Colour Management for Video Editors
- Which colour profile should you set your monitor to for video editing?
- What’s the difference between sRGB, Adobe RGB, DCI-P3 and others?
- What colour space is my NLE using?
- How do I correctly colour grade for internet delivery?
If you’re an editor looking to colour grade your own projects what are some of the technical things you should be aware of, to ensure your images look as good, and as consistent as they can?
How should you be managing your colour pipeline for the challenging multi-screen viewing environment of today?
I set out to answer these, and a whole bunch of other questions, to finally get to the bottom of how to properly manage my colour pipeline. (Or at least double check I was still vaguely doing the right things.)
This endeavour raised questions such as;
- How do you know what colour space to be working in?
- How does Premiere Pro handle colour differently to FCPX or DaVinci Resolve?
- What Colour Profile or settings should you have your monitor set to?
- Do you need to have an external video I/O box between your computer and the monitor?
- Why does the colour look different in Quicktime vs VLC vs YouTube vs Vimeo vs Chrome vs Safari, all on the same monitor?
If you’re wrestling with some of these questions too, then hopefully I can provide some answers, or at least an interesting technical read.
As I wrote this post I soon discovered that when you really dig into colour management it’s one of those technical rabbit holes that some people love (people who comment in forums) and some people don’t have time for (getting into the depths of nuance). I think I’m somewhere in between.
Of course, the kind of work you’re doing and the resources you have at your disposal will somewhat dictate how far down the rabbit hole you need/want/can go.
When I’m researching something like this I prefer to hear from professionals who demonstrate that they know what they’re talking about – both in theory and real world applications.
In putting this post together the excellent content created by the three professional colorists behind MixingLight.com (Robbie Carman, Patrick Inhofer and Dan Moran) was instrumental to defining my answers to much of this, as well as some key insights from Michael Kammes and his 5 Things Web series and Samuel Bilodeau of Mysterybox.us.
You would do well to check them out too!
That said, any errors in here are entirely my own and I’ll happily be corrected and informed by more learned opinions, in the comments.
I don’t want to read all this – just give me the answer!
The crux of post is to set your monitor to the calibrated colour profile that matches the standard you are delivering in. Grade within the spec of the standard and then anyone who sets their monitor/TV to the same standard, should see it as you intended.
Switch between calibrated profiles depending on the delivery requirements of the project. For example, if you’re delivering for web to sRGB or if you’re delivering for broadcast Rec. 709.
So if you’re grading on a computer monitor, delivering for the web then set and calibrate the monitor to sRGB Gamma 2.2.
To ensure a reliable colour pipeline from the software to the monitor you are advised to use an IO device, like an AJA T-Tap or Blackmagic Design Mini Monitor (or greater if you need 4K), so that your operating system or graphics card aren’t interfering with delivering a clean signal from the footage to the monitor via SDI or HDMI.
You also need a monitor that is reliably capable of displaying the full colour gamut of the colour space you are working in.
Before you jet out of here, scroll to the very bottom of this post to read the ‘One last thing’ section, on why you really do need a large external monitor.
The Goal of Colour Management in Post Production
Netflix’s own Calibration Best Practices document spells out the goal of what we’re trying to achieve quite nicely:
The wide variety of display types and viewing environments can lead to inconsistent quality results, unless a set of guidelines is put into practice which adhere to a common standard.
The guidelines provided below will need to be adopted by each contributor to the Netflix Digital Supply Chain, to ensure consistent quality.
If we all agree on a standard and stick to that standard throughout the process, then how I choose to make the picture look at my end, will be the way it should look for you at your end. And we’ll all be happy.
Grading to a standard
In television broadcast this process was pretty straight forward.
Rec. 709 was the standard colour space with a white point of D65. This was what everyone worked to, and why post suites had a big fat CRT monitor calibrated to this standard to view their images on. It was also what your TV at home should have been working to as well.
The agreed standard for the Web is currently sRGB.
This closely resembles the very similar specification to Rec. 709 although the difference between Rec. 709 and sRGB is that the Gamma curve changes from 2.4 for Rec. 709 to 2.2 for sRGB.
What this means in practice is that they’re basically ‘close enough’ to each other to work with and you shouldn’t worry too much.
