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Reconsidering 16 bit

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  • Reconsidering 16 bit

    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.

    Attached Files

  • #2
    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:

    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.


    • #3
      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.



      • #4
        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.


        • #5
          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.



          • #6
            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


            • #7
              <<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.



              • #8
                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.


                • #9
                  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. PS will "convert" to 16 bit mode and until version 7 will occurr a "quantization error" just because PS 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.



                  • #10
                    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.
                    Learn by teaching
                    Take responsibility for learning


                    • #11
                      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.




                      • #12
                        A post from Dan &quot;The Man&quot; Mangulis

                        ***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
                        8-bit files. This topic that has wasted far more time than it could possibly
                        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
                        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
                        length, and is therefore divided into three parts plus an appendix. I intend
                        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

                        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
                        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

                        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
                        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*
                        in 16-bit rather than 8-bit, and if there is, it is so enormous as to constitute
                        "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
                        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
                        it. It isn't up to you, me, or anybody else to show that it's *wrong* to do it.
                        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

                        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

                        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

                        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
                        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
                        and elsewhere. At
                        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

                        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
                        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
                        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

                        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
                        and review the retreat of the 16-bit advocates from the night-and-day
                        difference position.


                        • #13
                          Part 2 of the post

                          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
                          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
                          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
                          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
                          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
                          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
                          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
                          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
                          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
                          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.
                          were cautioned that, even if 8-bit is sufficient now, new types of output
                          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
                          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
                          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
                          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
                          never tried to do the same things to 8-bit files that they do to their 16-bit
                          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,
                          they state outright that they refuse to accept any proof that it is not. It has
                          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,
                          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

                          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.


                          • #14
                            Part 3 of post

                            THE CONSENSUS.
                            In early September, Andrew Rodney posted his own "real-world" example of
                            8-bit vs. 16-bit editing. As soon as it appeared, it was dismissed both by me
                            and by Lee Varis because it depended on an exotic RGB definition, the ultra-
                            wide gamut ProPhoto RGB, where the perceived impact of tiny variations is
                            much larger than in the RGB definitions used by almost everyone. Andrew
                            has known for at least five years that I consider testing in such RGBs
                            irrelevant--see "The Attempts to Obfuscate" below.

                            Even if we were allow Andrew to sneak this image in, it wouldn't show a 16-bit
                            superiority, for two reasons. First, he deliberately chose a zero-threshold
                            sharpening setting for his image to emphasize the differences between his
                            16-bit and 8-bit versions, when an equivalent setting that required no
                            additional steps was available. To back up the premise that you have found a
                            real-world difference, it's fair to say "I would like to do the following or
                            something equivalent, and I find that there is no way to do so without getting
                            an effect that displeases me." That would have been the case with any of the
                            four examples cited in Part II, "Where 16-Bit Can Be Better". It is, however,
                            fatuous to say, as Andrew does, "Of many possible equivalent settings, I have
                            intentionally chosen the one that displeases me, and now the test fails
                            because I am displeased."

                            Second, the standard is "totally obvious to anyone who looks," a "night and
                            day difference." Anybody who looked at the four examples cited above would,
                            in my opinion, prefer the 16-bit versions. The only person known to have been
                            shown printed versions of Andrew's samples preferred the 8-bit version.
                            Some areas of Andrew's 16-bit version are better than the 8-bit but larger
                            areas are worse. I think that a jury would rate the two versions as
                            equal, but if they did not, I expect they would choose the 8-bit version as
                            better overall.

                            Andrew's edits were not particularly severe. Conceivably more massive edits
                            would have created a pair of images with differences strong enough for
                            people to have a clear preference for one as opposed to the other. In view of
                            my testing with B/W images, I think it's likely that when there is an actual
                            preference, people would tend to prefer the version corrected in 8-bit.
                            However, there would also be cases where the smoothing effect of 16-bit
                            editing would be preferable. But again, the situation is not real-world. Anyone
                            knowledgeable enough to take advantage of the extra bits would be unlikely
                            to be editing in such an RGB in the first place. And nobody, not even Andrew
                            and his partners, advocates making big edits in an ultra-wide RGB in
                            Photoshop proper. Any move big enough to provoke a visible difference
                            because of bit depth, they would urge making in Camera Raw.

                            Lee, Andrew, and I all agreed that when the file was put into Adobe RGB
                            rather than ProPhoto RGB, and the same edits, including the zero-threshold
                            sharpening, were applied, there was no significant difference between the 16-
                            bit and 8-bit version. Whereupon Andrew stated,

                            "I will admit: If you work with a small(er)gamut space, the need for high bit
                            editing is reduced and possibly a non issue."

                            I think that this face-saving admission is acceptable--that for Adobe RGB and
                            sRGB, the two spaces that we almost all use--editing in 16-bit is no longer
                            highly critical, no longer the distinction between a professional and a
                            recreational user, no longer a matter of night-and-day difference, but rather
                            "possibly a non-issue."

                            In return for Andrew's concession, I cheerfully respond as follows: "I
                            categorically recommend against making major edits to photographs in ultra-
                            wide RGB spaces such as Wide Gamut RGB and ProPhoto RGB when any
                            reasonable alternative exists. If you nevertheless insist upon doing so, you
                            should take into account that under such conditions the bit depth of the file
                            may affect quality, so you should be aware of the circumstances in which 8-bit
                            editing may be superior as well as those in which 16-bit may be."

