  The Shape From Shading is one of a computer vision field. It studies the 3D
reconstruction of an object from a single grayscale image. The difficulty of
this field can be expressed in the local ambiguity (convex / concave). J.Shi
and Q.Zhu have proposed a method (Global View) to solve the local ambiguity.
This method based on the graph theory and the relationship between the singular
points. In this work we will show that the use of singular points is not
sufficient and requires further information on the object to resolve this
ambiguity.
