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Author Topic: Consensus needed on benefit of 16-bit editing  (Read 10588 times)
hdomke
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« on: September 16, 2005, 07:51:40 AM »
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Dan Margulis questions editing Photoshop files using 16-bit in his new book: “Photoshop LAB Color: The Canyon Conundrum and Other Adventures in the Most Powerful Colorspace”

In Chapter Six of the book he argues that even though high bit editing sounds sensible, in practice the theory doesn’t work. On images containing computer generated gradients, yes. But on color photographs, no. “In the last three years, around a dozen people, including me, have made serious efforts to find anything to support the proposition that 16-bit editing might be better under any circumstances. … nobody has found any quality gain at all.”

“At this point the evidence is overwhelming that there is no 16-bit advantage in dealing with color photographs. A few people argue otherwise, but it has now become a matter of religious belief, rather than reliance on demonstrations that they can't provide”.

This is a very important issue for all of us that use Photoshop.  Many of us now keep multi-layered files as 16-bit until we are ready to print. I have 10,000 files like this and I don’t want to double my storage requirements and slow my processing time by using 16-bit unless there is clearly a benefit. We need a definitive answer.

Please offer your opinion and back it up with evidence.
 
Thank you!
Yours truly,
Henry F. Domke
 
Henry Domke Fine Art
www.henrydomke.com
 
I am trying to get you, the experts to agree on this. I am posting this same question to:
Michael Reichmann: www.luminous-landscape.com
Tom Hogan: www.bythom.com
Tim Grey: www.timgrey.com
Adobe Expert Help: www.adobe.com/support/expert_support/main.html
Adobe Photoshop Forum: www.adobe.com/support/forums/main
Ron Galbrith: http://forums.robgalbraith.com
Phil Askey: www.dpreview.com
Bruce Fraser: www.creativepro.com
Stephen Johnson: www.sjphoto.com
Bill Atkinson: www.billatkinson.com
Katrin Eismann: www.photoshopdiva.com
Martin Evening: www.martinevening.com
Andrew Rodney: www.digitaldog.net
Dan Margulis: http://groups.yahoo.com/group/colortheory
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Henry

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Jonathan Wienke
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« Reply #1 on: September 16, 2005, 08:47:18 AM »
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Dan Margulis is a borderline kook on the 16-bit editing issue; his criteria for demonstrating benefit to 16-bit editing are rigged to completely negate the benefits of 16-bit. There are definitely measurable benefits to 16-bit editing; take a look at the simple comparison I did here. You can download the 16-bit source TIFF and the action set I used for the comparison, and verify the difference for yourself. 16-bit editing will not have such a profoundly positive impact on every image, but it will always improve on what you get in 8-bit mode, and will never be worse.
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jani
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« Reply #2 on: September 16, 2005, 08:56:31 AM »
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Henry,

I think you should do these people the courtesy of at least searching this forum for similar, earlier discussions.

We just recently had a discussion thread -- the one Jonathan mentions -- that was debunking Dan Margulis's claims, with photographic evidence to back it up.
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« Reply #3 on: September 16, 2005, 09:08:17 AM »
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The one exception is that some threads are gone or at least missing posts; with the recent crash I'm not sure if that particular thread survived. But Andrew Rodney did weigh in strongly disagreeing with Dan's position, which means Dan's statement that "nobody has found any quality gain at all" is either profoundly ignorant or an outright lie.
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digitaldog
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« Reply #4 on: September 16, 2005, 02:12:41 PM »
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From two posts on the Color Theory list that Dan runs. You can see for yourself in the files I’ve posted. Note that I’ve not heard anything back from Dan now that PS world is over!

On 9/2/05 9:33 PM, "DMargulis@aol.com"  wrote:

DM: "I repeatedly asked him whether he had ever personally run a test (or
seen anyone else perform such a test) where the same exact corrections were
applied in both 8- and 16-bit modes to a real-world color photograph, and
compared

I have such a file which I posted on my site for anyone to download. Unless I’ve suffered a major brain fart (or once again, the rules change), its quite clear to me that the 16-bit file is showing vastly superior quality with respect to noise and artifacts compared to the 8-bit file.

