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RE: filmscanners: What causes this and is there any easy solution ?



At 11:43 AM 12/05/01 -0500, Laurie wrote:
>While it is true that the conventional wisdom suggests that one scan at the
>highest optical resolution you scanner will permit; I do not believe it
>recommends downsampling as an the suggested practice for acquiring a lower
>resolution as contrasted to rescanning the original at the required lower
>optical resolution.  Resampling upward or downward in the scanner or
>elsewhere is a last resort option and not a recommended standard practice.

I'm not sure I agree with this theory.. My experience is that if I want, 
say, a 6x4 print at 200 dpi (ie 1200x800), I get perceptibly better results 
from an original scan of at least 2400 x 1600, that has been resampled 
down, and very lightly sharpened.  Edges are smoother, and even things like 
fleshtones are smoother and less 'gritty' ( a new technical term?)  I did 
some tests on this a while ago with a 1770 dpi  film scanner - I should 
have another go now at 2720..  If anyone's interested I'll post results.


And earlier, Art wrote:
>I am beginning to develop a theory about these anomalies that appear in 
>scanned images.  Is it possible that the CCDs are recording information 
>outside of the realm of human vision?  What I mean is could we be seeing 
>artifacts of either IR or UV (or other spectrums) information which are 
>being translated into the visible spectrum?

This intrigues me.  On an awful old Kodacolor 200 negative where I was 
trying to extract a very underexposed image, I was getting very annoyed at 
the rainbow coloured grain-aliasing/noise in the clearest areas of the neg 
(ie darkest areas of image).  Out of interest, I rescanned it upside down, 
and lo, the noise was in exactly the same pattern, ie on the film.  So it 
wasn't 'noise' at all.  I then stuck the neg in my slide projector to see 
what the scanner was 'seeing', and sure enough the patterns correlated very 
well to the horrible 'grain' I could see in the clear areas of neg.  When 
printed using conventional processing, this effect is almost invisible, 
partly I guess because of the nature of the diffused light source, and the 
fact that these grains are not really colored(?).  But maybe it also has to 
do with CCDs ability to see IR so well, and of course the blue noise 
problem, and aliasing.... sigh...

So what's my point? :)  Just that if we can determine the factors that are 
causing this problem, maybe there are ways to undo it, closer to the 
source.  I can but dream..

Mark T.






==========================================
Mark Thomas   markthom@camtech.net.au
http://www.adelaide.net.au/~markthom




 




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