Arnaud Bourge

Spatial and temporal filtering in a low-cost MPEG bit rate transcoder

The MPEG bit-rate transcoder with motion compensation, MC-BRT, that exactly derives from a simplified synchronized decoder/encoder cascade, is considered. Such a transcoder is cost effective but lacks features such as spatial and temporal filtering. These features are known to improve the encoder performance at low bit-rates. Such features would be highly desirable in the MC-BRT since most applications now involve critical bit-rates. This paper shows that spatial and motion compensated temporal filtering can be implemented in the MC-BRT at a negligible cost. The filters are analyzed and control variables are given. Simulations reveal the efficiency of the method in terms of noise reduction as well as its great impact on image quality.

Low-resolution optimized 3D-subband scalable codec

Today, 3D subband (3DS) video coding schemes are close to current standard solutions in terms of coding efficiency while they add the scalability functionality through embedded bitstreams. Spatial scalability may be regarded as a key-feature brought by such codecs, enabling adaptation to varying terminal capabilities and display sizes. However, this functionality still suffers from a lack of coding efficiency when motion compensation is used. Though enabling motion compensation at the temporal filtering stage dramatically improves energy compaction, it generates a strong motion vector overhead and introduces a reconstruction drift when decoding at lower spatial resolutions. This is because the Discrete Wavelet Transform and the motion compensation (MC) are not commutative. Some authors solve this problem by transmitting the drift signal as side information, but this increases the bit-rate. In this paper we present a low-resolution optimized MC-3DS scalable codec with no drift, that does not generate any overhead. Its structure is fully compliant with any subband-tree entropy encoder and preserves all the other scalability functions (temporal and SNR). Tests and simulations show that the new scheme remains quite efficient when decoding at full resolution, while it outperforms the previous solution as far as spatial scalability is concerned, especially with high-activity sequences.