[Ed_L]

I've been playing around again with 16 bit images, and I scanned one as such, then made a couple of levels adjustments. The image was duplicated, and the duplicate was changed to 8 bit mode for comparison. The exact same adjustment was made to each of them, and the resulting histogram showed voids in the histogram (8 bit), with two levels being completely lost next to each other, in two different places. Nothing else was done with the images, but the results tell me that if I had to make many more adjustments, I might wind up with quite a bit of lost data. Maybe I'll reconsider the 16 bit scan, if for nothing more than tonal adjustments. Here's a screen shot of the results.

Ed

[Stephen M]

Ed, the actual images do not look different though.

If you can afford to edit in high bits, then why not - but if you work is in a volume setting where actual final results matter then you may look at things differently.

If a histogram can be sold, then great! Most care about the image, although some care about data if that is what they are purchasing (although many just want a great result and would not care if the histogram was gappy).

A histogram is just a statistical report - it is up to you to decide what you read into the statistics.

For the pros/cons on this deep subject, I have collected some links from both ends of the extreme and general viewpoints:

http://members.ozemail.com.au/~binar...V_links.html#H

Ed, try this little test - the pic with the gappy histogram which looks like it has less data...convert that to another profile. Or rotate it 0.1 degree in one direction, then rotate it back. Or add 0.3 pix g/blur. All of these things will 'mung' the data and the statistical report will show a better file (if all you do is look at the histogram without any knowledge of the edit). So it is possible to make a histogram appear nicer, while the image may be worse than the gappy histogram one.

I would question the evaluation made by a histogram, unless I knew the exact editing history of the file - otherwise the histogram may or may not mean jack to the output quality of the file.

Stephen Marsh.

[Ed_L]

Hi Stephen,

Thank you for your input, and for such a great site. I've visited your site a number of times before, and I've had it on my bookmarks for quite some time. I have read quite a bit about the pros and cons of high bit scanning in the past, and it seems that some of the biggest names in Photoshop land can't agree about the benefits or lack of benefits of high bit scanning. To date, I haven't seen a print that I've made suffering from posterization or other easily seen effects from using 8 bit images. I know that running a filter, even the USM, will have an effect on the histogram. I did read, I think in "Photoshop 5 In Depth", that when you have 3 - 5 levels missing together, there is a very good chance of posterization, but I can't personally confirm that from my printed materials. I know there are some who are thoroughly convinced that high bit is the way to go, and it's something that I've wrestled with. A pretty histogram is not something I'm concerned with, but the final printed product is. Any testing I've done to date did not give me reason to scan in high bit mode, but every once in a while I make comparisons. Thanks again for the input, and such a great bunch of links.

Ed

[Stephen M]

Hi Ed, it is a thorny subject.

I agree with the principle and the math - it's just hard to justify at this point when actual results are compared and you do the bean counting.

I like to see some balance to this topic - it usually get's to be very one sided (pro hi bit) - when life is not that simple...but the advocates never seem to take a broader view, or their production workflow and deadlines must be very different to mine.

I can't wait for processing power to make high bit, high res files seem like low res thumbs...but while I am stuck with the slow processing on 8 bpc data I can't see high bits being an inducement to greater productivity, let alone output quality (for example, there might be 300 high res images to dust spot, colour correct etc in two to three days - every second counts).

Stephen Marsh.

[john_opitz]

There's a sample chapter from Dan Margulis on this subject.Chapter 15

He even has the original files(on the cd) with the curves he applied to them.

John

[garfield]

so you mean that scanning at 48 bits color will turn it into 16 bits image but why is it when its at 16 bits i cant apply any filter to it? I have to change it to 8 bits? Is this a glitch? is it better to scan at 48 bits rather than 24 bits? Thanks for reading my post

[john_opitz]

<<so you mean that scanning at 48 bits color will turn it into 16 bits image but why is it when its at 16 bits i cant apply any filter to it?>>

Some image-editing programs do not fully support 16 bit(high bit) editing.

<< I have to change it to 8 bits?>>

Yes......There is another way to edit 16 bit without converting to 8 bit. But the time and work that is involved does not warrant it(quality wise). ie.... selecting and pasting between documents.


