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Author Topic: Accurate Colors  (Read 35421 times)
digitaldog
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« Reply #20 on: July 11, 2009, 06:25:59 PM »
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Quote from: tho_mas
the "profiles" you are talking about are actually just a set of internal adjustments. Begs the question if the term "profile" makes sense here.

Maybe you can explain this further and how ICC camera profiles and DNG camera profiles are different.

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In any case you can't process the TIFs from ACR/LR without conversion to another profile but instead just embed the camera profile (as you can do it in Capture One).

No, you can't embed the DNG profile as a camera profile but you can any ICC profile you have on your system. How is having the data in the camera color space beneficial? You're exporting a output referred rendered image, presumably for further editing in Photoshop, so why not be in a well behaved RGB working space?
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« Reply #21 on: July 11, 2009, 06:46:17 PM »
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The DNG Profiles FAQ contains a "question" and the answer regarding DNG camera profile vs. ICC profile; it would be interesting to see the opinions of those participants, who are dealing with these issues.

Why introduce another camera profile format instead of using ICC camera profiles?

First, ICC camera profiles used by raw converters today are designed to process output-referred (i.e., rendered) image data, not scene-referred (i.e., raw) image data. Furthermore, the sequence and placement of color transformations described in an ICC camera profile can prevent other image processing stages (such as highlight recovery algorithms) from performing optimally. Third, there is no standard that describes the input color space of the ICC camera profile color transformation (it is often, but not always, a tone-mapped set of RGB camera coordinates). Consequently, ICC camera profiles are not portable: they can only be used with the raw converter for which they were explicitly created in the first place. Using an ICC camera profile designed for one raw converter with another raw converter nearly always produces incorrect (though sometimes entertaining) results.
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« Reply #22 on: July 12, 2009, 12:54:44 AM »
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I didn't mean to stir things up with my line of questioning, but think that it has encouraged me to think about the big picture a little more.  

I also thought that I might have misquoted Jack after I went back to his site again, but the exact quote is:  "We do not recommend using this product with Adobe Camera Raw, LightRoom or Aperture because they do not provide for the use of camera profiles." . . . as well as . . . "Adobe has decided that camera profiles just plain don’t work and therefore they do not support them."  

I think the missing modifier here is "ICC" profiles.  What Adobe supports are DCP profiles.  Like DNG, Adobe is trying to use their market clout to create a new standard that in practice might as well be proprietary at the moment, but is actually an open standard that they hope others will adopt.  The ability to couple the profile with a Raw file for easier sharing seems to be one of the bigger selling points for Adobe on why they went their own way.  

In researching DCP profiles a little more, primarily because I'd love to be able to stick with Lightroom over Capture One, an issue popped up that I hadn't heard of before.  Sandy McGuffog, author of dcp Tool, says that DCP files cause a change of tint when exposure adjustments are made.  I'm not sure how big an issue this is, but it certainly sounds like a concern when we are after "accurate" color, as this thread is about.  His tool, which is opensource and shareware, so theoretically not particularly biased by financial motivation, makes DCP profiles "invariate", to get around this limitation.  Intriguing stuff, and something I'd like to explore further, except for the fact that he says a working knowledge of XML and the DNG specifications is required, as it is a command line environment in both Macs and PCs.

How big a concern have you color experts found with the basic Adobe structural framework, if we are after "accurate" vs. "pleasing" color?  There are roughly 100 to 1 discussions online discussing pleasing color over accurate, but in this case some of us are after accurate.  Pleasing seems like child's play in comparison, for me, and as a Phase customer, I'm certainly not after duplicating my camera's LCD display and/or JPEG files.

For those of you interested and unfamiliar with it, Sandy has a fascinating paper online looking at how the Adobe profiles vary by twisting colors to create different looks.  
You can find it here:
http://chromasoft.blogspot.com/2009/02/vis...les-part-1.html

I'm currently thinking an ICC camera profiling application is probably in my future, but I'd sure like to find a way to work with Lightroom if possible, over Capture One.  The comparison is like OS X vs. Windows, in my book, but I'll bite the bullet if it ultimately saves me time tweaking colors one at a time.

