The Electrical Transmission of Pictures and Images

The objective of this paper is a discussion of some of the important principles underlying the electrical transmission of pictures rather than a description of detailed methods by which such transmission may be effected. The subject, which includes both still pictures and television, is treated as a special form of electrical communication, differing from other forms primarily in the nature of the information conveyed. The necessity for reducing the information represented by a picture or scene to a form where it may be expressed as a single-valued function of time is considered. This function is used as a basis for comparing picture transmission systems with the more familiar telephone and telegraph systems, and for evaluating the amount of information carried by each. The dependence of the rate at which information is train mitted upon the frequency range occupied by the signal is shown to be of fundamental importance. The major portion of the paper is concerned with a study of the relations between the original picture and the transmitted signal as it appears in the several parts of the system. Since the excellence of any system for the transmission of intelligence is measured by the fidelity with which it reproduces the original information, the effect upon the final picture of deviations from ideal performance on the part of each element is examined. Attention is given to the conditions governing the use of modulated waves for the particular forms of signal encountered in picture transmission.