<<is it better to scan at 48 bits rather than 24 bits?>>

If your scanner can give it to you, go for it. Otherwise, it "does not "make a world of difference. Or, as some 16 bit die hards use to say "night and day difference". Then convert to 8 bit for P.S.


John

[Stephen M]

I generally agree with John.

High bit is also only for flat images at this time, but many folk would like layered support (including me). To me layers are more important than high bits. But give me both and I am happy. <g> Even the new tool from Binuscan, PhotoRetouchPro - which works in high bit mode...does not offer layers - it uses brushes.

At this point in time, high bit processing is very memory intensive and tool support is limited. It takes a lot of time when there is often little perceived visual quality payback for the investment.

It depends on the version of Photoshop, v5.x had no native support for high bit filtering, but with third party support some basic filtering of high bit data is possible (there is even a freeware convolution plug that has high bit support). Photoshop 6 and higher have limited high bit support of some plugs and filters.

Often there is no appreciable visible quality difference between regular and high bit filtering, but with some large gaussian blurs the high bit operation can be a bit smoother in some cases. But to some folk the data is just as critical as visible results, these people often prefer high bit processing.

There should not be any significant speed difference between a high bit and regular bit scan, apart from the file writing time. One would hope that the scanner always scans at the highest bit rate and samples down when a lower output is requested. If performing scanner edits, it would be hoped that these are internally performed at the highest bit rate of the scanner as well.

What Photoshop 5.x or higher can do which scanners often do not is add minor stochastic noise to the high bit to low bit transform. This dither noise which is not really noticeable can add to file size but it can also be of help in breaking up banding or posterization and can be a good thing at times. So for some users it is a very good thing to scan in high bit even if they do not want it and to switch bit depths in Photoshop so that statistical dithered noise is added to the image.

This is not to be confused with the Photoshop colour settings advanced option for dithered noise in regular 8 bpc images - with high bit there is no option and the dither is always on.

Dan Margulis, a noted high bit work-flow critic even changed his viewpoint after some colour scans that were converted to 8 bpc in the scanner were poor after edits, while a high bit converted to regular bit in Photoshop and then edited the same was superior. It appears that the high bit to reg bit dither was the key difference.

Stephen Marsh.

[Markendorf]

Hi folks, greetings from Rio de Janeiro- Brasil.

I would like to add some points.

In my experience, if I have the 16 bit version I could extract many details in shadows and bring evem more in high lights.

Many 16 bit files from many and many manufacters are not really 16 bit, but 10/12 or evem 14. Photoshop will "convert" to 16 bit mode and until version 7 will occurr a "quantization error" just because Photoshop use only 15 bit's and take the 1 bit for some task that I can't remember.

Mr. Dan Marguillis are right when talk about the quality in final output BUT, in Imput side I really belive and see many improvements using 16 bit data for very first adjustments. My enviroment are big Add Agency and very pick art directors which would like to change the day light room to night or something else.

Excuse me for my poor english I'm still learning.
Regards,

Adriano

[Doug Nelson]

Now that Photoshop CS offers broad 16-bit support I rarely leave that mode if given a choice. Layers works fine in 16bit mode.

Look at it this way: if you lose one tone in an 8bit image, you've lost 1/256th of the available tones. If you lose one tone in a 16bit image, it's only 1/65536th of the available tones. In mild retouching this is perhaps trivial, but in restoration every single tone is precious.

I honestly don't understand why there is even a debate. If anyone even pauses to do the math to determine if it's worth the extra hd space, they have something other than image quality as their first priority.

[Markendorf]

I totally agree.

Anyhow, just for sake of compare. We have an publication in Brasil called "Publish" the best Writer and Prepress expert doesn't hold the breath in criticize the waste of time/storage working in 16 bits. Just because (in their opinion) the final output will be in 8..Jesus ! of course he did mentions about Marguillis.

Regards,

Adriano

[john_opitz]

***This is a post from the man, from the color theory list. Posted with his permission (post #12379 on the color theory list)***

Last month, it appeared that some the basics were finally being agreed upon
as to some of the advantages or lack thereof in color-correcting 16-bit files
vs.
8-bit files. This topic that has wasted far more time than it could possibly
merit
over the last half-decade. Because there was a lot of posturing that masked
the essential agreement, I suggested that we stop the thread, and I promised
that at a later time I would post a fuller response.

