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From: Yves Gauvreau
[mailto:gauvreau-yves@cgocable.ca]
Sent: Tuesday, December 18, 2007
6:46 PM
To: alt-photo-process-l@usask.ca
Subject: Re: OT: 16 bit editing myth
or reality?
I made a translation mistake in the PS below, here is a copy
"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."
I should have used "challenge" or even
"want" instead of "defy", in french both challenge and defy
can be translated to "défit", I think defy may be considered stronger
or even arrogant and it was not my intention. In other words I'd like
you to proove what you say which is, I would think, even more friendly.
----- Original Message -----
Sent: Tuesday, December
18, 2007 5:57 PM
Subject: Re: OT: 16 bit
editing myth or reality?
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.
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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