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Author Topic: DCamProf - a new camera profiling tool  (Read 767303 times)

Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #380 on: June 01, 2015, 12:51:09 pm »

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.

CGATS is not the best option. Switch to CSV to have pixel coordinates too, you will need those for flare/glare compensation splines - tpaps in matlab. And to assess linearrity and field flatness, too.
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #381 on: June 01, 2015, 01:02:30 pm »

you will need those for flare/glare compensation splines - tpaps in matlab.
haha, I think I need some math ed. before that...
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #382 on: June 01, 2015, 01:11:16 pm »

haha, I think I need some math ed. before that...
I will help you with relevant code if you will need it; but it is so straightforward I doubt you will need any help.
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #383 on: June 01, 2015, 03:03:20 pm »

I'll add some glare correction feature to the flatfield command. I need to read up a bit on how to best model glare first though. I had already started with some spline stuff, but got some issues concerning spectral flatness etc, which I need to investigate a bit first. Oh it would be nice to have Photo Research spectroradiometer now.
« Last Edit: June 01, 2015, 03:10:47 pm by torger »
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #384 on: June 01, 2015, 03:10:45 pm »

Just in case, I apply flare/glare removal stage before flat field, and the goal of the flat field is mostly to get uniform white balance across the target.
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #385 on: June 01, 2015, 03:14:54 pm »

> it would be nice to have Photo Research spectroradiometer now

Maybe some University will be interested :)
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #386 on: June 01, 2015, 03:17:12 pm »

Oh it would be nice to have Photo Research spectroradiometer now.
but are you not working in University or something like this yourself ? some vo... beer and voila...
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #387 on: June 02, 2015, 12:49:40 pm »

I will help you with relevant code if you will need it; but it is so straightforward I doubt you will need any help.
that you, that shall wait as I still need to polish the basics...

Iliah, a question, as you saw a lot of targets, the difference between QP202 (big one) and QP203 (small one) cards... QP203 looks like patches are painted on a substrate and not that glossy at all and QP202 looks like they are cut and glued and somewhat of lesser quality (like those printed paint samples from any hardware store) and glossy (and substrate glossy too)...  and measurements are quite different (while it seems that I remember from somewhere that you mentioned that spectralwise they are similar - I think from references supplied with makeinputicc)... can you comment on that ?

attached are the measurements :

« Last Edit: June 02, 2015, 12:53:40 pm by AlterEgo »
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #388 on: June 02, 2015, 03:03:37 pm »

Done a little bit of glare correction coding, and now a little bit of review of test shots. I'm not yet having satisfactory results, it breaks more than it fixes.

In a glossy homemade target shot indoor in a dark room with one StdA lamp outside family of angles, I get 5.57 stops between brightest and darkest color (not black, but super-deep purple, had no blacks in that target) with SSF virtual process (ie glare free) and 5.41 stops in the real shot, that is a 0.16 stop difference. Not too big DR difference, but the darkest patch is 1/3 stop too bright compared to what it should be. Measurement error in the instrument (if it's glare there too) may contribute to a smaller number than it should be.

Anyway, from the initial glare correction code tests it seems like the glare error may be too small compared to the uncertainties in the glare correction model.

Currently the code searches for neutral patches in the target by looking how flat the spectra is, then makes a reference value from provided illuminant spectrum+greenSSF (an "typical" SSF if no SSF is provided), and compares that with the actual value. This serves as input to a spline contrast correction curve. The intermediate points are estimated with TPS. Illuminant mismatch, SSF mismatch, deviation from spectral flatness, distance to nearest control point all contribute to error. However, I suspect the simplistic model of glare, ie just a contrast spline curve, contributes the most error. I'm not satisfied with that model, but haven't come up with anything better.

I've not given up yet though, I have a few things left to test.

