This posting describes a way to match skin color and white balance in Darktable using a reference palette.
This works similar to color adjustmens with a grey card or a color checker. This time a defined skin color is the reference to match skintones to.
Get a palette
First you need a skin color as reference. You find many reference palettes on the web
Find one that matches your needs and download it as a graphics file on your pc.
This example uses the reference color ‘Apricot’, #F9D1B8
Create a watermark file
Convert the image file into a vector graphic. You can use Inkscape for that with the following parameter:
inkscape -f palette.png -l palette.svg
Import watermark into Darktable
Just copy the SVG file into you Watermark folder like described in the manual
Load a portrait image
If you don’t have one already I recommend some free RAW practice files. I took one of these ones:
Photographer: William Clark
Model: Jess Gagen
MUA: Grace Coole-Green
Hair: Stephen Manton
Open your image in Darktable and add the palette watermark to it.
Place the reference palette
Modify the watermark’s dimension and position so that the palette is near a ‘good’ skin part. ‘Good’ means:
- Nice and even color
- No shiny/white areas
- No shadows
Find the right color
Search for a palette color that is most similar to your ‘good’ skin tone
Get reference sample
Move the watermark away from the skin to a corner and take a sample from its color using the color picker.
Get skin tone samples
Add more samples from ‘good’ parts of the skin. The samples should have similar values for red since you will start your modifications with red color in the next step.
The color samples should be taken with the ‘mean’ color setting to get the average color of their selected areas.
Now match the samples’ brightness with the reference color. Increase the exposure until the red color reaches the reference.
Note that the SVG overlay is not affected by your edits, the reference color will remain the same.
Adjust white balance
After brightness of skin tone and reference are near to each other start to modify the white balance.
Since red currently matches the reference, green is the next color.
Note that the values of red are being affected. This is not a problem because we will modify each color a few times.
Continue with the blue color. After that you will find that red and green have moved away from the reference. Adjust the values for red, green and blue again until they come as near as possible to the reference. For red adjustments you take the white balance now, not the exposure anymore.
After these modifications you can revert your exposure adjustment if you want.