METHOD AND APPARATUS FOR COMPRESSING/ EXPANDING IMAGE FOR BIT FIXATION

摘要

PURPOSE: To fix the number of bits and to stabilize the picture quality by differently setting up distortion areas for differentially setting up distortion in respective pictures in the case of executing the variable length encoding of continuous pictures against a still image, setting up the quantization interval of each distortion area larger than that of a normal area and executing compression encoding. CONSTITUTION: A video signal is blocked and a frame order adjusting part 21 in a differential distortion area setting part 20 differently sets up a distortion pattern in each picture. A circuit 30 detects the complexity and variation of a component signal and classifies the detected result into the prescribed number of classes, a circuit 40 sets up a compression constant for quantization by the average variation of the whole image and a DCT means 50 executes DCT transformation in each block in the order of normal distortion areas in each block. A bit allocating means 70 changes an allowable distortion value to the number of bits of a quantization coefficient by changing the quantization interval of the distortion area and allocates the number of bits per picture. Consequently the number of bits can be efficiently fixed and the quality of an image can be stabilized.