ave you walked through a mall lately? These
days, as you wander past most of the poster shops, there will be a large group
of people staring at the same poster with surprisingly weird expressions on
their faces. Some will be in the initial stages of denial or rejection---they
will be concentrating, some slowly rocking their heads backwards and forwards,
searching for an image that they have never seen before. Others will be grinning
from ear to ear, pointing at the poster, chuckling with their friends that a
member of their group hasn't seem them yet. "Come on Bill, come on!", they cry
and as Bill gets increasingly more frustrated he concentrates harder and harder,
until finally (if he's lucky) he sees a true 3D image, without the need for
special glasses or equipment.
These pictures are known
as Single Image Random Dot
Stereograms (SIRDS),
or Single Image Stereograms (SIS) depending on whether the picture contains
random dots as a base for the 3D effect, or a repetitive pattern. Unfortunately,
each commercial company has labelled them differently. Shop owners generally
don't know what you mean, unless you say "Hollusion" or one of the many other
specific names.