1. A method of adjusting the contrast of an input image formed of pixels in which each pixel has an input brightness level to produce an output image in which at least some of the pixels have an output brightness level that is different from their input brightness level, the method comprising: filtering brightness level data of the input image to obtain at least a low frequency component and a high frequency component; amplifying the high frequency component; and, summing the low frequency component and the amplified high frequency component to produce brightness level data of the output image; wherein the filtering is carried out by at least one recursive infinite impulse response filter having a single delay coefficient that is adaptive to areas of high contrast in the input image.