EDIT:  Here's another link to more from Sandy, which ties in with another thread here on LL regarding the profile twisting:
http://chromasoft.blogspot.com/2009/02/adobe-hue-twist.html
One thing dcp Tool does to get around this is to remove the hue and saturation variance from value changes in the LUT.  I feel a little like I'm trying to talk astrophysics with people who know it inside out, but I think I at least get this part.
« Last Edit: July 12, 2009, 01:05:13 AM by Colorwave » Logged

digitaldog
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« Reply #23 on: July 12, 2009, 09:44:58 AM »
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Quote from: Colorwave
"We do not recommend using this product with Adobe Camera Raw, LightRoom or Aperture because they do not provide for the use of camera profiles." . . . as well as . . . "Adobe has decided that camera profiles just plain don’t work and therefore they do not support them."
Which unless they update to specially state "ICC camera profiles" is nonsense. The second part (Adobe has decided that camera profiles just plain don’t work) is simply untrue. Someone is using marketing speak big time here! Adobe does of course use a camera profile as pointed out (and you mentioned above).
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I think the missing modifier here is "ICC" profiles.
Part of it yes.
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In researching DCP profiles a little more, primarily because I'd love to be able to stick with Lightroom over Capture One, an issue popped up that I hadn't heard of before.  Sandy McGuffog, author of dcp Tool, says that DCP files cause a change of tint when exposure adjustments are made.
I'm not sure that's solely attributed to the DNG profiles. There IS and has been from day one, the effect of saturation on tonal moves in the Adobe Raw engine and there's an article here on LL by Mark Segal about this. There are reasons why this was implemented.
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I'm not sure how big an issue this is, but it certainly sounds like a concern when we are after "accurate" color, as this thread is about.

Quote
How big a concern have you color experts found with the basic Adobe structural framework, if we are after "accurate" vs. "pleasing" color?  There are roughly 100 to 1 discussions online discussing pleasing color over accurate, but in this case some of us are after accurate.  Pleasing seems like child's play in comparison, for me, and as a Phase customer, I'm certainly not after duplicating my camera's LCD display and/or JPEG files.
Please, we need to STOP using the marketing term accurate color here. Its not accurate until you define accuracy colorimetrically and as scene referred. I posted a link to the ICC (a group that knows a few things about ICC profiles yes?) that attempts to define what accurate color really is and I can assure you, you don't want to send scene referred, colorimetrically ideal numbers to your printer. This goes back to my point about the 20 deltaE values not being a sound indicator of anything. There are all kinds of cases where correctly measured and defined "accurate" color values are NOT going to produce a match, let alone a pleasing color to the viewer. There are many cases where CIE colorimetry fails. No magic profile, input or output is change this.
« Last Edit: July 12, 2009, 10:06:05 AM by digitaldog » Logged

Andrew Rodney
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« Reply #24 on: July 12, 2009, 09:53:49 AM »
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Quote from: Colorwave
I didn't mean to stir things up with my line of questioning, but think that it has encouraged me to think about the big picture a little more.  

I also thought that I might have misquoted Jack after I went back to his site again, but the exact quote is:  "We do not recommend using this product with Adobe Camera Raw, LightRoom or Aperture because they do not provide for the use of camera profiles." . . . as well as . . . "Adobe has decided that camera profiles just plain don’t work and therefore they do not support them."  

The way the first sentence should read:

We do not recommend using this product with Adobe Camera Raw, LightRoom or Aperture because our products are incompatible with their camera profiles.

"Adobe has decided that camera profiles just plain don’t work and therefore they do not support them."

This is just pure, unadulterated hogwash that should just be removed from the site!

You're not to blame for stirring things up, I am. I'm just sick and tired of vendors (at least now their transparency as vendors is without question thankfully) providing technically thin, marketing thick crap to those who come to sites for information. I mean please, look at the quotes you provided and the actual reality of the situation and tell me that the BS factor is excessive.
« Last Edit: July 12, 2009, 10:07:15 AM by digitaldog » Logged

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« Reply #25 on: July 12, 2009, 10:22:49 AM »
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Quote from: Colorwave
How big a concern have you color experts found with the basic Adobe structural framework, if we are after "accurate" vs. "pleasing" color?