                            THE ATTEMPTS TO OBFUSCATE.
                            Throughout these five years, the 16-bit advocates have been trying to deflect
                            attention from the basics, which are that they bullied and berated users,
                            calling them ignorant and unprofessional, all because these users did not use
                            an inconvenient workflow that has never been shown to be of any use

                            The challenge is a simple one: to take any color photograph that might
                            conceivably be used in a professional setting, operate on it in any way that a
                            person, even an incompetent one, might try, and demonstrate a clear
                            superiority for 16-bit editing of that particular image. I do not say that no
                            image could possibly exist. I do say that we have not seen one yet, and a lot
                            of people, including me, have tried hard to find one.

                            The terms of the challenge are extraordinarily permissive, and the 16-bit
                            advocates have resorted to extraordinary whitewashing to cover up the fact
                            that they can't meet them. They keep trying to sneak in obviously inapplicable
                            stuff; when everyone laughs at it they accuse me of "changing the rules" and
                            click their tongues and say, "see? No matter how hard we try, our stuff is
                            always rejected on a technicality! Clearly there's no image in the world that
                            Dan would ever accept!"

                            We saw this on the list last year. A member posted as an example a
                            Photoshop file consisting of no more than small blue area with noise. He
                            asserted that this was a picture of a "sky." There was no way of verifying this
                            as there were no clouds or other detail that might identify it as a sky; no way
                            knowing that it wasn't computer-generated, for that matter. I said that it is
                            somewhat difficult to accept as a "real-world photograph" something that an
                            independent viewer can't identify as a photograph at all, let alone what it's a
                            photograph *of*. Andrew Rodney immediately went ballistic, again accusing
                            me of changing the rules and stating that this proved that I would never accept
                            any image as being real-world.

                            Similarly, the "real-world" corrections consisted of seven pairs of drastic
                            actions, each designed to reverse the other. Again, based on my assertion
                            that there was not the slightest chance that anyone would ever be stoned
                            enough to *dream* of doing something as crazy as that in the real world,
                            Andrew again asserted that there was a change in the rules.

                            In the 2005 ColorSync thread, I was again accused of changing the rules
                            because I should have made clear that "photograph" and "computer-
                            generated gradient" are two different items and that I would not accept a
                            gradient for testing. Also, it was alleged that I changed the rules because my
                            use of the words "color photograph" did not make it sufficiently clear that
                            grayscale images were excluded.

                            Andrew's recent image saw more of the same obfuscation. When I said that
                            the behavior of exotic RGB definitions is irrelevant, Andrew very piously said
                            what he usually does when caught cheating on such occasions: "I didn't
                            expect this scene or any additional scenes I can capture with this sub-$1000
                            camera to 'fit' your criteria since once again, that seems to be a moving
                            So I've come to the conclusion that no matter what one does to try to show the
                            advantage of high-bit editing, it will fall on at least two deaf ears."

                            I've never accepted such files for testing. Andrew Rodney knows this,
                            because he complained about this condition in 2000, in a thread that's
                            archived on our site. He correctly pointed out, and I agreed, that ultra-wide
                            RGBs are more likely to show a difference. I replied (remember, this is 2000):
                            "To me, it's like asking how many angels can dance on the head of a pin.
                            Nobody to speak of is using wide gamut RGB. There are a lot better uses of
                            our time than to investigate the question of whether it needs 16 bits. I *have*
                            looked at the issue in Adobe RGB and don't see that the extra bits are useful
                            there. As I mentioned earlier I would be anxious to see images from anyone
                            that might contradict this."

                            Further, in the 2005 ColorSync thread, I specifically suggested that the
                            ProPhoto space might sometimes show a difference between 16-bit and 8-bit
                            editing if the edits were extreme enough. Seizing that suggestion, Andrew
                            created his example--and then feigned shock that I wouldn't accept it, even
                            though he had known for five years that I wouldn't.

                            This type of behavior is only what we have come to expect. As has already
                            been pointed out, both Andrew and Bruce have tried to deny that they said the
                            wild things they did five years ago. And, particularly, the intentional
                            falsehoods on the Lindbloom site have been called to Andrew's attention
                            again and again on this list and elsewhere. Yet he continues to pepper
                            cyberspace with references to it. Every time he does so, he shames himself.

                            WHAT THE EXTRA BITS REALLY DO.
                            Understanding statistical concepts is not easy even for those with extensive
                            training in the field. Casinos have lost hundreds of millions of dollars to
                            mathematically astute players because the professors the casinos hired to
                            advise them on probabilities failed to comprehend certain statistical
                            interactions. The New York Times polled academics about a statistical-
                            interpretation puzzle called the Monty Hall Dilemma, and the majority of
                            professors of mathematics gave the wrong answer. Both of these examples
                            are absolutely child's play in comparison to trying to interpret what makes a
                            picture look good.

