A generalization of quad-trees applied to lossy image 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”. Although this graph requires more bits to be encoded, the reduction of the number of tiles by a factor of about two more than compensates this, especially when there is a big payload per tile such as polynomial or DCT approximations of image content. Therefore, together with an existing efficient coding scheme for this graph, a lossy coding scheme based on tile-wise rate-distortion optimized quantization of low-frequency DCT coefficients is developed. It is able to compete with JPEG2000, especially for images with smooth regions.