CRT monitors are slowly fading away. Can LCD and Plasma monitors fill their shoes?

As the world of video production moves further away from analog to digital, one inevitable consequence will be the demise of the CRT display. It won’t happen tomorrow, nor will it happen in the next two to three years. But there’s a good chance that professional CRT monitors will be on the EPA’s endangered species list by the end of this decade.
The reason is that manufacturing CRTs has become a low-margin, high-volume business. As a result, the bulk of CRT manufacturing is moving to China to cut materials and labor costs to the bone. In the meantime, the biggest plasma and LCD manufacturers are still holding out in Japan and Korea, and they would like to expand their products into every possible niche as soon as possible, including broadcast and media production.
The problem is, neither of these technologies is quite ready to take its place as the replacement for CRT imaging. LCD monitors still have problems with black levels, colorimetry and fast motion blur, while plasma monitors haven’t entirely licked false contouring and are hard-pressed to achieve high-pixel density in small sizes. And neither technology addresses its pixels quickly enough to overcome audio latency problems.
Other "fringe" technologies, such as organic light-emitting diodes and Canon/Toshiba’s SEDs, are still several years away from commercialization on a mass scale. While demonstrations of both have produced some breathtakingly beautiful images, it will be a while before either of these is ready for Primetime.
Flat-Panel Display Profusion
At various trade shows throughout the year, numerous companies showed a bevy of flat-panel displays suitable for some aspects of media production. Small LCD monitors are finding their way into production racks and field packs as space and energy-saving displays. Plasma monitors are being used in screening rooms and lounges.
But for critical production work, specifically compositing and color correction, neither has the resumà© of the time-tested CRT. Part of the problem is the difficulty in calibrating either display technology to produce a clean grayscale with wide dynamic range- something CRTs have been able to pull off for years.
LCD monitors, in particular, are hamstrung by high black levels, a problem inherent to any light-shuttering technology. Just as window blinds allow a small amount of light to leak through when closed, so do individual liquid-crystal molecules when twisted into their aligned (light-blocking) position. The best models I’ve seen have black levels 10 times higher than a reference CRT monitor.
Plasma monitors have no such difficulty, as they are emissive devices. But their pulse-width modulation (PWM) operation makes it very difficult to produce shades of gray below 10 percent. Only a few manufacturers have been able to pull this off; most of the monitors and TVs offered for sale still have black levels four to six times that of a CRT and cannot show a smooth 256-level grayscale without noticeable stair-stepping.
In terms of resolution, LCD monitors win hands down as they can stuff far more pixels into a small screen than a plasma monitor. In general, 15-inch to 42-inch LCD monitors have 768 lines of vertical resolution, and models at 45 inches and above have full 1920 x 1080 pixels.
In contrast, plasma monitors aren’t even made with screen sizes smaller than 32 inches, and the North American market is only receiving product at 37 inches and up- hardly practical for location shoots. At present, the highest pixel density in plasma monitors is 768 vertical lines, found in monitors with screen sizes up to and including 65 inches.
Where plasma holds an edge is in colorimetry. The phosphors used in a plasma display come much closer to the desired red, green and blue SMPTE-C coordinates than the filtered colors in LCD displays, which are derived by micro-miniature color filters on each pixel, capturing the desired spectral energy from a fluorescent backlight.
That’s not to say better color can’t be achieved from LCD technology. Monitors have been demonstrated that use light-emitting diode backlights, and the claimed color gamut is 105 percent of SMPTE-C. However, current consumption increases over a conventional LCD backlight, and there isn’t enough data on hand as to the life of LEDs in this application.
LCD R&D
Rest assured that engineers are working overtime to solve each of these LCD problems. For instance, its inability to show motion without blurring the image. One approach to getting the liquid crystals to shift positions faster is to use an "overshoot" driving technique: briefly hit the pixel with more voltage than is required to twist each LC into position, then quickly ramp that voltage back to attain the desired grayscale level.
Another trick is to insert black frames into the visual data. These black frames work pretty much the same as the mechanical shutter in a motion picture projector. Without it, we would see a hodgepodge of images and considerable motion blurring. With it, images appear to have more definition and motion appears smoother.
Black level issues in LCD monitors can be addressed with something akin to the dynamic iris technique now appearing in Panasonic and Sony LCD home theater projectors. The average and total luminance of each scene is measured and the backlight intensity adjusted accordingly to maintain the best shadow detail. (Philips uses pulse-width modulation of backlights to accomplish a similar thing.)
Changing the backlight intensity works because the contrast ratio of our eyes is not nearly as wide as the display devices they are capable of achieving, and we can’t keep up with the on-off state of a pulsed light source refreshing at 60Hz or greater speeds. The result is an image that looks very much like a CRT, in terms of contrast.
You’ll notice from earlier paragraphs that most of the engineering effort is going into LCD, and that shouldn’t be a surprise. Unlike plasma, LCD panels come in a range of sizes, so any improvements to LCD imaging will affect all products in the line from those tiny 7-inch rack-mount screens to the new 52-inch and larger panels coming to market.
Numerous companies are starting up or building the latest generation of LCD panel fabrication lines, including LG Philips, Sharp, Samsung and Chinese companies Chi Mei and AUO. Sony has bet on LCD as the smarter play in the future and has sunk considerable cash into a joint venture (SLCD) with Samsung to make LCD’s and TVs in all sizes.
As for plasma, it is still a strong player and holds the advantage of lower manufacturing costs in larger sizes. But most display analysts (including myself) believe that plasma’s future is in the consumer market as a replacement for larger CRT direct view and rear projection sets- that is, until LCD can catch up to it!
Write Pete at pputman@accessintel.com