A generalization of quad-trees applied to shape coding

Quad-trees are restricted to combined horizontal and vertical decomposition of tiles. If this restriction is dropped, anisotropic rectangular tiles result which can be arranged in a previously developed graph structure called “bush”. A new tiling algorithm is able to reduce the number of tiles by a factor of about two. Together with an existing efficient coding scheme for this graph, a lossless coding algorithm for bi-level and indexed color images is developed. It is compared to JBIG2 and PNG, and turns out to be efficient for situations with large uniform regions and high color payload.