Dan Margulis Applied Color Theory

LAB/RGB and RGB/RGB Conversions: How Accurate?

Subj: [colortheory] sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Sunday, September 17, 2006 8:20:29 PM
From: Richard Wagner

On Sep 17, 2006, Stephen Marsh wrote:

I know that Bruce (Fraser) has later changed his
position on the critical need for these extra spaces, but I find it
hard to accept that a very wide gamut space is now the best option for
image editing. Capture and Rendering is one thing, but image editing
is another thing, the problem as previously mentioned is moving
between larger to smaller matrix profiles. We know that there is no
perfect RGB editing space, each has it's good and bad points.

Stephen,

This has been a very interesting discussion, and I also appreciated your summary.

In going back and re-visiting Bruce Lindbloom's site (hadn't been there in a while), I followed the link you provided to another on the site, that discusses the problems in converting from 8-bit sRGB to LAB (and back).

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

Unless I'm missing something, this seems to be an even bigger issue than working in a wide-gamut color space, as one potentially ends up losing a vast amount of color information due to quantization.

To quote Bruce Lindbloom:
"Another interesting observation from the table relates to native Lab encoding. The established methods of integer encoding of Lab color (Lab TIFF, ICC, Photoshop) will clip some of the Lab Gamut. But even more devastating than that is the gross coding inefficiency (only 35%). This means that nearly two-thirds of Lab coding space is wasted on colors that do not even exist. This may be seen here. This inefficiency "squeezes" real colors tightly together, resulting in possible quantization losses. So converting an image into Lab for the purposes of applying a color correction in Photoshop can severly reduce the number of unique colors in your image. This is discussed further here. Whether this is a significant loss depends on the particular situation, but you should at least be aware of it."

This is shown visually here:
http://www.brucelindbloom.com/index.html?
LabGamutDisplayHelp.html#IntegerLab

and a more complete discussion is given here:
http: //www.brucelindbloom.com/index.html?RGB16Million.html

I'm not a color scientist, but this seems to be a potentially bigger problem than working in 16-bit, wide-gamut color spaces and later converting to smaller color spaces.

Thoughts?

--Rich Wagner
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Subj: [colortheory] sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Sunday, September 17, 2006 9:31:22 PM
From: Stephen Marsh

Richard Wagner wrote:
 
I'm not a color scientist,

Neither am I, which is why this stuff is "interesting" and good to know about, so I don't let it get in the way of making images look better. Being informed of the issues is good, which is where Bruce is coming from.

A few years ago I went to the ColorSync Users list an read in full, over 200 posts on the dangers/pitfalls of LAB (8 or 16 bpc) and why it should be avoided.

Dan has covered this in the past on list and in his recent LAB book.

Just as well Dan and his publisher and the market do not agree, or at least are open to using such a "poor method" after knowing the dangers.

but this seems to be a potentially bigger  
problem than working in 16-bit, wide-gamut color spaces and later  
converting to smaller color spaces.

All true in theory, but for many users this matters little.

Best,

Stephen Marsh.
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Subj: Re: [colortheory] sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Sunday, September 17, 2006 9:41:18 PM
From: Mike Russell

From: Richard Wagner

I'm not a color scientist, but this seems to be a potentially bigger
problem than working in 16-bit, wide-gamut color spaces and later
converting to smaller color spaces.

Thoughts?

It's not a problem in practice.  More generally, there are any number of problems that might seem to be potentially serious. Such problems are irrelevant curiosities unless they can be illustrated by specific images.

From a practitioner's standpoint, a theory's usefulness is determined by whether it bears on the quality of a specific, real world image.  AFAIK, no one has shown a photograph that actually suffers from Photoshop's Lab clipping, which is why it appears to be necessary to resort to diagrams of rendered color gamuts to illustrate the "problem".

Mike Russell
www.curvemeister.com/forum/
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Subj: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Monday, September 18, 2006 12:38:19 PM
From: Richard Wagner

On Sep 18, 2006,  Mike Russell wrote:

AFAIK, no
one has shown a photograph that actually suffers from Photoshop's Lab
clipping, which is why it appears to be necessary to resort to diagrams of
rendered color gamuts to illustrate the "problem".

Just to be clear, the problem is not "clipping" but rather quantization loss.  In the sRGB-->Lab--sRGB round-trip, multiple, distinct RGB colors are being lumped together as one color, at a ratio of about 8 to one.  This effect occurs throughout the sRGB gamut - not just at the borders.  It is in essence like using 7-bit RGB, with 129 steps  per RGB channel instead of 256, covering the same range.  Important?  Guess that's for the end user to decide.  Most of us scan at 12 - 14-bit, even though we can't initially "see" the difference, even given the fact that the image will likely end up as 8-bit.  As a general principle, I'm not crazy about the idea of throwing out  large percentage of the color information in an image before making any other changes.  As has been stated previously, there is no perfect working space...

{
(2,186,238)^^1/3 = 129
  2^^7 = 128
}

--Rich Wagner
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Subj: Re: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Tuesday, September 19, 2006 9:48:22 AM
From: Marco Ugolini

It does sound ominous to hear that, due to quantization, the 16+ million colors possible in 8-bit RGB are whittled down to about 2 million or so after conversion to L*a*b*.

But let's remember that most images don't have even close to that many unique colors in them. If you open an image (even one with bright and well-defined colors, and good detail) in ColorThink Pro and do a count of unique colors in it, you are likely to come up with numbers in the range of 200,000 to 300,000. How high could the count possibly go? 500,000 perhaps? (I'm guessing wildly, here.)

Compared to that, upward of 2 million unique colors would seem like a safe margin, unless there's something else I'm not considering.

Regards.

--------------
Marco Ugolini
Mill Valley, CA
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Subj: Re: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Tuesday, September 19, 2006 9:53:51 AM
From: Dan Margulis

Rich Wagner writes,

Just to be clear, the problem is not "clipping" but rather quantization loss.

No, there is no loss of any significance. Tests verify that if you are going back and forth between sRGB and other colorspaces, going to LAB returns a slightly larger variation from the original than ColorMatch RGB does, but sRGB>LAB>sRGB gets you a file significantly closer to the original than sRGB>Adobe RGB>sRGB does, and *way* closer than sRGB>ProPhoto RGB>sRGB.

