the original image is shown in (a).
Figure (b) contains only sudden intensity changes, called "zero-level
Figure (c) is the result of analysis on (b) by edge detectors and
(d) by bar detectors.
Edges are isolated lines and bars are formed out of two nearby parralllel
Figure (c) and (d) are then encoded in terms of the position; orientations,
lenghts and widths of edges and bars.
Figure (c) and (d) are primal sketches of the scenes in (a)
Des explications et un hors sujet !