Shadow removal from natural images

In this paper, we present a system for estimating the shadow field from a single natural image. The user of our system is provided with a broad brush to roughly specify the shadow boundary. 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. Since the strokes provided by the user may be sparse, an optimization scheme is proposed to propagate the estimated shadow field to the entire image. With this scheme, the amount of user interactions required for the system is reduced. The shadow field estimated by our system can be used to seamlessly remove the shadow from the image. It is also useful for other shadow editing tasks. Experimental results on a variety of photos are provided to show the effectiveness of the proposed system.