Stereograms and anaglyphs


Stereograms

Terminology

A stereogram, also called a stereograph, is a pair of images with each image designed to be viewed by a single eye.

A stereogram can be viewed using a special instrument called a stereoscope. The stereoscope shows the left image to the left eye and the right image to the right eye.

A stereogram can also be viewed with the naked eyes. But then, most people find it easier when the two images are switched. The result is called a "cross-eyed stereogram" by opposition to rhe initial configuration called a "wide-eyed stereogram". In a cross-eyed stereogram the lines of sight are crossing each other: the left eye looks at the right image and the right eye at the left iamge. This is more like normal viewing when the two lines of sight meet at some focal point.

Viewing a stereogram

The next illustration is an example of a cross-eyed stereogram. (It was created using ARBeads and ARPix.)





If you are not used to looking at cross-eyed stereograms, you can try this:

The 3D effect should appear in the central image. If you are still having some problems, try varying your distance from the screen.

Remark: This method is only valid for cross-eyed stereograms.

Anaglyphs

Anaglyphs on a white background

In an anaglyph, the two images are drawn on top of one another but with different colors: one is in red, the other is in cyan (aqua), all this on a white background.

To look at an anaglyph, one needs a pair of red-blue glasses.

Hence, on the anaglyph

Although the right filter is blue, the drawing must be in cyan, not blue. Otherwise, it would be visible for both eyes. This (probably) has to do with the nature of the colors and with the color sensibility of the human retina.

Viewing anaglyphs

If, when looking at the anaglyph, you see more red than blue or more blue than red, you may have a lazy eye problem. Try focussing your attention equally on both eyes so that your brain perceives equal amounts of red and blue. Once you got this, the 3D aspect of the image should appear in all its splendor. Like anything else, the more often we practice, the easier this gets.

Looking at stereograms and anaglyphs is not only fun. I find it to be a great eye exercise against lazy eye and strabismus problems. This is because to see the full 3D effect, both eyes have to work equally and both need to get the right orientation. And the feedback is immediate.



Anaglyphs on a black background

Up to now, we have assumed that the anaglyph was on a white background. If the background is black, we must have This way, and both views will appear bright on a dark background.



Advantages of stereograms over anaglyphs

Anaglyphs are fun but are a bit limited compared to stereograms.





Options:

  • Main page

  • Andre Ratel
    aratel@vif.com