I'd like to start from scratch and explain what the basic principles are, why
the
debate went on so long, and what it teaches us for the future. I do not believe
this is a topic significant enough for a magazine article, but this post is
article-
length, and is therefore divided into three parts plus an appendix. I intend
this
to be my last word on the subject until the next edition of Professional
Photoshop, unless there are some new developments from images I am now
studying.

DEFINITION.
A bit is the smallest addressable part of a computer's memory. It can be seen
as either 0 or 1, either on or off, either yes or no. Each bit therefore has two

possible states. Two bits taken as a pair have four possible states. Three bits
have eight, four bits 16, and so on, with the number of possibilities doubling
every time a bit is added.

Ever since the advent of digital color correction in the early 1980s, it has
been
standard to devote 8 bits of computer information to describe a single pixel in
a single channel. This gives a total of 256 possibilities. In three-channel
colorspaces like RGB, 24 bits (8x3) are required to fully define the pixel's
color, meaning that there can be 16,777,216 (256x256x256) possible colors
for a given pixel.

Nobody can see that many colors. Even the most optimistic estimates--and
that's the side you find me on--say that humans can only perceive a little more
than a million colors, and most experts put the figure considerably lower than
that.

Nevertheless, some believe that it makes sense to try to define more colors.
Some digital cameras try to record 10-bit (1,024 possible values per channel,
a billion possible colors). Modern drum scanners try for 12-bit (4,096 values,
69 billion possible colors). Whether these devices are accurate to that level of

precision is very doubtful.

In the mid-1990s, Photoshop introduced limited support for 16-bit files--
65,536 values per channel, 281 trillion possible colors. There was no
intermediate level. If you had a 10-bit file and wanted to get it into
Photoshop,
you had to decide whether to bloat it by making it 16-bit or compress it by
making it 8-bit. Also, few important commands other than curves would work
on a 16-bit file. We could not even make a layered file in 16-bit. As time went
on more support was added, and today almost anything we can do in 8-bit we
can do in 16-bit.

THE ISSUE.
The question before us is not whether to capture in 16-bit, store in 16-bit, or
output in 16-bit. The only issue is, first, is there any advantage in *editing*
files
in 16-bit rather than 8-bit, and if there is, it is so enormous as to constitute
a
"night and day difference" or to justify the statement that anyone who does not
edit in 16-bit is a "recreational, rather than professional" user of Photoshop.

16-bit files are twice as large as 8-bit files. They take longer to store and to

back up and require more disk space. Also, if the file size is large, it may
take
Photoshop much longer to perform edits. Plus, most output devices and many
layout programs won't accept 16-bit files, so we have to go to the trouble of
converting them to 8-bit eventually anyway.

For some, this isn't an issue. They process a limited number of images in
studio and, taking advantage of today's low prices, they have an infinite
amount of storage space. For others, like newspaper photographers on
deadline, doubling the file size would be so onerous as to be out of the
question even if there was a undeniable quality gain associated with it. For
everyone else, the doubled file size is an inconvenience to some degree. The
question must be whether we gain any benefit, and if so, what, because it's
possible we might want to use 16-bit some of the time and not others.

When someone advocates doing something inconvenient, whether
converting to LAB, or using Camera Raw, or doubling one's file size, or
putting 15 layers on a file, it's up to that person to make a compelling case
for
it. It isn't up to you, me, or anybody else to show that it's *wrong* to do it.
The
reason that the subject has refused to die is that the advocates of 16-bit
editing claim exemption from this rule: they take the position that whatever
they recommend, whether it's 16-bit editing or wearing garlic around the neck
while writing curves, must be taken as gospel and that they have no
responsibility to back up what they say.

AREAS WHERE EVERYONE AGREES.
Nobody AFAIK has ever doubted the following.

Extra bits are valuable in editing computer-generated graphics, especially
those that include gradients, or with image areas that are so heavily
retouched that they are essentially computer-generated as opposed to
photographic.

Scanners, digital cameras, and Camera Raw all operate natively with more
than eight bits. As there's no way to make them operate any other way, the
question of whether they *could* operate effectively with fewer bits is
irrelevant.

