关键词: 分形图像编码, 最小均方误差, 最佳匹配, 方差, 峰值信噪比

Abstract: The search method based on classification in accordance with average gray value，which uses MMSE（Minimal Mean Squared Error），can better improve the time expenditures of fractal image coding procedures，but limit the quality of the image reconstructed after decoding.In this paper，to obtain better image quality，a new error rule which makes use of variance’s reflecting changes of image gray level is proposed.The optimal match results of traditional way that use MMSE are improved again.Simulations show that after adding the new rule，higher PSNR of decoding image is achieved with no affection on time expenditures.

Key words: fractal image coding, Minimal Mean Squared Error（MMSE）, optimal match, variance, Peak Signal to Noise Ratio（PSNR）