Everybody knows about 3D movies. You pay extra and you get some special glasses. These used to be red and blue, but now they are polarized. Red things are blocked by one lens and blue things are blocked by the other and your brain puts the two separate images it is seeing together and makes it seem like it is 3D. The polarizing works the same way except that you can’t tell what is polarized when you take your glasses off. So one lens blocks vertically polarized images and the other blocks horizontally polarized images. With your glasses off you just see double.
One of my favorite games on the iPod is Pinball HD. They recently came out with a new pinball table for 99 cents so I bought it. And it got me thinking more about the game. One of the features of the game is that it is 3D. Or it can be. The camera follows the ball and you can tell everything is rendered as if it were a real table. But you can only see the 3D effect with special glasses. I used to have some paper glasses that I got for sending a self-addressed stamped envelope off to somebody who was giving them away so people could look at Mars rover pictures in 3D. Then at some point I picked up some more where one eye is yellow and the other is purple. Well, the game doesn’t support yellow and purple, but it does support red-cyan (essentially red-blue), green-magenta, and yellow-blue (actually the paper glasses seem to work for yellow-blue, but it is very dark).
Since I like the game, I thought I would try to find some cheap 3D glasses online, so I went to DealExtreme. I searched for the term anaglyphic and jackpot! They have a lot of 3D glasses, entirely too many actually. You can get glasses with red on the right or left. You can get magenta on the right or left. And I learned something, which was the magenta-green is supposed to be an improvement over red-blue because movies and pictures often have a lot of red and blue already whereas there isn’t as much magenta and green (not real sure I believe that; green is pretty popular). If you are making a 3D movie you have to avoid the colors that are in the glasses (which is why polarizing works so much better). I thought I would try magenta-green, but I wasn’t sure which eye the magenta should go over. With red-cyan, the red almost always goes over the left eye.
The glasses ranged in price from $1.79 (shipped!) to $20. The $1.79 pair is the most popular, but one of the reviews said it was kind of tight. There was another one for $3.40 that included two pairs of glasses, but these seemed like they might fit over regular glasses. They also had clip-on 3D glasses, but those were a little more expensive. And they had two pairs of paper ones for $1.14. I figure for $3.40 I can’t go wrong. Now I have to wait 3-6 weeks for them to show up.
re: “but I wasn’t sure which eye the magenta should go over”
At first I did not understand why it would matter. Wouldn’t your mind just put the two images together still? But then I realized you can’t just swap left and right and have the correct 3D. But then I thought about those lenses that make you see upside down until your brain will get tired of that and flip the image back. (And then your normal vision is upside down until it flips back… perceptual adaptation.) What does inverted 3D look like? Is it anti-3D? Would your brain learn and flip? Further research involving hours of pinball or movie watching may be required.
If there were no perspective where closer objects are bigger, then I think all you would see is things that are supposed to be far away would appear close and vice versa. But if the size of a moving object changes (and it should), then your brain would see a conflict where receding things are getting bigger and approaching things are getting smaller. I’m pretty sure this would make your brain melt.