Add a luminosity / luma / luminance channel to the curves.
This allows for changing contrast without altering color.
Selective Tone controls seem to be working with luminosity . It would be great if I could make curves behave in a similar manner by selecting the luminance channel.
Hello @Skies,
Thank you for the feedback. Just to let you know, you can vote for your requests in the top left corner of the post.
Regards,
Svetlana G.
Actually, a luma curve does alter perceived colors.
For example, if you use a (very classic) ‘S-shaped’ luma curve, increasing midtones contrast, you’ll see that perceived saturation drops.
Using RGB curve is a simple and extremely common trick to compensate for that…with some drawbacks.
If you really want a (luma; luma) curve, then you may also need a (luma; saturation) curve. 
That would be even better 
In fact, I use Davinci Resolve for video grading, and it has some reeeeaaly nice curve options like ‘Hue vs Saturation’ and ‘Luminosity vs Saturation’ 
Yeah, for some reason video editing apps often give more control over colors than their photo editing counterpart. I never quite understood that…
(luma; luma) and (luma; saturation) curves are must have!
But we actually already have some control on (hue; hue), (hue; saturation) and (hue; lightness) through the color wheel.
But curves would be more flexible…
The color wheel would makes much more sense if we were able to select colors not only by hue, but other criteria (saturation and lightness).
In my opinion a luma curve is very important, and nothing exceptional, photoshop or capture one have it. For colors there are many other options, I’m not against to have rgb curves, I used them, but I would like change just luminosity without changing color saturation
Or maybe better :
A lab mixer wich let tweak lightness, A opponent and B opponent individually, each one based on lightness, A opponent, B opponent and offset sliders (as other photo software have). It of course has to convert color space on the fly, do the job, and convert back.
I want to add more support to this request, whether via a ‘Luma curves’ or LAB support.
Using the RGB curve creates colour shifts that are practically impossible to fully correct for. The lack of a Luma curve conflicts directly with DxO’s recent aim to improve colour control features.