                            Progress in our field has been hampered considerably by "experts" who are
                            so terrorized by histograms that they don't understand that they feel they will
                            sound more authoritative if they try to terrorize their readers with them as

                            The calibrationism of the 1990s, the fear of applying easy curves to images for
                            fear of "irretrievable data loss", the phobia of LAB, the insistence on applying

                            profiles to things that obviously can't be profiled, are all symptoms of the
                            disease. The confusion between gradients and digital photography is one of
                            the best examples yet.

                            A computer-generated gradient is a perfect file. Each pixel gets its optimal
                            value. Working in 16-bit gives extra precision, and it's unconditionally better
                            for gradients than 8-bit is. It's possible that the two methods might give
                            equivalent results. It's possible that the 16-bit might be better. But it's not
                            possible that it would be worse. Also, it's easy to come up with a
                            demonstration that shows damage by editing such files in 8-bit as opposed to

                            Now, contrast that to a digital capture. It is shot through a lens that is not
                            perfectly clean; through air that contains particulates; it is captured by
                            whose performance varies with age and which may not be clean themselves.
                            The data is demosaiced by an algorithm that we know nothing about. The
                            vendors apply blurring to certain areas, and generally apply contrast-
                            enhancing curves in certain others. Finally, the data is written using an
                            unseen method to a format that may contain its own irregularities.

                            For all these reasons, the idea that even 128 levels per channel, let alone
                            256, are being captured with any degree of accuracy is very dubious. Yet if
                            you open a digital file, up comes what looks like a nice, smooth histogram.
                            That is enough for the 16-bit advocates to put their minds into neutral,
                            prostrate themselves in front of it, and start salaaming. They assume that
                            because the histogram looks like that of a gradient, the image will handle just
                            like a gradient does. That's like saying that because champagne tastes good,
                            motor oil must, or that because a helicopter can fly, it follows that a

                            In real life, parts of what the camera captures are much more reliable than
                            others. The better the shooting conditions, the more reliable the information.
                            An underexposed image has less than 8 bits of accurate information
                            anywhere. A shot in studio conditions has *more* than 8 bits of accurate
                            information in the midrange of its green channel, less throughout its blue
                            channel and in the shadows of each channel, and the rest is debatable.

                            CCD and CMOS devices, such as digital cameras, are notoriously poor at
                            extracting shadow detail. Every manufacturer tries to fight noise by using
                            some kind of blurring routine. Similarly, all digicams have difficulties with
                            noise in blue areas, such as skies, and result to all kinds of demosaicing
                            shenanigans to reduce it.

                            In these areas, the values that the camera spits out are approximations only.
                            In the darkest eighth of any channel, an 8-bit file has 32 available tones.
                            There is no digicam that I've ever seen that is even remotely close to
                            capturing these 32 tones reliably. An 8-bit file allows for more precision than
                            the camera has in shadow areas. In these shadows, the 8-bit file therefore
                            already consists of somewhat random numbers. Making it a 16-bit file adds *
                            totally* random numbers in these areas. The histogram-worshipers are fond
                            of using the term "quantization error", but this merely shows their statistical
                            naivete. In contrast to a gradient, where the 16-bit file is mathematically more

                            reliable, the 8-bit file is mathematically purer than the 16-bit in the shadows
                            a digital photograph. Since, in shadows, the extra bits are random numbers,
                            working with a 16-bit file simply adds soft noise in transition areas. Skies
                            behave similarly.

                            My apologies for lapsing into techspeak. A reminder that this effect is so tiny
                            as to be undetectable under real-world circumstances. However, if the file is
                            stressed sufficiently (as Andrew was doing with his exotic RGB definition and
                            his sharpening sabotage) then we may be able to perceive it--and what we
                            will perceive is that editing in 16-bit amounts to applying a blur to these
                            -a highly sophisticated blur that is hard to emulate by other means.

                            AFAIK, all of the claims about the images in which 16-bit supposedly is better
                            involve either skies or shadows. Makes sense--we often blur these areas
                            separately no matter how many bits are involved. The camera's algorithm
                            blurs them already, but sometimes it isn't enough.

                            Unfortunately, if you do enough to the 16-bit file that its inherent blurring
                            an impact in shadows and in skies, it's likely that it also may have an impact
                            areas where you *don't* want blurring. That accounts for the preference one
                            viewer had for the 8-bit version of Andrew's file. In the shadow areas it was
                            worse, but in the foreground areas that were full of detail, it was better.

                            An even more striking example showed up in the last two months, where
                            another 16-bit advocate posted a demonstration at http://www.visual-

                            The image is one of a barn constructed of dark wood, taken in normal
                            daylight. The complaint is identical to Andrew's, namely that correcting in
                            created undue noise in the shadows. The procedure in this image is similar to
                            Andrew's as well, but there are some variations--especially in the result.

                            1) Both are definitely real-world images. This demonstration is in sRGB, which
                            is fine. Andrew's is in ProPhoto, which disqualifies it right off the bat.

                            2) This image is intentionally sabotaged by acquiring it in such a way that it
                            enters Photoshop grossly dark, and is therefore immediately disqualified,
                            because in the real world, we do not sabotage images on acquisition.
                            Andrew's image, by contrast, was acquired fairly.

                            3) Both images now take Levels changes and, in Andrew's case, Hue/
                            Saturation. Fine.

