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Author Topic: DCamProf - a new camera profiling tool  (Read 767311 times)

AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #320 on: May 31, 2015, 02:29:07 pm »

Very interesting on the spectrometer performance on dark patches.

so may be then add a parameter to dcamprof make-profile (and may be also to dcamprof make-target) to allow (default - nothing excluded naturally) the exclusion (supply L* value for example, everything darker based on supplied target measurements / spectral data or if not XYZ/LAB / gets gutted) of dark patches (yes, we can edit  cgats with raw rgb data / target measurements, but a little bit of crude automation might be useful too ?) as "Error kicks in below L*=20, which, in the words of one of X-Rite guys on a seminar, is as deep as one may want to go for _printer_ profiling." ?
« Last Edit: May 31, 2015, 02:35:53 pm by AlterEgo »
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #321 on: May 31, 2015, 02:30:13 pm »

> caucasian skin tone

Do we have significant differences in hemoglobin, melanin, carotene spectral properties between different races?
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #322 on: May 31, 2015, 02:32:40 pm »

Normally, one can't reliably print below L*=15. That may be a good default.
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #323 on: May 31, 2015, 02:37:09 pm »

> caucasian skin tone

Do we have significant differences in hemoglobin, melanin, carotene spectral properties between different races?

only amount (of the same 3 organic chemicals) is different ... are you implying that we shall not bother then with all those skin spectral measurements at all ?
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #324 on: May 31, 2015, 03:08:47 pm »

Those skin samples are highly correlated, so very few patches are OK, while more than just a few may be useless or even trough things astray.
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #325 on: May 31, 2015, 03:35:30 pm »

Spectral databases generally has a lot of data with similar chromaticity, including skin databases, although there are racial differences of course. In any case in terms of correction the default setting of DCamProf is to group together nearby patches and make an average correction for those. There's also a distance weighting algorithm enabled per default so it won't hurt matrix optimization either.

Anyway, in the tests I've done the CC24 skin patch gets lippmann skin sub 1 DE for 90th percentile, ie no meaningful improvement in accuracy can be had. The worst targets I've tested in terms of skin tone still gets within 1.5 DE for 90th percentile. It's hard to make any meaningful improvement on that. So no, a skin database will generally not make any meaningful improvements, not for caucasian skin.

"Excellent skin tones" in camera profiles that often comes up in the medium format forums is not so much about accuracy, but about a designed subjective look, and probably designed for foundation makeup rather than real skin. I'm quite sure that an accurate profile will not please the typical portrait photographer used to profiles with a designed look. I'm not a portrait photographer myself though so I can't contribute much when it comes to the subtleties of skin reproduction. DCamProf is not suitable for designing profiles with a look, but is rather for those of us that prefer designing our own look in the raw converter (or photoshop or whatever), with an as accurate as possible starting point.

In terms of accuracy, skin tones does not seem to be that big challenge for modern cameras, maybe there's been some consious design decision concerning camera color filters to make them good at skin tones, I don't know.
« Last Edit: May 31, 2015, 03:38:24 pm by torger »
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #326 on: May 31, 2015, 03:43:27 pm »

so may be then add a parameter to dcamprof make-profile (and may be also to dcamprof make-target) to allow (default - nothing excluded naturally) the exclusion (supply L* value for example, everything darker based on supplied target measurements / spectral data or if not XYZ/LAB / gets gutted) of dark patches (yes, we can edit  cgats with raw rgb data / target measurements, but a little bit of crude automation might be useful too ?) as "Error kicks in below L*=20, which, in the words of one of X-Rite guys on a seminar, is as deep as one may want to go for _printer_ profiling." ?

Yes I will consider something like that, maybe think a bit more about filtering. When doing SSF profiles one may have lots of patches so it becomes really tedious to filter out one patch at a time manually.

Looked through some target data, and for DCamProf's sake excluding all sub L*20 patches does not seem to be a loss. It's possible to cover any reasonable chromaticities with L*20 and up.
« Last Edit: May 31, 2015, 03:54:19 pm by torger »
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #327 on: May 31, 2015, 03:51:12 pm »

In photography, tone is brightness and contrast (gradation), not colour. We can have excellent skin tones on black-and-white photo.
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #328 on: May 31, 2015, 04:14:37 pm »

so I decided to make SSF out of just __3__ (three) patches from IT8 shot - took most saturated R, G, B that were > ~30 L*... and... with AA7hVFAI00100.ARW from I-R for Sony A7 ( SSF -> StdA & D65 virtual targets with -p cc24 -> dual illuminant .dcp -> ACR ) :





it is fair to note that it was a matrix .dcp profile : CM + FM and no LUT
« Last Edit: May 31, 2015, 04:54:46 pm by AlterEgo »
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Bart_van_der_Wolf

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Re: DCamProf - a new camera profiling tool
« Reply #329 on: May 31, 2015, 04:23:36 pm »

so may be then add a parameter to dcamprof make-profile (and may be also to dcamprof make-target) to allow (default - nothing excluded naturally) the exclusion (supply L* value for example, everything darker based on supplied target measurements / spectral data or if not XYZ/LAB / gets gutted) of dark patches (yes, we can edit  cgats with raw rgb data / target measurements, but a little bit of crude automation might be useful too ?) as "Error kicks in below L*=20, which, in the words of one of X-Rite guys on a seminar, is as deep as one may want to go for _printer_ profiling." ?

