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: Tue, 19 Apr 2005 14:31:11 EDT
Marco writes,
>>I wish I had read Bruce Lindbloom's piece earlier. It would have saved some
of the
time I spent actually believing that Margulis' was an honest argument made
with an open mind.>>
I am obviously aware of the site but I have always considered it so pathetic
that I never responded publicly to it until late last year, when a member of
my own list publicly asked for a comment. Inasmuch as my honesty appears to be
called into question by Marco's post, I will take the liberty of reposting it
here.
Obviously, the word "Bruce" is always taken to mean Bruce Lindbloom, and not
my friend Bruce Fraser, who has enough personal integrity not to stoop to such
tactics.
With that, I'm outta here.
Dan Margulis
**************************
I have no objection to people who disagree with my opinions, even when they
aren't particularly civil about it; that's how things get sorted out eventually.
The site in question is a different animal. It involves a frustrated
individual deliberately posting information that he knows to be false. Bruce
Lindbloom's whole contention is that before I tested the 16-bit images, I converted
them to 8-bit and then reconverted them to 16-bit before applying curves. If that
were true, it would be like a test comparing how well two washing machines
work on the same kind of load, except that one of them had a bucket of mud
poured in it first.
Of course, it's ridiculous. What he is seizing on and deliberately
misinterpreting is a phrase in my original description of how I would proceed. I said I
would run a series of drastic corrections on two copies of each of many, many
files. One set of corrections would be done entirely in 16-bit and the
conversion to 8-bit would come only at the end; then, on a copy of the file, I would
convert to 8-bit immediately and load the identical actions, whereupon I would
compare the two.
Makes sense so far, but I added: if it turns out that the version done in
16-bit is significantly better, then, and only then, I'd run a third
test--converting the 8-bit file back to 16-bit before correcting it, to see if there
wasn't something about the calculation method that was producing the better result,
rather than just the extra data.
I've studied what happens when you do that, and it's pretty interesting.
However, it never was any part of my testing of the images, for the simple reason
that the corrections done in 16-bit all the way were never any better than in
8-bit, regardless of how drastic they were.
Bruce asked a lot of questions about this at the time, including
correspondence with me off-list. I was aware then that he was trolling, because he was
professing to be neutral on the subject, whereas on the ColorSync list he had
recently called 16-bit correction "a must" in certain circumstances. So, when I
saw he was trying to poke a hole in the methodology, I made sure that he
grasped completely what the purpose of the hypothetical 16>8>16 conversion was.
There is no possibility that he misunderstood this; indeed, he could not
conceivably be so stupid as to think that anyone would perform a test this way.
Nevertheless, he chose to post what he did, knowing that it was false.
While the content of the page collapses when this is understood, there is one
other side note. Bruce accuses me of keeping the results to myself and
appointing myself the sole judge, which he knows perfectly well is not true. I
printed 10 pages of side-by-side samples in my current book, many at extreme
magnifications. The versions are not identified until a box later in the chapter,
and readers are invited to judge for themselves which is which, plus, I indicate
how I voted when I first saw the proofs and did not know which was which. The
original 16-bit files, and the corrections I applied to them, are all on the
book's CD and anybody who likes can either verify what I did or do their own
experiments.
What prompted the accusation was an unfortunate incident involving my first
round of tests. The test files were provided by a list member whom I did not
know at the time. After I performed the tests, I was flabbergasted to learn that
he would not give me permission to exhibit the images and results publicly,
which I thought was the whole point of the exercise. He did confirm, several
times, on this list and at least two others, that he and I were not personally
acquainted; that he believed I did not realize he was not giving permission;
and that he had seen my results and that I was describing them accurately. When
Bruce challenged him, he offered to give him pieces of the pictures (and my
results) that would have been sufficient for Bruce to verify the findings, but
Bruce refused to take them.
Because of this incident, I changed the rules. I said I would not do any
testing on 16-bit files without an advance agreement enabling me to publish them
and to release the raw data to illustrate whatever was found. Ric Cohn and a
couple of other people kindly agreed to allow their images to be used in this
fashion. Consequently the files are available for anybody on the CD.
The upshot of this: you guessed it. With the rules now having been altered to
accommodate Bruce, Bruce wrote that the test was invalid, because the rules
had been changed.
In summary: the issue with the page is not its dishonesty as much as its
irrelevance. Bruce is the one advocating the inconvenient workflow, just as if he
said that there's a big quality difference if one only wears garlic around the
neck while booting Photoshop up. Nobody can disprove that, because if your
tests show that there's no difference, probably the garlic was too old or there
wasn't enough of it.
Similarly, nobody can disprove that 16-bit correction may be better under
some circumstances, because nobody can test every conceivable image with every
conceivable tool. However, the only two people who have ever run extensive
tests--Jim Rich and I--tortured the images almost beyond belief and still were not
able to identify any areas in which 16-bit correction did better with a color
photograph.
It's painfully apparent at this point that Bruce and the others have never
actually done side-by-side tests to support their theories. Otherwise, we'd have
seen examples long ago. For anybody wishing to successfully advocate the
16-bit workflow, the recipe is quite easy:
1) Here is a photographic image;
2) Here is what I did to it in 16-bit;
3) If you convert it to 8-bit first and then repeat what I did, it looks a
lot worse.
Without that demonstration, he has put up a blank page, IMHO.
Dan Margulis
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