Certain scanners and certain camera software do not generate 8-bit files
correctly. Therefore, where possible, these files should be brought into
Photoshop in 16-bit, and converted to 8-bit at a later time.

Most people who handle lots of images have from time to time been burned
because they failed to save a copy of the original, untouched image. People
crop the image or rez it down only to discover that the extra information comes
in handy a year later. The chances of a bug in Photoshop or the OS
inadvertently damaging a file when it is resaved are extremely small, but they
are not zero. That alone is a good reason to save a copy of the original 16-bit
file.

16-bit does no real-world harm other than the extra space and computing time
it requires.

THE INITIAL WILD CLAIMS.
While nobody has ever argued that people who are comfortable using 16-bit
for correction should stop doing it, the same is emphatically not true of 8-bit
users. Starting in 1999, a slew of self-appointed experts, largely but not
exclusively Andrew Rodney and his business partners, began to attack
anyone who didn't use 16-bit for *all* editing. The rhetoric they used was
apocalyptic. Editing in 8-bit was "amateurish". It was "highly critical" to edit
in
16-bit all the time. Those ignorant enough to edit in 8-bit proved themselves to

be "recreational, rather than professional" users of Photoshop.

Early on, a number of users questioned this, stating that they had compared
the two approaches found little difference in the results. Instead of accepting
the possibility that they might be mistaken, the 16-bit advocates dug in their
heels. I quoted the following from a single 2001 thread, where a squadron of
"experts" were berating their challengers. This is not a single speaker, but a
group of them, separated by ellipses.

"16 bit capability is critical during all aspects of tone compression…The
difference CAN be seen in the final output very easily. Most definitely on the
printed page, especially when using high-quality halftoning and even more so
to a film recorder…It's very easy to see that substantial color & tone editing
will eventually result in data loss and banding…If it means the difference
between taking a 16-bit image capture and editing that to the final image and
taking that same image in only 8-bit and editing that to the final image then
there is a difference like between the day and the night…Yes, if a histogram
full of holes has no impact on final output, then throw away the graphs and
just get on with the print run. However, all of us have Real World Output
showing the superiority of superior data acquisition…My advice? Take the
information you've read here to the bank. Stop doubting and start applying
what you've learned here…If you really start out with a RAW image in high-bit
form and a raw image downsampled to 8 bits, the difference really is night
and day. …it's totally obvious to anyone who looks that it's very advantageous
to do the big moves on high-bit data."

Nobody offered a single real-world image to show this enormous difference. It
was all histograms and gradients, gradients and histograms.

THE "CHALLENGE".
The type of color correction I teach does not depend on bit depth. The
methods work equally well whether you choose to use 8-bit or 16-bit. I have
never written an article or a column about bit depth. I don't even mention the
topic in my classes.

There are around ten pages of Professional Photoshop that discuss bit depth
and around five pages of Photoshop LAB Color. They are there is not
because they are necessary to my message in any way, but because the
advocates of 16-bit editing were so forceful in their denunciations of anyone
not using their methods that I kept getting hit with the question, both on this
list
and elsewhere. At http://www.ledet.com/margulis/ACT_postings/
ColorCorrection/ColorCorrection.htm there are several archived threads on
this topic dating from 1999. The only thing that I could answer was that I have
nothing against others using 16-bit, and use it myself in dealing with
computer-generated graphics and in very specialized cases with color
photographs. However, AFAIK there are no real-world circumstances under
which a non-expert would find it beneficial for editing color photographs.

Before putting anything in my own books, I try to verify that there isn't
something unusual about my own files that causes me to draw an incorrect
conclusion. I therefore posted a request for people who thought that they
could demonstrate an editing superiority for 16-bit to arrange to send me files
for testing. As my own testing (see Part II, "Where 16-Bit Can Be Better") had
already established that a grayscale file could conceivably show an
advantage either for 16-bit or (more commonly) for 8-bit editing, I specified
color photographs only, in one of the four standard Photoshop RGB
definitions.

Around a dozen people have since responded between 2001 and now. They
put together packages containing proofs and often several different versions
of corrections. Over a period of a full week in 2002, I analyzed image after
image trying to find any circumstances under which 16-bit editing would give
superior results.

