in the

3rd Dimmension

Angel supports stereo rendering, allowing you to produce left and right eye images of you scene. A range of options are available for viewing these. The best solutions require special hardware, and include dual screen visors, polarized projection, and shutter glasses synced to the video display. Fortunatly cheaper solutions are available:

Red/Blue Overlay

The classic stereo viewing system places a red filter over the left eye and a cyan filter over the right eye. By combining left and right images into different colour channels the viewer sees a stereo image. Everything works great as long as the source image is greyscale but things get messed up when the image is colour. Consider a red object - it would only appear in one eye. To get round this the image must be desaturated. Greater desaturation produces a better 3D image, but at the cost of colour. More colour - worse 3D. Fortunatly ome colours still work well, as we don't strictly desaturate, but rather blend red with green/blue.

Rboverlay converts a stereo pair to a single Red/Blue image. It can be run as either "rboverlay left.tiff right.tiff out.tiff" or simply "rboverlay out.tiff". If the second form is used then the prefixes "L:" and "R:" will be used to identify the source images (this matches the behaviour of Angel). In either case an optional saturation value can be given as the first parameter.

Rboverlay works great with stereo photographs too:

Rboverlay can be downloaded for OpenStep, freeBSD, NT and SGI.


A big downside of the  R/B overlay technique is that the image is difficult to view without glasses. ChromaDepth  is designed for advertising material which appears correct when viewed normally, but takes on a 3D appearance when viewed with special glasses. This is achieved by prismatic lenses which push back blues and pull reds forwards. Of course it makes true colour images impossible, but its fun anyway.

The chromadepth program converts a Zdepth file (typically a floating point tiff) into chromadepth false colours. If a second image file is provided then it is used for the brightness.

Chromadepth can be downloaded for OpenStep, freeBSD, and NT.

ChromaDepth, Red/Blue, Polarized Glasses and other 3D accessories are mass produced by American Paper Optics, and I got a rather handy promotional pack containing all sorts of toys from them. Other places to look are Ray 3D, ChromaTek, and Studio 3D.

Ian Stephenson.
DCT Systems
NCCA, Bournemouth University