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Technology Showcase: Home Theater Projectors

Aug 5, 2009 11:58 AM, By Jay Ankeney

The latest illumination options create more versatile home theaters.

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If you want to get the big picture, nothing beats a projector. Home theater projection systems are proving to be one of the most innovative market segments of the domestic entertainment business. Prices are coming down, new market segments are being developed, creative technologies are being introduced, and the options being offered cover the spectrum from relatively inexpensive models for those who want a big picture at a small price to the videophile who demands a home experience that rivals that of the local Cineplex—and in some cases exceeds it.

There is a major irony in this trend. Back in 1953, when 20th Century Fox released the first CinemaScope feature, The Robe, the studio also coined the term “letterbox” to describe the dimensions of the new, wider theater screen. The goal was to enable movie theaters to lure audiences out of their living rooms by offering a bigger picture than early TV sets could provide.

Now, many home theater setups can provide images that distend the viewer’s field of vision as fully as their neighborhood movie palace screens, without the sticky floors and overpriced popcorn. More recently, Hollywood has helped theater owners fight back with 3D attractions. But since these are based on digital cinema presentations, that technology is rapidly migrating into home theater projectors to the extent that, once 3D content for the home becomes more readily available, the stay-at-homes may once again have an option that will make them question the rising price of theater tickets.

Of course, ever since Kerns H. Powers proposed the 16:9 (1.78:1) aspect ratio in 1984 as a video compromise for all the different conventional and widescreen cinema formats, people increasingly have grown to expect watching rectangular images on digital home screens, and for many, 16:9 fits the bill. Videophile purists, however, want to get as close to the real movie theater widescreen experience as possible. So ignoring the fact that CinemaScope was originally 2.35:1 and that modern anamorphic productions are actually shot in 2.39:1, the companies producing DVDs often just round this up to 2.40:1. Projector manufacturers, however, usually reference the more accurate 2.35:1 ratio.

The imaging chips inside most projectors are still designed to present native 16:9 pictures from a 1920x1080 pixel array. If you can handle the compromise, adding black bars at the top and bottom of the screen will let your projector present most of the content contained in a widescreen display on your home screen. Those black bars represent unused pixels, reducing the 1920x1080 image frame to an effective 1920x817 picture elements. To see all those pixels you are paying for, the projector needs to be able to put out its images in vertical stretch mode—also called Mode One. Then you need to add an anamorphic lens to the front of your projector, and the good folks at Panamorph will be glad to provide you with one. Actually, almost 90 percent of the stretch-out lenses seen in America are from Panamorph or one of its OEMs. Internationally, the market is well-shared by Schneider Optics.

The energy needed to run those projectors has become an issue, however, as everyone wants to go green. One of the most hopeful responses to this has been the introduction of LEDs as light sources to replace the more common high-pressure mercury lamps (UHP or mercury vapor lamps) used by most projectors. Measured to the point when they put out half their rated illumination, most of these lamps last 2000 hours in full power usage or 3000 or more hours in what has become to be known as “eco mode.” It’s even less for the more expensive xenon lamps.

Now—especially at the recent InfoComm—we are starting to see LED lighting technology coming onto the market, with red, green, and blue LEDs eliminating the need for color wheels to achieve a wider and more consistent color gamut. What’s great about LEDs is they promise up to a 50,000-hour life free of maintenance and relatively low power consumption. Just for comparison, the implementation of LED illumination would let you run a home theater projector up to 24 hours a day, seven days a week for more than four years without changing a lamp.

The downside is that due to their heat output and the need for sophisticated drive circuits, among other considerations, LED projectors are limited to sub-1000 lumens in output so far. However, it is said that because of a phenomenon called the Helmholtz-Kohlrausch (H-K) effect, the increased color saturation of the RGB LEDs is perceived by the viewer as part of the image’s brightness. This is better known as chromatic luminance since achromatic luminance (also known as “white”) is the usual standard of comparison. As a result of the H-K effect, LED projectors appear to be about 25 percent brighter than a similar UHP lamp home theater projector rated at the same lumens.

Home projectors have been traditionally provided a satisfactory 1000-ANSI-lumen to 1500-ANSI-lumen output since they were intended for almost completely darkened home theaters. However, another evolution on the illumination front is improved light-source efficiencies that seem to be encouraging the development of a new market segment often called “living room projectors.” Their brightness of 2000 lumens or more permit these projectors to be enjoyed in parts of the house bathed in ambient light.

When it comes to resolution, 1080p and WUXGA resolutions are all the rage. This means many projectors using 720p output are now on the market at significantly reduced cost. Whether the average viewer can tell the difference on smaller screens is left to the eye of the beholder. In addition, the advent of short-throw designs—long popular in educational settings—eliminates the irksome problem of having people walk in front of the projector’s throw when it is mounted in the back of the room. Positioned only inches from the screen and easy to move from room to room, short-throw projectors may prove to be very accommodating in future home theater installations.

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