There are two main ways of viewing 3D stereoscopic images on a screen with no special hardware at all. These methods can be used with specially prepared photos, movies and websites.
See also: how 3D screens work
One type of 3D image which you can view on a 2D screen is called an anaglyph. You know, the type that’s viewed using those cardboard glasses with red and green lenses. You might consider this method old hat but it’s so simple and a lot more effective than you might remember. The first anaglyphs were monochrome but colour was added later. We'd be lying if we said that colour accuracy isn’t sacrificed, the end result can be pretty impressive.
An anaglyph comprises the left and right images superimposed on top of each other, one printed in shades or red and the other in shades of cyan. Because the red lens in the glasses passes the red image but stops the cyan image (it's not green, it's cyan) and vice versa. Each eye sees only the correct image. And because, between them, the two lenses allow all the three primary colours of red, green and blue to pass, a full colour image is achievable.
In terms of content, some DVD movies are available as anaglyph 3D versions and there is no shortage of galleries of anaglyph photos and movie clips online (try a YouTube search to see what we mean). Even Google Maps has anaglyph support – just press the T key while in StreetView mode (you must click on the image first). Glasses for anaglyph viewing are widely available for pennies if you buy them in bulk, otherwise you’ll pay a pound or so for a single pair.
Make sure you get the red-cyan glasses as opposed to the various alternative anaglyph glasses such as the red-green ones that are suitable only for red-green monochrome anaglyphs.
You can view Google Earth’s StreetView in 3D, even on an ordinary 2D monitor.
Side-by-side 3D photos
The second free method is even more surprising since you need nothing at all, not even a pair of cardboard specs. So-called 'freeviewing' involves having two images side-by-side on screen. Obviosuly, the left image is on the left and the right one on the right. All you have to do is persuade your eyes to see a 3D result.
Admittedly it does take some practice to get the knack and the size of the image is limited. However, as your skill at the necessary visual gymnastics improves you’ll be able to see larger images in 3D and you do get to see the end result without any dodgy colours. Some 3D YouTube videos can be viewed in side-by-side mode - just click the 3D button at the bottom of the video viewer to see the 3D viewing options.
To perform this feat, view the on-screen image pair below at a comfortable viewing distance and allow your eyes to go cross-eyed so that the left and right images merge. You’ll now find you’re seeing three images – the left image, the combined images, and the right image – but they’ll be blurred.
Try to relax your eyes so that the centre image drops into focus but without loosing that all-important overlap. When you achieve this the centre image will appear in 3D – practice makes perfect. In the main you’ll be using this method with 3D content you’ve created yourself but a Google search will reveal no shortage or galleries of 3D side-by-side images.