Transformation coding device

Claim 1

A transformation coding device comprising: a movement compensating unit which divides a digital image input signal series into a plurality of blocks, and thereafter compares respective blocks with preceding frame images located at the spatial same positions or in the vicinity of said images, detects the most similar portions of them from among said preceding frame image signals, and outputs a spatial amount of displacement between said blocks and the similar portions of said preceding frame image signals; a subtractor which subtracts a prediction signal between movement compensating frames produced in accordance with said amount of displacement from said digital image signal; an orthogonal transformation unit which applies orthogonal transformation to a difference signal between frames obtained from said subtractor and outputs a transformation coefficient; an adaptive quantization unit which selects one quantization characteristic from among a plurality of quantization characteristics prepared in advance corresponding to both the degree of similarity of the prediction signal between movement compensating frames for said block digital image signal series and the sequence of said transformation coefficient and applies quantization to said transformation coefficient; an adaptive quantization decoding unit which selects one quantization characteristic from among a plurality of quantization characteristics prepared in advance corresponding to both the degree of similarity of the prediction signal between movement compensating frames and the sequence of said transformation coefficient, thereby applying quantization decoding to the quantized transformation coefficient from said adaptive quantization unit; an inverse orthogonal transformation unit which applies inverse orthogonal transformation to the quantization decoded quantization transformation coefficient to produce a difference signal between decoded frames; an adder which adds said difference signal between decoded frames and said prediction signal between movement compensating frames to produce a decoded image signal; a frame memory which stores said decoded image signal temporarily to output said prediction signal between movement compensating frames in accordance with said amount of displacement; a variable length coding unit which outputs a quantization index from said adaptive quantization unit as coded data applied with variable length coding; and a transmitting buffer which stores said coded data temporarily, outputs them with a fixed bit rate, and at the same time, outputs an amount of buffer storage as a feedback signal in order to prevent buffer overflow.