For me, it's huge and why I suggested making the profile for your camera under a specific, repeatable light source. (IME -- and admittedly I never spent tons of time trying to perfect it -- the Adobe tool does not work for accurate color:  pleasing maybe, but not accurate enough for repro IMO.)   The other thing you need to understand is the tool you use accuracy -- generally speaking I've found Monaco generates tighter Delta-e's on the individual colors, but Gretag generates the almost perfect grays.  So the gold standard may be to build a dedicated profile with each tool, then average them...  But then that's me and no doubt some of the real "experts" here will disagree

Cheers,
« Last Edit: July 12, 2009, 10:23:36 AM by Jack Flesher » Logged

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« Reply #26 on: July 12, 2009, 10:55:09 AM »
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Quote from: Panopeeper
First, ICC camera profiles used by raw converters today are designed to process output-referred (i.e., rendered) image data, not scene-referred (i.e., raw) image data.
Partly right. The profiles are based on (measured) characterization data but modified (edited) to produce a certain "look". Too, at least in the case of Phase One camera profiles, they have a neutral grey axis and therefore are of course suitable for editing.

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Furthermore, the sequence and placement of color transformations described in an ICC camera profile can prevent other image processing stages (such as highlight recovery algorithms) from performing optimally.
why that???
In Capture One highlight recovery works perfectly (without halos or such fancy effects).

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Consequently, ICC camera profiles are not portable: they can only be used with the raw converter for which they were explicitly created in the first place. Using an ICC camera profile designed for one raw converter with another raw converter nearly always produces incorrect (though sometimes entertaining) results.
Correct.
On the other hand: processing my files in ACR without any adjustments (except pushing exposure +1 EV) as a ProPhoto TIF and then assigning my camera profile(s) in Photoshop is a much better starting point for editing as the weird colours and gradation ACR produces in default (so without extensive editing in ACR). This is far from (scene referred) acurate colours (because I have to go the circuit with ProPhoto) but it tells something about the usability of the icc camera profiles.
« Last Edit: July 12, 2009, 11:00:03 AM by tho_mas » Logged
Mark D Segal
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« Reply #27 on: July 12, 2009, 11:04:00 AM »
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Quote from: digitaldog
I'm not sure that's solely attributed to the DNG profiles. There IS and has been from day one, the effect of saturation on tonal moves in the Adobe Raw engine and there's an article here on LL by Mark Segal about this. There are reasons why this was implemented.

Andrew, for the benefit of those who haven't seen it and wish to, the link to my two articles on this subject is here: Curves. (One change in context is that different from what is stated there, I am now no longer a member of ACTL. )

I should add that Martin Evening took a welcome interest in that discussion and explored the subject in considerable depth, the result of which is his valuable research piece published in his Lightroom 2 book Martin Evening-Lightroom2, pages 575 to 580 inclusive.

I think it's important in this discussion to keep separate the question of hue shift from saturation change. However, it remains true that both could reflect departure from "accurate" colour, whatever that is, because for one thing even daylight alters colour perception of light-reflecting objects in real time. I can't help but agree with most of what you have been saying (for quite some time now, not only in this thread) about the issues surrounding rendition of "accurate" color. Just thinking out loud a bit, in the grand scheme of things, what we're trying to do here is funnel into a relatively restrictive set of output conditions scenes whose colour values are valid at the moment of capture and which have tremendously greater gamut and dynamic range than anything our output devices can reproduce. Compromises need to be made all along the chain to achieve anything people would accept. Raises the question of what is acceptable? For perhaps most people, pleasing would probably be the target. For certain applied applications, such as forensics, medical (some aspects) and commercial brand recognition "accurate" may be the target.

