Vector quantizers with direct sum codebooks

Survey of progressive image transmission methods

“…The generalised decoder uses a direct-sum structure that is jointly optimized for the source distribution and the uniform encoder. The direct-sum algorithm has been used successfully in the design of residual VQ Barnes and Frost (1993). Barnes and Holder (1993) reported significant improvements over a uniform decoder, especially at low bit rates.…”

“…The design of a residual coder considers the type of coder to use and the rate assigned for each stage. The coders should be jointly optimized (Barnes and Frost, 1993), although in practice this is not always possible owing to the computational complexity. Multistage residual coders are associated with the following advantages:…”

Predictive multistage vector quantizer design using asymptotic closed-loop optimization

“…The procedure is initialized with a set of P stage codebooks that are typically obtained by traditional sequential design [9]. It then iterates over the stages and optimizes each stage codebook while keeping the remaining stages fixed [11]. The re-optimization of quantizer Q p consists of updating its codebook.…”

Multistage vector quantizer optimization for packet networks

“…Second, the quantizer codebooks are optimized for the current training set partitions in what is termed decoder optimization. This is achieved by iterating over the stages and optimizing each stage codebook while keeping the remaining stages fixed [29]. The reoptimization of quantizer consists of updating its codebook.…”