Entropy Measurements for Nonadaptive and Adaptive, Frame-to-Frame, Linear-Predictive Coding of Videotelephone Signals

Linear predictive coding is an efficient method for transmitting the amplitudes of moving-area picture elements (pels) in a conditional replenishment coder for video-telephone signals. It has been conjectured that if the linear predictor can dynamically adapt to the speed and direction of motion in the scene, then greatly improved performance should result. To test this conjecture and to get a first-order estimate of the possible saving, computer simulations were carried out using pairs of video-telephone frames stored on digital discs. Using this data, picture quality could not be studied. However, differential signal entropies could be estimated, and this was done for several nonadaptive and adaptive linear predictors. Entropies (in bits per moving-area pel) for adaptive linear predictors were significantly lower than for nonadaptive predictors, indicating that substantial bit-rate savings should be possible. However, simpler implementations will have to be devised before adaptive prediction becomes practicable.