Article
Stereoscopic DIY
August 28th 2003 in the wee hours
A few weeks ago with arm painfully twisted, I went to see Spy Kids 3-D. It is
not a movie I would have picked if left to my own devices, but I was attending
in compliance with someone else’s devices so that took care of that. And,
to be honest, once I had about five minutes to consider the last time I saw a
3d movie my devices began to sway. Plus, if nothing else, there is the promise
of walking out with a pair of completely useless cardboard-framed glasses, which
I will gladly take over the beaten-out-of-sixteen-bucks-and-given-zilch-in-return
feeling I had when I left Bruce Almighty. While I’m not going to pour praise
onto Spy Kids, I did find it enjoyable. The plot was what you would expect, kid
friendly and predictable. The acting was for the most part non-distracting, except
for Sylvester Stallone who did perform as expected. The ending was about as uneventful
as they come. And yet, none of that matters though when you are a nerd watching
a movie set in a virtual world. I did think they did a great job of creating the
fictional world inside of a video game. This is also, of course, when the audience
was told to don their glasses and take part in the unconscious dodging and swaying
that is inevitable when it appears that a tire has just flown out of the screen
in your direction. It is priceless watching kids reach towards the screen only
to get a handful of their neighbor’s hair.
On the way out, I was feeling pretty good about the movie and concluding that
I would even watch it again if given the chance to do so at a reasonable price
when subject of 3d movie technology surfaced. I think the original question
that Steph posed was something along the lines of: “How do they do that?”
As the holder of an engineering degree, I am obligated to answer even if I have
to make up something and pad it with enough scientific jargon to distract from the original question. My reply was lengthy and went something
like “blah blah perspective blah blah polarization blah blah blue on left blah red on the right blah left right blah not present in conventional theatres blah.”
I was happy with it until the next day when I began to wonder if I could make
my own 3d movie-esque still images. I figured if nothing else, Steph might actually
believe my theory if I could produce an image of my own. Plus, I happen to have
just come across a pair of cardboard-framed glasses which were destined for
the garbage can if I couldn’t put them to use. After a little head scratching,
a little googling, and a great deal of photoshopping; I was starting to see
some results. When I finally stumbled across the term anaglyp, my
search for help got a little easier. I looked pretty funny browsing around the
web wearing my cheap 3d glasses trying to drive away the nauseous feeling you
get when your eyes don’t know what the hell you are doing to them. So
if you happened to have saved your glasses after seeing spy kids and want to
look at something completely pointless and unimpressive, here you go:


http://www.blogt.nl/images/juli2003/raareffect.jpg
It messes with your visual system without additional hardware.
Of course, as an engineer with some drafting ability, I immediately set out in Illustrator to reproduce the effect, with some success. (I have the file if you want it.) Little variances in feature size profoundly affect the phenomenon. I was never able to get an image quite as disturbing as that particular JPG, probably because the sizing is still a hair off.
All of this reminds me of a class I took in DSP/Image Processing, where one of the first things the professor did was start showing examples of the limits of the human visual system. What was disturbing was his discourse comparing visual system spatial frequency response to simple FIR filters. In particular, "ringing" around sharp spatial edges, e.g., bands in a picture of uniform black and white bars. (Yes, you have a low-pass filter installed in your wetware. This is why JPG works.)
Hmm.. You know, they make (polarized) 3D glasses that synch up with your graphics card (I think they alternate frames, one for each eye). In theory, you could then make any OpenGL stuff real 3d by using two viewpoints (one per eye) and rendering each one individually.
Hmm.. I think VTK (visual toolkit, basically a front end to OpenGL) has some calls to enable stereo mode.
My other stereo comment- the first couple days (weeks? Months?) at work, they didn't have much for me to do, so I just tagged along with some guys doing some viz stuff. One of the things they were doing was testing out a 3D version of some software on their 180 degree projection wall. Problem was, the 3D wasn't aligned quite right (for starters, the screens were backwards, so you had to wear the glasses upsidedown). Anyways, I got to be the guy in the front of the room saying whether things looked right or not. Bad 3D is enough to give a viewer a headache. Bad 3D on a giant surround screen is enough to make you.. fall over. Yucko..