In a former life, video deliverables were on videotape and no one seriously used the internet for any mission-critical media projects. TVs and high-quality video monitors used essentially the same display technology and standards. Every videotape started with SMPTE color bars used as a reference to set up the playback of the tape deck. Monitors were calibrated to bars and gray scale charts to assure proper balance, contrast, saturation, and hue. If the hardware was adjusted to this recognized standard, then what you saw in an edit suite would also be what the network or broadcaster would see going out over the air.
Fast forward to the present when nearly all deliverables are sent as files. Aesthetic judgements – especially by clients and off-site producers – are commonly made viewing MOV or MP4 files on some type of computer or device screen. As an editor who also does color correction, making sure that I’m sending the client a file that matches what I saw when it was created is very important.
Color management and your editing software
In researching and writing several articles and posts about trusting displays and color management, I’ve come to realize the following. If you expect the NLE viewer to be a perfect match with the output to a video display or an exported file playing in every media player, then good luck! The chances are slim.
There are several reasons for this. First, Macs and PCs use different gamma standards when displaying media files. Second, not all computer screens work in the same color space. For instance, some use P3-D65 while others use sRGB. Third, these color space and gamma standards differ from the standards used by televisions and also projection systems.
I’ll stick to standard dynamic range (SDR) in this discussion. HDR is yet another mine field best left for another day. The television display standard for SDR video is Rec. 709 with a 2.4 gamma value. Computers do not use this; however, NLEs use it as the working color space for the timeline. Some NLEs will also emulate this appearance within the source and record viewers in order to match the Rec. 709, 2.4 gamma feed going out through the i/o hardware to a video monitor.
As with still photos, a color profile is assigned when you export a video file, regardless of file wrapper or codec. This color profile is metadata that any media player software can use to interpret how a file should be displayed to the screen. For example, if you edit in Premiere Pro, Adobe uses a working SDR color space of Rec. 709 with 2.4 gamma. Exported files are assigned a color profile of 1-1-1. They will appear slightly lighter and less saturated in QuickTime Player as compared with the Premiere Pro viewer. That’s because computer screens default to a different gamma value – usually 1.96 on Macs. However, if you re-import that file back into Premiere, it will be properly interpreted and will match the original within Premiere. There’s nothing wrong with the exported file. It’s merely a difference based on differing display targets.
The developer’s conundrum
A developer of editing software has several options when designing their color management system. The first is to assume that the viewer should match Rec. 709, 2.4 gamma, since that’s the television standard and is consistent with legacy workflows. This is the approach taken by Adobe, Avid, and Blackmagic, but with some variations. Premiere Pro offers no alternate SDR timeline options, but After Effects does. Media Composer editors can set the viewer based on several standards and different video levels for Rec. 709: legal range (8-bit levels of 16-235) versus full range (8-bit levels of 0-255). Blackmagic enables different gamma options even when the Rec. 709 color space is selected.
Apple has taken a different route with Final Cut Pro by utilizing ColorSync. The same image in an FCP viewer will appear somewhat brighter than in the viewer of other NLEs; however, it will match the playback of an exported file in QuickTime Player. In addition, the output through AJA or Blackmagic i/o hardware to a video display will also match. Not only does the image look great on Apple screens, but it looks consistent across all apps on any Apple device that uses the ColorSync technology.
You have to look at it this way. A ton of content is being delivered only over the internet via sites like Instagram, Facebook, and YouTube rather than through traditional broadcast. A file submitted to a large streamer like Netflix will be properly interpreted within their pipeline, so no real concerns there. This begs the question. Should the app’s viewer really be designed to emulate Rec. 709, 2.4 gamma or should it look correct for the computer’s display technology?
The rubber meets the road
Here’s what happens in actual practice. When you export from Premiere Pro, Final Cut Pro, or Media Composer, the result is a media file tagged with the 1-1-1 color profile. For Premiere and Media Composer, exports will appear with somewhat less contrast and saturation than the image in the viewer.
In Resolve, you can opt to work in Rec. 709 with different gamma settings, including 2.4 or 709-A (“A” for Apple, I presume). These two different output settings would look the same until you start to apply a color grade (so don’t switch midstream). If you are set to 2.4 (or automatic), then the exported file has a color profile of 1-2-1. But with 709-A the exported file has a color profile of 1-1-1. These Resolve files will match the viewer and each other, but will also look darker than the comparable Premiere Pro and FCP exports.
All of the major browsers use the color profile. So do most media players, except VLC. These differences are also apparent on a PC, so it’s not an Apple issue per se. More importantly the profile determines how a file is interpreted. For instance, the two Resolve ProRes exports (one at 1-1-1, the other at 1-2-1) look the same in this first generation export. But let’s say you use Adobe Media Encoder to generate H.264 MP4 viewing copies from those ProRes files. The transcoded MP4 of the 709-A export (1-1-1 color profile) will match its ProRes original. However, the transcoded MP4 of the 2.4 export (1-2-1 color profile) will now look a bit brighter than its ProRes original. That’s because the color profile of the MP4 has been changed to 1-1-1.
Gamma changes mostly affect the midrange and shadow portion of a video signal. Therefore, differences are also more or less apparent depending on content. The more extreme your grading, the more apparent (and to some, obnoxious) these differences become. If these really bother you, then there are several ways to create files that are “enhanced” for computer viewing. This will make them a bit darker and more saturated.
- You can tweak the color correction by using an adjustment layer to export a file with a bit more contrast and saturation. In Premiere Pro, you can use a Lumetri effect in the adjustment layer to add a slight s-curve along with a 10% bump in saturation.
- You can use a QT Gamma Correction LUT (such as from Adobe) as part of the export. However, in my experience, it’s a bit too dark in the shadows for my taste.
- You can pass the exported file through After Effects and create a separate sRGB version.
These approaches are not transparent. In other words, you cannot re-import these files and expect them to match the original. Be very careful about your intentions when using any of these hacks, because you are creating misadjusted files simply for viewing purposes.
In the end, is it really right to use Rec. 709 2.4 gamma as the standard for an NLE viewer? Personally, I think Apple used the better and more modern approach. Should you do any of these hacks? Well, that’s up to you. More and more people are reviewing content on smart phones and tablets – especially iPhones and iPads – all of which show good-looking images. So maybe these concerns are simply much ado about nothing.
Or paraphrasing Dr. Strangelove – How I Learned to Stop Worrying and Love Color Profiles.
©2021 Oliver Peters