HDR display technologies have been flourishing since the launch of Ultra HD TVs and UHD Blu-ray players. HDR10, Dolby Vision, HLG, HDR10+…it’s not always easy for the viewer to know what’s what. This may be Dolby’ fault, as TV and UHD Blu-ray player manufacturers have to pay the company a royalty for the right to implement its high-dynamic-range (HDR) cinema-grade image technology. Consequently, royalty-free alternatives were quick to arrive on the scene.
What is HDR technology?
HDR imaging technology consists in displaying images with a high dynamic range. In other words, there is more contrast between the darkest and lightest parts of the images, resulting in a more nuanced image, especially in the brightest areas. To enjoy HDR images, you’ll need HDR-compatible equipment (TV, video projector) and HDR video content, for example, HDR Ultra HD Blu-ray discs or HDR VOD from Netflix, Amazon Prime Video or iTunes.
The different HDR technologies
There are no less than four different HDR technologies: Dolby Vision, HLG, HDR10 and… HDR10+.
Dolby Vision is the HDR technology Dolby developed for the silver screen. With 10- to 12-bit color encoding–versus 8-bit encoding for standard 4K and HD videos (SDR)–Dolby vision offers a more nuanced image. It is currently used for certain UHD Blu-ray discs and by iTunes.
HLG (Hybrid Log Gamma) is a technology developed by the BBC and NHK. Most HDR displays are currently HLG compatible, even though this technology is not yet implemented. Designed for television broadcasts, it should be implemented in the future by DTTV networks.
HDR10 is the most widely implemented technology, as it is royalty-free. It is used by UHD Blu-ray discs, NetFlix, Amazon Prime Video and iTunes. The number 10 indicates that each pixel is composed of 10 bits of data per primary color (3×10 bits).
HDR10+ is an enhanced version of HDR10, and it allows the display to adapt to the dynamic range of the incoming video stream.
Characteristics of HDR video
HDR video stream features such a high dynamic range that only certain high-end TVs are capable of displaying the signal. Other TVs, even some of those certified HDR, must reduce peak brightness level by “burning” the brightest areas of the image.
To prevent this phenomenon, HDR displays are capable of adapting the incoming video stream to correspond to their capabilities, based on metadata integrated into the video stream.
In this way, each HDR video stream contains metadata indicating the peak brightness level and the color space of the movie. Depending on the metadata it receives, the TV responds by compressing the dynamic range (brightness and colors) of the image in order to optimize its restitution. Results vary for each of the HDR technologies.
Example: with HDR10 technology, the metadata integrated into the video stream informs the TV that the peak brightness level of the film is 1,000 nits. Evidently, this peak brightness level only applies for certain images, but as HDR10 technology does not precisely indicate which these are, the display adds compressions to… the entire film.
With HDR10+, Dolby Vision and HLG technologies, the metadata is dynamic. Consequently, the TV knows precisely when it should or should not compress the dynamic range of the image.
As a result, only certain scenes–and not the entire film–are affected.
Are today’s displays up to the task?
The newest HDR-compatible Ultra HD TVs are not always capable of perfectly displaying an HDR image, especially in terms of peak brightness levels. While HDR films and series are mastered with peaks up to 1,000 nits (cd/m2), HDR-certified displays are rarely able to handle this. More often than not, OLED and LCD TVs only display 200 to 600 nits. However, the HDR-enabled Ultra HD displays currently on the market largely surpass the capabilities of the Full HD and SDR (standard dynamic range) Ultra HD displays which preceded them.
The VESA electronics standards organization has decided to clarify things in order to help consumers choose a new display. To this end, three labels will make their appearance in the coming months on new HDR-enabled OLED and LCD displays. The DisplayHDR 400 certification indicates that a TV can display a peak brightness level of 400 nits, while DisplayHDR600 TV can display 600 nits and a DisplayHDR 1000 TV can display 1000 nits.
My HDR display does not handle HDR10+, do I need to replace it?
No. An OS update will likely soon be made available for your display in order to make it compatible with HDR10+ content. This will not require more power, but only the ability to recognize dynamic metadata. If your display is already compatible with Dolby Vision HDR, it will most likely soon be compatible with HDR10+ as well.
Where can I find HDR content?
Ultra HD Blu-ray discs are no longer the sole source of HDR video content. Netflix and Amazon Prime video, for which the apps are integrated into most OLED and LCD displays, also propose HDR films and series.
Amazon recently announced the availability of a hundred new HDR10+ titles.
Important: In order to enjoy the 4K HDR content available from Amazon Prime Video or Netflix, you’ll need a very high-speed Internet connection. In other words, a Fast Ethernet connection of 100 Mbit/s minimum is required. An episode of The Grand Tour, available from Amazon Prime Video, has a size of about 25 GB for one hour of 4K viewing. Meanwhile, an episode of The Crown, available from Netflix, has a size of 12 GB for one hour of 4K viewing. The considerable difference between the two is due to the nature of the images in each show, as The Grand Tour incorporates much brighter images.
Are video encoding rates fast enough?
The good news is that the HDR video encoding rates implemented by streaming platforms are now similar to those used for Blu-ray discs. At least, this is the case for Amazon Prime Video, which has made significant efforts in this arena: for The Grand Tour, the video encoding rate is over 50 mbps, which is the same as for a Blu-ray disc. In the end, however, these rates fall short of those used in movie theaters. Making this comparison isn’t a stretch by any means, as the resolution of the video projectors used in movie theaters is not better than that offered by today’s UHD displays. However, in movie theaters, the video encoding rate can reach 250 Mbps, allowing the viewer to enjoy an exceptional level of details.French