How it Works: Why not all 3D is created equal

Posted on 13 April 2010 by Quaid

Today I wanted to spew forth my thoughts on this newfangled 3D thing hitting theaters. Now, you might think that I’m a little late to the party…what with Avatar blowing everyone’s minds with its stereoscopic shenanigans. But you’d be wrong. Because Avatar was the cream of the 3D crop…a crop that is a lot more varied than most 3D movie-goers realize.  I mean, did you see Clash of the Titans?  No, ladies and gentlemen, not all 3D is created equal, so I thought I’d take this opportunity to give you a quick technical breakdown of how the format works and why the effect is so varied.

When it comes to 3D there are really two different ways to look at it: how it’s shot, and how it’s projected. As we all know, all 3D movies are made by showing two different images that mimic the different pictures collected by your eyes. Then the images are shown, and some apparatus (usually glasses) is used to make sure that each eye sees only the image that corresponds to its placement.

In other words, there’s a left and right image and your left eye sees only the left image while your right eye sees only the right image.

But  you already know this. It’s 3D-101. What some of you might not know, however, is that there are a few different ways to shoot 3D movies.

Any movie that is truly native 3D will be shot with two cameras…or one camera with two separate lenses. The lenses are spaced some distance apart to mimic the distance between our eyes. These cameras are (usually) very carefully calibrated to match each other when it comes to color, exposure, focus and alignment. These days, the high-end 3D cameras use awesomely sophisticated electronic components to allow cinematographers to adjust the image “as one.”

These cameras can be either film cameras or HD video cameras. These days, though, most 3D is shot using digital cameras as they can allow the DP to capture a “cleaner” image. This is important when trying to trick your eyes into thinking something is real. Film grain and soft edges, while cool stylistic choices in 2D cinema, can kill the 3D experience.

Plus running hundreds of feet of film through two separate cameras on a single rig can be quite cumbersome. Thank God for on-board hard drives.

Even among digital 3D, though, there are multiple styles of shooting and schools of thought. One school says that the cameras should be perfectly aligned so the images match up perfectly across the entire frame. Lenses are pointed perfectly forward and remain 100% parallel.

Another school of thought–the one James Cameron subscribes to–says that the lenses should be tilted slightly inward, each one pointing directly at the main subject of the shot. The math on this is a lot harder to do, and there are some problems with it…mainly that the images on the periphery of the frame don’t match up perfectly, so if you aren’t looking at the thing the director wants you to look at, the 3D effect can be blown. And there can be eye strain.

But don’t worry, digital technology is helping to fix all that. Using a highly technical and boring post production process, movies like Avatar can correct for this misalignment in the raw footage by distorting the image digitally. So you get awesome 3D that mimics the way your eyes actually work…with no eye strain.

Needless to say, this is today considered the highest quality way to shoot 3D movies, and the technology is over a decade in the making.

But there is another way to shoot 3D movies. With a 2D camera.

See, those cool computers that aligned the images in the above example can do so much more. They can actually digitally create a second image that can closely approximate the image that would have been shot by a second camera slightly off-axis. This wholly created image is then projected to fool your brain into thinking the scene was shot by two cameras. And it’s kind of amazing…though probably not quite as elegant or effective as the in-camera approach.

So why do it? In a nutshell, cost. To shoot a movie 3D adds a whole other layer of logistical problems and an increased cost that some productions simply don’t want to pay for or deal with. This is the case for two movies of recent: Alice in Wonderland and Clash of the Titans.

What will strike you about these two if you’ve seen them, though, is that one (Alice) provides a great 3D experience while the other (Titans) shows us how utterly crappy the post-conversion to 3D can look.

Why the difference? Well, I’m dipping into speculation here, but I think it’s because the movies were shot differently. Alice was to be a 3D movie from its inception. It was shot with vast depth of field and with the effects artists making each choice based on how the 3D conversion would work.

Titans, on the other hand, was produced as a wholly 2D movie, and the decision to convert it came later. So the shooting decisions are not wholly consistent with what is needed to make 3D cinema effective. It was a ploy to make a quick buck, and it shows.

A quick note…there is a way to avoid all this drama and headache: be like Robert Zemeckis and design your movie digitally from the ground up. Then you can just make both images digitally and have total control over the 3D experience.

Once you have your 3D movie shot/rendered, though, a big choice confronts you: how will you project it? 3D movies fall into two categories: anaglyph and polarized.

Anaglyph images are the old 3D movies that require colored glasses. They suck. You can barely see the 3D. But they’re significantly easier to create and show than polarized images.

An anaglyph, dual-color 3D movie is made by showing two images concurrently, each one tinted a different color (usually blue and red), on top of each other. By using two colors, this composite stereoscopic image can be shown on any TV or screen…it’s a fully 2D image that (kinda) fools your brain into thinking it’s 3D.

Polarized images, however, are a little different. With this, two images are shown concurrently, but the light of each image is polarized so that when you put on your glasses each eye can see only one image. By polarizing the light, this method ensures that you get two crystal-clear images that aren’t tinted. But because the polarization occurs in projection, the images can not be composited into a simple 2D image. That means that there has to physically be two projectors showing two images. Which is why this technique can’t yet be used on your home TV.

Within this category, though, there are competing types of polarization. IMAX polarizes its images in a different way than Real-D. Which is why Real-D glasses won’t work in IMAX 3D theaters. Real-D polarizes images in a vertical and horizontal fashion. If you want to see what I mean, cock your head 90 degrees to the side when watching your next 3D movie. One of the images will disappear.

For my money, IMAX 3D polarization is the way to go. And you can see a real difference with the IMAX images feeling richer and more seamless. To me, Real-D images feel more multi-planar…like they’re 2D images occurring on multiple flat planes in the distance. To be fair, though, they both look pretty damn good.

There is a third technique of showing one image at a time. A pair of glasses will actually shutter many times a second to show one still frame on a screen and ensure that only one eye can see it. This effectively fools your brain into thinking each eye is seeing a different image at the same time when they’re actually taking turns. This method, though, is dying out fast because it’s super expensive and arguably not as effective.

So there you have it. Whenever you go to the movies to see a 3D film, you might want to do some research to fin out what you’re getting into. In the future, we can look forward to 3D TV (which I still argue is overkill) and honest-to-God 3D without the need for glasses.

Until then, though, enjoy those glasses-donning theater-going experiences. With Avatar being the success that it was, there’s going to be no short supply of 3D films in the near future.

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3 Comments For This Post

  1. Rachel Says:

    Very interesting :) I had no idea the ins and outs of 3D :)

  2. Liz Says:

    RealD uses circular polarization. You can tilt your head and maintain the 3D. It’s IMAX that messes up when you move.

  3. Quaid Says:

    Liz…right you are. Sorry for the slip. I still think IMAX looks better…as long as you keep your head straight, that is. :)

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