Design of a filter against artifacts for JPEG2000

Abstract

JPEG2000 Standard (ISO/IEC 15444, ITU-T T.800) is a new-generation image compression technique, enabling encoding images at low bit rates with acceptable quality. Since JPEG2000 is based on wavelet transforms, the reconstructed image will contain perceivable ringing artifacts in medium- and low-bit-rate regimes of lossy compression. We utilize a quad-tree partitioning scheme for postprocessing the reconstructed image in a spatially varying manner and presents a voting strategy to determine a set of morphological filters to be used for reducing the ringing artifacts. All this processing is performed at the encoder side, and the set of selected filters is conveyed to the decoder in the form of side information. Specifically, the adopted (eight) morphological filters are generated through the use of four predefined structuring elements (SEs) in conjunction with two morphological operations, namely, dilation and erosion. A voting strategy is used to select the morphological filter for each partition block to optimize the postprocessed image quality—through minimizing the sum of absolute differences under the constraint of a fixed quad-tree partition. Applying the chosen morphological filters to their corresponding blocks typically enhances the reconstruction quality—in the worst case, leaving it unchanged. Simulation results demonstrate that the proposed technique enhances reconstructed image quality compared to unprocessed JPEG2000 output at an equivalent bit rate, accounting for the side information overhead, in terms of both peak SNR (PSNR) and visible ringing measure (VRM).