Finding none, in Professional Photoshop Fourth Edition, I published almost
ten pages of comparisons, because to illustrate the points, pictures have to be
fairly large. Six full pages were devoted to showing images at various
magnifications. Because the 16-bit advocates had retreated to a position of
claiming that the difference was only critical when the corrections were large
ones, the examples I showed ranged from large to inconceivably huge, in one
case taking a picture that was so flat that it was unrecognizable for subject
and correcting it into something that could be mistaken for professional work. I

printed each image at high magnification, including some individual
channels. They were printed without identification and readers were invited to
guess which was which. I particularly chose images that would be the most
prone to the sort of banding that the 16-bit advocates claimed would happen.

Every person who has ever submitted files to me has agreed with my
assessments of image quality. Certain people have had procedural mistakes
that I pointed out, and they have always agreed that my objections were
correct. In the cases where I am stating that there was a qualitative difference

when done in a certain way but not in another. I have shown the results to the
person submitting the files and they have always agreed with my findings.

Similar independent testing was subsequently performed by Jim Rich. The
main difference between his testing and mine was that Jim's testing involved
real-world corrections of images, in that his corrections, although severe,
might actually be seen on an everyday basis. Mine, OTOH, were intentionally
set up to be far more demanding than any real-world scenario would ever
entail. Anybody having to deal with the type of challenges that I published has
many more serious workflow problems than bit depth.

Jim's testing, which was also independently reviewed by experts, got the
same results. Since that time, around a dozen people have performed similar
tests, trying to find any real-world scenario in which 16-bit editing of color
photographs might produce an advantage, however trivial, over doing the
same thing in 8-bit. Everyone has come up empty.

In my LAB book, I had one further example, in trying to dispose of a similar
myth. In the mid-1990s, one of the same people who now fiercely defends 16-
bit editing was even more fiercely opposed to the use of LAB. He asserted
that the very conversion from RGB to LAB to do the editing caused
"catastrophic damage" to the image. This opinion was, of course, based on
analysis of histograms and gradients. In response, in a 1997 book, I showed
side-by-side images, one of which had been converted back and forth
between LAB and RGB 75 times. No difference, of course. Nevertheless, the
myth persisted, and I would several times a year get questions about the
supposed damage. So, in the LAB book, I did another such example, 25 times
back and forth. I compared it mathematically to other conversions and
demonstrated that the variation between the RGB>LAB>RGB and the original
RGB version was less than that between many RGB to RGB conversions.

Shortly after announcing the "catastrophic damage" theory and finding that
there was no damage at all even after multiple conversions, the theorists
changed their theory. The catastrophe, they opined, only occurred the *first*
time that a file was converted; subsequent conversions of the same file would
be harmless. But, if at some other point in the correction, there would be for
some reason another conversion to LAB, *that* would be a catastrophe. This
was similar to one of the changes in their 16-bit theory. Originally, it was
"highly critical" to do all edits in 16-bit. Then, it was changed to "big
changes".
When it became clear that this theory didn't hold up either, it was changed to
"big changes done over a series of smaller changes."

Therefore, in total disgust, I spent five pages of the LAB book showing large-
size, magnified comparisons not of two variants, but of four, of each of two
different images. The images were specifically chosen because they had the
type of smooth areas that supposedly cause disaster in 8-bit editing and in
conversions to and from LAB. One was a 16-bit digicam capture, the other 16-
bit scanned film. They were compressed into a small 16-bit range, which is far
more challenging for the subsequent edit than starting with an original limited-
range capture.

To these images, I applied not one or two big corrections but, in accord, with
the theory, seven of them. These were done in RGB. I did the test once in 16-
bit, and once in 8-bit. But then I repeated the tests with a twist--after each
of
the seven moves, I converted unnecessarily to LAB and back again.
Therefore, between the most politically correct of the four variants (16-bit all

the way, no conversions) and the least (8-bit all the way plus a conversion to
LAB after each move) there were seven night-and-day, totally-obvious-to-
anyone-who-looks corrections *plus* seven catastrophic-damage
conversions.

Nobody could tell which was which even at high magnifications.

Dan Margulis

----------------------------
In Part II, I discuss the situations where 16-bit editing can actually be
better,
and review the retreat of the 16-bit advocates from the night-and-day
difference position.

