Ordinal characteristics of transparency.
Edward H. Adelson* and P. Anandan**
*Media Laboratory and Department of Brain and Cognitive Sciences, MIT,
Cambridge MA 02139, and **Department of Computer Science, Yale University,
New Haven CT 06520
Figure 1 shows an example of visual transparency. The image could arise from
a number of different physical causes. For example, a square of tissue paper
could be in front of a dark grey circle; or a circular shadow could be cast on a
plane containing a light grey square; or a dark circular filter could be lying on
top of a light grey square. Although the physics is uncertain, one can perceive
the image as a combination of two more primitive images.
We use the term "transparency" to cover the general case of such image
combination, including what would be called "translucency" in ordinary
language. Many physical phenomena can produce transparency. For
example, dark filters, specular reflections, puffs of smoke, gauze curtains, and
cast shadows, all combine with patterns behind them in a transparent manner.
When an image has been formed by the combination of two primitive images,
then it is usually more parsimonious to describe the image in terms of that