Camera contrast ratio of road markings at dual carriageway roads

Abstract

Road markings are road safety elements needed for both human drivers and for machine vision equipment. Their visibility depends on contrast ratio against the neighbouring roadway surface. To identify conditions, where their visibility was inadequate, exemplary roadway images were analysed. Average contrast ratio during good visibility conditions was 1.0 (Weber) or 0.30 (Michelson); dramatically lower values, average 0.1 (Weber) or 0.06 (Michelson) were measured when glare from sunshine was present. Hence, camera-based machine vision would be expected to fail. The use of Michelson equation for contrast ratio was shown as more useful than calculating ‘simple’ or Weber contrast due to moderating extremely high values. Under some conditions, edge detection could be simultaneously advantageous (improved detection of edge line) and disadvantageous (false detection of middle line).