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

  • David Cecil

    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.

  • Thank you , Cullen.

    • Cullen Kelly

      Glad you found it useful Pourang!

  • Marco Paba

    • Cullen Kelly

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

  • Yoav Assa

    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!

  • 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.

  • Isaac Rivas

    I googled splitter combiner math and found this lesson which is exactly why I wanted to know it for, went ahead and created the negative or subtractive version of the 3×3 matrix curves to complete it (with multiply blending), the splitter combiner is proving to be a very powerful tool for color control with many creative possibilities, that’s why I tried to reconstruct-build it from scratch with Davinci Color tools, without success. Let’s hope after watching all the Visual Math series I find a way to do it 😉

    • Cullen Kelly

      Hey Isaac! Glad you found this amid your search, and happy math-ing with your manual splitter/combiner attempts! Hint: start by focusing on one channel, ie: how can I use the RGB mixer to take RGB in and produce an RRR output?

  • Thanks for this series of gems!
    This last one was quite a headscratcher… Would it be possible you could write down the 2 assignments/challenges you gave at the end? I didn’t get it really (English is not my native language so could be it!) so it would be awesome to just have it in writing so I can read it a thousand times.

    Thank you Cullen! Started with your lessons on youtube and landed here to recieve more knowledge. Learned a lot in just a month.

  • Jabez Nelson

    Thank you Cullen, Where can I find a DCTL that can makes this all a bit simpler?

    • This reply was modified 3 months, 3 weeks ago by  Jabez Nelson.

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