Re: Colorimetric Accuracy in the Field
Andrew wrote: " . . . And measuring two samples of say output of a printer with a Spectrophotometer is a quite different from measuring a sample at the scene (which isn't what one proponent of colorimetrically accurate raw processing has done), since the illuminant in the measuring device is often quite different from the illuminate of the scene! You think that plays a role?" Henry: I suspect that camera manufacturers might disagree with you here in that they are probably very keen on understanding the response of their camera system as it records a scene.
As an expert in profiling and color management you've insisted that colorimetric matches aren't the purpose of profiling or a color managed workflow.
Andrew Replied: I've never said that. Or you completely misunderstood what I've said. Henry replies: I recall that you made that assertion in a thread regarding the failure of ICC profiles to produce matches to Pantone colors that are within a printer's gamut. It may have been someone else but I think it was you. I believe you went on to say or imply that it wasn't ever the intent or goal for ICC profiles. Pursuing the question in threads like this seems to always lead to more rabbit hole reasons for dismissing the idea of Colorimetric matching. Maybe I do misunderstand but I can't get through the confusion without some clarification, and maybe I'm not the only one who's confused.
Thus, colorimetric matches play an important part in evaluating your work - no?
Andrew Replied: . . . In the example above indeed! This is vastly different from saying a process is colorimetrically accurate without a 2nd set of measurements Henry replies: It sounds as though you are defining colorimetric accuracy based on close agreement in measurements. I'll go with that - up to a point. I don't know a better way to define it with consistency. Have you experienced a measured colorimetric accuracy of two samples that failed to be visually accurate? If colorimetric accuracy is so important on the one hand then why is it that on the other hand you dismiss the pursuit of it as too difficult or too complex? Nobody is suggesting that this is a simple task. Nobody is saying that the illuminant isn't a hugely important factor. Nobody is saying that a majority of photographers have an interest in this - at least for now. You conclude that it's not complex if people just accept what some people say. ? ? ? You say that people don't even understand how to ask the proper questions. ? ? ? I'm not exactly sure what the message is you're trying to communicate with all of that but it doesn't sound very nice. It makes me want to apologize for testing your patience. I get it, I get it, I get it: measuring two patches isn't the same as shooting in the field. But I think you would have to admit that there is a starting point for the camera in the field and that the manufacturer probably took a few measurements and did some research involving colorimetric matching. It would be very interesting to find that their R&D starting point was pleasing color instead of colorimetric. That would be a worse rabbit hole, don't you think? Henry
On Jun 6, 2013, at 10:54 AM, Henry Davis <davishr@bellsouth.net> wrote:
Henry replies: I recall that you made that assertion in a thread regarding the failure of ICC profiles to produce matches to Pantone colors that are within a printer's gamut. It may have been someone else but I think it was you.
Wasn't me. I don't mess with Pantone colors a lick. Go back and check where you heard this assertion!
Pursuing the question in threads like this seems to always lead to more rabbit hole reasons for dismissing the idea of Colorimetric matching.
No one is dismissing colorimetric matching that I've read. Some are dismissing what are claims of colorimtric matching without any colorimetry! Or when there is a match, it's not enough patches. This is the colorimeric accurac rabbit hole where basically it's colorimetric accuracy when party A says so even when no color measurements were made or presented.
If colorimetric accuracy is so important on the one hand then why is it that on the other hand you dismiss the pursuit of it as too difficult or too complex?
Nobody is suggesting that this is a simple task. Nobody is saying that the illuminant isn't a hugely important factor. Nobody is saying that a majority of photographers have an interest in this - at least for now.
You have it backwards. It's up to the "colorimetric accuracy in the field" to prove their points, not for me to dismiss them since I can't because they've falied to explain the process nor the aspect of colorimetry used. I'd really love for what they are saying to be true! They just have to prove it.
I get it, I get it, I get it: measuring two patches isn't the same as shooting in the field.
Excellent, you're making progress. I supsect you now see where actual colorimetry was used in the patch example. How about that capture in the field workflow?
But I think you would have to admit that there is a starting point for the camera in the field and that the manufacturer probably took a few measurements and did some research involving colorimetric matching.
I could make that assumption but will not because I don't know it to be a fact for one let alone all camera manufacturers. If someone has facts to back that up, I'll accept it as fact. And if the manufacturer(s) did, do you think they provided that data to anyone outside their company? And if they did, do you think that having just that data set provides all that is necessary to claim color accuracy in the field? I told you very simple way we can gauge a colorimteric match by measuring two samples. Where's the same process to back up the accurate colorimetry in the field?
It would be very interesting to find that their R&D starting point was pleasing color instead of colorimetric. That would be a worse rabbit hole, don't you think?
Yes and mostly no. Yes in that anyone can say the color isn't pleasing. That is subjective. No in that it doesn't matter, since it is subjective <g>. I thought Afgachrome looked like crap but there were obviously photographers who preferred it's 'pleasing colors' since the film was sold for years. The in-camera JEPG processes are different among cameras because like film, R&D is making assumptions to what they think their customers will find more pleasing then the competition. The rabbit hole is this in the field colorimetric accurate capture where nothing in the field is measured to prove any colorimetry is in effect. So I place this into the subjective until I see proof of colorimetry used and a metric of what constitutes accurate (dE 2000 to be specific). Andrew Rodney http://www.digitaldog.net/
From: "Andrew Rodney
This is the colorimetric accuracy rabbit hole where basically it's colorimetric accuracy when party A says so even when no color measurements were made or presented.
