Re: Scanner dMin dMax
Re: Scanner dMin dMax
- Subject: Re: Scanner dMin dMax
- From: Jim Rich <email@hidden>
- Date: Fri, 24 May 2002 17:47:05 -0400
On 5/24/02 12:34 PM, "joel" <email@hidden> wrote:
>
email@hidden
One measure of dynamic range is to use density from a target such as a gray
scale. You measure the whitest to the darkest tones the scanner can capture.
To find the darkest tones you usually have to look real close on your target
as to where the transitions betweens shadow tone values start and stop and
then become the same density value.
Here is a very simple formula to determine the scanners density range.
Density range formula : Dmin - Dmax = density range.
I have taken this measurement many times from many types of scanners using
a carbon dye based or conventional photographic dye transparent gray scale
as well as from reflection gray scales.
I bring up the type of transparent gray scale because you will find
different opinions as what kind of scale to use, such as carbon dye or
originals with conventional photographic dyes. Conventional wisdom says use
an original that is similar to the types of originals you scan, but that9s
just my opinion. My reasoning is that this method gets you closer to
realistic density range values for your process.
The last time we tested a group of scanners we used a target with
conventional photographic dyes such as an IT8 and when I published the low
dynamic range numbers a scanner vendor called me up to complain that their
scanner had a higher dynamic range. The obvious question I asked was what
type of scale they used. Their response was a silver based grayscale that
gave them higher dynamic range values. So you might want to be careful when
interpreting dynamic range and density range values.
Jim Rich
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