Choosing a Video-Display Technology

What kind of HDTV set is right for you? LCD? Plasma? Rear-projection? This crash course will help you choose the perfect HD television.

high-resolution pixel counts and even higher light output than plasmas, but, as you might guess, they pay the price for that light output in washed-out blacks and poor contrast. In brightly lit rooms LCD flat panels will actually hold their contrast better than plasmas, due to differences in the screen materials and reflectivity. On a showroom floor LCD’s sharper-than-life resolution, blazing light output, and on-axis immunity to ambient light draw people’s attention away from the plasma sitting next to it. But when these folks get home and dim the lights for movie night, the LCD’s weaknesses with blacks become apparent. Currently plasmas are a better choice for people who value watching movies with the lights down; LCD is a better choice for smaller screen sizes in brightly lit rooms, when movies aren’t a paramount consideration. Another spec that LCD manufacturers cite over and over again is response time. Images unequivocally linger on LCD panels longer than with plasma. Early models showed distinct trails with moving objects on screen. New models are better and, indeed, boast improved response times, but it’s important to know that specified response times can be based how long it takes the driving electronics to switch the pixels to “off,” which is not a true indicator of how long the images actually take to decay on screen. Some people will be bothered by this phenomenon more than others, but the fact is plasmas don’t have lagging response time.

All of LCD’s issues seem to be exacerbated at larger screen sizes. (These bigger sets are also more expensive than comparably sized plasmas.) Some manufacturers apparently realize this and are selling plasmas in screen sizes of 37"-and-above, and LCDs in the smaller sizes, where they are priced more attractively.

The wild card in flat panel is Toshiba’s SED (Self-Emitting Diode) technology, a hybrid of plasma and CRT in both technology and performance. Toshiba claims SED will yield full 1080p pixel counts with better light output and vastly better blacks than plasma. Early demos have looked promising, but we won’t know more until we see production units in 2006.

RPTVs: Big Screens in Transition

Like the direct-view category, RPTVs are rapidly transitioning to fixed-pixel microdisplay technologies with mixed results in terms of performance. CRT RTPVs are still available, and last we checked were offering excellent performance at bargain prices.

There are two kinds of people in the world: those who have a cool flat-panel Outside of typically minor geometry and convergence errors, CRT RPTVs potentially offer few performance compromises. Resolution and colors are excellent, and thanks to deep blacks, contrast is phenomenal and currently unmatched by fixed-pixel RPTVs. While some microdisplays may offer higher light output, CRT RTPVs are plenty bright and capable of making terrific pictures even in fairly brightly-lit rooms.

Microdisplays mostly eliminate convergence and geometry issues and offer a bright image that’s very crisp due to the nature of discrete pixels. Most casual observers will subjectively find a fixed-pixel display “sharper” to the eye than a CRT that actually has higher resolution. But the big thing microdisplays offer is that they’re much smaller and lighter than the CRT big screens. And that’s not even counting the 7" deep models that can hang on the wall!

DLP has made enormous inroads in RPTVs just as it has in front projection. DLP RPTVs are available only in single- chip configurations, which means a color wheel and its concomitant problems are front and center. Viewer fatigue and color separation rainbow artifacts have been diminished greatly in recent-generation DLPs but are nevertheless a fact of DLP life.

Further, DLPs are now showing up with lower pixel counts, using “Smooth Picture” pixel-shifting technology to generate 1280x720 on-screen pixels from 640x720 chips; soon, this same technique will be used to create1920x1080 pixel images from 960x1080 DLP chips. Our initial observations suggest that this technique is not entirely seamless, but we need to see more examples to be sure.

DLP’s chief advantage over other projection technologies is in its rich, dark, ever-improving blacks. Interestingly this advantage doesn’t seem to hold up in rear-projection applications. Perhaps having the lamp always on, in conjunction with the mirrors and other light-path components of RPTVs, makes that impossible. But what this also means is that the rapidly expanding three-chip technologies we’re seeing in RPTV have an advantage over DLP. Why live with a color wheel if you don’t have to?