Andrew, I had a rough day yesterday so maybe I am a bit myopic today, but I found your post very confusing. Firstly, where do we get access to everything Dan said - i.e. his full response? It would be good to see the whole text. Secondly, there is a co-mingling in your post of two issues: colour spaces and bit depth. Since this is a thread about bit depth, the discussion should stick to that, unless the choice of colour space impacts the bit depth argument - if it does, the specific effect of choice of colour space on 8 ver 16 bit image editing needs to be clarified and its impact on the choice of 8 versus 16 explained - for the benefit of those of us who haven't personally tested all the permutations and combinations.
Here’s the entire post. At the bottom you’ll see how you can access it or join his list (bring aspirin):
Prior to my trip to Photoshop World, Andrew Rodney posted a link to an image
as part of his never-ending attempt to explain how his business partners can
say that correcting in 16-bit is what differentiates a professional from a
recreational user, how it creates a night and day difference, how the advantage is
totally obvious to everyone who looks, etc., etc. Lee Varis posted a response
with which I concur, but I did not myself have time to look at the image
closely and said I would do so in future weeks.
As I indicated in my first brief response, the example is meaningless,
because it assumes a condition that I have always excluded, and that wasn't even
known at the time his partners said those things. I have always made clear that
exotic RGB definitions, such as 1.0 gamma, or ultra-wide gamut RGBs, are not
tested because, first, almost nobody uses them, and second, those knowledgeable
about color correction would be unlikely to edit in them except under very
Andrew's test depends on using such a space, an ultra-wide gamut RGB known as
ProPhoto. This space was not installed in Photoshop until 2003, and since his
partners made the remarks about night and day differences and professionals
and recreational users long before that, they cannot possibly have been
referring to it.
The image is an outdoor scene. A laborer, on his knees, is laying a cement
deck or patio. There is greenery and yellow flowers in the foreground; the patio
takes up almost a third of the picture. The laborer is relatively small. His
face is in shadow. The background ground cover is yellowish. On the whole one
would describe the colors as subdued. The picture isn't ridiculously dark but
it certainly needs to be lightened.
Lee Varis correctly characterized such spaces as "like using a sledge hammer
to drive finishing nails". By that, he meant that the are too imprecise to be
used in serious image manipulation, because most of their possible color
values are either well out of any reproduction gamut or totally imaginary. This
image is a perfect example: the large patio is basically gray, however there is a
certain amount of variability, with some parts slightly redder and others
cooler. During the correction process, we need to be sure that these colors don't
get out of hand so that the patio looks like a rainbow rather than cement.
Doing so is no sweat in any rational RGB. We just try to have the three RGB
values be approximately equal throughout the area, understanding that exactly
equal isn't going to happen.
But in an ultra-wide gamut RGB, it's much more difficult, as the values have
to be kept much closer to absolute equality, because colors get brilliant very
rapidly in such a space. Consequently, maintaining neutrality in such an
image during correction is a nasty problem in an ultra-wide gamut RGB and no
problem at all in LAB, CMYK, or a rational RGB.
Because any small variation in an ultra-wide gamut RGBs is actually a huge
variation in output color, the tiny differences between a file prepared in 8-bit
and one in 16-bit are magnified. In realistic RGBs, these differences are so
slight that nobody notices them no matter how much they are affected by later
edits. But in an ultra-wide gamut RGB, it is at least conceivable that certain
images will look better if they are worked on in 8-bit and others will look
better if done in 16-bit.
In Andrew's procedure the image is not edited in Camera Raw, but is exported
to 16-bit ProPhoto. The test calls for making a second copy which is then
converted to 8-bit. Then, to both, one master-channel Levels command is applied,
followed by one increase to master saturation in the Hue/Saturation command,
followed by one unsharp mask filter.
In examining the image, I looked at not just these two variants, but several
others in ProPhoto, as well as 8-bit and 16-bit Adobe RGB using exactly the
same commands, and 8-bit sRGB where I used the same commands but attempted to
strengthen them to match the look of the ProPhoto files.
The error in Andrew's method is in his final step. After the levels and
Hue/Sat moves, the two versions can't be told apart without great difficulty.
However, his sharpening settings have a Threshold (noise reduction) of 0. This
causes a problem specific to ultra-wide gamut RGBs.
Any file corrected in 8-bit will be very slightly grainier than one corrected
in 16-bit. In rational RGBs, this difference is so imperceptible that it
makes no difference in the sharpening process. In an ultra-wide gamut RGB, it can
be seen IF you specifically use a zero threshold. In that case, you will see
two definitely different images, as we do in this case. (Andrew concedes that
when these same moves are applied in Adobe RGB, the two images are the same for
all practical purposes).
