The properties of the frame-difference signals arising from updated "moving" areas and nonupdated "stationary" areas in conditional replenishment interframe encoders are examined. Expressions for the correlation functions and power density spectra of these signals are developed assuming an infinite image field undergoing uniform linear motion. These expressions are modified so as to include the effect of camera integration. Experimentally obtained power spectra are in good agreement with those predicted. Three-dimensional frame-difference correlation functions are evaluated using a realistic image correlation function. The properties of the frame-difference correlation functions in directions parallel and perpendicular to the direction of movement, and in the temporal direction are delineated. It is shown that the correlation function of the frame-difference signal arising from temporally uncorrelated noise is fundamentally different in updated areas compared with nonupdated areas.

This paper is concerned with the problem of transmission errors in digitally encoded television signals. Various techniques for reducing the visibility of transmission error effects in the reconstructed signals have been evaluated using computer-produced film sequences. It is found that the visibility of errors in element difference coders is sharply reduced if an erroneous line is replaced by an average of adjacent lines. It is shown that the visibility of errors in two coders that use spatial prediction is low and can be further reduced by using a "leaky" predictor. The implications of these results for in-frame, interframe, and facsimile encoders are discussed.