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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
RTA (quoting physnews)
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...
"When a ball dreams, it dreams it's a frisbee"
Using cellophane to convert a laptop computer screen into a three-dimensional display
Keigo lizuka
Department of Electrical & Computer Engineering
35 St. George Street
University of Toronto
Toronto, Ontario, Canada M5S 1A4
Abstract
We present a novel, inexpensive, stereoscopic technique for generating 3D displays from cellophane and a laptop computer screen. Stereoscopy requires independent manipulation of the left and right eye views.1 Our technique takes advantage of two facts; the first is that the light from the liquid crystal display of a laptop computer is polarized light 2, and therefore we can easily manipulate its transmission with a polarizer sheet. The second fact is that a cellophane half-waveplate can change the direction of polarization of light. The direction of polarization of one half of the laptop screen was rotated by the cellophane half-waveplate. Two images displayed with orthogonal polarization on two halves of the screen become separable by wearing a pair of glasses of orthogonal polarization.
A distinct advantage of our technique is its simplicity; a laptop screen can be converted into a 3D display with minimal knowledge of optics. An additional advantage of our technique is that we can eliminate the need for the observer to wear special glasses by making the computer wear the glasses instead. This is possible because a laptop computer normally has only one viewer at a time, and the relative orientation of the viewer's head and the laptop screen is sufficiently stationary. A further significant discovery is that we verified that cellophane (costing mere pennies) proved to be a better half-waveplate than a commercial half-waveplate (costing hundreds of dollars for the required size) for rotating the polarization of white light.
1. Properties of cellophane
Let us begin by examining the properties of cellophane. Cellophane is fabricated by protruding an alkaline viscose solution through a narrow die into an acid bath. Because of the unidirectional strain during the protruding process, cellophane is an anisotropic material and it behaves like a calcite crystal. The refractive index ny of cellophane measured by a light wave component polarized in the direction of the longer dimension of the rolled cellophane (in the y direction) is larger than nx, measured by a light wave component polarized in the direction of the shorter dimension (in the x direction).
As a result, the component polarized in the x direction propagates through the medium faster than the component polarized in the y direction. After transmission through such a medium, a phase difference arises between these two light wave components. The difference ny-nx in the refractive index and the thickness of the cellophane determine the amount of the phase difference between the components polarized in the x and y directions. A medium that creates a 180o phase delay is a half-waveplate. The phase difference incurred in plain ordinary colorless cellophane (our sample had a thickness of 25 microns was measured to be 170.2o , which is about 95% of the phase delay of an ideal half-waveplate. These measured results are within acceptable limits for a number of practical applications that do not require a precise 180o phase delay. Having demonstrated the feasibility of using cellophane as a half-waveplate, we now examine what a half-waveplate does and how it can be used to create a 3D display.
One of the most important functions of a half-waveplate is its ability to rotate the direction of polarization of the transmitted light. We found that cellophane's performance in rotating the direction of polarization of white light was superior to that of a commercially available half-waveplate designed for a specific wavelength. An added bonus is that cellophane is very inexpensive. Before describing the role of a half-waveplate in generating 3D images, we need to introduce some basic stereoscopic principles.
2. Stereoscopic principles
Figure 1 explains the basic principle of
Using cellophane to convert a laptop computer screen into a three-dimensional display Keigo lizuka
Department of Electrical & Computer Engineering
35 St. George Street
University of Toronto
Toronto, Ontario, Canada M5S 1A4
Abstract
We present a novel, inexpensive, stereoscopic technique for generating 3D displays from cellophane and a laptop computer screen. Stereoscopy requires independent manipulation of the left and right eye views.1 Our technique takes advantage of two facts; the first is that the light from the liquid crystal display of a laptop computer is polarized light 2, and therefore we can easily manipulate its transmission with a polarizer sheet. The second fact is that a cellophane half-waveplate can change the direction of polarization of light. The direction of polarization of one half of the laptop screen was rotated by the cellophane half-waveplate. Two images displayed with orthogonal polarization on two halves of the screen become separable by wearing a pair of glasses of orthogonal polarization.
A distinct advantage of our technique is its simplicity; a laptop screen can be converted into a 3D display with minimal knowledge of optics. An additional advantage of our technique is that we can eliminate the need for the observer to wear special glasses by making the computer wear the glasses instead. This is possible because a laptop computer normally has only one viewer at a time, and the relative orientation of the viewer's head and the laptop screen is sufficiently stationary. A further significant discovery is that we verified that cellophane (costing mere pennies) proved to be a better half-waveplate than a commercial half-waveplate (costing hundreds of dollars for the required size) for rotating the polarization of white light.
1. Properties of cellophane
Let us begin by examining the properties of cellophane. Cellophane is fabricated by protruding an alkaline viscose solution through a narrow die into an acid bath. Because of the unidirectional strain during the protruding process, cellophane is an anisotropic material and it behaves like a calcite crystal. The refractive index ny of cellophane measured by a light wave component polarized in the direction of the longer dimension of the rolled cellophane (in the y direction) is larger than nx, measured by a light wave component polarized in the direction of the shorter dimension (in the x direction).
As a result, the component polarized in the x direction propagates through the medium faster than the component polarized in the y direction. After transmission through such a medium, a phase difference arises between these two light wave components. The difference ny-nx in the refractive index and the thickness of the cellophane determine the amount of the phase difference between the components polarized in the x and y directions. A medium that creates a 180o phase delay is a half-waveplate. The phase difference incurred in plain ordinary colorless cellophane (our sample had a thickness of 25 microns was measured to be 170.2o , which is about 95% of the phase delay of an ideal half-waveplate. These measured results are within acceptable limits for a number of practical applications that do not require a precise 180o phase delay. Having demonstrated the feasibility of using cellophane as a half-waveplate, we now examine what a half-waveplate does and how it can be used to create a 3D display.
One of the most important functions of a half-waveplate is its ability to rotate the direction of polarization of the transmitted light. We found that cellophane's performance in rotating the direction of polarization of white light was superior to that of a commercially available half-waveplate designed for a specific wavelength. An added bonus is that cellophane is very inexpensive. Before describing the role of a half-waveplate in generating 3D images, we need to introduce some basic stereoscopic principles.
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).
Here's a short but decent article on the same research.
Yes, those animated GIFs achieve a 3D effect. They do so via motion, however, not via stereo--a completely different mechanism. You can actually be blind to depth from motion and still perceive stereo and vice versa. The fact that it works by alternating between stereo pairs has to do with the way motion perception works.
Using motion to indicate depth has a long history in computer graphics. The obvious problem is that it requires the viewpoint or the object to move significantly, not always desirable.
Images that use motion to indicate depth don't have to look as horribly jittery as those animated GIFs: the effect works just as well with nice, smooth motion sequences. So, get out your camcorder and make some nice animated images.