Display technology

Displays are changing fast; don't be left behind.
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Some of us remember Conrac monitors in broadcast stations being the crème de la crème. Conrac still manufactures CRTs for broadcast use (4:3 only), but along with many other manufacturers, it will soon be out of the broadcast CRT monitor business when new and replacement CRTs are no longer available because of environmental issues. How soon will this happen? This year — now. Not ready for change? Let me try to illuminate your options.

Replacement display options

Figure 1. LED backlit LCD TV penetration (Courtesy Displaybank)Select figure to enlarge.

With CRTs disappearing, we're left with variants of flat-panel displays. Consumer products based on both LCD and plasma technology are readily available and of good quality. Some manufacturers buy panels from the “fab” factories in the Far East and modify the electronics to make the performance more precise, repeatable and closer in results to CRT monitors. Emerging technologies hold great promise, though they are not yet ready for commercial production in sizes applicable to most professional uses. Organic LED (OLED) technology falls into this category.

In general, the closest technology to CRTs (in terms of contrast ratio and colorimetry) is plasma. Both use phosphors and are emissive technology, but plasmas have some drawbacks. They do not modulate an electron beam per se, but rather modulate the “dwell” time for each pixel to effect amplitude modulation of the light. This means that the pixels must be flashed at a rate considerably faster than the frame rate. Brighter simply means it is on longer. Early plasmas suffered from contouring because of the appearance of insufficient pixel depth, though it was simply an artifact of the speed of modulation and number of bits used in the temporal modulation. More recent designs have largely eliminated this effect by improving the modulation near black and number of bits used to represent the pixel.

LCD monitors are transmissive, i.e. they require illumination from behind. (See Figure 1.) The ability of LCDs to make deep blacks is limited by the ability of the panel to completely cut off the backlight. They also suffer from “lag,” which is the decay of pixels slower than the frame rate. Both artifacts can be ameliorated by technology. Lag can be reduced by updating the panel much faster than the frame rate, with some panels flashed at up to 480Hz in consumer displays. With arrays of LEDs in the backlight unit (BLU) behind the panel instead of continuous illumination from cold cathode light units, it is possible to turn off the light behind dark regions, improving black level substantially. At the same time, it is possible to extend color gamut to digital cinema specs and beyond by managing the color of the backlight in regions. At NAB, one manufacturer of digital cinema hardware introduced an excellent 42in panel with this technology, using all of these techniques.

OLED technology is also emissive and has been touted for years as the logical replacement for CRTs. Because OLEDs are emissive, and because the pixel sites can be quite small, OLED displays could scale to large arrays with almost unlimited resolution. Power consumption is low as well. When cells are turned off, they produce inky blacks. This sounds promising.

The problem is that volume production for either professional or consumer use in large sizes is still a ways off. Also, the state of the art still has less than satisfactory aging characteristics, though that is improving. When I asked one manufacturer of small OLED panels why it doesn't scale production up considering its superior performance, I was told the answer was economic, not technical. The same company had built a fab factory for LCDs at a cost of billions (with a “b”) of dollars. I was told OLED production would be delayed until that factory produced a sufficient LCD product. Case closed, for now at least.

Consumer display technology

If you are getting the impression that future professional monitors will be based, at least in part, on consumer technology, I think you are right. Simply put, there are not enough professional monitors to make it worth the investment to develop primary technology that cannot also be effective in consumer distribution channels. But that does not mean that CRT replacements are not going to be as good, or delayed, until consumer sets are as good as professional sets. Let us not forget that consumer sets can already display the same resolution as professional monitors and are improving rapidly in other respects. For instance, LED BLUs for LCDs are in general distribution for consumer use now. A monitor with calibration features appropriate for professional use is not a daunting task. There are mainline manufacturers of monitors that participate in the professional marketplace as well, and they have a vested interest in providing high-profit, high-performance monitors to the professional marketplace.

At the same time, there are interesting technologies in development and deployment. You can now buy a consumer set with a four-color BLU, which can produce an extended gamut. Research on this was demonstrated at the 2006 Hollywood Post Alliance Technology Retreat in the United States and received considerable interest — so much interest that a patent infringement suit was filed the next year against consumer manufacturers using what was alleged to be the same approach.

Conclusion

All of this display upheaval has produced interesting effects. We used to be able to color correct to a known standard, the repeatable performance of a CRT monitor. But now film work has to use DCI color specs, often on projectors, and video production has to guess what the dominant display technology will be. Let's say the four-color display becomes dominant because of consumer interest in what might appear to be better pictures. Does a post company switch to displays replicating that approach? When can we say we know what the dominant consumer display has become? Or do we use tools that produce repeatable and scientifically correct output?

For instance, transmissive displays have a map built in to correctly display the content, knowing that the signal may have gamma assumptions that do not apply to the physics of their operation. Plasma monitors are inherently similar in physics to CRTs and don't need that correction. Can we assume that the displays have correctly adapted to the input, or has the manufacturer decided to make the picture more pleasing at the expense of accuracy? While not a scientific answer, I would opine a guess that the multitude of options available to consumers (“cinema mode,” “standard” and other menu selections) means that we have to assume the worst. The only realistic answer is to produce standardized images and educate consumers and CE companies to make sure the whole distribution system permits holistic results.

John Luff is a broadcast technology consultant.

Send questions and comments to: john.luff@penton.com