This is all beginning to sound like Humpty Dumpty in 'Alice through the Looking Glass' :- 'When I use a word,' Humpty Dumpty said, in rather a scornful tone, 'it means just what I choose it to mean - neither more nor less.' 'The question is,' said Alice, 'whether you can make words mean so many different things.' 'The question is,' said Humpty Dumpty, 'which is to be master - that's all.' I have to keep reminding myself that every color that comes out of a digital camera is a guesstimate. Some peoples guesses are different to others, but they are all guesses. Humpty Dumpty would have a field day with this subject!! Bob Frost
On Jun 7, 2013, at 2:07 AM, Bob Frost <bobfrost@btopenworld.com> wrote:
I have to keep reminding myself that every color that comes out of a digital camera is a guesstimate. Some peoples guesses are different to others, but they are all guesses. Humpty Dumpty would have a field day with this subject!!
Yup, reminds of this too: http://www.youtube.com/watch?v=UwAookPFWZQ That's accurate comedy! Andrew Rodney http://www.digitaldog.net/
Repeating, I am just delighted to be in the wabbit whole. Cheers David B Miller, Pharm. D. member, Millers' Photography L.L.C. dba Spinnaker Photo Imaging Center 3809 Alabama Street Bellingham, WA 98226-4585 360 739 2826 spinnakerphotoimagingcenter@dnmillerphoto.com On Jun 7, 2013, at 1:07 AM, Bob Frost wrote:
From: "Andrew Rodney
This is the colorimetric accuracy rabbit hole where basically it's colorimetric accuracy when party A says so even when no color measurements were made or presented.
This is all beginning to sound like Humpty Dumpty in 'Alice through the Looking Glass' :-
'When I use a word,' Humpty Dumpty said, in rather a scornful tone, 'it means just what I choose it to mean - neither more nor less.'
'The question is,' said Alice, 'whether you can make words mean so many different things.'
'The question is,' said Humpty Dumpty, 'which is to be master - that's all.'
I have to keep reminding myself that every color that comes out of a digital camera is a guesstimate. Some peoples guesses are different to others, but they are all guesses. Humpty Dumpty would have a field day with this subject!!
Bob Frost
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David B Miller, Pharm. D. member, Millers' Photography L.L.C. dba Spinnaker Photo Imaging Center 3809 Alabama Street Bellingham, WA 98226-4585 360 739 2826 spinnakerphotoimagingcenter@dnmillerphoto.com
At 9:54 AM -0700 6/6/13, Henry Davis wrote:
Have you experienced a measured colorimetric accuracy of two samples that failed to be visually accurate?
YES! OH YES! With regular cinema projectors, observer metamerism is so great that on occasion a group of golden eyes could not agree on whether a color matches or not. Luckily that has nothing to do with whether the colors are pleasing. Next check out laser projectors! Have you measured your eyes lately? Which category of standard observer are you in NOW? (It changes with age) Lars PS. Just after finishing this message, in my inbox arrives a paper titled "COLOURIMETRIC OBSERVER CATEGORIES AND THEIR APPLICATIONS IN COLOUR AND VISION SCIENCES" by Sarkar, A., Blondé, L. What a coincidence!
Henry Davis wrote:
Nobody is saying that the illuminant isn't a hugely important factor.
The main reason that the illuminant is a factor is that many/most cameras aren't colorimetric. By that I mean that their spectral sensitivities don't match a human observer. If they did, and their (light level) linearity was known, then (by definition) they'd be a high spatial resolution colorimeter. The practical situation is analogous to the one with cheap display colorimeters: They can be very accurate with a correction matrix if the spectral nature of the samples they are reading is known. With a display device that has colors that are (largely) a liner combination of the three primary spectra, a matrix does nicely. For a camera, it can't be that easy, because real world object colors are composed of many metamers, and the spectrum hitting the camera sensor is that times the illuminant spectrum. So a "calibration" matrix can fudge it for a range of expected object spectra x expected illuminant, but ultimately it's going to work the best over the widest range of conditions if the camera spectral sensitivity is closer to a human observer. It would be interesting to know which current cameras best fulfil this ideal :-) Such a camera would capture "what you see" with much less need for manual post capture tweaking. Graeme Gill.
On 06/07/2013 01:53 AM, Graeme Gill wrote:
So a "calibration" matrix can fudge it for a range of expected object spectra x expected illuminant, but ultimately it's going to work the best over the widest range of conditions if the camera spectral sensitivity is closer to a human observer.
It would be interesting to know which current cameras best fulfil this ideal :-)
Such a camera would capture "what you see" with much less need for manual post capture tweaking.
Graeme Gill.
Or the other way ... that camera could be one that can detect the metamers with more filters than RGB and use software to create a human observer condition instead of using RGB filters that match the human observer. Sony used a more Cyan filter together with RGB filters on some sensors. There have been more examples. White balance gets more accuracy too. An analogy is in the HP G4050 and G4010 scanners. Two CCFL lamps with different spectral distributions, one scan run with each and adequate software to represent the actual colors. Image Engineering tested the G4050 against other desktop flatbeds and it performed better on acrylic paint samples and inkjet print colorants than the other flatbeds did. For photo dyes the accuracy was not better but that is to be expected as most flatbeds are designed for scanning photos. I see a difference between the old Epson 3200 and the newer V700 though, the first does a better job with reflective scans (non-photo originals) than the last. Sensor spectral differences I guess. It could be that the Epson 4990 and V350 also in that test by Image Engineering behave alike. -- Met vriendelijke groet, Ernst Dinkla http://www.pigment-print.com/spectralplots/spectrumviz_1.htm December 2012: 500+ inkjet media paper white spectral plots.
participants (7)
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Andrew Rodney
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Bob Frost
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Ernst Dinkla
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Graeme Gill
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Henry Davis
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Lars Borg
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Spinnaker Photo Imaging Center