Title: The Magic Eye
Author: Yun Hwang
Category: Cool Science


Have you ever gazed into a piece of paper with a series of seemingly random dots but focused into the distance? This picture of random dots, of course, is a ‘Magic Eye’ picture. When you follow the instruction and focus in the distance, magically, you see a three-dimensional image (3D) on a two-dimensional (2D) sheet of paper.

Like most magic, creating a 3D image is done in a very clever fashion. What is different about this ‘magic’ is that there is no deception involved; the ‘magic’ effect is a very simple manipulation of how you use your eyes to generate depth perception.

There are two ways that your brain processes the 2D visual image into a 3D picture. One way is through learning and deducting from past experiences. For instance, if you see a car behind a person, your brain assumes that there is a car behind the person. Or if you see a car and a house that are the same size, your brain assumes that the house is farther away than the car, since your past experience tells you that a house should be larger than the car. This deduction from past experience is a basis for many optical illusions, such as ‘The Shrinking Room’, where the room looks much longer than it actually is because certain objects are smaller than they should be according to the brain.

This method is not really usable on a single sheet of paper. Instead, Magic Eye pictures employ a method that is hard-wired into your brain. Each eye creates a visual field that corresponds to what it sees. This visual field is what you see when you close one eye and look at the world through the other one eye. Because we have two eyes located on a slightly different place on the face – the difference is only minor, but that is sufficient – each eye’s visual field is different from that of the other.

A simple demonstration: put your finger in front of your nose; now cover one eye and look at the finger noticing where the finger is in relation to the background. Now, cover the other eye and look at the finger. The finger should be in a different place relative to the background.

Focusing on one object and comparing the degree of discrepancy between the two visual fields allows the brain to judge the distance from the object.

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The clever ‘trick’ in the Magic Eye pictures is that you focus on a point that is behind the Magic Eye picture you are looking at. By putting a Magic Eye picture before the focal point (see diagram), you effectively present two different images of the Magic Eye picture in your left and right eye. Your brain interprets the differences as a 3D image. Which just goes to show – you can’t be cool without science.

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