The Potential of Specular Reflections for Facade Image Analysis

Abstract

Several approaches for window detection have been proposed in recent years, which all use the window size, shape or position within the façade as characteristics for the detection. In this paper another property of windows is proposed for their detection: Windows are made of glass, so they tend to specularly reflect sun light, while the surrounding wall diffusely reflects it. To this end, colour values in multiple views are analysed to detect specular reflections. In the experiments, walls often show a high homogeneity of small colour differences, and many windows are clearly visible in the form of colour differences. Nevertheless, it is difficult to segment windows from the façade if there is no prior knowledge about the intensity of the scene’s illumination. Promising results are obtained if the façade lies in the shadow, e.g., of another building or a tree.