Williams and Jacobs, "Stochastic Completion Firlds"
Wertheimer, "Laws of Organization in Perceptual Forms"
Hummel and Zucker, "Foundations of Relaxation Labeling Processes"
Langer and Zucker, "Shape from Shading on a Cloudy Day"
Koenderink, "What Does the Occluding Contour Tell Us About Solid Shape?"