How To Build Your Own ‘RGB Crosstalk Curves’ Node Matrix

June 14, 2022

In Part 7 of Cullen Kelly's 'Visual Math' series, rebuild Resolve’s RGB Mixer with splitter/combiner nodes to control with Custom Curves.


Visual Math Part 7 – Rebuild and supercharge Resolve’s RGB Mixer

In this Insight you’ll gain a clearer understanding of Resolve’s RGB Mixer and 3×3 matrices by rebuilding their functionality with splitter/combiner nodes — but that’s just the beginning! Armed with this new knowledge, you’re going to explore a more nuanced matrix manipulation technique we wouldn’t otherwise have access to — which I like to call Crosstalk Curves.

AND since this is our last Insight in this Visual Math series (for now, at least), I leave you with some additional ideas for expanding this matrix toolkit even further on your own.

What is a matrix?

No, we’re not talking about Neo and his choice of taking a blue pill or a red pill (but if you follow along, you may find yourself awakened to a level color grading possibilities).

The matrices you’re learning to build in the node tree are one of the most versatile and powerful tools in image science. Normally, our interaction with matrices in Resolve is limited to the RGB mixer, which offers only one particular type of matrix.

If you can deepen your understanding of this simplest and most common form of matrix, you’ll have a better grasp of everything from camera sensors to color space transforms. Just as important, this understanding opens the door to an incredibly potent look development tool with limitless possibilities.

To give just one example, my model for Kodak 5219 negative is built on nothing but fancy matrices!

Key takeaways from this Insight

What are the main concepts I hope you’ll learn?

  • The math underlying a 3×3 matrix, and what that math does for us that primary corrections can’t.
  • The creative possibilities that exist beyond a 3×3 matrix’s basic form.
  • The value of letting your imagination drive you to expand or alter tools such as our hand-built 3×3 matrix.

Comment or questions?

This is the last of my planned Insights for this series. And this one has the biggest challenge I’ve given you, here on Mixing Light. If you think you’ve figured out the challenge I left for you (at the end of this Insight), let me know in the comments. If you can’t figure it out, share your approach and let’s see if members working with each other can come up with the solution?

– Cullen

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Homepage Forums How To Build Your Own ‘RGB Crosstalk Curves’ Node Matrix

Viewing 5 reply threads

    • David C

      Really fantastic insight Cullen! Ever since I started diving into the Fusion side of look dev, it’s been very intriguing to see what all can be developed in it versus the color page, and how you can create workarounds in one or the other to get the same results.

      Speaking of, could you go in depth into why you might choose one dev room over the other in certain circumstances? Since Fusion allows for DCTLs to be baked into a look, it definitely allows for more versatility and ease of use, though I can also see the point of doing work in the color page so you physically “see” what is being done for comprehension sake of instead of just inserting a matrix DCTL and calling it a day.

      Not to mention the unfortunate bug with Davinci resetting certain DCTL parameters on reboot. You could easily do a “six in hand, half a dozen in the other” mentality when it comes to building a much larger node tree like the one shown in this insight on the color page and knowing it will be saved, versus one or a set of crafted DCTLs that you need to screenshot every time you take a break in the dev process. Can’t wait for that to be fixed.

      • Cullen Kelly

        Glad you enjoyed it David! Lately I find myself leaning toward leaving my look dev stack live/dynamic in Resolve as opposed to building it in Fusion and then outputting a LUT. Forces me to keep it simple and to continue simplifying my DCTL look dev tools, and I like having that dynamic control as you mention. That said, most of the look dev I do for colorists and facilities ends up being delivered as a LUT (or several), so I tend to do a lot of that work in Fusion.

    • Pourang

      Thank you , Cullen.

      • Cullen Kelly

        Glad you found it useful Pourang!

    • Marco P

      A great explanation. Similar to

      • This reply was modified 2 weeks ago by Marco P.
      • This reply was modified 2 weeks ago by Marco P.

      • Cullen Kelly

        Thanks Marco! I’d forgotten about this post from Benoit!

    • Yoav A

      Thank you Cullen. Loved the all insights you gave this series.

      About coding dctl, do i need to learn the all c++ language in addition to the dctl documentation that comes with resolve? I never understand how you know exactly what to write and where to write it

      • Cullen Kelly

        You got it Yoav! For a deep dive on DCTL, check out my Creative Coding series here on ML — gives you everything you need to start coding your own tools!

    • Stefano M

      As always your explanations are great.
      But how this node structure can be applied in a real grade?  And what are the real benefits over a direct trim in the RGB mixer?

      thank you!

      • Cullen Kelly

        Thanks Stefano! If you’re just wanting a standard 3×3 matrix, there’s no real benefit to doing it this way other than the opportunity to better understand the math. But the “crosstalk curves” for example are something you couldn’t get any other way, so this approach offers some unique benefits. If you wanted to deploy practically, I’d definitely place everything in a compound node and use it as more of a macro look dev tool than something to change on each shot. Hope this helps!

    • Patrick Inhofer

      Quick note: For Premium members, the .drx for Cullen’s node matrix is now available as an Additional Download at this Insight.

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