This effect occurs throughout the sRGB  
gamut - not just at the borders.  It is in essence like using 7-bit  
RGB, with 129 steps  per RGB channel instead of 256, covering the  
same range.

No, because there is no correspondence between the LAB and RGB channels, the way that there is between the red of sRGB and the red of ProPhoto. It would be fair to say that you're using 23-bit LAB instead of 24-bit, but that's far more than you need. You're generating 256-level RGB channels, but you're not looking at 256 levels in each LAB channel, because you can't--they have nothing to do with RGB channel structure. The only thing you can look at is all three together--more than a million levels, from which you need to extract only three sets of 256.

That unique colors are temporarily missing is irrelevant, if you have valid RGB channels after the conversion. The flip answer would be to run a Gaussian Blur at .1 pixel once you return to RGB. That would work--it would generate millions of new, statistically significant, unique colors. There's no need, however--you will be generating them yourself, anyway. *Any* manipulation of the new RGB channels results in millions of new unique colors--for example, printing to any output device (they all have to generate new channels corrected in some way for luminosity) or even opening it on your screen--the monitor's translation routine will generate millions of new, valid unique colors before it displays the file.

While I hope that the above technical discussion is useful, I agree with the other posters that the test is with real images. If you feel that there is some damage occurring, don't give us a theory based on gamut charts, ouija boards, histograms, and the like--get out some real images and see what you can show us. I believe you'll find it rather difficult. If you do, by chance produce an image that appears to show damage, though, you should also repeat your procedure by converting the file from sRGB to ProPhoto RGB rather than LAB. Any damage that you can cause by conversions to LAB will be greatly magnified in the conversions to ProPhoto.

Dan Margulis
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Subj: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Tuesday, September 19, 2006 2:55:41 PM
From: Richard Wagner

On Sep 19, 2006, at 8:38 AM, Marco Ugolini wrote:

It does sound ominous to hear that, due to quantization, the 16+ million
colors possible in 8-bit RGB are whittled down to about 2 million or so
after conversion to L*a*b*.

Marco,

This was not the "16+ million colors in 8-bit RGB" getting whittled down to 2 million or so, but rather any number of colors in 8-bit RGB getting whittled down to a fraction of what you start with.  Read Bruce Lindbloom's piece again carefully.  This is a quantization effect.  Multiple unique RGB colors are replaced with a singe Lab color, at a RATIO of about 8:1.  http: //www.brucelindbloom.com/index.html?RGB16Million.html  It's not like you get to keep the 2 million to work with.

But let's remember that most images don't have even close to that many
unique colors in them.

Agreed.

If you open an image (even one with bright and
well-defined colors, and good detail) in ColorThink Pro and do a count of
unique colors in it, you are likely to come up with numbers in the range of
200,000 to 300,000. How high could the count possibly go? 500,000 perhaps?
(I'm guessing wildly, here.)

Here's a problem.  ColorThink Pro is not very good (or accurate) in counting "unique colors" in an image.  It apparently samples the image and  then (? converts to lab) to do the counting.  Start with the sample image provided by Lindbloom - it will not give an accurate pixel count or number of unique colors in ColorThink Pro.  Rather than a 4096 x 4096 pixel image with 16 million colors, CT Pro gives a 500 x 500 pixel image with 250,000 total pixels and 210,551 unique colors - before doing anything!  It is not a reliable tool for this analysis.

I'm on the road, so I don't have my programming tools with me.  I'll look into this after I return home.

The problem is certainly real, in that color information WILL be lost, because in the integer system that is used, there are simply not enough Lab colors available to encode all of the sRGB colors, by a ratio of about 8:1.  It would be interesting to do this exercise with other color spaces.

--Rich
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Subj: Re: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Tuesday, September 19, 2006 6:16:08 PM
From: Jim Rich

I just wanted to add that in this thread it seems most everyone is counting color in millions etc. In the printing business of putting ink on paper with a press, my experience is that you are lucky to get between 12 thousand and 18 thousand colors printing CMYK inks on a #1 sheet.  So in the context of this thread you might want to take that into account.

Jim Rich
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Subj: Re: [colortheory] Re: Adobe Lightroom Beta
Date: Wednesday, September 20, 2006 8:18:14 AM
From: Dan Margulis

Stephen writes,

Fair enough, my poor memory seemed to recall a lot of scorn and derision
being placed upon 1.8 gamma spaces not too long ago. Now that ProPhoto
RGB is everybody's darling, not much is made of this.

Your memory is quite good. Between about 1998 and 2001, there was indeed a lot of berating of users (and of Apple) for not realizing that 2.2 was far superior, because only it was perceptually uniform, and that anyone who calibrated to any other standard (read: 1.8) could not be considered to have a calibrated monitor, and if anyone who did not have a calibrated monitor could only produce ninth-rate color. Particularly, there were several attacks on me for suggesting that it wouldn't make any difference which of the two a person used.

The two main justifications for BruceRGB were its 2.2 gamma, which, it was said, was far superior to that of ColorMatch RGB, and the fact that it was smaller than Adobe RGB, which. it was said, is obviously too wide-gamut for practical use.

Almost overnight, however, there was an Orwell-like change. 1.8 gamma suddenly became a good thing. And Adobe RGB, instead of being too wide for practical use, became too narrow. There was some commentary at the time on the fact that  simultaneously Kodak, which believed both in ultra-wide RGBs and 1.8 gamma, was beginning to spread around money to various parties for "consulting services", but doubtless this was a coincidence.

That's all water under the bridge now, except for one amusing note. You will recall that at that time, the same folk who were so vehement about the necessity of 2.2 gamma were also strongly cautioning that converting to LAB inflicted "catastrophic damage" on the file, and that nobody should ever use LAB. Then, as now, the statement was based not on any real images, but rather analysis of histograms and gradients. The "test" of choice is: begin witha grayscale gradient in Adobe RGB. Convert same to LAB. Observe holes in histogram. Observe that if you convert instead to BruceRGB, there are no holes in histogram. Conclusion: "Catastrophic damage", "Quantization error", "Levels Loss", and "Irretrievable Data Loss".