[john_opitz]

WHERE 16-BIT CAN BE BETTER.
A 16-bit file can have very minute differences between pixels--1/256th of the
minimum difference in an 8-bit file. Anything that small will have no impact on
the final reproduction--no possible sequence of editing events could ever
create a variation that anybody could see. The maximum initial difference
between a pixel of an 8-bit and a 16-bit file would be slightly less than half a

level. That is, in a 16-bit file there might be a value of 128.49, which would
be
treated as a value of 128.00 in 8-bit. That half-level difference won't do
anything, either, *unless* some unlikely sequence of commands drives it
much, much further away from where it would be if it were an 8-bit file.

For technical reasons that will be discussed later (see What the Extra Bits
Actually Do, Part III), if you look hard enough and at a high enough
magnification, the 16-bit edit always looks marginally smoother and the 8-bit
more active. To date, I know of four types of natural photographs that, if
edited
to an extreme, show differences large enough for people to prefer one or the
other. (There are also some times in retouching and image conversions
where working in 16-bit helps, but they are so esoteric that I have rarely
written about them.)

1) If we apply massive edits to a grayscale file, the difference between an
8-bit
and a 16-bit correction may become noticeable. The 16-bit version would be
preferred if the image featured areas where smoothness is desirable, like
skies; the 8-bit when the subject is full of detail. In my testing, even with
very
big grayscale edits, well over half of the images showed no difference. Of the
others, the result of 8-bit editing was preferred roughly twice as often as
16-bit
edits. But definitely 16-bit editing got better results in certain images. The
reason that this does not carry over into color images is that when three
channels are superimposed on one another any variation in one is less
visible. Similar massive edits to the RGB files that were the ancestors of the
grayscale files showed no difference of any consequence.

2) Early in my testing, one list member provided a demonstration based on
applying the same edits to one 16-bit and one 8-bit file, both generated by a
scanner from a single scan. I verified that when the edits were applied the 8-
bit file looked distinctly worse. However, when the tests were repeated on a
copy of the 16-bit file that had been converted into 8-bit not by the scanner
but
in Photoshop, there was no difference in quality. I communicated this finding
to the list in 2001 and recommended that people take 16-bit files from
scanners where possible.

3) A second user provided a similar exercise where edits were applied to 16-
bit and 8-bit files generated in Canon acquire software from the same digital
capture. (The original had deliberately been acquired incorrectly in order to
make the differences more apparent, which disqualifies it as a real-world
example, but in view of the interesting nature of the problem I followed
through with the testing.) Again, I verified that there was a quality loss by
editing the user's 8-bit file, again I retested by converting his 16-bit file to
8-bit
in Photoshop, and editing that. As with Example #2 there was now no longer
a quality difference, so I recommended to the list that we avoid taking 8-bit
files directly from a camera package when a 16-bit file is available. I do not
know whether the same problem exists in Camera Raw but I will be testing it
in coming months.

4) In 2005, a third user provided a Camera Raw file of a scene of a city at
night. He sabotaged the image by moving the exposure slider within Camera
Raw all the way to the left in spite of the fact that the image was already too
dark. Then, he acquired the image in ProPhoto RGB, an ultra-wide gamut
RGB definition that is rarely used in professional work. The image contained a
large area of sky. Applying the drastic curves that were needed to lighten the
image to the 16-bit file resulted in a perceptibly smoother and more attractive
sky than the one done by converting the file to 8-bit in Photoshop and
applying the same curves there. When the same image was captured with the
same sabotage in Camera Raw into either of the RGB definitions that most of
us use--the narrow-gamut sRGB or the wide-gamut Adobe RGB--there was
no significant difference between correcting in 8-bit or 16-bit.

THE RETREAT.
Ever since the initial assertions that 16-bit editing would create an enormous
difference, its proponents have been in full retreat as users have asked them
again and again for any example to support the notion. They have provided a
blizzard of gradients and histograms, but never a real image. One author's
idea of illustrating the concept was to compare an *original* image to one that
had been edited in 8-bit and then showing the histogram. In a second book,
he compared reasonable editing in Camera Raw (which is 16-bit) with idiotic
editing in 8-bit Photoshop, in each case claiming that it showed the superiority

of 16-bit editing.

