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



Mark,

I am not going to say that you did not experience what you say you
experienced; but I will say that is has not been my experience to date.
Nevertheless, whether your experience or mine is the normal case, it does
not really matter when one considers the conventional wisdom as stated by
the Steve Greenbank that one scans at the best optical resolution and
downsamples to lower resolutions in light of his stated goal of archiving
the file at the best quality for future uses at unknown sizes since one
downsamples a file one loses informational data that cannot be regained
apart from a new scan at the higher optical resolution.  When taken out of
this context, then our differences in experience may come into play and
become more relevant. However, taking the context into consideration is one
of the reasons why I suggested using Genuine Fractals to save the file in
and to resize and change resolution of the image using the wavelet and
fractal technologies to smooth out the grain structure and minimize the
gritty edges.

-----Original Message-----
From: owner-filmscanners@halftone.co.uk
[mailto:owner-filmscanners@halftone.co.uk]On Behalf Of Mark T.
Sent: Saturday, May 12, 2001 7:45 PM
To: filmscanners@halftone.co.uk
Subject: 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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