Equivalent of Rawtherapee's Lab->chromaticity slider in Darktable

I spent about a year getting familiar with RawTherapee and then a roughly equal time fighting with Darktable. Now a deep breath. I’m trying to compare the two worlds.

Working over an ancient Adobe psd file from old scan of a an even older 35mm slide I found RawTherapee’s Lab->chromaticity to be particularly useful, for reconstructing the scan’s washed-out rendition of fall colors in Montana Cottonwood trees.

I’m not sure how to do the same thing with Darktable. Color Zones and various DT saturation sliders come close. But it’s not quite the same thing.

Is there a direct equivalent? Of RT’s lab->chromaticity in Darktable?

Rawpedia says:

The Lab Chromaticity slider increases or decreases the chromaticity of the image, by applying a contrast curve to the a- and b-channels of Lab space. Setting this slider to -100 removes all color, making the image black and white. The best way to convert an image to black-and-white is by using the dedicated and powerful Black-and-White tool in the Color tab.

http://rawpedia.rawtherapee.com/Lab_Adjustments#Chromaticity

This sounds like you have to go to the ‘tone curve’ module, set it to ‘LAB independent channel’ and add contrast to A and B channels.
(note that I am not a Rawtherapee user and may be wrong here)

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Interesting. That seems to work (darktable tone curve adjusted separately on A and B of LAB independent channel).

A tad less convenient but perhaps but a bit more flexible/powerful too.

In RawTherapee, you can also use the a and b curves if you prefer.

All very interesting.
Here’s a preliminary comparison summary, coming from a beginner’s amateur perspective rather than professional.

Both are a gift. Not only free but both are good softwares too.

RawTherapee is easier for beginners to dive into, for various reasons I won’t list just yet. But RawTherapee does (also) have strong stuff under the hood too, once you are ready to go there. It is easier for newbies to get started with.

Darktable is far harder to learn, perhaps because there are so many optional choices. The right side menu options often scroll off the screen for me (the yellow mask toggle button disappears for me when manipulating sliders at the top of the exposure menu. That’s probably because I’m old and have bad eyesight, and had to increase font size. That took a week to figure out. The vertical right-side menu options slider only appears on mouse over, so it’s hard to use, even when you know it’s there. On balance I am in love with Darktable.

I have 10 year old digital images that never looked so good.

The biggest difference, by far, between the two worlds is masking, which comes with the mix inside Darktable but not (not yet anyway) in RawTherapee. But that doesn’t mean you can’t use masking in RawTherapee. My workflow that way is to create various layers and masks inside Gimp and then to apply them to disparately edited versions of the same raw in RawTherapee. I like being able to create black and white masks in gimp and perhaps manually edit them with various brushes, shrink, expand blur etc. And then to reuse that same mask multiple times, for exposure, contrast color correction sharpening blurring etc. I can’t do that with the Mint Linux (set ppa update) apt-get install darktable I work with.

Global sharpening for long lens telephoto wildlife photography is a disaster because you still want a nicely blurred background. Masks are not optional. The only question is who how where and what way to use them.

Do I like one direction better than the other? Too soon to say. I use them both now. Thank you developers.

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I have not read the whole thread but the answer seems to be simple: it is the saturation slider in the contrast brightness saturation module. The module works in Lab.
However, I also use both programs and from my experience I can tell you that although in theory the two sliders are the same thing they just do not produce the exact same result. They somehow calculate differently. I personally like the way the saturation slider indt pushes the colors better. But white balace also has an influence on this. It is complicated…

Hello, I am new to pixls.us.
IMHO the best way to increase color saturation is using curves on the lab a and b chanels. It alows you to increase contrast independently on the red or green of chanel a and of the yellow and blue of the b chanel. Dan Margulus has written articles and books on how to work with lab color model. Althought based on Photkshop, one can easely adapt his ideas to RT or DT.

A more simple version of changing curve steepness would be the color contrast module.
Give this a try and see if it helps! :smile: