Improved Reconstruction of DPCM-Coded Pictures

In most picture communication systems that employ any type of quantized encoding, samples are sequentially encoded, transmitted by the channel and reproduced at the receiver. Pulse-Code Modulation (PCM) systems assign one of the many quantization levels to the amplitude of each sample, whereas differential pulse-code modulation (DPCM) systems assign a quantizer level to the prediction error of each sample.1 Thus, in PCM systems, no use of the correlation between the adjacent picture samples is made either at the transmitter for coding or at the receivers for display. In DPCM, the "previously" coded sample values are used for computing the prediction of the "present" sample at the transmitter, and thus correlation of the present element with the previous pels is utilized. However, no use of the "future" samples is made at the transmitter or at the receiver. In this paper, we present techniques for coding and display that use correlation between the present sample, and its past and future neighbors. At the transmitter, this improves the prediction; and at the receiver, this results in a more accurate reproduction of the intensity for display. The technique can be used at the receiver, or at the 969