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Abstract

A method and apparatus for compressing digital data for transmission and reception in a narrow bandwidth, the method comprising preliminarily smoothing raw data according to a spatial convolution or running average technique, sampling the convoluted or averaged data to produce a subset having information from the full set of raw data, but fewer data points, determining the energy of the subset with a transform coder, encoding the transformed image, predicting the full set of raw data points at and between the points in the subset by means of a prediction algorithm, subtracting the raw data from the thus-predicted values to develop a difference signal, encoding one field of the difference signal and transmitting the encoded transformed data and the encoded difference signal to a receiver employing the same prediction algorithm. The signal is decoded in the receiver to produce both the transformed image and the difference signal. The decoded transformed image is applied to the predictor, and then subsampled and added to the decoded difference signal, thereby recovering the raw data. Statistical techniques are used in encoding to assign the shortest of variable length data words to the most frequent occurrences of given data values. The preliminary convolution or averaging reduces the extent of standard deviation of data values. The apparatus includes video processing hardware adapted to the method, and may include parallel processing for producing the convoluted average, subtraction, encoding, decoding or addition.

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