Shareware Beach

Wednesday, 2 February 2005

The World as an Illusion

Filed under: Life & The Universe — Jan @ 21:31

Optical illusion or real world image?Many people are fascinated by so-called optical illusions—cleverly designed drawings or objects that make us think we see something that’s not really there. Recently someone pointed me at a web page with “a coupe of rather neat optical illusions“. But are these really illusions?

Illusion #1, the artist claims, tricks the brain into perceiving square B as being lighter than square A, while in fact they are the same color. If you open the image in a graphics program, the pixels in square A and B indeed have the same color.

But is this an illusion, or just a perfect example of why the brain’s color perception works the way it does? If you had a real checkerboard where square A is really darker than square B, and you put an object on it to cast a shadow on square B but not square A, your eyes would receive the same amount of light from both square A and square B. This corresponds with the fact that both squares have the same RGB values in the computerized image. Your brain in turn interprets the scene seen by your eye, using all your knowledge of the real world. Such real world knowledge includes light and shadow effects, as well as probabilities. The odds that random blotches of color would appear just like a checkerboard with a cilinder on it are too remote. Therefore, the brain concludes checkerboard and cilinder have to be real, and you will see them that way.

There’s no illusion here at all. The brain is doing what it is supposed to do. If your brain didn’t see square A as darker than square B, you would never be able to make sense of the real world. While the image here is a manufactured one, a photograph of a cilinder on a checkerboard would appear just the same. The camera’s metering would give squares A and B the same brightness, and your brain would still see them as different.

For the same reason, people are often disappointed with their holiday snapshots. When you look at somebody while the sun is shining on his or her back, you can see both the person and the bright background perfectly clear. But when you look at the picture you took, you see a black silhouette in front of a bright scene. The camera’s metering cannot handle the difference in brightness between the person and the background the way your brain does. When you look at the picture, the context of the city or landscape is gone. The context becomes the photo album or the back of your camera, and your brain no longer has the frame of reference it needs to see through the illusion.

Seeing square A as being darker than square B is not an illusion. It is seeing the real world as it is, not as it represents itself on your retina.

No Comments

No comments yet.

Sorry, the comment form is closed at this time.