As a preface, when you project the slide much of that grain is masked by the
surface texture of the screen you are projecting on as well as by the
distance you need to use to project to those projection sizes as well as to
view the projected image; but the grain is probably still there just as it
is in the scanned image ( this can be determined by looking at the
transparency under a high powered loupe). When you scan at 4000 dpi, you
are probably both picking up the grain as well as any other noise and
exaggerating it so as to make it more sharply defined and apparent.
Why are you scanning at an optical 4000 dpi? Could you scan at a lower
optical resolution if necessary? While for 35mm slides and negatives 4000
dpi optical resolutions may be good if you are going to engage in extreme
enlargement and/or cropping, they may not be required ( and even be
problematic in the case of some films and images) for prints 8x10 and under.
I have heard that one sometimes can scan materials that generate the sorts
of problems that you are experiencing at lower resolutions and save them in
Genuine Fractals' lossless mode to a .stn file, which upon opening can be
both resized to almost any size as well as upsampled with the added bonus of
frequently smoothing out the sharpness of the grain presentation being
displayed via its use of fractal and wavelet technologies. I have not tried
it for that purpose (e.g., to smooth out the sharp appearance of grain
structure displays); but if you are having the problem it might be worth a
try. None the less, I would reduce the scan resolutions and see how low you
need to go to eliminate the problem versus the minimum resolution you need
to output the portion of the image that you want at the size you want.
-----Original Message-----
From: owner-filmscanners@halftone.co.uk
[mailto:owner-filmscanners@halftone.co.uk]On Behalf Of Steve Greenbank
Sent: Friday, May 11, 2001 6:15 AM
To: Filmscanners@halftone.co.uk
Subject: filmscanners: What causes this and is there any easy solution ?
Today I'm going for the dual prize of most boring picture (see attachment)
and most dumb question ever on the list.
Mark asked me about a problem in the background of some pictures
The problem is that my sample (a bit of sky) from a slide projects with
perfect continuous tones at any size even 40 inch by 60 inch and it still
looks reasonably sharp (within reason) but yet when I scan it at 4000dpi I
get a grainy effect that will show up in an A3 print and a soft image in
general. The problem often gets worse with sharpening . I have found that a
unsharp mask threshold 9+ usually avoids sharpening the graininess.
Alternatively a gaussian blur removes it but if you do this to the whole
image you end up with an even more soft image but on the plus side you can
sharpen it more aggressively and use a threshold of 3-4 which means much
more gets sharpened.
Obviously carefully selecting the sky/problem area and blurring that
separately is probably the best option but it takes ages to do this
accurately and you still may get noise problems elsewhere.
Am I right to assume the noise is grain, CCD noise and chemical faults on
the film ?
Does every see this noise ?
Should I see less with SS4000/A4000 scanner (is mine and Mark's a bit duff)
?
And what do you do about it ?
Steve
