D-Max of Scanners
D-Max of Scanners
- Subject: D-Max of Scanners
- From: rick lucas <email@hidden>
- Date: Tue, 5 Dec 2000 20:33:49 -0400
Unfortunately the D-Max that scanner manufacturers specify do
correspond to reality. To test this,take a calibrated step wedge such
as those available from Stouffer and scan it raw. Make sure to block
off any stray light (flare) from the sides of the step wedge so that
all you can see is the wedge. Then measure the darker steps until no
change occurs. The point at which there is no change is the D_max.
Also look at the noise at this step which should be fairly obvious.
To get an usable D_max value for your scanner with an acceptable
amount of noise, find the darkest step that has an acceptable amount
of noise for your needs.
Using this technique you will find out what is the actual D_max of a
scanner and be surprised at how much different it is compared to what
the manufacturers claim. Not to pick on any one manufacturer, here
are the D-Max readings that I've obtained from three different CCD
based scanners.
Actual Claimed
Lino Saphir Ultra 3.0 3.4
Imacon Flextight Precision II 2.8 4.1
Nikon LS-2000 2.35 3.6
As can seen there does not seem to be any correlation between
manufacturers specs and reality. Keep in mind that the D-Max of
transparency film varies between 3.0 to 3.5 depending on film type
and processing. All three scanners above would not be able to see the
detail in the dark shadows of a transparency.
I have not tested these two scanners in this manner but I hear that
the Scitex Eversmart Pro Supreme (CCD) has a D-Max of 2.9 with very
low noise due to the fact that they cool the chip. The other scanner
Aztec (PMT) which is modified Howtek 8000, claims to have a D-Max of
4.0.
It would be very interesting if anyone on this list has done similar
tests and is willing to publish their results.
--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Rick Lucas
Digital Attributes/Lucas Imaging Assoc.
3606 Ridge Brook Trail
Duluth, GA 30096
770-798-9663
770-757-0712 Cell
email@hidden
email@hidden
www.digitalattributes.com