LCD and DLP projectors
Mar 1, 1999 12:00 PM,
Peter H. Putman
There is a trend sweeping through the professional A-V industry. Slowly butsurely, plug-and-play LCD and DLP projectors are making their way into thefixed-installation market, displacing the venerable CRT projector. Some companiesalready offer a full range of installation-grade display systems. Others,without a competitive product, scurry around making OEM deals.
In my October 1998 column, I talked about this new wave of projectionsystems and how their features measured up to the rigors of theinstallation marketplace. Since then, the trickle of products has grown.Sanyo, the company that kick-started the plug-and-play LCD projectorrevolution with its XGA-resolution PLC-9000N, is working to stay in thelead with its higher-brightness PLC-9000NA and the upcoming PLC-EF10N. Sonyresponded with the quad-lamped VPL-X2000, 2,000 lumen boardroom projector,while Barco has taken a long-anticipated step into the smaller, brighter,lighter arena with the BarcoGraphics 6300. Epson, a company long identifiedwith portable projectors for desktop presenters, now has the 1,000 lumen,12 pound (5.4 kg) PowerLite 7300 with 5xBNC connectivity, and Hughes-JVCcontinues to improve its D-ILA G1000 SXGA box, currently rated at 1,000lumens but shooting for double that in the next year.
Proxima, another company long associated with desktop projectors, made astrong entry into the boardroom market with its version of the Sanyoprojector (Pro AV 9310) and is currently touring a totally integrated A-Vroom exhibit, “The Conference Room of The Millennium,” in conjunction withDa-Lite and Crestron. Eiki, a reseller of Sanyo products, is also makingbold gestures toward system integrators with its version of the PLC-9000series, forsaking numbers for the catchy “Powerhouse” moniker.
Sharp continues to ship the full-featured XG-3500, a real eye-catcher atthis year’s INFOCOMM Shoot-Out that is aimed at the boardroom market.Electrohome, AmPro and Telex are in the fray with their respective privatelabelings of Fujitsu’s 1,000 lumen desktop design, and, of course,Mitsubishi continues to make waves with the LVP-X200, one of the betterdesigns in terms of sync compatibility and a nice picture-in-picturefunction, well-suited for videoconferencing.
This surge towards the fixed-install market has caught more than a fewcompanies off-guard. Davis North America, which just a couple of years agoturned its back on LCD projectors in favor of DLP engines, recentlyannounced the new DPB 1200 boardroom LCD projector with 1,200 lumens, widesync capability and picture-in-picture. Score 100 points if you correctlyguessed that it is the Mitsubishi X200.
An even bigger puzzle is presented by In Focus, who is single-handedlyresponsible for most of the buzz about the LCD boardroom invasion. Itsfull-featured, 1,000 lumen Lite Pro 1000 previewed to favorable comments atCOMDEX 1997, but shipments did not begin until almost 6 months later. As ofearly February, In Focus has decided to hedge its bets with the new LitePro 1200, another full-featured boardroom projector with 1,200 lumens, widesync capability and picture-in-picture. Score another 100 points if youagain guessed that it is the Mitsubishi X200.
Replacing years of CRT technology with a plug-and-play box is not as easyas many companies would have you believe. CRT projectors certainly havetheir drawbacks; they are heavy, take up a lot of space, requireconvergence, have virtually no lens options and cannot produce nearly asmuch light as even a simple ultraportable projector.
On the other hand, the ability of a CRT projector to trace an infinitenumber of picture resolutions and aspect ratios with no strings attached,combined with complete control over optical alignment and picture geometry,still makes them a standard of comparison for other display systems, and donot not forget the purity and color quality of CRT-generated images either,still preferred by virtual-reality and simulator designers.
If you are caught up in the installation-projector wave, there are a fewthings you will want to consider before you start swapping out tubes forTFTs. For some applications, the functionality of a slide projector is allthat is required. For others (particularly retrofits), we will demand a lotmore from our projection system.
