How to Fix RGB Gamut Excursions with Software (mostly)

August 13, 2016

If you're color correcting digital video for professional distribution, nothing is worse than having it rejected for RGB Gamut excursions!


Series

Part 2: Rethinking Saturation in DaVinci Resolve

How would you like to spend a week color correcting a show that’s been in production and post-production for 8 months—only to have it rejected by a broadcast, cable or internet network?

Just when your client thinks they’ve made it to the finish line, the line judge throws a Red Card and puts their show on the bench… and it’s your fault! If you’ve been running DaVinci Resolve with ‘Broadcast Safe’ enabled, and you’ve been managing your overall saturation levels—then the likely culprit for your rejection? RGB Gamut excursions.

Dealing with RGB Gamut errors can be a nightmare.

RGB Gamut errors are difficult to identify and very hard for post-production software to manage. Here on Mixing Light, we’ve talked about this problem many times:

  • RGB Gamut Errors: Robbie talks about the overall problem and a few strategies for dealing with these errors
  • Legalizing Video Parts 1-6: Robbie and I tackle how to legalize in Speedgrade, PremierePro, DaVinci Resolve and using Hardware Legalizers. The link I’ve provided takes you to the part of the series where I talk about DIY Legalization. Once there, just above the headline of that Insight are the links to the rest of that Series—including, how to legalize with the Harris DL-860 that I talk about in this Insight
  • From the Mailbag—Legalizing without a Legalizer: Robbie, Dan and I chat about our legalization strategies in this roundtable discussion.
In this Insight, I rethink some of the tools we can use for legalization in Resolve.

I’ll also echo some key points in our earlier legalization videos, including how you can guess if you’ll have an RGB Gamut error by using the Parade Scopes in DaVinci Resolve.

For me, the key is to use two scopes provided by Divergent Media’s Scopebox. If you want to learn how I’ve set up my scopes, here’s my Scopebox overview video. I’ve since made a few modifications, but my basic setup is still the same.

Enjoy!

-pi

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Comments

Homepage Forums How to Fix RGB Gamut Excursions with Software (mostly)

  • Thanks Patrick, great insight!
    I thought it was interesting when you used soft clip you went per channel, I would probably go with linked channels and maybe in that case won’t have to desaturate shadows?
    Don’t know, would have to look at the image to tell 🙂
    Thanks again!


  • Patrick Inhofer
    Guest

    Actually, normally I would lock all three channels. But sometimes I don’t, especially the blue channel. Often you can pull that up and end up with a more natural looking image.

  • Great insight, thanks Patrick!


  • Patrick Inhofer
    Guest

    Thanks Colin!

  • So this the “display broadcast safe exceptions” option in resolve inaccurate?

  • Hi patrick,
    what about using the actual low&hi level clip in the softclip curves?
    By moving it ever so slightly would’t you clip the problematic pixels leaving the black level where you initially wanted it?


  • Patrick Inhofer
    Guest

    It’s not that the option isn’t accurate… it’s not comprehensive enough. It fixes what it says it’ll fix but if you’re delivering to a distributor, it’s doesn’t go far enough.


  • Patrick Inhofer
    Guest

    The softclip will lift blacks, especially if you’ve got large excursions. If I can, I’d rather desaturate those blacks first to see if it’ll fix the problem. If not, then I’ll go to the Hi / Lo softclips and use those.

    One thing I didn’t mention in this Insight (but has been covered in other Insights dealing with the Hard and Soft Clips) is using the Hard Clip and setting it one or two IRE above zero black, which can also help (but is not a guarantee).

  • So with this final fixes presented in this video done, this Clip should be exported as “Data Levels” not “Video Levels” and still be broadcast save? Am I right?


  • Patrick Inhofer
    Guest

    Correct. Technically, this has nothing to do with ‘Broadcast Safe’. It’s about how the grayscale bit values get represented within the ‘bit container’ of the file that gets written to disk – so that other apps read those bit values correctly.

  • The video in the insight is unavailable. “Video URL cannot be accessed….blah blah”


  • Robbie Carman
    Guest

    hey justin – sorry about that, a causality of our switch over to ML 2.0 Should be working now.

  • Thanks! Brilliant. I often use lum vs sat and sat vs sat creatively – nice to see that these same tools can be used to fix gamut excursions. Super useful insight.

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