Methods and apparatus for construction of an object shape from an image using a light-space graphical model are disclosed. A set of normal vectors for a set of pixels in an image is defined. Each normal vector is defined in terms of an azimuth and a zenith measured in a spherical coordinate system centered on a light source illuminating the image. The zenith of each normal vector is constrained based on an observed shading of a respective pixel. A shape is constructed from the image. Constructing the shape includes minimizing an energy function to specify an azimuth value and a zenith value of each normal vector. Minimizing the energy function further includes constraining the azimuth of each normal vector based on an image gradient of the image at each respective pixel to enforce a coplanar assumption between the image gradient expressed in a three-dimensional space and the respective normal vector.