The main difference between the two, is that a lower gamma number (2.2) produces a brighter image.
The theory being that most people looking at computer monitors are doing so in a brighter, day-time environment. Or in the street on their iPhone.
Whereas broadcast TV standards expect you to be watching TV in the evening in a darkened environment, so the Rec. 709 broadcast standard is Gamma 2.4.
This post on Mixing Light was super helpful, on the difference between 2.2 and 2.4 Gamma and how to choose between them. It’s also worth a read to understand the human visual perception of contrast happens in relative terms, rather than absolute, and why the monitor you’re viewing on is more likely to effect your choice of Gamma setting.
Also just to say Rec. 2020 is coming which has a much wider colour gamut that Rec. 709. Adobe RGB also provides a wider colour space than sRGB and is more for professionals working with print. I’ll leave them there for now.
That’s not to say that once you’ve carefully set up your system and graded your project that the end viewer won’t whack up the brightness of their TV, add more contrast and boost the saturation. The web equivalent might be a producer critiquing a grade late at night on their iPhone with Nightshift turned on.
Understanding Colour Pipeline Management
Video Signal Chain: Source Footage > NLE > OS > IO/GPU > Cable > Monitor
Video Processing/Viewing Chain: Source Footage > NLE > Export Codec/Bit Rate > Viewing App > Web Service Compression > Web Browser > Monitor
To understand all of the steps that your video image will go through to get from a digital file to your eye-balls it’s worth breaking down all the parts involved in the journey.
Depending on your particular set up, things will be a little different so I’ll try to describe the general theory (as I currently understand it) and then get into some of the specifics of my own workflow.
Let’s say you want to get a Rec.709 10bit video image to your eye-balls the whole time, what would you need to do?
You would need to take a Rec. 709 10bit video file, edit it in your NLE maintaining that bit depth and colour space, output that video signal to your external monitor in 10bit and in Rec.709 and view it on a monitor with a 10bit panel, calibrated to Rec.709.
Now that Mac OS X displays native 10bit video, does this mean I no longer need an I/O box to get the signal from the software to the monitor faithfully in 10bit and Rec. 709?
Well it depends on what’s happening in the NLE.
If the NLE Viewer is displaying 10bit video in the UI/viewers then I think so (?). (See “Do you still need a dedicated I/O box for Video” below for more.)
So let’s take a quick look at what Premiere Pro, FCPX and DaVinci Resolve are all doing in the timeline viewer and on export.
This detailed post from Mystery Box was exceptionally helpful in answering my questions on this topic. I would highly recommend reading it in full!
Both Adobe Premiere and FCPX work on a “what you see is what you get” philosophy. If your interface display is calibrated and using the proper ICC profile, you shouldn’t have to touch anything, ever. It just works.
As the Mystery Box post makes clear, Premiere Pro is anticipating you to be working in a Rec. 709 colour space all the way through. This makes life fairly straight forward if you’re delivering for broadcast or the web.
Further googling uncovered these interesting tidbits;
Color processing: https://forums.adobe.com/thread/825920
Premiere processes everything in 4:2:2 YUV, but converts to RGB 4:4:4…
a) For GUI Display
b) For RGB-based effects (then back to YUV again)
c) For outputs if export settings or the target file format require it
CUDA effects are always processed in 32-bit float.
Colorspace and Gamma are defined by your display.
Bit depth: http://blogs.adobe.com/VideoRoad/2010/06/understanding_color_processing.html
The timeline processes in 8-bit, but maximum bit depth is ultimately limited by your source footage.
Checking Render at Maximum Depth in the Video Previews or Render dialog will promote either one to 32-bit float to take advantage of source footage over 8-bits.
Therefore two crucial things to make sure you have checked on every export from Premiere Pro are:
- Render at Maximum Depth (otherwise it will default to 8-bit)
- Max Render Quality
This post from Patrick Inhofer on MixingLight.com was again very helpful for clarifying numerous things about grading in Premiere, not least what Max Render Quality actually does.
Apparently this setting is actually about the quality of the scaling of images between their original resolution in the footage and the timeline frame size. Patrick says this is actually weighted more towards down-scaling, than up-scaling. So if working with 4K footage but delivering in HD then you want to make sure this is checked!
