That fact that projection screens have emerged as a subject of hot debate might make the general public question the sanity of A/V aficionados. After all, these are flat white sheets we're talking about, right? Are we as nuts as oenophiles who enthuse about aromas of freshly reaped alfalfa in their pinots?
The subject of screens has certainly become more complicated. As projectors (and therefore screens) have become more practical and popular, more companies have entered the market. And where once screens seemed as uniformly white as the outfits at Wimbledon, we now have gray screens and even black screens. We have woven screens. We have ultrawide screens and curved screens. And a screen might cost a few hundred dollars or tens of thousands of dollars.
That's why Sound & Vision decided to do its first major projection-screen roundup. We borrowed some of the most interesting offerings from today's leading manufacturers, ran all of them through a series of measurements, then spent weeks swapping them out, watching movie after movie to figure out what everyone really needs to know about this newly complicated category.
There's a surprising amount of technical stuff going on with screens, but if you understand the concept of gain, you're halfway there - and you'll be deep into one of the most controversial subjects in video. Gain is the amount of light a screen reflects back at you. A matte white surface is said to have a gain of 1.0. ( A piece of printer paper comes close to that.) A screen with a gain greater than 1.0 focuses and intensifies light, while a screen with a gain less than 1.0 diminishes it.
Gain can produce a brighter image, but today's fixed-pixel (DLP, LCD, and LCoS) projectors are so powerful that brightness is seldom a concern. Gain is still important, though, because of its side effect: directionality.
In order to push a screen's gain past 1.0, the manufacturer has to coat it with something that increases the directionality of the light reflecting back. That means the reflected light is most intense if you're directly in front of the screen, and decreases as you move to the side. Here is where most of the controversy about screens lies.
Directionality can be a bad thing because it can result in "hot-spotting," in which the center of the screen looks brighter than the corners. Purists hate that. But directionality can also be a good thing, because it lessens the reflection of light off your walls. If your walls and ceiling are painted, say, white or beige, light from the screen will reflect off of them, and some of it will end up back on the screen. This reduces contrast. Also, if your walls are painted any color other than white, gray, or black, that color will reflect back onto your screen and mess up your color accuracy.
As you've probably noticed from the installations featured in Sound & Vision, most home theaters don't have dark gray walls. So gain has a practical advantage in a typical home theater environment: It lends the interior designer greater creative freedom without adversely affecting the picture.
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