US Patent 7587121 Method and system for multiple field modulation

A system for selectively increasing and decreasing the intensity of scan lines in a plurality of fields of a video signal over a time interval and not increasing or decreasing the intensity of the video scan lines in the remaining plurality of frames, thereby enabling a decoder to use an average intensity value comparison or to accumulate the differences in signal strength when fields are changing state from encoded to unencoded or encoded to unencoded to determine whether an auxiliary signal is present during the time interval.