HDR or “High Dynamic Range” is primarily an increase in the brightness range that a monitor or TV can display. Until recently most TV’s and monitors could not show a very large brightness range, typically around 6 stops. New display technologies such as OLED (Organic Light Emitting Diode) and advancements in LCD back light technology have made it possible to produce screens that can show 10 or more stops of dynamic range. These screens are not just brighter, they also have better contrast in the darker parts of the image.
The images above are a simulation the difference you might see between an SDR image (left) and HDR Image (right) when you have an HDR TV or monitor. The wider dynamic range and wider colour range of the HDR display will allow a greater highlight range and a greater range of colours to be displayed.
Many of us have been shooting using HDR ready formats such as Log or Raw for many years. To capture content suitable for HDR you need to record with using a format with a very large dynamic range. When I shot the Fagradalsfjall volcano in Iceland I shot using a mix of Sony’s S-Log3 and ProRes Raw using my Sony FX6 and FX3 cameras. When you shoot with S-Log3 or raw with these cameras you are capturing a very large dynamic range, perhaps over 14 stops. This is more than even the best current HDR TV’s and monitors can show and these formats allow you to manipulate the image in post production via the grading process to produce great looking HDR content. Many of Sony’s camera also include a dedicated HDR mode and in this mode the cameras use a gamma called “HLG”. HLG is one of the display gammas use in HDR TV’s and content shot using HLG does not need to be graded, it is already HDR straight from the camera and will be seen in HDR on a suitable HDR TV.
This type of workflow is going to become more and more important in the coming years as the need to deliver content for both SDR as well as HDR increases. I use DaVinci Resolve for my colour grading and the included ACES colour managed workflow. ACES is the “Academy of Motion pictures Color Encoding System”. It has been designed to provide a uniform colour managed workflow that can be included in many different edit and grading applications. Within Resolve and ACES using the colour management preferences, I tell ACES that I filmed with S-Log3 and that I want to deliver in HDR and the software performs all the necessary complex transformations between how the footage was shot and how it will be displayed in HDR. There is no need to use Look Up Tables (LUT’s) or any other tools, the software does all the hard work for you. I then grade the footage to fine tune the final look. If I then need an SDR version all I need to do is tell Resolve/ACES to output in SDR/Rec709 rather than HDR and then instead of an HDR output I will have an SDR output. Colour management tools are now incorporated into most of the better editing and colour grading systems, include Adobe Premiere and Final Cut Pro.
This is an area where we are seeing many changes right now. Go back four or five years and HDR displays were rare. Today they are appearing all over the place. Most premium phones now have HDR screens. HDR TV’s are now common and not significantly more expensive than similar quality SDR TV’s. Computers are catching up too and HDR displays are appearing on more and more laptops. But not everyone has an HDR screen and if you display HDR content on an SDR screen without doing anything it looks quite wrong. Fortunately, platforms such as YouTube now have the ability to convert a video uploaded in HDR to SDR so that when a viewer with an SDR display watches the clip it is played back in SDR. Those with HDR displays will see it in HDR. But, in order for this to work, YouTube etc. needs to know that the clips is HDR. This is done using metadata.
Metadata is “data about data” and there is a lot of metadata added to a video file when you encode it. One of the big benefits of using a colour managed workflow is that when you encode a file – within a colour managed workflow – the encoding software will normally add the correct metadata tags that will flag the file as HDR. Not only will the metadata flag the file as HDR but also the specific type of HDR with information on the target gamma and colourspace. When I use DaVinci Resolve to export a file from either ACES, or Resolve’s own colour managed workflow, the encoder by default automatically adds metadata tags that match the project’s target output settings. This way, when I upload the finished clip to YouTube, YouTube knows it is HDR and knows what type of display I viewed it on when I graded it. This information then allows YouTube to convert the file to other viewing standards – so no matter whether the viewer has an HDR display or an SDR display they will always see a correct looking image even though I only uploaded a single HDR file.
In addition to the metadata you also need to use a very high quality codec, preferably a 10 bit codec. This is because the greater dynamic range and increased contrast of an HDR image will show up any compression issues much more easily. One of the most commonly used codec for the distribution of HDR video clips is H.265. H.265 is 10 bit codec that uses very efficient compression to keep the file size very compact. Most HDR TV’s can directly play back H.265 encoded video clips from a USB stick plugged into the TV. YouTube, Vimeo etc all support H.265 and even at modest bit rates the quality remains very high. I encode my 4K H.265 files at 35Mb/s as this is the highest H.265 bit rate that many HDR TV’s support.
Please see image for encoding setting I used for the HDR volcano video.
HDR is here and it’s here to stay. In the future HDR will be normal and SDR will be a thing of the past. While this isn’t going to happen overnight, the need to deliver in HDR will continue to increase as more and more devices gain HDR screens and owners demand higher quality HDR content. At the same time, it is becoming much easier to shoot and deliver great looking HDR content. There are new things to learn for film makers, such as ensuring your content has the correct metadata, but once learnt, delivering in HDR is no more difficult than SDR. In HDR the video of the Fagrasdalsfjall volcano looks far closer to the way it looked to me when I was there than it does in SDR, so there is no doubt in my mind that this is how I would like people to see it.
If you’d like to know more about this shoot, why not read my 4 Seasons In A Day And A Red Hot Volcano article.