                            4) Now, the attempt to slip in the sabotage. Andrew sharpens using a zero
                            Threshold, which is clearly intended to bring out noise and thus disqualifies it

                            as a real-world move, since in the real world one could achieve the same
                            sharpening affect with a Threshold of 2 or even 1. The other demonstration
                            does this not just one better, but five better: it tortures the image with four
                            consecutive zero-threshold sharpens, plus two applications of Shadow/
                            Highlight, which is a form of sharpening. Again, not real-world: in the real
                            world, when we have two alternatives, we choose the one that looks better,
                            not worse. The purpose of sharpening is to make the picture look more
                            natural, not more noisy.

                            5) And the startling bottom line: while both exercises show more undesirable
                            noise in the shadows in the 8-bit versions, images don't consist entirely of
                            shadows. They need to be evaluated as a whole. I'm familiar with how juries
                            vote when given unidentified samples to choose from. We have one report
                            that with Andrew's image the 8-bit version was chosen as better. I don't think
                            that a jury would agree--I suspect the verdict would be a tie. With the other,
                            however, I have no doubt. The shadows are worse, for sure, but a jury would
                            pick the 8-bit version as better overall, because the same blurring effect in
                            bit that helped the shadows also blurred the main interest object of the image,
                            the wood of the barn.

                            If editing in 16-bit were truly "better", there wouldn't be examples where
                            editing in 8-bit appears to give superior results--it couldn't, any more than
                            editing an 8-bit gradient can possibly produce a superior result to doing it in
                            16-bit. Also, it is very telling that the examples being used always are either
                            skies or shadows, and never the third major category of image that we
                            frequently have to blur: fleshtones. I would suggest that the reason is that
                            camera captures of fleshtones are very much more reliable than either of
                            skies or of shadows. There is therefore less need to blur due to inadequacies
                            of the original capture. Even though the extra bit depth in fleshtones is
                            probably real information and not noise, it doesn't serve a useful purpose.

                            OTHER VIEWS.
                            I would like to close by quoting at some length two other experts who have
                            conducted their own tests.In the 2005 ColorSync thread, Jeff Schewe
                            emerged after I had left, and, unbothered by the overwhelming evidence that
                            there is no quality difference at all, reiterated the same old silliness:
                            "I would argue that it [is] critical that ALL MAJOR tone and color moves be
                            done in 16 bit."

                            Jim Rich replied,
                            "As working in 16 bits to avoid all of these Urban Legend pitfalls such as:
                            The color being day and night different from 8 and 16 bit images.
                            That 8 bit files are fragile in terms of color reproduction.
                            Or that you will get artifacts like banding in gradients after a lot of
                            That 10% percent of images require 16 bits so they don't break.
                            Or that you need to work in 16 bit because of device responses.
                            Let me say again on those points, I am more than skeptical that you require
                            16 bits. My experiences with RGB photos, CMYK print and Inkjet printing do
                            not indicate that one should jump to those conclusion. And we know that
                            mileage will vary.
                            And until I see a test or some other type of hard evidence that all of these

                            problems really exist and are as wide spread, as reported I can't buy into the
                            notion that there is an advantage to going to a full 16 bit workflow for a few
                            renegade images.
                            It would be interesting if some one would please show me a suite of images
                            where the benefits of 16 bit images jumps off the sheet and it is clear what is
                            an 8 bits and what is 16 bit file. Then I can really buy into the 16 bit way of

                            It's hard to know what more could be asked. Jim admits that it is impossible to
                            prove that there will *never* be a case where 16-bit is beneficial, any more
                            than one can prove that it would never be beneficial for a righthanded person
                            to work with the mouse on the left-hand as opposed to the right-hand side. As
                            indicated above, several 16-bit advocates have said explicitly that
                            demonstrations don't matter: it is so obvious that 16-bit is the better way that
                            requires no proof.

                            Tim Grey, one of the rising stars in the Photoshop field, wrote this in his
                            September newsletter:
                            "In a general sense, I do indeed agree with Dan. The way I explain this
                            issue is that 16-bit editing provides more 'headroom' for editing, ensuring you
                            won't create posterization in the final result. However, I've also tried to make
                            clear that the vast majority of the time, you will never see any benefit at all
                            from optimizing your images in 16-bit. The simple fact is, even if you strip out
                            significant number of tonal values in your image, you'll still have an adequate
                            range to produce what appears, to our eyes, to be perfectly smooth
                            gradations. I often do a demonstration in my workshops as I posterize an
                            image and ask students to tell me when they see posterization. In general, I
                            get down to about 32 levels per channel before anything is visible, when
                            there are 256 available in 8-bit per channel images. So why do you need 16-
                            bit? The short answer is, if your computer resources can handle it, you might
                            as well keep your images in 16-bit to preserve as much detail as possible,
                            especially considering that output devices continue to improve, and at some
                            point we may have output that tests the limits of our 8-bit files, where you'd
                            actually see a difference.
                            The only time 16-bit would make a difference, for all practical purposes, is
                            you need to make extreme adjustments to the image. If that's the case, you
                            probably would throw the image away, right? So 16-bit isn't a significant
                            advantage to most of us. Still something I recommend as a 'just in case', but
                            not likely to provide any practical benefit."