By default, [FCPX] processes colors at a higher internal bit depth than Premiere, and in linear color which offers smoother gradients and generally gives better results.
You also get to assign a working color space to your library and your project (sequence), though your only options are Rec. 709 and Wide Color Gamut (Rec. 2020).
This quote comes from the Mystery Box post, and makes it clear that working in FCPX is also relatively straight forward, and the default is Rec. 709 again.
More rummaging around on the internet turned up this nugget in the comments of a post from Larry Jordan explaining the Wide Colour Gamut in FCP 10.3 (which is worth a read too, as is this one about P3 on the new Macbook Pro).
Question: One thing I’m curious about that Apple doesn’t include in their white paper is whether macOS internal color management is flagging and adjusting gamma along with color gamut. Rec. 2020 specifies 2.4, the same as Rec709 did, but Apple displays, including the new P3 ones are all 2.2 gamma, while all digital cinema projection (the viewing environment where most of us can actually see P3 content for the foreseeable future) is 2.6 gamma.
LJ Answer: “macOS internal color management does adjust gamma along with color gamut based on the color profile of the display. When viewing Rec. 709 or Rec. 2020 footage on an sRGB or Apple P3 display, the gamma adjustment is controlled by ColorSync. To view footage on a broadcast or studio display with 2.4 gamma, an external video out device, like an AJA or Blackmagic Thunderbolt to SDI device, can be used.
By default, on a Mac it applies the monitor ICC profile to the interface viewers, with the assumption that your input footage is Rec. 709.
Fortunately, changing the working space is incredibly easy, even without color management turned on – simply set it the color primaries and EOTF (Gamma curve) in the Color Management tab of the Project Settings.
With color management off, this will only affect the interface display viewers, and then only if the flag “Use Mac Display Color Profile for Viewers” is set (on by default, MacOS only.) [Arrow in image above.] – MysteryBox
Of all the applications in this list DaVinci Resolve has by far the greatest level of customisation and control over what’s happening internally with the video processing, what’s sent to the monitor and your project’s working colour space.
This also means that to get the most out of it you need to know a little bit more about what you’re doing. Luckily, chapter 6’s of the manual (Data Levels, Color Management, ACES and HDR) provides you with 31 pages of details on this in various scenarios.
It’s particularly worth reading the section on Resolve Colour Management (RCM) which aims to make life much easier for everyone when working with different kinds of source footage.
Here’s a quote on how it makes life easier for editors in particular.
Resolve Color Management for Editors
RCM is also easier for editors to use in situations where the source material is log-encoded. Log-encoded media preserves highlight and shadow detail, which is great for grading and finishing, but it looks flat and unpleasant, which is terrible for editing.
Even if you have no idea how to do color correction, it’s simple to turn RCM on in the Color Management panel of the Project Settings, and then use the Media Pool to assign the particular Input Color Space that corresponds to the source clips from each camera.
Once that’s done, each log-encoded clip is automatically normalized to the default Timeline Color Space of Rec.709 Gamma 2.4.
So, without even having to open the Color page, editors can be working with pleasantly normalized clips in the Edit page.
It can be 10-bit on macOS, there’s a prefs setting.
— Alexis Van Hurkman (@hurkman) February 27, 2018
I had read that DaVinci Resolve only supplied an 8-bit preview in the viewer window but thanks to Alexis’ tweet this isn’t the case under Mac OS.
Check what you’re set up as under DaVinci Resolve > Preferences > Hardware Configuration. (See the red rectangle in the image above)
Do you still need to use a dedicated I/O box for video?
If all of this sounds like too much trouble then you might just want to make your life easier by using a dedicated I/O device to send the signal from your software of choice, direct to your monitor.
The reason to use a dedicated IO card is that it gives you a properly managed colour pipeline that by-passes the operating system’s GPU and colour profile settings and gets you straight from the NLE to your monitor without alternation (unless you’ve got some hardware calibration going on too).
That way, if you know you’ve got a 10bit Rec. 709 video file and you’re outputting it via the IO to a 10bit Rec. 709 calibrated monitor you should be good to go.
That’s the gist that I picked up from this conversation from the MixingLight.com Mailbag podcast, anyway.
