  In this paper a new fractal image compression algorithm is proposed in which
the time of encoding process is considerably reduced. The algorithm exploits a
domain pool reduction approach, along with using innovative predefined values
for contrast scaling factor, S, instead of searching it across [0,1]. Only the
domain blocks with entropy greater than a threshold are considered as domain
pool. As a novel point, it is assumed that in each step of the encoding
process, the domain block with small enough distance shall be found only for
the range blocks with low activity (equivalently low entropy). This novel point
is used to find reasonable estimations of S, and use them in the encoding
process as predefined values, mentioned above, the remaining range blocks are
split into four new smaller range blocks and the algorithm must be iterated for
them, considered as the other step of encoding process. The algorithm has been
examined for some of the well-known images and the results have been compared
with the state-of-the-art algorithms. The experiments show that our proposed
algorithm has considerably lower encoding time than the other where the encoded
images are approximately the same in quality.
