The contrast of a time varying video signal is enhanced. Each digital picture is represented by samples having gradation levels in a range from a lower limit C to an upper limit U. The mean value of the gradation levels of the samples representing a first digital picture is determined. A first transform function is constructed in dependence on a distribution of samples with gradation levels less than or equal to the mean value. A second transform function is constructed in dependence on a distribution of the samples with gradation levels equal to or greater than the mean. The first transform function and the second transform function are used to form a contrast enhancement transform, which is preferably constructed in the form of a look-up table. The contrast enhancement transform is applied to a set of samples representing the first digital picture or representing the temporally subsequent picture.