Matching Color Balance
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Divide and Multiply
Welcome to a quick tutorial on how to seamlessly color match poorly shot or strongly color-imbalanced source footage with a clean piece of CG or a screen insert. By utilizing basic division and multiplication within a linear color space in DaVinci Resolve, you can perfectly integrate your elements without the guesswork.
Here is how you can set up this simple, highly effective workflow.
Convert Your Source Footage to Linear
The footage used in this example is Blackmagic RAW shot on a Sony FX30. Because this specific project is not color-managed, the first step is to get the original footage into a linear working space using a Color Space Transform (CST) node.
Set the input color space to S-Gamut3.Cine and the input gamma to S-Log3 to match how the original material was shot.
Leave the primary color space settings alone so you do not apply an unnecessary extra color matrix.
Change the output gamma setting to Linear.
Turn off tone mapping to ensure the footage is perfectly set up for compositing.
Prepare Your Output and Viewer
Before you begin compositing, you need to ensure your output returns to its original state and that you can actually see what you are doing.
Copy your initial CST node, paste it at the end of your node tree, and hit the swap button to invert the transform back to log.
Turn on the Viewer LUT in the upper right corner of the Fusion page, because linear footage is not meant to be viewed on standard monitors.
Edit the Viewer LUT settings by changing the input color space to match your working space, which is S-Gamut3.Cine Linear.
Set the output to Rec.709 or sRGB depending on your monitor, and turn on tone mapping to view the footage properly.
Match the Screen Insert Color Space
Your CG or screen insert. This likely has no color imbalance at all. You must bring this insert into your linear working space.
Add a new CST node directly after your screen insert.
Set both the input color space and input gamma to sRGB.
Set the output to S-Gamut3.Cine Linear.
Turn on Apply Inverse OOTF, which helps properly calculate the sRGB input going from a display to scene space.
Remove the Color Cast Using Division
Instead of trying to manually color correct the screen insert to match the imbalanced plate, it is much easier to remove the color cast completely from the source footage, composite your elements, and then reapply the color cast at the end.
Add a Channel Booleans node (the one labeled with an 'S') and set its operation to Divide.
Set the alpha channel operation to do nothing.
Add a Background node and use the color picker to sample a neutral area in your original footage, such as a white Starbucks cup.
Connect your source footage to the background input and your sampled color to the foreground input of the Channel Booleans node to divide out the linear color imbalance.
Composite and Reapply the Cast Using Multiplication
With the color cast removed, you can composite your screen insert (A over B) in a clean environment. You can even add original plate reflections back on top of the insert by using a Merge node with the alpha gain set to zero, restricted by your corner pin alpha.
Once the composite is built, it is time to reapply the color cast to the entire image.
Add a second Channel Booleans node right before your final log-conversion CST node.
Set the operation on this node to Multiply, which acts as a linear gain.
Use the exact same color-sampled Background node from the division step to multiply that color imbalance back into the stream.
Conclusion and Alternative Tools
By dividing out the cast and multiplying it back, everything integrates beautifully. Reapplying the original light also naturally takes care of lifting the black levels of your insert. When you return to the color page, you can grade the entire shot as one cohesive piece of media.
If you want an alternative to standard Channel Booleans, look into the Grade Fuse tool available on Reactor from Muse. It includes a built-in reverse function, allowing you to easily reverse a correction, do your compositing work, and reapply the correction without needing separate divide and multiply nodes.
