Field of Science

Try this at home: Make your own stereogram

Have you ever wanted to make your own 3D movie? Your own Magic Eye Stereogram? This post will teach you to create (and see) your own 3D images.

Magic Eye Stereograms are a relatively new technology, but they grew out of the classic stereograms created in 1838 by Charles Wheatstone. For those of you who don't know what a stereogram is, the word broadly refers to a 3D-like image produced by presenting different images to each eye.

The theory is pretty straight-forward. Focus on some object in your room (such as your computer). Now close one eye, then the other. The objects in your field of vision should shift relative to one another. The closer or father from you they are (relative to the object you are focusing on), the more they should shift.

When you look at a normal photograph (or the text on this screen), this difference is largely lost. The objects in the picture are in the same position relative to one another regardless of which eye you are looking through. However, if a clever engineer rigs up a device so as to show different images to each eye in a way that mimics what happens when you look at natural scenes, you will see the illusion of depth.

For instance, she might present the drawing below on the left to your right eye, and the drawing on the right to your left eye:

If the device is set up so that each picture is lined up perfectly with the other (for instance, if each is in the center of the field of vision of the appropriate eye), you would see the colored Xs in the center at different depths relative to one another. Why? The green X shifts the most between the two images, so you know it is either the closest or the farthest away. Importantly, because it's farther to the left in the image shown to the right eye, it must be closer than the blue or red Xs.

You can demonstrate this to yourself using a pencil. Hold a pencil perfectly vertical a foot or two in front of your face. It should still look vertical even if you look with only one eye. Now, tilt the pencil so that the bottom part points towards your chest (at about a 45 degree angle from the floor). Close your right eye and move the pencil to the right or the left until the pencil appears to be perfectly vertical. Now look at the pencil with your right eye instead. It should appear to slope down diagonally to the left. That is exactly what is happening in the pictures above.

A device that would fuse these two images for you isn't hard to make, but it's even easier to learn how to fuse them simply by crossing your eyes. There are two ways of crossing your eyes -- making them point inwards towards your nose, and making them point outwards. One way will make the green X closer; one will make it farther away. I'll describe how to use the first method, because it's the own I typically use.

Look at the two images and cross your eyes towards your nose. This should cause each of the images to double. What you want to do is turn those four images into three by causing the middle two to overlap. This takes some practice. Try focusing on the Xs that form the rectangular frames of the images. Make each of those Xs line up exactly with the corresponding X from the frame of the other image. If you do this, eventually the two images should fuse into a single image, and you will see the colored Xs in depth. One tip: I find this harder to do on a computer screen than in print, so you might try printing this out.

That is the basic technique. You should be able to make your own and play around with it to see what you can do. For instance, this example has a bar pointing up out of the page, but you can also make a bar point into the page. You also might try creating more complicated objects. If you want, you can send me any images you make (coglanglab_AT_gmail_DOT_com), and I will post them (you can try including them as comments, but that is tricky).

One final tip -- you'll need to use a font that has uniform spacing. Courier will work. Times will not.

Finally, here's another stereogram that uses a completely different principle. If you can fuse these images, you should see an illusory white box floating in front of a background of Xs. In a future post, I'll explain how to make these.

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