How to see Stereograms
Posted on: 11/04/2014
What does this have to do with video games or emulation? Nothing! This is my attempt to write a tutorial on how to see stereograms because I have failed to teach my friends time and time again, leaving them frustrated and me disappointed. What is a stereogram? These simply appear to be images containing nothing more than a repeating pattern that slightly deviates each time the pattern is repeated. But there is a hidden image in that pattern! You just have to trick your eyes to see it. Hopefully by the end of this tutorial, you will be able to see what this picture holds!

Hold your fingers together in front of your face, but instead of focusing on your fingers, focus on the distant background (such as the wall, a clock, a chair, anything that is a moderate distance from where you are).
Part 1: A Small Experiment

It's important to understand how and why we can see these things in the first place. First, lets try a little experiment.
And this is what you will see... Your fingers now looks like sausage links! This happens because your eyes cannot focus on both near and distant object. If you concentrate on your fingers, then the background will double. If you focus on the background, then your fingers will double. When your fingers are doubled, the brain is tricked into thinking it is looking at a solid object because the two "ghost" fingers overlap which are around the same size and color.

BONUS: Slowly pull your fingers apart, and watch the floating sausage!

Part 2: Understanding the Concept

So now you know how to do the sausage-finger trick. As I mentioned before, this happens because your eyes are limited when it comes to focusing depth. The secret to seeing a stereogram is to trick your eyes into thinking you are looking at something much farther away than the image itself. This causes the image to "double", two similar points converge, and the image comes into focus.
First, this is what you might think you "should" see when holding your finger close to your face.
But this is not how our eyes and brain work. Because we are focusing on our finger, the background appears to be doubled.
When the background is brought into focus, then the finger becomes out of focus and doubled. It is essential here to understand exactly what it is you are doing with your eyes, because this is the secret to seeing a stereogram. Practice this for awhile, until you get a good feel of what you are doing with your eyes. After awhile, you should be able to willingly force your eyes out of focus.

So in short, to see a stereogram, you have to force your eyes to focus "beyond" the image, as if you are looking through a window at a distant background! When you get a good feel of how you are adjusting your eyes, try forcing your hand and other objects to "double". With practice, this will become second nature. Keep doing the hand/background exercise until you are a pro.

Part 3: A Simple Exercise

Now we're going to take what we learned here and apply it. Before trying to see a stereogram, lets try a simple exercise to converge two similar points to create a new image. This is the most important step, if you can't get this, then you won't see stereograms.
The object of this exercise is to force your eyes out of focus until the two crosshairs line up with each other. When they overlap, the brain will "lock" them in place. Think back to the finger and the background. Here you will have to force your eyes to think it is looking at the background, not the finger! If your eyes are in focus, then nothing will ever happen.

If you cannot force your eyes out of focus, then here is a simple trick you can perform. First get a general idea of where the X is in the image. Close your eyes, and put your face up to the screen, with the X between your eyes. Open your eyes. The two crosshairs should already be overlapping. Slowly pull your face away from the monitor, doing your best to keep the crosshairs "lock". And that's it. Practice makes perfect here, you do NOT want your eyes to focus on the near object!
When you are successful, the above image will look a lot like this, with the center crosshair looking slightly "3D"! Again, before you can move on, you MUST be able to turn the first picture into the second picture using only your eyes, brain, and wits.

And one last thing... when you blink, you will most likely lose your focus. This is why it is important to understand how to force your eyes out of focus, as explained in the "finger" sections of this tutorial.

Part 4: I Want to See Stereograms NOW!

It's time. Assuming you understand everything so far, and gained the ability to manipulate the image above using your eyes, you are now capable of seeing stereograms! The idea is the same, you look for two similar points and converge them.
This is a simple stereogram. See those 2 hearts in the green circles? You want to appy the same trick as mentioned in the previous section to bring them together. But do not do it in this image! Do it in the next one!
Now without the circles... The result should be a big 3D heart that is about the size of the entire image!

Part 5: I Won, or I Failed

So if this tutorial taught you how to see stereograms, great! It's now time to go enjoy your new found ability. A simple search on the web for the word "stereogram" or "magic eye" will bring up all kinds of fun picture to look at! If this tutorial failed to teach you, then don't feel bad. I'm apparently very bad at explaining how to see these things, but I was hoping this would be what changed that.

Part 6: Extra Section - Hemisphere Dominance in the Brain

If you can see magic eyes, then you can actually test your brain to see which hemisphere is dominant using the image below! The object is to use the same trick as the crosshairs, only this time, you make the circles overlap.
If the blue circle overrides the red, then the right hemisphere of the brain is currently dominant. If the red circle overrides the blue, then the left hemisphere is currently dominant. The goal is to be able to see both circles at once, which will create a cross in them. Doing this exercise can actually help improve communication between the two hemispheres of your brain!

For more information, visit this interesting link:
As a warning, the test on that page can actually hurt your eyes becase the circles are too far apart!