Luma adjustment without increasing saturation?

[Nicolas Hanson]

How can I adjust the luma without increasting saturation/changing chroma? Thought I could use the luminance lift/gamma/gain only for this, but it looks like it affects the chroma as well.

[Yoav Raz]

Hi there Nicolas

I think in resolve you can use the curve Y only 

cheers Yoav

[Nicolas Hanson]

Thank you. How is the y only curve different than the lift gamma gain individual luma only controls when it comes to saturation?

[Orash Rahnema]

It's not different, the problem with y curves or lgg is that perceived saturation is less when y gets brighter then RGB ad the reletionship between the three chanell behaves like that, contrary when y decrese saturation appear stronger. 

The thing is that y is a derivation of the reletionship of RGB , It doesn't really exist by itself so RGB Will always bè effected in someway. 

To get what you are looking for you need a different math. 

Using a lab colourspace you can control the luminance only chanell

Another way is to get a layer node and set the composit mode to luminance. Then on the second input change lgg to taste

[Nicolas Hanson]

I will try LAB colorspace as suggested, as it seems like the chroma is affected with both lgg luminance only adustments and y curve. Most times this will not be a problem, but I need total isolation for a particular project I'm working on. 

[Anton Meleshkevich]

I used luminosity blending mode on a layer mixer node for this task on my last project.

[Jussi Rovanperä]

11 hours ago, Nicolas Hanson said:

I will try LAB colorspace as suggested, as it seems like the chroma is affected with both lgg luminance only adustments and y curve. Most times this will not be a problem, but I need total isolation for a particular project I'm working on. 

You can't really isolate Luma from color, those will always affect each other, because the output is still RGB, and it's easy to push values out of gamut with Luma/Chroma corrections. For example you can't have dark saturated yellow or light saturated blue, those are way out of gamut, but the Luma/Chroma tools will happily try to push the color there, and clip the color channels.