|Cyan is a nice color touchup for black and white images, this example guides you through how to make this with darktable and how to control the tone. You can choose any tone of your like for this tutorial...||
This procedure uses monochrome, channel mixer and splittoning modules.
Prepare the image for the cyan toned steps by adjusting the base settings such as exposure,black level, contrast etc. for a correctly looking image.
Black and white
Enable the monochrome module (Section 188.8.131.52, “Monochrome”) to make the image black and white.
Add color tone
This step selects the base tone of the image using channel mixer (Section 184.108.40.206, “Channel mixer”), we are going for cyan tone but you can choose any tone that you like here.
Enable the channel mixer module
Select the red channel destination and set the red color value to 0.7
Select the green channel destination and set the green color value to 1.15
Select the blue channel destination and set the blue color value to 1.15
As you notice we mix blue and green color to get a cyan tone, we substract 0.3 from the red channel and add them to blue and green.
The result of the previous step does also add a color cast on highlights that we actually want to have white for a prettier result. We also want to add some blue color cast to the shadows in order to emphasis them. Module splittoning (Section 220.127.116.11, “Splittoning”) can accomplish this.
Enable the splittoning module
Select a blue/cyan tone for shadows and set saturation around 50%
Set highlights saturation to zero, to remove saturation on highlights
Set compression to zero
Use the balance slider to tune the effect, our example uses a balance of 70/30