Abstract: A method is proposed to estimate illumination direction from cast shadows in images of outdoor scenes.First,shadow areas in the foreground are separated using a shadow detection method,and the brightness rate(BR),which is independent of reflection properties of the material but dependent on illumination intensity onto the material,is computed in shadow areas.A BR line is fitted onto the points that have minimal BR values.Second,based on the property that illumination intensity at the points in a cast shadow area varies depending on their locations,illumination direction is estimated by modeling the height of the object,incident rays from the source of the illumination,and the BR line.Finally,experiments with known illumination direction in indoor scenes,experiments in outdoor scenes,and comparative analyses are carried out.The results show that our method enables illumination direction to be estimated accurately and efficiently,without complicated image segmentation.