Patrick Inhofer, of Mixing Light.com, kindly read through this article, and pointed out that in the table above (from the Myterybox article) neither Premiere Pro nor FCPX by-passes the ICC profile used by the OS.
When you use an I/O card you also install drivers that plug into your NLE. Those drivers help the NLE bypass OS-level color management and output a standards-compliant image that shows you what the actual bits and bytes on your hard drive represent. – Patrick Inhofer
So do you still need an IO interface?
Displayport has 10-bit 4:4:4 as well as YCbCr. These new monitors should be able to produce an accurate image over the Flanders or Sony 1080 panels i’ve been using as reference monitors for the past six years?
I thought all we were waiting for was proper 10-bit color from the OS and video cards? – MrCdeCastro
This quote from the egpu.io forum basically raises the question fairly succinctly.
However, this thread on the BMD forum seemed to have some very knowledgable folk putting forward solid arguments for and against this kind of workflow, depending on the specifics at play.
I’ve quoted representative snippets here, but be sure to click through to check out the full posts from this comment from Davis Said:
- Signals sent out via GPUs to monitors may not be representative of an actual video signal.
- I would agree with others who’ve said that using a BMD video output device to a properly calibrated (and suitable) external video display is the only guaranteed way to know that the signal path is one that is proper for previewing video. Also, having a display that can show all the pixels from a video frame without any scaling is very valuable when scrutinizing the effects of filters and other grading choices.
- (Edited/Added for clarity) As Andrew K. mentions a bit further down in the thread, it is possible for a monitor directly connected to a computer via a GPU to display a proper image (with a valid signal path). As Andrew also mentions, a benefit would be not having to convert from RGB to YUV/YCbCr to RGB. It’s more of a software issue than a hardware issue nowadays. – Davis Said
and this comment from Craig Marshall (quoting colorist Jason Myres):
GPU output (DP/HDMI) and a Decklink/mini monitor card output) … are two very different things and it goes way beyond whether they are 8 or 10-bit.
The first one is a standard graphics card output, the second (Mini Monitor) is a Baseband SDI/ HDMI video output.
The difference comes from the fact that one is intended (and modified) to suit a computer display, and the other is a fully legitimate video signal intended for broadcast monitoring.
They are two different signal types with different color spaces and signal paths. Don’t try to compare them, as they literally have no relation to one another.
and then this comment from Andrew Kolakowski.
Well- this is bit of myth and legacy approach. Here is another view which is adjusted to current technology possibilities.
Resolve and other grading tools work in RGB and use GPU to do its magic. The GPU is connected directly (in typical case) to a monitor. This is all what we need.
This link is actually more accurate and better than using video card because:
– data goes directly from GPU to monitor without any additional delay
– it’s rather always 4:4:4, where probably 80% of typical studio setups still uses 4:2:2 YUV path (to save bandwidth)
– it avoids RGB->YUV->RGB conversion (which is never 100% lossless)- this happens on every YUV video chain
– it uses less resources- no need to copy data from GPU to card
– saves money and slot (no need for any additional card)
– it can be even 16bit pipe, where most video cards can do max 12bit
– it can use V-sync to guarantee proper sync, like video chain does
– it actually avoids problems on wrong conversion between RGB<->YUV (it’s 1:1 RGB pipe from GPU to monitor)
– it’s not restricted to specific refresh rates (just by connection bandwidth limits, e.g. HDMI 2.0 ect)- it can do about everything what your monitor will accept, e.g. 120Hz
– it’s the only easy solution which allows atm. to monitor 8K (or 4K 50/60p 4:4:4)
Accuracy- it’s just a matter of software.
It’s fairly easy to separate preview from any OS influence. There are software which already do it – just not Resolve.
When we talk about grading software which works in RGB and then about video pipe (which in most cases is YUV) then whole point of video pipe almost loses sense. An RGB pipe to the monitor is what you ideally want. The YUV pipe is juts a compromise to save bandwidth.
If we were talking about some broadcast chain which operates in YUV then yes – you don’t want to go to RGB anymore (we already left RGB world when YUV master was made).
In the case of Resolve, compositing, finishing tools you want RGB preview to your device and GPU is ideal for providing it.
Issues with GPU monitoring:
-because it uses HDMI/DP technology cable length is limited (use converter to SDI to gain distance if needed)
-maybe interlacing issue, although it can be sorted and it’s soon will be gone anyway.
