The two sets of figures at 
left illustrate the logic of 
stereograms. Suppose that the 
smaller square in the upper set 
of figures is in front of the 
larger square and that you are 
looking at them head-on. To the 
left eye, the projected image 
would appear as figure A; to the 
right eye, it would appear as 
figure B. These two patterns, 
when combined, create the 
impression of depth. If the 
smaller square were behind the 
larger one, they would appear 
to the two eyes as in the lower 
set of figures. Notice, therefore, 
that depth can be reversed 
stereoscopically simply by 
transposing the left and right 
stereogram patterns. Inverting 
or reversing the left-right 
orientation of the patterns will 
have the same effect.

Viewed as stereograms, the 
upper set of figures will appear 
as a small square floating in 
front of a large square, and the 
lower set of figures will appear 
as a large square floating in 
front of the small one.