Optical correctionBecause of a ceiling-mounted pro-jector’s requirements, there has to be away to adjust the focal plane to compensate for off-axis imaging thattypically leads to keystoned images. CRT projectors compensate by not onlytilting the angle of their three lenses slightly (about 12 degrees), butalso providing keystone adjustment of the electron beams. By effectivelykeystoning the rasters in the opposite plane, the tilt is compensated, andviewers see a perfectly rectangular image.
Not so with LCD and DLP projectors. Tilt a projector off its center axis,and you will get a keystoned image. There are two ways to compensate forthis. The first (and sensible) method is to provide a motorized lens shift,changing the vertical alignment of the projection lens with respect to theprojector’s image plane, the same process used in view cameras to correctfor perspective distortion when tilting up or down.
The second, less effective method is to re-map the image electronicallyacross less or more pixels in a trapezoid shape. This is a similar approachto shifting the electron beams in a CRT projector, except that theresolution of a CRT projector is unaffected by keystone correction.Re-mapping images across more or less pixels in a trapezoid shape affectsresolution and results in a jagged, aliased edge to the image, not asolution expected in a professional installation. Although this re-mappingproblem becomes less apparent at higher resolution, it is still inadequate.Optical lens shift is the way to go, and having the ability to tilt theimage-forming plane of the projector (typically, the combining prism)several degrees would help even more.
Sync compatibilityThis is a no-brainer for CRT projectors, which have no native or fixedresolution; just tell them the horizontal scan rate and vertical refresh,and they do the rest. Not so with LCD and DLP projectors, who mustcontinually sample and time incoming signals to make sure they fit into theavailable resolution of their imaging panels. Now, we must be concernedwith pixel clocks and sync frequencies and phase.
Various names have been given to auto-synching circuits used by the manycontenders for the boardroom flat-matrix projector market, but not allcircuits are created equal. In my tests, I have found a wide disparityamong projectors in their abilities to sense, grab and lock up a perfectimage from various SVGA, XGA and SXGA sources. Even repeated manualadjustment may not clear up the problem entirely.
Although not as apparent with still photos and simple test charts, imageswith high detail and fine text will suffer the most from sync compatibilityproblems. This has been particularly true with some of the higher syncrates, like XGA-5 (57 kHz, 70 Hz refresh) and XGA-6 (61 kHz, 76 Hzrefresh). Even SVGA rates like SVGA-6 (48 kHz, 72 Hz) have been problematicfor boardroom projectors.
If you are considering a flat-matrix projector for an installation project,you cannot be certain your customer will not ever cross paths with aproblematic image source. XGA notebooks are becoming more commonplace, andit is not unusual to haul a workstation into a meeting these days. One wayto head off trouble beforehand is to use an outboard sync pattern generator(like Extron’s VTG-200) when you demo a projector. Step through everypossibly needed sync rate, and take careful note of the results,particularly on the small “H” text pattern. If the projector passes thistest, you are probably safe.
Video qualityMore and more clients are expecting top-notch video quality frominstallation-grade projection systems. In terms of color quality andgrayscale rendering, they may already be spoiled if they were previouslyusing a CRT projector. Spreadsheets with 256 colors are one thing, but avideo-conference is far more demanding in terms of image realism.
Video quality will be affected by everything from the projection lamp tothe video decoder. If the projector uses a metal-halide light source, checkto see how much control you have over not only red, green and blue drive,but also bias. About presetting white balance, some lamps will not yield aclean white field, no matter how hard you try to balance colors. Xenonprojection lamps do a much better job, but they are more costly to operateand replace. Projectors made by companies long used to the installationmarket will generally provide better color control.
How about the video decoder? In my own tests, about 25% of thefixed-install projectors I have seen use decoders inferior to commerciallyavailable, low-end video scalars. Do not assume you can just pump videothrough the projector as easily as an RGB signal. If your application isheavy on video (videoconferencing, stand-alone kiosks, museum exhibits,image magnification come to mind), processing it outboard is better
Line doublers, triplers and quadruplers are slowly giving way to digitalvideo scalars, and there are some good models available. Granted, a qualityscalar will increase installations cost, but there is a direct correlationbetween price and image quality with scalars, and the difference isapparent in controlled viewing environments.