The image  was shot with a Canon 350D (ISO 100). I used Adobe Camera RAW 3.X with all defaults and auto settings OFF. No sharpening in ACR either. The file was brought into Photoshop in 16-bit in ProPhoto RGB from ACR. Then I duplicated the file and converted the dupe to 8-bit. I applied levels corrections (nothing super radical), USM and a boost in saturation (+20 in Hue/Sat). The IDENTICAL corrections were made on the high bit file (hold down option key and the other key command to call levels, USM etc to get exact values) or drag and drop history from one to the other.

Cache is off In histogram. The 8-bit Histo isn’t awful like I see in Bruce’s book. But there is a very noticeable amount of noise in the 8-bit file not seen in the high bit file. I also converted from ProPhoto into LAB and did the same corrections (well not exactly since levels in LAB can’t be duplicated exactly as you would from an RGB file). Again, the 8-bit file shows severe noise introduced by the corrections that simply don’t show up in the high bit file. At 200% zoom, it shows up like a sore thumb.

I’ve taken a section of the image since in high bit, it’s quite large and cropped it down as the 16-bit ProPhoto RGB file. In the zip archive are screen dumps of the corrections made. I also generated a Photoshop action; one duplicates the 16-bit file, converts to 8-bit and applies the three corrections. The 2nd would be used on the original (doesn’t duplicate) making a bit easier to apply both sets of corrections.  After that, zoom into the green (slightly out of focus) bird feeder at 200% and look at the differences. The biggest issues in the 8-bt file appear to show up in shadows which makes sense. This is another reason why even superior quality would be produced on linear encoded data within ACR. It also illustrates the need to “expose to the right” for RAW data since the first 2048 steps of data are all within the first stop of highlights.

This is a real world image and the corrections are not severe and identical on each. The Zip archive is about 1.8mb.

I’m seeing this effect on other files shot and processed in this manner. I can of course supply the RAW data but it’s pretty large. If anyone wants it, let me know and I'll put it on my public idisk.

The file is here:

http://www.digitaldog.net/files/16bitchallange.zip

Andrew Rodney
Author "Color Management for Photographers"
http://www.digitaldog.net/

Andrew Rodney writes,

>>The image  was shot with a Canon 350D (ISO 100). I used Adobe Camera RAW 3.X
with all defaults and auto settings OFF. No sharpening in ACR either. The
file was brought into Photoshop in 16-bit in ProPhoto RGB from ACR. >>

First of all, thank you for posting it, I agree that it is a real-world
picture with real-world corrections. I have played with it a little bit but won't
have any final comments until I get a chance to manipulate it more, which will
be after Photoshop World. At that time, I will probably take you up on the
offer to provide the raw file, provided you are willing to give me permission to
publish it.

It would not surprise me if this or a similar file containing mostly dull
colors, if left in ProPhoto RGB, would get a better result from 16-bit correction
than 8-bit. I have tested Adobe RGB, ColorMatch RGB, LAB, and sRGB files
enough to be highly doubtful that there are any natural color photographs at all
where the extra bits would be helpful in any real-world context. However, I've
always pointed out that I have *not* extensively tested exotic alternatives, such
as 1.0 gamma files, or ultra-wide gamut RGBs such as ProPhoto. The reasons
they are not tested are 1) they have limited market presence and 2) I strongly recommend against their use in color correction.

I do have another ProPhoto file where 16-bit definitely produced a better
result than 8-bit. However, it was not a real-world exercise in that the file was
intentionally sabotaged in Camera Raw by moving the exposure slider all the
way to the left when the actual final intent was to lighten the file. We did
repeat the same exercise, including the sabotage, with the same file output to
Adobe RGB, and there was no problem with the 8-bit correction.
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Andrew Rodney
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PeterLange
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« Reply #5 on: September 17, 2005, 03:12:23 AM »
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Quote

Henry,

Doesn’t your question somehow already contains the answer. If it’s possible to create reasonable synthetic examples, it is / should be just a question of effort to find practical ones.