I don't immediately accept that L*= 20 is a/the limit, not without some more empirical evidence. A stepwedge. e.g. one from Stouffer like the R2110, might reveal a non linearity in the L* readings towards D-Max, or not. If internal glare is in play, which I somewhat doubt because that would require a bright patch and a dark patch at the same time, then the slope would not be close to the expected step delta 0.10 Optical Density . When the i1pro2 sees only a dark patch, then there is not enough light for a significant glare contribution. Maybe it's electronic noise that creates a threshold, but then a light trap would also give a signal.

Cheers,
Bart
« Last Edit: May 31, 2015, 04:39:13 pm by BartvanderWolf »
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== If you do what you did, you'll get what you got. ==

torger

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Re: DCamProf - a new camera profiling tool
« Reply #330 on: May 31, 2015, 04:30:52 pm »

so I decided to make SSF out of just __3__ (three) patches from IT8 shot - took most saturated R, G, B that were > ~30 L*... and... with AA7hVFAI00100.ARW from I-R for Sony A7 ( SSF -> StdA & D65 virtual targets with -p cc24 -> dual illuminant .dcp -> ACR )

How is that SSF desgined? Is it that matlab script? I have not had the time to investigate that, but my guess is that it uses a database of measured SSFs and then does some fitting against that? This probably means that with as little data as this there's an element of luck involved, that is if the SSF matches well another SSF in the database you can get a good result.
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #331 on: May 31, 2015, 04:31:52 pm »

I don't immediately accept that L*= 20 is a/the limit

but that's why you shall be able to use whatever number you want as a parameter or not use that and so all patches included - makes it easier to test then... Iliah says that was said by X-Rite people, I think he 'd not/never quote somebody who was just a marketing person, right ?
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #332 on: May 31, 2015, 04:33:17 pm »

Is it that matlab script?
basically yes, I did just some mods - to read CGATS from rawdigger (instead of using dcraw, etc), use my target illumination spectrum and use my target measurements from external files and as camera's database (certainly - we do not know who good were there measurements with monochromator - what it is what it is) is the same - I made eigenvectors constant... gutted also whatever junk is there.
« Last Edit: May 31, 2015, 04:35:20 pm by AlterEgo »
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #333 on: May 31, 2015, 04:39:32 pm »

This probably means that with as little data as this there's an element of luck involved
there is only one Sony there... if one to assume that each manufacturer stays along some "brand color" in CFA design (SSF-wise) then it is fitting well w/ the database consisting mostly of Nikon and Canon :

Canon1D Mark III
Canon20D
Canon300D
Canon40D
Canon500D
Canon50D
Canon5D Mark II
Canon600D
Canon60D
Hasselblad
Nikon3dx
NikonD200
NikonD3
NikonD300s
NikonD40
NikonD50
NikonD5100
NikonD700
NikonD80
NikonD90
NokiaN900
Olympus EPL2
PentaxK5
PentaxQ
Phase One
PointGreyGrasshopper
PointGreyGrasshopper2
Sony Nex5N



CGATS/Raw RGB :

1579.63   727.59   279.61
392.85   1445.76   2621.2
246.83   1708.88   406.09


Target (380 : 10 : 730:

0.006771   0.012186   0.019083   0.022492   0.018859   0.015078   0.01285   0.012292   0.013557   0.01626   0.02006   0.02377   0.025309   0.023362   0.020727   0.019255   0.018586   0.018996   0.02305   0.036697   0.070012   0.131161   0.215468   0.306025   0.390381   0.459813   0.513263   0.554692   0.590821   0.622936   0.652642   0.677777   0.69902   0.717879   0.739663   0.765332

0.007337   0.034702   0.090921   0.207428   0.320195   0.375344   0.384487   0.368493   0.33102   0.273935   0.212965   0.157102   0.109939   0.073874   0.051659   0.039648   0.032222   0.027431   0.026041   0.029307   0.035212   0.038126   0.03505   0.03127   0.030014   0.029921   0.0298   0.030836   0.035664   0.047068   0.067224   0.098205   0.137844   0.183507   0.236008   0.29608

