Re: artifacts, scanner noise or grain ? was Software creating output?

["Rafe B." <rafeb@channel1.com>]

At 09:38 AM 6/12/99 +0200, rohcris@vtx.ch wrote:
>Well, at this point, I see only two potential causes for artifacts :
>
>1) scanner noise
>2) film grain
>
>I own a Polaroid Sprintscan 35 Plus with a max resolution of 2700 and get 
>very visible "grain" scanning Kodak Ektapress PJ400. Does anyone know 
>wether the scanner introduced this pseudo-grain (scanner noise), or wether 
>the scanner got the emulsion grain ? What would be the difference between 
>scanner noise and emulsion grain ?  Would a Kodak PJ400 have enough 
>grain to be caught with a 2700 scanner, or is there another problem here ?
>
>Note that when scanning at 1350 dpi instead of 2700 dpi, I get much less 
>noise/grain and note that the Polaroid Sprintscan 35 plus is a very good 
>scanner, which despite his age still competes well with the new Nikon LS2000 
>in some reviews I've read.


No question about it; at this resolution (2700 dpi)
you can see film grain, loud and clear.

I don't have any experience with the film you mention
(PJ400) but I do have experience with different ISO
speeds of Kodacolor, and Fuji Reala.  If the 400 
refers to the ISO speed, then even more so.  That's
fast, and that means grain, big-time.  Ask yourself:
what would a print from this film look like, if made
via "conventional" darkroom techniques and media?
There's no reason to expect the digital process to
have *less* grain than the "wet" process.

I have the same scanner as you.  Until a couple of
months ago, I was working primarily with a much
cheaper scanner, the Microtek 35t+, which has a 
resolution of 1950 dpi.

Even with the Microtek, I could clearly resolve,
and identify by sight, the differences in grain between
ISO 400, 200, and Royal Gold 100 Kodacolor.  I was
actually shocked and amazed at this, but the difference
was extremely plain.  Not subtle at all, but glaringly
obvious.

To really separate out these issues (film grain vs.
scanner noise) try scanning some some slides taken with 
an extremely slow, fine-grain film.

As to *dealing* with scanner noise and film grain, I
have a few ideas for that, also.  One trick I use is
inspect the individual color plates and see where the
bulk of the noise/grain is coming from.  Most often,
it's the blue channel.  When it's time to apply
unsharp masking to the image, I quite often exclude
the blue (noisy) channel from this operation, or even 
apply a wee bit of gaussian blur to the blue channel, 
while sharpening the other two.

"Blue channel" problems are in fact electronic in
origin.  From my understanding, the blue channel of
the CCD is the one with the lowest gain, and hence
to poorest signal-to-noise ratio.  I've noticed with
all of the film scanners that I've used to date, that
if there are "streaking" issues, they will almost 
always be centered on the blue channel.  The Microtek
was more prone to this than my new SprintScan Plus,
but even on the latter, this ugly effect has been 
seen, on certain images.


rafe b.

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Please: Stay on topic. Trim quoted messages.
http://www.leben.com/lists for list instructions.