Slashdot Mirror
Using Cellophane For 3D Displays On Your Laptop
prestidigital writes "From the abstract:
[the authors] present a novel, inexpensive, stereoscopic technique for generating 3D displays from cellophane and a laptop computer screen.
(Once again my physnews update sends me email that doesn't suck!)"
http://perljam.net/cache/individual.utoronto.ca/i
-ted
Taking advantage of the fact that light emitted from a laptop display is naturally polarized to begin with, a 3D stereoscopic effect can be achieved by covering half the screen with a cellophane sheet in order to construct orthogonally polarized left and right scenes while the viewer wears eyeglasses holding two polarizers oriented 90 degrees apart...
You appear to have missed the parent poster's point.
If the images for each eye are on different halves of the screen, then polarizing is pointless. It removes phantom images, but the phantoms are far away from the real image, so there's no advantage to doing so.
Polarizing filters, as the parent poster pointed out, are useful when you have both images in the same place on the screen (overlapping). As overlapping images can't be distinguished by position, some other method is needed (polarization, colour, light direction, etc). When the images don't overlap, they can be distinguished without aids (just cross your eyes).
cellophane has a poor separation quality, i.e the difference between 90 degrees (blocked) and 0 degrees (pass) polarized light is little.
Real lab-quality polarizer crystals are way to expensive and generally too small for this application.
however, sheet polarizing material can be bought in photo equipment stores and cut to size with normal scissors. It's more expensive than cellophane but less expensive than lab polarizers and has a quality that is waaaaay better than cellophane. I paid about 15 bucks for 25*25 cm. about 8 years ago in Germany. Hama sold them at the time
This animated GIF technique showed up on Metafilter a couple of weeks ago, and for me it was one of those "Why the hell didn't anyone try this sooner" epiphanies for me. Yes, the constant jitter while flipping between frames gets old, but not nearly as old as straining your eyes with the 'cross-eye' viewing method.
If the images for each eye are on different halves of the screen, then polarizing is pointless. It removes phantom images, but the phantoms are far away from the real image, so there's no advantage to doing so.
Actually, there's a huge effect in filtering out the "wrong" image from each eye. The eyes naturally focus much better on separate images if there are no clues that they are separate. That's why stereoscopic viewers have a divider between the two eyepieces for "parallel-eye" viewing (you can equally just place a sheet of paper, if your eyes can decouple well enough without extra optics). Note that images meant for parallel-eye viewing will look "inside-out" when viewed cross-eyed.
So I didn't RTFA.
I'm assuming its similar to this .
I just hope the solution was more inventive than doing the old theatrical movie stunt about using relative shifting of color information and celluloid glasses - which gives you depth information at the expense of color information. Spy Kids 3D just did this using a blue or green image for the left eye and a red image for the right.. That one's been around since the 40's. In both movie and book. Cute trick but it gives me headaches to see it for any length of time.
"Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]
No. The cellophane (which is placed on half the screen) isn't a polariser, it's a half-wave plate. That means it rotates the polarisation of any light passing through it by 90 degrees.
In effect, they're making the left half of the screen emit light with horizontal polarisation, and the right half with vertical polarisation (or vice versa).