Small step in understanding Color Calibration

[BorisRabit]

Well, I solved a little mystery for myself earlier and I thought I would share. Apologies if this was obvious to others, it was not obvious to me.

I had two instances of Color Calibration in use on a photo, and was wondering if I could just combine the adjustments into a single instance to make it easier to apply to other photos. (Anyone guess where this is going, yet?)

Using just the first instance, photo loaded with the camera’s custom white balance from shooting a gray card:

Now here is with the second instance of Color Calibration, with small tweaks to the Green and Blue output tabs (along with an exposure adjustment to compensate):

“sigh,” I thought. “This would be better if I just put all these adjustments together.” Well, the result was …

screams…

Spot my mistake?

I found this in the manual: " Channel mixing is performed in the color space defined by the adaptation control on the CAT tab."

This applies to the R, G, and B output tabs as well (Yep, that didn’t dawn on me; color me embarrassed). If I take that second instance of Color Calibration and set “CAT16” and “same as pipeline” on the CAT tab, the same thing happens as when I mistakenly combined them:

If you’ve made it this far, thank you for taking the time. I don’t post here all that often, but I’m happy the community exists. You’ve helped me through a lot since I started visiting. This little girl wasn’t even born yet when I found you, and SARS-COV-2 wasn’t a thing.

I only recently started using the extra tabs in Color Calibration to make corrections. It hasn’t been as scary as I had worried it would be. I look forward to using the new modules for color adjustments I’ve been reading about here when they land this Winter Solstice.

– Russ

[Terry (Terry Pinfold)]

Hi Russ,
unless I am missing something very obvious, I don’t see a need to use two instances of CC in your case. I sometimes use two instances and use localised masks for the second instance when I have mixed lighting.

[BorisRabit]

Maybe one instance would work, but copying the settings from an instance with adaptation set to bypass to the main instance set at CAT16 did not work. It took me a while to figure out what had happened. I’d imagine the same goal could eventually be reached using one instance. but the numbers themselves would be different.

I like to use a second instance from the one used for initial white balance because I can turn it off and on.

[priort (Todd Prior)]

If you start with the default CC then it performs the CAT. If you set it to same as pipeline then no CAT but the other tabs will work in the selected CAT space. If you set it in bypass no CAT and the colorspace will be the working color space… So there can be 3 conditions under which your adjustments are made… I don’t think this precludes getting the same result but the same slider values will be different …not sure how visually different in each case…

I guess what one would ask is what would be the goal of making a color change with the channel mixer or other tabs in the Cat space vs the Working space… I don’t have a clear answer… Maybe to allow for a custom CAT

[kofa (István Kovács)]

The masked application is for when you have two different light sources, each illuminating an area.
Two instances, one with CAT, the other without, is different: the 2nd instance is basically a channel mixer. There’s even a preset for that.

@BorisRabit : you’ll probably like the new rgb primaries module coming in darktable 4.6, which is an alternative interface to the channel mixer, making it easier to use. It will even be embedded into sigmoid (but can also be used on its own). New Primaries module

[BorisRabit]

I’m sure I will like the new module, thanks. It’s because I’ve been reading about it that I started experimenting more with Color Calibration. I have not compiled from master recently, as I normally wait until a point release to do so. Depending on how badly I want the new module, I may make an exception.