What is an anaglyph?
Anaglyphic stereograms (anaglyphs) are stereo pairs of images in which each image is shown using a different color. The two images are overlapped and then viewed using red/green or red/blue or red/cyan glasses (depending on the colors used). This means that the color channel is used for the stereo separation and therefore the perception of anaglyphs is monochrome (black and white), although color anaglyphs can be made.

The word anaglyph comes from the Greek anagluphos, meaning “wrought in low relief”; this comes from the word anagluphein, which means “to carve in relief” (ana = up + gluphein = to carve).

Who invented the anaglyph?
The discovery of anaglyphic 3D came in the 1850s as the result of experiments by the Frenchmen Joseph D’Almeida and Louis Du Hauron. In 1858 D’Almeida projected 3D magic lantern slide shows in which color separation took place using red and blue filters, and the audience wore red and blue goggles. Louis Du Hauron created the first printed anaglyphs using early color printing and photography techniques.

William Friese-Green created the first 3D anaglyphic motion pictures in 1889, using a camera with two lenses, which were first shown to the public in 1893. Anaglyphic films called “plasticons” or “plastigrams” enjoyed great popularity in the 1920s. These used a single film with the green image emulsion on one side of the film and the red image emulsion on the other. In 1922, an interactive plasticon, entitled “Movies of the Future,” opened at the Rivoli Theater in New York. The film provided the viewer with an optional ending. The happy ending was viewed using the green filter, while the tragic ending could be seen using the red filter. Many science fiction films of the 1950s were in anaglyphic 3D and have been shown on television (although today they are often shown in theaters using polarized 3D).

Anaglyphic images have been used in comic books, newspapers, and magazine ads. In 1953, 3D comic books were invented and distributed with red/green “space goggles.” Three- and four-color anaglyphic images are in use today in comic books and by some advertisers, but most often images are two-color.

What about colorblindness and anaglyphs?
People who have colorblindness will not have major problems viewing red/green or red/blue anaglyphs. One out of every 20 white males has some form of red/green colorblindness, and about 1 in 1000 people of all sexes and races are completely colorblind. In anaglyphs, the color is important only as a way of having one or the other image pass the filter in front of the respective eyes. It is not important that one then be able to distinguish the color of each image.

In fact, normally sighted people often suffer from “color bombardment” when viewing anaglyphs because their brain revolts at seeing the same object as being different colors with each eye. A redgreen colorblind person sees both colors as gray and therefore is not bothered by this effect. Redgreen colorblind people do sometimes have difficulties with red-green anaglyphs since although the colors appear similar, the intensities are rather different — the red image typically looks darker than the green.

How do the red/green glasses work?
When you look through the red lens, only red light is allowed through. The eye that is covered with the red lens will see the green image. By the same token, the green lens only allows green light through, so the eye that is covered with the green lens will see the red image. In an anaglyph, when a given color filter stops the other colors, it is called subtractive filtration. Because the red and green images are slightly offset, each eye sees a slightly different view of the picture. This disparity simulates the distance between our two eyes, which provides two views of the same scene, therefore providing us with the perception of depth, or binocular stereopsis.

How can Anaglyph Photos be made?
There are LOTS of ways to make anaglyph photos. In simplest terms: The basic idea is to use the principle of complementary colors to encode your stereo information. A stereo photograph requires a left eye view and a right eye view; to view a photo in stereo the left eye must see ONLY the left eye view and the right eye must see only the RIGHT eye view. Any combination of two complementary colors can achieve this.

In practice... You can produce an anaglyph stereo photo in camera one of the following methods:

1. By double exposing the film through complementary colored filters: click off one exposure through one filter for the first eye view, shift the camera over for the other point of view without advancing the film, change filters and expose for the other eye view. You must, of course, use color film.
   
2. You can take left and right stereo negatives and print them one at a time through complementary filters onto color positive paper to get an anaglyph photo in the darkroom. This works best with black and white negatives, but color negatives can be used, too, it's just a little trickier getting a pleasing color balance in the middle of the spectrum.
   
3. You could project left and right stereo positive slides (black and white is easiest, but color is not impossible) with complementary colored filters over the projection lens. The results tend to be muddy, but it does work with simple subjects.
   
4. Use a Polaroid camera with double exposure capability; use color film. Take the left eye exposure through one filter, re-cock the shutter, change filters, shift the camera and exposure the other eye view. Presto! An instant stereo anaglyph print.
   
5. Using a mirror box and beamsplitter rig, you can make anaglyph movies or stills by taping complementary colored gels over the left and right mirror openings. A company in England made such a device for amateurs, who don't want to set up dual projection or who don't care to split the already tiny 8mm frame for left and right eye views.
   
6. Well, this could go on and on. Just apply the basic principle to whatever situation you are in and to what you have to work with.

FILTER CHOICE: Pretty broad range here, too. Many have already been suggested. Kodak's "Filters for Scientific and Technical Use" is the ideal reference with its very useful spectrophotometric graphs. Some people like to use the pair of Wratten #29 with #44; or you might try #24 with #60; maybe a 26 with 38A, or #25 with #55, etc. What you use depends upon the lighting (daylight or tungsten) and what kind of film you are using. You'll find yourself experimenting A LOT; so you may as well buy quite a few of the filters as gelatin squares from Kodak, and be prepared to play around.

A good choice to start with is the #29 with a #44 to make anaglyph color slides. Basically, color slide film has red, green and blue sensitive layers (well that used to be the case, but now there are also lots of other layers added to improve color rendition) The red, green and blue layers are replaced with dyes that are cyan, magenta and yellow. Generally, if your filters achieve a good split between red on one side and green/ blue on the other, the positive slide will have one eye view in cyan dye and the other eye view in magenta/ yellow dye or red. If you juggle the amount of "crosstalk" between red and green, but stay away from blue, you can achieve a good yellow in the positive image, but this is really tricky.

Printing anaglyphs
Print ink colors are a problem, and the best way is to specify PMS colors and to treat the print-job as a two color run. Try PMS 151 as the red/orange color, and PMS 333 as the blue/green color. Printing with process inks (CYMK) is an even bigger problem, but sometimes the only choice in production printing of magazines etc.

How about software for the Computer??
Of course, Anaglyph images can also be created using one of the numerous freeware and shareware programs available from the Stereoscopy.com Downloads section.

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