Zeichenkontrast und visuelle Leistung am Bildschirm

The generation of characters on VDU’s exhibits specific raster problems in view of contrast and visibility evaluation. The luminance modulation of rasters is theoretically and experimentally analysed, resulting in the specification of local inner, local outer and mean contrast of characters. An analytical model of contrast thresholds is presented including the effects of background luminance, size, stimulus duration etc. in order to estimate the visibility of characters.On the basis of detection, identification and search experiments as well as of subjective appraisals it is shown, that the inner local contrast of characters is the determinant for the effect of contrast on visual performance and acceptance. The inner local contrast also provides an adequate criterion to optimise the adjustment of contrast of VDU’s in a given environment.