A stereoscopic picture where the left and right eye images are superimposed, but in different colours. A colour filter over each eye only transmits the image component suitable for that eye and the brain interprets the result in three dimensions.

Your ability to see "depth" is based on the fact that each eye sees an object or scene from a different perspective. The brain puts these different views together as a stereoscopic image. An anaglyph involves the use of two pictures of the same image taken from different positions, "fooling" the brain into thinking it is seeing two different views, which creates a stereoscopic image.

1. No optical gymnastics are required (no need to go cross eyed or wall-eyed).
2. Anybody with normal vision can see 3D in an anaglyph.
3. The image covers the whole computer screen, not just half the screen. Spatial and stereoscopic resolution is twice as good as image pairs.
4. Red - Cyan stereoscopic glasses are common and cheap, often coming free with magazines showing 3D.
5. A singe digital projector can show anaglyphs on a screen for a large audience, who see three dimensions through the same, cheap, coloured glasses used for computer or print viewing. This avoids the hassle and expense of two separate projectors as used for polarised viewing.

These are the best cardboard glasses
for watching 3D anaglyph

A pair of eyeglasses with two filters of the same colors, once used on the cameras (or now simulated by image processing software manipulations) is worn by the viewer. In the case above, the red lens over the left eye allows only the red part of the anaglyph image through to that eye, while the cyan (blue/green) lens over the right eye allows only the blue and green parts of the image through to that eye. Portions of the image that are red will appear dark through the cyan filter, while portions of colors composed only of green and blue will appear dark through the red filter. Each eye therefore sees only the perspective it is supposed to see.