Variable length coding method and variable length decoding method

Abstract

According to the present invention, an image coding apparatus (103) that encodes quantized coefficients corresponding to an image signal as target data to be processed is provided with a run-length encoding unit (RLE2) that assigns variable length codes to the quantized coefficients using code tables. The run-length encoding unit (RLE2) forms a second code table by optimizing a first code table to the target data to be processed, and selects one of the first and the second code tables as a code table that is to be employed for the assignment of the variable length codes in accordance with a quantization parameter (QP) or a variable length coding selection signal (VlcSel), whereby redundancy of information included in the target data to be processed can be effectively eliminated, and the compression ratio for the image signal or the like can be further increased.

Description

TECHNICAL FIELD [0001] The present invention relates to a variable length coding method and a variable length decoding method and, more particularly, to a method for converting plural coefficients which are obtained by quantizing frequency components of image data (quantization coefficients) into coded data according to a variable length coding process, and a method for decoding the coded data according to a variable length decoding process to reconstitute plural coefficients. BACKGROUND ART [0002] In recent years, we have entered the age of multimedia in which audio, video, and other data are integrally handled, and conventional information media (i.e., means for transmitting information to persons), such as newspapers, magazines, televisions, radios, and telephones have been adopted as subjects of multimedia. Generally, “multimedia” means to represent not only characters but also diagrams, speeches and especially images simultaneously in relation with each other. In order to handl...

AI Technical Summary

Benefits of technology

[0151] As described above, according to the present invention, there is provided a variable length coding method for coding coefficient data which is composed of plural coefficients including: a coding step for subjecting the respective coefficients to a coding process of transforming the coefficient data into coded data which is composed of plural codes, by using plural code tables that indicate correspondences between numerical information representing the values of the coefficients and codes, and this coding step includes: a code table selection step for selecting one of the code tables in accordance with at least one of information about a processed coefficient which has been subjected to the coding process and a parameter relating to generation of the coefficients; and a code assignment step for assigning a code to an uncoded coefficient which has not yet been subjected to the coding process, using the selected code table. Therefore, redundant information included in coefficient data which are to be subjected to the variable length coding process is effectively eliminated by selection of a code table according to characteristics of coefficients that constitute the coefficient data or states of a coding process for the coefficients, thereby greatly increasing a coding efficiency of the variable length coding process for image signals or the like.

[0202] According to the present invention, there is provided a storage medium that contains a program that makes a computer execute a variable length decoding process for decoding coded data that is composed of plural codes, obtained by performing variable length coding to coefficient data that is composed of plural coefficients, and this program includes a decoding step for subjecting the respective codes to a decoding process of decoding the coded data to reconstitute the coefficient data which is composed of the plural coefficients, using plural code tables indicating correspondences between numerical information representing the values of the coefficients and the codes, and further this decoding step includes: a code table selection step for selecting one of the code tables in accordance with at least one of information about already-processed coefficients which have been subjected to the decoding process and a parameter relating to generation of the coefficients; and a value detection step for detecting numerical information corresponding to an undecoded code which has not yet been subjected to the decoding process, by using the selected code table. Therefore, a variable length decoding process corresponding to a variable length coding process having a higher coding efficiency, which can effectively eliminate redundant information included in coefficient data by switching code tables to encode the coefficient data can be implemented by software.BRIEF DESCRIPTION OF THE DRAWINGS

Problems solved by technology

So, as for the information media described above, it is not practical to handle such massive data as it is in the digital format.

For example, picturephones have already been put to practical use by ISDN (Integrated Services Digital Network) having a transmission rate of 64 kbps˜1.5 Mbps, but it is impossible to transmit an output image of a television camera having a large quantity of data as it is by the ISDN.

In the variable length coding process by the coding unit, redundant information included in the quantized coefficient (data to be processed) cannot be removed sufficiently and, thus, the compression rate is susceptible to improvement.

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