CODER FOR DIGITAL PICTURE SIGNAL

摘要

PURPOSE:To attain a high compression rate by controlling the fineness of quantization by both luminance and activity so as to suppress deterioration in the image quality when coefficient data generated by cosine transformation is quantized. CONSTITUTION:AC coefficient data and DC coefficient DCT are generated from a DCT transmission circuit 4. The AC coefficient data are quantized by a quantization circuit 7 and subjected to variable length coding by a VLC encoder 11. A quantization number controller 10 detects the degree of luminance from the DC coefficient data of a Y signal and classifies the data into macro blocks based on a maximum value of the absolute value of the AC coefficient data. A data quantity estimate device 9 selects a quantization number in the quantization table for each of 5 macro blocks and it is fed to the quantization number controller 10 and the quantization number is adjusted by class information. A class of most rough quantization is allocated to a macro block whose luminance is high to make the deterioration in the image quality unremarkable.