In the grand scheme of technology, how we monitor television in professional facilities seems like a rather trivial, obvious matter, but it's actually quite the opposite. Our television system was designed around the physics of cathode-ray display tubes, particularly the nonlinear response of the cathode to voltage, which gives rise to gamma correction. The colorimetry of imagery was controlled by the chemistry of display phosphors for many years, beginning with some of the very earliest successful professional displays. CRTs are a precision device, particularly so when built to tight tolerances needed to act as reference displays for creating and evaluating the quality of video images.
But two factors have conspired to turn the professional monitor marketplace on its head. The first is the same economic motivation manufacturers have always faced, which puts pressure on the development of point source products for our industry alone. When color television was first used commercially, the only markets for television displays were in fact for the sole purpose of watching moving images, and home displays and studio displays shared much in technology. That's not the case these days. As the computer display market has matured, it has become perhaps more economically important than the market for consumer televisions, but at the least the computer display marketplace is orders of magnitude larger than the professional precision video monitor industry. Thus, we have little economic clout to drive the development of products that have very small potential numbers.
The second important factor in the changing monitoring landscape is driven by the pace of innovation, pushed by the desire of consumer electronics to sell new products. Two types of CRTs essentially owned the precision market for about two generations: dot triad delta gun models and stripe tube “Trinitron” models. But innovation in flat-panel displays, which initially were made only for laptop displays, has exploded into a rich mix of monitoring choices, many of which can and have been adapted for professional use. When HDTV first became a viable market, the natural choice was flat panels, which by the late 1990s were available in sizes that CRTs could not match. Flat-panel monitors provided good performance at steadily dropping prices, fueled not by the professional market, but rather by the consumer market. Studio CRTs were on their last legs.
Those innovative technologies include plasma and other emissive displays, and many variants of LCD transmissive displays. None of the new display technologies inherently need gamma correction, but it is a fact woven into all of our system standards and is hard if not impossible to remove in the short term.
This fact gives us fits. Since flat-panel displays dominate the world market today, we must use sophisticated technology solutions to render video images correctly. From all indications I see we have done a pretty phenomenal job. Pictures are stable, repeatable and of generally good to excellent quality. But the imaging artifacts we fight, notably the lack of true blacks in transmissive displays, make adapting consumer products to the professional market at best problematic unless nearly heroic levels of technology are thrown at the problem.
By using arrays of LED backlights instead of cold cathode light sources, or LED edge-lit displays, we can achieve contrast similar to CRTs. In fact, with sophisticated image processing and wide gamut display/backlight combinations, we can exceed the color gamut of essentially all professional monitors of the past. The trade-off is that LCD “grade one” monitors with complicated backlight strategies are expensive. Transmissive displays just have different physics at work. It is hard to completely cut off the light unless the source itself can be extinguished by local dimming, as in LED array backlight units. Secondly, small, rack-mountable, high-quality displays are not very profitable due to the low piece count that comes with the video monitoring in our industry. The best LCD monitors are above 40in in size, and they can produce great pictures, though I can't remember seeing a rack big enough for a 42in LCD in a production truck.
The EBU produced a document defining the features and performance that a professional CRT replacement should exhibit if it is to truly supersede the CRT in capability. Some of the stipulated requirements are relatively easy to understand and achieve without designing new physics for the display itself, but some like black level performance and off-axis performance are harder to do nearly as well as a CRT. Some features required in the document seem a bit anachronistic, like blue-only mode (used for NTSC and PAL lineup), and pulse cross (useful in analog transmission, but I think of less relevance with digitally sampled and transmitted pictures).
OLEDs are on the rise
The industry is ripe for a totally different technological approach to monitoring. Many proposed technologies have been shown in small devices that are custom built in labs. Fewer have made it as far as delivery of real products. This year, OLED-based monitors have begun to show up after years of promises about performance rivaling or surpassing CRT. Two manufacturers are delivering products, and the performance is as good or better than any other flat-panel technology. As one might expect, the prices are high since there are not many on the market. OLEDs are not only used for video monitoring, and in fact first showed up in portable devices where their exceptional power efficiency is valuable.
OLED offers several potential advantages. Since it is emissive, not transmissive, like plasma, black can indeed be truly black, even better than CRT performance when properly set up. (See Figure 1.) The OLED triads can be packed into small spaces, making large, exceptionally high-resolution displays possible. One manufacturer has built in a self-correction loop that measures the light output of the panel and continually adjusts the drive to each color to keep colorimetry consistent with little maintenance intervention over the life of the panel. The bad news is that the blue OLEDs age at a different rate than the green and red, and when the self adjustment runs out of range, the panel must be replaced. It is unclear what the panel replacement cost will be, but one manufacturer estimates that its panels should last several years in heavy use before that threshold is passed, comparable to the life of a CRT.
Currently, OLED monitors are available in a small range of sizes for professional use and are priced on the high end. Sizes range from 7in, likely for field monitor use, to 15in and 24in sizes for conventional precision monitor applications. Consumer-scale large OLED displays are rumored to be on track for late 2011 or 2012.
We have arrived at the end of the CRT's useful life in this industry, but unfortunately the options, LCD/plasma/OLED, are just achieving the price and performance we are used to. For the short term, expect CRT replacements in precision monitoring applications to be pricey and limited to a small number of sizes.
John Luff is a broadcast technology consultant.
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