1/28/2004   slide 15
Rule 5: Smooth curves in 2D are smooth curves in 3D  & 
Rule 6: Curve in 2D = rim of a 3D surface (silhouettes)
•“Always interpret a curve that is smooth in an image as smooth in 3D.” [Hoffman 1998 p33.]
•“Where possible, interpret a curve in an image as the rim [contour/edge] of a surface in 3D.” [Hoffman 1998 .p.39]
–i.e., as bounding part of a surface, not just a curved line hanging out in space
Not a proximity or grouping effect.
Says that in general, lines stay lines and curves stay curves. Cohesion of matter?
A 2D curve is probably curved in 3D
It’s also probably the result of a 3D curved surface—vs. a 2D “line” that is curved and hanging out in 3D space.