How to use "Denoise" on a secondary rendered image I can achieve that by rendering the image 2 times, but only using denoise on the first image. But that would double my render time, so i can't do that.

I want to use denoise, but on some places of the image i don't want denoise so i want to erase the denoised image and reveal the underlying non denoised image in photoshop.
Maybe there is a way to use "denoise" on compositing stage.?

Is this possible?
Just create two render layers and turn on denoising only one of them. You will get both image the same time.