Dear all,
I think we need to stop and think right here. The errors in pixel
values of images are neither Poisson (i.e. forget about taking square roots)
nor independent. Our ideas about image statistics are already disastrously
poor enough: the last thing we need is to make matters even worse by using
compression methods based on those erroneous statistical arguments!
With best wishes,
Gerard.
--
On Fri, Aug 24, 2007 at 01:20:29PM +0100, Harry Powell wrote:
> Hi
>
> Lossy compression should be okay, provided that the errors introduced are
> smaller than those expected for counting statistics (assuming that the
> pixels are more-or-less independent) - i.e. less than the square-root of
> the individual pixel intensities (though I don't see why this can't be
> extended to the integrated reflection intensities). So it's more important
> to accurately retain your weak pixel values than your strong ones - an
> error of ±10 for a pixel in a background count where the background should
> be 40 is significant, but an error of ±10 for a saturated pixel on most
> detectors (say, about 64K for a CCD) wouldn't affect anything.
>
> >On the question of lossy compression, I think we'd have to ask some data
> >reduction guru's how much the "noise" would affect the data reduction. I
> >suspect that the main problem is that the noise added would be
> >correlated across the image and would therefore affect the background
> >statistics in a non-trivial way. Although the intensity measurements may
> >not be badly affected the error estimates on them could be...
>
> Harry
> --
> Dr Harry Powell, MRC Laboratory of Molecular Biology, MRC Centre, Hills
> Road, Cambridge, CB2 2QH
--
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