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Projecting with LCDs:
LCD technologies have been used for years and years for relatively low-quality
projectors — the kind you might have in the conference room at work for
projecting those ubiquitous PowerPoint slides on the white board during
mind-numbingly boring meetings.
Well, the LCD has come of age in the era of home theater, and now you can
buy front-projection systems based on the LCD that provide a high-quality
(often HDTV) picture at a price that is typically lower than that of CRT frontprojection
systems. (Note that LCD RPTVs aren’t much cheaper than CRT
RPTVs and may even cost more, simply because the small tubes used in
RPTVs are dirt cheap.)
LCD projectors typically use three small LCD panels (a couple of inches across
at most) — one each for red, green, and blue picture information. Behind these
panel is a strong lamp that provides the light. LCDs (and the DLP and LCoS
projectors we discuss next) are fixed-pixel displays, meaning that they display
video at a certain resolution. For example, Sony’s most recent LCD RPTV displays
at 1,366 pixels horizontally and 768 pixels vertically (this exceeds the 720
vertical pixels required for 720i, so the set is HDTV-ready). An internal device
called an image scaler converts the incoming signal (such as 480p from progressive
scan DVDs or 1080i from an HDTV broadcast) to the 1366 x 768 resolution
for display. LCD projectors are inherently progressive, so even standard
NTSC broadcasts are converted to a progressive-scan mode for display.
The quality of the image scaler — how well it converts other signals to the
fixed-pixel resolution native to the LCD — is a key factor in a projector’s picture
quality. In Chapter 21, we talk about external image scalers (and related
devices such as line doublers and quadruplers) that can improve the picture
quality of a projection system — and not just for fixed-pixel displays, but also
for CRT projection systems as well.
Because you never know who’ll come up with a better system the month after
this book is printed, we generally avoid dropping brand name recommendations.
However, we find that scalers from one company, Faroudja (now owned
by Genesis Microchip — www.gnss.com), are always excellent. You can find
many different brands of projectors (and HDTVs in general) that use Faroudja
chips (notably the DCDI chip) to scale, or upconvert, images.
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