Analysis of one-dimensional transforms in coding motion compensation prediction residuals for video applications

In video coding, motion compensation prediction residuals are typically compressed by applying two-dimensional transforms such as the two-dimensional discrete cosine transform (2D-DCT). Using direction-adaptive one-dimensional discrete cosine transforms (1D-DCTs) can provide significant additional bitrate savings. However, this requires optimization over all available transforms to minimize the overall bitrate, which can be expensive in terms of time and computation. We examine the use of only the horizontal and vertical 1D-DCTs in addition to the 2D-DCT for coding motion compensation residuals. By reducing the number of available transforms, the amount of required computation decreases significantly, with a potential cost in performance. We perform experiments using a modified H.264/AVC codec to compare the performance of using different sets of available transforms. The results indicate that for typical applications of video coding, most of the performance benefit from using directional 1D-DCTs can be retained by keeping only the horizontal and vertical 1D-DCTs.