[ericwbenson (Eric)]

Originally Posted by LightningNZ

Two points here:
1) Noise may be quantified but only by estimating a distribution. You cannot know the exact noise term in each pixel and remove it perfectly leaving only a perfect image.

This is true, and hence why decon is a "wicked" problem.

Originally Posted by LightningNZ

2) As I already mentioned in an earlier post, you cannot model right across the whole changing wavefront of the sky, so some approximation is always to be expected. This is no different from estimating the dark noise, bias noise, amplification noise or shot noise for any given pixel.

Not exactly sure what you're getting at. But remember calibration does not remove noise (dark, bias or shot, it actually adds some itself), it only removes unwanted signal (dark, bias, fixed pattern and vignetting), that is artificially added by the measurement system. Decon is not removing a measurement artefact, the smeared wavefront is the same no matter what telescope/camera is looking at it.
As a byproduct of decon optical aberrations can be 'removed' (if your algorithm is good enough, e.g. TinyTim for the blurry Hubble) since the decon assumes the original PSF was a symmetric gaussian/moffat etc, and that's where it steers the solution. I've never had any success with that however, bad data due to miscollimation or the like always sticks around to annoy...

Originally Posted by LightningNZ

I've never seen this written before and I think it's not strictly true.

Well, here's another way to look at it, notwithstanding wikipedia : the image contains information, decon reallocates that information. Decon is not a free lunch, the amount of spatial resolution gained is limited by (among other things) how much signal to noise contrast you can/want to give up.

Originally Posted by LightningNZ

This says that deconvolution will always be limited by SNR but it is NOT a trade-off.

Sorry I don't understand how you draw this conclusion.

Originally Posted by LightningNZ

You imply with your statement that "you can always improve SNR" that the possibilities of decon are endless and that you could somehow achieve better resolution than half the wavelength of the light you are looking at - you can't. You can restore to this point, and the question of what can be resolved varies by empirical measure (Dawes, Rayleigh, etc), but you can't beat it, ever.

Wait a sec...you can always improve the SNR of the raw data, just collect more data (granted it's asymptotic but not if you get a bigger scope...)
Where did I say the possibilities of decon are endless?? They are in fact quite the opposite, decon in most cases gives a marginal or no real improvement to the image since it can easily create structures that aren't real by amplifying noise. Doing decon right is not easy at all, the best way is to have really good data to start with, and be very careful as you wield that sword.

EB