Anaglyph, old hat but still useful

Bob Pank#

Author: Bob Pank#

Published 1st January 2011


There are now many technologies for viewing 3D on television or the cinema. The oldest, dating from the 1850’s, is the anaglyph glasses. I’m sure everyone is familiar with the ‘red’ and ‘green’ style of old, though those particular single colours are hardly used these days.
The basis of an anaglyph is to separate left and right image components for viewing by each eye using mutually selective colour filters. A red filter is typically used for the left and a cyan filter for the right. The red image is removed by the cyan filter. Because cyan is composed of green and blue, the cyan image should be blocked by the red eye filter. To create a 3D image suitable for viewing with these glasses, it is obviously necessary to overlay the left eye picture in red with that for the left in green and blue.
These are not the only colour schemes possible for anaglyphs as you can permutate any combinations of RGB that are exclusive for each eye. A combination of blue and yellow has been widely promoted in recent years but, to make this work, the yellow filter has to be dark amber to compensate for the low blue energy in RGB. Technically the systems using green and magenta (red/blue) should be a better choice in this respect and the higher energy of green in one eye is better balanced by the red/blue in the other. The viewer’s brain not only fuses the left/right separated images for 3D, but also the split RGB components for an illusion of full colour.
Different people get widely varying results and experiences with television anaglyphs. The concept has acquired a bad name particularly because of some public trials using blue/amber combinations. Realistically anaglyph does not really have much of a place for mass entertainment in a market where passive and active polarised systems are coming right down to an affordable level and have a wider consumer acceptance.
What anaglyph does have to offer is a cheap and convenient means of easily monitoring 3D content on a standard 2D display. It also does not suffer the half reduction in vertical resolution you get on a typical line-alternate 3D polarised display. Anaglyph does not handle colour images effectively. If there is a pure saturated object in the scene, only one eye might see it! The anaglyph technique is at its best with monochrome 3D and allows full-resolution monitoring. This can be very useful both on-set and in post production.
The Cel-scope3D stereoscopic analyser includes a selectable anaglyph output. For preview, this can show monochrome or full colour images in any filter combination. Additionally, it allows the operator to play with the left-eye/right-eye RGB colour balances to optimise for a selected blend of anaglyph glasses.

Robin Palmer is Managing Director of Cel-Soft and is currently involved with software solutions for 3D & TV quality control and measurement technology.

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