| 摘要 |
<p>PROBLEM TO BE SOLVED: To improve a JPEG based-line compressing method, so that a digital image of high picture quality can efficiently be compressed with as a small resource load as possible. SOLUTION: Respective pixel blocks are subjected to DCT3 and AC coefficients are put in one sequence through zigzag scanning 55. Then the AC coefficient sequence is encoded by Hofmann encoding (57) and linear Hofmann encoding, where zero run-length is not considered and only coefficient values are considered, is carried out here. A linear Hofmann table 11 used here is an extraction of parts of run-length = 0 from a conventional two-dimensional Hofmann table and includes no event for the coefficient value = 0. For the purpose, AC coefficients, having a value '0' are replaced with a value '1', and the Hofmann encoding is carried out. In final bit stream generation 7, frequency information for Hofmann table generation is included in an output bit stream, and the frequency information has contents by which the conventional two-dimensional Hofmann table can be generated.</p> |
