A method and apparatus for detecting a main lighting direction from the input image, which corresponds to a key light. The system is operative to nm on data-parallel architectures allows for incoming light direction estimation in real-time. More particularly, the method and apparatus detect a key, or principal light direction relative to the position/orientation of an acquisition device. It method involves image analysis to find a maximum intensity value, maximal values filtering, and conversion of the input image position to a direction in space.