Friday, August 24, 2012

Part 1 - Sitting Too Close To Your 3D TV Will Make You Go Blind?

Well, not really.  One of several things my Mom said would make me go blind is sitting too close to our black and white standard definition 2DTV many years ago.  Today the question is... how close or how far from a modern 3D display device should a person sit to achieve a satisfying, immersive experience?

If you read the literature as most early adopters do, you’ll find conflicting information on the proper way to set up your new 3DTV home theater to achieve an optimal experience.  Unfortunately, to some people, it’s all too intimidating to bother with or they end up calling the retail store “experts” to properly set-up their home theater environment.

In my opinion, you can forget about textbook advice on the “proper” distance to sit in a 3D home theater environment or for that matter, where to sit in a movie theater.  In my blog, "People Who Hate 3D Movies Should Have Their Eyes Examined," I discuss how no two people see 3D in quite the same way and that much of the difference depends on the balance of visual acuity between a person’s two eyes as well as the accuracy of their gaze, such that the field of view of each eye falls onto the proper retinal location.  In this context, most of the technical considerations for the proper “zone of comfort” fall away.  The real question is what’s most comfortable to the individual given the quality of their vision and/or their form of optical correction and also what is the type of immersive experience the individual is trying to achieve.

The Rule of Thumb is That There are No Rules.

You’ll often read that the proper distance to sit in a 3D movie theater is 1.5X the height of the screen.  I guess that means that if you find yourself outside of the ‘sweet spot’ of the theater you might as well forget about getting the maximum experience from the movie.  Maybe taking a page from the latest airline playbook where some are charging for aisle or window seats, theaters should start charging extra for the 'preferred' center seats in the row that’s 1.5X from the screen.

When I‘m in a 3D movie theater, I typically sit in the middle/center of the auditorium.  I prefer not to sit too close to the screen, nor do I like to sit too far to one side of the screen. In many of the new luxury theaters, like Cinepolis, all of the seats are adequately centered on the screen.  In other theaters, sitting too far to one side of the screen can negatively affect the 3D experience because each eye receives a skewed perspective of parallax.  However, no matter what type of theater I go to, there are seats that are too close for my comfort.  But that’s just me.  Some people feel that the best seats are as close to the screen as possible so they can get what they consider to be a ‘full’ immersive experience. Indeed, there are some people who expect an IMAX type experience in the first row of a theater where their entire field of view is the screen.  And that's their personal preference. However, typically, the closer you sit in a theater the more the 3D effect tends to diminish.  If you are sitting in the front row of a theater and an object appears to be 50% of the distance between you and the screen, that same object will also appear to be 50% of the distance between you and the screen even if you're sitting in the back of the theater.  But of course 50% of the distance between you and the front seat relative to 50% of the distance between you and the back of the theater creates two different types of immersive experiences.  In the later, the entire volume of the theater comes into play.  Of course, the farther you move back from the screen, the more distortion there is in the image, where a round ball is no longer round but elongated, but the average moviegoer will not notice.  However, of greater importance, the closer to the screen that you sit the more likely your eyes will tire from the strain that comes from decoupling accommodation and convergence.  You see, watching a 3D movie is very different than the way we experience the third dimension in our every day lives.  In my blog, “Engaged in2D Movies and Immersed in 3D Movies,” I explain this difference and point out how physiologically unnatural a 3D movie is to our binocular vision.  That doesn’t mean it’s bad.  It’s just different.  In conclusion, the best place to sit in a 3D theater is where you, personally achieve the most satisfying 3D experience, keeping in mind that sitting too close to the screen places demands on our binocular vision that can cause discomfort and/or headaches.  Thanks Mom.

It’s a shame that some people give up on stereo simply because their first experience in a 3D theater was uncomfortable.  Maybe that’s why some film critics complain that the 3D was horrible or added nothing to the film, or worse, that it detracted from the film.  Maybe, in addition to visiting their optometrist, as I’ve suggested before, they might also simply need to adjust their seating location.

