Robotics Reference
In-Depth Information
C
P
A
B
Figure 30.
Line drawing of an image of a rectangular solid
information, Roberts' algorithm could generate an image of an object, in
perspective, point by point.
Roberts' program detected edges by noting where the intensity of
light in an image changed significantly between one pixel and an adjacent
pixel. When these change points in an image formed a straight line, that
line was assumed by Roberts' program to be an edge. In this way his
program was able to convert images into line drawings.
Roberts worked with models of four straight-edged shapes: a cube,
another rectangular (but not cube-shaped) solid, a wedge with two tri-
angular faces, and a hexagonal prism. When the program encountered a
shape in an image, it first made an intelligent guess as to which of these
four shapes was the most likely. For example, in Figure 30 the point
P connects the three polygons A, B and C, and a search of the models
stored in the program reveals that a cube has three quadrilaterals meeting
at a point, so the cube is one possibility for the shape of this object.
Having identified a possible shape as the source of the image in a line
drawing, the program then “mentally” rotated that shape so it could be
viewed from every angle, and compared the various views with the line
drawings it had created from the image. When a good match was found,
the program noted which shape it had come from, as well as the size of
the shape, which angle it had been viewed from and where in the image
the shape occurred. Roberts' program was also able to recognize an object
made up by joining two of the shapes that it knew about. As parts of a
line drawing were recognized by the program, for example a triangular
part (suggesting a wedge shape), the program would eliminate from its
“sight” those parts it had already recognized and then it would attempt
to recognize whatever remained in the drawing.
Roberts' work was so fundamental to the study of computer vision
that most of the elements of his 1965 program can be found in modern
