Re: Dynamic Range testing
Re: Dynamic Range testing
- Subject: Re: Dynamic Range testing
- From: Jim Rich <email@hidden>
- Date: Tue, 04 May 2004 16:40:02 -0400
On 5/4/04 3:18 PM, "Douglas Rhiner" <email@hidden> wrote:
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I wish to test the Dynamic Range of my two scanners, a TANGO and an
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LS-8000.
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What do I need to accomplish this? I.e. what target would I scan?
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How should the scanner be set up for the test?
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Any procedural aspects to look for so I get a "true" reading?
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Also, what would be the best way to test how large of a color
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space/gamut the scanner can capture?
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Possibly create profiles and compare the results with ProfileEditor or
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similar application?
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Any info on how to do this in a scientific method compatible way would
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be of great use!
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>
TIA
Doug,
Here is something I put to gether a few years ago about Dynamic Range.
One method to determine dynamic range is to scan a continuous tone gray
scale such as a Kodak ST34.
During this process the scanner controls are adjusted to do accomplish three
things.
(1) Select the lightest white area of the gray scale Dmin.
(2) Select the darkest black area of the gray scale Dmax.
(3) Insure the tones between the white and black points are separated well.
The purpose of this method is to try and distinguish between all the
possible tones of the gray scale. Separating the images tones is usually
done with the scanners image processing controls such as midtone or gamma
adjustments. When done correctly it is possible to identify subtle
differences between the shadow details and tones of the gray scale. The
shadow details of the gray scale that don't have any differences shows the
limits of the scanner.
After scanning the gray scale identify the Dmin density area and the shadow
density area where there are not any tonal differences. Subtract the Dmin
density (highlight area) from the shadow density areas. This is how dynamic
range is determined using density. This is accomplished by monitoring and
measuring either gray scale or RGB values through an application like Adobe
Photoshop.
To provide a sense of what to look for, imagine that theoretically RGB
values for the blackest area would measure to be 0. Practically, shadow area
measurements will range between 50 RGB to 0 RGB values. It takes some trial
and error experimentation and skill to figure out how to use the scanners
image processing tools, what areas to measure and the values to look at to
determine dynamic range.
This means experimenting with the tools to find out how they respond.
Identify their range and how to finesse them to set the white and black
point while ensuring the shadow details and tones have been separated to
their optimum point. When this is done it should be possible to determine
the dynamic range of the scanner.
The formula is for dynamic range is to identify the shadow areas with
details minus highlights with a minimum of details.
For example if a gray scale shadows tones are the same at a density over
2.55D and the highlight is.05D the dynamic range of the scanner is 2.50D.
My .02.
Jim Rich
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