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AssigneeMatsushita Electric Industrial Co., Ltd.
InventorChoong Seng Boon
Estimating the term…
In an image coding method of the present invention, after a process such as DCT is performed to digital image data, quantization process is performed, and then, to resultant quantized transform coefficients, variable length coding process is performed with reference to a variable length code table showing how variable length codes are allocated, and in a comparison process between an event derived from the quantized transform coefficients and a reference event included in the variable length code table, transformation process is performed to increase a possibility of performing variable length coding with satisfactory coding efficiency.
An image coding method in which variable length coding process is performed to the transform coefficients by referring to a variable length code table comprising a plurality of reference events, consisting of Last, Run, Level, paired with reference variable length codes wherein the variable length coding process comprises:
An image coding method in which variable length coding process is performed to transform coefficient by referring to a variable length code table comprising a plurality of reference events, consisting of Last, Run, Level, paired with reference variable length codes, wherein the variable length coding process comprises:
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Compression ; Expansion; Suppression of unnecessary data, e.g. redundancy reduction: conversion to or from variable length codes, e.g.…
Conversion to or from variable length codes, e.g. Shannon-Fano code, Huffman code, Morse code: using table look-up for the coding or decoding…
Using table look-up for the coding or decoding process, e.g. using read-only memory: for the decoding process only
Compression ; Expansion; Suppression of unnecessary data, e.g. redundancy reduction: conversion to or from run-length codes, i.e. by representing…
Term ended 13 Nov 2020 (estimated)
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The present invention relates to image coding and decoding methods, image coding and decoding apparatuses, and recording media for image coding and decoding programs, more specifically, to an image coding process in which a variable coding of high versatility is performed and an image decoding process performed to the result of this image coding.
Compression coding is essential for efficiently storing or transmitting a digital image. As a method of compressively coding a digital image, used is discrete cosine transformation (DCT) that is a dominant technology in typical standards like JPEG (Joint Photographic Experts Group) and MPEG (Moving Picture Experts Group); In addition, waveform coding methods such as subband coding, wavelet transformation, and fractal are also used as the coding methods as well. To remove redundant signals between images, intra-frame coding is basically preformed based on a spatial correlation within one still image; in addition to this, inter-image coding is also performed in which inter-image prediction using motion compensation is performed based on a temporal correlation between each set of adjacent still images, and a difference signal obtained is subjected to waveform coding. Use of the both methods makes it possible to obtain coded data with a high compression ratio.
In the conventional image coding process according to the MPEG standard or the like, after the DCT process or the like, quantization process is performed, followed by variable length coding process. More specifically, a process such as DCT, subband, or wavelet is performed to digital image data, and the transform coefficients obtained by the above process are quantized using a prescribed quantization scale to generate quantized transform coefficients to which variable length coding process is to be performed.
FIG. 1 is a flowchart illustrating the procedure of a variable length coding method according to a first embodiment of the present invention.
FIG. 2 is a block diagram illustrating the configuration of an image coding apparatus according to the same embodiment.
FIGS. 3(a)-3(b) are explanatory diagrams illustrating examples of a code transformed by the variable length coding method according to the same embodiment.
An image coding method according to a first embodiment of the present invention is intended to increase chances of using a variable length code table by performing transformation process to events which are objects to be coded, thereby improving coding efficiency.
FIG. 1 is a flowchart showing the procedure of a variable length coding method according to the first embodiment of the present invention. Further, FIG. 2 is a block diagram illustrating the configuration of an image coding apparatus performing the variable length coding process according to the first embodiment, and FIG. 3 are diagrams showing examples of the result of the variable length coding.
Initially, a description is given of the image coding apparatus according to the first embodiment, using FIG. 2. As shown in the figure, the image coding apparatus according to the first embodiment comprises: a first adder 202, a coder 203, a second adder 210, a variable length coder (VLC) 211, a frame memory (FM) 213, a motion extractor (ME) 214, and a motion compensator (MC) 215, and it receives from an input terminal 201 digital image data which is an object of coding process and outputs from an output terminal 206 the coded data which is the output of the image coding apparatus. The coder 203 contains a discrete cosine transformation unit (DCT) 204 and a quantizer (Q) 205, and the decoder 207 also contains an inverse quantizer (IQ) 208 and an inverse discrete cosine transformation unit (IDCT) 209.