Since then, the same people have been reciting the same lines, not being able to accept that people who transfer files *other* than grayscale, or gradients, into LAB don't seem to lose levels, and not realizing that the only thing that the "test" demonstrates is that the L channel does not have a 2.2 gamma.

Interesting, though, now that their favored RGB does not have the gamma they used to think was so essential, the same "test" can be done with respect to the Adobe RGB to ProPhoto conversion--with exactly the same results as Adobe RGB to LAB, the same number of holes in the histogram.

Let that be a warning to all those who bought into this demonstration of "levels loss" in LAB: beware of ProPhoto RGB! Converting into it causes "Quantization error", "Irretrievable data loss", "Catastrophic damage"! Worse, for the reasons I stated in a post to Rich Wagner, conversions to ultra-wide RGBs are inherently less reliable than conversions to LAB because the channels are more closely related to the source space even though the gamuts are about the same. So, anyone who believes that conversion into LAB is a catastrophe must surely believe that conversion into ProPhoto RGB is, well, a catastrophically catastrophic catastrophe.

Personally, I'd just look at the images and see whether there was any damage, but to each his own.

Dan Margulis
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Subj: Re: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Wednesday, September 20, 2006 8:19:07 AM
From: Marco Ugolini

In a message dated 9/19/06 12:28 PM, Jim Rich wrote:

I just wanted to add that in this thread it seems most everyone is counting
color in millions etc. In the printing business of putting ink on paper with
a press, my experience is that you are lucky to get between 12 thousand and
18 thousand colors printing CMYK inks on a #1 sheet. So in the context of
this thread you might want to take that into account.

How do you reach that count?

--------------
Marco Ugolini
Mill Valley, CA
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Subj: [colortheory] sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Wednesday, September 20, 2006 12:10:42 PM
From: Olivier Desmaison

Also, so that we can progress with this, what *is* a good and
accurate way to count unique colors in an image file, in your opinion?

This is definitely the issue and probably why one can always argue "you don't see it, don't bother".

The color count is meaningless in so-called achievable values (whether RGB or Lab), but sensible in DeltaE variations. So even though the value count is less it will be the DeltaE count (let aside posterization and other computer related issues, since the initial hypothesis is "real world" image)that will perceptually make the converted file colors acceptable or not. No one would eventually care if 2 RGB values get clustered into a single one or if one is lost as long as those two values were not intially perceptually differenciated.

Olivier Desmaison
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Subj: Re: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Wednesday, September 20, 2006 12:37:38 PM
From: RJay Hansen

On 9/20/06, Marco Ugolini wrote:

Besides the fact that this whole issue still sounds a bit mysterious to me,
I would love to see a practical example of how this quantization problem
affects an image, meaning something that I can see and evaluate visually.

Watch out Marco. You're sounding like Dan.

RJay Hansen
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Subj: Re: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Wednesday, September 20, 2006 12:41:08 PM
From: Jim Rich

Marco,

Good question. I personally did not do the counting and at this exact moment I don't know the specific scientific method used to derive those numbers.

Over the last 30 years I  have found this information from a few sources. One source is by reading research from TAGA proceedings, another  is though my experiences with press vendors and with colleagues at RIT.
 
Jim Rich
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Subj: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Wednesday, September 20, 2006 12:51:14 PM
From: Richard Wagner

"Marco Ugolini"wrote:

Is that something that you know from having tested it, or simply an
impression?

From testing.  As I described, if you start with Bruce Lindbloom's 4096 x 4096 pixel image containing unique RGB values CT Pro generates a 500x500 pixel image to work with (using what algorithm? No idea...) and then reports fewer than the expected 500 x 500 = 250,000 unique pixels.

I wonder whether Steve Upton is reading this and would care to comment.

I have posted a bug report.

Also, so that we can progress with this, what *is* a good and accurate way
to count unique colors in an image file, in your opinion?

Well, if you still have OS 9 running, Bruce Lindbloom wrote a program called Levels 1.2 that did precisely this, and more. I have an archived copy, but I don't currently have Classic running. There in not much commercial software that I am aware of (a Corel app?) that can do this.

"Apparently" doesn't sound convincing to me. Can you offer something more
substantial to back your assertion?

No. I have no idea what algorithms Steve is using, or why the data is invalid, but it clearly is. It could simply be due to the image sampling that reduces the working image size - i.e., averaging error. This could be tested by using smaller images that (hopefully) don't get down-sampled.

Note that a quantization error will occur with any RGB image, regardless of color space, that is converted to Lab - the question is, what is the relative magnitude of the effect relative to the RGB color space, and what is the significance in practical terms. Because the volume of the sRGB gamut occupies a smaller percentage of the Lab gamut than larger color spaces like Adobe or ProPhoto, I would expect the quantization loss to be larger with sRGB than the others.  I'll work on an objective answer to this after I return home.

--Rich
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Subj: Re: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Wednesday, September 20, 2006 3:30:47 PM
From: Lee Clawson

on 9/20/06 11:58 AM, Rich Wagner at Richard Wagner wrote:

Well, if you still have OS 9 running, Bruce Lindbloom wrote a program
called Levels 1.2 that did precisely this, and more. I have an archived
copy, but I don't currently have Classic running. There in not much
commercial software that I am aware of (a Corel app?) that can do this.

Rich,

I can run OS-9. Looked on Bruce's site for levels 1.2 but didn't see it. Any ideas where to download a copy ???

Also, while we're on the topic how many colors can the average person actually see ????

Lee Clawson
2/\V/\7 Studio
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Subj: Re: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Wednesday, September 20, 2006 6:54:14 PM
From: Marco Ugolini

In a message dated Sep 20, 2006 7:34 AM, RJay Hansen wrote:

Watch out Marco. You're sounding like Dan.

Ugh...

That's a risk I'll have to take.

Unlike Dan, I do not have any solid certainties to defend, and I'm easily convinced when I am shown evidence, which so far hasn't happened, since the whole discussion has remained purely theoretical. In the old commercial's words, "where's the beef?".

