Of interest in this discussion:
and
Money quote from Dan Margulis: "The bottom line of all my tests was,
with one important caveat that I'll get to in a moment, there is no
16-bit advantage. I blasted these files with a series of corrections far
beyond anything real-world; I worked at gammas ranging from 1.0 to 2.5
and in all four of the standard RGBs, I worked with negs, positives,
LAB, CMYK, RGB, Hue/Saturation, what have you. While the results weren't
identical there were scarcely any cases where there would be detectable
differences and in those one would be as likely to prefer the 8-bit
version as the 16. So, I have no reservation in saying that there's no
particular point in retaining files in 16-bit, although it doesn't hurt
either.
I'll show all these results later, but the surprise was in the files
that Ric [Cohn] sent, which appeared to show just the sort of damage
that 8-bit editing is supposed to cause, in an image with a dark rich
blue gradient, a worst-case scenario in conjunction with the very dark
original scan, which in itself was an attempt to give an advantage to
16-bit editing.
Ric provided both original 8-bit and 16-bit versions of these files.
Granted that the necessary corrections were very severe, they still
showed that what he said was true: the 8-bit version banded rather badly
and the 16-bit did not. I tried several different ways of trying to get
around the disadvantage and could not do so without excessive effort.
Ric's 8-bit original, however, was generated from the 16-bit scan not by
Photoshop but rather within his own scanner software. Therefore, I tried
further tests where I applied the same extreme corrections to the image,
but this time not to Ric's 8-bit image but rather a direct Photoshop
conversion of Ric's 16- bit image to 8-bit. Shockingly, this completely
eliminated the problem. There was no reason to prefer the version
corrected entirely in 16-bit.
When Photoshop converts from 16-bit to 8-bit it applies very fine noise
to try to control subsequent problems. Most scanners don't. I would have
expected this to make a difference but not to the point that the scanner
8-bit file would completely suck and the Photoshop 8-bit file would be
just as good as the 16- bit version. I don't know whether this is all a
function of Photoshop's superior algorithm or whether the scanner is
doing something bad. Furthermore, I don't care. One way or another, the
8-bit scanner file is bad and the 8-bit Photoshop file is good."
Preston Earle
PEarle@triad.rr.com
(Still in Group 3.)
----------------------------------------------------------------------------------------
Unsubscribe by mail to listserver@halftone.co.uk, with 'unsubscribe
filmscanners'
or 'unsubscribe filmscanners_digest' (as appropriate) in the message title or
body
