Detection and concealment of transmission errors in H.261 images

The detection and concealment approach to transmission errors in H.261 images is proposed. For entropy-coded H.261 images, a transmission error in a codeword will not only affect the underlying codeword, but also may affect subsequent codewords, resulting in a great degradation of the received images. Here a transmission error may be a single-bit error or a burst error containing N successive error bits. The objective of the proposed approach is to recover high-quality H.261 images from the corresponding corrupted H.261 images, without increasing the transmission bit rate. In the proposed approach, using the constraints imposed on compressed image data, all the groups of blocks (GOBs) within an H.261 picture can be correctly located. After a GOB is located, transmission errors within the GOB are detected by two successive procedures: (1) whether the GOB is corrupted or not is determined by checking a set of error-checking conditions under decoding and (2) the precise location (block-based) of the first transmission error (i.e., the first corrupted block) within the GOB is located by a block-based backtracking procedure. For a corrupted block, a set of concealed block candidates, SC, is generated, and a proposed fitness function for error concealment is used to select the "best" concealed block candidate among SC as the concealed block of the corrupted block. Based on the simulation results obtained in this study, the proposed approach can indeed recover high-quality H.261 images from their corresponding corrupted H.261 images.