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



----- Original Message -----
From: "Laurie Solomon" <laurie@advancenet.net>
To: <filmscanners@halftone.co.uk>
Sent: Friday, May 11, 2001 5:13 PM
Subject: RE: filmscanners: What causes this and is there any easy solution ?


> 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.
>

So the projection effectively helps mask the grain what a happy coincidence.
The point about the distance may be the main reason. In a normal room you
switch on the projector (with no slide if you have a relic like me) and
suddenly realise that you have dust floating everywhere. Over a longer
distance there will be more dust that will effectively randomly filter the
smallest details i.e. the grain.  I wonder if you used the screen in a chip
FAB unit (exceptionally clean environment) whether the grain would be more
apparent.

> Why are you scanning at an optical 4000 dpi?  Could you scan at a lower
> optical resolution if necessary?

Lower sampling rates lead to higher noise to signal ratios.
Whilst resampling down from 4000dpi will reduce noise to signal ratios.
I am pretty certain that it is always best to scan at best optical and then
resample down if you require a lower resolution.

> 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 am hoping to archive the pictures in a form that will allow any one to be
selected at random to be output at any size that I may require at that time.
Perhaps I'm being a bit over ambitious, but I don't see a lot of point in
archiving them digitally if I can still get better prints from the fading
original.

> 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.
>

I did try this by resampling a 4000dpi to 2000dpi and 1333dpi and then
resizing back (without GF), but you have to reduce the pixel count too much
and you are better off blurring the original. GF would have produced
marginally better results, but in my experiene GF is slightly better in the
2x-3x range not a miracle worker so I still think a slight blurring would be
better.

> -----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
> 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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