Optoma H56 DLP front projector Is Letterboxing Okay For Home Theater?

Is Letterboxing Okay For Home Theater?

Optoma's H56 DLP projector uses DMDs with an aspect ratio of 4:3. This means that if you watch a steady diet of widescreen programs, you'll need only the center 576 vertical pixels (at most), while the remainder of the DMD lies dark or semi-dark. NEC's HT1000 (reviewed in July/ August 2003) uses the same technique, mapping 16:9 content to a 1024x576 pixel array. This does provide higher resolution than SVGA DLP projectors that map to 848x480 pixels, but it's not true HD. Should you care?

Obviously, a projector that uses 4:3 DMDs will sell for a lot less than a widescreen DLP design. The same applies to LCD projectors—models with 4:3 XGA-resolution panels can be had for well under $3000, while the least expensive widescreen LCD projector is Epson's Powerlite TW100, at $4995. There is a definite cost savings in using 4:3 imagers.

The argument that "1024x576 is more resolution than wide VGA" doesn't mean much if the projector can't do a decent job of scaling up the resolution of 480i and 480p sources. In that case, you'd be better off with an SVGA projector; mapping widescreen DVDs is almost a 1:1 pixel match.

HDTV from 1080i and 720p signals can look quite nice on all business-oriented projectors, which is why manufacturers use lots of HD content to demo these boxes. But HD video resolution is reduced by 20% for 720p, and by almost 50% for 1080i. This, combined with high-frequency rolloff in a projector, can make HD content look softer than it should.

Another issue is unlit pixels projecting onto a screen. That is, when you use a 4:3 chip to display a 16:9 image, the inevitable black bars above and below the image will not be completely black. They can be no darker than the blackest blacks the projector is capable of, which is never completely black in any projector (CRTs still do it best). You might be better off using the letterbox mode on these projectors exclusively and adding extra masking to the top and bottom of your screen to absorb light from the projector's unlit (but still dark gray) pixels. This is how NEC demonstrated the HT1000 at CES 2003 and CEDIA Expo 2002.

Using this approach, widescreen DVDs and HDTV using the 1.77:1 and 1.85:1 aspect ratios will pretty much fill the 16:9 area of the screen, while wider-aspect movies will leave a little bit of black at top and bottom. You can then watch plain-vanilla 480i, 4:3 content by selecting the projector's "native" mode for a near-1:1 pixel map, filling the height of the screen and leaving black pillars at left and right.—PP

TJN Comments: I must add a caution here. If you choose a 4:3, business-oriented projector for home-theater use and want to get the best results, be sure to choose a model that has a 16:9 setting, and always set your DVD player to 16:9. The 16:9 setting on the DVD player ensures that you'll get full resolution from "enhanced for widescreen" (also called "anamorphic") DVDs, and the 16:9 setting on the projector will correctly unsqueeze the image so that it looks properly proportioned. Without that 16:9 setting on the projector, you'll have to set the DVD player to 4:3 to get a properly shaped image. The player's 4:3 setting downconverts the anamorphic DVD image to an ordinary letterbox, throwing away 33% of the scan lines in the process.

Most projectors designed strictly for business applications do not have a 16:9 setting, but most projectors sold for home-theater use do—always check to be certain. The difference between the full-resolution playback of an anamorphic DVD and the same DVD downconverted to an ordinary letterbox, as seen on a big screen, is comparable to the difference between a first-rate DVD and a high-definition broadcast of the same film.—Thomas J. Norton