The Nonadditive Mixing of Television Signals
Winslow L. Hurford · Journal of the SMPTE · 1964
A method of combining video signals for lap dissolves is described in which at every instant the larger signal is transmitted and the smaller signal is suppressed. This nonadditive method of combining signals has the advantage over the customary mixing methods of keeping the output video level constant, independent of the distribution of peak-to-peak voltages in the input signals. A secondary advantage of this method of performing dissolves is that the same equipment may be used for the generation of keyed inserts and for the production of special effects.