Display options
Jan 1, 2007 12:00 PM, DAVID AUSTERBERRY, EDITOR
The video engineer may be wedded to the waveform monitor and vectorscope, but the ultimate arbiter of quality is to view a picture monitor. Picture monitors allow broadcasters to visualize what viewers watch on a high-quality receiver.
For the director of photography, a high-quality and standard monitor is essential. Since the beginning of television, the CRT has been an industry standard. Today, home viewers who have recently purchased a receiver most likely have a flat-panel LCD or plasma display. This raises the question: What should broadcasters use as a representative display?
The print industry has developed a color-controlled workflow where each device, source, display or printer has a profile. Assuming that the display has a wider gamut than the printer, it is possible to visualize the final result of subtractive color reproduction with CMYK inks or pigments on paper using an additive RGB display.
The print industry operates in a controlled environment. The destination of a broadcast is a consumer device over which the broadcaster has no control. The CRT acted as a constant, but as we migrate to plasma, LCD and future technologies, there is little standardization beyond emulating (often badly) the gamma of the CRT.
Printers were able to move to a color-controlled workflow without disruption. Every job was set up for optimum reproduction. Broadcasters are not in that position, so how do you change gamma or color profile yet retain backwards compatibility? The move from analog composite to MPEG coding has retained the same display characteristics, save minor tweaks to chromaticity. A step change like a different value for the transmitted gamma would be difficult to implement. Television standards are based on the transfer characteristics of the CRT gamma. Even current compression standards, MPEG-2 and AVC, use visual masking based on the gamma of the CRT.
Gamma and chromaticity differences can be resolved relatively easily in the receiver. The dynamic behavior of displays is much more difficult to resolve. The reconstruction of motion from the discrete fields or frames is never going to look the same comparing a CRT, with a single brief flash from a phosphor, with the illumination for full frame of the LCD light valve or the variable mark-space ratio of the plasma and DLP devices. Production personnel complain of “smearing” with flat screens.
Digital video processing introduces several artifacts that can most easily be seen on a picture monitor and cannot be seen at all on a waveform monitor. Compression problems are typical, with motion artifacts and blocking. These can be viewed on a CRT, but a flat-screen display includes a display processor to scale and de-interlace if required. These processors can and do introduce motion artifacts, so what are you looking at: a real problem or a display problem? In an ideal world, the measuring instrument should not perturb the parameter being measured. There are professional quality display processors, and these can be relatively transparent.
The control room monitor is not just to visualize what the viewer sees; it is also to detect unwanted artifacts.
Are we being impatient? The early color CRTs were not reference quality. It took 20 years before they reached the necessary quality for monitoring. Others say we need a new technology. But the broadcast sector is not calling the shots. The consumer electronics industry is.
Rec. 709 is a standard for colorimetry. But other creative industries are looking at extended gamut systems. Another development is high dynamic range (HDR), but television transmissions are based around 8-bit coding. Broadcasters need to keep pace with these improvements to offer premium entertainment.
However, we cannot just call for a new type of display; broadcasters have always been niche customers for CRT manufacturers. The scale of LCD manufacture now means that broadcasters are completely insignificant as customers. It is a consumer electronics product that has to be adapted to our market.
There are groups looking into this problem, including the SMPTE. We need a solution fast, as the CRT is not going to be around much longer. I wish these groups good luck.
Send comments to: editor@broadcastengineeringworld.com
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