Detection and/or enhancement of contrast differences in digital image data

Abstract

A method for obtaining and/or enhancing local contrast differences (LD) in digital image input data (in), wherein a local contrast measure (SAD) approximating a two-dimensional sum of absolute difference (SAD) measure is obtained by obtaining a first-dimension sum of absolute difference measure (energyV(m, n)) representing a sum of absolute difference (SAD) in a first dimension of at least one image region, and obtaining the local contrast measure (SAD) as a second-dimension convoluted first-dimension sum of absolute difference measure by convoluting the first-dimension sum of absolute difference measure (energyV(m, n)) in a second dimension of the at least one image region, is proposed, wherein the step of obtaining the local contrast measure (SAD) as the second-dimension convoluted first-dimension sum of absolute differences measure further includes an addition step wherein an energy term (Δlpf(j)) representing a first-order difference on a distance (J) of a low pass filtered signal used in obtaining the first-dimension sum of absolute differences measure (energyV(m, n)) and in obtaining the second-dimension convoluted first-dimension sum of absolute differences measure is introduced while obtaining the local contrast measure (SAD).