On the use of directional transforms for still image coding

Significant research has been performed on the use of directional transforms for the compression of still imagery, in particular on the application of block-based and segmentation driven directional adaptive discrete wavelet transforms. However, all of the proposed methodologies suffer from the extra side-information that needs to be encoded. This encoding overhead and added complexity is unfortunately not negligible. This paper describes various considerations and trade-offs that were made during the search towards a practical solution for using directional adaptive transforms in still image coding. We propose two codec instantiations respectively based upon quadtree-coding (QT-L) and JPEG 2000's EBCOT engine and discuss various experimental results.