| 摘要 |
<p>PURPOSE: To prolong the run length of '0' data regardless of the kind of pictures and to improve compressibility by changing the pattern of zigzag scanning corresponding to the distribution shape of a spatial frequency coefficient. CONSTITUTION: A DCT transformation part 92 transforms a picture into spatial frequency distribution for respective small blocks of the pictures divided into 8×8 picture elements. Since a spatial frequency is provided with nonuniform distribution, when quantization by a quantization table 96 is performed and then appropriate array conversion is performed in a zigzag scanning part 94, entropy compression-encoding is performed in a Huffman encoding part 93. In this case, a scanning pattern storage part 21 stores the plural patterns of array conversion to be performed in the zigzag scanning part 94 and a table selection part 22 reads the array conversion pattern corresponding to the output of a distribution shape judgement part 20 and sets it to the zigzag scanning part 94. For instance, when clear horizontal stripes are present in the pictures, since the distribution of the spatial frequency coefficient is concentrated on a first column, the first column is scanned first.</p> |
