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difficulty drum scanning negatives



 
 
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  #1  
Old March 31st 04, 06:34 PM
Jytzel
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Default difficulty drum scanning negatives

I sent some negatives and slides to drum scan to have the operator
claim that negatives show more grain in the final scan than slides. I
used 6x6 Fuji NPS 160, a film has low granularity rating. The other
film I used was E100G slide film. I find it hard to believe the
operator's claim. It seems that he is doing something wrong. What
could it be and how to get the best scan out of my negatives?
By the way, they use Crosfield drum scanners.

thanks
J
  #2  
Old March 31st 04, 09:56 PM
Don
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Default difficulty drum scanning negatives

This sounds like grain aliasing. The mathematics of this are rather complex
because it involves the MTF of the scanner spot and lens, the line spacing
of the scanner, and the grain size distribution of the film being scanned.
It occurs when the grain size is small enought that it exceeds the Nyquist
limit of the sampling process. It results in the high frequency portions of
the grain being duplicated as lower frequency noise, and adds to the normal
low frequency component of the granularity. The result is an apparent
increase in granularity.

There are only two solutions to this that I know of. The first is to
introduce an anti-aliasing filter in the optical path of the scanner. This
almost has to be done by the manufacturer of the scanner, as it must be
carefully matched to the MTF of the spot and optics. The second solution is
to scan with a higher lpi and a smaller spot size (and better lens MTF). If
that can be done with the scanner that you are currently using, you're in
business. Otherwise, you will need to find a scanner that can handle film
with the small grain size that you have.

Don



"Jytzel" wrote in message
m...
I sent some negatives and slides to drum scan to have the operator
claim that negatives show more grain in the final scan than slides. I
used 6x6 Fuji NPS 160, a film has low granularity rating. The other
film I used was E100G slide film. I find it hard to believe the
operator's claim. It seems that he is doing something wrong. What
could it be and how to get the best scan out of my negatives?
By the way, they use Crosfield drum scanners.

thanks
J



  #3  
Old April 1st 04, 01:15 AM
Kennedy McEwen
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Posts: n/a
Default difficulty drum scanning negatives

In article , Don
writes
This sounds like grain aliasing. The mathematics of this are rather complex
because it involves the MTF of the scanner spot and lens, the line spacing
of the scanner, and the grain size distribution of the film being scanned.
It occurs when the grain size is small enought that it exceeds the Nyquist
limit of the sampling process. It results in the high frequency portions of
the grain being duplicated as lower frequency noise, and adds to the normal
low frequency component of the granularity. The result is an apparent
increase in granularity.

There are only two solutions to this that I know of. The first is to
introduce an anti-aliasing filter in the optical path of the scanner. This
almost has to be done by the manufacturer of the scanner, as it must be
carefully matched to the MTF of the spot and optics. The second solution is
to scan with a higher lpi and a smaller spot size (and better lens MTF). If
that can be done with the scanner that you are currently using, you're in
business. Otherwise, you will need to find a scanner that can handle film
with the small grain size that you have.

With a drum scanner the spot size (and it's shape) *is* the anti-alias
filter, and the only one that is needed. One of the most useful
features of most drum scanners is that the spot size can be adjusted
independently of the sampling density to obtain the optimum trade-off
between resolution and aliasing to suit the media being used, but there
is usually an automatic option which will achieve a compromise at least
as good as any CCD device.

I doubt that this is just aliasing though, especially if both were
scanned at 4000ppi or more. Remember that negative images are
compressed on film (the corollary being that negative film has more
exposure latitude and the ability to capture a wider tonal range).
Consequently, when producing a positive from the film image, whether by
scanning or by conventional chemical printing techniques, the image must
be contrast stretched. So, even if the grain on the film has the same
amplitude as the same as in slide film (a reasonable assumption for
similar speed films of the same generation from the same manufacturer,
the resulting image from the negative will always appear more grainy
than the image from the slide film.

There is a lot of truth in what the drum operator told Jytzel. Whether
its the truth, the whole truth and nothing but the truth is another
story. ;-) However, when viewed at 100% scaling, the size of the
original has little bearing on the results so I would expect to see more
grain on the 6x6cm negative image than from the 35mm slide under those
conditions.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's ****ed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)
  #4  
Old April 1st 04, 07:21 AM
David J. Littleboy
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Posts: n/a
Default difficulty drum scanning negatives


"Jytzel" wrote in message
m...
I sent some negatives and slides to drum scan to have the operator
claim that negatives show more grain in the final scan than slides. I
used 6x6 Fuji NPS 160, a film has low granularity rating. The other
film I used was E100G slide film. I find it hard to believe the
operator's claim. It seems that he is doing something wrong. What
could it be and how to get the best scan out of my negatives?


I also find that negative materials scan grainier than slide films (although
I haven't tried either of those films). Try shooting some Reala
Konica-Minolta Impressa 50.

Here's a page with a lot of scan samples to get an idea of what to expect.

http://www.terrapinphoto.com/jmdavis/

David J. Littleboy
Tokyo, Japan


  #7  
Old April 1st 04, 04:40 PM
David J. Littleboy
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Posts: n/a
Default difficulty drum scanning negatives


"Paul Schmidt" wrote:
Gregory W Blank wrote:

What are the best films for scanning say one or two brands/types
in each of these categories:

B&W (what's best old tech, new tech, chromogenic)


None of the above. Silver films don't allow the use of ICE* and the
chromogenics are grainy (this latter one is a minority viewpoint: my
definition of "acceptable grain" is Provia 100F, and the chromogenics are
seriously gross compared to Provia 100F.)

