Vector quantizer

Claim 1

A vector quantizer comprising: a frame memory 712 capable of storing past picture signals of at least one frame; a subtractor 704 which calculates the difference between the block of predictive signals formed by blocking the picture signal sequences of one-frame cycle preceding frame read from the frame memory 712 and the block of picture signal sequences formed by blocking every K (K = a plural number) present picture signal sequences to provide a predictive error signal block; a limiter 747 which receives the predictive error signal block given by the subtractor 704 as an input vector, regards the input vector as a zero vector when the distortion of the input vector from the zero vector is smaller than a predetermined threshold and gives a zero vector detection signal; an output vector code table memory 726 which stores the respective output points of 2 n partitions of K-dimensional signal space including the input vector, formed in a binary tree structure of n steps (n = a positive integer) by repeating binary partitions, as a set of output vectors; a parallel distortion calculating circuit 728 which calculates the distortions between the input vector and two output vectors of each step of the binary tree structure; a distortion comparator 758 which compares the distortions between the two output vectors and the input vector and selects one of the output vectors which has smaller distortion from the input vector; an index register 761 which stores indices corresponding to addresses for reading the output vectors in steps according to the result of the comparison implemented by the distortion comparator 758 and updates the index every time the distortion comparison result for each step is given; a coding controller 749 which receives the index for each step, controls the amount of data by controlling the number of steps of the final step, and processes the zero vector detection signal and the index through variable-length coding; a second code table memory 756 having the same contents as that of the output vector code table memory 726; a decoder 708 which receives the output of the encoder processed through variable-length coding, decodes the zero vector detection signal and the index, read an output vector from the second code table memory 756, and gives the output vector or the zero vector; an adder 710 which adds the regenerated predictive error signal block given as an output vector decoded by the decoder 708 and the predictive signal block to calculate regenerated picture signals to be used as past picture signals after being delayed by one-frame cycle or more by the frame memory 712; and a transmission buffer 744 which controls the number of steps of the final step by feedback control.