Friday, January 23, 2009

Apple #366: 3D Movies

Recently, I went to see My Bloody Valentine 3D. That's right, your Apple Lady went to see a strictly-gore-fest movie. And it was fun. So there. Plus, I got a swanky pair of glasses -- to keep.

As I was ducking flying pickaxes, dodging tree branches, and telling the people on screen not to walk backwards, didn't they know they were in a horror movie? I was also impressed by the 3D. I wondered, how does this work? Why don't they make more movies in 3D?

  • To understand 3D, you have to understand plain old regular vision.
  • We have two eyes, spaced about 2 to 3 inches apart. Your left eye takes in one stream of information from its position while your right eye takes in a slightly different stream of information from its position. Imagine two separate flashlight beams shining into the back of your head through your eyes.
  • Your brain -- genius thing that it is -- takes those two steams of information, correlates them, and builds one picture of the landscape in front of you, in three dimensions.

How your brain creates a 3D image based on the 2 separate images taken in by your eyes.
(Excellent diagram from Tom's Hardware)

  • If you had only one eye, you would still be taking in some information like colors and shadows that tell you that objects have depth and distance and so on. But it would be much harder for your brain to build an accurate picture of the relative position the objects have to each other, how far away they are from you, or how rapidly they are traveling toward you. If you shut one eye and try to catch a ball someone throws to you, you'll see what I mean.
  • 3D movies mimic the way in which your eyes take in two sets of information and your brain processes them into one.
  • I gather that the technology is a bit more sophisticated than this, but 3D movies are essentially filmed using two cameras. In the old color 3D movies, one camera would film in red, the other in blue. This creates the set of two slightly different streams of information about the same landscape.
  • When the movie is shown, two projectors are used, one to show the red while another one shows the blue. The images are slightly off. I haven't seen an explanation of this, but I suspect it might be some function of the distance apart that our eyes are and the distance the seats are from the screen.
  • The glasses play a key role because the lenses are different from each other, and they work like filters. One lens lets in the red color only and the other lens lets in only the blue. So you're getting two sets of slightly different information about the same landscape coming into your brain, and your brain correlates them and builds them into a single three dimensional image.

A color 3D movie is shown by two projectors, one red and one blue, onto the screen, and then the color 3D glasses filter the image into one blue and one red version.
(Extremely helpful diagram from

  • Current 3D movies do the same thing, except that instead of splitting the image on the basis of color, they're even more sophisticated. They are still filmed with two cameras, but one represents what the left eye would see, the other the right.
  • Again, the movies are shown using two projectors -- but actually, the current technology has gotten more sophisticated. The two images are spliced onto one piece of film, keeping one set on the left and another on the right. The very special digital projector takes in the data from both sets of film and buffers it, then projects the left and right images, back and forth and back and forth very fast, at 144 frames per second. In addition, so that the image on the screen doesn't appear to flicker, each left and right image is repeated three times.
  • But ultimately what you get is two streams of information, one for the left and one for the right, being displayed on the screen and bounced back to your eyes.
  • The glasses, again, have a special role to play. The left lens is polarized in one direction to allow only the left-side image to enter, while the right lens is polarized in another direction to allow only the right-side image.

Polarized 3D glasses have one lens that allows in light traveling in one direction while the other lens lets in light traveling in another. If you want to know more about polarized lenses in general, check out a previous entry on the topic.
(Diagram from the Museum Victoria in Melbourne)

  • Your brain then correlates and synthesizes the two slightly different streams of information and builds them into a single three-dimensional landscape.
  • People say that the polarized 3D is much better than the color 3D because the images and colors are more precise -- that's true in my opinion -- and it also doesn't give you a headache. Here, I'm going to qualify this.
  • I wear glasses and my right eye is slightly weaker than my left. I can tell I'm going to need a new pair of lenses soon because I've sometimes noticed this difference lately. When I first put on the 3D glasses (over my regular glasses; they were large enough to allow for that) and started watching the movie, I found myself adjusting the 3D glasses so that my eyes felt like they were taking in comparably not-blurry images. Then about 2/3 of the way through the movie, my brain started to feel tired and a little headachey. I suspect that if I didn't need regular glasses, I probably wouldn't have felt that way by the end of it.

What the glasses look like. They're made by a company called RealD, which makes most of the 3D movies currently in production. Their website is totally unhelpful.
(Photo from ZDNet)

  • By the way, those Magic Eye books work on the same principle. You know, those books that have really complicated images in them and you're supposed to hold them a certain distance from your face, let your vision go fuzzy, and you'll see a 3D image. Those are called stereoscopic books. They have one image overlaid on another, a slight distance apart. When you hold the book at the right distance away from your eyes -- it's a function of how far apart your eyes are -- you're supposed to see the third 3D image float before you.
  • Those Viewmaster viewers with the circular discs of pictures also worked the same way. Each picture is actually two photos of the same thing, taken from a slightly different position. The Viewmaster splits the photos so that you see one with left eye, one with the right. The result appears to be in 3D.

