Make your own 3-D stereograms


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Materials needed: Your computer (or alternatively, just a typewriter), paper, and your imagination.

Do you like to look at the Magic Eye (Copyright N.E.Thing Enterprises) feature that appears in some Sunday comics? (The Magic Eye is called a "single image random dot stereogram".) Do you wish that you could make one? Do you wish that you understood what is going on? Well, I can't explain it rigorously (and you wouldn't want me to), but I can give you a rough idea how these work and how you can make your own.

In the 1960's, a psychologist, Bella Julesz made 3-D pictures with apparently random dots to see if people could perceive distance without any clue such as size.

In the real world, we use our binocular vision to perceive distance. Each of our eyes sees a slightly different picture of the scene viewed. The brain, through experience, has learned to interpret the two flat images into a three-dimensional one. We have had the capability of viewing flat pictures in 3-D since the stereoscope was invented by Sir David Brewster of England in 1849. Older readers will remember the stereopticons that people and schools used in the last century and the first part of this century. Younger readers are familiar with the Viewmaster that you can buy today. Both of these devices use the same principle. Two pictures are made of the same scene with a camera with two lenses or with two different cameras (or two pictures made by the same camera in different positions.) The lenses, cameras, or positions are usually separated by what is called the interocular distance (the distance between the centers of an average person's eyes.) Then when you view the two pictures it is as if you are viewing the actual scene.

The Magic Eye takes advantage of the fact that a normal person causes their two eyes to converge at different angles depending on the distance of an object being observed. (When we look at an object that is very close to our eyes, we say that it causes us to be cross-eyed.) In the case of the Magic Eye, the images are broken down into a series of dots. Then the dots are placed in a single image with the corresponding dots placed an appropriate distance apart so that when viewed, the brain "sees" a three dimensional image.

You can make your own 3-D pictures fairly easily. Consider the following chart:

* * A A A A A A B B B B B B A A A A A A

Bring your eyes close to your monitor such that each eye sees the two asterisks separately; move your eyes until two of the four asterisks are superimposed so that you see three asterisks. Then slowly move away from the monitor so that the combined image comes into better focus. You should see what appears to be three levels in the scene. The A's appear to be in the middle level and some of the B's are in front of the A's, and some of the B's are behind the A's. You can see that the A's are spaced at equal distances (10 spaces between them) but the B's are alternately spaced: 11 spaces then 9 spaces. What is happening is that one eye sees one B and the other eye sees an adjacent B slightly offset. The brain tries to interpret this as one B at a nearer or farther distance than the A's.(Note: If you are using a browser that allows you to change the font size, the 3-D effect will probably be easier to view using a small font.)

We don't have to space the B's at alternately different separations. If we make them closer or further apart than the A's we can trick the brain into thinking they are nearer or farther. Consider the following:


In this example, the ANT's are separated by more space than the BEE's, and the BEE's are separated by more space than the FLY's. We can actually make the above using pictures of ants, bees, and flys.

The following picture illustrates a 3-D picture using the first method above with graphics instead of letters.

If you want to make a stereogram using only letters, you can make it using a text editor on your computer and then printing the resulting text. You do not need the asterisks, but it is easier to view the stereogram if you have the asterisks in your text.

Near the center of the page, enter 2 asterisks separated by 10 spaces.

Leave a blank line and then enter a word (such as "HATE") several times with the words separated by 10 spaces.

Leave a blank line and then enter a word (such as "LOVE") several times with the words separated by 8 spaces.

You should have something like the following:


If you have done this correctly, when viewed in 3-D you will see that you have brought LOVE to the front and pushed HATE to the back. You can experiment with more lines of text; and you can try various spacing between the words.

If you want to experiment with graphics, you can use a graphics package to place like images at various horizontal spacing to see how the spacing affects the apparent distance from the viewer. If you do not have a graphics program or if you do not know how to use a graphics program, I have an alternative.

Print this collection of cat and dog images. Then cut out each image on the dashed lines. You will have several cat images and several Scottie dog images. Place several cat images in a horizontal line (on a flat surface) with each image spaced the same distance from the previous image. On another line, do the same with the dog images but use a greater or lesser spacing. You should be able to view your arrangement in 3-D. You can experiment with various spacing and make more than 2 rows of images. If you find an arrangement that you like, you can paste the images to a blank piece of paper. You may also use different graphics. For example, you may find a drawing of a different type of animal. Take it to a copy machine and make several copies of it. Then cut out the separate images and place them as described before.

You can have a lot of fun experimenting with 3-D.

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