As the number of High Dynamic Range (HDR) content productions continuing to grow, so does the need for professional HDR monitors. But how can users choose the right model for their needs?
Earlier this year, the EBU Video Systems group organized an HDR monitor testing activity hosted at BBC R&D’s Southlab (London, UK). Results of these tests are now available as EBU Tech Report 081 (public) and supplements (EBU Members only).
The three main goals of this exercise were for participants to get general impressions of current model professional HDR monitors on the market, to share approaches and experiences regarding monitor measurements, and to update relevant publications such as EBU Tech 3320 and 3325 as well as related test material as required.
Monitor trade-offs
Current professional HDR monitors are based on either LCD or (O)LED technology. Each technology has its inherent pros and cons. Negative aspects may be mitigated by ‘adding complexity’, such as by using dual instead of single layer LCD panels, or by using dimming to reduce power consumption and wear, or by applying it locally to enhance the overall picture contrast.
However, such optimization methods generally come with their own trade-offs, which may reduce image quality under different circumstances. For example, better off-axis performance can come at the price of lower on-axis peak brightness, and local dimming can cause blooming.
As a result, monitor characteristics vary strongly, as do their prices. This also means that THE ideal monitor does not exist, not the least because the required (minimum) specifications depend on the monitor’s application.
Monitor classification approach
Since 2019, the EBU has included HDR monitors in its ‘EBU Grade 1,2,3’ monitor classification system (Tech 3320) to help its Members specify or select appropriate models:
- EBU Grade 1 A/B, a ‘measurement device’ for quality control, camera shading, colour grading, lighting, etc.
- EBU Grade 2, for use in editing suites, control walls, as preview monitors, etc.
- EBU Grade 3, for use in audio production, commentary positions, for signal presence monitoring, etc.
The 1A/B approach intends to bridge the gap between what the underlying video standards define and what monitors currently available on the market may be able to reproduce. A Grade 1A monitor can accurately reproduce all aspects of the standard it was designed to display. A Grade 1B monitor may not be capable of reproducing the full range of colour or brightness defined in a standard, but will otherwise fulfil all the requirements of a Grade 1A monitor. Grade 1B may be deprecated in future.
As a concrete example it is currently not possible for manufacturers to achieve a practical monitor that can properly reproduce the green primary of the ITU-R BT.2020 Wide Colour Gamut.
Panels and processing
The number of brands offering professional HDR monitors and the range of characteristics (including sizes, I/O options, and ‘helper’ features) is growing. But the number of actual panel factories is limited, and different makes and models of monitors can share the same panel inside.
However, claims such as ‘using the same panel as model Z’ are of limited value. Earlier work (see EBU Tech Report 047) has shown that light emitting panels are only half of the equation, and that processing can make a huge difference in terms of the resulting monitor quality.
The desire for lower prices
The high end of the market has so far been dominated by a handful of ±30” display models with list prices of around 35k EUR. These instruments can be regarded as measurement devices with predictable performance and good consistency in colour reproduction from model to model.
Due to their high price tag, and probably due to shrinking budgets and democratization of HDR production, professional users have been looking for lower-cost alternatives, sometimes reverting to computer monitor style devices or even considering using high-end home TV sets.
Occasionally, the (false) argument is made that the great inter-model variability of CE television sets means that reference monitors are less relevant. We think this is wishful thinking. There is no alternative for a clear reference, which is also stable over time and can be calibrated when needed, especially when the variability of the receiving device population is large.
The ‘missing monitor’
From the users’ perspective, there clearly is a desire to see the addition of more products that offer:
- A peak brightness of at least 1000 cd/sqm
- Dark blacks
- A good coverage of the ITU-R BT.2100 (or at least P3 ) colour gamut
- A relatively wide viewing angle with low variability in terms of brightness and colour shifts – so multiple people can see the same image, e.g. in editing suites
- No or very limited artefacts when playing back moving images (blooming, edge effects, ghosting)
- A price tag in the < 20k EUR range
Creating a monitor that meets all these at once, is far from trivial, but it is encouraging to see that the high-end HDR monitor market is quite dynamic (pun intended).