Using colour to create the illusion of depth
The term Chromo-stereoscopy means stereo-vision (depth perception) through colour. The principle is to produce an image where depth is coded by colour. By watching the image with special glasses, the colours are decoded into depth perception, such that features of a certain colour appear at a certain depth. The principle of using colour for depth perception dates back to the theory of Einthoven in 1885.
The method has been made easily available by Steenblik, R.A.: U.S. Patent No. 4-397-634 and are available commercially as 3D Chromadepth glasses, made by Chromatek.
The key to understanding this 3d technique are the special glasses. The micro-optics of each pair of glasses contains the action of two back to back prisms, which point opposite directions. One prism is a highly chromatic dispersive prism, the other a low chromatic dispersive prism. The key is to have the dispersive characteristics of the two prisms as contrasting as possible. We call such a pairing of prisms a superchromatic prism. The highly dispersive prism separates the colours, and the low dispersive prism ensures the rays reach the eye.
The two figures on the right show the action of the superchromatic prism, where the two prisms may be interchanged.
1. A superchromatic prism
(low before high dispersion: red deeper than blue)
| 2. A superchromatic prism
(low before high dispersion: blue deeper than red)
With a pair of superchromatic prisms (the case with high before low dispersive action are used), depth can be simulated with colour. A red image appears to the front of the real image, and a blue image appears further away than the real image.
Superchromatic glasses, which make a red image appear closer and a blue image appear farther.
- The normal red an blue rays have been shifted parallel from the white ray for clarity.
In order for the depth to become clear, the colour needs to contrast with a background colour. For the RGB (Red-Green-Blue) colour scale, the background colour is black. For the CMY (Cyan-Magenta-Yellow) colour scale, the background colour is white. The CMY colours are simply the complement colours to RGB in the colour cube. The middleground colour is the complemtary colour of the background colour and appears at the average depth of the image. For the RGB colourtable black is background and white is middleground. For the CMY colourtable the roles are reversed.
Download a colour-table, which is linear in depth (not in RGB scaling): RGBpalette
1. Red-Green-Blue colours on a black background
2. Cyan-Magenta-Yellow colours on a white background
The background and middleground colours are vital for the perception of depth in the technique of chromo-stereoscopy. Darkening a colour (e.g. RGB(FF,00,00) to RGB(55,00,00)) will pull it to the background, independent of colour.
- Brightening a colour (e.g. RGB(FF,00,00) to RGB(FF,55,55)) will pull it to the middleground. Colours which appear in the foreground will be pulled deeper, and colours in the background will be pulled forward.
3. Darkening a colour draws it to the background.
4. Brightening a colour draws it to the middleground.