From:


To test it out, I took some photos of the sky at ISO's ranging
from 100 to 3200.


I can make a trivial de-noiser which will produce zero noise under your
test conditions: simply replace all pixels with the average value.

The reason I chose the sky for my test is because that's where the
noise usually shows itself in my pics. On areas with lotsa detail the
noise isn't so problematical. In fact, it sometimes may even look
beneficial as it adds artificial detail and texture to the scene.
Kinda like film.