Compositional differences: Real D VS. IMAX

Compositional differences: Real D VS. IMAX

http://community.reald.com/blogs/real_d_blog/archive/2008/02/15/547.aspx

The history of western art, of painting and then photography, has been informed by the rectangle.  Virtually all painting and photography exists within the confines of a rectangular frame, and it is the edges of the rectangle that create the compositional boundaries and structure.  You don’t look through a rectangle when you’re seeing the visual world but the rectangle abruptly limits the visual field in a painting, or a photograph, or a projected motion picture image.  The placement of objects in space within the limits of the rectangle determines the composition.  Up until now visual artists have had to deal with the rectangle.

With the introduction of head-mounted displays, the rectangle could take a rest – or at least try to disappear.  The idea of virtual reality or augmented reality as exemplified by HMDs is a relatively new idea.  You can find references to the concept in science fiction in which images are piped directly into the brain.  

Granted, most HMDs have a limited field of view and the rectangle remains apparent.  But the idea, in its full embodiment, would be for the image to subtend most or all of the visual field, and over the years I’ve seen devices that were designed to do just that – to immerse the viewer in a visual experience.  The reason that I take the trouble to describe this is that the IMAX experience is one that attempts to immerse the viewer in the totality of the image – to remove the rectangular boundaries.  The Real D experience, and most other motion picture projection, involves the rectangle.  The audience member will be aware of the rectangle; and the traditional concepts of composition apply.  The kind of balance, juxtaposition and placement of objects within the image field is critical in classical composition but is different for IMAX screens.

In IMAX, in which people are sitting close to a giant screen, the periphery of the screen is more difficult to discern and the rectangle becomes relatively unimportant.  The idea behind IMAX is to immerse you in the experience.  So people who shoot IMAX movies have to think about a different kind of composition. I’m concerned with the stereoscopic cinema so my remarks are predicated on that interest.  In the stereoscopic cinema, the rectangular boundaries are important because of the well-known effect of the conflict of stereoscopic cue of parallax and the extra-stereoscopic cue called interposition.  If off-screen (negative) parallax values are occluded by the screen edges – and this is especially true for the vertical edges of the screen – there will be a conflict of cues, which some people (possibly most people) interpret as a region of confusion.  Some people may say that the image looks like it’s pulled back into the plane of the screen; some will report that the image looks odd.  In any event, it’s something that has to be dealt with in the conventional stereoscopic cinema and doesn’t need to be dealt with in IMAX because the screen is so large that it’s hard to see the edges of the surround. (Another thought to put into the mix that might further confusion rather than understanding is that we are in a time of transition in which people are learning how to look at stereo movies and maybe with the passage of time the screen edge conflict will come to be accepted.)

The big screen changes the way IMAX composes a stereoscopic image.  In fact, when looking at IMAX movies in stereo, everything appears to be playing into theater space.  I define theater space as that which is in front of the plane of the screen, and screen space is that which plays behind the plane of the screen, and the boundary layer between the two (at the zero parallax condition) is the plane of the screen.  In IMAX, the plane of the screen more or less disappears.  It becomes not necessarily unimportant, but it certainly has a different meaning from that in the conventional stereoscopic cinema, or the rectangle-bounded stereoscopic cinema.  A lot of IMAX films are set up so that the background points will have about 2-1/2 inches of positive parallax – which is the average interpupillary separation for the adult male population – so in most cases it will avoid producing divergence to produce a comfortable result when viewing background points.  

The net effect of looking at an IMAX screen for many people is that everything is playing out into the theater.  Some people report that they feel immersed in the screen or in the image and that they feel within the image – and that’s certainly what IMAX is trying to accomplish.  Since they don’t have to worry about the conflict of cues at the screen surround, and they’ve got such a big image, their compositional theory is a different one from the conventional stereoscopic cinema.  

The upshot of this for IMAX is that it has a tremendous parallax budget.  Since they don’t have to worry about a conflict of cues at the screen surround, they’re free to have large values of parallax.  In fact, the last IMAX film I saw in a preview (and because it was in preview I don’t think it’s fair to critique it or mention what the film was) had parallax that was measured not in inches, not in feet, but in yards!  

To some people this is fun.  But to me, it produced an obtrusive image that I felt like I couldn’t get away from. The truth is that, for me anyway, the IMAX stereo experience is not a lot of fun.  Most people may not share that experience and the last time I went to see an IMAX 3-D feature with my family my wife and kids had a good time even if I didn’t.  I also find the big parallax values tiring on the eyes, and the increased ghosting with just a little bit of head-tipping not to be a plus.

For the Real D cinema and for other stereoscopic processes projecting on conventional cinema screens, which are typically between 20 and 50 feet in scope, the experience is different. Directors of stereography like Phil McNally and Rob Engle, at DreamWorks and at Sony Imageworks respectively, have been using a technique that allows the conventional cinema to also have a very large parallax budget.

It was almost two years ago that I sat with Phil McNally in the Egyptian Theatre on Hollywood Boulevard and watch films at the 3D Expo.  We saw shorts that had been shot by Raymond and Nigel Spottiswoode in the ‘50s.  These were in black and white in the 1.3:1 aspect ratio.  Before we went into the theater, Phil had talked about the idea of the floating window that he said he’d read about it in my book, Foundations of the Stereoscopic Cinema.  Phil and I sat together and watched the Spottiswoode films with the floating window, and Phil said (with a British accent): “This is gonna work”; and he used it while he was the stereo supervisor at Disney for Meet the Robinsons.  He used vertical edges that were added to the left and right edges of the picture frame to build a virtual surround – in other words, a floating window that hovers in space between the screen and the audience so that images with large parallax values at the edges of the screen will not have a conflict of cues.  

One paradox of the stereoscopic cinema is that from the plane of the screen to stereo-optical infinity there is a parallax budget of only 2-1/2 inches (after which divergence sets in).  But you can have many inches of off-screen parallax without bothering anybody’s eyes.  While it may not be an order of magnitude – maybe it’s half an order of magnitude – that gives you a big parallax budget, certainly good enough to represent any shot.  The problem that is solved is that there is no longer a parallax-occlusion conflict occurring at the edges of the screen.  Movies like Meet the Robinsons and Beowulf have used the floating window to good effect to increase the parallax budget.

Since the allowable theater space parallax is much greater than the screen space parallax, this gives the filmmaker a chance to exploit the medium and to increase the depth effect.  In fact, it is now on a par with that which is in IMAX theaters.  However, the image is still contained by the rectangle.  People talk about this stereoscopic method as being immersive, but who knows exactly what that means?  They may very well feel more immersed in the picture because it is a stereoscopic picture with a bigger range of parallax.  One thing is certain:  A trade-off has been made between parallax budget and off-screen effects.  That’s because the amount an object appears in front of the screen is compared to the plane of the screen that is usually defined by the screen surround (the physical black border around the screen edges).  With a printed on surround the frame of reference is now literally the virtual window floating in space.  But the parallax values of the windows can be varied from shot to shot, and even within a shot and the values for the left edge don’t have to match the right edge so shots requiring off-screen effects can be had.  The virtual window can be thought of as an animated window that can be placed at the Z location at will so off-screen effects can be accomplished.

Published Friday, February 15, 2008 10:04 AM by Moderator