J. Draréni, P.F. Sturm and S. Roy.
Coplanar shadowgrams provide an affordable mean to retrieve the 3d shape of an object especially when classi- cal stereopsis fails (eg:textureless objects). Its principles are similar to the concepts used for Shape-From-Silhouettes with the only exception that here, light sources and cam- eras are interchanged. However, it is well known that any attempt to use the shadowgram to retrieve light sources po- sitions is subject to a 4-parameter ambiguity. In this paper, we show how using the light spot visible in the camera re- duces this ambiguity to a single parameter. We also sug- gest some practical solutions to gain a supplemental con- straint on light sources positions and break the ambiguity. We demonstrate the effectiveness of our method using syn- thetic and real images.
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