----- Original Message -----
Sent: Tuesday, December 18, 2007 5:57
PM
Subject: Re: OT: 16 bit editing myth or
reality?
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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