If we're talking Adobe raw conversion software in particular, it's not as if they don't know exactly what they are doing. Tons of research and experimentation has gone into this stuff over a period of many years now and it has matured tremendously since ACR 1.0, so that while not infallible, it's probably safe to say that what they've produced IS by design. I think it's also safe to say that these tools have been designed with such tremendous flexibility that, e.g., anyone who wants to reproduce a particular hue and saturation of a particular glass of beer can do so very exactly right. For those who would find it too time-consuming to make such adjustments on each image, the software also allows the development of profiles and presets to automate an initial rendering more to ones' preference. Maybe I'm missing something, but apart from the informational question of what kind of profiles LR and ACR accept, I'm having trouble seeing what is the major problem here in using this software for achieving the colour appearance one needs.
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Mark D Segal (formerly MarkDS)
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« Reply #28 on: July 12, 2009, 11:12:06 AM »
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Quote from: Jack Flesher
For me, it's huge and why I suggested making the profile for your camera under a specific, repeatable light source. (IME -- and admittedly I never spent tons of time trying to perfect it -- the Adobe tool does not work for accurate color:  pleasing maybe, but not accurate enough for repro IMO.)   The other thing you need to understand is the tool you use accuracy -- generally speaking I've found Monaco generates tighter Delta-e's on the individual colors, but Gretag generates the almost perfect grays.  So the gold standard may be to build a dedicated profile with each tool, then average them...  But then that's me and no doubt some of the real "experts" here will disagree

Cheers,
Jack, I don't pretend to be a "real expert" on the subject of profiling, so let me ask you: you create a profile that produces what you would define as accurate colour (which is what?) under one specific lighting condition. Would that be portable (i.e. perform as well) under any other lighting conditions? When you talk about "not accurate enough for repro", what does this mean? If by "repro" you mean printing presses for example, would it be fair to say that it may not be too challenging to achieve accurate (by your definition) rendition of scene colours which are within the gamut of the output device, but what happens when they are not?
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Mark D Segal (formerly MarkDS)
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« Reply #29 on: July 12, 2009, 11:35:39 AM »
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Quote from: MarkDS
Jack, I don't pretend to be a "real expert" on the subject of profiling, so let me ask you: you create a profile that produces what you would define as accurate colour (which is what?) under one specific lighting condition. Would that be portable (i.e. perform as well) under any other lighting conditions?

Not really. It might perform reasonably well in brighter or dimmer values of the exact same temperature -- and why the Northlights are so good for repro -- but IME you want a dedicated profile for your standard copy sets.

Quote
When you talk about "not accurate enough for repro", what does this mean? If by "repro" you mean printing presses for example, would it be fair to say that it may not be too challenging to achieve accurate (by your definition) rendition of scene colours which are within the gamut of the output device, but what happens when they are not?

What I mean is for art reproduction -- like copying an original oil or some historical document for archival purposes. Here you are trying to capture the entire gamut of the original, and reproduce it as accurately as possible on your output media, in this case a digital print.  (And we assume here the output profile is tuned for the viewing-room temp.)  Most current MF cameras and scanning backs will handle enough gamut to capture anything made with historical pigments, so that's not usually a problem (though it can be for newer works). With the newer wide-gamut printers you can get very close on output, though clearly still not perfect depending on the original -- but usually close enough you need to measure the differences with your spectro because you probably won't see it with your eyes.

Cheers,
« Last Edit: July 12, 2009, 11:36:32 AM by Jack Flesher » Logged

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« Reply #30 on: July 12, 2009, 11:54:11 AM »
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Quote from: Jack Flesher
For me, it's huge and why I suggested making the profile for your camera under a specific, repeatable light source. (IME -- and admittedly I never spent tons of time trying to perfect it -- the Adobe tool does not work for accurate color:  pleasing maybe, but not accurate enough for repro IMO.)   The other thing you need to understand is the tool you use accuracy -- generally speaking I've found Monaco generates tighter Delta-e's on the individual colors, but Gretag generates the almost perfect grays.  So the gold standard may be to build a dedicated profile with each tool, then average them...  But then that's me and no doubt some of the real "experts" here will disagree

Couple things I don't understand:

