How do I see them?

Brought to you by Stuart Inglis

Most Stereogram pictures are usually generated so that if you look at (converge your eyes on) a position twice as far away as the picture, and focus on the picture, generally after a few minutes you see a surprising 3D image!

Most people find this extremely difficult for the first time. You have to focus on a point which is different from where you are looking. This is known as "de-coupling" your vision process. Instinctively people focus at the same point they are looking at, and this is the main obstacle in seeing images of this type.

This is why most posters come with a reflective surface such as glass or plastic covering them---if you try to look at your reflection you will be looking at a point twice as far away as the actual poster. It has been noted by almost everyone that while this sometimes helps beginners see the 3D effect for the first (and perhaps even the first few) times, experienced viewers to not need any help like this, and indeed the reflection is usually very distracting and decreases the quality of the 3D effect.

There are many ways to teach this de-coupling to either yourself or to others, including (in almost no particular order):

NOTE: It is generally easier to see Stereograms under bright light. I have been told this is because you eye relies less on focus under harsh conditions. Another point, to see stereo images, you need to have "passable" use of both eyes. If you wear glasses try with and without them on. Some short-sighted people can see them easier without their glasses on (if they get closer to the picture).

The pull-back

Hold the picture (or move your face) so your nose is touching the picture. Most people than can not possibly focus with something this close to their eyes, and they will be content with their inability to focus. With the picture up close, pretend that you are looking straight ahead, right through it. Now slowly pull the picture (or your face) away while keeping your eyes pointed straight ahead. If you do this slow enough, an image usually appears when the picture is at the correct distance.

The reflection

As mentioned above, with a reflective surface it is sometimes a lot easier to converge your eyes in the correct position. You simply focus on your nose or some central reflection in the picture, and wait until you focus on the image.

The drunk-eyes

This method is used to describe the feeling of the process of deconverging your eyes. It is very much like being drunk or having "staring-eyes". Your eyes don't look at the object, but rather through it. This state is common to some in the morning before the coffee caffine fix.

The wall, or the finger

Hold the picture so that it is half between you and a wall. Look *over* the top of the picture towards the wall, and focus on something such as a picture hook or mark. While keeping this "gaze" either slowly lift the picture or lower your eyes while keeping them converged on the wall.

A similar approach (but for cross-eyed viewing) is to stand arm's length away from the picture and put your finger on the picture. While slowly pulling your finger towards your face, keep looking at your finger, you will notice the picture becoming blurry, and at an intermediate position you will (eventually) see the 3D image.

The see-through

Photocopy the picture onto a transparency. Then focus through the transparency onto something twice as far away. This is similar to (The wall, or the finger) above except now you don't need to change the position of your gaze.

Wide-Eyes

This method involves building a device to widen your interocular distance, as well as allowing the adjustment of the convergence of your eyes. It's so simple, you almost don't have to be there!. I have had a look through such a device, and the results were very good.

(diagram pending...)

Cheating...

To cheat, photocopy the image onto two transparencies, then overlay them and carefully shift them horizontally so they are about an inch or two out of alignment. Somewhere around this position you will see a rendition of the image. Obviously in 2D not 3D, but you will at last finally believe there is "somethere in there."

And if you're still having difficulty, this comment by jhakkine@cc.Helsinki.FI (Jukka Hakkine), may apply to you:
"Richards (1970; Experimental Brain Research 10, 380-388) did a survey among 150 MIT students and noticed that "...about 4% of the students are unable to use the cue offered by disparity, and another 10% have great difficulty and incorrectly report the depth of a Julesz figure relative to background." He further concludes that inability to use stereopsis is an inherited defect and is related to "three-pool"-hypothesis of binocular neurons."

But don't dispair, don't give up until you're tried for at least a month!


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