In fairness, the demand for images placed the advocates in a difficult position.

There is no reason to doubt that they actually believed their original wild
claims were true; as has been made abundantly clear since, they never
bothered to run tests before making them. By the time they learned that there
was serious doubt that there was any 16-bit benefit at all, let alone a night
and
day difference, they had already begun to promote seminars about the
benefits of the 16-bit workflow. Furthermore, Adobe, largely at their
suggestion, had begun to add 16-bit capabilities to Photoshop which were
being heavily hyped. As many of these advocates take money or other
support from Adobe, it would have been exceedingly awkward if they had
abandoned the you-are-not-a-professional-if-you-don't-use-16-bit line.

Since they could not abandon their position but could not produce anything to
back it up, they resorted to smokescreens. The usual method was personal
attacks on me. They repeatedly referred to some mysterious "agenda" of
mine. They called me lots of names, but never could get around to showing
what the people were asking for. They asserted that I said 16-bit was
worthless under all circumstances and presented gradient after histogram to
prove that it wasn't. They spent scores of hours telling users that they were
"too busy" to prepare demonstration images that could have been made very
quickly if the difference was even a tenth as critical as what they were
touting.
They constantly tried to evade responsibility by saying that the burden was on
me to prove that 16-bit doesn't have advantages, as if *I* were the one who
was saying that anyone who didn't work my way was unprofessional and *
they* were the ones who were tolerating either way.

One of the more prominent advocates, Bruce Lindbloom, was so frustrated by
his inability to produce a persuasive image that he posted a web page that
accused me of sabotaging my 16-bit images before testing them. Also, he
asserted that I kept my results private and that nobody else could verify them.
Both statements are categorically false, and Lindbloom knew that they were
false when he posted them. 16-bit advocates Andrew Rodney and, to a lesser
extent, Bruce Fraser, both of whom are well aware that the Lindbloom page is
a crock from the word go, nevertheless repeatedly post links to it, hoping that
if they post the falsehood enough times, it will magically become true.

The gyrations that these advocates went through to explain why they could
not produce even a single real image that would support the notion that 16-bit
editing was "highly critical", would produce a "night and day difference", and
so forth are so remarkable that they are excerpted at length in Part IV.

This list did get a glimpse of the rationale from Jeff Schewe in 2002, in a
thread that is posted in our archives. He defended his assertion that those
using 8-bit are "recreational, rather than professional" users of Photoshop as
follows (note: Jeff frequently uses ellipses [. . .] in his messages; in the one

case where I have deleted an extraneous section of the message, I use ***):

"Nope. . .Dan and the rest of you are welcome to continue scanning in 8 bits
and doing whatever you want to do to your images. . .but if you want absolute
total control over tone and color without the risk of breaking the image
somewhere down the road. . .you better learn to edit in 16 bits.***And yes, I'll

stand by the line 'recreational' if you squander and waste your data bits just
getting an image tone/color corrected in 8 bit. . .cause if you do that, you're
working with considerably less than 8 bits/channel and deserve the banding
you are likely to incur."

I replied, "Rather than continuing to post the same defensive bluster to every
group credulous enough to listen, it must be a better use of your time to
produce even one image that demonstrates the point. After all, this is
supposed to be critical, night and day, the difference between professional
and recreational imaging. If an image exists that shows such a dramatic
difference, why not show it, rather than just make claims?"

The evidence Jeff offered in response was, "Pretty much all of my work the
last 5 years was scanned in 16 bit for initial tone & color correction. You are
welcome to look at my work and see for yourself, no banding. . .even after
hours of editing and extreme manipulations. I'll let my work speak for itself."

Within a year, however, others had backed off the original claims. The new
emphasis was on "flexibility for the future." The night and day differences were

no longer found in really big edits, but only in ones with multiple big edits.
We
were cautioned that, even if 8-bit is sufficient now, new types of output
devices
might arise that would require more bits. The ad hominem attacks on me and
my purported motivations continued whenever users asked on-line for
specific images.

