Long coding time is the main problem in fractal image compression at present

to which classification of image blocks is an important and efficient solution.However

there is an contradiction between coding speed and image quality in most classification methods.Aiming at the contradiction we first give out the guide lines of the performance for classification methods

hence propose a technique called "Adaptive Classification"

which is then used in the classification by mass center combined with satisfied match

thus obtain a fast method for fractal coding.Experimental results indicate that at the same compression ratio

the proposed method improves the speed of fractal coding and the quality of decoded image

in contrast with the original uniform classification.