1. What's the definition of accurate above and how do you measure/decide that ACR isn't accurate?
2. What's the delta that separates "accurate" from pleasing and how does one produce such stats?  
3. I will not argue the differences between Monaco and GMB profiles (I certainly have measured data from output profiles that confirm what you say) but how does one "average" this using both, when ultimately, you have to take the average measured data and send it through one or the other package to generate a profile? I will point out too, that in the case of pleasing color output from Monaco vs. GMB, despite the delta differences which are easy to produce, often, the GMB profile produces a more pleasing print. Something useful to consider when just examining BtoA and AtoB table accuracy.
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« Reply #31 on: July 12, 2009, 11:56:05 AM »
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Quote from: digitaldog
Please, we need to STOP using the marketing term accurate color here. Its not accurate until you define accuracy colorimetrically and as scene referred.
Andrew-
I use the word accurate in the absence of a better term for me.  I'm open to a change of nomenclature, if there are better descriptions for what I want.  To me, pleasing color is something with an appropriate gray balance and perceptually right looking colors that are less critical in that they are generally continuous tone, like typical photographic subjects and scenes.  The scene looks right to our eye, but is not held up to the scrutiny of side by side comparison because it is impossible to compare a three dimensional scene captured elsewhere with a printed reproduction of it.  Accurate color, or whatever the better way to say it might be, is color that can be looked at more critically and compared.  For art reproduction, this often means solid, discrete colors that in their own way are not unlike a color chart.  Artists want to be able to place a print right next to the original and see as close to the same, exact color as possible, in the same light source, on both pieces.  Product photography is much the same.  I realize that there are other variables in getting from an original to a final print, but I seem to have far less issues with my linearized and profiled printer than my camera.  I think the greater variables come from input vs. output.  I'd feel better if I could measure the RGB values of a known target and start with something in my raw converter that was extremely close, once gray balance and exposure were adjusted.
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« Reply #32 on: July 12, 2009, 12:05:25 PM »
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Quote from: Colorwave
Andrew-
I use the word accurate in the absence of a better term for me.  I'm open to a change of nomenclature, if there are better descriptions for what I want.

That's a problem because the lack of accuracy is inaccuracy and we often need some metric to define each. That's why pleasing color is more useful since all it has to do is become acceptable to you (or the client) and no measured, numeric metric is really needed. Matching color is fine too assuming you understand that two colors may appear to match which are totally different in terms of their measured color. I don't know, other than the iStar process (do a search, it was discussed here recently), we have a means of defining matching colors based on color appearance models. That is, we can have two colors that appear to match that are not accurate if we measure them and view the measured values. Which begs the question about accuracy. If they match but we have no way to define numerically using instrumentation that they match, how do we define this accuracy? When you and I both see a visual match, that an instrument tells us the values are different isn't important. We've added a true observer into the mix.

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Artists want to be able to place a print right next to the original and see as close to the same, exact color as possible, in the same light source, on both pieces.

I agree that's the goal but I'd disagree that defines accurate color but not pleasing color. Maybe the word pleasing needs adjustment. But certainly, accurate is incorrect because we really don't have tools to colorimetrically define this accuracy in all cases.

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« Reply #33 on: July 12, 2009, 05:57:36 PM »
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Quote from: Jack Flesher
What I mean is for art reproduction -- like copying an original oil or some historical document for archival purposes. Here you are trying to capture the entire gamut of the original, and reproduce it as accurately as possible on your output media, in this case a digital print.  (And we assume here the output profile is tuned for the viewing-room temp.)  Most current MF cameras and scanning backs will handle enough gamut to capture anything made with historical pigments, so that's not usually a problem (though it can be for newer works). With the newer wide-gamut printers you can get very close on output, though clearly still not perfect depending on the original -- but usually close enough you need to measure the differences with your spectro because you probably won't see it with your eyes.

Cheers,

These solutions make an attempt at accurate and pleasing ColorSage and HP Artist
Opinions?

Cheers,
Kumar
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« Reply #34 on: July 13, 2009, 07:15:20 AM »
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don't know, other than the iStar process (do a search, it was discussed here recently), we have a means of defining matching colors based on color appearance models.

Hi Andrew. I wrote the following last year on the subject, whilst discussing CIECAM02 in digital imaging. It may be of interest to you. Sorry to the rest a bit off subject.

In order to construct a chromatic adaptation model it was necessary to obtain data on the way
the visual system adapted to changes in viewing conditions. Several experiments were carried
out including those by Mori et al. from the Color Science Association of Japan, McCann et
al., and Breneman using a haploscopic matching technique; Helson et al., Lam and Rigg and
Braun and Fairchild using the memory matching technique; and Luo et al. and Kuo et al.
using the magnitude estimation method. (LUO AND CHANGJUN 2007 P263). These experiments
produced data sets called Corresponding Colours.

