Apparatus for combining video signals comprises first and second static effect channels for generating first and second full-field video signals respectively. A transition control signal generator generates first and second transition control signals each having a full-field domain and a predetermined range, the sum of the first and second control signals nowhere exceeding the predetermined range. Arithmetic circuitry multiplies the first video signal by the first transition control signal to generate a first addend signal, multiplies the second full-field video signal by the second transition control signal to generate a second addend signal, and sums the first and second addend signals to provide an output video signal.