Digital BW, The Print

Andre,

Read what he is discussing VERY carefully.  He is discussing COLOR, NOT B&W.
They are entirely different in the regard he is discussing.  It is fine to
use 8 bits/color for color, as you get 24 bits total (3 x 8), but for B&W,
it is not as "forgiving", and you can severely degrade the image doing tonal
manipulations in 8 bits/pixel.

Austin


> -----Original Message-----
> From: Andr\ufffd Vallejo [mailto:avs@...]
> Sent: Monday, May 20, 2002 9:15 PM
> To: DigitalBlackandWhiteThePrint@yahoogroups.com
> Subject: [Digital BW] The old "8 x 16 bits" again...But worth reading!
>
>
> The following post is reproduced from a message by Dan Margulis in another
> web forum I join. I decided to reproduce it here 'cose even the
> subject has
> been discussed a lot here some time ago,it looks to me like a very
> enlightning about the subject ,written by someone who knows a lot
> about the
> subject (he's the author of "Professional Photoshop-A guide to color
> correction",one of the best books I've read). Sure it started a
> long thread
> in the forum,but that's the way it has to be...He gave me his ok for
> cross-posting.
> Andr\ufffd
>
>
>
>
> Shortly before leaving for Europe, I completed several days of work
> comparing
> the results of correcting 16-bit files versus performing the same edits on
> 8-bit files. I'll have a full discussion of what this showed in my book
> later
> this year and will include the files on the CD so that others can verify
> what
> went on. However, since there was one finding that came as a surprise and
> would cause me to change workflow in some cases, I thought I would let
> people
> know here first.
>
> As many of you know, there has been this ongoing debate as to whether
> there's
> merit in leaving files in the cumbersome 16-bit mode as long as
> possible on
> the theory that corrections will be more accurate. There are
> those who have
> strenuously argued that this is the only way to go, that there is a
> night-and-day difference in the results, and that people who do things any
> other way are rubes. None of these experts has ever shown anything other
> than
> a histogram to demonstrate that this is so, and my own tests have shown up
> to
> now no substantial difference.
>
> I therefore issued a challenge for those who could come up with any color
> photographic image where any reasonable course of events might conceivably
> show an advantage for working in 16-bit as opposed to just converting
> immediately to 8-bit, and said if I could verify it I would admit it and
> print the results.
>
> Naturally, none of the people who are so vehemently in favor of 16-bit
> correction had any such files to show, but some list members did, and sent
> them to me. Particularly, Todd Flashner allowed me the use of his
> scanner to
> produce several high-bit images that were disastrously flat and would
> presumably magnify any advantage that 16-bit might have. Ric Cohn
> sent over
> 2
> gigs of images and an ungodly number of Epson proofs of images
> that he felt
> did demonstrate that working in 8-bit caused banding and other problems.
>
> 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
> 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.
>
> I also don't know whether other scanners would have the same problem that
> Ric's appears to have, but suspect that they might.
>
> The whole thing suggests to me that if one's scanner is capable of
> generating
> a 16-bit file, one should probably take it. Thereafter, whether
> one converts
> it to 8-bit in Photoshop early or late, it doesn't seem to make a
> difference.
>
> Dan Margulis
>
>
>
>
>
> Please visit the Group Homepage to check the Files, Bookmarks,
> Polls and other resources as they are often being updated. The page is at:
>
> http://groups.yahoo.com/group/DigitalBlackandWhiteThePrint
>
> Please follow these basic guidelines:
> - Include your full name with your message.
> - Include the address of your website, if you have one.
> - As threads develop, trim off excess portions of earlier
> messages to keep them short.
> - As the topic of a thread changes remember to change the subject header.
> - Good manners are required at all time. No personal attacks or
> "flames."
> - Complete your Yahoo profile.
> - Before posting a question, search the message archives and the
> various resources on the homepage.
>
>
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>