August 13, 1996 (Updated 3/12/00 by dgp.)

HOW TO DO STEREO

The basic idea is to alternately open the left and right shutter of the lcd glasses as the display quickly alternates between the left and right views of a stereo image. When these are synched properly, the left image goes to the left eye and the right image goes to the right eye and you get great stereo.

Here's what you need:

1) 3d lcd shutter glasses (several vendors listed below). For $150 3d-tv sells a pair that are not quite research grade. The main issue is the extinction rate of the lcd panels, as well as the transmission rate once the lenses are closed. There is visible bleed-through on my pair. Either type of Stereographics lenses seems ok, although I'd get the pair that had lower closed transmission rates. Stereographics is a pain to deal with, for some unknown reason. Or you can use passive polarizing glasses with an active lcd circularly polarizing panel (I'm using the tektronix 18").

2) A method of controlling the 3d glasses. Plans for kits are available free on the web; search for SEGA 3d glasses (or some combination). I'm sure I have the plans around somewhere if you get desperate. 3d-tv sells a controller with their mac kit that works, except for a peculiar bug where the left eye remains dark after you turn the glasses off. The sega kit also seemed to have this bug. It could be a software problem; anyway, it's an issue. I don't know about the stereographics mac product, except that I'd be wary of any product that takes the signal directly from the video cable, because you need a way of figuring out which eye is dark when you flicker your image.

3) A 90 hz or 120 hz monitor. The only Macintosh video device I know of that's capable of going that fast is the PowerMac built-in video using the new 7300/7500/7600/8500/8600 driver that Denis got Apple to supply. [I think the TrueVision NuVista can be programmed to run fast too. -Denis]

4) A monitor with a fast phosphor decay rate. If you darken the left eye and open the right eye and show the right image you get the right image only going to the right eye. However, if the left image still persists on the screen, you will get some ghosting. Whether you use a monochrome or color monitor, be aware that the light emissions from different phosphors decay at different rates, and that even a white "monochrome" phosphor at the microscopic level is actually a mixture of several different phosphors with different dominant wavelengths and decay rates. Thus all color and contrast calibrations should ideally be done through the shutters. If you have big bucks, check out the new projection systems that use a mirror system on a chip. These have zero persistence, but may not go to 120 hz. NView has info on these.

5) A method for alternating between the two images of a stereo pair at 60 hz (or whatever half your video rate is). This is the hard part. There are 3 ways to do it:

5A) Some computers are fast enough to update the screen for every frame. TimeVideo will tell you what fraction of the screen you can update on every frame, for each pixel depth. E.g. the PowerMac 7500/100 can update 88% of a 640x480x8-bit screen at 120 Hz.

5B) Some video cards have multiple frame buffers than can be switched instantly. Unfortunately very few Macintosh video cards have this feature. Early mac video cards (the Toby card) had multiple buffers in 16 color (4 bit) mode, and an earlier article by myself in BRMIC describes how to use these. The videotoolbox has routines to access these buffers. And Apple has just released free system extensions called Games Sprocket, designed for game developers, that makes it easy to swap frame buffers (if the hardware supports it). On my PC system (90 mhz pentium, hitachi 21" color monitor) I'm using the hercules terminator professional VGA board w/ 4 meg vram; it goes up to 120 hz for lower resolution (640x480) or 90 hz for higher res (800x600), but so far i've only used static images, which take up to 2 seconds to load from disk. Since Apple now provides software support for multiple frame buffers, and Macs and PC's now both use the same PCI bus I'm hoping that we will soon be able to buy multiple-frame-buffer video cards for Macs.

5C) The tried and true method of clut switching, which, if your monitor takes less than 1 refresh to load the clut, (again, use Timevideo to check; isn't that a great program?) should work fine. Unfortunately, with an 8-bit-input clut (256 color), you only end up with 4-bits (16 colors) per eye. Using the 24-bit-input mode (actually a separate 8-bit-input clut for each of the three RGB channels) I get 4-bits per channel for each eye.


STEREO SOFTWARE

Tom Busey's AdjustStereoPicts.c software uses clut switching "to display color stereo 3-d pairs for use with LCD glasses. This code uses sequential-frame presentations synched with LCD glasses controlled via the serial port to provide the illusion of depth. While this technology is old, what is new is my code takes two PICT files and reduces the millions of colors to what amounts to 4 bits per red, green and blue channel for each picture (on monitors with millions of colors) or 2 bits per channel for monitors with thousands of colors. I add the two pictures together and I use clut switching to switch between them. The stereo 3-d code uses calls from (not surprisingly) the VideoToolbox code library. As with all the code I write, this code is freely available to anyone who wants it. I'm currently working with LCD glasses distributors to have it distributed free to purchasers of LCD glasses (which cost about $150).


STEREO GLASSES: PASSIVE

Reel 3-D Enterprises sells polarizing and anaglyph (red/blue) 3d glasses.

Rainbow Symphony sells polarizing and anaglyph 3d glasses.

3D GLASSES DIRECT sells polarizing and anaglyph 3d glasses.

3D Company sells polarizing and anaglyph 3d glasses.

(Does anyone know of a reason to prefer one of these suppliers over the others?)


STEREO GLASSES: ACTIVE

Vision Research Graphics sells various fancy 3D glasses.

Stereographics Corp. "CrystalEyes is a high-quality (60 frames per second per eye) product with good transmission and blocking characteristics, and it's light-weight, too. Silicon Graphics bundles them with their 3D workstation packages so I guess I'm not the only one who like them." (Dan Costin via MacPsych.)

3d-tv sells various kinds of LCD glasses. (Server not found on 6/9/00.)


LINKS

3D Gate "content, community, and commerce for 3D professionals".

3-d web "The premier site for three-dimensional imagery."

Linda Jacobson's 1994 book Garage Virtual Reality has a list of sources, and "it's a cool book." (Dan Costin via MacPsych.)