Conjectures on the Perception of Elongation

The papers start by discussinq some of the background to the problem of the perception of length together with some known illusions in this field. The difference is then drawn between image contraction and image thinning, both processes of which serve to introduce the proposed conjecture. The suggested conjecture is that lenqth is perceived by a mechanism which first forms a minimal closed path (hull) around the object and then performs an isotropic image reduction operation on the hull of the image. It is conjectured that the elongation of the image is exemplified in the resulting path so obtained; no path should result if the original image possesses no elongation. The conjecture is used to explain the known illusions discussed and a few new ones are suggested. An isotropic image reduction technique is described and experimental results testing the conjecture , obtained using a variety of imaqes, are presented.