Video special effects with cascaded control logic

Abstract

Each of the video signals to be combined to create the special effect is applied to the first input of the corresponding one of a plurality of mixing units. The outputs of the mixing units are connected in common. Each mixing unit has a second input. The synchronization and burst signals of one of the video signals is applied to the second input of one of the mixing units. The gain of each mixing unit relative to the applied signal at the first input varies as a function of a corresponding control signal. Each control signal has an amplitude varying directly with the amplitude of an externally applied input signal and inversely with the amplitude of the next following input signal. Where n video signals are combined, n input signals are provided and the first control signal is a signal at the output of n - 1 cascaded amplifier stages, the first of which has a main input connected to receive the corresponding input signal, an override input connected to receive the next subsequent input signal and an output connected to the main input of the next cascaded stage. The override input of the next cascaded stage is connected to receive another selected input signal. The final control signal applied to each mixing unit is thus the corresponding input signal decreased in proportion to each subsequent input signal. The strength of the component in the video output signal corresponding to the video signal furnished by the mixing unit controlled by the control signal is similarly decreased relative to the strength it would have in the absence of the remaining input signals.