A three-stage approach to shadow field estimation from partial boundary information.

In this paper, we present a system for estimating the shadow field from a single natural image. Unlike previous works that require extensive user assistance, our system only needs the user to roughly specify the shadow boundary with a broad brush. As the user finishes drawing a stroke, the system starts to estimate the shadow field around the stroke and generates pretty accurate result even if the underlying surface is highly textured. We also propose an optimization scheme to propagate the estimated shadow field to the entire image, achieving a further reduction of user effort required for the system. The shadow field estimated by our system can be used to seamlessly remove the shadow from the image. It is also useful for many shadow editing tasks such as pasting an object's shadow from one image to another. Experimental results on a variety of photos are provided to show the effectiveness of the proposed system.