HIGH EFFICIENCY CODER AND HIGH EFFICIENCY DECODER

摘要

PURPOSE:To improve the picture quality of a character and the surrounding of the character. CONSTITUTION:A code quantity constant circuit 22 receives a DCT transformation coefficient to calculate a normalizing coefficient alpha1 smaller than a normalizing coefficient alpha and a normalizing coefficient alpha2 larger than the normalizing coefficient alpha based on a total activity. The DCT transformation coefficient is given also to a character detection circuit 21. The character detection circuit 21 detects a character block based on the DCT transformation coefficient and its distribution and gives normalizing coefficients alpha1, alpha2 with respect to the character block and a non-character block to a basic quantization table 6. A quantization circuit 7 uses the basic quantization coefficient multiplied with the normalizing coefficient alpha1, alpha2 to quantize the DCT transformation coefficient thereby quantizing the character block with a finner quantization width than that of other block. Thus, the code quantity allocated to the character block is increased and the picture quality of the character block is improved.