Technology Showcase: Home-theater Projectors
Aug 1, 2008 12:00 PM, By Jay Ankeney
The most innovative front-projector systems.
Then came the move toward HD television. The first consumer HD system — developed by Japanese broadcaster NHK in 1969 — used a 5:3 aspect ratio, which was copied by the United States for the first demonstration of HD in 1981. When the Grand Alliance backed the HD standard developed by the Advanced Television Systems Committee — which was adopted by the Federal Communications Commission in 1996 — it was more concerned with bandwidth and resolution than adhering to any previously established aspect ratio. Thus, to the dismay of many veteran cinematographers, the 16:9 aspect ratio was set as the standard for HD presentations.
Back in the heyday of Hollywood, movie palaces could accommodate different aspect ratios by changing the lenses on projectors and shielding the screen by moving curtains in or out from the sides. But fitting theatrical widescreen into HD widescreen in the home required cropping the celluloid image to fit the HD display. For those who can afford it, that is not to be tolerated.
Everything would be so much simpler if theatrical films were actually shot in exactly 2.35, but the fact is that the real ratios used by directors of photography can vary considerably. In fact, the true mathematical ratio set by the Society of Motion Picture and Television Engineers in 1993 for the unsqueezed image is 2.39 — and some DVD and Blu-ray Disc cases list their version as 2.40. Still, 2.35 has become the generally recognized ratio for the most uncompromising home theater. The problem is that it is considerably wider than the specs for an HD frame.
How do you square that circle? The same way French astronomer and inventor Henri Chrétien did in the early '20s with a film process that he patented as Anamorphoscope, which uses what we now call an anamorphic lens. It takes the wide, rectangular image in front of the lens and squeezes it horizontally it until all the people look tall and skinny in the recorded frame. Upon playback, a similar lens reverses the process.
This proper aspect ratio can sometimes be seen in an unmodified HD display with letterbox black bars on the top and bottom. The easiest and cheapest way to eliminate those bars is to use a projector with a powered zoom lens and vertical lens-shift capability. However, this means you are only using some of the pixels put out by your projector's light engine, so you are sacrificing its potential resolution. Or you use some kind of inboard or outboard signal-processing scaler to squeeze the 2.35 film image onto your HD display and then shoot it out through an anamorphic lens. Because all the vertical pixels on the imaging system are in full use, this is often referred to as a “constant height system.” Now all the pixels on the projector's original imaging system can beam out that tall/skinny image through the lens' horizontal stretch, and voilà, you have a 2.35 widescreen image that takes advantage of all the resolution the projector can put out.
Since 2001, Panamorph has made the most popular of these anamorphic lens systems. These can involve either a fixed lens that has to be manually placed in front of the projector or a robotically controlled lens system that slides out on a sled when it is needed and retracts when it is not. Although this system can cost many times the price of entry-level projectors, for those installing state-of-the-art screening rooms, it is just butter on the popcorn.
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