It seems to me that there is an emerging case, with the latest technology and calibration at all points, that you *might not* need an external monitor and IO card – but pretty much only if you’re never going anywhere near broadcast.
Obviously this is only feasible if the monitor you’re viewing it on is capable of accurately maintaining it’s colour profile and the software is set up to give you accurate video in the preview window. Apparently this is may not the case with DaVinci Resolve due to scaling issues and other things.
I’ll leave you to wade in and make up your own mind.
If you’re specifically using DaVinci Resolve it’s well worth reading their latest Configuration Guide to see their recommended hardware set up for desktops, laptops and so on.
Here’s what Blackmagic Design recommend for a 2013 Mac Pro.
It’s also worth pointing out that on page 660 and 661 of the DaVinci Resolve manual you get this information on the ‘Limitations When Grading With the Viewer on a Computer Display‘:
Most computer displays do not operate at the color critical tolerances or specifications required for broadcast or theatrical delivery.
An additional issue, however, is that the Viewer does not necessarily display each clip’s image data as it is displayed by the calibration that your operating system applies to your computer display, depending on which OS you’re running DaVinci Resolve on.
This makes your computer display potentially unsuitable for monitoring projects destined for the sRGB standard of the web in its default state.
For example, if you grade a project using the Color page Viewer on your computer display, the resulting clip may not look the same in the QuickTime player, or in other post-production applications.
You can address this in one of two ways:
1) If you’re using DaVinci Resolve on Mac OS X, you can turn on “Use Mac Display Color Profile for viewers” in the Color Management panel of the Project Settings.
This lets DaVinci Resolve use one of the pre-existing profiles in the Color tab of the Displays panel in the System Preferences, thereby taking advantage of ColorSync on Mac OS X to let DaVinci Resolve display color the way your computer monitor does.
NOTE: custom calibrated .icc profiles are not supported at this time.
2) Alternately, you can apply a dedicated Color Viewer LUT for calibration, using?the 1D/3D Color Viewer Lookup Table pop-up menu that’s found in the Color Management panel of the Project Settings.
This lets you analyze your computer display for calibration in the same way you would calibrate an external display, using a probe and color management software, and apply the resulting calibration LUT in DaVinci Resolve.
Keep in mind that monitor calibration can only make a high-quality display standards-compliant, it cannot make up for a display gamut that’s too small.
For more information, see the “Look Up Tables” section of Chapter 3, “Project Settings and Preferences.”
Strictly speaking, if you’re doing professional work, you should restrict your grading to a calibrated, 10- or 12-bit class-A external broadcast display of some type, connected via a Blackmagic Design video interface.
Assuming everything is running properly, an image output to video from DaVinci Resolve should match an image output to video from any other post-production application you’re using, and this should be your basis for comparison when examining the output of two different applications.
What about HDR?
I’ve chosen not to get into HDR in this post for simplicities sake and because I’ve personally not worked in it, but as a starting point here is an excellent short video from Ripple Training explaining what HDR is and how it works in FCPX.
To add to this here is a quick word from Patrick Southern of Lumaforge, on working with it in relation to IO boxes:
You have to use an AJA IO 4K or IO 4K Plus with Final Cut Pro X to output proper HDR. You’ll only get an 8-bit image with a Blackmagic box out of FCPX, and you’ll only get the proper HDR metadata to the display using AJA.
Resolve, on the other hand, must use one of the Blackmagic IO boxes to properly output HDR.
In neither case will HDMI direct from the computer work.
With HDR, every bit counts. Since HDR is about smooth gradation in an expanded luminance range, you need at least 10-bits to properly display HDR.
That’s why it matters which IO box you use with each application.
A helpful watch to get your head around the concepts and considerations.
Colorist Marc Bach does a great job of explaining what HDR is, how it works technically and creatively and in relation to the human visual system! A great presentation from the LumaForge ‘Faster Together’ booth at NAB 2018.
Colour management workflow when delivering video for the Web
So if you’ve made it this far into the post (congrats) but you’re thinking “but I’m an editor who is only editing projects for YouTube or Vimeo or other places”, what do I need to do?
