Quality Adapted Fractal Image Compression for Multimedia Communication

In multimedia communication, the communication bandwidth is a key factor for real time data transfer. Image compression, such as fractal compression, is used for image communication. Encoding speed is a key factor rendering the fractal image compression unsuitable for real time multimedia communication applications. In this paper, we propose a mechanism for speed-quality control, which is capable of speeding the encoder by a specified factor with reasonable quality decay. This control strategy enables us to control the compression ratio and the reconstructed image quality in advance depending on the need of multimedia communication. The speedup method is accomplished through a classification scheme in the frequency domain using only 2 DCT coefficients, which produces very little overhead. Image qualities can be preserved as well since the scheme makes use of edge property of image blocks, in which the fractal similarity is embedded. Simulations using number of classes ranging from 1 to 30 are performed. When the number of classes is within 30, the speedup ratio can be approximately achieved with very little quality decay. As the number of classes is set to 30, the actual encoding speed can reach up to 29.1 times and there is only 0.57 dB quality decay.