Here you can see the two photos that the stereoscopic viewer helps your brain to process as a single 3D image.
(Photo from Hermes Press)


Well, okay, maybe we wouldn't want them all to be in 3D (though I'm not sure why not), but at least, why aren't there more 3D movies?

Maybe you wouldn't want every movie to do this. But then again, maybe you would.
(Image from Tom's Hardware)

Answer: it's expensive.

The current polarization 3D movies require lots of pricey equipment.
  • Then you have to print the images on that special film that's got one set of images on the left, one on the right.
  • Then the theater has to have that super-fancy digital projector. Those things cost a theater "tens of thousands of dollars," according to an article from Wired.
  • Apparently, there's more involved than just the projector; an entire "3D system" is required, which can tack on an additional $20,000 to $50,000.
  • It's not clear from that Wired article, but I suspect that system may include the cost of installing a special silver screen -- literally, a silver screen -- which helps to keep the image polarized.
  • Several film studios have made deals with theaters, agreeing to help pay for some of the cost of making the conversion so that the theaters will be equipped to show their movies. A lot of the theaters are converting first to digital technology, and then they will acquire some of the other equipment needed to show the 3D movies.
  • By the way, the cost for 20,000 screens to go digital: over $1 billion.
  • As of April 2008, there were 4,6000 digital-ready screens, and only 1,000 capable of showing 3D movies. The theater industry hopes to get 4,000 screens ready to show 3D movies by summer 2009.
  • To put that number in perspective, there are over 38,000 indoor movie screens in the United States. So they're hoping to get the number of 3D-ready screens up from 1% to 4%.
  • So if you can't see My Bloody Valentine in the 3D version in your area, that's why.
  • That's also why the ticket to see that 3D movie will be more expensive than what you usually pay. Prices range from $10 to $15 per seat, depending on what part of the country you're in. That higher price -- and the fact that home movie-viewing can't replicate the 3D experience yet -- is why movie studios and theaters want more 3D movies.
  • Here are some upcoming movies that will be released in 3D:
  1. Coraline - February 2009. Animated. A young girl (voice by Dakota Fanning) unlocks a door in her house and discovers a parallel reality, where her mom has buttons for eyes.
  2. Monsters vs. Aliens - March 2009. Animated. A young girl gets hit by a meteorite and turns into a monster and is recruited to fight the aliens by a bunch of underground monsters. Stephen Colbert does the voice of the President.
  3. Harry Potter and the Half-Blood Prince - July 2009.
  4. A Christmas Carol - November 2009. Animated. Jim Carrey does the voices of Scrooge and of all the ghosts. Gary Oldman is Bob Crachit and Tiny Tim. Sounds a bit schizo to me.
  5. Avatar - December 2009. It's a James Cameron movie with Sigourney Weaver, about humans in the future on another planet and they have to fight the native planet people.
  6. Alice in Wonderland - 2010 ish. Animated. Tim Burton's 3D take on Alice in Wonderland.
Trailer for Coraline:

Howstuffworks, How 3-D Glasses Work, How 3D IMAX Movies Work
Betsy Schiffman, Movie Industry Doubles Down on 3-D, Wired, April 14, 2008
National Association of Theater Owners, Statistics
Patrick Corcoran, National Association of Theater Owners, The Reel Blog, DCIP signs digital cinema agreement with five studios, October 1. 2008
Patrick Corcoran, National Association of Theater Owners, The Reel Blog, 3D - the back seat driver of digital cinema, April 14, 2008


  1. a good 3d Movie explanation!

    2009 is the year for 3D movies

  2. With so many movies advertising that they will be in 3-D, I have been wondering how it works. Thanks for the info.

  3. "Monsters vs. Aliens"

    I'm disappointed this one won't be the cast of "Monsters, Inc" battling the Aliens from the "Alien" movie franchise.

    A couple of years ago we went to the 3D re-release of Nightmare Before Christmas. It was kind of disappointing, not least because the 3D animated short they showed beforehand exploited the 3D so much more than the main feature.

  4. fork stealer, I agree. The title even sounds like that's what it's supposed to be.

    Sorry you were disappointed in that one 3D movie a few years ago. There are other movies, you know, and some time has elapsed which means the technology has probably improved over what you saw.

    Not everything is like Memphis, you know. [wink]

  5. hi friends
    this is excellent blog which gives good idea about 3d conversion process,excellent work all the best


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