My issues with 3D

I went to see Avatar last week. In my recap, I wrote,

Another issue with the 3D is that it’s shot like a conventional 2D film. I believe 3D needs a different shooting style

The largest issue to me is depth of field.

With conventional two-dimensional motion pictures, the viewer focuses on the image and all is well. The cinematographer decides what parts of the image are in focus and what parts are not. It may seem like a no-brainer to always have all of the image in focus, but selective focus is often used to isolate an object or character. In those cases, a perfectly focused background is a distraction. So the cinematographer uses a fast lens, opens it up, and blurs the background into a mish-mash of softness and colour, leaving the subject in sharp focus. It’s a very effective technique … and purely a product of 2D imagery.

Our eyes do work in the same way, but we almost never realize it. If you’re paying attention to someone talking to you, and they’re quite close, whatever is behind them is blurry. You don’t notice this, however. If you were to look, your eyes would automatically re-focus on the background in a split second. Blur? What blur?

So a blurry background is a photographic technique to draw the viewer’s attention to the important part of the image. How does this translate to 3D motion picture? Poorly. Many people report eye-strain and headaches when viewing 3D films. I’m sure there are many causes, but I can’t help but believe that using selective focus to generate blurry backgrounds is large among them.

Let’s go back to conventional 2D films for a moment. If the entire image is in focus, your eye can sweep across it and take it all in without changing focus. From the person in the foreground to the horizon in the background, your eye sees it all clearly by focusing on the screen. If the background is blurry, your eye isn’t fooled because it focuses on the screen and knows the image is blurry.

This all goes out the window with 3D films. Objects appear to be varying distances away and they all require your eyes to go through most of the same motions as when viewing real objects. Technically, your eyes don’t need to refocus, but they do need to vary their viewing angle in relation to each other, to work their depth-perception magic and allow your brain to build a three-dimensional image of the film. With 3D, your brain believes the image is not flat, so when you look at an area that’s obviously blurry, your eyes try to re-focus to correct the problem. Even when blurry, the parallax between your eyes indicates to the brain the relative distance of the blurry object. You brain knows it’s not a flat image, so the blur must be a focus issue. Eyes? Get focusing! But your eyes fail because they can’t fix the problem.

The only way I can see to correct this is to maximize the depth of field and make everything sharp and clear. The viewer can then look at whatever he or she pleases and everything will appear as it should.

Maybe. In the real 3D world around us, our eyes have to do two things. They each focus to generate a nice clear images of our surroundings (one image from each eye), and they have to vary their viewing angle so both of our eyes are looking directly at whatever it is that has our attention. Our brain then uses this angle to combine the two images into a single view with depth perception. When viewing a 3D film, our eyes need only focus on the screen. No further focusing is necessary, but our eyes still vary their viewing angles allowing our brains to calculate depth. Perhaps having to maintain the same focus and vary our eyes’ viewing angle causes eye-strain for some.

Another issue is shot-to-shot transitions.

Imagine a scene in which two characters, standing face to face, are conversing. Typical cinematography has the viewer jump back and forth, from behind one character to behind the other, so we can always see who is talking. We certainly don’t do this is real life, but this shooting style ensures we don’t miss anything. If the imaginary conversation goes on for any length of time, some of the shots may be from father away, showing the whole room, and then closer, giving us an over-the-shoulder perspective. We’ve all seen this before and it’s easily for us to assemble the very different and suddenly changing viewpoints in our heads.

Now imagine the same scene in 3D. We don’t know when the shot will change perspective, nor do we know what the perspective will be, but the depth in the image requires our eyes to rebuild a stereo image every time. I find no real issue with this when the ‘distance’ to the subject remains the same or varies only slightly when the shot changes, but if an over-the-shoulder shot changes to a room-wide view, there’s a moment of discontinuity as my eyes and brain work together to recalculates the image and my position relative to it.

In thinking about it, I realize that there seems to be a middle range where a perspective change is most disorienting. Cutting from behind one character to the other with little change in the distance to the speaker is a smooth transition. Similarly, cutting from a character to a landscape is also a smooth transition to me. But reverse from an over-the-shoulder to half-way across the room, and my enjoyment of the story is briefly interrupted as my eyes and brain play catch-up.

Unlike the selective focus issue, this sudden distance change never occurs in real life. Even if you move with your eyes closed, your senses give you a good idea where you are. When you open your eyes, you know what to expect. We don’t, however, teleport to various places within a room every second or five.

Certainly there are ways around this issue as well, but they’re unusual in current cinematography. Panning back and forth between two people talking is unusual because it’s so uninteresting. Individual shots of extremely long duration are difficult.

I wouldn’t be the least bit surprised if we discover that most of the cause of 3D fatigue is technical. Those can be fixed. At the same time however, I’ll be very surprised if the problem is entirely technical. Filmmakers are going to have to learn some new techniques, and unlearn some old ones, if 3D is to become a serious film-making medium.

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One Comment

  1. Shawn
    Posted January 21, 2010 at 07:53 | Permalink

    You made my brain hurt

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