Tech Talk: Laser-Driven DLP Projectors Page 2

If the laser wavelengths are chosen properly - and there may be technical restrictions on what wavelengths Mitsubishi is able to use - the color gamut can increase substantially. If, for sake of argument, Mitsubishi has green at 520 nanometers (nm), blue at 470 nm, and red at 620 nm, the range of laser-reproducible colors (the triangle between those three points) will include the entire video color space and then some. Let's hope that Mitsubishi has managed to find lasers close to these wavelengths.

If it has, some interesting questions arise. Accurate reproduction of video signals requires sticking to the standard video color space and displaying its colors exactly, even though that space itself may have warped the colors it encodes. For example, normal video equipment will probably record an intense blue-green seascape such as you see around tropical islands as a less saturated blue-green, since the natural color lies outside the video color space. With an expanded color space available, designers may be tempted to somehow warp the colors back to where they were in the original scene, even though a video signal contains no information that would allow such a transformation. The opportunities for creative color distortion are enormous, and I just hope that if Mitsubishi does give in to them in its laser-driven DLP projectors it also supplies a back-to-normal-color button. As it is, if the company does everything right, "normal color" could come out dead-on true to the original signal.

Lasers' fast switching times lend themselves to playing some tricks in pursuit of higher contrast ratio, seemingly the fetish-spec of the hour. The light bulbs in today's DLP sets are always on and going full blast (hence the heat, and the noisy fans in some models), and even when reproducing an all-black signal there is usually enough stray light bouncing around a DLP optical system that the projected image isn't a pure black. Since lasers respond much faster than light bulbs, it is theoretically possible to turn down their intensity on a frame-by-frame basis when reproducing dark images to decrease the amount of stray light, possibly down to invisible levels, thereby increasing contrast ratio. They could even be turned off entirely when an all-black frame is shown to obtain a ridiculously high "sequential" contrast ratio (a spec derived by measuring light output from all-white and all-black frames displayed in sequence). But the problem has always been to reproduce deep blacks when the image isn't entirely dark, as in a scene with very bright highlights and very deep shadows, where laser-intensity modulation won't work. I'm eager to see how Mitsubishi has attacked this problem, too.

See the previous David's Dartboard entry.

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