PURPOSE: To obtain a picture compression processing system in which a repro duced picture with less picture quality deterioration is obtained regardless of high compression rate.

CONSTITUTION: A nonlinear quantization means 106 applying nonlinear quantization to a difference is provided to a pre-stage of an orthogonal transformation circuit 108 calculating the difference between fields or between frames to execute orthogonal transformation in the case of executing compression coding of digital data to send or record color picture information. Then the coder is provided with a quantization means 120, in which a code is assigned to a detailed block to the small difference and its vicinity and a code is assigned to a rough block to the large difference and its vicinity. Furthermore, the picture decoder is provided with a means of inverse nonlinear quantization to decode the code into the difference and the picture is compressed by utilizing the correlation of the picture in the timewise direction and the human visual characteristic.