> Still, all this is academic and makes assumptions about the 'purity' of
> 16bit data which may be incorrect in practice. Like Margulis, I'd agree
> that empirical evidence matters more than theory. I know I have managed
> produce posterised sky areas in 16 bit, even with modest manipulations.
> Whether better or worse than if I'd used 8 bit I cannot say without
> returning to the image and trying both.
> Tony Sleep
> http://www.halftone.co.uk - Online portfolio & exhibit; + film scanner
> & comparisons
In my experiments I have found that a gamma correction of 1.5, say, in Nikon
Scan produces no posterisation whilst the same operation in Photoshop
produces fairly severe posterisation. Both in 16-bit.
Makes me feel nervous about PS. I notice, these days, that I can get PS to
posterise relatively easily - and no, I'm not talking about curves that have
horizontal or vertical sections or curves that double-back on themselves.
It's interesting to ponder whether grain/aliasing helps to hide "errors" or
makes them show-up more. There is, maybe, an argument in favour of
dithering the image (adding noise - preferably shaped in the frequency
domain - a bit like dither in digital audio systems) before manipulation, if
one's first attempt showed heavy posterisation, in a bid to perform the same
manipulation with less posterisation.