Lossless re-encoding of JPEG images using block-adaptive intra prediction

This paper proposes a kind of transcoding scheme which compresses existing JPEG files without any loss of quality. In this scheme, H.264-like block-adaptive intra prediction is employed to exploit inter-block correlations of quantized DCT coefficients stored in the JPEG file. This prediction is performed in spatial domain of each block composed of 8×8 pels, but the corresponding prediction residuals are calculated in DCT domain to ensure lossless reconstruction of the original coefficients. Moreover, block-based classification is carried out to allow accurate modeling of probability density functions (PDFs) of the prediction residuals. A multisymbol arithmetic coder along with the PDF model is used for entropy coding of the prediction residual of each DCT coefficient. Simulation results indicate that the additional reductions of coding rates obtained by the proposed scheme are 18-28% for monochrome JPEG images.