When you book an 8-bit trip from sRGB to Lab and back to sRGB, this either adds noise or breaks continuous color transitions – depending on the dithering setting in the main color settings tab.  Both effects may not instantly be obvious, however, it just requires some further moves, e.g. increase of contrast or USM with low threshold to make things clear.

Somehow I think that Dan has problem to combine his 8-bit philosophy with his new favorite: Lab.  Whereas such bit precision issues are probably just a side story.  In many cases Lab-edits can be substituted by PS blending modes, Hue / Color / Saturation / Luminosity which offer access to a special version of the HSL color model (where the Luminance axis is computed as a weighted average of R/G/B; which is one reason for the similarity with Lab).  Also I don’t see that anyone (except Bruce Lindbloom) has overcome the in-built hue bending with Lab, which occurs upon changing color saturation in Lab mode.

Anyway, it may be a valid point that 8-bit often are better than expected.  It seems likely to me that Raw converter do not change from 12 to 8 bit unless gamma-encoding is done.  Application of a gamma curve would definitively tear 8 bit shadows apart.  If this assumption about the sequence of happenings is correct, any 8-bit file we receive in PS would already have its 12 bit history...

Cheers! Peter


P.S.: I’d be pleased if you would you like to summarize the results of your survey at the end  .

--
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LeifG
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« Reply #6 on: September 17, 2005, 06:52:58 AM »
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In Chapter Six of the book he argues that even though high bit editing sounds sensible, in practice the theory doesn’t work. On images containing computer generated gradients, yes. But on color photographs, no.
Henry: In my experience, for well exposed images without extreme highlights and/or shadow detail, there is little advantage to working in 16 bit mode. BUT if you have to make large adjustments (e.g. large midpoint shift in curves) or do contrast masking to bring out shadows, then yes, editing 16 bit mode is essential to avoid posterisation and loss of detail.

16 bit scans from my Minolta 5400 are 200MB. As this is huge, I edit the file in 16 bit mode, then save the finished result in 8 bit mode. Later on if and when I do further (minor) edits, I convert to 16 bit mode again. It prevents posterisation, even though converting to 8 bit mode jettisoned a lot of detail. If I need to do large changes, I rescan to re-generate the original 16 bit file.

You can easily verify this for yourself by editing some images.

Leif
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Dan Sroka
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« Reply #7 on: September 20, 2005, 09:22:32 AM »
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In my experience, for well exposed images without extreme highlights and/or shadow detail, there is little advantage to working in 16 bit mode. BUT if you have to make large adjustments (e.g. large midpoint shift in curves) or do contrast masking to bring out shadows, then yes, editing 16 bit mode is essential to avoid posterisation and loss of detail.
That sums it up well. You stay in 16-bit to give yourself "room" for editing. I often explain it this way: Imagine you are driving down a road. If you are driving straight, that road can be as narrow as your car, and work perfectly well (8-bit). But if you ever need to make a 3-point turn on that narrow road, you'd get your wheels stuck in the mud. Better to have a wider road (i.e. 16 bit) just in case you need to turn.
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howard smith
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« Reply #8 on: September 20, 2005, 09:27:08 AM »
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I reprocessed some old images in 16-bit instead of 8.  I can see a nice difference in shadows, and in the details on a black tux at a wedding.  On my computer, the execution time was noticable longer, but worth the time.  For me.
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Mark D Segal
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« Reply #9 on: September 20, 2005, 08:39:08 PM »
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Note: For those of you who received my post of several minutes ago in your inboxes, I have deleted it, because of the remote possibility that there could be a copyright concern regarding an individual's view I mentioned there. This is an edited version with any risk of copyright issues expunged, and my apologies to the person concerned - just in case.

Now to the remaining content of my deleted post:

I believe this is technically a very complex subject, insofar as the more one reads about it, the more one appreciates the possibility that "it depends" - on all kinds of things including how the testing is done. This flavour even comes out on page 133 of Dan's book. He is less doctrinaire about it than some of the discussion would lead one to believe. So the idea that there will be a "consensus" on this issue I think is DOA (dead on arrival).

There is other expert opinion, which you can research, that is more in line with Dan's view of this matter, also based on testing with actual prints, but obviously coming to different conclusions than those of some contributors here.

So when one contrasts these views relative to some very knowledgeable contrary views in this discussion thread, one begins to understand perhaps why I think the highest common denominator of agreement on this issue is likely to be two words: "it depends".
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Mark D Segal (formerly MarkDS)
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« Reply #10 on: September 20, 2005, 08:56:04 PM »
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I will go so far as to say that editing in 16-bit mode benefits some images more than others, and the extent of the benefit is directly proportional to the severity of the edits required to get the image into a printable state. With some images, the benefits of 16-bit editing may not show up in a print, but with others, the difference will be very noticeable. And other images will fall somewhere in-between. But 16-bit editing will never have a detrimental impact on image quality; the only drawbacks are increases in file size and edit execution time.
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Ray
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« Reply #11 on: September 20, 2005, 10:00:54 PM »
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Jonathan,
That sums it up pretty well. I guess with almost automatic everything now available in photography, most of the images that most people take do not require extensive editing and therefore there is likely to be no noticeable benefit editing in 16 bit with images that just require a bit of 'levels' tweaking, hue adjustment and sharpening.

I generally do all editing in 16 bit (if it's available) because I already have enough decisions to make without pondering over the issue of whether or not a particular image is likely to benefit from 16 bit editing. However, none of my computers have less than 2GB of RAM, except my laptop.
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hdomke
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« Reply #12 on: September 21, 2005, 10:17:44 PM »
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From: Henry F. Domke
www.henrydomke.com

I posed the question of 16 vs. 8-bit editing in Photoshop to a variety of Photoshop experts. I was hoping to get a consensus of the experts and I got it.

Yes to 16-bit editing: 9 experts
No to 16-bit editing: 1 expert -Dan Margulis
Awaiting input: 4 experts

All 9 experts that answered me (Andrew Rodney, Tom Hogan, Adobe Expert Help, Bruce Fraser, Martin Evening, Stephen Johnson, Katrin Eismann, David Biedny, Ron Galbrith) clearly supported 16-bit editing. Most agreed that the benefit was subtle for most photographic images.  Most mentioned the advantage of keeping your options open for the future by using 16-bit since our monitors and printers may one day be better able to show the advantage more clearly.

I could not find a single expert to support Dan Margulis’s comment “At this point the evidence is overwhelming that there is no 16-bit advantage in dealing with color photographs. A few people argue otherwise, but it has now become a matter of religious belief, rather than reliance on demonstrations that they can't provide.” However, I have not heard back from 4 experts Bill Atkinson, Tim Grey, Michael Reichmann and Phil Askey.

What follows are excerpts from the email response I got from each expert.

Andrew Rodney: www.digitaldog.net
Use 16-bit
“I have such a file which I posted on my site for anyone to download. http://www.digitaldog.net/files/16bitchallange.zip
… its quite clear to me that the 16-bit file is showing vastly superior quality with respect to noise and artifacts compared to the 8-bit file.” “…the 8-bit file shows severe noise introduced by the corrections that simply don’t show up in the high bit file. At 200% zoom, it shows up like a sore thumb.”


Tom Hogan: www.bythom.com
Use 16-bit
“With RAW (and 16-bit data) you are prepared for any future changes in output capability.” “Is Margolis' argument valid? Within a narrow range, yes. If I had control of everything from capture to output, I could imagine an 8-bit editing sequence”


Adobe Expert Help: www.adobe.com/support/expert_support/main.html
Use 16-bit
“The fact that most monitors and printers will only display information in an 8-bit per channel color mode means that the only advantage to maintaining images in 16-bit color is if the images will require processing within Photoshop that affects the entire tonal range of the image.” “if you find you need to apply many adjustments to a single image on a regular basis, 16-bit editing may give you an advantage.”

“16-bit per channel images do have noticeable improvements when working with computer-generated images … and outputting directly to film.”

“In practice, most people may never notice the difference between 8-bit and 16-bit when working with standard photographs. (In much the same way most people will not notice much difference when listening to an audio CD, or an MP3 file--and for the same basic reasons.)”


Bruce Fraser: www.creativepro.com
Use 16-bit
“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. Bruce Lindbloom has elegantly pointed out the futility of entering into the dispute when the deck is already stacked.”

“If you find the extra bit depth doesn't buy you anything, don't use it. But don't come crying to me years hence when your monitor has a 1000:1 contrast ratio, your outputs are hitting a dMax of 2.8, and all your legacy files are breaking.”

Martin Evening: www.martinevening.com
Use 16-bit
“From a practical viewpoint, yes, once I have an optimised image in 16-bits there is not always a lot of point keeping it in 16-bits, and so I mostly then convert to 8-bit, especially if I am using lots of layers. I don't worry after that. But consider this - what of the future of HDR imaging? … the technology is now emerging to allow us to display images at true 16-bit depth on the new prototype LCD displays of the future.”


Stephen Johnson: www.sjphoto.com
Use 16-bit
“With all due respect to Dan, my experience is quite different.”

Katrin Eismann: www.photoshopdiva.com
Use 16-bit
“Yes, I am a 16 bit person...well actually I’m flash and blood!”

David Biedny http://attentionphotoshoppers.libsyn.com
Use 16-bit
“As in the worlds of pro audio and "film", higher bit depths are important for processing and enhancement, as well as mastering.

With an eye to the future, I feel you have made a wise decision to work in 16 bit. Can't hurt, and storage is cheap.”

Ron Galbrith: http://forums.robgalbraith.com
Use 16-bit
“…for quality work I prep files in 16-bit because I've demonstrated to myself it's useful to do so.”

Bill Atkinson: www.billatkinson.com
No answer yet.

Tim Grey: www.timgrey.com
No answer

Michael Reichmann: www.luminous-landscape.com
No vote yet  “haven’t read the book”

Phil Askey: www.dpreview.com
No answer yet
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Mark D Segal
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« Reply #13 on: September 21, 2005, 10:58:39 PM »
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You'll find Tim Grey's answer if you are a subscriber to his copyrighted DDQ and have access to the archive.

Did you ask each of the respondents whether they have personally tested this proposition rigorously and conclusively? Anyone who is answering based only on the appearance of histograms shouldn't count, because it is not easy to infer the impact on a print of various patterns of histogram break-up.

By the way, I work in 16 bit also - as an "insurance policy". But I must add, the several photographs I've worked in both showed indistinguishable results. However, they were not photographs needing massive adjustments. I'm not sure how massive an adjustment needs to be before 16 bit really makes a visible difference on a print without a loupe. The experts in testing for this issue should have addressed this matter of the adjustment threshold and can tell us.

I believe Jonathan cut to the chase very succinctly and probably correctly several posts ago. One thing about Dan is that he has extensively worked and tested everything he explains and demonstrates in his published material and seminars, so I have a lot of time for what he says about this stuff, regardless of whether he is a minority of one or several.
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« Reply #14 on: September 23, 2005, 01:06:48 PM »
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Dan has finally responded and I’m not surprised that once again, the “rules” of his 16-bit challenge have shifted. I’m not going to post his entire reply but rather mine to his list. Note that NOW, the issue is wide gamut RGB spaces (which he hasn’t defined) but ProPhoto RGB falls into that camp. I’d say LAB certainly does as well but we’ll see what he has to say about that one. The files I posted are there for anyone to examine. I still feel that my Rebel 350 capturing nothing more than a snapshot clearly produced an image outside of Adobe RGB (1998) and I can clearly show that there are output devices such as my Epson 2400 that do as well. High bit editing is about headroom and flexibility but Dan doesn’t see it as an advantage. He questions the use of wide gamut spaces and says only 1% of users are working with such spaces and they are not all that intelligent in doing so. I have no stat’s to back this up nor does he. He doesn’t tell us why using high bit on wide gamut spaces is a problem (other than the file is twice as big) nor the advantages to us in working with a smaller gamut space simply to avoid the noise that presents itself when editing in 8-bit. So I don’t get it! Anywhere, you’ll get the overall idea of what was side from both sides in my response below. For a guy who’s done a lot for the industry and come up with some compelling uses of LAB, I find it hard to side with someone who goes out of his way to hide from the obvious facts seen in just this test and who continues to measure with a rubber ruler.
----------
On 9/23/05 10:54 AM, "DMargulis@aol.com"  wrote:

> 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
> unusual circumstances.

With all due respect Dan, that’s nonsense. Nobody uses the? The edits here are unusual? Many professional users, many digital photographers use ProPhoto RGB. Every edit in Adobe Camera RAW no matter what color space encoding you select or what bit depth happens in ProPhoto RGB with a 1.0 gamma prior being presented to the user.

I can (and I think did) illustrate that to anyone that wants to examine the image in Adobe Camera RAW, the scene gamut cannot be fully exploited in Adobe RGB (1998) and can in ProPhoto in 16-bit (as it can in 8-bit with obvious appearing noise).

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 target. 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. Others who wish to download the image can clearly see for themselves the downside of using 8-bits compared to high bit with the example I posted. They can decide for themselves that there ARE real world, non synthetic images that fall outside Adobe RGB (1998) gamut (as does my $800 Epson 2400) that benefit from high bit editing.

> 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.

Dan, you can see the effect of the noise in the 8-bit version without any USM. NONE was applied in ACR, the image is in serious need of sharpening but none the less, the noise is present without it. More editing will produce a greater effect of showing this. We have no idea what will happen with future editing, conversions to other color spaces for output, resizing etc. As I’ve stated in the past, the use of high bit simply provides more editing headroom. To dismiss the obvious effect of this noise by saying that “this or that edit” isn’t kosher when the edits do not show degradation in the high bit file is simply another effect of sticking one’s head in the sand. This is and has always been the advantage of high bit editing!

> Any file corrected in 8-bit will be very slightly grainier than one corrected
> in 16-bit.

Noiser in shadows with a very odd speckling? Yes, I see that. That’s not a useful attribute to induce on a file unless you want such an effect. It’s not seen on the high bit file.

> (Andrew concedes that
> when these same moves are applied in Adobe RGB, the two images are the same
> for
> all practical purposes).
  
Yes I do, with a significant amount of color information I can use tossed away in the process. It sounds like you’re in favor of using ultra-small gamut RGB working spaces in 8-bit.

Dan, you can apply a Gaussian blur to the image and remove the noise but no one is suggesting this is a good way to remove the noise or smooth out a histogram. Bottom line is one editing routine doesn’t produce this effect of noise, the other does. I want the color available for output without the noise, I can accomplish this in high bit.

> 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.

>> While it's arguable whether the image taken as a whole is better or worse,
>> certainly Andrew is entitled to object to the graininess.

Well I consider that some progress <g>

> 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.

Indeed it is. The scene and the file require this wide gamut space since I can, will and want to use those colors to the output devices I have available today. In the future, I would expect even wider gamut devices to be at my disposal. Other than the file being twice the size, what’s the problem?

> If you are misguided enough to work in an ultra-wide gamut RGB, that is.  

The same effect can be seen in LAB which is a ultra wide gamut space! I can clearly see similar noise issues in 8-bit LAB versus high bit LAB.

