Nader Moayeri

Trellis coded vector quantization

A vector generalization of trellis coded quantization (TCQ), called trellis coded vector quantization (TCVQ), and experimental results showing its performance for an i.i.d. Gaussian source are presented. For a given rate, TCVQ yields a lower distortion that TCQ at the cost of an increase in implementation complexity. In addition, TCVQ allows fractional rates, which TCQ does not. >

Wavelet video coding with ladder structures and entropy-constrained quantization

A subband decomposition using wavelet filters has become an effective basis for image compression. The use of a ladder structure for the subband filtering provides a fast implementation and allows the system to be useful at video rates. A system is proposed that provides good quality video for moderate motion, roughly common intermediate format-f 0-t (CIF-) sized images at bit rates under 500 kb/s, and for teleconferencing scenes at bit rates from 180 kb/s to below 128 kb/s (basic rate ISDN). The system uses subband coding, a modified version of H.261, and entropy-constrained quantization to achieve the desired bit rate and image quality.

Theory of lattice-based fine-coarse vector quantization

The performance of a lattice-based fast vector quantization (VQ) method, which yields rate-distortion performance to that of an optimal VQ, is analyzed. The method, which is a special case of fine-coarse vector quantization (FCVQ), uses the cascade of a fine lattice quantizer and a coarse optimal VQ to encode a given source vector. The second stage is implemented in the form of a lookup table, which needs to be stored at the encoder. The arithmetic complexity of this method is essentially that of lattice VQ. Its distortion can be made arbitrarily close to that of an optimal VQ, provided sufficient storage for the table is available. It is shown that the distortion of lattice-based FCVQ is larger than that of full search quantization by an amount that decreases as the square of the diameter of the lattice cells, and it provides exact formulas for the asymptotic constant of proportionality in terms of the properties of the lattice, coarse codebook, and source density. It is shown that the excess distortion asymptotically equals that of the fine quantizer. Simulation results indicate how small the lattice cells must be in order for the asymptotic formulas to be applicable. >

Decision trees for vector quantizer codebook searching

Several incremental algorithms are presented for designing fixed length decision trees for searching the codebook of a vector quantizer (VQ). These trees are then used as the basis for a two-stage VQ, wherein the first stage is a high-rate, structured VQ with a fast quantization algorithm and the second stage is a low-rate optimal VQ. The mean square error and complexity of the resulting two-stage VQs are presented for i.i.d. Gaussian and speech sources, and are compared with both TSVQ and previous tree based two-stage VQ designs.<<ETX>>

Some issues related to fixed-rate pruned tree-structured vector quantizers

It is shown that the generalized BFOS algorithm is not optimal when it is used to design fixed-rate pruned tree-structured vector quantizers (PTSVQ). A simple modification is made in the algorithm which makes it optimal. However, experimental results show little difference between the rate-distortion curves generated with the original algorithm and the one proposed in the present paper. An asymptotic analysis is presented which shows how the two algorithms prune the TSVQ and explains why their results are so similar. The analysis also shows that in designing fixed-rate variable-depth TSVQs one can get as good a rate-distortion performance with a greedy TSVQ growing algorithm as with the optimal pruning of a large tree. >

Fast subband video coding with ladder structures

A subband decomposition using wavelet filters has become a popular and effective basis for image compression. The use of a ladder structure for the subband filtering provides a fast implementation, and allows the system to be useful at video rates. In this paper, a system is proposed that provides good quality video for CIF sized image transmitted from 240 kbits/s down to 128 kbits/s (basic rate ISDN). The system uses subband coding, motion-compensated prediction, adaptive DCT coding, and entropy-constrained quantization to achieve the desired bit rate and image quality.