Video system for superimposing character patterns on a video signal

摘要

A main video signal (1) is selectively replaced by a subvideo signal (11) when the subvideo signal is larger than a first predetermined value (REF1). During periods when the subvideo signal, typically its luminance signal, is larger than a third predetermined value (REF3), the subvideo signal is clamped at a second predetermined value (REF2) that is smaller than the third predetermined value (REF3) when line non-correlation or field non-correlation is detected in the subvideo signal.;This prevents noise pulses (B) of high level to be mixed into the main video signal, if their amplitude is larger than the predetermined value REF1.