| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide a reversible 8-element discrete cosine transformation by which a transformation value is provided close to substantial 8-element discrete cosine transformation. SOLUTION: An image signal is transformed into a transformation coefficient by a reversible discrete cosine transformation circuit 1. The transformation coefficient is subject to variable length coding together with a value of a JPEG (joint photographic expert group) compatible quantization table at a variable length coder 2. In the case of decoding the coded image by a conventional JPEG algorithm, a dynamic range of the reversible discrete cosine transformation coefficient is corrected by properly deciding a value of the quantization table so as to improve the image quality of the decoded image. Similarly in the case of the MPEG(moving picture expert group), a quantization matrix is used and the decoder side corrects the dynamic range. As to a DC component that cannot be corrected by the quantization table/matrix, the dynamic range is corrected by changing a quantization period and an inverse quantization period for three stages in 6 stages of 2×2 matrix conversion relating to DC component calculation from those of the other 3 stages.</p> |