                            This is a sensible summary. Personally, I doubt that there's a realistic
                            possibility of benefit, but certainly you never know, and if you care to
                            speculate on it and have the disk space and computing time to spare, nobody
                            is criticizing. I believe it's more likely that some weirdness in an output
                            will create a benefit than anything at the high-end. Naturally, I also think
                            the most likely image to show an advantage would be one consisting of a sky
                            and little else, or an image with almost no detail outside of deep shadows.

                            LESSONS FOR THE FUTURE.
                            From the perspective of people who purport to be Photoshop authorities there
                            is a lesson to be learned about giving non-experts a hard time in public. You
                            never know when it's going to turn out that your views are mistaken, and then
                            you look ridiculous.

                            Second, admitting that one has been wrong is not a disgrace. Rather, I think it
                            gives one more credibility. Image processing is an infinitely complicated field.

                            In every new edition of Professional Photoshop I've pointed out areas where I
                            was previously incorrect. In the LAB book I talk about how I misunderstood
                            some of the sharpening issues. In at least two sections I pointed out images
                            that I had corrected badly.

                            Third, we have to grant that the difference in results between 8-bit and 16-bit
                            editing is not trivial to comprehend, even by people with a lot of color
                            knowledge, even after a lot of testing. OTOH, anybody who claims that
                            converting to LAB causes "catastrophic damage", that working on several
                            adjustment layers creates better data than applying the same corrections
                            consecutively, or that there is a "night and day difference, totally obvious to
                            anyone who looks" between 8-bit and 16-bit editing, is either too lazy or too
                            incompetent, or both, to do the ten minutes of testing that it would require to
                            cast serious doubts on these assertions.

                            Fourth, some sense of priorities has to be invoked. Some of the people who
                            have been most strongly in favor of 16-bit editing don't know how to set
                            highlights and shadows. Some actually edit not just in Levels but using the
                            master setting rather than channel-by-channel. Under these circumstances
                            the gain (if any) from 16-bit editing is about #4,807 on the list of things that

                            might help the image look better. Remember: even if some exceptional image
                            does show up that indicates an advantage for 16-bit editing, in all probability
                            the edge will be so minor that it can easily be compensated for. But to this
                            point, we haven't even gotten that far.

                            Users aren't blameless either. The entire imaging field is pervaded by
                            purported experts peddling solutions, myself included. Users tend to be
                            properly skeptical of claims made by unknown vendors, but a surprising
                            number of people are buffaloed by histograms and claims of mathematical
                            precision. Before buying into anybody's pet theories, readers should insist
                            upon images, not a bunch of pseudoscientific gobbledygook. If the speaker
                            can't phrase the concept in a manner you can understand, perhaps he can't
                            understand it either.

                            Users would be well advised to steer clear of anyone trying to justify
                            conversion or color correction theories with gradients, using terms like
                            "quantization error", or trying to convince us that a good-looking histogram is
                            more important than a good-looking image. Above all, when people come up
                            with new nostrums, ask to see images, not theories.

                            Finally, it should be remembered (as always) that color knowledge is always
                            evolving and that today's conventional wisdom is likely to be considered
                            wrong in ten years. I hope that the history of the correction method that
                            out as "extremely critical", a "night and day difference," the difference
                            a professional and a recreational user," and became "possibly a non-issue"
                            will be an instructive one.

                            Dan Margulis


                            • #15
                              Part 4 of post

                              This is an appendix to my three posts on the 8-bit vs.16-bit editing issue.
                              Much of my post is critical of those who insist that 16-bit editing is of
                              paramount importance yet decline to show any real-world images where
                              there is any indication that editing in 16-bit is better. I am posting here
                              extensive excerpts of what they say in their own defense as to why they do

                              Before turning it over to them, I have only one remark. These individuals have
                              argued that editing in 16-bit is "extremely critical", that it is "the
                              between professional and recreational users of Photoshop", that doing so
                              results in "a night and day difference" that is "totally obvious to anyone who

                              If anything even remotely close to that were true, a demonstration could be
                              made of it almost instantaneously. For example, if I had to argue for why
                              gradients should be created and edited in 16-bit and not 8-bit, I could create a

                              convincing example showing why in less than ten minutes. Both of the
                              invididuals quoted here spend a great deal of time in on-line groups. They
                              have each, conservatively, spent tens of hours, possibly more than a hundred
                              apiece, explaining why they are too busy to take these ten minutes.

                              Dan Margulis

                              Note: Jeff Schewe, one of the posters here, often uses ellipses (. . .) in his
                              messages. Where these appear, they are in Jeff's original and do not
                              represent deletions. Some extraneous paragraphs have been deleted from
                              the beginnings and ends of messages, but there is no editing of the text.

                              Jeff Schewe - 10:32pm Aug 5, 2001 Pacific
                              I have no interest in "Educating Dan". That's his job. Dan is right about a lot
                              and wrong about a lot. It's very easy to see that substantial color & tone
                              editing will eventually result in data loss and banding. A lot of people have
                              banding problems, very few people know when and where that banding
                              occurs, but it's due to the fact that editing 8 bit files causes the banding.

