In the end it comes down to signal-to-noise. The default gain is quite low, I have to gamma-boost it for people to see *anything* indoors. That's the main source of noise - with default settings it's not that noisy, except you can't see anything. I already experimented with hooking up the noise reduction elements from the main cam to see if it can help mirror, but there seem to be some hard-coded values in there which make this difficult to do in a way accessible to users (and since it's a Nokia license I can't even clone/tweak it as another element).

EDIT: I *could* trade resolution for less noise, e.g. get 320x240 via binning (this is not the same as recording in 320x240 !), but that's a lot of CPU usage there unless I can harness the DSP.