0.006708   0.006364   0.008263   0.007945   0.006133   0.004683   0.003775   0.004248   0.005308   0.008668   0.016754   0.033854   0.063985   0.107077   0.154427   0.184376   0.184275   0.158114   0.120697   0.085062   0.053481   0.028621   0.013728   0.00766   0.006021   0.005722   0.005607   0.005918   0.007386   0.011355   0.019664   0.035081   0.058581   0.09012   0.130444   0.180574
« Last Edit: May 31, 2015, 04:49:38 pm by AlterEgo »
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #334 on: May 31, 2015, 04:44:11 pm »

then there is not enough light for a significant glare contribution. Maybe it's electronic noise that creates a threshold, but then a light trap would also give a signal.

that is beyond my knowledge to discuss, sorry... I can say that with black trap from Datacolor SpyderCube and not in a pitck dark room and with operator errors (the main again being not in a lightless room) I was never getting > 0.1 L* if I make decent effort fitting i1pro2 to the hole
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Tim Lookingbill

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Re: DCamProf - a new camera profiling tool
« Reply #335 on: May 31, 2015, 04:59:10 pm »

Spectral databases generally has a lot of data with similar chromaticity, including skin databases, although there are racial differences of course. In any case in terms of correction the default setting of DCamProf is to group together nearby patches and make an average correction for those. There's also a distance weighting algorithm enabled per default so it won't hurt matrix optimization either.

Anyway, in the tests I've done the CC24 skin patch gets lippmann skin sub 1 DE for 90th percentile, ie no meaningful improvement in accuracy can be had. The worst targets I've tested in terms of skin tone still gets within 1.5 DE for 90th percentile. It's hard to make any meaningful improvement on that. So no, a skin database will generally not make any meaningful improvements, not for caucasian skin.

"Excellent skin tones" in camera profiles that often comes up in the medium format forums is not so much about accuracy, but about a designed subjective look, and probably designed for foundation makeup rather than real skin. I'm quite sure that an accurate profile will not please the typical portrait photographer used to profiles with a designed look. I'm not a portrait photographer myself though so I can't contribute much when it comes to the subtleties of skin reproduction. DCamProf is not suitable for designing profiles with a look, but is rather for those of us that prefer designing our own look in the raw converter (or photoshop or whatever), with an as accurate as possible starting point.

In terms of accuracy, skin tones does not seem to be that big challenge for modern cameras, maybe there's been some consious design decision concerning camera color filters to make them good at skin tones, I don't know.

This Capture 1 tutorial on achieving uniform skin tone confirms what you've indicated about attempting to solve this through a profile due to so many variables that affect skin tone appearance, the effects of makeup base being the tip of the iceberg. It shows that one has to go to the lengths of editing the images color tables manually using Capture 1's Color Editor Tool...

http://blog.phaseone.com/get-uniform-skintones/
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #336 on: May 31, 2015, 05:30:43 pm »

Adding more highly correlated patches normally does not help, especially with LUTs. If spectrals are known, it is usually better to eliminate highly correlated samples and patches at the very first step.

For repro work, for example, we make targets that consist only of basic pigments used in painting (a profile for every particular painting, if it is for archival and preservation purposes). Lightness and saturation do not matter - they are anyway achieved through the mix of the basic pigment with something like titan white and soot, both being spectrally very flat (hence in repro work 2.5D or 2D profiles are used more often than not if it is a serious museum).

With CC24/CCSG decent profiles can be obtained from 5-6 non-neutral patches + grey step wedge.
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #337 on: May 31, 2015, 05:37:15 pm »

of basic pigments
how do you find a number of different "basic" pigments if you have a patch (one patch of whatever color) and spectrophotometer then ? is it possible ?
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #338 on: May 31, 2015, 05:42:51 pm »

There is a reason why for certain measurements Gretag used to offer polarizing filters with Spectrolino. Light is scattered back from both gloss and textured surfaces, causing flare and glare and making readings from very dark patches less reliable for semigloss and gloss substrates, and glossy black/dark pigments.
i1Pro is cost-optimized not for target measurements, but for printer profiling. IMHO it is only very logical in terms of engineering.
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #339 on: May 31, 2015, 05:45:19 pm »

With CC24/CCSG decent profiles can be obtained from 5-6 non-neutral patches + grey step wedge.
so for dcamprof as a matter of automation for hoi polloi (dcamprof make-dcp/make-icc steps) it is better to find out and select(make it as a command line parameter/option of course) only non-neutral ( or for example with C* from L*C*h* > N ) patches, calculate CM/FM and possibly 2.5D LUT and then proceed (make it again as a command line parameter/option ) to neutral patches and adjust LUT (or even possibly a tone curve) ?

certainly with CC24 there are so few patches that it might be moot point (bare minimum of non neutral patches) - but for CCSG and homemade targets
« Last Edit: May 31, 2015, 05:49:35 pm by AlterEgo »
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