Improving the quality of coded still images by postprocessing

Coding techniques, such as JPEG and MPEG, result in visibly degraded images at high compression. The coding artifacts are strongly correlated with image features and result in objectionable structured errors. Among structured errors, the reduction of the end of block effect in JPEG encoding has received recent attention, with advantage being taken of the known location of block boundaries. However, end of block errors are not apparent in subband or wavelet coded images. Even for JPEG coding, end of block errors are not perceptible for moderate compression, while other artifacts are still quite apparent and disturbing. In previous work, we have shown that the quality of images can be in general improved by analysis based processing and interpolation. In this paper, we present a new approach that addresses the reduction of the end of block errors as well as other visible artifacts that persist at high image quality. We demonstrate that a substantial improvement of image quality is possible by analysis based post-processing.