A high contrast overlay, using either colour or large brightness variations, is added to the graphical image. A histogram 30 of pixel intensities is displayed and an operator selects a low-contrast range of interest 31 using a window 32 of variable level and width. Pixels with intensities falling within this range 31 have the overlay added to them. Thus detail in low contrast areas is more easily discerned by use of visual cues. This system is particularly useful with medical diagnostic images, either static or real-time e.g. NMR, X-ray, ultrasound, CT, nuclear medicine. <IMAGE>
VERFAHREN ZUM HERVORHEBEN VON SCHWACHEN KONTRASTEN IN GRAPHISCHEN ABBILDUNGEN