Well, as you’re not delivering for broadcast, there will be no Quality Control rejection of your file by the powers that be. You can upload whatever you like and only your client’s opinion will really matter. If they’re happy and you’re happy, then what’s to worry about?
Personally, that’s not enough for me.
I want to know for sure that I’m getting the best out of the equipment I have and that what I’m looking at is an accurate representation of the file I’m working on. I also want to have some kind of fall-back position if the client says “Hey it looks kind of …. to me.” (On their screen.)
I’m on a 2013 Mac Pro with an LG 31MU97 4K monitor set to it’s sRGB profile. This is hooked up with a Display Port cable feeding a 10bit signal. I do most of my grading in Premiere Pro or DaVinci Resolve.
I’ve also got a new 2017 Macbook Pro 15″ laptop and an iPad which I can use as some basis for comparison to my image on screen. I’ll also upload a test file of my export to YouTube (if that’s where it’s going to be delivered) and see how that looks on various screens.
Sometimes I’ll add a 10% contrast and saturation bump adjustment layer to the whole thing and see if that ‘looks better’ in the final viewing conditions.
What I’m painfully aware of is that I need to get my screen re-calibrated in all of it’s various profiles, just to give it a ‘spring-clean’.
I also should probably fork out for a 4K I/O box. Although that’s a fair amount of money for someone who actively avoids being booked to do colour grading specifically, it feels like an important next purchase.
Dealing with QuickTime, VLC, YouTube Vimeo and Browsers
One of the most perplexing things is when you export your final file and open it in QuickTime, VLC, DaVinci Resolve, Final Cut, Premiere Pro, YouTube, Vimeo, Safari, FireFox and Chrome all at the same time and it looks different in each one.
This is because each one does it’s own thing when interpreting the image. Some refer back to the system wide ColorSync ICC profile, some don’t. Some refer to the display. It’s a mixed bag.
I’ve read different opinions about it online, but other than calibrating your monitor to the correct spec, I’m not sure there’s much more you can do, depending on the innumerate variables that could be in play in your specific circumstances.
Or follow the advice of Alexis Van Hurkman in the Resolve manual, quoted in the last section above. (p.660)
In the Mixing Light post I referenced above, colorist Patrick Inhofer, answer this question in the comments:
Do platforms on the internet adjust gamma at all?
Gamma adjustments happen all over the place; on your computer, in your browser, when uploading to a video sharing service, when displaying from a video sharing service.
You can, and should, expect your gamma will get bounced around once you’re outside a carefully color-managed room, like in digital cinema or a grading suite. That’s why we grade to a standard… the standard is a center-point around which all our devices will orbit.
One Last Thing – Why you really do want an external display
Watching Dunkirk the way Christopher Nolan intended pic.twitter.com/vYpROyla6D
— Chris (@chriswashere321) March 3, 2018
In emailing with colorist Patrick Inhofer about this article, he made a really astute comment on this whole topic of monitoring, which I felt was worth quoting at length here:
The value of a large dedicated external display. That value isn’t just a color managed image… it’s an emotional value.
I can’t imagine judging an actors performance, the effectiveness of my edits, or the quality of my color corrections on 1/3 of a 27″ computer display – surrounded by distracting User Interface elements of my software.
A full-time dedicated display is essential to judge the emotional effectiveness of the work we do – in real-time.
But, if part of your ‘pitch’ to your clients is that you can do color correction and that’s part of what they’re buying from you – then you’re selling them (and yourself) short if you try to get by making color-critical decisions on a cheap display with terrible characteristics through an ICC pipeline that has problems of its own, in regards to professional video.
In the end, spending a few thousand dollars on a pro display is about integrity, doing great work, and having atomic-level self-confidence in what you do for a living and your confidence in selling your skills and the final, emotional product you’re producing.
This is a hugely important point and definitely something to consider when you’re making your next monitor purchase.
As I said, within my home edit suite, I have a large 31″ 4K display which allows me to work, I feel, in an uncluttered way with a 1:1 1920 x 1080 HD image, which is what 95% of the projects I work on are delivered in.
But I’ll always review my work by standing at the back of the room and watching the edit on a full-screen preview to make sure everything is working as it should.
If I had the space for a second display I would definitely seek to make that happen for the reasons Patrick has made clear.