How to view Single Image Stereograms

The worst thing for learning is stress. this knowledge is especially true for trying to see the Autostereograms for the first time, because it may take several minutes of concentration. There exist several methods for viewing, some of them for wall-eyed and others for cross-eyed viewing. When watching a picture designed for cross-eyed viewing in the wrong way, i.e. with a wall-eyed method, you see the perspective inverted. That means that instead of objects

popping out of the image, they seem to be sunken in. (Nevertheless you can view the 3D-image and get the three-dimensional-impression !) [BACC 1994]

WHAT YOU HAVE TO DO

In general you have to de-couple Convergence and Accomodation of your eyes, that means that you have to focus on a point different from the point you look at. This process is easier when watching the picture under bright light. If you wear glasses you should try with and without them. There exist two classes of pictures:

Pictures rendered for wall-eyed viewing can be seen "behind" the plane. Therefore you should try to see through the plane (orient the axes of your eyes to infinity) while focusing on the image plane. To achieve that, it is useful to view a picture with a reflecting surface because when trying to look at your reflection you look "through" the plane. [INGL 1994]

Pictures for cross-eyed viewing are a bit more difficult to see, as they lie between the viewer and the plane. To see those pictures one has to focus on the plane but must turn his eyes towards his nose until the axes of the eyes are crossed. The advantage of this method is, that it is possible to generate very large images that can be viewed from a long distance, whereas wall-eyed pictures are limited in their size. [INGL 1994]

HOW TO DISCONVERGE THE EYES

The first and the second method are the most "reliable" ways to see 3D-images and they are recommended by Tom Baccei in his book "Magic Eye" [BACC 1993] [BACC 1994]. When you cannot see the images with these methods, you can use the other approaches, developed by Stuart Inglis. [INGL 1994]

The pull-back method
Hold the picture just in front of your face. Pretend that you are looking straight ahead, right through the picture. When your eyes relax and do not focus on any point anymore, you begin to slowly move the picture away from your eyes (about 1 centimeter per second). When you reach the usual reading-distance you should be able to view the three-dimensional-picture. Do not focus on the image or it will vanish and you have to start again !
The reflection-method
Stereograms usually come on reflecting paper. Hold the picture in a direction that produces a light-reflection on the paper. Try to focus on this reflection and after a few seconds you should see the three-dimensional image.
The drunk-eyes
This method describes the feeling of the process of disconverging your eyes. As your eyes begin to move independently you see double-images, like when you are drunk. Your job is to control each eyes movement so that the axes of your eyes get crossed (for cross-eyed pictures) or (almost) parallel (for wall-eyed images).
The wall or the finger
For wall-eyed images you may hold the picture half in between you and a wall. Then you look over the top of the picture towards the wall. Focus on a special spot on the wall, for example a picture hook. Then move the picture slowly up until it is full in your sight (do not move your eyes !). Now you should see the 3D-image.
For cross-eyed pictures you should stand arm-length away from the picture. Hold your finger on the picture and focus on the finger. When you slowly move your finger towards your nose, you should see the image about half the distance between your nose and the picture.
The see-through
This is the most convenient way for viewing wall-eyed pictures. Copy the picture onto a transparency and hold the transparency in about your usual reading distance. Now focus through the transparency on a point about twice as far away. Now you should immediately see the 3D-image!
The wide-eyes
There exist special devices for widening your eye-distance and manipulating the convergence of your eyes. With such a device, you simply put the image into it and get the three-dimensional impression.

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