Direct Allocating the Dihedral Transformation for Fractal Image Compression

Fractal image compression exploits the self-similarity of an image to achieve the purpose of compression. In the standard algorithm, eight Dihedral transformations are applied on domain blocks to increase the codebook size, and therefore, the quality of reconstructed image can be improved. However, such mechanism consumes approximately eight times of the encoding time. On the other hand, if no transformation is performed in order to speedup the encoder, the image quality will decay because the codebook is not large enough. In this paper, we propose a direct allocating method to predict the desired orientation and the similarity measure is performed on this orientation only. Simulations show that the encoding time is almost the same as that of the method without transformations while the image quality is close to that of the standard method.