Re: Dynamic Range testing
Re: Dynamic Range testing
- Subject: Re: Dynamic Range testing
- From: Oz Wille <email@hidden>
- Date: Thu, 06 May 2004 17:42:13 -0500
As I recall the Stouffer scale is silver based. Silver based film is known
to scatter a portion of the light striking it instead of letting the light
pass through on the light's original path. This is called the Callier
effect. High density areas scatter more of the light while low density areas
pass a larger percentage of the light. The net result in a black and white
print is a loss of highlight and shadow detail. In other words a reduction
of density range. In any case that is why many advanced black and white
darkroom printers use diffused "cold light" heads on their enlargers. The
diffused light source nulls out the light scattering of the silver because
the light is already scattered.
What does that have to do with the topic of this thread? Silver based
grayscales are probably not appropriate for determining the density range of
scanners, unless the scanner has a true diffused light source, which
fluorescent tubes, cold cathode tubes and LEDs are not. The only scanners
that I've seen that might be considered to have true diffused light sources
were some of the Kodak RFS scanners that used a flash tube behind a sheet of
white acrylic plastic or opal glass.
Perhaps a dye based or carbon based scale would be provide more accurate
information on a scanner's density range, unless of course, you are scanning
silver based originals ;-)
--
Oz Wille
Color Specialist
Chromaticity Incorporated
1642 Broadway NW, Suite 100
Grand Rapids, MI 49504
616-361-7773 ext. 130
413-254-4433 Fax
www.chromaticity.com
email@hidden
on 5/6/04 3:54 PM, Robert Lyon <email@hidden> wrote:
>
I recently utilized the Stouffer 21 step greyscale. It was very helpful
>
in comparing a number of high end scanners in terms of measuring there
>
maximum density. It was odd that none of the scanners tested came close
>
to their advertised claims in terms of max. density. I double checked
>
the scale on an accurately calibrated densitometer to verify its
>
claims.
>
>
Scanner manufacturers told me that they measure density a different
>
way, Can anyone shed some light on this?
>
>
Thanks, Bob
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