Build Your Own Qualifier In HSL Color Space Using Curves

February 1, 2022

Learn an alternate method for creating masks limiting adjustments to particular luminance regions, using Curves and Splitter/Combiner nodes.


Series

Visual Math Part 2: Using Custom Curves for more natural HSL Qualifications in DaVinci Resolve

Most colorists seeking to isolate an adjustment to a particular range of hue, luminance, or saturation will use qualifiers to create the necessary mask.

But qualifiers have a number of downsides: Their ranges are non-intuitive, and they can easily create artifacts and unnatural-looking results. The greatest strengths of qualifiers are also their greatest weakness. Qualifiers are precise and powerful — somewhat akin to a surgeon’s scalpel. As a result, we often need to use a combination of Matte Finesse tools to soften and hide the effects of the Qualifier’s scalpel, introducing new problems.

The hard edge of qualifiers usually requires activating a combination of Matte Finesse controls, of which there are many (neatly organized into a single panel pictured here in Resolve 17.4)!

In my mind, what’s more desirable is a tool that allows us to gently sculpt our image qualifications, rather than perform invasive surgery requiring all sorts of additional processing. I’ve found that using Custom Curves to draw our mask facilitates just this sort of broad and gradual manipulation.

Learn my alternate method for creating ‘masks’ to limit an adjustment to a particular luminance region

To get around the drawbacks of HSL Qualification I like to use a combination of:

  • Custom Curves – Allowing us to very easily and visually see the harshness of the qualification we’re creating
  • Color Space Transform nodes – Moving our image from RGB space to HSL (or if you prefer, HSV) space
  • Splitter/Combiner nodes – To extract the L-channel, use it to feed the alpha channel of another node, and perform the color correction that we desire

You can change your qualifications to a Hue- or Sat- only selection by choosing those channels from the splitter, instead of the L- channel.

The key to understanding this solution: You’re creating an alpha channel in the tonal range that you want to qualify and feeding that alpha into a color grading node.

Let me know if you like this method of qualification?

I’m curious to hear if, after giving this a spin, you like what you see here? Use the comments below to let me know – or ask questions if any of this confuses you.


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Comments

Homepage Forums Build Your Own Qualifier In HSL Color Space Using Curves

Viewing 6 reply threads

    • Rajab Y
      Guest

      Hello Cullen, can you make a tuto showing the techniques that company 3 uses ? thanks


    • Clement B
      Guest

      Love your work Cullen.
      Your perspective on grade and tech/creative tools is really refreshing.

      Cheers from Sydney.


    • Pat Inhofer
      Guest

      Note: We’ve posted the node tree that Cullen built in this Insight to the ‘Addtional Downloads’ section of this Insight, for Premium members.


    • Cullen Kelly
      Guest

      Thanks Clement!


    • Cullen Kelly
      Guest

      Hey Rajab! Company 3 probably has the single largest roster of colorists in the business, each of whom bring their own experience, philosophy and techniques to the table. But you can read about different artists’ approach by digging around on Google and forums!


    • EMİR Y
      Guest

      Beautiful insight as always Cullen

      I’ve been using the “use luma as matte” option for a while now, adding a serial after it, shaping it with curves like you do and connecting it as a matte back to another node i’ll be working on. I wonder if these 2 approaches give the same result?
      Also, what’s your experience with the H and S part of things? Do you think it’s possible to get better results than the HSL qualifier?


    • Tharan T
      Guest

      Hi Cullen, big fan of your work and your student from Grade School and a new member of ML 🙂
      Would you be able to provide a scenario where this method would work better than the qualifier? Why would you choose to use this instead of the qualifier as it would affect your grading speed?
      How is using this method for qualification fundamentally different as compared to using the qualifier with a decent falloff? And how this would match to using the highlights control in log wheels?


      • Cullen Kelly
        Participant

        Hey Tharan! Really good questions. The Insights in this series have the dual purpose of showcasing a practical technique, but also helping you to better understand image science and math. On the practical side, while I wouldn’t permanently retire my qualifier, there are definitely instances where I use this technique with better efficiency and better results than pulling a key. For starters, since I have a histogram of the signal I’m keying, I don’t need to manually “sweep” the entire range to find the values I’m looking for, and the interface of a curve naturally inclines me to draw simpler and softer keys, which is always a good thing. I should note here that even when I’m qualifying, I never simply “eye-dropper” the image to get my ranges, because that’s the fastest way to get a narrow, noisy selection. This approach would be tough to beat speed-wise, but that efficiency comes at the expense of a clean result, so I don’t see it as a valid point of comparison.

        Regarding log highlight wheels, you can always pull up a grayscale ramp and look at what happens to your waveform when you adjust them. To my taste, the curve you’ll see when you do isn’t smooth enough, and I can get a better one with custom curves — or with the right mathematical function! But that’s a conversation for another day…

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