Optical Effects: Moiré Patterns 1
by Gianni A. Sarcone and Marie J. Waeber

Superimposed patterns
When a pattern printed on a piece of transparent acetate sheet is laid over a second one (background pattern), the combination of both patterns can create an interference pattern called “moiré”.

A similar visual effect is produced when a piece of sheer cloth is folded over itself, or when copying a halftone reproduction on a flatbed scanner (some moiré effects can also be created with a toy called a spirograph).

In technical language, we say that the combination of the layers creates an “alias pattern” and this effect is known as “aliasing”. Photographers don’t appreciate moiré patterns because they can sometimes ruin a printed photo (in printing, the result from incorrect screen angles of overprinting halftones creates an undesirable moiré effect).

But moirés are also an interesting subject to study and play with. Moving one pattern over another can generate fascinating visual effects. You can experiment on your own with the moiré effect by making a transparent photocopy of each following basic pattern (dotted, concentric or radial patterns) combining it with its original background. The use of color will add a dramatic dimension.

The following represents small samples of the astounding variety of moiré patterns possible:

Animated moiré effects Effects generated by regular textures (dots) Effects generated by random textures (dots) Effects generated by colored textures (dots)   Continue to page 2 (radiating optical effects)
Optical illusion cards	Hypnotic patterns	Amazing T-shirts