                              If you start with an 8 bit file and do tone and color adjustments, you lose

                              levels. . .maybe only a few. But, combined with data loss due to rounding
                              errors running filters, rounding errors due to layer blending, errors due to re-
                              brushing all accumulate to eventually produce enough loss of data from the
                              orriginal that eventually you get banding.

                              But. . .I have no interest in debating Dan's position on the value of 16
                              editing. . .I prove him wrong every day. If he wants to pay me to come teach
                              him the value of 16 bit editing, I'll be happy to. . .but I'm certainly not
                              going to
                              do his job for him for free <BG>.

                              He asked me to prove it to him. . .I declined. If he wants to take one of
                              classes, he's welcome to. . .I'll give him a discount. . .

                              User 1 - 11:53am Aug 9, 2001 Pacific
                              Jeff, I will address you here, but my point really goes out to all. Please don't

                              take it personally.

                              Regarding Margulis' challenge Jeff writes: "He asked me to prove it to him.

                              . .I declined. If he wants to take one of my classes, he's welcome to. . .I'll
                              him a discount. . . "

                              While I appreciate your humor here, I am mystified as to why you (and
                              others who feel as confident as you in the matter) decline his challenge...
                              Taking Dan's challenge would be to our benefit, not Dan's

                              Here is a sampling of Dan's challenge to you:
                              "…. I have for several years asked here and elsewhere for those who
                              advocate these methods if they might not be able to provide me, say, two or
                              three sample original high-bit images, with a record of what moves were
                              applied to them, so that I could verify that there is a quality gain, however
                              slight, in applying them to a 16-bit image as opposed to an 8-bit one.
                              Since I have been making this request, what I have received is a large
                              number of histograms purporting to prove that 16-bit is better, a large number
                              of assurances that '16-bit has worked better for me', and a large number of
                              excuses for why the images in which it has worked better are either
                              unavailable or under NDA. As time has gone on I have grown to suspect that
                              perhaps the reason no one can supply such images is that there are no such
                              images to supply.
                              Can you help me out? If you or anyone else can supply such example
                              images and they really demonstrate the merit of working in 16-bit, I'll be glad
                              to let this list know and if the differences are significant I'll print them in
                              column at a size large enough for people to see. If you or anyone else has
                              such images, just let me know and I'll give you shipping instructions."

                              To my mind Dan is being very fair in the matter, while those who decline
                              his challenge prove his accusations right, even if his assumptions about bit
                              depth may be wrong. He is certainly in the minority opinion on the subject, yet
                              he is the only one to my knowledge who is willing to back up his assertions
                              with examples. Why not back up your declarations to the degree that Dan is
                              willing to back up his?

                              Jeff Schewe - 08:16pm Aug 9, 2001 Pacific
                              I know Dan pretty well. . .I have ZERO interest in being a subject of an
                              upcoming article (I feel one coming from Dan) where he can takes what Bruce
                              or I may say about 16 bit and twist it around. Suffice it to say that remaining
                              under Dan's radar is far more comfortable <BG>

                              In the old days (before learning the value of editing in 16 bit) I suffered
                              slight to severe banding on transparency and CMYK output. since switching
                              to the 16 bit appraoch, I no longer get banding. . .that's all the proof I need.
                              have no need to "prove it to Dan". Sorry. . .I say what I say. . .I'm willing to

                              spend time teaching how to work in 16 bit (and do things the engineers never
                              dreamed of), but I have zero interest in proving anything to ol' Danny boy. . .

                              I doubt Dan has ever seriously manipulated an image or done a 6 element
                              assembly. I seriously doubt that Dan is after the most suprime high end
                              quality. . .even if it's only marginally better. . .but working in 16 bit is
                              a better habit leading to better quality in the end. . .which is all I care

                              P.S. ask Dan about copyrights some time. . .he's got his head firmly lodged

                              up an oriface about that as well <BG>.

                              User 1 - 09:53pm Aug 9, 2001 Pacific
                              Well, I hear ya, but…….
                              I was just hoping that someone would prove the point in the material world,
                              rather than theoretically, or anecdotally. Somehow this has become about
                              Dan Margulis the man, rather than the point he makes. It's ironic that although
                              it's him against the world on this, he's the only one (seemingly) willing to
                              evidence to support his claims. Shouldn't the benefits of a 16-bit workflow be
                              demonstrated anyway, regardless of the fact that Dan has issued a
                              challenge? Why, with all that is published about PS in print and on the web, is
                              such a presentation not already extant? That's just weird.

                              User 2 - 08:00am Aug 10, 2001 Pacific (#37 of 52) [Another 16-bit advocate]
                              wrote: "What do you want someone to do? Prepare a costly print run or film
                              recorder output using both good image preparation and bad image
                              preparation so that you can be satisfied that we know what we're talking

                              Certainly not, that would be unreasonable. That's why I asked if the
                              difference could be seen on a monitor, and you said at 100% magnification or
                              higher it could.

                              Even so, I'm not asking that you supply images for monitor viewing. Your time
                              is valuable, and you have been very generous with it on this forum.

                              OTOH, it seems that someone who advocates a 16 bit work flow could
                              supply a set of files for comparison. Lots and lots and lots of time has been
                              spent discussing this issue, here and elsewhere, which is still unresolved in
                              the minds of many people, and it could so easily be put to bed by just showing
                              us the comparisons. Otherwise, as Rich said, it becomes tiring.

