There are different ways to remove or reduce noise, and there are also ways of removing watermarks from images. But Nvidia has recently introduced a deep learning-based approach which has learned to fix photos by looking only at corrupted photos.
The quality of long exposures is determined mostly by the amount of noise a camera produces. The lower the noise levels, the better the exposure. This is especially true if you are shooting lots of nightscapes or night skies, where most of the photo is black.
And Brendan Davey shoots a lot of night photos, in fact he shoots enough of them that it was worth a while for him to create a database which compares the amounts of noise each camera (or camera sensor) produces.
When it comes to noise in photos, we are pretty accustomed to using DeNoising tools. When it comes to video, there are similar options that apply that same logic to footage, rather than to a single frame.
The folks over at Film Riot took two of the more popular options, Neat Video and Denoiser II (both at about $100) for a test drive and compare the results. Ryan talks about a third plugin called Dark Energy which he says surpasses them both, but sadly, it fell of the comparison for costing $100 more.