Using mask in DeNoise - whole image turns red?

I have an image in DeNoise and I’ve entered Mask mode. I have chosen “Sub” because I want to remove the noise reduction in select areas.

When I brush an area, the whole image turns red and I cannot see where I’ve brushed. Is this normal behavior? If yes, could someone please point me to documentation on DeNoise?

I’ve looked at several videos and searched the help on this site and I cannot find any help on the mask function.

The red should show the areas that you have brushed, either in or out. This is common with similar features in other apps too and often optional.
Actually, I have just taken a look at the masking feature myself, since I don’t use it. It is behaving very erratically I agree, and is also very slow to show what’s been masked and what not. I use it in Sharpen AI a lot and it’s always been fine.
Take a look on the main DeNoise AI thread for the version you are using (I am on the latest, ie 3.0.3) to see if anyone else has issues with it. It could be a bug.
I am on a MacBook Pro 2019 running OS Big Sur.

1 Like

If you want noise reduction to apply to only a certain part of your image, start by using the “Add” (not “Sub”). Then, mask the area where you want noise reduction. However, in some cases—like your example—it is easier to mask the area where you don’t want noise reduction, and then invert the mask (under “Options”).
You can always uncheck the “Overlay” option so that you can see what has been masked. The “Sub” option allows you paint over part of an existing mask to reduce its scope. Starting with “Sub” seems to make the assumption that the entire image has been masked (which is why the entire image turns red).

1 Like

When I played around with it earlier, I cancelled masking and started again, but the mask inset was still showing some areas in black and some in white. I seriously think there is an issue here. I have to add that this was on a low-light image so I had the brighten function turned on. I have now tested again on a correctly exposed image and haven’t had that issue.
However, on this image, it’s a pain to have begin on add rather than subtract, since it’s only a small part of the image that I don’t want denoise to be applied to. I suppose the best solution is to do a rough job with subtract and then go back to add and then to use the refine edge tool.

I may be misunderstanding the issue here, but for situations where you want to exclude a small portion from denoising, I think it is easier to mask that portion first and then invert the mask.

1 Like

Brilliant. I hadn’t thought of that, forgetting there is an Options pulldown with Invert as one of them.