                              Jeff Schewe - 09:40am Aug 10, 2001 Pacific
                              Your points are taken. . .but proving anything is not my job. When I do notes
                              for classes or lectures, it takes on average about 8-12 hours to prepare them. I

                              do have notes on editing in 16 bit on my web site (I'm going to be changing
                              the url this weekend for an upcomming class but they will be in the site map),
                              but those are just techniques for working in 16 bit. To go through and offer
                              scientific "proof" is something that would require even more time-which I don't

                              Jeff Schewe - 05:30pm Aug 12, 2001 Pacific
                              All this debate is pretty typical of good old Dan. You notice he recently said
                              that he has not taken the position that editing 16 bit is NOT better. . .only
                              he's never had anybody PROVE it to him.

                              I'm almost getting pissed off enough by Dan's "positioning" that I might
                              decide to "prove it". But I don't have a great deal of time in the next week or
                              so it would have to wait a bit.

                              Date: Wed, 15 May 2002 22:37:56 -0500
                              From: Jeff Schewe
                              Subject: Re: 8- and 16-bit correction
                              I watched, with amusement, when Dan challenged anybody to come up with a
                              bit image that could prove the benefits of editing in 16 bit over 8 bit. I
                              now understand there's a bounty out there of $100 if somebody can prove that
                              edits in 16 bit vs edits in 8 bit is superior. . .

                              That's a waste of time (and believe me, $100 is no incentive to me).

                              Fact is there is no image that can prove that one to several edits in 16 bit
                              vs 8 bits is better. I've never advocated editing in 16 bit merely as a
                              method of improving a few tone/color corrections. That's silly. The edits
                              done in the beginning of a tone/color correction does not cause banding. It
                              does indeed "spend bits" and I advocate spending your bits wisely. Where the
                              _REAL_ difference between 16 & 8 bit editing comes is well down the road.
                              Well after your original edits.

                              Photoshop is pure math. . .everything is numbers. Everything done in
                              Photoshop is the result of an algorithm. And believe me, Photoshop's
                              precision is not infinite. Where the benefits of original 16 bit editing
                              shows is down the road after doing corrections and applying a filter or two
                              (or dozen). Add a dozen layers with various opacities and blending modes
                              maybe a layer effect or 2. Do a gradated adjustment layer. Do any series of
                              extended retouching or manipulations that many image artists do every day.
                              Then you'll find out that at some point in the process, you've rounded
                              enough data and spent enough bits that the gradation between point "A" and
                              "B" no longer has enough bits to produce a smooth gradation of tone or
                              color. Guess what, you've got banding. And, guess what else, you've just
                              proved that _STARTING_ with your initial tone/color edits in 16 bits and
                              conserving your data bits to spend later in the editing process allows you
                              to avoid the dreaded banding.

                              If you scan a chrome and do a slight to moderate curve correction and
                              transform from RGB > CMYK, should you scan in 16 bits? Nope. If you do
                              slight to moderate to even substantial tone/color edits and then plan on
                              assembling 1/2 dozen composited images with filters, layer blending and
                              effects and maybe 20 hours in image manipulations, will you benefit a _LOT_
                              from doing your original edits in 16 bits? You bet your ass you will.

                              I started scanning in 16 bits because I ran into constant problems of ending
                              up spending hours working on an image only to find that at some point, a
                              tone gradation in an image banded. Once banded, there's nothing you can do
                              to recover the lost spent data.

                              My point is that if you need maximum flexibility and edit ability and you
                              don't want to worry about banding, start your creative retouching in a
                              "perfect 8 bits/channel". That only comes after doing initial tone/color
                              corrections in 16 bit.

                              Sure, you can use the scanner software to do tone/color corrections in the
                              scanner's high bit depth and thus benefit from 10, 12, 14 or 16 bits of
                              data. The big problem I have with that workflow is this. . .there ain't a
                              scanner on earth who's software allows you to do "local" corrections of
                              tone/color. Scanners don't come with the ability to put a lasso around an
                              area to adjust just that area. The other weak point of scanner (or camera
                              software for that matter) is that a scanner preview just purely isn't as
                              accurate as Photoshop to show exactly what the pixels look like. Scanners
                              give "previews" but you don't see the full resolution till _AFTER_ you've
                              applied the tone/color corrections during the scan. At that point if you
                              touch it again you won't have a full 8 bit file. . .you're spending the bits
                              on a wasted edit. I also think, and perhaps I'm biased, that Photoshop is
                              the best "pixel viewing" application on the planet. I know of no other app
                              that is as accurate in showing on screen, exactly how a set of pixels will
                              look when you output. . .either photo or halftone reproduction. So, if I
                              want the most accurate on screen representation of just exactly how those
                              pixels will look reproduced, I'm just not interested in using a scanner
                              software or camera capture software's interpretation of those pixels.

                              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.

