US Patent 7242328 Variable length coding for sparse coefficients

Coding quantized transform coefficients as occur in image compression includes, for a subset of coefficient amplitude values coding by a first method corresponding to each amplitude of the subset, events of a run of zero or more zero-valued coefficients ending in the single non-zero amplitude, coding by a second method events of a run of zero or more zero-valued coefficients ending in any single non-zero amplitude not in the subset, and coding by a third method the amplitude values of the concatenation of the non-zero amplitude not in the subset. The coding methods produce variable length codewords. The method is suitable for series that have scattered non-zero-valued coefficients.