From Primal Sketch to 2.5D Sketch
The primal sketch model (Guo/Zhu/Wu 2003) is a parsimonious, graphical, token representation for generic natural images. Based on this representation, we compute the layered representations (2.1D sketch) and surface (2.5D sketch), following David Marr's conjecture. The 2.5D sketch is also called the needle map (surface normal field), and can be computed through the so-called Shape-from-X (X stands for visual cuescues, such as stereopsis, shading, texture, motion, defocus, photometric stereo, ...).
We studied two projects for computing 2.5D representations based on the primal sketch. The sketchable parts represents the structural primitives, while the non-sketchable parts are filled in through MRF based on a surface-smoothness assumption.