                              Yes, the tools are more limited and yes the files are 2x the size. . .so?
                              Ram is cheap and so are hard drives these days. I've learned to edit in 16
                              bit to the point where even the Photoshop engineers couldn't believe how far
                              one can go if you're determined. You can paint (using history), you can
                              copy/paste (using clone between 2 16 bit documents), you can use
                              layers (in an 8 bit duplicate and save out as a setting), you can use color
                              range in 8 bit and transfer the 8 bit selection into 16 bits for
                              application. You can clone and heal and run enough filters to do just about
                              anything you need to do to start off your imaging in the "perfect 8 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.

                              Dan and others who claim 16 bit editing isn't better than 8 bit editing for
                              routine scanning and corrections are correct. But, I'm a photographer and
                              image manipulator. I choose to spend my data bits wisely because because
                              what I do to images isn't routine. I manipulate the heck out of images. I
                              choose to do all initial tone/color correction in 16 bit to avoid banding
                              down the road. And, personally I feel no compulsion to prove anything to
                              anybody except my clients that pay me a lot of money.

                              Jeff Schewe
                              16 bit advocate and proud of it. . .

                              Date: Fri, 15 Apr 2005 14:36:12 -0700
                              From: bruce fraser
                              The major problem with the methodology (leaving aside the minor ones)
                              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!

                              Date: Sun, 17 Apr 2005 15:00:55 -0700
                              From: bruce fraser
                              Subject: Re: 16 bits = 15 bits in Photoshop?

                              At 12:39 PM -0400 4/17/05, Dan Margulis wrote:
                              >So, I ask if the following is a fair summary of your position:
                              >1) Bruce states that the argument has never been that identical edits applied
                              >to 8-bit and 16-bit files would produce better results in the 16-bit version,
                              >but he argues that it is possible that they might.
                              >2) Bruce has not offered up any images that would demonstrate such a
                              >superiority for 16-bit correction (as opposed to identical edits
                              >applied to 8-bit),
                              >but he suggests that such images might exist.
                              >3) Bruce's comments on "night and day difference" and "totally obvious to
                              >anyone who looks" are based on his experience and perceptions; however,
                              he has
                              >never personally tested a series of corrections done to a 16-bit
                              >file on a live
                              >image versus identical corrections done to an 8-bit one.

                              No, that's a when-did-you-stop-beating-your-wife characterization.

                              My position is very straightforward.

                              I proved to my own satisfaction many (>10) years ago that many of the
                              problems I encountered with 8-bit files-posterizaton, striped skies,
                              exaggerated saturation accompanying contrast moves, and unwanted hue
                              shifts-largely disappeared when I edited (and converted to output
                              space, which is a big edit) in 16-bit instead.

                              I seem to be far from alone in having noticed this phenomenon.

                              I quite sensibly decline to do all my work twice with the goal of
                              making half of it fail, and with the exception of beta-testing
                              procedures that need examples for bug reports, I don't make a habit
                              of saving the failures.

                              If someone wants to pay me my day rate to do so, I'm quite certain
                              that I can come up with real-world examples, but I decline to donate
                              my time to a foolish quest with whose premiss I'm in disagreement.

                              Anyone who sees no benefit to working in 16-bit space simply
                              shouldn't bother doing so. But they shouldn't come crying to me when
                              their images fall apart on output.

                              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.

                              Date: Fri, 22 Apr 2005 01:29:17 -0500
                              From: Jeff Schewe
                              Subject: Re: 16 bits = 15 bits in Photoshop?
                              To: <colorsync-users@...>

                              Jim Rich said:
                              > It makes sense to capture everything as high bit images.Everyone seems
                              > agree on this.

                              > Save the high bit parent file in your archive.

                              > Create derivative 8 bit files from the parent file for production.

                              > Use Adjustment layers.

                              > If the 8 bit file breaks ( as they can in rare cases), then go back to
                              > the parent 16 bit file and use the previous Adjustment Layers.

                              I agree with the capture in high bit.

                              But I would argue that it critical than ALL MAJOR tone and color moves be
                              done in 16 bit. Ideally with Adjustment Layers for the simple reason that
                              setting black & white points (unless you do it accurately in say Camera Raw)
                              are the tip of the spear so to speak. Major gamma adjustments are second,
                              such as when you stretch one area and compress another area of the image's

                              I would also argue that depending on the color space you may be in while in
                              16 bit, it would be a good idea, if at all possible, to do any major color
                              transforms while in 16 bit.

                              Bruce Fraser - 11:41pm Sep 16, 05 PST
                              If you want to work in 8 bit/channel mode, go ahead. But don't come crying
                              to me if your file breaks. That's really all I have to say on the subject.
                              OK. A little more.
                              Dan's "tests" are based on applying exactly the same traditional levels-
                              and-curves-based edits to 8-bit and 16-bit files, then looking for differences.
                              Those will likely be fairly hard to find. For the type of work Dan does, 8 bits/
                              channel is undoubtedly adequate, otherwise, being a rational person, he
                              wouldn't do it. Others may have different needs.

                              Bruce Fraser - 1:07pm Sep 19, 05 PST
                              I'd also suggest that you need to weigh the consequences of working in 8-
                              bit and finding you need 16 versus working in 16-bit and finding you only
                              need 8. My lack of clairvoyance is one of the factors that leads me to work in
                              I've demonstrated many times things that work better in 16-bit than in 8
                              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


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