There are, of course other things that can add to discomfort in theater, like a terrible story line, horrible acting, poor directing, etc.  You know the drill. But as far as 3D is concerned, unless the movie is badly shot or poorly converted, sitting further away from the screen will often help mitigate most physical complaints.

My Home Entertainment Theater

When I’m in my home entertainment center I prefer to watch 3D Blu-ray movies with the lights off to simulate the theater experience.  But, I don’t sit 6 feet from the screen as we’re often instructed in the literature.  Instead, I crank up the 5.1 and sit as far back from my passive, 55’ LG screen as possible.  Again, that’s just me. Of course in sitting so far back from the TV, I achieve a relatively narrow viewing angle of the screen, but it allows me to take in the entire screen, which is my preference.  And while taking in the entire screen means that the screen edges become part of my field of view, in my dark man-cave that’s not an issue. It does not detract from my suspension of disbelief.

If I sit as far back as 15 feet from my 3DTV (which takes me out onto the patio watching the movie through the French doors), the snow in Scorsese’s’ Hugo seems to engulf the entire room in front of me.  To me, being immersed under those conditions is a visual experience like no other.  In fact, I enjoy Hugo much more in my home theater than I did the five times I saw it in on the big screen.  Can you tell I love that film?

Floating Windows

The only time my preferred narrow field of view of the screen becomes an issue is when a movie is released in Blu-ray without floating windows.  Floating windows are an adjustment to the edges of the screen that filmmakers typically apply in post-production to compensate for what we call 'edge violations'.  An edge violation occurs when an object that with negative parallax (coming out of the screen), breaks one of the edges of the screen (in this case, edges are referred to as the window) such that one of our eyes sees more of the object than the other.  Our peripheral vision registers this as unnatural because if the object is in front of the screen it cannot also be in back of the screen.  This creates a cognitive disconnect that cannot be resolved by our brains, causing a form of “brain-pain” called ‘ocular rivalry’—when our two eyes compete to resolve the conflict based on their different and conflicting inputs. When this occurs our brain tries in vane to reconcile the discontinuity between the images in each eye, causing a type of double image at the edge of the screen that can be uncomfortable to view.  Floating windows are an adjustment to the edge of the movie frame that’s typically applied shot by shot to eliminate this rivalry between our two eyes in the event of edge violations.  By moving the edge of the frame in one eye so that the double image at the edge disappears, both eyes will be seeing the same amount of the object but the object will appear slightly behind the screen rather than in front of it.  It’s called a floating window because the window adjustment floats in and out from shot to shot, and even within a single shot floating windows will sometimes be animated in and out to better achieve a more comfortable stereo effect.

There are some film directors who don’t believe in applying floating windows.  I’ve heard some say that, “if the audience is paying attention to the edges of the screen then I haven’t done my job in directing their attention to the story point in the shot.”  What these directors don’t realize is that people enjoy watching 3D movies in many different ways.  To me, floating windows are an essential part of 3D moviemaking because no matter where you sit in a movie theater or home theater, unless your nose is pressed up against the screen, edge violations are inevitably perceived by our peripheral vision and can cause discomfort.  Edge violations are simply contrary to what our brains anticipate and will inevitably take the viewer out of the moment.  It’s particularly important to me because I prefer to sit back from the screen, which always exposes the edges of the 3DTV, and while I tend to follow the convergence intended by the filmmaker, extreme negative parallax at the edges (objects in front of the screen, but cut in half by the edge of the TV) without floating windows inevitably causes discomfort.  However, when floating windows are skillfully applied by the filmmaker, the edges melt away and my experience is all encompassing, even though the screen takes up only a narrow portion of my field of view.

The Bottom Line

I believe there are no hard and fast rules to the ‘proper’ viewing of a 3D movie.  Theatergoers and home theater enthusiasts should simply experiment with proper viewing angles and distances to find the optimum 3D experience for themselves.

In Part 2 of this topic, I’ll relay an interesting experience I had at 3D-Con, the 38th National Stereoscopic Association Conference.  A conference where the attendees were extremely knowledgeable stereo photographers and where I learned more than I had bargained for regarding ‘proper’ viewing distances.