Joint source and channel coding for Internet image transmission

Abstract

Images are usually transmitted across the Internet using a lossless protocol such as TCP/IP. Lossless protocols require retransmission of lost packets, which substantially increases transmission time. We introduce a fast lossy Internet image transmission scheme (FLIIT) for compressed images which uses forward error correction to eliminate retransmission delays. FLIIT couples an embedded quantization scheme with optimized shielding of important portions of the image. We describe a joint source and channel coding algorithm for images that minimizes the expected distortion resulting both from network packet losses and from inexact quantization of transform coefficients. The algorithm adaptively allocates quantizer resolution bits and redundancy bits to image subbands to control quantization errors and expected packet transmission losses. Our packet loss model incorporates the effects of burst losses using a Markov packet loss model with empirically derived parameters. Our preliminary results show a dramatic reduction in the amount of forward error correction needed to achieve a given expected fidelity as compared to a fixed-rate channel coding scheme.