A recent conversation on cinematography.net inspired me to work out a better technique for calibrating footage with the Color Checker Video Passport. I previously hadn't taken the time to fully understand the arrangement of the individual color chips until Adam Wilt's explanation made it click.
Here's a quick and dirty clip recorded on my Sony F3 in s-log in mixed lighting conditions:
The top has a shiny black, 40% IRE, and bright white target. On the bottom, the top row aligns with the vector scope (the big aha moment) and the second row is different skin color targets.
This is how the clip looks in Resolve when imported as is:
For this experiment a couple of quick nodes - a couple of garbage mattes that allows us to isolate individual aspects of the target on the scopes for easier workflow. And the last node with all the adjustments:
For step 1 we need to adjust the curve to offset the slog and bring the white and black into their legal ranges and set the middle gray around 40% IRE, using a curves adjustments. Once the ranges are sitting properly, decoupling the curves for the whilte balance on the RGB parade:
For step 2 on to the color calibration. Changing the garbage matte to the top row chroma chips bring up the star pattern nicely. On the right the RGB parade, which is impossible to interprete for that...
Because the white balance was already dialed in with the curves the color vectors are almost spot on. A small hue rotation adjustment of 3 degrees and some extra saturation refines the settings:
Lastly, switching to the last garbage matte highlighting just the skin color chips and turning on the skin color indicator on the vector scope confirms that the skin color is sitting perfectly:
Here is the final color checker with all adjustments:
From this clip we could now export a 3D LUT to be applied to the project or select clips, or the correction could be copied onto a group pre-clip node to apply to all clips that were shot under the same lighting conditions / camera settings.