Corresponding Colours can be defined as a pair of colours or stimuli which are perceived to
be of the same appearance when viewed under different conditions. (FAIRCHILD 2005 P 160)
Of the methods used to determine Corresponding Colours, as mentioned above, Haploscopic
Matching involved visually isolating each eye and creating two different viewing
environments. Each eye would therefore adapt to its own environment. A test sample would
be presented on one eye and various samples presented to the other. When there was a match
the CIEXYZ value would be noted. Over time a set of Corresponding Colours would be
created. This experiment  assumed that independent adaptation occurred in each eye but does
not account for the cognitive response (FAIRCHILD 2005 P160).

Magnitude Estimation involves assigning a numerical value to appearance attributes to
different stimuli. The observer is adapted to one particular viewing condition and is asked
to describe the colour in terms of Lightness, Chroma, Hue, Colourfulness or Brightness.
(FAIRCHILD 2005 P161). The experiment would be repeated using the same set of colours but
under different viewing conditions. Colours obtaining the same attribute score would be
deemed a corresponding pair. This experiment takes into account both the
sensory and cognitive adaptation mechanisms.

To produce a more natural method of matching colours, a technique called Memory Matching
was used. The observer would se a colour under one viewing condition and then try to match
the colour under the second viewing condition by using memory only. In the experiments
by Helson Judd and Warren in 1952, Munsel patches were used as the primary samples.
(FAIRCHILD 2005 P161).

From these experiments a wide range of corresponding colours data was produced. This
information was a the starting point for a chromatic adaptation model. The CIEXYZ values
of the test colour under viewing condition 1, now had corresponding CIEXYZ values of its
appearance match under viewing condition 2. The difference between XYZ1 and XYZ2  is
known as the adaptive colour shift and it is the shift that the chromatic adaptation transform
attempt to calculate. (HUNT 2004 P590)


Fairchild, M. (2005) Colour Appearance Models Reading, MA: Addison Wesley.

Hunt, R. W. G. (2004) The reproduction of Colour (6th edition), Tolworth: Fountain
Press.

Luo, M.R. and Changjun, L (2007), CIE Colour Appearance Models and Associated
Colour Spaces, Colorimetry, Understanding the CIE System, J Shanda (Ed), John
Wiley & Sons, Inc., Hoboken, New Jersey.

 

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« Reply #35 on: July 13, 2009, 09:33:18 AM »
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Quote from: Kumar
These solutions make an attempt at accurate and pleasing ColorSage and HP Artist
Opinions?

Cheers,
Kumar

Yep, Color Sage looks very impressive, but it was developed after I got out of repro so I have no direct experience with it. And I use Epson printers .  But Robin likes it and IMO he is probably one of the top three or four color gurus out there -- and probably THE guy when it comes to art repro...

Thanks for the link Kumar!

,
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« Reply #36 on: July 13, 2009, 09:43:40 AM »
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Quote from: Jack Flesher
Yep, Color Sage looks very impressive, but it was developed after I got out of repro so I have no direct experience with it. And I use Epson printers .  But Robin likes it and IMO he is probably one of the top three or four color gurus out there -- and probably THE guy when it comes to art repro...

Agreed. In terms of very high end repro work, I can't recommend anyone higher than Robin.
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« Reply #37 on: July 14, 2009, 12:02:26 AM »
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To answer briefly some of the DCP/DNG/ICC profile questions that have come up in this thread:

Hue twists are independent of the profile format. You can have ICC camera profiles with hue twists, too (and many do). You can also have DNG camera profiles without hue twists (and many do). The term "hue twist" is probably not the most politically-adept term I could've come up with. I used the term at the time because it seemed the clearest, most direct way to describe one of the characteristics of some camera profiles; however, it draws attention (perhaps too much attention) because it sounds like something devious is going on. The truth is that many rendering systems (e.g., raw converters, or in general image processing applications doing some type of tone mapping or gamut mapping) will perform hue twists, rather often to the photographer's delight.

