A FAST PICTURE COMPRESSION TECHNIQUE

One of the most efficient image compression techniques investigated is the Discrete Cosine Transform (DCT). Within this paper we present a m ethod where through the use of pruning the speed of implementation of the algorithm is dramatically increased. This paper also describes its use in image compression. The advantage of the pruning algorithm in s uch cases being that, only a small proportion of the DCT values are re tained hence why calculate the values which are not retained. Results show that for an 8 by 8 image block it is only necessary to calculate a 4 by 4 subset of the DCT values to retain acceptable image quality, this gives a considerable speed up in calculation time compared with c alculating the full 8 by 8 DCT block. Another advantage of the techniq ue is that parallelisation can be achieved using the data partitioning method. For the JPEG standard, the image is split into 8 by 8 blocks and the DCT of each block calculated, each block is independent of its neighbours and hence can be calculated in parallel, as with all paral lel applications data transfer times are crucial, here the pruning alg orithm has a second advantage in that only a subset of the results of the DCT need be transferred back to the root process. Results are pres ented for its application to the JPEG standard. The paper discusses bo th the effects of pruning on the image quality and the effects of prun ing on parallelisation and speedup.