| 摘要 |
PURPOSE:To precisely perform an encoding process by carrying out quantization with quantization step which does not cause a range to be exceeded. CONSTITUTION:A maximum detecting circuit 3 detects a maximum value among transformation coefficient after the orthogonal transformation of a DCT 1. Then the maximum value among transformation coefficient in a set range to be detected is inputted to a quantization step width calculating circuit 7. A mode-2 signal 8 which inhibits the range from being exceeded or allows the range to be exceeded by a specific number of bits is inputted to the circuit 7 from outside and quantization step width (QS2) is determined and outputted to a quantization step width selecting circuit 9. Quantization step width (QS1) which is adaptively obtained from the storage amount of a transmitting buffer is also inputted to the circuit 9. The circuit 9 selects step width which is smaller in absolute value between the QS1 and QS2 and outputs it to a quantizing circuit 10. The transformation coefficients are quantized in range-over permissible mode and if the range is exceeded after the quantization, a clipping circuit 11 limits it to specific bits. |
