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Abstract
Encoding speed is a key factor rendering the fractal image compression unsuitable for real time applications. Therefore, a lot of researches are concentrated on speeding up the encoder. In this paper, the authors propose a mechanism for speed quality control, which is capable of speeding the encoder by a specified factor with reasonable quality decay. 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, i.e. the dihedral transformation, is embedded. Simulations using number of classes ranging from 1 to 950 are performed to produce the speed quality control curve. When the number of classes is within 40, the speedup ratio can be approximately achieved with very little quality decay. As the number of classes is set to 100, the actual encoding speed can reach up to 86.5 times faster and there is only 1.2 dB quality decay.