Adaptive intra block update for robust transmission of H.263

An adaptive block based intra refresh algorithm for increasing error robustness in an interframe coding system is described. The goal of this algorithm is to allow the intra update rates for different image regions to vary according to various channel conditions and image characteristics. The update scheme is based on an “error-sensitivity metric,” accumulated at the encoder, representing the vulnerability of each coded block to channel errors. As each new frame is encoded, the accumulated metric for each block is examined, and those blocks deemed to have an unacceptably high metric are sent using intra coding as opposed to inter coding. This approach requires no feedback channel and is fully compatible with H.263. It involves a negligible increase in encoder complexity and no change in the decoder complexity. Simulations performed using an H.263 bitstream corrupted by channel errors demonstrate a significant improvement in terms of error recovery time over nonadaptive intra update strategies