TrueJournals

Last semester, I was informed of a class at my university called “Virtual Reality Programming”, and I took immediate interest in it.  My university has a visbox 3D projection room in our engineering building, and I’ve been interested in that room ever since I found out about it.  After seeing Avatar, I became even more interested in that class, and in how 3D projection works.

I’m not going to try and say 3D projection is simple.  Quite frankly, it requires precise timing, and the technology behind it is amazing.  However, I’ll try to explain everything as simply as possible, so the information can be accessed by all.  Let’s start out with old school: those red and blue glasses.

Anaglyph

The technical name for those 3D images created with red and blue is an “anaglyph“.  This works because the color blue doesn’t contain any red, and the color red doesn’t contain any blue.  By using a blue filter, you are making sure nothing that is projected blue enters the eye with a blue filter over it.  A red filter does the same thing, only for the color red.  Anaglyphs are great because they allow a 3D image to be displayed on any surface — even in print!  However, the colors fall short.  Because color is used to filter the left and right image, these images usually have slightly crazy colors, or are in black and white.
Pros: Cheap glasses, display anywhere
Cons: Weird colors

Linear Polarization (IMAX 3D technology)

First, let me take a small break and explain the polarization of light.  Normally, light travels as a wave, going off in any direction.  Polarizing light makes the wave travel in one and only one direction.  Linear polarization takes advantage of this, and causes the waves to travel either left, or right.  With a polarized filter, we can filter out either the left or right image.  However, we don’t have a way of printing polarized images, so we must project these.  There are two methods for doing this: either use two projectors, or one really fast projector.

The two-projector method is simplest: simply get two projectors that are exactly in-sync, and put filters over the lenses that correspond with the left and right eye filters in the glasses.  Alternatively, this CAN be done using one projector: have the projector show the image at twice the rate it normally would, switching between the left and right eye image, and switching between left and right polarized filters.  Because our eyes can only see images moving so quickly, this creates a solid 3D image.

The problem with linear polarization is that the lines in the glasses and the projected image must be aligned.  This means that your head must be exactly horizontal, or you won’t see the 3D image correctly.  This works out OK, but can cause troubles if you’re on a weird viewing angle to the screen.
Pros: Relatively cheap, full-color images
Cons: Head tilt can screw up image, no guarantee polarization is perfectly aligned

Circular Polarization (RealD 3D technology)

Circular polarization is a step up from linear polarization.  Instead of having horizontally polarized light, we polarize the light clockwise, or counter-clockwise.  This means that any angle, any head-tilt has no effect on the viewed image.  In my opinion, this is currently the strongest 3D technology.  This can also use either one or two projectors, as described above.  RealD only uses one projector to achieve this.  The main problem is that polarization of light isn’t (currently) a viable solution for home use, because each pixel on a TV can only have one color, with fixed polarization.  The solution for the home would be to either make smaller pixels, so we can alternate rows of polarized light (this has been done), or figure out a way to dynamically change polarization in LCD pixels.
Pros: Relatively cheap, very sharp images, full-color
Cons: Practically projection-only

Active Shutters (3D TVs)

Active shutters is an interesting solution to the problem of not being able to polarize LCDs.  Instead of relying on passive polarization to display a 3D image, the TV alternates (VERY quickly) between the left and right image, and you wear a pair of goggles that alternates covering your left and right eyes.  The TV sends signals to the glasses on when to open and close each eye, so the image is always in sync.  However, the glasses are quite bulky and expensive, because they require power to operate.  The TVs capable of refreshing quickly enough to display the 3D image are also currently quite expensive.
Pros: Viable for home use, full-color
Cons: Expensive glasses, expensive display method

Interference Filters (Inifitec, Dolby 3D)

The idea of an interference filter is an interesting one, though I don’t think it would be better than any of the above technologies.  The idea is similar to an anaglyph, but allows for colors in the images.  It goes something like this: instead of having a variety of wavelengths, pick six specific wavelengths (three for each eye: red, green, and blue).  A filter is placed in front of the projector to filter out wavelengths that aren’t in the ones selected, and the user wears glasses to pick out colors for each eye.  Each eye also has another filter layer which corrects colors back to normal.  Unfortunately, I haven’t had a chance to try this out, either.  However, it would seem to me that the colors that could be projected would still be slightly off.  The benefit to this method of projection is that, unlike polarization, it does not require a special “silver screen”.  Any reflective surface works.  However, this method still seems to require two projectors, and, from what I can tell, would not work on a normal TV.
Pros: Cheaper for theaters, cheap glasses, can change from 3D to 2D by simply removing filter
Cons: Colors?, need two projectors

Hopefully this will help you sort through the different 3D technologies.  As stated, my personal favorite is circular polarization due to the crisp images, and relative cheapness.  However, I haven’t been able to try out any active shutter or interference filter glasses.

Regardless, I have a feeling 2010 will be a booming year for 3D projection technology.