Paul,
"Dynamic range," typically refers to tonal range or the contrast range that
the scanner can capture. 3.6 is considered very good for a CDD ( or is it
CCD, I get confused) based scanner; drum scanners can get up into the 4.0 to
4.4 range. I believe 5.0 is the upper limit of the scale; but no scanner
even gets as close as 4.6 to the best of my knowledge. "Color bit depth"
refers to the number of bits per pixel; often it is divided by 4 to give the
color bit depth per pixel per color channel; hence, 48 bits per pixel
becomes 12 bits per channel. Standard bit depth is around 8 bits per
channel with 12 bits per channel being usually called high Bit depth. It
defines the amount of color and image information possible per color
channel. However, not all that information is always used since most
printers and programs work in the standard bit depth of 8 bits/channel or in
24 bit depth per pixel for all channels. The extra information comes in
handy when the printer or program compresses the tonal scale or contrast
range in permitting it to better determine where the gamma should be placed
and where the highlight and shadow compression should take place. More
information available the better the estimate by the application or device.
Hope this helps. I know of no particular source that deals specifically
with this, although it can be found discussed in a number of different books
on scanning and on Photoshop.
-----Original Message-----
From: owner-filmscanners@halftone.co.uk
[mailto:owner-filmscanners@halftone.co.uk]On Behalf Of patton paul
Sent: Friday, February 02, 2001 12:14 AM
To: filmscanners@halftone.co.uk
Subject: filmscanners: Re: bit depth and dynamic range
I've just been reading some Nikon literature about their new scanners, and
I have some questions about the terminology. The ad states that the
coolscan IV ED yeilds 48 bit images (48 bits per pixel?). Later, it
states that the scanner has a color bit depth of 24 or 36 bits. What does
this refer to? It also states that the scanner has a dynamic range of
3.6. What is a scanner's dynamic range? Can anyone suggest an article
somewhere on the web or elsewhere that explains all this? Thanks.
__________________________________________________________________
Dr. Paul Patton
Beckman Institute Rm 3027 405 N. Mathews St.
University of Illinois at Urbana-Champaign Urbana, Illinois 61801
work phone: (217)-265-0795 fax: (217)-244-5180
home phone: (217)-344-7863
homepage:
"The most beautiful thing we can experience is the mysterious. It is the
source of all true art and science."
-Albert Einstein
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