15/04 Discomfort

Sweeping statements make me nervous. Daniel Engber's claim in this article for Slate, that "3D" always has and always will hurt your eyes, is a case in point. Mind you, it's always nice to hear some dissenting views about an industry trend with no shortage of enthusiasm associated with it.

I find it interesting that Daniel finds viewing 3D films uncomfortable - an experience that to some extent I share when watching 3D in regular cinemas which use a single projector (rather than one projector each for the left and right-eye views). These projection systems display the two views of each frame sequentially in time, and use a polarising or spectral filter that flips in synchronisation with the projector along with polarising or spectral filter glasses to perform the "separation" that ensures left-eye images are seen only by the left eye (at least in theory) and so on.

Personally, I see a characteristic "shimmer" when viewing such "time-sequential" 3D systems that is most obvious when I move my eyes around the picture. During this kind of "saccadic motion", the human visual system effectively switches off (or otherwise ignores) much of the signal coming from the eyes, in order to prevent you from experiencing a sensation of motion as your eyes move from place to place. If you're watching a time-sequential 3D image, that means each time you move your eyes, they effectively "switch" off and on at times that are completely unsynchronised with the projector, and there may be a perceptible period during which one eye sees no light at all, leading to the perception of flicker in one eye. It's just a personal theory that this is the cause of the "shimmering" I perceive and a contribution to eyestrain, of course, and if any visual psychologists happen to read this, I'd love to chat about it. But the point here is that this is a minor limitation of current projection technology. It's not a fundamental limitation of stereoscopy.

Daniel is wrong to claim that fundamental advances in 3D technology have not been made in the last 50 years though. Film projectors (and cameras) suffer from registration problems: the mechanisms that move the film behind the camera or projector shutter are mechanical, and there is always a certain amount of inaccuracy in the positioning. If the two images in your stereoscopic 3D presentation dance around the screen due to poor registration, that's going to cause major eyestrain. Digital cameras and projectors have no such moving parts, and the single-lens, time-sequential method of projection in particular ensures that the two eye-views are perfectly overlaid without requiring careful calibration. But there are plenty more ways to give people headaches than with poor registration.

For example, as Daniel correctly points out, viewing a stereoscopic image is fundamentally different to viewing a real-world scene, in that the convergence of the eyes and the distance at which they are focussed is decoupled in the former case. This is an extremely well-known issue, and there are a number of ways of dealing with it artistically: keeping things that the audience will want to concentrate on (usually the expensive actors) at a depth close to the screen, for example.

In the long term, I'm not entirely convinced this will still be an issue: anyone who's ever worn glasses has learned to adjust to a different relationship between convergence and the focussing of the eyes - the whole purpose of glasses is to change the way your eyes focus, after all. People with varifocal glasses learn (and usually learn late in life) to cope with lenses in front of their eyes that cover a whole range of focal lengths depending on the part of the lens they look through, which also effectively decouples convergence and focussing.

Stereoscopic film and television is an evolving, immature medium. It's ludicrious to claim that it would be the ideal medium for every genre that we have now (after all, those genres evolved to suit the medium of 2D film and television). But I think it is equally ludicrous to claim that its well-known limitations will lead to inevitable audience discomfort. There are plenty of technological and artistic challenges to be addressed, particularly if broadcasters want to start 3D television services, but I don't think there's a fundamental discomfort issue that precludes the success of the medium.

Oh, and as for the idea that stereoblindness might preclude the success of stereography - did colour blindness preclude the success of colour?