|
Mark,
Happy holidays to you and all others on the
list.
In my last message, I hope I was able to tell every
one the context in which this (my) experiment was done. Though I think most
of the list member had the intuitive or learned knowledge that working in
higher bit resolution would minimise quantization errors or simply result in higher
quality image, it wasn't obvious to me and probably to most of us here how this
improved quality translated into actual quantitative values.
As for doing what you suggest below, it should be
obvious that such an exegarated transform would result in poor quality image for
both resulution, though the 8 bit would probably suffer the most. (I like very
much porcupines...)
If I where to do an in depth analysis of the
"benefit" of using 16 bit resolution on B&W image, I would try to
recreate a typical set of editing transformation as would be done on an actual
image. Any out of the ordinary editing would be counter productive in my opinion
and the result wouldn't be that useful since they wouldn't have any connection
to real world image and real world editing. In this type of analysis I would
also use PS for the simple reason that recreating the math behind some of the
editing transform would be way to much work and it wouldn't be relevant to the
initial goal. When all four image would be ready to print that
is image #1: original unedited 16 bit image, image #2: image #1
converted to 8 bit, image #3: edited from image #1 and image #4: edited using
the same editing step as for image #3 but from image #2 instead, to be print
ready image #3 would have to be converted to 8 bit. Then I would load image #2
to #4 (image #1 is redoundant) in my program or whatever to count the
looses if any. I could also do a little bit better by recording each individual
editing step by itself, this would allow one to evaluate the contribution of
each type of editing transform and the more global result of applying all
of these transform steps together. To be even more complete, this analysis could
be done on a color image and the stats should also include CIE delta
errors (1976) this would give a more complete picture then just measuring
quantization errors as I did.
I'll first seach to see it as been done before and
if not, I just might give it a try out of curiosity and provide you with the
result.
Regards
Yves
----- Original Message -----
Sent: Sunday, December 16, 2007 1:24
PM
Subject: Re: OT: 16 bit editing myth or
reality?
Yves,
If you have a good 16 bit image, try
this:
duplicate the image and convert to 8 bits.
Take both
images and do a levels adustment by only moving the white point slider to the
left until you hit a value of say 50. This will compress the date a
great deal.
Now do another levels adjustment and hit AUTO.... examine
the histogram of both images. You will see that the 16 bit image has no
gaps in the histogram and there is still enough fidelity to make additional
adjustments.
The 8 bit image is going to look like the back of a
porcupine.
It has long been the standard to work in 16 bit.
I
might add though that Photoshop is actually a 15 bit program. If you
work with Camera Raw or Scans where the software does do true 16 bit, best do
as much of the adjustments that you can there.
Happy
Holidays
Best Wishes,
Mark Nelson
Precision Digital Negatives -
The System
PDNPrint
Forum at Yahoo Groups
www.MarkINelsonPhoto.com
**************************************
See
AOL's top rated recipes
(http://food.aol.com/top-rated-recipes?NCID=aoltop00030000000004)
|