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



>So the projection effectively helps mask the grain what a happy coincidence

While there maybe some merit to your comments about dust in the air masking
flaws in the slide being projected, I had the actual surface texture of the
projection screen in mind as well as the actual viewing distance independent
of any dust.  The further away from the screen you view the image the less
likely you are to see things like grain in that like a Surrat painting your
eyes tend to blend the individual particles of grain into a single
continuous tone structure even though under a loupe or standing up close you
will still see the individual grains.  As for screen texture, most screens
have a pebbled or/and rectilinear surface intended to gather and concentrate
light so as to make them brighter (they are not smooth surfaces without any
texture); this surface texture also tends to break up individual noise and
grain patterns so as to mask the grain structure of what is being projected
unless it is really very graining so as to have the appearance of an old
newspaper 65 line screen halftone.

>Lower sampling rates lead to higher noise to signal ratios.

I think there is probably a point at which there is NO PERCEIVABLE decrease
in the signal to noise rations and further increased optical resolutions are
of little practical point except to permit increases in output sizes while
still maintaining a reasonably high quality non-interpolated resolution or
to permit cropping and enlarging of small portions of the original while
maintaining reasonably high quality non-interpolated resolutions.  Most
monitors cannot use resolutions over 100 dpi and most printers cannot use
resolutions over 300 dpi.  Since the less noise you have the more apparent
the display of grain will be, it may be a good thing to compromise and allow
some noise to be introduced in order to tone down the sharp appearance of
grain structure.

>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.

Although resampling down from 4000 dpi may or may not reduce the appearance
of noise but not the actual existence of noise, b it also will result in the
loss of informational data that cannot be gained back later and the possible
production of other troublesome artifacts.  The reduction in resolution that
does reduce signal to noise rations is not via the use of resampling but via
the actual reduction in optical resolutions being used from 4000 dpi to some
optical resolution under that if your scanner has an optical resolution of
4000 dpi.  If it has a maximum optical resolution of less than 4000 dpi than
any scan over that is an interpolated scan that has been upsampled by the
scanner software and not an optical resolution, while any scan less than the
maximum optical scan resolution is an optical resolution.

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.

What I was suggesting was that if you compromise and reduce your scan's
optical resolution by 500 to 2000 dpi you might be able to reach that sweet
spot for that particular image and film combination where the noise is not
all that perceivable nor is the grain structure of the original.  Remember
different films have different grain structures and different images display
grain differently.  An optical resolution that is optimum for one type of
film and image combination may not be optimum for another.  In short some
grain structures scan better than others and allow for higher optical
resolution scans than others.

>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.

A little over ambitious and over optimistic with expectations that might be
a bit too high. Technically, you will always get better prints from film
than from digital as of the digital hardware available today, although that
is changing and may not be true in the near future.  Besides, I thought we
were talking about transparencies (i.e., slides) that were being projected
at some point and not negatives; hence, I do not understand your remark:
"...I don't see a lot of point in archiving them digitally if I can still
get better prints from the fading original."  Are we talking about color
negative film of slide film?  There is a difference and that difference
entails some differences in how they scan comparatively.  Transparency film
tends to be a lot more contrasty than negative film which can result in
emphasizing the grain structure more than is the case for negative films;
also negative films are more within the dynamic range of consumer film
scanners than transparency films which means that the latter tend to block
up in the highlights and shadow areas more when scanned.

>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.

My suggest was not to do the resampling via Photoshop or some other image
editing application but specifically with GF in both directions.  By
resizing back to 4000 dpi using Photoshop or some other image editing
program  and not GF, you defeated the purpose of the exercise which was to
let the GF technology work for you in smoothing out the noise and grain
structure.  The other forms or modes of resampling use different
technologies which will not result in any smoothing but may produce the
opposite.  As for GF being slightly better in the 2x-3x range, I am not sure
what you are referring to; I have found that it works just as well if not
better with respect to both resizing the image as well as re-resolution the
image at much higher ranges than that (e.g., the 10x-15x range).  I have
been very successful resizing a portion 2 1/2 x 3 1/2 @ 600 dpi image to a
16 x 20 @ 600 dpi image which printed out without any artifacts, unwanted
noise, or unexpected grain.  GF does have a sweet spot in terms of the file
sizes that it works best on (which are in the 20-40 MB range); but it does
work well with smaller and larger file sizes - although larger file sizes
take forever to encode and decode.

However, you failed to say if you tried the GF demo which limits the size
files you can work with to small to moderate size files no larger than
around 40MB or the full retail version of GF which has no such limitation;
you also neglected to mention if you used lossless or virtually  lossless
modes of encoding in GF.

By the way, GF comes closest to filling you desire for an archiving solution
that "... 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."  The only
drawback is that you would have to save and keep the files in GF's .stn
format, which would require GF to open and resave the files - at least for
the present.  This means that we do not know if in the future GF and .stn
format will disappear or if it will become an established standard format
like JPEG and TIFF which all image editing programs will open and close,
encode to and decode from.

-----Original Message-----
From: owner-filmscanners@halftone.co.uk
[mailto:owner-filmscanners@halftone.co.uk]On Behalf Of Steve Greenbank
Sent: Saturday, May 12, 2001 5:40 AM
To: filmscanners@halftone.co.uk
Subject: 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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