Saturday, April 5, 2008

The Art of Optical Illusion

Not long ago, we drove to San Jose to see the M.C. Escher exhibit at the contemporary art museum. I've always been a fan of his work.

Many of his works use simple formulae to achieve the illusion effects that made him one of the most notable artists to use this form of art.

By definition, mosaic art lends itself to the use of optical illusion very well.

See how the fish and turtles seem to come to life?

For your viewing pleasure, I have put together a collection of other optical illusions that I found on the web along with a little information about their history.

To experience the full effect of this first one, please click the photo to enlarge:

Bezold Effect

The Bezold Effect is an optical illusion, named after a German professor of meteorology, Wilhelm von Bezold (1837-1907), who discovered that a color may appear different depending on its relation to adjacent colors.

In the above example, the red seems lighter combined with the white, and darker combined with the black.

This next one is called the café wall illusion. It is an optical illusion, first described by Doctor Richard Gregory. He observed this curious effect in the tiles of the wall of a café at the bottom of St Michael’s Hill, Bristol. This optical illusion makes the parallel straight horizontal lines appear to be bent.

To construct the illusion, alternating light and dark “bricks” are laid in staggered rows. It is essential for the illusion that each “brick” is surrounded by a layer of “mortar” (the grey in the image). This should ideally be of a color in between the dark and light color of the “bricks”.

The Cafe Wall Illusion

The Chubb Illusion
The Chubb illusion is an optical illusion wherein the apparent contrast of an object varies dramatically, depending on the context of the presentation.

Low-contrast texture surrounded by a uniform field appears to have higher contrast than when it is surrounded by high-contrast texture. This was observed and documented by Chubb and colleagues in 1989.

Hermann Grid
The Hermann grid illusion is an optical illusion reported by Ludimar Hermann in 1870 while, incidentally, reading John Tyndall’s Sound.

The illusion is characterised by “ghostlike” grey blobs perceived at the intersections of a white (or light-colored) grid on a black background. The grey blobs disappear when looking directly at an intersection.

Zöllner Illusion
In this figure the black lines seem to be unparallel, but in reality they are parallel. The shorter lines are on an angle to the longer lines. This angle helps to create the impression that one end of the longer lines is nearer to us than the other end.

This is very similar to the way the Wundt illusion appears. It may be that the Zöllner illusion is caused by this impression of depth.

In this next illusion, the image shows what appears to be a black and white checker-board with a green cylinder resting on it that casts a shadow diagonally across the middle of the board. The black and white squares are actually different shades of gray.

The image has been constructed so that “white” squares in the shadow, one of which is labeled “B,” are actually the exact same gray value as “black” squares outside the shadow, one of which is labeled “A.” The two squares A and B appear very different as a result of the illusion.

Adelson's Checker Illusion

Here is a great little video about how to draw some optical illusions. The soundtrack is pretty obnoxious, and I apologize for that. I watch it with the sound turned off.

1 comment:

Bethel of Bethania said...

Wooh this was interesting especially the little video .. thanks ... gotta say not a good thing to read/watch on the day you have a migraine ... ha ha or the day after for that matter ... OOroo ... Bethel

Stacy Alexander