HD monitors
Jan 1, 2010 12:00 PM, By Michael Bergeron
Consider your needs when deciding between LCD and plasma.
Some newer LCD models, such as Panasonic’s BT-LH1760, can mitigate image persistence by driving the display with a 120Hz refresh rate, as opposed to the standard 60Hz. The additional 60 frames allow the insertion of a black frame between each picture, which clears each image before the next one is displayed.
Like many broadcast and production professionals, I have the same kind of nostalgia for cathode ray tube (CRT) monitoring as I have for film negative, baseband workflows, tape recording and even analog infrastructure. The CRT may not have been ideal: It was easily damaged, it was unwieldy, it used quite a bit of power, and it was fragile. However, it was a fixed standard, and everyone learned how to work with it and anticipate what the image should look like.
Consumers had the same core technology, so judgments could be made with confidence. Now that consumers are leaving the CRT behind, broadcasters share the same types of choices, but of course have different requirements.
For the most part, broadcasters trying to decide between LCD and plasma. With more technologies in the pipeline, the choices are driven by which of the following criteria is most important to you.
Portability and toughness
Plasma displays tend to be heavy and fragile like CRT displays. However, a plasma will still be easier to work with than a CRT of the same screen size, so if other plasma qualities are required, they are still worth any transportation difficulties.
The LCD display is most portable, of course. The LCD panel itself is susceptible to damage, so many professionals and rental houses add a Plexiglas cover for added protection. The build quality of the chassis is the differentiator between LCD display brands. A monitor built with a die-cast metal chassis makes a big difference when using monitors in dangerous territories on set.
Color fidelity
Color fidelity is driven by the display technologies and the supporting circuitry. While a plasma display still generates the widest gamut in generally available flat-panel displays, LCD displays have come a long way in recent years. LED backlighting may even raise the bar further, but some CFC backlit LCD displays have already surpassed the color gamut of the CRT. Once the CRT gamut is surpassed, a lookup table can be used to map the color possibilities into the full ITU 709 color space, as is done with master quality LCD-based displays and less expensive models. These monitors are even being mapped to reproduce larger color gamut such as Adobe RGB. Some evaluation monitors even allow for user-defined LUT settings. One color space known as P3 was developed for DLP digital cinema projectors and represents one of the widest display gamut in use right now.
Contrast and viewing angle
Once the CRT gamut is surpassed, a lookup table can be used to map the color possibilities into the full ITU 709 color space, as is done with master-quality LCD-based displays as well as less expensive models, such as the Panasonic BT-LH2550.
Another thing to keep in mind when choosing a field display monitor is contrast and viewing angle. How much contrast does it display? How are contrast and color impacted by where the viewer is sitting?
The king of contrast is still plasma. Nothing has matched the blacks that this technology can produce. However, with new developments in LCD technology, performance has been greatly improved. Comparing contrast, black levels and off-angle viewing performance of various LCD display models is not something easily summed up on a spec sheet. When evaluating displays for contrast and off-angle viewing, bear in mind what will be most important for your application. Will many people look at the display? Will the viewing environment be dark? Knowing what specifications are negotiable can lead to a smarter decision.
Sharpness
Sharpness is a function of contrast and resolution. Some manufacturers tend to stress the pixel counts as this is the most intuitive to the consumer, but it should be considered as just one specification rather than the single magic number for determining image performance. All else being equal, a 1080p display should be sharper than a 720p display, but all else is rarely equal. Poor contrast or a lack of dark blacks could easily undermine good native resolution.
Motion blur and latency
Plasma displays handle motion well by nature, similarly to a CRT screen, but they do have several frames of latency. LCD displays tend to exhibit more motion blur. Some of this is due to image persistence. In other words, one frame of video does not fade away completely before the next image is displayed, causing an increased appearance of motion blur. Some newer LCD models can mitigate image persistence by driving the display with a 120Hz refresh rate, as opposed to the standard 60Hz.
Noise and artifacts
Noise and artifacts tend to be more apparent in LCD and plasma displays than in CRT monitors, and many pointed this out as a shortcoming of flat-panel displays when they were introduced. This may be true for the home viewer. However, the noisiest looking display might be the most beneficial for the codec engineer trying to minimize compression artifacts and determine what the final picture will look like.
Conclusion
When comparing display technology, rather than judging one as better than the other, consider the most critical need for your specific application. Perhaps a good focus assist feature trumps resolution, and, of course, the best-looking monitor in the world could turn into a doorstop if it stops working after a fall on set. Moreover, with the rapid pace of new technological developments, it pays to look at what is available at what price each time you are shopping. You might find something new.
Michael Bergeron is strategic technical liaison for Panasonic Broadcast.
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