This is an interesting question
(and this is how to achieve the Walter's suggestion which I agree with)
So, if you're ok to make it in Fusion, you could try this way. It doesn't require anything else than Fu and your eyes...
Prior to anything, spot the gain and gamma button below the viewer, click it and up the gain a bit to make any change obvious...
1/ add a blur node after your image (let's call this latter "mainpic"), and add just enough blur to treat the noise of an image.This kind of cheap & basic denoise process actually shows you the amount of blur you need to kind of denoise mainpic
You may want to try the same later on after separation of luma and chroma if you like, but I don't think it's necessary to master the global process2/ add a grain node after the blur one and also activate the dual view in this viewer : put the original mainpic on the left and the grain node view on the right. Now when you move the separation bar, you can see more left or more right image in the viewer.
3/ reduce the grain node power almost all the way left, probably until 0,0x and play with the grain size and grain softness in order to have this view look the same as the other one (original mainpic).
4/ Finally play with the red, blue and green "difference" sliders to fine tune.
Now moving the dual view bar in the viewer from left to right and backwards shouldn't show you any difference on the image : you can wipe the blur node and keep the Grain node : it's the grain of mainpic which is ready to be applied on another pic