DCT based simple classification scheme for fractal image compression

In this paper, a fast fractal encoding algorithm using simple classification scheme is proposed. During the encoding process, the range blocks and domain blocks are classified first. Then, each range block is limited to search in the corresponding domain class to find the best match. Since the searching space is reduced, the encoding speed is improved. Three classes of image blocks are defined, which are smooth class, diagonal/sub-diagonal edge class and horizontal/vertical edge class. The classification operation is performed using only the lowest horizontal and vertical DCT coefficients of the given block. Thus the classification scheme is simple and computationally efficient. Moreover, since the classification mechanism is designed according to the edge properties and the intrinsic idea of fractal coding, the quality of the decoded image can be preserved. The thresholds for the classifier are also adaptively determined from the range pool so as to reduce the overhead and to guarantee a stable speedup ratio of 3. Simulation results show that the stable speedup ratio of the proposed algorithm can be achieved and is independent of images while the quality of the decoded image is almost the same as that of the full search method.