3D Projection Differences - from NAB 2007

Monday, April 16, 2007
Digital Cinema At the 2007 NAB: 3D Controversy

Apr 16 2007 3:00PM

Continued from 'Digital Cinema At the 2007 NAB: Steady Progress'....

The last presentation in this panel, from Dave Schnuelle, Senior Director of Image Technology at Dolby Labs, bears closer scrutiny. As I previously mentioned, the presentation of Chicken Little that I saw in late 2005 was branded as 'Dolby Digital Cinema' but used Real D 3-D projection and glasses technology, a moniker morass that I found confusing at the time. I'm less confused now, because Schnuelle tossed the audience the first few tantalizing crumbs of Dolby's unique long-term approach to 3-D projection.

To explain what little we now know about Dolby 3D Digital Cinema (note the name change), I'll begin by reminding you that the objective of any 3D display system is to present unique, perspective-altered versions of a given scene to a viewers' right and left eyes. Real D, as I've earlier mentioned, does this by successively projecting 'right' and 'left' versions of a given frame, with varying polarization characteristics, coupled to varying polarization responses of the right and left lenses in the viewers' glasses. NuVision's approach, conversely, projects the right and left views of a scene polarization-unaltered; it relies on alternately blocking-and-passing LCD shutters in the glasses to route the correct image to its matching eye.

The original approach to 3D, however, is the so-called anaglyph technique, known to any of you who've ever donned a set of red- and blue-lens glasses. The right and left versions of the scene, contained within the same image (therefore making the approach amenable to conventional 24 fps projection equipment), are correspondingly color-deficient. And, as any of who who've ever donned a set of red-and-blue glasses also know, anaglyph doesn't work very well. Among other things, there's a fair bit of image leakage to the unintended eye; said more precisely, the technology's extinction ratio is low. And each eye's view is missing a significant percentage of the full visible spectrum, requiring imperfect interpolation 'blending' image repair within the viewers' brains.

Dolby is, it seems from what Schnuelle said Saturday morning, going Back The Future with their under-development 3D technology. Schnuelle put the classic color gamut 'triangle' on-screen and then, in very general terms, explained that in Dolby 3D Digital Cinema, each eye's image would be based on slightly different RGB 'primaries' (presumably filtered by more exotic filtered lenses in the glasses). Unlike with anaglyph, with Dolby 3D Digital Cinema each eye gets a full RGB image, and Schnuelle took great pains to emphasize that the left- and right-view images would be color-indistinguishable from each other when viewed through the glasses.

Some other notes from Schnuelle's pitch:
Three fundamental design goals for Dolby 3D Digital Cinema were that it must be practical (must integrate easily into current theater operations), high quality (superior pictures, eliminate previous limitations), and cost-effective (must be a good investment for exhibitors and studios). It uses a color filter wheel, albeit not in image-forming path, instead in the path of the lamp assembly feeding the light engine. It employs a standard projector with a simple filter accessory; filter placement reduces stress on the optical assembly. Dolby 3D Digital Cinema works fine with a standard white screen (it also works with silver, but this isn't necessary). It delivers great 3D from every seat, using comfortable, lightweight passive glasses, and providing sharp, clear images with excellent color fidelity. It also provides a simplified, less costly process for creating and distributing 3D content.