OTHER TECH

•Photo Gallery

The projection lens dominates the HD70's front. All of the inputs - HDMI, component video, VGA, S-video, and composite video - are on the back panel. The HD70 also has an RS-232 control port, an IR receiver, and a 12-volt trigger relay, plus a fan and a power supply. Digital signals, coming from a source such as an HD DVD player or a receiver with HDMI outputs, are sent to an internal digital receiver circuit. Analog component-video signals are sent directly to an analog-to-digital converter (ADC), while S- and composite-video signals go to a video decoder, which breaks them down to component-video format. It includes a comb filter that separates composite video into S-video - chrominance (color, or C) and luminance (black and white, or Y) signals. S-video passes to a color decoder that finishes the job by splitting the chrominance signal into its constituent color-difference components. The resulting component-video signal then goes to the ADC.

Because the various digitized signals can have different resolutions, they're then sent to a scaler, which converts them to the DMD's native resolution. In the HD70, the scaler is part of the DLP chip set. Step-up models might have a separate scaling chip, and some have a separate deinterlacing chip to handle interlaced signals. Many high-end projectors are designed to be paired with a high-performance external scaler/processor. Optoma's $7,999 HD81 package, for example, bundles a single-chip 1080p DLP projector with a high-quality Gennum VXP scaler and 10-bit motion-adaptive high-def deinterlacer. Along with all the scaling and deinterlacing being handled by a higher-performance component, all of the inputs are located on the processor instead of the projector, making it easier to add or remove source components. This also means there's only one video cable (plus a control cable) running to the projector itself.

Because DLP is a reflective technology, the light source is in front, and to the side, of the DLP board, facing the rear of the projector, where the DMD chip is located. Light from the lamp is reflected through a filter (which screens out detrimental ultraviolet light) and then through a condensing lens before passing through the color wheel. The HD70 uses a seven-segment wheel - two segments each for red, green, and blue, plus one clear segment to help boost brightness. The colored light then goes through a light rod, which focuses it and disperses it evenly across the surface of the DMD. After it exits the rod, the light goes through a relay lens before striking the the mirror surfaces.