HDR Video | From Cameras To Post Production
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HDR Video Editing is one of those buzzwords that’s always been tossed around, but does it have any meat? Will having an HDR-ready workflow actually get more work? Major streaming services like Netflix, YouTube, Apple, and Vimeo seem to back it. But, will that be enough?
In this article, we’re going to cover the basics. What is HDR, and why does it matter? More article on this topic will be posted in the near future- so, stay tuned!
WHAT IS HDR (High Dynamic Range)?
Dynamic Range is the measure between the darkest and lightest points in a reproduced image. It’s measured in stops:
- The Dynamic Range of the Human Eye is considered to reach 14 stops of range
- The Dynamic Range that has been considered “standard” for HD (SDR) is between 6 and 10 stops of range
- The Dynamic Range that is considered HDR, reaches 13 stops of range.
The goal is to show a range of light much closer to that available to the human eye. There are quite a few different methods to produce and exhibit HDR content, as a number of different tech companies have been working hard to reach the range of your vision.
- DolbyVision – The most well-known at the moment is DolbyVision– It’s a technology standard is called PQ, or Perceptual Quantization. This is the standard currently utilized by Netflix, as it provides a variable peak brightness, depending on the Television set displaying the signal
- HDR10 was the first standard, which requires delivery only of a maximum peak point, and doesn’t vary.
- HDR10+ is the latest standard- utilized by Amazon and Samsung, bringing the variation by display concept into the HDR10 standard
- HLG, or Hybrid Log Gamma is a standard co-developed by the BBC and NHK- and while most content produced today in America isn’t concerned with it, it will become a much bigger deal in the Broadcast world in a very short period of time, as the next generation of television is rolled out in the US.
There are a few other ones out there, but these are the big ones confronting us.
COLORSPACE: CIE Standard Illuminant D65
Colorspace, to quote the tech out there, is a mathematical abstraction of a color system. You’ve most likely seen the Dreaded Triangles before- here they are, and let’s make some real sense of them for you.
The first thing that’s important here is the Illuminant D65 dot in the middle of the chart. Because when we talk about these color spaces, they apply to digital cinema projected images, as well as images on monitors and television. The D65 is the white point. The key for any color image display is to first understand where “true white” is located on this scale (If you’d like to know more about white points, and how they are decided, look at this).
The other very important thing to know is this overall colored curved triangle-ly shape. This is what the human eye can see. If it’s outside of the colored area your eye cannot see it.
- Rec. 709 – So, the first, smallest triangle is Standard Dynamic Range or SDR. There’s a technical designation of this that is known as Rec. 709. – pronounced “wreck 709”. That is the range of color you are used to- television as you’ve seen all your life.
- DCI-P3 – The second larger triangle is what is called DCI-P3. Digital Cinema initiatives is the range of color you can see projected via most movie theater digital projectors. As you can see, the amount of blue, red and orange in that triangle is close to the SDR Triangle- the colors are similar in both “color spaces” at that part of the spectrum. This triangle or color space will show you up to 45% of the colors your eye can differentiate.
- Rec. 2020 – The third, and the largest triangle is the Rec. 2020 color space- it’s known as a Wide Color Gamut, WCG for you and me who are in the know. As you can see by it’s shaping, it includes most of the possible reds, yellows compared to the human eye.
SDR will show you about 16.8 million different possible shades of color. HDR will show you about 1.07 billion different possible shades. Having bigger triangles does a lot more for you.
So, as we get back to the stops of exposure- one of the easy ways to see the power of HDR is a dim room with bright windows behind it. We all know from our production school background that we can either set the camera to be able to see what is outside in the bright light, plunging the room into darkness- or we can set the camera to see what is in the room, and the windows bloom into bright, featureless blobs. HDR will allow you to see both, at the same time.
HDR Deliverables For Netflix and Beyond
So now we understand quite a few things about how HDR works and how to compare colorspaces, just how do we “do” HDR?
