US05235623Adaptive transform coding by selecting optimum block lengths according to variatons between successive blocks
AssigneeNEC Corporation
Assign./FiledAug. 10, 1993/ Nov. 14, 1990
InventorsSugiyama; Akihiko, Iwadare; Masahiro, Nishitani; Takao
SummaryTransform coding with adaptable input block size.
AbstractSubblocks of input digital samples are stored into a buffer at frame intervals and segmented into blocks having an integral multiple of the length of the subblock. Each block is encoded into transform coefficients and stored into a memory. Each coefficient is squared and those of the squared transform coefficients which correspond to high-frequency components of the input digital samples are summed and a minimum value is detected therefrom as corresponding to an optimum block length. Those transform coefficients which correspond to the optimum block length are selected from the memory and multiplexed with a signal representative of the optimum block length. In a modification, interblock differences are detected between successive transform coefficients of equal block length and squared. Those of the squared interblock differences which correspond to equal block length are summed, producing a set of squared sums for each block length. A variation is detected between a representative squared sum of a given set and a representative squared sum of a successive set to identify a block length which corresponds to the variation as an optimum block length.