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Mark,
I'm sorry to say this but the second phrase you
wrote below is not true in the strict sence of words. In fact it's
practically sure there will still be gaps in 16 bit edited file, I'll admit they
could and probably will be much less then it would have if all editing had
been done in 8 bit, I have no problem with that, my first message is the proof
of that.
Comparing me to a brainless whatever doesn't proove
that I'm wrong. Have you tried the little experiment I suggested, it will take
you less then 10 minutes? In case it's already in the waste basket here it is
again.
Find yourself a hi bit color image, one your sure
it as more then 8 bit depth (as you said yourself below, some claims of hi bit
depth can be deciving). Make a copy of it and convert the copy to 8 bit, to make
sure PS doesn't just put a tag on the image and keep the hi bit values in
memory, save the copy, close it and reload it. Now you are sure you have both an
8 bit and a hi bit image to work with. For the effect to be more convincing I
suggest you don't use any form of random editing or one you can't repeat exactly
on both image, in principle a random process (gaussian stuff) can not be
repeated twice and for the effect to be more evident I recommend not to use them
for now.
Now you can edit your heart out on both image as
long as you do the "exact" same thing on both image I also suggest you be
reasonable, do as you would in a normal situation, it would be easy to do
things to fool the test but you wouldn't normaly do this in your usual workflow,
when your done convert the hi bit image to 8 bit and just to make sure you
truly have an 8 bit image, save it, close it and reload it.
Next, click on image->apply image... choose
substract and set the offset to 128, click ok (don't forget to select the other
image).
Now at what magnification do you begin to see some
difference in levels in your test image? (I wasn't able to see anything until I
was at 200% mag with carefully chosen edits and at 100% with some carelessness
and I'm an old guy my vision is not that of a teenager at its
prime)
You can also look at the histogram which will give
you some data you could use to evaluate the test. If you applied the exact same
editing steps to both images and no random steps, the histogram will tell you
something like this, the vast majority of the millions of pixels in the
resulting image are at or very near 128 (A - B = 0 + 128 = 128) and within
3 to 5 levels (more or less depending on how carefull you where) on each side
there will probably be nothing to see.
There are some small different between the images
which implies there is probably a difference in both type of editing, the
histogram prooves that but where the edits the exact same? Now these relatively
small difference are spread all over the area of the test image and if you where
to view the two final image side by side you probably couldn't see any of these
difference on your monitor unless of course you know where to look for or if you
magnify to the sky.
Now lets raise the bet sort of speak, lets print
those 2 images at whatever size you like, I ask you only one thing, view
them at the recommended distance based on their size, fair enough, ask anybody
around you to compare the two image and ask them to tell you which one was
edited in hi bit mode or which one looks better if you which, if the
results of doing this test with a couple dozen of people differ significantly
from using a coin flip to decide which one was edited in hi bit, I'll buy your
book, just to say it's not a bet.
Lets come back to the real world for a minute,
above I asked you not to use random editing because you can't do the same exact
edit twice. In the real world it would be almost impossible to edit two
image in the exact same fashion (which probably happened already above), we have
these random edits and we also have local edits and whatever else you can
think of that are quasi impossible to do twice exactly the same way. In the
test above I tried to elimimate these as much as possible to reduce the
difference to its minimum. In real life it would be surprising someone would
loose his time to do this but lets say one those (any normal edits), the only
difference would be a wider histogram and then you could say Ha! Ha! I told you
so. It happen I did it, yes, so I know and the difference are still very
hard to see at 200% magnification on the actual images on the screen,
I wasn't able to see them but don't take my word for it, try it yourself
(which is probably what you did already).
By the way, have you or anyone else for that
matter, thought that converting a 16 (15) bit image to an 8 bit one mean a
compression of at least a 100 to 1, it's impossible not to loose quite a
bit in the process, just remember that.
Happy holidays
Yves
PS For the others on this list, I wont buy your
stuff but I defy you to "proove" what you say with facts (not just words) and
thus proove me wrong at the same time.
----- Original Message -----
Sent: Tuesday, December 18, 2007 1:31
PM
Subject: Re: OT: 16 bit editing myth or
reality?
Yves,
It is true that most printers currently print
in 8 bit mode and even if you send a 16 bit file to them, the file is
converted to 8 bit mode—HOWEVER...
Editing a 16 bit file will leave a
rich file that when converted to 8 bit mode for printing has no gaps in
tone....
Editing in 8 bit mode will leave gaps that will still be
there when printed, possibly causing posterization.
As Ryuji stated,
this issue is really a "no-brainer" and has been considered such for years by
the experts. I'm not sure what your point is other than maybe setting up
a model to illustrate what the actual final difference is in tonal richness
for the same file in both 8 bit & 16 bit mode when given the same
adjustment. If you can come up with a model that would demonstrate it,
it would be interesting to know, but it won't change the reality that 16 bit
files are superior.
By the way, supposedly the newest Epson printers
working with Mac Leopard will be able to make "16 bit" prints as soon as Epson
releases the drivers to do so. Also one of the other printer
manufacturers has a plugin that is supposed to give around 14 bit
prints......so the 8 bits/printer thing may soon be a thing of the
past.
Another side note, a custom scanning house
of "good reputation" was making drum scans for people that were supposedly 16
bit drum scans.... in fact, they were scanning in 8 bit because that was all
their drum scanner would do, then converting them to 16 bit and sending them
out. This is, however, rather easy to detect. Of course they were
charging extra for their "16 bit scans".
Happy Holidays,
Mark
Nelson
Precision Digital Negatives -
The System
PDNPrint
Forum at Yahoo Groups
www.MarkINelsonPhoto.com
In a message dated
12/18/07 12:18:13 PM, gauvreau-yves@cgocable.ca
writes:
All this above is true while in hi bit mode but the
question is what happen to these extra bits when you need to print the image
knowing the majority of consumer printers out there are 8 bit printers? The
simple answer is, they go back to the black hole they came from. The true
benefit of editing in hi bit mode is so small, it is for all practical
purpose insignificant on actual prints but I'll give you this it looks much
better while in this hi bit mode.
**************************************
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