Adaptive intra block update for robust transmission of H.263

An adaptive block-based intra refresh algorithm for increasing error robust ness in an interframe coding system is described. The goal of this algorith m is to allow the intra update rates for different image regions to vary ac cording to various channel conditions and image characteristics. The update scheme is based on an "error-sensitivity metric." accumulated at the encod er, representing the vulnerability of each coded block to channel errors. A s each new frame is encoded. the accumulated metric for each block is exami ned, and those blocks deemed to have an unacceptably high metric are sent u sing intra coding as opposed to inter coding. This approach requires no fee dback channel and is fully compatible with H.263. It involves a negligible increase in encoder complexity and no change in the decoder complexity. Sim ulations performed using an H.263 bitstream corrupted by channel errors dem onstrate a significant improvement in terms of error recovers time over non adaptive intra update strategies.