Credit: Wikimedia commons

The principle behind it

The 3D effect behind a stereogram is based on the same theory of our everyday 3D vision. Because we have two eyes separated by a small distance, the images that arrive to each of them have a slightly different perspective. Each of these images are combined by the brain and transformed into a single one that carries the 3D feature in it. The same thing happens with a stereogram: you trick your brain to capture two different perspectives of a single image (by looking deeper than you would normally) and the image appears in 3D. Unfortunately, there are some people that are 3D blind: due to inherent eye problems (lazy eye, previous eye operations) they cannot see images in 3D. But don’t worry, if you have a normal vision you should be able to see those!


Principle behind the 3D effect of autostereograms
Credit: Maria F.

How to see an autostereogram

It takes a bit of practice at first, but once you’re there it’s lots of fun! We’re going to start with the orange one above. Here’s how you do it:

  1. Place the image (on the screen or printed) at a distance of about 50-60cm (2 feet) from your eyes.
  2. Try to focus on an imaginary point behind the image (as if you were trying to look at the wall in front of you if on the computer or your foot under the table if you’re practicing with the printed version).
  3. Relax. Something will show up, it’s just a matter of time.
  4. When you see something blurry appearing, don’t lose it! If you hold on to it, your eyes will do the rest. Did it appear?
    “Yes!!!” Well done! It’s beautiful, isn’t it? Now try with the one underneath (the 3D effect is even more pronounced than the image shows on normal vision)
    “No...” go to step 5
  5. Focus and unfocus several times. Sometimes this helps.
  6. Stop for a while and try again later. It’s a matter of practice. Some people learn in 5min, some people need weeks. But you will learn, after all we all see the real world in 3D!
3D stereogram of a chess board
Credit: Wikimedia commons
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For more fun autostereograms to discover, here's an awesome book filled with them!