Re: 16 bits = 15 bits in Photoshop?
Re: 16 bits = 15 bits in Photoshop?
- Subject: Re: 16 bits = 15 bits in Photoshop?
- From: email@hidden
- Date: Sat, 16 Apr 2005 08:14:21 EDT
Bruce Fraser writes,
>>I didn't write a good chunk of what you quoted, so I'll let the other
quotees speak for themselves.>>
You really need to be more careful, then, about who you give your account
passwords out to. If you don't want to be associated with the idea that the
difference between 16-bit and 8-bit manipulation is night and day, or that it's
totally obvious to anyone who looks that it's very advantageous to do the big
moves in high-bit (and who *would* want to be associated with those ideas at this
point?) then I hope you are able to track down the guy who attached your name
to the following.
********************
BEGIN UNEDITED QUOTE
Bruce Fraser - 02:58pm Aug 12, 2001 Pacific
I think a lot of people are overlooking the fact that Dan is playing with a
stacked deck here. I very much doubt that his “tests” start out with a raw
scan from an 8-bit capture device. At very least, black and white points are
probably being set in the scanner, probably in 12-bit space. Maybe some rough
tonal shaping too.
In which case, the debate simply becomes one of whether it’s advantageous to
do gross corrections in the scanner software or in Photoshop.
I started using a primarily 16-bit workflow primarily because most scanner
software did such an abysmal job of transferring color correctly to Photoshop,
and because I don’t like making critical image decisions on a
postage-stamp-sized prescan.
>From a quality standpoint, it makes little difference whether you carry out
the manipulations on the high-bit data in the scanner software or in Photoshop.
I prefer doing it in Photoshop because it gives me more control than most
scanner software (or maybe, honestly, because I know Photoshop’s controls better
than I know any scanner software), and because I can see every pixel in
Photoshop.
If you really start out with a RAW image in high-bit form and a raw image
downsampled to 8 bits, the difference really is night and day. But very few
people do anything of the kind.
Those of us who have adopted a 16-bit workflow in Photoshop have done so
because we’re less likely to make dumb moves based on the postage-stamp preview,
and because high-bit files in Photoshop give us much more editing flexibility
and headroom than an 8-bit file produced from manipulating high-bit data on a
scanner or digital camera. But if someone prefers to do the gross manipulations
in the scanner or camera software, I won’t argue with them. It doesn’t
really matter, beyond personal preference and skills, where one manipulates the
high-bit data.
But it’s totally obvious to anyone who looks that it’s very advantageous to
do the big moves on high-bit data.
********************
END UNEDITED QUOTE
>>Probably tens, if not hundreds of thousands of people have made this
comparison rather than the dozen you claim. I'm not sufficiently
arrogant or delusional to believe that all these people are editing
in 16-bit just because I say it's a good idea. Rather, they've made
their own comparisons and come to the same conclusions as I did.>>
Remarkable, is it not, that not a single one of these users has managed to
memorialize even one of these comparisons so that anyone else can look at it and
draw their *own* conclusions? And that the only people who have displayed
their works to others unanimously state that they see no significant difference,
no matter how extreme the edits?
>>However, I've published one relatively trivial example on page 23 of
Real World Camera Raw.>>
That is *not* a comparison of 8-bit vs. 16-bit editing. You have Image A in
Camera Raw. You export it as Image B, unedited, to Photoshop, where you convert
it to 8-bit. You then return to Image A and edit in in Camera Raw, thus
applying a change that cannot be duplicated in Image B. You then turn to Image B
and edit it in Photoshop, thus applying a change that cannot be duplicated in
Image A. Having ensured that the test is utterly meaningless because the
competing files are no longer comparable, you then export Image A to Photoshop and
produce a scintillating demonstration that would, (if the images you showed were
larger than 2x2) prove beyond all doubt that applying the same curve to two
different files produces two different results.
If you want a valid comparison, just export Image A from Camera Raw when
you're ready. Then make a copy of it as Image B and convert to 8-bit. At that
point you're good to go. You have two equal images. Do your damndest to break
Image B--but whatever you do, you have to do to the 16-bit Image A as well. When
you're finished, convert Image A to 8-bit, and then you'll have a "night and
day" difference when you compare A and B--or so the guy who is using your name
says.
While such a comparison would be valid whether you edited first in Camera Raw
or no, I might respectfully suggest that you *not* edit in Camera Raw, but
rather export linear data, and then open it in some 2.2-gamma workspace. As
foolish a workflow as that would be in real life, it would be useful here because
it would force you to make massive corrections, probably a series of them, to
get an acceptable image. That would, I am sure you agree, constitute the type
of "big moves" that the guy who was using your name assures us produce an
advantage for 16-bit editing that's "totally obvious to anyone who looks."
Hint: people have already tried it, with images that were susceptible to
banding. Everyone who's looked at the results has agreed, no significant
difference. But the tests that have been done so far involved exporting linear data and
opening it in Adobe RGB. Perhaps if you open the linear data in Prophoto that
might stress the file enough to make a difference.
>>I don't tell other people what to do...>>
Now that I know that you aren't the one who said "it’s totally obvious to
anyone who looks that it’s very advantageous to do the big moves on high-bit
data. " I guess the point will have to be conceded.
>>...I simply point out the consequences of different courses of action. If
you can't see the difference, then for you there is no difference, and you
should work
in 8-bit sRGB, bouncing into Lab and CMYK and back again, as your
correction needs dictate, until the heat-death of the universe. Happy?>>
I'm certainly happy to hear that you aren't the one making all the "night and
day" and "totally obvious to anyone who looks" remarks. If it were otherwise,
granted that you do not seem to be personally aware of even a single
real-world example in which editing in 16-bit mode yielded the slightest advantage,
one might have to look at you somewhat quizzically.
I am, however, disappointed that I was not able to improve my color
correction skills. You--unless it was that other guy using your name--posted, "What
Dan's tedious and fundamentally specious arguments deliberately miss is that the
need for greater bit depth has absolutely nothing to do with reproduction and
everything to do with editability." Those words seemed so decisive that I
thought that you might possibly be able to demonstrate, with a real-world image
under real-world circumstances, what this "need for greater bit depth" is all
about, since so many people are reporting that they can't demonstrate it.
As for what the eye sees, of course I agree. For example, you or a person
using your name once wrote, "For 8-bit-per-channel images, I always use a Curves
Adjustment layer...because when you use Adjustment Layers to edit the image,
all the edits are calculated at the same time when you flatten the image. This
approach degrades the image much less than burning successive rounds of
corrections into the image one by one. . . ."
I assume that you must actually have compared the two methods and have seen
the massive degradation in the successive-rounds-of-correction image for
yourself. If your eyes are sensitive enough to detect that kind of difference in
files that are pixel-for-pixel identical, then I can certainly understand how
they might be able to see what the other guy calls a "night and day" "totally
obvious to anyone who looks" kind of difference in 16-bit v. 8-bit correction.
When you're ready to show an example, I'll be here for you.
Anyway, I've read your Raw book, and it's great. Everybody who uses Raw is in
your debt.
Dan Margulis
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