Shadow matting and compositing

Abstract

In this paper, we describe a method for extracting shadows from one natural scene and inserting them into another. We develop physically-based shadow matting and compositing equations and use these to pull a shadow matte from a source scene in which the shadow is cast onto an arbitrary planar background. We then acquire the photometric and geometric properties of the target scene by sweeping oriented linear shadows (cast by a straight object) across it. From these shadow scans, we can construct a shadow displacement map without requiring camera or light source calibration. This map can then be used to deform the original shadow matte. We demonstrate our approach for both indoor scenes with controlled lighting and for outdoor scenes using natural lighting.