I does look tempting though to just skip glare correction and instead relax lightness correction in ultra-saturated violets-purple as that's where the errors seem to be located.
« Last Edit: June 02, 2015, 03:08:28 pm by torger »
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #389 on: June 02, 2015, 03:21:08 pm »

My glare correction method is based on comparing contrast between the neighboring black and white patches on the shot of the target to the contrast between the same patches in the reference measurement of the target. It is done on all 4 channels independently. The correction coeff. is than placed at the coordinates between the patches, and a spline is constructed. I use 2 splines, one to compensate for the overall veiling glare (bias), uniform additive model; and the second in multiplicative model, to correct for scene-dependent flare and glare - that one is not uniform.
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #390 on: June 02, 2015, 04:12:26 pm »

the contrast between the same patches in the reference measurement of the target.
and contrast using XYZ is something like log2(Y from white patch / Y from black patch), right ?
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #391 on: June 02, 2015, 04:57:20 pm »

> contrast using XYZ is something like log2(Y from white patch / Y from black patch), right ?
Contrast is Y1/Y2; but if you want it to convert to photographic stops, log2(Y1/Y2) or log2(Y1)-log2(Y2). For counter-flare splines, I use just contrast, not log2
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #392 on: June 02, 2015, 04:59:22 pm »

> contrast using XYZ is something like log2(Y from white patch / Y from black patch), right ?
Contrast is Y1/Y2; but if you want it to convert to photographic stops, log2(Y1/Y2) or log2(Y1)-log2(Y2).
yes, stops... thank you.

PS: out of curiosity - what the best (min) difference you achieve yourself with your own setup between the contract from measurements and the contract from your shots, before any math. corrections... ? for example I checked my shots and it seems that so far the best (in stops) difference is somewhat around what Torger mentioned (~0.17)... how small you can realistically get by setup (target, light, isolating everyting else that might throw a bad reflection to target/lens, hood, angle of light, etc) before you need to start using corrections with the data ? the mere fact that you are correcting says that you do not achieve zero, do you ? so it is interesting how far that 0.17 is from what you can do in a natural way.
« Last Edit: June 02, 2015, 05:07:12 pm by AlterEgo »
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #393 on: June 02, 2015, 05:11:01 pm »


attached are the measurements :


it seems I forgot about the troubles with new RAR format - here are zip files in case the issue still persists
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #394 on: June 02, 2015, 07:34:36 pm »

> what the best (min) difference you achieve yourself
 For a 7-stops SG target, lens with concave rear element, same setup:
D4s - slightly less than 0.2 EV reduction
Df - 0.3 EV reduction
D750 - 0.5 EV reduction
lens with convex rear element - approximately +0.1 EV, making D4s 0.3 EV and so on
For an 11-stops target, it starts with 0.9 EV and goes to 1.2 EV
With mirrorless camera, flare is very lens-dependent, but with 100mm Zeiss I can reliably get to 0.1 EV reduction on SG.
MF back on SG - got 0.43 EV reduction.
But if the target is shot out of studio, on location, as you've seen on the other forum, things with flare are not so controlled.
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #395 on: June 02, 2015, 07:36:10 pm »

Simply unrar'ed on Windows. I e-mailed QP guys for an explanation. My pair of 202 and 203 were very close; and the site also gives one reference for both.
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #396 on: June 02, 2015, 09:22:02 pm »

Simply unrar'ed on Windows. I e-mailed QP guys for an explanation. My pair of 202 and 203 were very close; and the site also gives one reference for both.
my QP203 is 3 years old and my QP202 is just couple month old.... the difference of newer QP202 is very big vs your files (black patch specifically),  it does not look like an operator or instrument error to me (I have one more set of measurements with i1pro from 3 weeks ago and colormunki measurements from 6 weeks ago), like black patch L* = 20.4x (ColorMunki) ... 20.9x (i1Pro2) vs L* = 29.x in your files... just a note.
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hugowolf

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Re: DCamProf - a new camera profiling tool
« Reply #397 on: June 02, 2015, 11:17:18 pm »

Could be the QP203 hasn't aged well. Has it seen much light?

Brian A
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #398 on: June 03, 2015, 12:22:02 am »

Could be the QP203 hasn't aged well. Has it seen much light?

Brian A

the issue is with a new (2mo old) QP202, not with QP203.
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Alexey.Danilchenko

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Re: DCamProf - a new camera profiling tool
« Reply #399 on: June 03, 2015, 03:02:31 am »

the issue is with a new (2mo old) QP202, not with QP203.
Have you got it from them directly or via reseller?
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