Image compression using multiple transforms

Discrete cosine transform (DCT) is used in practically all commercial image and video compression systems. It has been found to be the best choice among all unitary transforms in compressing natural images. We are also quite convinced that it is difficult to find any clear alternative for DCT in typical transform coders. Instead, we decided to change the problem. If another single transform cannot outperform DCT, how about using a set of transforms? This paper tries to give an overview about this idea. It was tested in several experiments, which show that the use of several transforms can improve compression ratio despite the side information needed. The result is a compression method that can be described as an intermediate stage between traditional transform coding and vector quantization. It can be used for compressing natural images, but it would be suited best for real multidimensional data.