Enhancement of an image compression algorithm by pre- and post-filtering

We present an algorithm that improves the overall performance of compression algorithms by applying low-pass filtering before the compression process and inverse filtering after decompression. Prefiltering images prior to encoding removes high spatial frequencies from the original image, thus increasing the compression ratio of the encoder. The image degradation caused by the filter together with the nonlinear transformation of a typical compression algorithm reduces the entropy of the original image, thus increasing the compression ratio. In addition to improving the compression ratio, the suggested scheme reduces the blocking effect that is common to block-based compression algorithms, such as the Joint Picture Experts Group (JPEG). © 2001 Society of Photo-Optical Instrumentation Engineers.