And unlike Dan *I* don't keep raising the bar to fend off contradiction or embarrassment... :-)

Marco
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Subj: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Friday, September 22, 2006 5:21:22 AM
From: Richard Wagner

OK, some preliminary results.   All image conversions were done in PS CS2. Where appropriate, conversions were made using RelCol and BPC, with no dither.  Image level counting was done using Levels 1.2, (c)2001 Bruce J. Lindbloom, running under Classic 9.2 on Mac OS 10.4.7.  The test file was the 8-bit 4096 x 4096 pixel image containing all unique colors provided by Bruce Lindbloom via his web site. http://www.brucelindbloom.com/index.html?RGB16Million.html  This is a good file to start with, as it does not contain JPEG artifacts and it has not been previously subjected to profile conversions that might bias the results.

Original Image:
File Name: RGB16Million.tif
Image Dimensions: 4096 x 4096 = 16,777,216 pixels
Color Type: RGB
File Format: TIFF
Bits/Channel: 8
Color Space: sRGB (assigned in PS CS2)
There are 16,777,216 unique colors in this image.
==========

Convert the above image to Lab:
There are 2,186,765 unique colors in this image.
==========

Convert the Lab image back to sRGB:
There are 2,186,295 unique colors in this image.

Note that this data matches very closely what is presented on Bruce Lindbloom's site.  I'm not sure why the slight difference - changes in the CMM? Also, as he stated, "back and forth" trips to Lab do not result in increased image degradation.  It is primarily the first trip to Lab that results in quantization loss.  I have confirmed this. (additional data not shown.)
==========

OK, how about Adobe to Lab?  Better than sRGB, as I predicted in a previous post.
There are 3,135,822 unique colors in this image.
==========

And ProPhoto to Lab - should be better yet - and it is. As expected, moving from a wide-gamut color space to Lab results in less quantization loss than moving from sRGB to Lab.
There are 6,236,954 unique colors in this image.
==========

In testing some of my own scanned wildlife images, the quantization loss was frequently around 50% - 70% when converting from AdobeRGB to Lab. For example, a 14-bit scan of a Kirtland's Warbler began with 18,617,959 unique colors; conversion to 8-bit resulted in 513,680 unique colors, and  conversion of that image to Lab resulted in 279,760 unique colors.

Is any of this significant?  In looking at the images, it doesn't appear to be, although the same can be said for many other operations that result in data loss. It is not clear what effect this may have on an image if many operations follow.  Avoiding the transition to Lab avoids the data loss, although this obviously gives up the advantages tof techniques unique to Lab.

--Rich Wagner
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Subj: [colortheory] Re: Counting unique colors...
Date: Friday, September 22, 2006 5:22:35 AM
From: Marco Ugolini

Something that works in Mac OS X, please...

--------------
Marco Ugolini
Mill Valley, CA
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Subj: Re: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Friday, September 22, 2006 6:55:53 AM
From: Mike Russell

From: Ric Cohn
.....
So far the only one who I know has attempted this kind of thing is
Dan. I'm not saying he has all the answers or is always right, but at
least there's something to look at instead of talk about!
my 2¢.

My two cents as well, Ric.  I couldn't have said it better.  The appearance of the final image is the bedrock.
---
Mike Russell
www.curvemeister.com/forum/
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Subj: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Friday, September 22, 2006 12:32:11 PM
From: Richard Wagner

One last test before I leave - or before my wife wrings my neck for making us late...

Start with what I like to call the "perfect synthetic test image" DeltaE_8bit_gamma2.2.tif on http: //brucelindbloom.com/index.html?ReferenceImages.html  It has dimensions of  3072 x 2048 = 6,291,456 pixels and contains no noise, and is tagged with an ICC reference profile (sRGB primaries and white point).  It has 134,683 unique colors.

Again, using Levels to count unique colors.

Original (8-bit) image:

Red   channel has 250 unique levels in the range [  0, 255]
Green channel has 253 unique levels in the range [  0, 255]
Blue  channel has 253 unique levels in the range [  0, 255]

There are 134,683 unique colors in this image.
=======

Convert to Lab:

L* channel has 251 unique levels in the range [  0, 255]
a* channel has 162 unique levels in the range [ 58, 219]
b* channel has 203 unique levels in the range [ 17, 219]

There are 89,691 unique colors in this image.
=====

Convert back to sRGB:
Red   channel has 251 unique levels in the range [  0, 255]
Green channel has 253 unique levels in the range [  0, 255]
Blue  channel has 254 unique levels in the range [  0, 255]

There are 89,651 unique colors in this image.

This again shows that the data loss occurs in the first trip to Lab.  Not unexpected.

It would be interesting to test the other images shown.

--Rich
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Subj: Re: [colortheory] Re: sRGB to LAB conversions (was Re: AdobeLightroom Beta)
Date: Friday, September 22, 2006 12:35:28 PM
From: Bob Frost

Lee,

Not surprising. As you age, your lenses (in your eyes) yellow, and you therefore see less blue than when young. Anyone over 50 may notice (or not notice) this. Plus anyone over 60 is likely to have some clouding of the lenses which gives a nice Gaussian Blur effect!

Bob Frost.
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Subj: Re: [colortheory] sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Friday, September 22, 2006 12:36:36 PM
From: Matthew Rigdon

Andrew,

I downloaded the 16-bit challenge and saw the damage you're talking about. However, Photoshop and Aperture tell me this file was shot with a Digital Rebel (300D) at 200 ISO. Is this not correct?

I have a 300D as well and I find that it gets really noisy in the shadows as little as 200 ISO. I just got a 20D in the last week, so I haven't shot enough to see whether it has the same problem. I've been told that ISO 100 and 200 are almost indistinguishable on the 20D (and 350D), but my experience with the 300D is that there's a very discernible difference.

I can understand that working in 16-bit would be preferable if an image is noisy to begin with, but how much noise? Would you still have the same problem at ISO 100 on the 300D?

The file I'm looking at is CRW_0775.CRW. All my 300D files start with this prefix. My 20D files start with IMG (actually _MG, but I wrote an automator action to rename them in Image Capture).

