You should potentially beware of TVs labelled as "HDR compatible". It often means they accept the HDR signal - but they can't display it properly.
We always pick up good information from Paul Gray, Principal Analyst & Researcher with IHS Technology, a company delivering "information, analytics and expertise". At the recent Global Press Conference for IFA 2017, when we cornered him in the hotel bar on a variety of subjects, he passed us the slide above, showing IHS's projection for shipments of HDR TVs up to 2020.
HDR is High Dynamic Range - the ability to show more gradations between dark and light. True HDR performance has a huge effect not only on shades of grey but also on the available colour portrayal, given all the incremental differences in colour strength. HDR doesn't necessarily mean 'brighter', though it is generally so with LCD HDR televisions, which achieve the required dynamic range by delivering higher peak 'nit' levels -- the latest Samsungs are pushing 2000 nits. With OLED, however, it is the ability to show more carefully graduated blacks that achieves the same or even higher 'range' (see the ladder image below).
But in the chart above, the projected numbers of HDR LCDs and HDR OLEDs are dwarfed by "HDR compatible" models. And 'HDR-compatible' is not really HDR at all, just the ability to accept an HDR signal.
This, says Gray, is a worry. IHS is expecting such TVs to be marketed as "HDR-ready' or "HDR-compatible" or "HDR-enabled". These TVs will accept a 10-bit HDR signal but are unable to display it properly, either using only 8-bit video processing internally or having standard backlights with 10-bit panels, not the technology that allows a true HDR picture to be enjoyed.
[ABOVE: A ladder to the light, showing the relative dynamic range of current LCD and OLED TVs within the new PQ range and compared with Rec.709 (i.e. non-4K) TVs. Remember it’s not only how high the arrow reaches, it’s about length (which indicates the total dynamic range)].