| 摘要 |
<p>PURPOSE:To improve the encoding efficiency of compressing gradation picture data by separately using a prescribed two-encoding system for the unit of blocks. CONSTITUTION:The gradation picture data for the unit of blocks are orthogonally transformed by a two-dimensional discrete cosine transformation device 3 and go to be a transformation coefficient equivalent to one block. Then, the data are uniformly quantized by a first quantizing device 4 and the coefficient number and polarity number of a fixed length code are obtained. These pair numbers are stored in a block buffer memory 6 and a ranking device 5 distributes the block from the coefficient number into plural ranks. In a second quantizing device 7, quantization is executed by a quantizing width, which is determined based on a rank number and setting compression factor, and the cut rate of a high frequency component. Then, in an encoding device 8, the two systems of encoding are executed. Then, one system of the encoding uses both a Huffman code and run-length code and the other system of the encoding uses the Huffman code. In the block of the small quantizing width, or, in the block of a large high frequency cut degree, only the Huffman encoding is used. Then, a code length is shortened and the encoding efficiency is improved.</p> |