Matthew Rigdon

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Subj: Re: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Friday, September 22, 2006 12:37:20 PM
From: Bob Frost

Dan,

All the figures you mention seem very low. Have a look at this answer to the same question from Frank Welte at the University of Massachusetts Medical School, and he says that most estimates are about 10 million colors. He also points out that people vary in the number of colors they can see, and what color they perceive from the same color input to the retina.

http: //www.hhmi.org/cgi-bin/askascientist/highlight.pl?kw=&file= answers%2Fstructure%2Fans_011.html
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Subj: Re: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Friday, September 22, 2006 12:37:56 PM
From: Mark Segal

OK, next time I'll ask my wife to assess what I've lost from a trip back and forth between Lab and ProPhotoRGB - that'll settle it. But really, this has to be complete nonsense. Apart from which, as I look around me I can't believe there are 100 million colours to be seen. And how do these bean counters distinguish between hue and luminosity? The same solour can look different with each subtle shift of L. How often have you had the experience of making really subtle adjustments to various Curves in Photoshop, run the file on a printer as good as an Epson 4800 and tried hard to see the difference? I think we're all getting too refined by half relative to the tools we work with.

Mark Segal
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Subj: Re: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Friday, September 22, 2006 7:52:19 PM
From: Dan Margulis

Marco writes,

And unlike Dan *I* don't keep raising the bar to fend off contradiction or
embarrassment... :-)

No, the bar is right where it's been for the past several years.

I believe that what Marco is referring to is that those who support his position, who are not able to provide any real-world examples to suggest there's any merit in it, have adopted a standard tactic. They hand in a bogus example that they know in advance I will not accept, such as the Andrew image that Marco is now touting, and then feign astonishment that I don't accept it, and tell the world that it proves that I keep changing the rules and will never accept any image.

There have been a couple of most comical examples of this already on this list, but I'll let the list enjoy one that took place on the ColorSync list last year.

Marco posted some extravagant claims about the great difference that 16-bit processing has made for him, and I politely inquired as to whether by any chance he had a real-world color photograph that would show this great advantage, which of course he did not. What he *did* have to show the advantage was not acceptable, whereupon I was accused, as you can see, of raising the bar, as follows:

"Dan, there is no pleasing you! You ask for an example of banding, and I give it to you. No good, because it's a synthetic image! Never mind that all it was meant to do was alert people to an inherent weakness in the pixel structure of an 8 bit image, which per se does NOT invalidate the whole edifice of 8-bit imaging. I give you another example, this one from a B&W 16-bit scan. No good, because it's not color! You keep raising the bar."

Or, in loose translation:

1) "The only thing you said was 'color photograph' ". How could I possibly know that you wouldn't accept a black and white?? You keep changing the rules!"

2) "How am I supposed to know that 'photograph' means you won't take a computer-generated graphic? You keep raising the bar. It's a waste of time for me to show you a real example, because you're just going to invent a reason to reject it. But they exist--trust me. I know it for a fact."

Dan Margulis
___________________________________________________________________________

Subj: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Friday, September 22, 2006 7:55:25 PM
From: Andrew Rodney

The "stats" I got (somewhere years ago) were 12 million colors so this is a lot closer to the value I'd expect. Again, this isn't the ability to see 12 million colors simultaneously! I may now update my presentations and use 10 million to be more conservative in this estimate.

The 100 million seemed pretty "out there" FWIW.

Andrew Rodney
___________________________________________________________________________

Subj: Re: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Friday, September 22, 2006 7:55:57 PM
From: Lee Clawson

on 9/22/06 8:09 AM, Mark Segal at Mark Segal wrote:

OK, next time I'll ask my wife to assess what I've lost from a trip back and
forth between Lab and ProPhotoRGB - that'll settle it. But really, this has to
be complete nonsense. Apart from which, as I look around me I can't believe
there are 100 million colours to be seen. And how do these bean counters
distinguish between hue and luminosity? The same solour can look different
with each subtle shift of L. How often have you had the experience of making
really subtle adjustments to various Curves in Photoshop, run the file on a
printer as good as an Epson 4800 and tried hard to see the difference? I think
we're all getting too refined by half relative to the tools we work with.

Mark,

My understanding is that they "see" unique colors as any change. Not necessarily using our definitions that make a clear separation of hue, value and saturation.

Lee Clawson
2/\V/\7 Studio
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Subj: [colortheory] "Pixel slaughter"? (was Re: sRGB to LAB conversions)
Date: Friday, September 22, 2006 7:57:33 PM
From: Marco Ugolini

Hi Richard.

Again, we should not get wowed simply by the math. What appears like "pixel slaughter" may turn out to be nothing of the sort. Mine is a call for caution before we jump to conclusions, which at this stage would seem premature, though this quantization process is undeniable.

In the 16- vs. 8-bit debate the damage is clearly visible (for a good example, see the RAW image which Andrew Rodney mentioned on this forum a few days back: connect to his iDisk: "thedigitaldog"; in the ensuing dialog box enter the name: "public"; password: "public"; go to folder "16bit challange"; the file is called "CRW_0775.CRW". Apply his action to see the results).

Just as clear-cut as the evidence looks in that case, it would also be helpful to see what this quantization damage looks like, if it is actually visibly detectable.

Can anyone provide an example? Thank you.

Marco Ugolini
___________________________________________________________________________

Subj: Re: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Friday, September 22, 2006 7:58:37 PM
From: Marco Ugolini

In a message dated Sep 22, 2006 5:09 AM, Mark Segal wrote:

How often have you had the experience of making really
subtle adjustments to various Curves in Photoshop, run the
file on a printer as good as an Epson 4800 and tried hard
to see the difference?

Good point.

I think we're all getting too refined by half relative to the tools we work with.

Well, I see another pie-throwing contest coming. And I think it serves no one to do that, other than indulge some people's inflated idea of themselves.

Please, let's not descend yet again to a favorite pastime on this forum, i.e., "circling the wagons" and retrenching in a priori positions that can only be called premature before the evidence is in. And that applies to both sides of an issue, or however many sides there may be.

Let's do less posturing, and more debating instead, with an open mind, possibly.

Thank you.