HDR 10, or DolbyVision Color is dialed in by a colorist with a color grading system that is capable of working with these wide color gamuts, using monitors and scopes that also understand and show these color spaces. You will need different equipment most likely to fit this much different need- and Key Code Media can help you with that. You’ll need some new workflows, understanding of how to schedule and change your billing (it will take longer), and Key Code Media can help you with those things as well. And you’ll need to be able to QC this work, hopefully, you’ll have so much of it you either send that out or need to put in a special QC station – Those are what are known as good problems!
But the first thing to do is get the deliverable specifications from the end-client. And while we can help point you in the right direction, many specs will change based upon things like genre, production, end-client, or technology changes.
Let’s take a look at everyone’s favorite HDR deliverable example – Netflix Originals. Netflix provides a document outlining their standards- here’s an example from July 2018. Page 8 gets into the nitty-gritty details of what Netflix requires.
Some important things to note here- color encoding is 12 Bit, RGB 444 full range, in the P3 D65 colorspace, with an EOTF to SMPTE-2084. Sounds like an ancient dead language? Let’s break it down:
- P3 D65 – That P3 D65 rings a bell- that’s the middle triangle on the colorful graph we saw before, with that black dot signifying the true white point.
- EOTF – that’s short for Electro-Optical Transfer Function. It means the setting on your HDR monitor for EOTF is set to ST-2084 or DolbyVision.
- 12 bit 4:4:4 – That’s a very “deep” SDR was, back in the day 8 bit 4:2:2. This isn’t an old school DNX 115 output to SR tape or a ProRes file. This uses a much “thicker” media that will take up more drive space. It’s thicker as it has one of the much larger triangles we talked about before to fill. We also aren’t talking about image size at this point, as HDR can apply to the material at either HD, UHD or 4K raster sizes. If you have questions about 4K systems and storage, please reach out to us, and we can discuss what you need to do this- your laptop most likely won’t do this heavy lifting.
- IMF Package – A Color Grading system like DaVinci Resolve, set to 12-bit 444 RGB color encoding in a P3/D65 colorspace, going to an HDR monitor set to DolbyVision EOTF. This particular delivery will end up being what is known as an IMF package- and there are tools that will correctly package your delivery to this specification after color and finishing. But there are some very important hints for us in these specs for the process of post and color well before we get to the final packaging.
Good HDR Starts At Capture
One of the key points here is you’ll need your finishing process for HDR to begin by conforming from either OCN* (original camera negative), or DPX/EXR files. And, these files will need to begin at a bit depth of at least 10 bits– preferably more. This will begin on set, at acquisition, with correct camera settings. Typically shooting in RAW or LOG colorspace will provide everything needed for an HDR color pass. It will be important to test media coming from the camera/set prior to primary photography to ensure that the needed media is going to come into the pipeline. This may be a discussion with the Cinematographer or Director who should understand just what they will need to be acquiring for. If you look back to our pictures of the dark room with the bright windows- if you don’t know about it while shooting, you could end up with a great scene ruined by “Melanie and Fred,” the gaffers sitting outside the window having some coffee. They were lost in the white bloom before, yet here they are now showing up in the Color Session. Having an HDR capable monitor on set will also be helpful to show everyone just what is being created.
*OCN is the file format captured by a particular camera in it’s widest format. This may be ProRes, DPX or other codecs. It is a camera original and should be backed up prior to shipping from set.
1 CD/m2 = 1 NIT
How bright is bright? The amount of light coming from an image is measured in what is called Candelas per square meter – CD/m2 . That is all well and good for the physics teachers and we don’t use the metric system, so it’s simply referred to as NIT. 1 CD/m2 = 1 NIT.
So the important measurements:
- SDR = 100 NITS
- HDR10 =. 1000 Nits
- 1000-10,000 NITS (Above 1000 is typically Dolby Theatrical)
- 1000 NITS- NIT curve is Logarithmic, compatible with SDR displays
Quite the Gamut of information – hopefully it is feeling more in your range now!
One last thing to know. When HDR deliveries are specified, the usual SDR deliveries are usually going to be expected as well. You’ll generally need to perform 2 separate color passes, so count on more time needed to complete and package the work.