4. Silhouettes

Problem 4.3.
In silhouette reconstruction a duality appears between the visual hull and the convex hull. Is there an algebraic version of this? 
Problem 4.4.
Can we find the fundamental matrix from silhouettes? If the silhouettes are bounded by algebraic curves are there algebraic constraints on the fundamental matrix?
Cite this as: AimPL: Algebraic vision, available at http://aimpl.org/algvision.