I was playing around with Open Camera with a very long exposure (10 seconds), with a somewhat high ISO (3000ish), with my camera placed against a flat object so it doesn’t see any outside light. This is a great way of capturing sensor noise, though it does seem to be brighter around the outside, and less in the middle. Light leakage? Or just how the sensor works?
Anyways, I did that, and then played around with every nearly filter the stock photos app on my phone had, which results in some neat wallpapers.