How Stereo Works
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Why do we see in Three Dimensions? We do not really see what we think we are looking at. We are really seeing a "ghost" image created by our brain constucted from the different information sent by each of our eyes. This will probably surprise you. Unless you have only one functioning eye, you don't see what each eye sees, you see the "ghost" image. Each of our two eyes sees the world slightly differently because each eye is seeing it from a different place. On average that different place is about 2.5 inches to the side of the other eye. But that makes all the difference. |
In this drawing, figure 1 represents how you would see a row of 3 cylinders, each directly behind the others, if you had only one eye. It would look like only one cylinder unless you were looking from a slight height as in the drawing. But it is still difficlult to see the different cylinders.
Figure 2 shows what that row would look like if you were looking at it, again from directly in front, but using both eyes. It has become clear that there are three cylinders.
 Figure 3 shows the reason. From directly in front of the row, each of your eyes sees a different view of that row. Your brain assembles the information it receives from the two images and constructs your ghost image as seen in figure 2.
A stereo photograph creates this "ghost" image in your brain so it appears to you that you are actually looking at the original scene exactly
as if you were there looking at it with both of your eyes. The method is simple. The stereo photograph is actually two photographs, taken from a position about 2.5 inches apart. (This seperation must be increased or decreased for very close or distant objects but that is not important to discuss here.)
To finish the illusion of the stereo photograph, you must look at each of these two pictures seperately, one with each eye, at the same time.
Your brain will construct that same "ghost" image which is the trhee dimensional image you think you are seeing. |
| If you have never looked at a stereo picture in this way, all of your effort to learn how to do it will have been worh it. You will be amazed and astounded by what you see. If you can't do it, all you have missed is a fun way of looking at stereo pictures. Some people never learn to do it. Some people do it very easily. And a small percentage of people cannot see 3-D at all, even in their normal vision. |  |
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One method to free view stereo pictures The quickest and easiest method to try is to lean forward until your face is centered on the double picture but you are way to close to see it. It will look completely out of focus. Allow your eyes to relax and move slowly away from the screen.
Hopefully, you will begin to see three images in front of you instead of the two that you know are actually there.
If that happens, continue to move slowly away while directing your attention only to the picture in the center.
That's the ghost image being formed by your brain. If you continue back until the picture in the center is in focus, you will be looking at the three dimensional picture. If this is the first time you are seeing one, you are in for a treat.
If that doen't work, try the method below. If that doesn't work, perhaps you should make it easy and just purchase a low cost viewer. |
Some people can do this with no effort at all and some people need to work at it a bit. Another method. Move forward again to place your nose about 20 to 24 inches from the center of the two pictures.
If you are looking at the pictures the same way you are looking at these words you will see two pictures that look pretty much the same as each other.
Allow your eyes to look through the pictures and try to see them printed on the back of the monitor, the same as you did with the word focus.
If you do it right you will see the pictures become unclear.
If you do it perfectly (with practice you can) you will see three pictures instead of two.
The picture in the middle will probably look like two pictures superimposed but very close.
As you relax your eyes you will find you can make those two pictures get closer or further from each other.
What you are trying to do is to get them to come together so you will see only one solid picture in between the two side pictures.
When you accomplish that, you can just pay attention to that center picture and enjoy the three dimensions in the view.
You are now looking at the same ghost image that would have been made by your brain if you were standing where I stood when I took the picture.
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