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Making the top monitor grade

22 August 2012
Making the top monitor grade

There are technical and aesthetic issues that contribute to the stubborn reluctance of the industry to replace the CRT. Do current displays meet core requirements? Dick Hobbs talks to the players involved. “With the RoHS and environmental issues faced by CRTs, not to mention the lack of spare parts, the reality was that it had to happen.” That’s how Kris Hill of JVC summarises one of the biggest challenges faced by broadcast engineers: how do we look at what we are putting out? The CRT is dead: but what replaces it? The mass migration to flat panel displays changed the business as well as the engineering of monitoring. As JVC’s Hill points out, flat panel displays are smaller, lighter and cheaper, and by being on top of this advance JVC now takes the largest overall market share in monitors in Europe. It also brought about the multiviewer revolution: take advantage of the larger screen sizes available by putting multiple feeds onto one display. There is one screen, though, that remains to this day a problem: the grade one monitor, the reference display. As the BBC’s Richard Salmon (pictured) puts it, we need a monitor that shows us not how good the signal is but what is wrong with it, so we can put it right. It was in 2007 that Sony stopped manufacturing its grade one CRT, which was pretty much the only game in town. Since then, there has not been any practical replacement, and much engineering time has been devoted to nursing the installed base of grade one CRTs along. As Michael Byrne of WTS Broadcast said, “there are both technical and aesthetic issues that contribute to the reluctance in the industry to replace the CRT. Technical issues relate to the limitations of current alternatives; aesthetic issues relate to visual differences, which result in the viewer losing confidence in the accuracy of the image.” The EBU set up a task force to look into the issue: Richard Salmon was one of its leaders. It published documentation earlier in 2012. “It has taken us five years to produce the final documentation,” he said, adding “it has taken the manufacturers that time to come up with displays that start to really meet the core requirements.” The EBU, as a broadcast body, looked to maintain core broadcast standards, and so the new specification, EBU Tech 3325, essentially aims to define what should replace the venerable Sony CRT. But, as Salmon admits from his experience in BBC studios, “it is very difficult to replace a CRT with a flat panel display, because you have to keep the colours the same. “We put some LCD panels in a production environment, and the guys controlling the lighting found that they could not agree what the colours were. As you moved around the colours changed. The CRT was a stable reference.” But manufacturers have been working alongside the development of the standards for the last five years, so you would expect that there is a broad choice in modern grade one monitors. Sadly, you would be wrong. On target Friedrich Gierlinger of IRT is another member of the EBU task force, and at the launch event he said: “At the moment there are two displays which nearly meet the requirements for grade one displays.” These are the Dolby 4200-PRM, which is an LED backlit LCD display, and the Sony BVM250 OLED display. According to Gierlinger, the Dolby display nearly fulfils the requirements apart from concerns about the viewing angle. The Sony OLED is described as much better in terms of black level and viewing angle, but it may be too small – 24.5” diagonal, as opposed to the Dolby’s 42” – to spot HD artefacts. According to Daniel Dubreuil of Sony, the company has sold more than 10,000 of its OLED monitors since the launch in February 2011. “It set a new standard for colour graders and editors in terms of deeper blacks, high contrast ratio, colours in low lights and image stability,” he said. OLED is an emissive technology, and black really does mean no light coming out of the display, thereby addressing one of the biggest problems for quality flat panel displays: very poor linearity at the low end of the scale. The Dolby monitor, on the other hand, combines a high quality LCD panel with an active LED backlight: approximately 1500 RGB LED triads, each of which are both individually dimmable and colour controllable. Together with the modulation of the LCD panel, it results in extremely high linearity across the full range from black to white. Prices are broadly comparable, too. Sony did not comment on price, but Dolby acknowledged that the $1000 an inch rule of thumb that used to be applied to grade one CRTs is still a good guide. So is the advice to go for a Sony OLED unless you need something larger, in which case the Dolby is also excellent? The answer is not quite so simple. As Paddy Taylor of Autocue – also in the reference monitor business – points out, “If consumers are not watching their content on CRTs, then what logic is there for basing the ‘standards’ on it? Certain aspects of a video signal will perform differently between technologies so there is a strong argument to use the most common denominator when grading an image.” Steve Hathaway is managing director of Oxygen DCT, which distributes the Penta line of reference monitors. “The Penta series are a ‘leveller’ for the industry,” he says, “enabling broadcasters, post houses and production companies to all operate the same, industry compliant colour standards, and provide the picture accuracy necessary through the proliferation of high definition formats.” Moving fast Sony’s Dubreuil points to “enhanced motion reproduction” as one of the major benefits of the OLED display, and many will have seen demonstrations at NAB or IBC featuring ridiculously fast text crawls which are perfectly reproduced. That is a huge benefit when engineers are trying to capture transient problems with a signal, certainly, but at the same time it could be a temptation for a creative artist to make something that looks good on the reference monitor but could never be reproduced at home. So Ian Lowe of Dolby has a point when he says “The thing that makes the PRM-4200 genuinely different is its built-in ability to emulate other display devices as standard.” From the front panel it is possible to change the response of a single monitor from grade one equivalent to emulation of consumer LCDs and plasmas. This adaptability goes the other way, too, and that is important because broadcast HD grade one is not the only premium standard to which facilities aspire today. As well as SMPTE Rec 709 HD, many suites will want a graded monitor for digital cinema work, which means DCI P3 and emerging 12-bit signals, in 2K and even 4K resolution. The Dolby monitor supports 2K DCI, switching reference luminance and gamma as required. Not only is it ready for 12-bit colour space, it also supports 48 frames per second DCI for high frame rate projects. These higher resolution signals are no longer a theoretical concern: when the Blackmagic camera, launched at NAB, comes to market we will have a source of greater than 2K signals at consumer prices. It is a safe bet that engineers will need to take a careful look at these signals. For dealer WTS Broadcast, Michael Byrne makes the excellent point that “the advantage of modern monitoring technology is that it is far more flexible and extensible, using easily upgradeable software to support new standards.” Looking to the future, Dubreuil commented: “Sony sees OLED monitoring technology as the best available at this point in time, and we will continue to develop Trimaster EL OLED products.” Competition is coming up from other vendors looking at active backlit LCD, too, such as Autocue – its T Series won a TVBEurope Editors’ Award at IBC2011. “Probably the biggest advantage of all of LCD in the professional market is the price point,” claims Taylor. “Grading monitors are now available for less than £10,000 but with many features you would normally only find on monitors many times more expensive.” Penta offers the HD2line Pro, again based on high quality LCD panels and also hitting very attractive price points. The range features 16 bit video processing and comprehensive support for calibration, lengthening the life of the screen. It has an even longer heritage than other offerings: Penta started work on reference flat panel monitors in 2006 in its native Germany, working in collaboration with broadcasters and national standards body IRT. Hathaway adds that the 16-bit oversampled input and processing “ensure the highest possible signal quality, often exceeding EBU Tech 3320 Grade 1 performance for many signal metrics.” He also claims Penta is the only manufacturer to guarantee every monitor to Rec 709 colorimetry. Ian Lowe of Dolby wraps things up by bringing us back to the EBU’s current findings. “It has taken five years to better the CRT with only two monitors,” he says. “While there may be new technologies and display devices discussed, the real question has to be will they achieve the new standard specified by the EBU? If a device does not meet this standard, then it will not be considered a reference device.”

 

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