Marco Ugolini
___________________________________________________________________________

Subj: Re: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Friday, September 22, 2006 11:10:41 PM
From: Dan Margulis

In a message dated 9/22/06 12:37:21 PM, Bob Frost writes:

All the figures you mention seem very low. Have a look at this answer to
the same question from Frank Welte at the University of Massachusetts Medical
School, and he says that most estimates are about 10 million colors.

I don't know where he's getting his information from. I haven't been active in this area for several years, but I can tell you that when I was, my opinion wasn't just on the high end--it *was* the high-end. Every vendor put out figures that were much lower than mine.

We'll never know, because it's impossible to devise a test that would show us--we don't have either output devices or measuring devices with the necessary precision. Plus, there's a terminology problem. "Different colors" means, to me, that not only can a person see that two samples are not the same, but that there is some clue as to in what *way* they are not the same.

Those who were giving figures in the 50,000 range were extrapolating from average performance on the Munsell-Farnsworth test, among others. Certainly the number of errors that the average human being makes on that tests suggests that 50,000 is fair. My point was that there are limitations as to how that is interpreted, and that in any case a substantial number of people get perfect scores on that test and, inasmuch as it was not technically possible then (and I doubt it is now) to construct a more precise one, it's hard to know exactly *how* precise the vision of the perfect scorers was.

Dan Margulis

P.S. The extreme figure on the low side, 2,500, was, believe it or not, Kodak's gospel.
___________________________________________________________________________

Subj: Re: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Friday, September 22, 2006 11:11:47 PM
From: Mark Segal

Marco,
   
  I have no wagons to circle and no a priori positions - how could I - alot of this is so arcane that it would be truly presumptuous. The purpose of my intervention was to try to correlate principles with practice. That is often a sobering exercise, as it defines the useful parameters of the discussion, which can go a long way to achieving the laudable approach you describe here.
   
  Cheers,
   
  Mark Segal
___________________________________________________________________________

Subj: Re: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Saturday, September 23, 2006 4:19:21 PM
From: Mark Segal

Interesting - we now have a range from 100 milliion colours (for my wife) to 2,500 (for Kodak). In my line of business, if I ever presented a range for any variable that had a ratio of 1 to 40,000 it would be the last contract I ever obtained. This is a clear symptom of a gradullay maturing science characterized by alot of methodological uncertainty. Hence the need to tread carefully before being carried away by unproven and perhaps unprovable propositions.
   
Which brings me back to the relationship between principles and observable reality. I have observed on the monitor (LaCie 321) and prints (Epson 4800) several real-world colour images processed in 16 bit mode from raw files in ProPhoto colour space, printed, converted the same files to Lab mode, looked at them on the monitor, printed them, moved back to RGB, looked at them on the monitor, re-printed them, compared the prints and frankly couldn't detect any differences. Nor could I see any instant differences on the monitor. I also showed the prints to my wife who is supposed to be able to detect 100 million colours and after looking at the outcomes she wondered why I was sitting here wasting time, ink and paper. Maybe when monitor and printer gamuts really expand by multiples (which judging from the recent rate of progress will be a gradual evolution) such exercises will be worthwhile, but until then my experience indicates it will be hard to sustain a systematic empirical relationship between these procedures and results having a high probability of repeatability.
   
Now turning to this issue of "quantization errors" - to put my "what I'm not" cards on the table, I'm not a colour scientist and not a professional mathematician, BUT I hope I can formulate a certain amount of logic and ask some of the right questions. So here goes. I was rather mystified by the notion that one loses millions of colours shifting between RGB and Lab, especially because I don't see the logic underlying this proposition and as explained above couldn't detect it empirically, eventhough Bruce Lindbloom is supposed to have explained it.
   
The reason I am mystified is that I'm not sure what's going on "under the hood" between the various ways of portraying colour using Curves. Lab has only two curves for portraying all colours in that colour space, while RGB has three for any of its colour spaces. But what does that mean? Is it not possible - indeed the case - that Lab *a* includes ALL the hues along the green-magenta axis and Lab *b* includes all the hues along the blue-yellow axis both within Lab space, which was supposed to have been developed by the Commission Internatiionale de l"Eclairage (CIE) based on observed reality of human visual perception? I think Yes unless advised to the contrary. (BTW, how many *unique colours* is that?)
   
Then one switches between colour spaces. What happens? Presumably all the colours that fit within a gamut common to both get included in the conversion. Presumably the colours that are in gamut for the space one is moving FROM but out of gamut for the space one is moving TO, are the ones that will be clipped or modified depending on how the colour space conversion handles the rendering. And how many of those affected colours are within our device gamuts say expanded by 30% to account for projected technical progress over the next X years that could be of any practical interest? If I could get a clearer understanding of these questions the debate may begin to make sense to me.
   
Mark Segal
___________________________________________________________________________

Subj: Re: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Saturday, September 23, 2006 4:21:19 PM
From: Marco Ugolini

I think we should move beyond the shock of the numbers to actually colorimetrically *measuring* what is being lost to the "quantization effect".

I wish that someone with both enough patience and a sufficiently scientific and methodic mind would sit down and try to sort out how perceptually significant these quantization losses truly are.

Again, my suspicion so far is that they produce tiny color differences, in the order of fractions of a Delta E 2000. That is to say, well below the average viewer's ability to perceive them.

(Alright, sure, maybe those tetrachromat wonder-women can see them...but this is not for them.)

Regards.

--------------
Marco Ugolini
Mill Valley, CA
___________________________________________________________________________

Subj: RE: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Saturday, September 23, 2006 4:21:42 PM
From: Howard Smith

Mike, I've been following these heated and often fascinating discussions for quite awhile.  As much as I agree that the appearance of the final image is all that's really important, everyone seems to be missing the point that these are more intellectual arguments than practical recommendations.  Each expert is certainly entitled to his or her own opinion, but in the end all we really want is a good image. Whatever method achieves that goal is the best method for that image.  It's doubtful that anyone involved in these discussions really believes that everyone else will fall into line if their argument is just presented with enough irrefutable logic.  On the other hand, the arguments do keep us from being complacent.  Photoshop is such an incredibly flexible program with such almost unlimited potential for experimentation that it's good to keep an open mind and look for clues that may advance our skill and knowledge.  We should never fall into the trap of arguing against things we know in our hearts to be unreasonable without first looking to see what we can use from new ideas.  Or from old ideas that won't die a natural death.  Even if a theory turns out to be bogus, there may be some things in it that will prove very useful in practice.

