Revisiting the RGB Mixer (in DaVinci Resolve)

Day 1: 25 Insights in 25 Days 2019 New Year Marathon!

Different uses for the RGB Mixer tool

I feel the RGB Mixer is rather underrated. There’s a version of it in the Quantel ‘fettle’ curves, or whatever that’s called now days. Premiere Pro has a Channel Mixer effect. I think in Baselight it’s called ‘Colour Matrix’ (please correct me if that’s wrong!). Avid|DS and Symphony called it Channels. The idea in all those platforms is simple: Feed the information from one colour channel into the output of another colour channel. It’s very powerful.

Balancing a tricky shot

Have you ever come across a shot where you simply couldn’t get a good white balance because there was virtually no information in one of the colour channels? Most white-balancing methods rely upon putting varying amounts of gain (and/or lift) into the red, green and blue signals. Cameras do this when white balancing. In post we do it by manipulating the raw data or with primary corrections. But if there’s hardly any signal in a color channel to start with then you may never get a good balance. Or if you do, you get a lot of boosted noise because you had to add gain to a low-level signal.

However, chances are good that one of the other colour channels has data which you can use by feeding it into another colour channel’s output. After all, we’re only dealing with three channels of ones and zeros which are destined to drive three different colour pixels on a display. Using the RGB Mixer we’re just sending a proportion of one colour channel to drive pixels of a different colour.

I’ve used this tool for to fix various extreme lighting conditions. I like it especially for murky underwater scenes.

It’s interesting to note that when you use Resolve’s RGB Mixer to create a monochrome image, it actually shows the proportions of each channel used to make the Y-only (luma-only) black and white image as defined by Rec. 709.

While writing this Insight I came across some more useful information about this kind of tool in the Avid|DS manual which is also here on page 111 of the Avid Symphony User Guide (pdf). 

Creative uses for the RGB Mixer

Once you start to get your head around using the RGB Mixer it opens up some creative possibilities. By considering what colour values you have and what colour you want to have, you can start to use the tool to pull the vectorscope and waveform and make overall hue and saturation adjustments. In this example I used it to compress the colour vectors along the skin/cyan axis.

Of course, the RGB Mixer is best used in conjunction with other tools. You may not want to tint neutral highlights or to add overall saturation, both of which can be side effects of using this technique. It’s not necessarily better than doing something similar in the curves menus, it’s different and well worth experimenting with.

(video credits: http://www.multihyphenate.net & http://eggcreativeproductions.com )

Comments

Homepage › Forums › Revisiting the RGB Mixer (in DaVinci Resolve)

• Creator
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• January 1, 2019 at 3:00 am #32804
  
  Jamie Dickinson

  Participant

  This is the discussion thread for the Insight: Revisiting the RGB Mixer (in DaVinci Resolve)

• Creator
  Discussion

• 
  Jordan Maders

  Guest

  January 25, 2019 at 1:45 pm

  Very Clear and great insight.
• 
  Greyson A

  Guest

  January 25, 2019 at 5:04 pm

  Such a simple concept, yet something I hadn’t considered before. This insight has certainly changed the way I will approach balancing. Thanks Jamie!
• 
  Zdeněk Klusáček

  Member

  March 28, 2023 at 9:39 am

  I still have no clue how it works. Would be nice to have a bit more in-depth explanation of the concept of behind this tool.
• 
  Jamie Dickinson

  Member

  March 28, 2023 at 9:47 am

  I think the demonstration with the Splitter Combiner helps to visualise it? You can easily see each of the colour channels, the information destined to the red, green or blue pixels on your TV but we’re altering that and sending a proportion of the one channel to the output of another channel.
  • 
    Zdeněk Klusáček

    Member

    March 29, 2023 at 6:51 am

    Thanks for reply. You are right this RGB split does help.

    What I do not really get is why substracting blue in red channel moves blues (and reds) toward cyan. Btw. substracting green in red does kind of similar thing, just little different. I know I can experiment with the operator, but I would prefer to have better understanding of it.
• 
  Jamie Dickinson

  Member

  March 29, 2023 at 7:25 am

  If you had someone with a red face wearing a blue shirt and use the blue channel (around 3 o’clock on the colour wheel) to subtract from the red output, it will swing the image away from red (towards 6 o’clock) but it will have more affect on the blue areas (where the blue channel has a high value) than on the other areas (where the blue value is low). So the blue shirt on the output goes towards cyan. That was my thinking.
  • 
    Zdeněk Klusáček

    Member

    March 29, 2023 at 7:31 am

    Ok makes sense. Thank you.
    • 
      Patrick Inhofer

      Administrator

      March 30, 2023 at 1:28 pm

      The visual way of thinking about it: If you pull up the vectorscope and look at the color channel being manipulated, adding more of any of the R/G/B channels shifts the color TOWARD that color. Removing any of the R/G/B channels shifts the color 180° AWAY from that color’s target on the vectorscope. So if you’re removing from a color channel it maps out like this: Red > Cyan, Green > Magenta, Blue > Yellow.
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