Since its early beginnings darktable has a tone curve module that is able to alter the gray level distribution of an image. Recently we did an enhancement: tone curve is now able to control the full Lab color space with separate curves for the L, a and b channel. People who are used to curve tools in RGB, at first might get puzzled over the results of these three curves; they show marked differences to the typical RGB curve. Especially a and b channels need to be dealt with in the right way; not doing so will give you strong off-colors. To spare you frustration here are some explanations and examples.
Thnk you for your well written article !
Kindly help me figure out as to how to change the luminance of the ‘A’ or “B” channel using the tone curve module [or an alternate module]
[In photoshop I would ‘apply’ the ‘A’ or ‘B’ channel to luminance channel in overlay blend mode …]
kindly advice if a manover here will give me equivalent outcome…thanks …regards
The advanced changes in DT color science isn’t supported by the tone curve module and the Lab color space but I think if you want to use it you can use the blend mode for the a channel…going a bit from memory as I am not at my computer but I think there are modes to blend in lab L A and B channels…