Patent ID: 7042522

Claim:
A method for adaptive contrast enhancement, which comprises: obtaining a time varying video signal including a plurality of temporally ordered digital pictures, each one of the digital pictures represented by a set of samples, each one of the samples having a gradation level in a range from a lower limit C to an upper limit U; constructing a contrast enhancement transform including at least a first transform function and a second transform function by performing steps of: a) for a first one of the digital pictures, selecting a first value between the lower limit C and the upper limit U, b) dividing the set of the samples representing the first one of the digital pictures into at least a first portion having samples with gradation levels not greater than the first value and a second portion having samples with gradation levels not less than the first value, c) selecting the first transform function in dependence on a distribution of the gradation levels in the first portion, and d) selecting the second transform function in dependence on a distribution of the gradation levels in the second portion; and enhancing contrast of a digital picture by applying the contrast enhancement transform to a set of samples representing the digital picture.