But then looking at it this way takes all the fun out of it, doesn't it? Let the arguments continue to flourish!  But maybe without getting so personal....

Howard Smith
___________________________________________________________________________

Subj: Re: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Saturday, September 23, 2006 4:25:29 PM
From: Marco Ugolini

In a message dated 9/22/06 3:59 PM, Dan Margulis wrote:

I believe that what Marco is referring to is that those who support his
position,

"Support my position"? I don't have one!

I'm still trying to figure this one out!

who are not able to provide any real-world examples to suggest
there's any merit in it, have adopted a standard tactic.

No, they are people in good faith, who are puzzled by something that appears fraught with danger. Where to go next from there is the question here.

They hand in a bogus example that they know in advance I will not accept,
such as the Andrew image that Marco is now touting,

What you call "touting" I call "looking with my own eyes" (certainly not yours). I see what I see, and you would have to prove to me that I am having some serious vision problems in order to convince me otherwise.

and then feign astonishment that I don't accept it,

So, you have already made up your mind about the quantization effect? Please share your conclusions with us, instead of impugning our good faith.

and tell the world that it proves that I keep changing the rules and will
never accept any image.

There have been a couple of most comical examples

Ha ha, I'm laughing already...

of this already on this list, but I'll let the list enjoy one that
took place on the ColorSync list last year.

Marco posted some extravagant claims

Extravagant, yes. You know, Marco is more than a bit loopy...

about the great difference that 16-bit processing has made for him,

So I am in Dan's formidable crosshairs now. You truly have a big axe to grind. I never said anything of the sort. If you want to present my position, quote me, don't freely paraphrase with such obvious bias.

and I politely inquired as to whether by any chance he had a real-world
color photograph that would show this great advantage, which of course
he did not.

"Of course": has anyone told you how arrogant you sound?

What he *did* have to show the advantage was not acceptable,
whereupon I was accused, as you can see, of raising the bar, as follows:

"Dan, there is no pleasing you! You ask for an example of banding, and I give
it to you. No good, because it's a synthetic image! Never mind that all it
was meant to do was alert people to an inherent weakness in the pixel
structure of an 8 bit image, which per se does NOT invalidate the whole
edifice of 8-bit imaging. I give you another example, this one from a B&W
16-bit scan. No good, because it's not color! You keep raising the bar."

Or, in loose translation:

1) "The only thing you said was 'color photograph' ". How could I possibly
know that you wouldn't accept a black and white?? You keep changing the
rules!"

2) "How am I supposed to know that 'photograph' means you won't take a
computer-generated graphic? You keep raising the bar. It's a waste of time for
me to show you a real example, because you're just going to invent a reason to
reject it. But they exist--trust me. I know it for a fact."

In other words: all of you out there, here is how you "debate", Margulis-style: Force others to adhere to *your* rules (specially on your forum: like Mel Brooks said, it's good to be king), and accept nothing that violates those rules (of which you are the judge, remember!), no matter what else those examples may show or prove (banding, etc.).

A closed mind is essential. A stalinist attitude a helpful option.

And since you are the one making the rules, you are guaranteed never to lose. Sweet.

And don't forget the most important part: put words in the other person's mouth that he never actually uttered! Specially ones that make him sound really stupid.

Got it?

--------------
Marco Ugolini
Mill Valley, CA
___________________________________________________________________________

Subj: Re: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Saturday, September 23, 2006 4:33:00 PM
From: Marco Ugolini

In a message dated 9/22/06 10:02 AM, Andrew Rodney wrote:

The "stats" I got (somewhere years ago) were 12 million colors so this is a
lot closer to the value I'd expect. Again, this isn't the ability to see 12
million colors simultaneously! I may now update my presentations and use 10
million to be more conservative in this estimate.

It could be that humans can see a *total* of 12 million or so colors, but never at the same time. There could well be a *much lower limit* to the number of colors that humans can see under any one individual illuminant, and the 12 million total could be the sum total of *all* these distinct viewing environments.

Incidentally, does this total take into consideration the effects of chromatic adaptation, or instead only counts absolute colors?

--------------
Marco Ugolini
Mill Valley, CA
___________________________________________________________________________

Subj: Re: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Saturday, September 23, 2006 5:57:21 PM
From: Jim Rich

Marco,

I don't know if this test has been done recently, but a few years ago, I and others did work in this area. This is a excerpt from the article that was published in DO magazine. It can be found at http: //www.jimrich.com/tips.shtml.

In December 2002 at a color management conference, I setup and ran a test comparing eight-bit and sixteen-bit RGB images. For this test I printed eight-bit and sixteen-bit images via Photoshop (with profiles) to my Epson 5500 printer. Photoshop was set up to for an RGB workflow. Nothing was done purposely to bias the test. Transparent and reflection images were scanned by various brands of scanners as eight-bit and high-bit images and then were converted into the Adobe 1998 working space.

The images used were at risk to posterize due to the combination of their image content and the extraordinary image processing that was applied. A majority of the images in the test had over 30 edits applied. A number of images were converted from RGB to LAB modes two or three times. Some of the tone edits involved over a 25% change in both RGB and LAB modes. At the conference, I placed 28 Epson prints on a table and let a group of imaging experts (pre-press types and photographers) inspect and review them. The test was not for color accuracy between prints. Participants were given a form with yes and no response categories.

Test Results
The initial feedback from the group of experts who did not choose to fill out the form but who took a few minutes to compare the images was that they could not precisely see any differences between the eight-bit or sixteen-bit images.

They all went on to say that any response they would have would be a guess. This result was verified again with the approximately 20 test forms that were filled out. The overall outcome showed all participants were guessing (40% to 60% of the time and  they were wrong) at which images were eight-bit or sixteen-bits.

The Bottom Line

Let me make this clear. The position I have taken on the eight-bit verses sixteen-bit argument is based on facts. It was the advocates of sixteen-bit images who did not back up their argument with hard evidence that peaked my interest to do this test. If I see that evidence I am willing to reconsider my position.