By 2004 the embarrassment was such that the protagonists began to deny
ever having made any of the apocalyptic statements. In November, Andrew
Rodney posted the following astonishing statement to this list: "And no I've not

seen any text that says '16-bit is absolutely critical, creates a night and day
difference, that anyone who doesn't do it is an amateur, etc., etc'. It's simply
a
reflection of math and physics." When Ric Cohn pointed out that Andrew's
own business partners had frequently used precisely those words, the
following day Andrew denied having denied it. Thereupon I produced
Andrew's original denial--and he denied ever denying he had denied it. And
throughout the rest of the thread he resumed the position that nobody had
ever said such things. And held to it, even after the quotes were posted.

Earlier this year, on the ColorSync list, of which I am a member but don't
normally participate, Bruce Fraser once again took shots at my motivations
when the list turned to the bit depth topic. He wrote, "What Dan's tedious and
fundamentally specious arguments deliberately miss is that the need for
greater bit depth has absolutely nothing to do with reproduction and
everything to do with editability."

At that point I entered the thread to point out that I did not miss that point
and
that on the contrary, the files that I had been testing were edited beyond all
recognition, beyond any possible claim of real-world practice. And I pointed
out how many other people had performed similar tests with the same results,
and again asked why he could not produce any images to back up his claims
of a "night and day difference" that was "totally obvious to anyone who looks".

Bruce denied having ever said these things, whereupon I produced the
original files where he did say them. After further exchanges in which he
waffled somewhat on these phrases, I asked pointblank whether he had ever
personally run tests of 8-bit editing vs. 16-bit editing, before or after having

laid down these ukases about how the difference would be night and day. He
refused to answer. After being further pressed, he stated that it would be a
waste of time because it was obvious that the 16-bit would look much better (if
you don't believe he said this, don't take my word for it, go to Part IV). And,
having refused to accept the possibility that something he hadn't tested might
not be true, he ended with a typical slur: "My personal opinion is that this is
a
manufactured controversy--I decline to speculate on the motivation of those
who have manufactured it--and I'm utterly disinclined to waste my time
arguing the point when I have better things to do with it."

In many of these threads, other users have chimed in claiming that they are
positive from first-hand knowledge that 16-bit editing avoids problems of
banding. I'm aware of around thirty such posts, including a couple to this list.

In about a dozen cases, I've gone off-line to ask these people how they are so
sure. Without exception, they have never performed any testing--it's all a
hunch. They, like Jeff and Bruce, merely are supremely confident that their
work would show banding or other artifacting if they did it in 8-bit. But
they've
never tried to do the same things to 8-bit files that they do to their 16-bit
files,
so they can't know for sure, and they refuse to accept the word of others who *
have* performed such tests.

The people who have doubted that there is a night-and-day difference
between 16-bit and 8-bit correction, or that correcting in 8-bit is amateurish,
have generally said they are willing to be persuaded otherwise by examples,
as I am. Some members of the other side take a different tack. It is so obvious
to them that their view is right that not only do they require no proof of it,
but
they state outright that they refuse to accept any proof that it is not. It has
been
remarked by others that such a position is a religious rather than a rational
one, and I agree. The closest analogy I can think of would be to the person
who says that it is so obvious that the world is flat that it needs no proof,
and
that any demonstrations that it is round will be ignored because they can't
possibly be right, since it is well known that the world is flat.

It actually gets better. Since that time, Bruce Fraser has, incredibly,
announced that direct comparison of 8-bit to 16-bit editing is invalid, and
conceded that side-by-side tests will show no advantage for 16-bit. He writes,
"I've demonstrated many times things that work better in 16-bit than in 8 bit,
but Dan has rejected these because they don't fit his narrow criterion of doing
exactly the same things to a 16-bit and an 8-bit file, then comparing the
results." Separately, he clarifies, "The major problem with the methodology...is

that by making identical edits to the 8-bit and the 16-bit, you're throwing out
any benefit the extra bits may bring. They aren't useful unless you DO
SOMETHING with them!"

The extra bits may indeed be useful if you do something, but there's no way of
knowing for sure without trying to do the something without them, and seeing
if there's a significant difference. A lot of people have done this. The answer
they have unanimously come up with is that there is not.

Dan Margulis

----------------------------
In Part III, a 16-bit advocate finally comes up with a "real-world" example that

turns out not to be so real-world, and a consensus develops about bit-depth
and choice of colorspace.