DNG profiles have multiple components and the color processing model described in the DNG spec allow standard raw processing steps to be inserted between those components. For example, you can perform linear light operations (e.g., if you wanted to do linear exposure adjustments, or Guillermo's Zero Noise-like compositing) in between the color matrix math and the 3D lookup table. Therefore, if you adjust exposure, and the following 3D table has colors that depend on lightness, then yes, colors may appear to shift.

(In passing, I should also mention that market clout has very little to do with Adobe's desire to use a different profile format for input. For Camera Raw and Lightroom, we do use ICC profiles where we feel they work well, technically and portably -- such as for a working space (RIMM for Camera Raw and LR) and for output (display, print, and export)).
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« Reply #38 on: July 14, 2009, 08:13:23 AM »
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Quote from: digitaldog
Couple things I don't understand:

1. What's the definition of accurate above and how do you measure/decide that ACR isn't accurate?
2. What's the delta that separates "accurate" from pleasing and how does one produce such stats?  
3. I will not argue the differences between Monaco and GMB profiles (I certainly have measured data from output profiles that confirm what you say) but how does one "average" this using both, when ultimately, you have to take the average measured data and send it through one or the other package to generate a profile? I will point out too, that in the case of pleasing color output from Monaco vs. GMB, despite the delta differences which are easy to produce, often, the GMB profile produces a more pleasing print. Something useful to consider when just examining BtoA and AtoB table accuracy.

Andrew,

From what Jack said above, it seems that the definition of "accurate" would be that in the specific case of trying to reproduce a digital image of a fine art original (e.g. an oil painting), if you were to measure the colour of a specific location on the painting with a spectro and then measure exactly the same location in the final digital print with the same instrument the readings would be the same, or so close that the eye would not notice the difference if the two were compared side by side (complicating operational factor: can the spectro actually measure accurately the colour of light reflected by these two very different kinds of materials?). In Jack's example, the colours of the original painting are not out of the gamut of say an Epson 7900, so gamut compression math would not be called upon and therefore nothing here to create the necessary compromises between "accurate" and "pleasing". But if there were out of gamut colours then either Perceptual or RelCol would produce (different kinds of) "inaccuracy" which by the logic of the process seems inescapable regardless of what profiling one does - so better for purposes of this discussion stick with a constraint of "everything is within printer gamut".

Now, if I were photographing paintings (and I used to do this with 4*5 inch Ektachrome sheet film I processed myself (for "accuracy" - hah) decades before photographer-controlled colour management was a gleam in our eyes) today, I would do this digitally with "daylight" floods" but also do test shots with a GMCC and use the second to lightest grey patch for neutralizing (if any) colour cast using the eyedropper tool in LR 2.4. We don't have control over what the camera's firmware does with the raw image data before it is exported to the raw converter, so we're talking about what happens in the raw converter. When we do the grey-balancing, we (speaking for myself and I suspect a great many others) are making the presumption that the math in the raw converter corrects every other colour commensuately such that all those colours become "accurate". So that's the question - if by design it's not happening in LR/ACR's default algorithms - is it possible to achieve such accuracy (here asking Eric or others who also actually work the math of this stuff) using the profile modifcation steps which Eric mentions above? And if so, for the benefit of those who need this flavour of "repro accuracy", could we be pointed to some specific instructions for actually implementing it?

Mark
« Last Edit: July 14, 2009, 08:15:47 AM by MarkDS » Logged

Mark D Segal (formerly MarkDS)
Author: "Scanning Workflows with SilverFast 8....." http://www.luminous-landscape.com/reviews/film/scanning_workflows_with_silverfast_8.shtml
digitaldog
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« Reply #39 on: July 14, 2009, 08:39:03 AM »
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Quote from: MarkDS
From what Jack said above, it seems that the definition of "accurate" would be that in the specific case of trying to reproduce a digital image of a fine art original (e.g. an oil painting), if you were to measure the colour of a specific location on the painting with a spectro and then measure exactly the same location in the final digital print with the same instrument the readings would be the same...


You sure about this?
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Andrew Rodney
Author “Color Management for Photographers”
http://digitaldog.net/
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