*: I've only scanned one roll of silver film: Tech Pan. It was quite gritty
(the lab that processed it may have messed up: I was expecting it to be the
eighth wonder, and was disappointed) and dust stood out incredibly
obnoxiously against the grain. (There's no dust in the crops below, though.)

http://www.terrapinphoto.com/jmdavis/ugly-c1.jpg
http://www.terrapinphoto.com/jmdavis/ugly-c2.jpg

Colour Consumer films ( what's best Slide or Negative?)


The scans I've seen of these indicate they should be avoided at all cost.
One exception: Sensia.

Colour Pro films (what's best Slide or Neagtive?)


Here, the usual suspects are all fine. My favorites a

Negative: Konica Impressa 50, Reala
Slide: Provia 100F, Velvia 100F, Astia 100F

David J. Littleboy
Tokyo, Japan



  #8  
Old April 1st 04, 04:57 PM
Bill Tuthill
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Posts: n/a
Default difficulty drum scanning negatives

In rec.photo.film+labs Gregory W Blank wrote:

I find NPS to be really a horrible film to scan for whatever reason,
E100 films are T grain color emulsion. NPH (400 asa) scans better
than NPS.


Agreed. NPS *is* grainier than 100G using the 2.5 RMS conversion formula:

NPS RMS 4 * 2.5 = 10
100G RMS = 8

Currently 100 speed slide films are better (lower grain, higher resolution)
than 100 speed negative films, with the possible exception of Reala.

However 400 speed print films are better (lower grain, higher resolution)
than 400 speed slide films, although Provia 400F is better than some.

  #9  
Old April 1st 04, 05:07 PM
Gregory W Blank
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Posts: n/a
Default difficulty drum scanning negatives

In article ,
Paul Schmidt wrote:

What are the best films for scanning say one or two brands/types
in each of these categories:
B&W (what's best old tech, new tech, chromogenic)
Colour Consumer films ( what's best Slide or Negative?)
Colour Pro films (what's best Slide or Neagtive?)
Paul


I don't use consumer films only Pro films.
I don't shoot chromogenic B&W film.
At this point I primarily shoot MF &LF
so my experience may differ somewhat
but I agree with David that Provia 100
is one of the best, The kodak E films
are also very good in terms of grain however
I tend to like fuji film for color. As for B&W
I get really good scans from most of my B&W
negatives, mainly because I shoot 4x5 so grain
is a much smaller issue.
--
LF website http://members.bellatlantic.net/~gblank

For best results expand this window at least 6" at 1152 x 768 resolution
  #10  
Old April 1st 04, 06:51 PM
Jytzel
external usenet poster
 
Posts: n/a
Default difficulty drum scanning negatives

Kennedy McEwen wrote in message ...
In article , Don
writes
This sounds like grain aliasing. The mathematics of this are rather complex
because it involves the MTF of the scanner spot and lens, the line spacing
of the scanner, and the grain size distribution of the film being scanned.
It occurs when the grain size is small enought that it exceeds the Nyquist
limit of the sampling process. It results in the high frequency portions of
the grain being duplicated as lower frequency noise, and adds to the normal
low frequency component of the granularity. The result is an apparent
increase in granularity.

There are only two solutions to this that I know of. The first is to
introduce an anti-aliasing filter in the optical path of the scanner. This
almost has to be done by the manufacturer of the scanner, as it must be
carefully matched to the MTF of the spot and optics. The second solution is
to scan with a higher lpi and a smaller spot size (and better lens MTF). If
that can be done with the scanner that you are currently using, you're in
business. Otherwise, you will need to find a scanner that can handle film
with the small grain size that you have.

With a drum scanner the spot size (and it's shape) *is* the anti-alias
filter, and the only one that is needed. One of the most useful
features of most drum scanners is that the spot size can be adjusted
independently of the sampling density to obtain the optimum trade-off
between resolution and aliasing to suit the media being used, but there
is usually an automatic option which will achieve a compromise at least
as good as any CCD device.

I doubt that this is just aliasing though, especially if both were
scanned at 4000ppi or more. Remember that negative images are
compressed on film (the corollary being that negative film has more
exposure latitude and the ability to capture a wider tonal range).
Consequently, when producing a positive from the film image, whether by
scanning or by conventional chemical printing techniques, the image must
be contrast stretched. So, even if the grain on the film has the same
amplitude as the same as in slide film (a reasonable assumption for
similar speed films of the same generation from the same manufacturer,
the resulting image from the negative will always appear more grainy
than the image from the slide film.

There is a lot of truth in what the drum operator told Jytzel. Whether
its the truth, the whole truth and nothing but the truth is another
story. ;-) However, when viewed at 100% scaling, the size of the
original has little bearing on the results so I would expect to see more
grain on the 6x6cm negative image than from the 35mm slide under those
conditions.


thanks Kennedy,

Now I need some definitions of some terms: "spot size", "sampling
density", and "grain aliasing". And how can I tell if it's real
amplified grain or "grain-alaising"? Is there any solution to this
problem or should I give up using negatives altogether?

J.
 




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