claims (4)

[Claims] 1. A correspondence list in which code data of a specific character and its compression code data are associated with each other, and it is determined whether or not the compression target data exists in the correspondence list, and the compression target data is If it exists in the above correspondence table, the compression code data corresponding to that character code is taken out from the above correspondence list and output. If the data to be compressed does not exist in the above correspondence table, that character code A data compression method characterized by outputting data as it is. 2. The data compression method according to claim 1, wherein the information for identifying whether or not the output data is compressed data is output prior to the output data. 3. Storage means for storing a correspondence list in which code data of a specific character and its compressed code data are associated with each other, and whether the compression target data exists in the correspondence list stored in the storage means. And a determination means for determining whether or not the compression target data is present in the correspondence list by the determination means, and the compression code data corresponding to the character code is extracted from the correspondence list and output. If the data to be compressed does not exist in the correspondence list, the data compression device is provided with an output unit that outputs the character code data as it is. 4. The data compression apparatus according to claim 3, wherein the output means outputs information for identifying whether or not the output data is compressed data, prior to the output data.