two important modifications in DCT based coding algorithm are suggested after making deep study on the generally used scheme of H.263 coder.First
we find plenty of invalid computation in the transformation part of the H.263 coder and an improved scheme based on the pre transform decision to avoid invalid computation is proposed.Second
in the motion estimation part of the coder
we find that normal search algorithms are not effective
which neglects different levels of motion in image sequences
and we suggest a new search algorithm which has variable search region based on the difference of motion level.Combining the pre transform decision scheme with variable search region method in motion estimation
a global decision coding scheme is provided
which greatly increases the coding speed of H.263 coder.