A video signal is enhanced using a non-linear combination of left and right difference signals (L and R), constrained to be zero if either L or R is zero, using a minimum absolute value function. Edge enhancement is provided when the polarities of L and R are the same and peak enhancement when the polarities are different. Difference signals are derived with delays (2 and 4) and a subtracter (3). The non-linear combinations are derived in a lookup table (30).