An MPEG-based image contrast enhancement algorithm for people with low vision is presented. Contrast enhancement is achieved by modifying the inter- and intra-quantization matrices in the MPEG decoder during the decompression stage. The algorithm has low computational complexity and does not affect the MPEG compressibility of the original image. We propose an enhancement filter based on the visual characteristics of low-vision patients, and report the results of preference experiments with 24 visually impaired subjects. Subjects favored low to moderate levels of enhancement for two of the tested video sequences, but favored only low levels of enhancement and rejected higher enhancement for two other sequences that had fast motion.