Further lossless compression of JPEG images

In this paper we present an algorithm to further compress JPEG images without loss. The main contribution of this work is a sorting transform that allows reducing inter-block redundancy not exploited by the standard JPEG still image compression algorithm. Inter subband redundancy is also reduced by grouping of coefficients with similar statistics and entropy encoding in adaptive contexts. Tested on randomly selected JPEG images from the Internet, our approach reduces image file size on average by 14%.