Keyed, true-transparency image information combine

Abstract

A keyed, true-transparency combine and keyer receive a plurality of image information signals V.sub.i, each having a corresponding input key signal Bk.sub.i, over a respective channel. The image signals are dynamically ranked in a prioritized order, even on a field-by-field basis. However, rather than switch the individual image signals as the prioritized order changes, the order of the channels is dynamically and switchably interchanged within a keyer by switchably interchanging a plurality of substantially identical keyer units while generating a plurality of processed true transparency image key signals Pk.sub.i. While there may be some structural distinctions among the keyer units, there is commonalty of function among the keyer units within the keyer. The keyer also generates processed background key signals Pk.sub.B. The keyer units are switchably changed to produce true transparency processed key signals such that processed key signal Pk.sub.i for an i-th channel is produced by the i-th respective one of the substantially identical keyer units. The i-th keyer unit can modify the value of its input key signal Bk.sub.i with the values of the input key signals Bk.sub.j in the higher priority channels to generate a true transparency processed key signal Pk.sub.i for the i-th priority channel so that: ##EQU1## where Bk.sub.0 =0 and Pk.sub.1 +Pk.sub.2 + . . . +Pk.sub.N +Pk.sub.B =1.0. The combiner also cuts each respective image signal V.sub.i and background signal V.sub.B by its respective processed key signal and combines the plurality of cut signals to generate the special video effect of an image information combine V.sub.C so that: