Photoshop Training with Dan Margulis

I attended a seminar at Graph Expo last month where we were told only 16 Bit images should ever be brought into the LAB color space for manipulation.

The presenter did not seem to have much information to support the statement, but no one in the audience seemed to disagree either.

Does anyone out there know what the peril could be to working on 8 Bit images in the LAB color space?

Thanks in advance,

Pat Theobald

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On 11/9/04 3:49 PM, “pt210w” wrote:

This is a controversial topic and some folks get all wrapped around it.

So my .02 says this:

If you ask folks who are pro 16 bit and who possibly have religion then you might hear you are doomed to work any other way.

The peril is supposed to be that you get obvious banding due to image editing and then when you print you might see it if you don1t use 16 bits. Oh yea and your histograms will have gaps. But then again, we don't sell those histograms.

And people on the other side of the argument the 8 bit lovers might say it doesnt matter.

The hard evidence (prints viewed by experts) I have gathered as well as others on this list like Dan, indicates that there is no discernable difference between 8 and 16 bit images that have made the trip to LAB, heavily edited and then printed.

However, IMHO there is not reason to fight over this, because of how Photoshop works today, I don't see a problem working in either 8 or 16 bits modes in RGB or LAB or even cmyk.

Jim Rich

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Here1s the deal. The wider the gamut of a color space, the more steps between what is only being defined by 256 total steps. So editing can cause banding and excessive data loss due to view bits describing more data. You also have to get into LAB from something (RGB usually) and while Photoshop does this with 20 bit precision, every time you convert from a smaller to a wider gamut space in 8 bit, especially with a color space gamut mismatch, you lose even more data. For example, if the working space is Adobe RGB, which has 256 values available, converting to 8-bit Lab reduces these down to 234 values producing a loss of 22 levels. Doing the same conversions from ProPhoto RGB reduces the values to only 225 producing a loss of 31 levels. Bruce Lindbloom a well respected color geek and scientist has a very useful 3Levels Calculator2 that allows one to enter values to determine the actual number of levels lost to quantization (see the 3Calc page2 at http://www.brucelindbloom.com ).

Andrew Rodney

http://digitaldog.net/

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While CMYK and RGB may be related, Lab does not work the same when working in curves in Photoshop. Therefore, the peril could be that Lab is such a potentially powerful tool for color manipulation that one could easily overdo things causing major problems. It is true while doing moves in RGB/CMYK may still cause major problems if things are overdone, it seems it’s allot easier to screw things up while in Lab. One needs to look at their own situation, for myself - everything that comes to me is 8bit, so 8bit is my world. Perhaps that is why no one in the Expo group seemed to disagree. I would also add that doing some manipulation in Lab is very beneficial to the images I work on, however I have to admit I probably only take my images into Lab on rare occasions and that is usually to perform some blending function with my original RGB/CMYK image to make adjustments to a particular color channel. I would hate to take a hacksaw to some of Dan Margulis’s chapters in his book just because someone told me that 16 Bit images should ever be brought into the Lab color space for manipulation. Especially if they can’t support it very well.

Ron Scratch

RR Donnelley

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A image-editor has to know his limitations (his skill when using it) when it involves lab. While their is “color theory” (mathematically)

from a scientific stand point. Their is also “applied color theory” (hands-on)from the application level. Sometimes one contradictes the other. Which one contradictes the other?.........Trial and error.

John Opitz

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Pat Theobald writes,

Par for the course. Someone should have asked the speaker to demonstrate on a real image what the terrible consequences of working in 8-bit would be, either in LAB or elsewhere. It would then have been discovered that the speaker had no such image available. Research the issue, and you’ll find a lot of “experts” saying that correcting in 16-bit is absolutely critical, creates a night and day difference, that anyone who doesn’t do it is an amateur, etc., etc., etc. What you won’t find are any side-by-side examples of how working in 16-bit creates a better result at all—let alone a huge increase in quality—as opposed to doing exactly the same thing in 8-bit.

Most of the 16-bit discussion pertains to working in CMYK or RGB, but the proponents, none of whom actually work in LAB or understand very much about mathematics, argue that there are mathematical reasons why working in LAB is worse in 8-bit. In fact, it’s the opposite—it’s technically (although as a practical matter, inconsequential) more damaging to work in 8-bit RGB than 8-bit LAB.

Thousands of people use LAB successfully every day, including hundreds of my own students who report back to me with complaints and problems as they arise. If anybody was actually encountering this problem, we’d all know about it.

Dan Margulis

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on 11/11/04 5:56 AM, Dan Margulis wrote:

http: //www.brucelindbloom.com/index.html?DanMargulis.html

Also be sure to check out Bruce1s background. And no I1ve not seen any text that says 316-bit is absolutely critical, creates a night and day difference, that anyone who doesn’t do it is an amateur, etc., etc2. It1s simply a reflection of math and physics.

Andrew Rodney

http://digitaldog.net/

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On Nov 11, 2004, at 9:33 AM, Andrew Rodney wrote:

Gee, I sure have. Jeff Schewe was saying exactly this a few years ago. I don’t know his current views. I assume he’s backed away from this somewhat as I don’t think he’s at all stupid. However, I continue to see this claimed every day.

Personally, I still think 16 bit editing has a place, but I think there are about a hundred other editing issues that will lead to more visibly higher quality. For the vast majority of images I don’t believe there will ever (with today’s or tomorrow’s reproduction methods) be a viewable improvement from working in 16 bit, yet I see very few images that IMO couldn’t be improved from where they end up. In my experience the big difference between capture devices (scan or digital) is the quality of the bits. A device that outputs bad data will look just as bad in 16 bits as in 8 bits. This is a separate issue from whether a device needs to be able to use more than 8 bits. Any decent camera or scanner I’m aware of already uses 12 to 16 bits under the hood. I would agree that if we are taking the Raw data and the Raw data needs a large correction (which it generally does) that working in 16 bits will be necessary.

Just my 2¢.

Ric Cohn

www.riccohn.com

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Ouch!! ;^)

Thanks for this reference, Andrew. I would love to see Dan’s response.

Regards,

Bill Morse

Digital Eye Editions

343 Medford St., Studio 2A

Somerville, MA 02145

(617) 429-3298

PS- from a “16-bit Advocate”, but hopefully not a closed-minded one.

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on 11/11/04 9:09 AM, Ric Cohn wrote:

I know Jeff still is a big proponent of working in high bit.

I agree. But that doesn’t dilute both the math behind what happens in 8 bit, or the fact that we don’t have a crystal ball that tells us what could happen in the editing process in the future to our files. I for one have a RIP that fully supports 16 bit files for output (ImagePrint) driving my Epson’s. So while I doubt ink on paper processes will ever require a high bit file, today I have a printer that clearly takes advantage of this data. And I have no idea how many printers will come onto the scene in a year, let alone 10 years that will allow this.

There are users who need to edit a file and output it once (to say a press). They really don’t need to be all that concerned with high bit capabilities. There are others producing very demanding output that do. It’s all about flexibility. To suggest, based on one kind of output useage that high bit editing is smoke and mirrors is pretty close minded considering how editing and output devices have improved since desktop imaging started with Photoshop 1.0.7!

Andrew Rodney

http://digitaldog.net/ ___________________________________________________________________________

Andrew Rodney writes,

As is so often the case when one of Andrew’s pet color concepts goes down the tubes, his memory becomes unreliable.

In the current edition of my book, I quote at some length a 2001 thread in AdobeForums where a number of “experts” were on the defensive, because several participants were asking them why, if 16-bit corrections were so dramatically better, they couldn’t supply any images that showed this. The experts said they were too busy to do so, but that we should take their word for it, and tried to change the subject into a discussion of whether I was a wicked and evil person. Apparently feeling that if they only sounded decisive enough the skeptics might go away, they said the following things, all direct quotes, separated by ellipses, many different speakers, I forget which one is Andrew.

"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."

The following year there was considerable discussion here, in which Andrew participated vociferously, of the merits of the following statement by one of the above experts, who presented it in writing to a class at a major trade show:

"I’m not sure just how to stress the importance of doing color and tone corrections in 16 bits in Photoshop. One can point to the obvious advantages...I suppose the difference could be characterized as professional vs. recreational use of Photoshop"

That thread can be found at

http: //www.ledet.com/margulis/ACT_postings/ColorCorrection/ACT-16-bit-2002.htm

Now, certainly, none of these experts would be likely to say any such thing today (although, AFAIK, none of them have just bitten the bullet and said that they were wrong, as I hope the rest of us would if we were in their shoes). It is, however, always useful to look back on what they *did* say at the time, lest revisionist historians suggest that they didn’t.

Dan Margulis

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From: Bill Morse

This is an old reference. This is not anything new. Not speaking for The Man, but if you have The Book..... in Chapter 15, starting on page 310 he explains the 8 bit vs. 16 bit. The images and the curves The Man applied are on the cd. Also you can find it here...

http: //www.ledet.com/margulis/PP7_Ch15_Resolution.pdf

Refer to page 16 of this pdf.

John Opitz

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Bill Morse writes,

I find the whole topic so distasteful that I ordinarily pay no attention when it arises, but since it has come up I will make one post, but no more.

I have no objection to people who disagree with my opinions, even when they aren’t particularly civil about it; that’s how things get sorted out eventually.

The site in question is a different animal. It involves a frustrated individual deliberately posting information that he knows to be false. Plus, Andrew Rodney, who knows full well that the page is a troll, repeatedly posts links to it.

Bruce Lindbloom’s whole contention is that before I tested the 16-bit images, I converted them to 8-bit and then reconverted them to 16-bit before applying curves. If that were true, it would be like a test comparing how well two washing machines work on the same kind of load, except that one of them had a bucket of mud poured in it first.

Of course, it’s ridiculous. What he is seizing on and deliberately misinterpreting is a phrase in my original description of how I would proceed. I said I would run a series of drastic corrections on two copies of each of many, many files. One set of corrections would be done entirely in 16-bit and the conversion to 8-bit would come only at the end; then, on a copy of the file, I would convert to 8-bit immediately and load the identical actions, whereupon I would compare the two.

Makes sense so far, but I added: if it turns out that the version done in 16-bit is significantly better, then, and only then, I’d run a third test—converting the 8-bit file back to 16-bit before correcting it, to see if there wasn’t something about the calculation method that was producing the better result, rather than just the extra data.

I’ve studied what happens when you do that, and it’s pretty interesting. However, it never was any part of my testing of the images, for the simple reason that the corrections done in 16-bit all the way were never any better than in 8-bit, regardless of how drastic they were.

Bruce asked a lot of questions about this at the time, including correspondence with me off-list. I was aware then that he was trolling, because he was professing to be neutral on the subject, whereas on the ColorSync list he had recently called 16-bit correction “a must” in certain circumstances. So, when I saw he was trying to poke a hole in the methodology, I made sure that he grasped completely what the purpose of the hypothetical 16>8>16 conversion was.

There is no possibility that he misunderstood this; indeed, he could not possibly be so stupid as to think that anyone would perform a test this way. Nevertheless, he chose to post what he did, knowing that it was false.

While the content of the page collapses when this is understood, there is one other side note. Bruce accuses me of keeping the results to myself and appointing myself the sole judge, which he knows perfectly well is not true. I printed 10 pages of side-by-side samples in my current book, many at extreme magnifications. The versions are not identified until a box later in the chapter, and readers are invited to judge for themselves which is which, plus, I indicate how I voted when I first saw the proofs and did not know which was which. The original 16-bit files, and the corrections I applied to them, are all on the book’s CD and anybody who likes can either verify what I did or do their own experiments.

What prompted the accusation was an unfortunate incident involving my first round of tests. The test files were provided by a list member whom I did not know at the time. After I performed the tests, I was flabbergasted to learn that he would not give me permission to exhibit the images and results publicly, which I thought was the whole point of the exercise. He did confirm, several times, on this list and at least two others, that he and I were not personally acquainted; that he believed I did not realize he was not giving permission; and that he had seen my results and that I was describing them accurately. When Bruce challenged him, he offered to give him pieces of the pictures (and my results) that would have been sufficient for Bruce to verify the findings, but Bruce refused to take them.

Because of this incident, I changed the rules. I said I would not do any testing on 16-bit files without an advance agreement enabling me to publish them and to release the raw data to illustrate whatever was found. Ric Cohn and a couple of other people kindly agreed to allow their images to be used in this fashion. Consequently the files are available for anybody on the CD.

The upshot of this: you guessed it. With the rules now having been altered to accommodate Bruce, Bruce wrote that the test was invalid, because the rules had been changed.

In summary: the issue with the page is not its dishonesty as much as its irrelevance. Bruce is the one advocating the inconvenient workflow, just as it would be if he said that there’s a big quality difference if one only wears garlic around the neck while booting Photoshop up. Nobody can disprove that, because if your tests show that there’s no difference, probably the garlic was too old or there wasn’t enough of it.

Similarly, nobody can disprove that 16-bit correction may be better under some circumstances, because nobody can test every conceivable image with every conceivable tool. However, the only two people who have ever run extensive tests—Jim Rich and I—tortured the images almost beyond belief and still were not able to identify any areas in which 16-bit correction did better with a color photograph.

It’s painfully apparent at this point that Bruce and the others have never actually done side-by-side tests to support their theories. Otherwise, we’d have seen examples long ago. For anybody wishing to successfully advocate the 16-bit workflow, the recipe is quite easy:

1) Here is a photographic image;

2) Here is what I did to it in 16-bit;

3) If you convert it to 8-bit first and then repeat what I did, it looks a lot worse.

Without that demonstration, he has put up a blank page, IMHO.

Dan Margulis

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I must admit that I haven’t done extensive personal testing on the question of 8 bit vs.16 bit editing.

Why not? Well, I’m getting along just fine in 8 bit. I have no problems that I know of that 16 bit editing would fix, and I know of several problems I would have using 16 bit.

What problems are those? Much bigger file sizes, limited editing tools, more time watching the beach ball revolve, clogged hard drives and a lot more CDs and DVDs to burn and catalog, to name a few.

What problems would 16 bit editing solve? Well, I suppose, I wouldn’t get as much banding in a heavily edited file. But wait, I don’t get banding now, and I routinely do some pretty serious curving. I can only think of one image where banding was a problem in output. I must admit that I didn’t think to try 16 bit editing; I just selected the sky and added a bit of noise.

Maybe I’m missing something, but I don’t know what I’m supposed to get out of 16 bits except maybe a bit of status with the color geeks. Anyone? Richer colors? Sharper results? More shadow detail?

And what if you don’t make heavy edits on a file? Is there any theoretical advantage to 16 bits here? In other words, does the average image have anything to gain from 16 bit, or is it just the very rare ones?

The only examples I’ve seen that purported to show the benefits of 16 bit editing were terrible photographs to begin with. The author (Bruce Fraser) was trying to make a silk purse out of a pig’s ear, and it didn’t work in my opinion. If 16 bit is only effective on this type of image, then I think I’ll do my best not to start with a piece of crap to begin with.

My comment relating to this thread is that it seems like another case of people reacting to what they see in the process, and not the result of that process. Many others on this list have observed that we don’t sell histograms to which I concur.

What I have proven to myself in my own personal work is that I can get excellent results in 8 bits. Certainly, my files are usually pretty good to start with; for example they’re not scans of negatives that are two-stops underexposed. Your situation may be different, I realize. Just don’t expect to start from this position and get a result that’s as good as could be done properly, using only 8 bits but with a good original.

Those of you who are using 16 bit editing, have you proven it to yourself that it’s necessary? Vital? Beneficial? Noticeable? Detectable? All the time? Sometimes? Ever?

If you have, but you go a long way down that progression, perhaps you should reconsider your workflow.

And if you’re up at the front of the progression, congratulations! You’ve just won the 8 vs.16 bit challenge. Now please post your images for all to see.

Finally, ask yourself this question: is it not true that if two techniques yield the same result, the better method is the simpler, faster, the one that is a much lighter weight to bear?

Perhaps some of you are taken in by the old logic that you used to use in photography: the bigger the camera, the better the pictures. That doesn’t hold true here; this isn’t 4x5 vs. 35mm; more bits aren’t necessarily better.

Cheers,

Ron Kelly

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I will tell you something 16 bit IS good for... charging customers by file size. Everyone from color management consulants, to scanning services, to camera salesman, to photographers uses this trick.

I agree with Dan, this is a tiresome debate. I also agree with Ron. I personallly think that only dogs can hear in 16 bit.

On a similar note, I work with the BetterLight camera, shooting 8 bit files for fine art reproduction. No one has ever had a problem with 8 bit files. I have encountered printers who tell me my files are too lo-rez for their printers, since I scan at 300ppi. The files I am producing are over 4000x5000 pixels. I know from my own experience that you can print photographic images banner-sized from these files. Still, I encounter printers who want to up-rez the files to match their print dimensions. This makes for softer images and cumbersome file sizes. Has anyone else had this problem sending work to print?

-Mike Bevans

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on 11/11/04 5:14 PM, Dan Margulis wrote:

Post a quote and a reference please.

If you1re going to put quotes here you better get your facts straight bud. You may not remember? Then either find the exact post and a reference or pull my name from this bogus list of quotes. Be accurate Dan.

I1m still waiting for you to respond to Bruce Lindblooms page.

Andrew Rodney

http://digitaldog.net/

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Bill Morse writes,

Well Dan wrote a lot but didn1t address anything Bruce challenged him on. Bottom line is on this list, Dan1s right. There1s no need to argue science. I actually considered cc1ing this to Bruce but in the end, it1s a waste of bandwidth. Read Bruce1s page, do your own tests. Consider the math (that1s all computers understand) and consider what will happen to the file in the future and what devices it might be sent to. Then consider the downsides of 16-bit editing and do what you feel is right.

Gee, I wonder why the vast majority of input (even consumer devices) produce more than 8 bit per color????

Andrew Rodney

http://digitaldog.net/

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The message I received seemed to do a fairly good job of addressing the issues raised on the Mr. Lindbloom’s page.

Dan Margulis on 11/11/2004 23:17

Computers have is math, humans have more flexible forms of perception - what we perceive is not necessarily what is there or not there. That goes for this little verbal fire storm as well as the bit level of files. If you don’t like Dan’s results, perhaps you can invent you own tests and publish your own results.

F D Yocum

Graphic Designer

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Check out:

http: //www.photoshoptechniques.com/forum/archive/index.php/t-336.html

This appears to be one of the first or original sets of discussions (including the bit about recreational users). You1ll find no posts by yours truly. You1ll also find some sensible advise from Bruce Fraser such as:

"I have never, anywhere, claimed that 16 bits is superior to 8 bits. What I’ve

said is that from my own experience, 16 bits gives a great deal more editing

headroom and flexibility than 8 bits. If you don’t need it, don’t use it. I’ve

always been pretty straightforward about the plusses and minusses, and I’m not

trying to sell anyone on 16-bit workflows."

Andrew Rodney

http://digitaldog.net/

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Andrew Rodney writes

The dynamics of modern digital cameras is such, that you have a much wider contrast range than (most — and surely more than any slide-) film could produce. When I process RAW files into TIFF files I have the possibility to shift 2,5 Stops each way without getting into serious problems (Canon EOS1Ds with C1 PRO from Phase One). In my understanding it’s here where the more than 8 bits of the camera come into play.

Could this be the answer to your question, or am I getting things wrong?

Werner Tschan

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Werner:

Try this test:

Lock your camera down on a tripod and photograph some scene that has a full dynamic range, ie shadows with detail and highlights with detail, maybe some speculars too.

Bracket your photographs. Choose one that appears to be the best exposure for the scene, and choose one that is 2.5 stops darker than that.

Open up the darker one, and manipulate it in software to match the “best exposure” and compare the results. Use on-screen and/or prints for your comparison, but be sure to use the criteria that you most often have for “the final result.”

What does your comparison show? Are the results identical?

Ron Kelly

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People:

I was just out jogging and I was mulling over the whole 16 bit vs. 8 bit thing. As I rounded a curve by the river, I was thrilled to see a gorgeous sunset.

Naturally, this got me to thinking: what color space does God use? What bit depth?

After consulting my fellow jogger, who is very strong in physics, we decided that God uses 64 bits. He said, (sic) “There is just no way that you need any more than 64 bits to describe ALL the colours, x-rays, and gluons or whatever. I don’t know exactly how many wavelengths that is, but it’s A LOT.”

Which begs the obvious question: what if you used 128 bits for edits? I know, I know, there are no devices, software, or monitors for this (yet!) BUT JUST THINK! Maybe someday you could have better color than God! (VERY Big ; - ) )

I don’t really want to re-ignite the whole thing, but I just couldn’t resist.

God Bless all of you who contribute; we may not all have the same opinion but that doesn’t mean we can try to understand each other, and have a little bit of fun too.

Sorry for wasting your bandwidth,

Ron Kelly

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Ron Kelly wrote:

God uses double precision floating point. At the end of the day, unlike His creations, God is big on pictures and scant on words.

BTW, He is not big on upgrades and is still using an early version of CP/M, running on an overclocked Sol, with hard sectored 8 inch floppies.

Mike Russell

www.curvemeister.com

www.geigy.2y.net

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Makes me wonder what color looked like a few billion years ago.

Was Sol redder or more yellow? Were natural dust and volcanic dust filters

warmer than our carbon filters? Moreover, what sort of profile would it take

to match the cones of early hominids?

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Ron,

At first seeing your amusing comments about God and higher bit depth I wrote what I had hoped to me would be an entertaining response:

But what if you don1t believe in God. Then are you stuck with those devilish 8 bits?

Then it became clearer that you are on to something here that has been alluded to all along. This is a true religious experience for a lot of folks who are on both sides of the issue. The 8 v 16 bits argument is now is about his or her belief system and for those people who know they have religion because they have been to the mountain, there is a need to stand their ground no matter what the evidence says. And that this argument is more about peoples core beliefs (and egos) than it is about technology and facts.

Sounds just like the our last presidential election.

My .02.

Jim Rich

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There was none. Color only exists in the mind of an suitably-equipped observer!

Bob Frost.

From: “David Deaubrey Tighe”

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David Deaubrey Tighe wrote:

There’s no need to guess about this, as this is dictated by the molecular structure of the light senstitive dyes, and they have a well-documented time line in our DNA, and that of other species. Chevreaux documented the adaptive nature of color vision 100 years ago - we use something more like individual curves, not profiles, for our vision.

Looking at our retinas under a microscope, cones come in three colors, cyan, magenta, and yellow. Rods, which are the more primitive sensor, are senstive to monochrome only, and used for edge detection at normal light levels. So, it may be argued, with anatomical support, that we are CMYK creatures, with sharpening in the K channel, not RGB ones.

There’s nothing magical about three cones. Multispectral is the order of the day for many animals. Certain birds, including Mallards have five different light sensitive pigments. Add the rods, and you have hexachrome or hifi color.

It would not take much, just the presence of a fourth type of cone, for a person to have multi-spectral vision - and such people may be walking among us in small numbers. Perhaps a member of this discussion group could design a billboard that would be readable only by these people.

Mike Russell

www.curvemeister.com

www.geigy.2y.net

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Mike,

Wow, interesting stuff.

Awhile back I was reading something about color-blindness (specifically what is called red-green color blindness). I recall the article said it should more accurately be called “magenta-green” color blindness. This explanation made color blindness sound like it was occurring in a LAB model.

I don’t know anything about the biology of color, but it’s fascinating.

David

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David,

An excellent book to read is ‘Vision and Art - The Biology of Seeing’ by Margaret Livingstone (Harvard neurobiologist).

Bob Frost.

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Mike Bevans writes,

Certainly. This goes hand in hand with Terry’s post yesterday. There are some very knowledgeable printers who hang out on this list and elsewhere who know most of what there is to know about prepress. As I remarked yesterday, however, the chances of finding a printer who knows what his own dot gain is or has any idea of what black generation to use are not high. Similarly, few printers have any clue as to what resolution is necessary.

What you get, therefore, is some minimum-wage person who runs the incoming job through FlightCheck or something similar and demands that whatever the program thinks it requires be complied with.

Since this is the kind of treatment that *I* often get from printers (who often get all huffy when I say that the resolution is sufficient, and tell me I should go off and read a book called “Professional Photoshop” before having the gall to challenge a printer on what they do best), I can only imagine what a PITA it is for other people.

Unfortunately, there’s nothing for it but to improve one’s own knowledge—if you don’t know more about image prep than the typical printer does, there’s a problem. In the this-is-hard-to-believe department, I offer just three examples:

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1) My publisher calls me up asking how to deal with another author’s book. The book is about Excel or some other non-graphics software. There are no color images other than screen grabs, and there are about 500 of them. It’s on press, but the printer says it won’t print the book unless each and every one is upsized to 300 ppi. Author refuses. Publisher being berated by printer for providing inadequate files. It actually takes a call from me explaining what the purpose of resolution is, and why 300 ppi is three times higher than what you need for a screen grab, before the printer will relent.

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2) I get a call in the middle of the night during the REPRINT of one of my books—that is, after the book has already printed successfully, using the same exact files. Following dialog ensues:

Printer’s CSR: Sir, I’m sorry to wake you, but we’ve had to stop the pressrun because there’s a problem with one of your files. It doesn’t have enough resolution and the pressman is saying that it looks like [doo-doo] in print.

DM: What picture is it?

CSR: It’s the one on page 147, top left.

DM: I do love my book but not quite enough to have a bleeping copy of it here with me in bed. What is the picture of, please?

CSR: I don’t know. The pressman didn’t tell me.

DM: Well, do you have the bleeping dyluxes in front of you?

CSR: Yes, sir.

DM: What does the caption for that picture read?

CSR (reading): “This image illustrates the perils of printing with inadequate resolution.”

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3) The following is unsolicited correspondence:

Subj: Question concerning Levels.

Date: Friday, February 21, 2003 10:48:15 PM

To: dmargulis@aol.com

Hello Dan,

I just purchased your 4th edition of Professional Photoshop. It is just as friendly and wonderful to read as the first one. I work in a Screen print shop and rarely get to use a majority of your cool moves. Earlier today, while studying your book and duplicating your moves, the Production Manager tried to explain to me why the moves wouldn’t work for high end printing. His evidence laid in the levels dialog box. After the moves, the levels would show up spiky and with gaps. He insisted the image would print like crap. He had me enlarge the image by one pixel and upon checking the levels, they were now smoother. I looked at him like he was crazy and muttered that I would look into it. My question to you, is he crazy or does he have some sort of valid point?

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You can’t make this stuff up.

Dan Margulis

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Mike,

The actual peak response of the three types of cones in our eyes is in the violet, green and yellow regions, so that perhaps makes us VGY creatures!. The rods also have peak response in the green region. Fish apparently do have cones that peak in the red region, but we don’t.

But it is not so simple since each cone has a very broad response to light. The longwavelength (or ‘Blue’) cones peak in the magenta but respond over the range from UV to green. The middle wavelength (or ‘Green’) cones peak in the green but respond over the whole visible range of UV to red, as do the shortwavelength (or ‘Red’) cones which peak in the yellow but respond more strongly in the red than do the middlewavelength cones. This means we can’t tell anything about the color of the light from the response of a single cone type. Only by comparing the ratios of the responses of all three cone types can the brain work out what wavelengths of light have stimulated them.

In a way, rods are our fourth type of color receptor! Which is why colors seem different at dusk when the rods come into play and our cones become less efficient. During the daytime when we are using mainly our cones for color and luminance detection, if we look at a blue bowl with red cherries in, it appears that the cherries are brighter than the bowl. But at dusk as our rods play a greater part in detecting luminance, the blue bowl becomes brighter than the red cherries, because the rods are more sensitive to blue light than to red!!

Bob Frost.

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On Nov 13, 2004, at 11:41 AM, Mike Russell wrote:

This is fun and instructive, but how come we can see way outside the current CMYK spaces?

(I’m aware that “current” may be part of the answer)

Laurentiu Todie

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Backing away from the trees here a minute and looking at things as a relative novice, I seem to recall that the ability of the human eye and brain to recognize (perceive) adjacent similar color differences is quite limited. If one uses 8 bit colors and generates sufficient adjacent color differential as the direct result of an edit, then there may be a case for the use of 16 bit color. However, at the pixel level, one cannot discern close adjacent color differences without extreme magnification and an electronic meter. The eye blends colors quite well and uses a built in AWB to compensate for what we “think” the right color is or should be. Even at 72 ppi on a decent monitor, adjacent pixels are blended, thus leaving the 8 vs. 16 argument moot for the most part.

Having said that, I can also imagine an image with an incredibly narrow density range being artificially expanded with a curve (Dan’s fans don’t use levels :-)) which would stretch the gaps between colors and create a wider range between adjacent pixels (black cat in a coal bin, polar bear on ice), which in turn would show up in favor of the 16 bit camp after some extreme editing to prove a point. I suspect that, mathematically, one could crunch some numbers to make a case for 16 bit under extreme editing conditions. I also suspect that in the real world, 8 bit is indistinguishable from 16 bit with “normal” images. I have tried some tests similar to Dan’s and have yet to “see” anything that would encourage me to change to 16 bit files. I’m still testing. In the real world, I don’t stretch black objects from black thru gray to white.

Mike Davis

mldavis2 AT sbcglobal DOT net ___________________________________________________________________________

David Tighe writes,

That would be me. I tested a group of color-blind people and found that their condition could best be approximated as an extreme inability to perceive variations in the A channel. The group appeared to be at least as sensitive as normally-sighted people to changes in the B channel (further testing needed to say this for sure) but even the ones with the closest to normal vision could not see a difference in the image when 50% of the contrast in the A channel was removed. The ones who were most spectacularly colorblind could not see a difference even when the A channel was inverted, i.e. magenta objects turning green and vice versa.

Dan Margulis

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Dan,

Yes, now I recall you discussing that. Sorry I couldn’t give you attribution in my original paraphrase.

Was that in your book or from online? I was going through some old files this week from CompuServe’s Pre Press Forum and perhaps you mentioned it there?

My graduate advisor, a painter, is color blind. I’ve also discussed some of these interpretations with him. FYI, I used to be a commercial pre press guy, now I am an artist/printmaker and mixing the old world methods with today’s high tech.

David

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David Tighe writes,

It was in a column in Electronic Publishing.

Dan Margulis

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Mike Davis writes,

I thought that such a thing would happen myself, which is why I included exactly such images in my tests. To my surprise, there was no advantage to editing in 16-bit even in such an extreme case. If anybody else has tried a side-by-side test on such an image and gotten a different result, I’d be happy to hear about it.

Dan Margulis

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Andrew Rodney writes,

The argument concerns Andrew’s revisionist claims that he has never heard anyone (like, for example, his own business partners) say that correction in 16-bit creates a night-and-day difference, or that anyone who doesn’t work that way is a recreational as opposed to a professional user. I posted two lengthy quotes showing that he had in fact heard exactly those things from his friends. Now, we get the above—a reference to an unrelated group posted a year after the one I cited, where the poster has already changed his mind considerably.

Because of the possibility that the group may be misled by this obvious red herring, I reluctantly post the complete, unedited text of the 2001 posting by the person Andrew now quotes as taking a soft line on the issue. A reminder that this individual was only one of several persons posting substantially similar comments at the time. And, as Andrew’s later post shows, neither this person nor anybody else in their right mind would say such a thing today. I trust this brings this episode to a close.

NOTE: With respect to the first paragraph, the poster was immediately corrected publcly by the person providing me with many of the raw scans used in my book. The originals *were* untouched, *were* in 16-bit, and had not been toned in any way, whether by setting white and black point or any other modification. Some of the tested moves were almost inconceivably extreme, far more than would be encountered in any plausible real-life scenario. Therefore, they are precisely the kind of files that the speaker then thought would be so much better in 16-bit that “the difference really is night and day” and “it’s totally obvious to anyone who looks.” As those who have read my book know, it is in fact extremely difficult to tell the two sets of images apart, even at high magnifications.

My apologies to the group for the waste of bandwidth.

Dan Margulis

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Bruce Fraser - 02:58pm Aug 12, 2001 Pacific (#46 of 52) I think a lot of people are overlooking the fact that Dan is playing with a stacked deck here. I very much doubt that his “tests” start out with a raw scan from an 8-bit capture device. At very least, black and white points are probably being set in the scanner, probably in 12-bit space. Maybe some rough tonal shaping too.

In which case, the debate simply becomes one of whether it’s advantageous to do gross corrections in the scanner software or in Photoshop.

I started using a primarily 16-bit workflow primarily because most scanner software did such an abysmal job of transferring color correctly to Photoshop, and because I don’t like making critical image decisions on a postage-stamp-sized prescan.

From a quality standpoint, it makes little difference whether you carry out the manipulations on the high-bit data in the scanner software or in Photoshop. I prefer doing it in Photoshop because it gives me more control than most scanner software (or maybe, honestly, because I know Photoshop’s controls better than I know any scanner software), and because I can see every pixel in Photoshop.

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. But very few people do anything of the kind.

Those of us who have adopted a 16-bit workflow in Photoshop have done so because we’re less likely to make dumb moves based on the postage-stamp preview, and because high-bit files in Photoshop give us much more editing flexibility and headroom than an 8-bit file produced from manipulating high-bit data on a scanner or digital camera. But if someone prefers to do the gross manipulations in the scanner or camera software, I won’t argue with them. It doesn’t really matter, beyond personal preference and skills, where one manipulates the high-bit data.

But it’s totally obvious to anyone who looks that it’s very advantageous to do the big moves on high-bit data.

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On Sun, 14 Nov 2004 10:03:21 EST

Dan Margulis wrote:

I’m afraid that rather crude math used in some image editing programs may be one of the reasons.

Best regards,

ib

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on 11/14/04 8:00 AM, Dan Margulis wrote:

No, I said I never said that and challenged you to quote me on saying that. Big difference.

That1s an assumption only Dan would make. I suggest you contact Mr. Schewe and see if indeed he1s of that belief or not. I posted a reasonable and rational response from Bruce Fraser from that 2001 post. But again, you1ll have to ask Bruce if he still feels that way or not. Unlike some, I try not

to put words in other people1s mouth or misquote.

This debate which has gone on for years in this and other forums is simply getting to the point that it1s like a religious belief of both parties. It1s pointless.

Here are some facts and some color theory:

Fact. Nearly all tone and color corrections (color space conversions included) cause data loss. It1s simple math. This can1t be disputed. The question becomes can anyone see this data loss? See it where? On what output device? At one point in the editing process? The fact that data loss happens is not something that should keep users awake at night worrying about but it should be something they recognize.

You1re taking an image and printing out to a halftone dot once (as far as you1re concerned). Should you be alarmed that editing 8 bit data will cause data loss and be seen? From some or the more open minded users who have posted on this subject, the answer based on their experiences is clearly no. They point out that 16 bit files take up double the file size and slow down processing and workflow and demand more storage space. Now space isn1t a big issue for some, it is for others. Processing speeds are getting faster all the time but none the less, that cost money and takes time. Some have pointed out that the editing options in 16 bit are less then 8 bit. True indeed. Not theory, fact. Photoshop CS opened up a lot more options in respect to what users can do in 16 bit. That doesn1t alter the facts about workflow, speed and storage.

Now despite the fact that some only view the world in CMYK ink on paper, it1s a fact that some users have far greater needs from their data. There are users who like Mr. Schewe will not only be doing on going editing to images and printing them out to all nature of devices we have today, but devices that are now in the lab. In 2001, when the quotes above were made, there were few devices that would actually accept and use 16 bit data at print time. Today I can drive my 2200 with a RIP (ImagePrint) that supports, uses and produces better results from 16 bit files. I didn1t know this would be possible in 2001. I don1t know what will be possible in 2006. IF my goal is to have a file that retains as much useful data today and in the future (which is far cry from the service bureau or print shop), my needs are vastly different.

Let1s not forget what1s coming (very soon) for some users. HDR! An example can be seen here:

http://www.ict.usc.edu/graphics/HDRShop/

Some users produce imagery that requires by their choice the least amount of data loss in order to keep the data as pristine as possible for present and future uses. Others don1t care and have to handle data quickly and move on. NEITHER is right for the other user. One does paint the user into a lesser corner then the other. That1s not a color theory, that1s a color fact. This argument over bit depth is like the current argument now in vouge (shoot RAW or let the camera process the RAW data on the fly and toss the RAW away).

The latest take on high bit editing I1ve seen from Bruce Fraser is in his fine book “Real World Camera RAW2 page 8. It takes both debates and puts them into a useful perspective:

3Don1t be overly afraid of losing levels-it1s a normal and necessary part of image editing, and it1s effect can be greatly reduced by bringing images into Photoshop in 16 bit/channel files rather then 8 bit/channel ones-but simply be aware of the destructive potential Photoshop edits.2

Andrew Rodney

http://digitaldog.net/

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From: Dan Margulis

16 bits allows you to pile more changes on top of each other without accruing round-off errors. You can make some global edit (e.g., Curves, Levels, Hue/Sat, etc.), then decide it’s not quite right so make another edit, then another, then another, without worrying about the fact that in 8-bit mode, each tweak can add up to half an lsb worth of quantization noise in some areas. In most images it won’t matter, but it frees you from worrying that you’re approaching the point where you’re v