Anaglyph 3D format
Anaglyph 3D format is a format for displaying 3D images (still or moving) which can be viewed with appropriate glasses. It uses color filtering to make the two stereoscopic images have different color shades, so they can be overlaid together and viewed with a differently colored lens on each eye to separate them again.
This is an old format, going back to the 1800s, which does not require a lot of complicated technology. The images can be stored and transmitted via any medium that can handle color images, and the glasses have simple tinted lenses that are inexpensive to manufacture.
In its simplest form, this consists of two monochrome images, one for each eye, where the single color of each (against either a white paper or a black screen, depending on the medium) is of a different color (red and cyan are common, but other color combinations have been used). The eye looking through the red lens (traditionally the left eye) can't see the red lines, and similarly for the other eye, so different sets of lines are seen from each eye. (Where the two lines coincide, a combined color is seen making it visible from both eyes; this works best with complementary colors in the two lenses.)
More complex anaglyph pictures can be made with a wider range of colors, still filtered differently for each side, resulting in a more colorful image (though still differing from natural colors due to the filtering and lenses).
This style of 3D image was used in the 3D movies that were a brief craze in the 1950s, as well as in other things such as comic books. It's been out of fashion more recently in favor of other 3D techniques that allow for a more naturally-colored image, separating the two images by such means as lens polarization or carefully-synced blanking displaying alternating images.
