Image coding apparatus, image decoding apparatus, image coding method, and image decoding method

Abstract

An input image signal is divided into MC block units and, when coding processing is performed in these divided units, a motion compensation section generates a motion-compensated prediction image by detecting movement amounts in predetermined MC block units, a smoothing filter section performs, with respect to the prediction image, smoothing of pixels located at the boundaries of adjoining MC blocks on the basis of predetermined evaluation criteria, and a prediction residual signal, which is obtained from the difference between the prediction image obtained by the smoothing, and the input image signal, is encoded.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is a continuation of U.S. application Ser. No. 10 / 480,642, filed Dec. 24, 2003, the entire contents of which is incorporated by reference. U.S. application Ser. No. 10 / 480,642 is a national phase application of PCT / JP02 / 00614 under 35 U.S.C §371, filed Jun. 28, 2002, which claims priority to the Japanese Patent Application JP 2001-199685, filed on Jun. 29, 2001.TECHNICAL FIELD[0002]The present invention relates to an image coding apparatus, an image decoding apparatus, an image coding method, and an image decoding method that perform the transmission and storage of images with a small encoding data volume and that are applied to a mobile image transmission system or similar.BACKGROUND ART[0003]Conventional image coding systems are constituted to divide image frames into blocks of a fixed size and then perform coding processing in these divided units. Typical examples of conventional image coding systems include the MPEG (...

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Benefits of technology

[0024]The present invention was conceived in view of these problems, an object thereof being to provide an image coding apparatus, image decoding apparatus, image coding method, and image decoding method that make it possible to use relatively simple computation to perform processing, with respect to a prediction frame image generated by block-based motion-compensated interframe prediction (MC), to adaptively smooth a discontinuous waveform generated between MC blocks of the prediction frame image, whereby the efficiency of low bit rate coding that employs interframe MC can be improved.

[0029]According to this constitution, smoothing is performed for pixels located at the boundaries of adjoining partial image regions on the basis of predetermined evaluation criteria, with respect to the prediction image, and it is therefore possible to perform correction in the direction in which only the smoothing processing, that corrects discontinuity in partial image regions, is allowed. It is therefore possible to improve the coding efficiency by suppressing discontinuous waveforms generated in the prediction residual. Accordingly, it is possible to use relatively straightforward computation to perform processing, with respect to a prediction frame image generated by block-unit motion-compensated interframe prediction (MC), to adaptively smooth a discontinuous waveform generated between MC blocks of the prediction frame image, whereby the efficiency of low bit rate coding that employs interframe MC can be improved.

Problems solved by technology

However, when coding is carried out with a high compression ratio, a satisfactory rendition of the residual signal is not possible and the discontinuous boundaries are sometimes apparent and perceived as distortion.

Further, it has been identified that, because the DCT is also a closed orthogonal transform in fixed blocks, in cases where the transform basis coefficients are reduced as a result of coarse quantization, the signal waveform which naturally connects between blocks cannot be reconstituted and unnatural distortion is generated between blocks (block distortion).

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