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



Yes, I see the "noise," and it looks like classic grain-aliasing to
me...brownish pixels in a blue sky shouldn't be there, unless it's Los
Angeles or Cleveland or __________ (your least-favorite city goes here)! :-)

The solution looks so easy that I probably don't understand the problem
completely. :-) There are two quick ways you can do corrections:
1) make two scans the same size in Vuescan; one normally, the second with a
slight positive offset of manual focus (about +1 to +1.5). The second scan
will have "corrected" much if not all of the g-a, and the subject will be a
little blurred--but surprisingly little (you might even decide to stay with
that one, unless you're doing large blow-ups).
2) load the first scan into Photoshop or your favorite image processor.
Select "All" and copy it. Then load the second frame in (it's OK to delete
the first one without saving, since you have a copy). Paste the copy over
the second, blurry copy, and Erase the sky from the top layer down to the
blurred layer.

If you can get a Selector to work, like the Magic Wand for example to select
just the sky portions (I almost never can--I think the wand is over-rated),
it's even  simpler--select the sky only, and have-at-it with any or all of
the blur filters. :-)

Another way is to use Channels (if they're available in your programs)
either to select and copy a mask, or--as I'd say in this case--to isolate
the redish pixels in the sky and eliminate them.

My having said this, someone will invariably point out to me that I missed
the problem in the first place. But this time, I beat you to it in the first
paragraph! At least I tried. ;-)

Best regards--LRA

PS, the suggestion to reduce the resolution was valid--but NOT on the
scan--that makes it worse! Reduce the dpi by resampling.
BTW, I'm sending you a copy of my tongue-in-cheek report "under seperate
cover," and it covers some of this stuff, too.

------Original Message------
From: "Steve Greenbank" <steve@gccl.fsbusiness.co.uk>
To: Filmscanners@halftone.co.uk
Sent: May 11, 2001 11:15:00 AM GMT
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
http://www.grafphoto.com/grain.html

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


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