In the ProPhoto version the difference manifests itself in a more
active-looking 8-bit file. It has more noise in shadow areas, particularly in the
worker's face and in an area of the background. I agree that these things are bad.
However, it has slightly more believability in the foreground greenery and in
the concrete, which are more prominent items. I believe that this is the reason
that when Lee Varis printed out the two files and showed them to another
observer without explaining which was which, the observer picked the 8-bit version
as being better.
While it's arguable whether the image taken as a whole is better or worse,
certainly Andrew is entitled to object to the graininess. What he is not
entitled to do is, when there are several equivalent ways available with no extra
effort, intentionally choose the one that magnifies the effect that he says he
doesn't like. In the sharpen filter, the Amount and Threshold commands work in
tandem. A higher Threshold slightly diminishes the sharpening effect, and we
compensate by raising the Amount. Minute changes are possible, so that there
are, in effect, many different ways of creating substantially the same effect. By
raising the Threshold even to 1 (although I would choose 2) and adding a
corresponding increase in Amount, the 8-bit and 16-bit images are again q
ualitatively equal regardless of which of the three settings is used for the 16-bit
file. I also experimented with much larger sharpening Amounts with the same
It should also be pointed out that the graininess is more a function of the
ultra-wide gamut RGB than it is of the bit depth. As noted, I did another
version in 8-bit sRGB. It's impossible to duplicate the 16-bit ProPhoto exercise
exactly, as much stronger corrections are required in sRGB to achieve the same
look. But I got as close as I could, including sharpening with a zero
Threshold. The 8-bit sRGB file looked smoother than the one done in 16-bit ProPhoto.
In short, this image does not show an advantage, because the part of it that
Andrew complains about could have been avoided with no extra effort and no
loss in quality. Intentionally choosing an inappropriate sharpening setting is
not a real-world move.
What *would* constitute an advantage? As I indicated in my first post, a list
member showed one. An overly dark image needed to be lightened. However, it
was deliberately sabotaged in Camera Raw by turning the exposure control all
the way down. Then, it was exported into 8- and 16-bit ProPhoto and Adobe RGB,
where simple curves were applied to lighten the image grossly. In Adobe RGB
there was no preference between the two versions. In ProPhoto, however, serious
noise developed in the sky in the 8-bit version that wasn't present in the
16-bit. Now, unlike Andrew's image where it might reasonably be argued that the
8-bit version was *better,* in this one everybody would agree that it was worse,
no question. And, unlike Andrew's image, there was no means of avoiding the
problem in the same number of steps. The 8-bit picture would have to be
corrected further to match the quality of the 16-bit.
The image showing 16-bit superiority isn't real-world because it was
sabotaged in Camera Raw. Andrew's image, which wasn't so sabotaged, doesn't show
superiority. OTOH, it wasn't corrected particularly brutally either. So, I would
have to suspect that it would be possible to find a real-world image that is
somewhere in the middle--that is, no sabotage, but a more extreme correction,
causing clear superiority in the 16-bit version. Similarly, one would expect to
find certain files that would correct better in 8-bit than 16-bit.
If you are misguided enough to work in an ultra-wide gamut RGB, that is.
To summarize: working with actual images is a useful exercise, and we should
thank Andrew for making this one available. It does not actually show an
advantage for 16-bit manipulation in ProPhoto RGB, but in all probability he could
have constructed an image that did if he had worked harder at it. If somebody
wishes to produce such an image, I will be happy to note it parenthetically in
the next edition of Professional Photoshop, but I am not interested in
further testing of ultra-wide gamut RGBs as correction spaces myself, as their
disadvantages are such that their use can be recommended only in highly specialized
At bottom, though, it's just another attempt to blow smoke over the inability
to back up his partners' extravagant claims. Granted, this time it's not a
histogram or a gradient or a sabotaged image. But still, it requires a certain
revision of the original 2001-2002 claims. Perhaps Andrew will allow us to
revise them: instead of saying that there is a night-and-day, totally obvious to
everyone who looks, professional vs. recreational user difference when
correcting color photographs in 16-bit, we can modify it as follows:
"If you correct in 8-bit rather than 16-bit, you are not currently a
recreational rather than professional user, and you will not currently see a
night-and-day, totally-obvious-to-anyone-who-looks difference, but if you continue to
do so, in two or three years when ProPhoto RGB is introduced into Photoshop,
you *will* be a recreational rather than professional user, by God, and you
*will* see a night-and-day, totally-obvious-to-anyone-who-looks difference, unless
you are one of the 99.9% of users intelligent enough not to attempt major
edits in an ultra-wide gamut RGB."
If Andrew can live with that as a resolution, I certainly can.
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