~F8THE ALGORITHM: INTRODUCTION.

	CRE  consists  of  five  steps:  thresholding,    contouring,
nesting,    smoothing  and  comparing.  Thresholding, contouring  and
smoothing perform conversions between two different kinds  of images.
Nesting  and contouring  compute topological  relationships within  a
given image representation. In summary the major operations are:

	MAJOR OPERATION.	OPERAND.	  RESULT.

	1. THRESHOLDING: 	6-BIT-IMAGE,	  1-BIT-IMAGES.
	2. CONTOURING: 	 	1-BIT-IMAGES,	  VIC-IMAGE.
	3. NESTING:		VIC-IMAGE,	  NESTED-VIC-IMAGE.
	4. SMOOTHING:	 	VIC-IMAGE,	  ARC-IMAGE.
	5. COMPARING:		IMAGE & FILM,	  FILM.

	Although the natural  order of operations is  sequential from
image thresholding  to image comparing; in order  to keep memory size
down, the first four steps are applied one intensity level at  a time
from the  darkest cut to  the lightest  cut (only nesting  depends on
this  sequential  cut  order);  and  comparing  is  applied to  whole
images.

	The illustrations on  pages 21 and  23 show an initial  video
image  and  its  final  smoothed  contour  image;  the  illustrations
immediately below  and  on  page 24  the  corresponding  intermediate
sawtoothed contour images.  The illustrated  images are each composed
of  seven intensity  levels, and  took 16 seconds  and 13  seconds to
compute respectively (on  a PDP-10,   2usec memory).   The final  CRE
data structures contained 680 and  293 nodes respectives, which comes
to  2K and 4.5K words respectively;  the initial video image requires
10.2K words.

FIGURE: PUMP SAW TOOTHED CONTOURS.
~I1973,800;F8- 22 -