Submitted by Al …
(Adapted from The Encyclopedia of Photography ©1963)
An anaglyph is a simple stereograph in which the two pictures, instead of being printed in black and white, are printed in two complementary colours. When viewed through a viewer fitted with the same two colours (but in opposite sequence), the image appears in relief (three dimensional).
Red and green are universally used for anaglyphs. If the left-hand picture of the anaglyph is red and the right-hand picture is green, then the left eyeglass of the stereoscope will need to be green and the right glass red.
The effect of a single image in relief, which is produced by this combination, is based in the principle that a picture of one pure colour disappears when viewed through a glass of the same colour and is most visible, appearing black, through a complementary colour.
When the coloured eyepieces are used, the left eye through a red filter sees the green image in black on a red ground, or only its corresponding image. Then the right eye through a green filter sees the red image in black on a green ground, and cannot see the green image. And the object viewed appears on a ground of colour not far removed from the tint resulting from the mixture of coloured lights transmitted respectively by the two filters, but with momentary predominance of one colour or the other, according to the state of fatigue of the eyes.
The effect of relief is achieved because those parts of the object which are printed in coincidence appear to be in the same plane as the anaglyph, while the other elements of the object appear to be in front or behind this plane.
Anaglyphs have two advantages over other stereographs:
The size of the picture is not limited. Because the two pictures can be superimposed, the space used is only one half that necessary for the same size in other stereographs.
The viewing glasses may be simple cellophane masks, flat and very inexpensive.
There are several disadvantages to this system of stereoscopy however:
It is difficult to get proper dyes.
Too much light is absorbed through the masks.
The green and red colours do not fuse into white around the edges of objects against a light background. Instead they leave an edge of colour over that part of the background which is obscured by a foreground object in one of the views but not in the other.
Anaglyphs are most satisfactory for publication purposes. Some magazines publish them and insert viewing masks in each issue. Scientific publications have made use of them, chiefly on books on anatomy, geometry, geography, geology, and astronomy.
Anaglyphs have also been used with striking success in motion pictures. Two adjacent spot lights, one red and one green, are placed at the back of the stage, resulting in a remarkable projection of shadows of the moving figures.
Anaglyphs can be made very easily from any pair of stereo negatives exposed in any ordinary two-lens stereo camera using modern colour printing paper such as Kodak Ektacolor paper. Remembering that the paper produces a colour complementary to that of the printing filter, all that is necessary is to print the left-eye negative onto the paper using the same colour filter as will be used to view it. Then the right-eye negative is printed, using its filter. After this the paper is developed in the usual colour processing baths.
The result will not be quite the same as one is accustomed to in anaglyphs printed by older methods. For instance, if the left-eye filter is red, the image printed from it will not be green but cyan (a blue-green or aqua colour). Likewise, if the right-eye filter is green, the image resulting will not be red but magenta. However, since these colours are complementary to those of the printing filters, they will each appear black through their original filter, and the object of having each eye see only one image will be attained.
Using a transparency film such as Kodak Color Positive film, the same system can be utilized to make a transparent anaglyph which can then be projected on a screen. This has the advantage over other stereo projection systems of requiring only one projector. Its disadvantage is that only black-and-white pictures can be projected this way. This system has been used in motion pictures for the same reason; the resulting film can be projected in any ordinary theater projector, whereas processes using Polaroid and similar systems require either two projectors running in synchronism or specially designed double projectors. A recent Warner Bros. film, “The Mask”, used this system very successfully for three dream sequences in 3-D.
Some adjustment of image position can be made by choice of the image placement on the film. If a distant object and its two images are made to coincide on the paper or film, then all objects nearer than this will appear to lie in front of the paper or projection screen. On the other hand, if the images of a near object are made to coincide, then all objects beyond this will lie behind the screen. The former condition, even though much more effective to the audience, entails some eyestrain in viewing, especially when projected on a large screen at some distance. The latter condition, while easier for the audience to fuse into a single image, is less striking. In general, it is best to place some object in the middle distance at the plane of the screen so some near objects appear to be in front of the screen, while farther ones lie behind it. Such viewing appears most natural and involves the least eyestrain.
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