Since I have spoken about this test, I have met some high-bit end-users who will not believe a word of the results. My final comments to them is that the hard evidence indicates in most cases that you cannot see a difference between eight and sixteen-bit image prints. If you do see a difference, it is only a guess.
 
So at least up until 2002  there was a lot of evidence in this direction. Technology might have changed since then, and if it has my guess is that it got better and not worse.

And. of course...  others like Dan M did this type of test well before I went there.  And their conclusions were the same.
 
Jim Rich
___________________________________________________________________________

Subj: Re: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Sunday, September 24, 2006 12:26:02 PM
From: Ron Kelly

 On 23-Sep-06, at 3:03 AM, Marco Ugolini wrote:

"Support my position"? I don't have one!

Marco,

I would venture to say that your position seems to be this: certain computer/mathematical tools indicate that switching certain color spaces leads to loss of a huge number of colours.

Others have pointed out that there isn't any observable effect when this happens: it can't be verified on a monitor or a print.

Seems to me we are looking for WMDs again.

Ron Kelly.
___________________________________________________________________________

Subj: Re: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Sunday, September 24, 2006 12:25:07 PM
From: Marco Ugolini

In a message dated 9/23/06 8:18 AM, Howard Smith wrote:

Mike, I1ve been following these heated and often fascinating discussions for
quite awhile.  As much as I agree that the appearance of the final image is
all that1s really important, everyone seems to be missing the point that
these are more intellectual arguments than practical recommendations.

Right, they should be seen as starting points for further debate. Often enough (and very understandably), a new issue gets tackled before one has all the answers.

To be fair, I would say that people's concerns arise from some kind of verifiable occurrences. In 8-bit quantization, unique colors *do* indeed get "collapsed" into a smaller number of unique colors as a consequence of a trip from flavors of RGB to Lab.

What I am personally trying to establish at this point (since, like others, I'm still far from a conclusion) is (a) how truly "unique" and perceptually distinct these colors are to begin with, and (b) whether or not there exist practical ramifications, and whether they ought to be viewed as either relevant or negligible.

To make one example, if a given group of "unique colors" within a consecutive series (e.g., in ProPhoto RGB, with R, G or B in increments of 1 from 0 to 255) gets collapsed after a trip to Lab, and the difference of this group of colors from the next adjacent group is, say, in the neighborhood of 0.5 Delta E 2000 or even less, for all practical purposes this difference could be viewed as trivial, and those formerly "unique colors" (now collapsed into one) could legitimately be treated as just *one* color without undue fear.

That's what I would like to explore, as well as the possible opposite scenario (the possibly more destructive one), plus its implications in real-world work. A forum like this one (dedicated to "color theory" of all things) should not fear debate of these subjects, should it?

Each expert is certainly entitled to his or her own opinion, but in the end
all we really want is a good image. Whatever method achieves that goal is
the best method for that image.

As laudable as pragmatism is in most cases, a claim of pragmatism can also become an excuse to hold on to outdated preconceived notions that don't wish to be challenged. There *must* be room for theory too, obviously enough, though theory as well may turn frivolous and get sidetracked into esoterics and irrelevancies, needing to be subjected to reality checks on a regular basis.

It1s doubtful that anyone involved in these discussions really believes
that everyone else will fall into line if their argument is just
presented with enough irrefutable logic. On the other
hand, the arguments do keep us from being complacent.

Hopefully. Good point.

Even if a theory turns out to be bogus, there may be some things in it
that will prove very useful in practice.

Yes, I would say that even if a theory should prove incomplete (without being utterly "bogus"), it may still contribute essential bits of truth to the larger debate.

Regards.

--------------
Marco Ugolini
Mill Valley, CA
___________________________________________________________________________

Subj: Re: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Sunday, September 24, 2006 12:31:03 PM
From: Marco Ugolini

In a message dated 9/23/06 7:40 AM, MARK SEGAL wrote:

Interesting - we now have a range from 100 milliion colours (for my wife) to
2,500 (for Kodak).

The article that Andrew mentioned
(<http: //www.post-gazette.com/pg/06256/721190-114.stm>) stated that only tetrachromats can perceive something in the neighborhood of 100 million colors. Tetrachromats are individuals who have a fourth functioning cone (one more than the great majority of the rest of humans) in the area between reds and greens, roughly in the orange range. (Kind of like a Hexachrome-ish type of vision, only much more psychedelic!)

For genetic reasons, tetrachromats can only be women (now, I ask of you, is that fair...?), and the estimate is that only two to three percent of all women are tetrachromats (which would amount to roughly as many as 100 million women on the whole planet).

So, it's not *all* women, far from it. The other 3+ billion females of the species are still struggling with limited ranges very similar to ours (if that can make us dudes feel any better...).

So, we guys need not resent our wives or daughters (unless they're tetrachromats, of course!).

Regards.

--------------
Marco Ugolini
Mill Valley, CA
___________________________________________________________________________

Subj: [colortheory] Re: sRGB to LAB conversions (was Re: Adobe Lightroom Beta)
Date: Sunday, September 24, 2006 3:03:20 PM
From: Richard Wagner

On Sep 24, 2006, Jim Rich wrote:

In December 2002 at a color management conference, I setup and ran a test
comparing eight-bit and sixteen-bit RGB images. For this test I printed
eight-bit and sixteen-bit images via Photoshop (with profiles) to my Epson
5500 printer. Photoshop was set up to for an RGB workflow. Nothing was
done purposely to bias the test. Transparent and reflection images were
scanned by various brands of scanners as eight-bit and high-bit images and
then were converted into the Adobe 1998 working space.

Jim,

If this same test was done using a 16-bit workflow starting from a profiled scanner, a wide-gamut working space like ProPhotoRGB and a profiled, wide-gamut printer like the Epson 4800, and comparisons were made to the same images scanned at 8-bit, converted to sRGB and printed on the same printer, would you expect observers to be able to detect the difference?

Thanks,

--Rich Wagner
___________________________________________________________________________

Subj: Re: [colortheory] Re: sRGB to LAB conversions