Because the number of domain blocks is not sufficient in the Jacquin's fractal image coding method

the matching between domain blocks and range blocks is not very effective. To improve the matching efficiency

this paper puts forward a new fractal image coding method

which increases the number of domain blocks through linear rotation transforms and gets the optimal matching. Unlike in the ordinary methods

in order to exploit fully the self similarity in the image

this method chooses domain blocks from multiple directions in the image

then generates new sets of domain blocks through a symmetric transform and linear rotation transforms. The Isometries transforms proposed by Jacquin can be viewed as a special case of this method when the rotation direction number is fixed to 4. This method modifies the number of rotation directions

thus amends for the inadequacy of domain blocks in the Isometries transforms

and gets a better compression result. An acceleration algorithm based on a lookup table is also established for the linear rotation transforms

which effectively shortens the encoding time.