[filmscanners] Re: understanding contaminated blacks--SS4000--newbietype question

["Anthony Atkielski" <anthony@atkielski.com>]

I think that this is a result of the very limited headroom available in deep
shadows on the film.  As the luminosity and exposure drop, the differences
in sensitivity between different colors on the film become more and more
obvious, and the color balance shifts dramatically.  What you are seeing is
a tendency for the color to shift as exposure drops to zero.  Every film
I've scanned shows this to some extent, and usually the color that stands
out is green (i.e., the deep shadows are "contaminated" by green).

It's very difficult to create a film with absolutely linear response to
color for all possible exposures; the colors always shift a little depending
on the exact amount of light a given spot receives.  For the extreme
highlights and shadows, the shift gets pretty big.

There might be scanner artifacts in this as well, but I've seen similar
results on all the scanners I've used (all Nikons, admittedly--but you are
seeing the same thing on a Polaroid).  It also might be the encoding of the
image--at the low end of a scan, a one-bit difference in a pixel is a full
stop, whereas at the high end, it's only 1/8 of a stop; this is an artifact
of the way images are digitized, and has nothing to do with the scanner or
film (and it's not something that can easily be changed, either).

There's no easy solution, IMX.  Photoshop doesn't help much unless you
really resort to hand-retouching, and that takes hours.  Try to set a black
point in the image, that can help.  Steepen the curves for the shadows, so
that the darkest parts remain black.  Change the color balance for the deep
shadows to remove green and get a more neutral black.  But it's difficult.
A deep scan (more than eight bits, and multiple passes) can help a little
bit, if there is extra shadow detail to be had on the original film.

----- Original Message -----
From: <snsok@swbell.net>
To: <anthony@atkielski.com>
Sent: Sunday, September 08, 2002 06:14
Subject: [filmscanners] RE: understanding contaminated
blacks--SS4000--newbietype question


Here is a small area from one of the transparency scans.

www.tallgrassimages.com/test

The blacks in this scan are muddy and specked with brown.

Stan

-----Original Message-----
From: filmscanners_owner@halftone.co.uk
[mailto:filmscanners_owner@halftone.co.uk]On Behalf Of Pat Cullinan, jr.
Sent: Saturday, September 07, 2002 6:55 PM
To: snsok@swbell.net
Subject: [filmscanners] Re: understanding contaminated
blacks--SS4000--newbietype question


Stan,

Can you post an image somewhere on the web?  Or send me an image (not
too big) at
pcullinan@mindspring.com?

Regards,

Pat Cullinan, Jr.

snsok@swbell.net wrote:

>When scanning high contrast Velvia transparencies, I am seeing detail loss
>in the shadows along with areas that just look muddy brown. I understand
>what causes detail loss from shadows with high contrast films but I am
>unclear what causes the muddy appearance. When I view the image at 100%
>level in PS, I see areas of brown pixels speckled through the blackest
>areas.
>
>I can't magnify the actual transparency enough to see at that level. Is
what
>I am seeing due to noise being introduced into the darkest areas? Is it due
>to the contrast range of the transparency exceeding the capabilities of my
>scanner? Is this due to the dust on the mirror causing noise artifact in
>areas it's most apparent?
>
>Is there anything I can do with Photoshop to remove some of this?
>
>Stan Schwartz
>
>
>
>
>



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