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.


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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