Abstract: A post-processing filter apparatus for use in an image signal decoding system, capable of improving the image quality of the system, comprises a memory for storing decoded image data of a current frame; a filter for filtering target pixel data in the stored decoded image data to thereby produce filtered target pixel data, wherein the target pixel data represents the value of a pixel to be filtered; a calculator for calculating an absolute difference value between an original target pixel data and the filtered target pixel data; a first circuit for selectively generating a first or a second threshold value based on the decoded image data and the target pixel data; a second circuit for updating the stored target pixel data with the filtered target pixel data if the absolute difference value is smaller than the generated threshold value; and a third circuit for sequentially updating the stored target pixel value with corrected target pixel data T times if the absolute difference value is equal to or larger than

Abstract: A method for reducing ringing and blocking artifacts in a decompressed image models an image in a relatively small area as several smooth regions separated by edges. The method uses JPEG MxM pixel blocks and is compatible with JPEG decompression. To reduce ringing, a block is examined for uniformity, segmented and smoothed. Then, after a DCT transform, a projection is performed to guarantee that the DCT coefficients of the resulting image block will be within the initial quantization interval. The resultant image is produced by an inverse DCT. To reduce blocking, the method is modified to employ a large outer window for uniformity checking, segmentation and smoothing and a small inner window for DCT projection.