DT tone curve - automatic scale chroma strength


When using tone curve in Darktable, I usually leave “scale chroma” set to “automatic” to prevent perceptual under- or over-saturation of the result. However whenever I do stronger curve changes, I usually find that the chroma scaling is just too strong - the saturation is increased or decreased too much and to my eyes it just does not remain perceptually the same as the original. Did anyone else notice this?

For simplicity I’d like to avoid having to change the a/b curves manually, it would be great to have a “strength” slider for the auto chroma scale. Or is there some easy workaround? Sometimes the “automatic in XYZ” or “automatic in RGB” options provide better (less saturated) results, but it’s not ideal.


(Christian Kanzian) #2

Yes, you can use blending mode coloradjustment as described here:


Actually you cannot achieve similar results of “automatic” chroma scaling by manually changing the a/b curves. The reason is that automatic chroma scaling works based on luminosity (i.e. decreases saturation for shadows and increases it for midtones). The coloradjustment blending mode is the only way to tune the amount of automatic chroma scaling IMO.


Thank you, that’s exactly what I needed!