DAVID AUSTERBERRY, EDITOR /
06.01.2011 12:00 PM
CRTs, LCDs and OLED
David Austerberry discusses various display technologies with regards to critical monitoring and color correction.

It doesn't seem that long ago I was writing about the end of the CRT and all the shortcomings of the LCD display for grade one monitoring. I used to work for a manufacturer of CRT monitors, and one of the issues back then was sourcing tubes with phosphors of a suitable colorimetry for broadcast applications.

The LCD was not designed initially for the display of full-motion video, but as a monochrome display for low-power applications. Color versions soon followed and were adopted for mobile consumer equipment. The laptop and mobile phone could not have come into being without the LCD or some similar technology.

However, the demands of the portable market, and the consumer market in general, are very different from a grade one broadcast monitor. As the LCD and plasma displays took over the consumer TV market, and LCD the workstation market, the niche broadcast market for CRTs was a casualty.

The LCD has been pressed into service for television monitoring, and although it is adequate for most purposes, as a grade one display it had drawbacks that vendors have striven to overcome. From a long list, I highlight a few: motion artifacts, viewing angle, and poor display of deep grays and black.

Color CRTs had a half-century of development, gradually overcoming the engineering problems and successfully transitioning to HD. LCD monitors have been around a much shorter time, and unfortunately CRTs were withdrawn from production before LCD designs optimized for grade one applications became available. The CRT was not without its problems, including convergence, registration and EHT stability.

No monitor can ever reproduce motion in the same way as we see the original scene; the television system is sampling motion at the frame or field rate. CRTs were good at showing fast motion due to the nature of the scanning; however, this same scanning gives rise to wide area flicker. In contrast, LCDs sample and hold the brightness level for the full frame and do not exhibit flicker. LCDs and CRTs are not going to look the same with moving objects.

With great ingenuity, a few manufacturers have developed innovative ways of overcoming some of the initial shortcomings of the LCD. However, there are still characteristics that separate the two technologies. The CRT is emissive, and the LCD is a light valve. From this stems the issue of achieving good blacks in the LCD.

The LCD has only just evolved to meet monitoring requirements, when along comes another technology: OLED. After a slow start, it is becoming much more common. I use a phone with an OLED display, and it is easy to read with its very fine pitch. Now, full-size monitors are shipping. Will they quickly replace the LCD for critical applications?

The manufacturing of OLED is not without it challenges, and the developers are striving to create displays with a long life and stable colorimetry. There has been huge investment in LCD manufacturing facilities, so for many vendors there is no headlong rush to move to OLED.

You cannot sensibly color-grade on inferior monitors, and trying to assess motion artifacts in equipment such as encoders or standards conversion is difficult if the display is adding its own. Broadcasters were forced away from the CRT by the economic realities of being a niche industry. The LCD has been successfully adapted to broadcast requirements. But there are still issues such as off-axis viewing. If I were designing a grade one monitor, I wouldn't start with an LCD panel, but then there are realities to consider. You have to work with what is available.

Are you trying to create a pleasing picture, or are you trying to see issues in the video signal? For most broadcast applications, a regular LCD suffices, but for color grading or displays for video engineers, a grade one monitor is essential. Will the OLED solve the problems?

The audio guys must be amused by all this. They have had accurate monitors for decades. But then audio is a different physical manifestation from video.

Send comments to: editor@broadcastengineeringworld.com



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