> At bottom, though, it's just another attempt to blow smoke over the inability
> to back up his partners' extravagant claims.
  
Anyone other than Dan taking this statement at face value should consider looking at the RAW file, converting both ways and using whatever corrections they wish. There’s no smoke here. The data is there for anyone to see. But since once again, the rules of this silly challenge have changed, I have to join the ranks of those such as Bruce Lindbloom as someone that finds more smoke in Dan’s challenge than anything else. So know we have to show a difference between the two using what gamut working space?

> "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."

I think that quote about recreational users is someone else's however, I still agree that it’s pretty obvious in the current example that there’s a visible and obvious benefit of the high bit editing versus the 8-bit editing. And if you can back up the statement that 99.9% of users do not use ProPhoto RGB, I’d love to see some empirical data to back that up. Once again, you appear to the one blowing smoke by implying you have the “ear of the industry” by saying that less than 1% of users are working in this space. I have no stat’s to provide but I do know of many digital photographers are working in this space. I certainly would not go on record as you have to say it’s a mere 1% and all of them are lacking intelligence.

Once again, I’ve provided empirical data to show that many scenes captured with just a prosumer digital camera fall way outside Adobe RGB (1998) gamut as does a number of Prosumer desktop printers. If those colors are not important to you, fine. The challenge is so undefined and moving that you should really add that the “tests” have to be done in this or that space, using this or that edit, using this or that RAW converter. The effects of the edits on an 8-bit file ARE visible in synthetic images and have always been so but that didn’t wash with you. Now, with a real world image that is basically a snapshot, the issue is the working space. What next?

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« Reply #15 on: September 23, 2005, 01:32:57 PM »
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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.
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« Reply #16 on: September 23, 2005, 01:37:08 PM »
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Quote
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
unusual circumstances.

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
result.

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
situations.

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.

Dan Margulis




 
 
 
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« Reply #17 on: September 23, 2005, 01:38:22 PM »
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Further, bit depth and the gamut of a working space DO have connection. In 8-bit, the wider the space, the farther apart the 256 steps. For a guy who’s proposing LAB, there isn’t much wider a space to work with (True, ProPhoto has blue that falls outside human vision).
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« Reply #18 on: September 23, 2005, 02:06:45 PM »
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Andrew,

Thanks for citing the entire post. I appreciate it. I shall read it attentively. Yes I did join Dan's list quite a while ago, and didn't need aspirin, but then again I haven't been there very often. Maybe the dosage of the medicine correlates with the dosage of the exposure - but I doubt that - it's just me - I can't get too emotional about any of this. I depend on what I see in my prints and I refuse to get fussed over it. I think there are probably a great many out there like me who haven't seen any readily obvious differences between printed images processed from 8 or 16 bit files but do the latter anyhow for insurance. Storage is cheap, computers are fast, so why not.

And yes - thanks for reminding me - the wider the colour space the longer the distance between levels and logically the greater the risk of posterization. BUT the authority I can't quote (because the information is copyrighted and the permissions insufficiently clear), mentioned that you can shed down TO something like 38 levels per channel before you'd see a difference in the prints (I must say I found this hard to swallow - but the source has considerable professional credibility and would seem to have hard evidence up his sleeve). I expect he made that comment in the context of RGB98 working space, but that wasn't specified in his material. Now if THAT's true, it has some pretty clear inferences for the 8 versus 16 bit editing issue, which was the context of his discourse.
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« Reply #19 on: September 23, 2005, 02:28:31 PM »
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Andrew, I have now read Dan's entire (cogent and closely reasoned) post carefully; I thank me for suggesting that it be made available and you for doing so. I am now satisfied that there won't be a consensus on 8 versus 16 bit editing and there needn't be one either. People should edit in whatever mode floats their boat. I decided some time ago that 16 versus 8 was not worth the expenditure of valuable additional time trying to prove or disprove and I am now thoroughly reinforced in that decision - but again, that's just me. For others, I'm sure "la lutta continua".
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