Some possibilities for the compression of television signals by recoding

Abstract
The paper describes first the excessive redundancy in television signals, using the term in the sense of communication theory. The information in a picture is largely contained in the edges and boundaries, but in practice these occupy a very small part of the total area. The unequal probabilities of signal elements lying in boundary and smooth surface regions are considered, together with the transition probabilities between adjacent elements. Compression is shown to be possible by making such probabilities more nearly equal, using a system of recoding.Such recoding may be achieved by a variable-velocity scanning system if the scan velocity is made high for all regions of the picture having low picture-detail and low for regions having high picture-detail. Picture-detail is defined precisely and measured values are given from observations on working programme material.Finally, compression is shown to be theoretically attainable in both the vertical and the horizontal directions. Correlation between successive line-scan waveforms is interpreted in terms of transition probabilities, and again a redundancy is seen to exist. Suggestions are made for reducing this by storage of every successive frame and scanning alternately in the horizontal and vertical directions, in both cases using a variable-velocity system. Finally, the paper should not be read as describing an existing working system, but purely as a discussion of possibilities.

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