At ISO 100 the Olympus TG-820 produces clean, noise-free images.
ISO 200 is similarly free of noise with good shadow detail.
At ISO 400 a hint of noise creeps in, but it's not to any great detriment of general image quality.
ISO 800 is where noise becomes more visible, even at smaller image sizes.
ISO 1600 shows a marked softening and loss of detail as the TG-820's noise-reduction kicks in.
ISO 3200 sees a huge drop in image quality with shadow areas reduced to an indistinguishable blur.
You'll be able to get an image in very dim light at ISO 6400 but the image quality will be dreadful.