Signal-adapted transform coding of sequences

In standard DCT coding schemes like MPEG, the sequences compression is achieved by motion compensation, transformation, quantization and entropy coding. In this paper, we have followed the same path by adapting to the image signal the elements of the coding scheme. The motion compensation is achieved by a block-matching method, where the size of the blocks is adapted to the signal. Great attention has been paid to the relevance of the motion field. Combined with the motion compensation, the two fields of each frame are merged, taking into account the measured motion vectors, to compose a pseudo-progressive frame. The encoding is applied to this "motion-compensated progressive " frame. A wavelet decomposition is then applied on each (inter or intra) frame. The wavelet transform used is described in [22]: it is a generalized biorthogonal wavelet transform. Such a transform, intrinsically owning linear-phase and perfect reconstruction properties, has been optimized for maximizing a perceptually weighted coding gain. The wavelet coefficients are thereafter vector-quantized, in order to reach the maximum perceptual SNR frequency weighting is taken into account. The relevance of the measured vector field allows a precise spatio-temporal quantization optimization. The vectors are entropy coded taking into account the remaining inter-band dependence, by an adapted entropy code. A simplified version of such a coder has shown promizing results [6]. Results obtained from 1 Mbit/s to 8 Mbit/s will be shown for moving sequences at the conference.