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Author Topic: DCamProf - a new camera profiling tool  (Read 767296 times)

AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #400 on: June 03, 2015, 09:31:45 am »

Have you got it from them directly or via reseller?
QP202 from B&H ... do you think B&H is enterprising and making 'em in their basement ? QP203 was from QPCard directly back in 2012.
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Alexey.Danilchenko

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Re: DCamProf - a new camera profiling tool
« Reply #401 on: June 03, 2015, 09:44:42 am »

QP202 from B&H ... do you think B&H is enterprising and making 'em in their basement ? QP203 was from QPCard directly back in 2012.
No - was worth a check though. I got my 203 from re-seller in UK and had to replace it - it was a bad batch apparently.
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #402 on: June 03, 2015, 10:13:06 am »

No - was worth a check though. I got my 203 from re-seller in UK and had to replace it - it was a bad batch apparently.
but yours was small QP203, not big QP202 ?
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #403 on: June 03, 2015, 11:29:43 am »

Done some more testing on glare and glare reduction algorithms. Core of the problem is that there are many unknowns when modeling glare so it's hard to make accurate results, and the more glare it is the harder it is to make any sane correction.

One of my conclusions is that (semi-)glossy targets produce so much glare when shot outdoors that a glare correction algorithm is bound to fail. You easily halve the dynamic range of the target in diffuse outdoor light. With that kind of input it's really hard to make good results, much better to use a matte target.

So for DCamProf the rule is that if you have a glossy target you must shoot it indoor in controlled conditions. I've done so in attached photo, lit a glossy target with a single light in a dark room, the uneven light corrected with flatfield correction (which can unlike glare be modeled which high accuracy, so really one light is ok). A minor amount of glare can be measured, but comparing the SSF results (glare free) with the target generated profile the differences are so small that my conclusion is that in the context of all inaccuracies there is in camera profiling the glare issue can be ignored. This assumes photographers will be able to follow instructions when it comes to shooting a target, which I guess is not always the case in real life. I'll be adding a "glare detection" log in the make-profile step so it least is noted when suspicious input is given.

(If there is a significant amount of glare this is seen as the SSF profile generating sane and accurate colors while the target profile will make dark patches too dark or if large amount of glare, the whole target too contrasty and saturated.)

Remaining case is matte targets shot outdoor, there I see both visible effects of glare, but fortunately also low enough glare to be able to make a reasonable correction. I shall do a little bit more testing on that.
« Last Edit: June 03, 2015, 11:32:04 am by torger »
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #404 on: June 03, 2015, 11:41:34 am »

One of better lighting setups is what Imaging Resource are using for their hVFAI shots of SG target. Checking those shots with and without applying of flare correction, the colour transforms using flare correction are 2 dE2000 more accurate.
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #405 on: June 03, 2015, 12:23:55 pm »

the colour transforms using flare correction are 2 dE2000 more accurate.
2 ! I certainly need to try to write a code in Matlab then...  at least I can do this during the daylight time  :D
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #406 on: June 03, 2015, 02:54:04 pm »

One of better lighting setups is what Imaging Resource are using for their hVFAI shots of SG target. Checking those shots with and without applying of flare correction, the colour transforms using flare correction are 2 dE2000 more accurate.

Thanks for the tip, I played around with animaging resource image:
http://www.imaging-resource.com/PRODS/canon-5d-mkiii/E5D3hVFAI000050.CR2.HTM

with the reference data from here: http://www.babelcolor.com/main_level/ColorChecker_content/Digital%20ColorChecker%20SG.txt

Profiling fails miserably, some dark colors pull in opposite directions compared to lighter colors. By excluding the darker, many which are redundant in terms of chromaticity anyway, a good profile is had (sanity-checked comparison with the colorchecker24 result in the same image). Can the dark color errors only be due to glare, or is the reference file bad?

(compared to the reference data it does show a quite large amount of glare, the black patches are ~1.1 stop too bright in the test shot.)
« Last Edit: June 03, 2015, 03:00:50 pm by torger »
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #407 on: June 03, 2015, 03:03:05 pm »

Can the dark color errors only be due to glare, or is the reference file bad?
as far as I know BabelColor Patchtool reference file is what was in ProfileMaker... so it is from the same company that makes CCSG... so if they keep the process steady since 2005 it is more or less accurate (within their tolerances) and you can also compare with what Iliah supplied with makeinputicc...
« Last Edit: June 03, 2015, 03:05:36 pm by AlterEgo »
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #408 on: June 03, 2015, 03:12:35 pm »

> Profiling fails miserably
That is exactly so. Now, if you will have a look at their lighting setup, http://www.imaging-resource.com/ARTS/TESTS/HMI.HTM and some more here http://www.imaging-resource.com/ARTS/TESTS/SLMULTI.HTM you will see they do try, and from seeing what others do, Imaging Resource is among the best.

I was looking at their Canon 6D target, and flare mounts to 0.83 EV easily, dark patches (not just black, but all the dark ones, including pure blue and red) are not very usable; and plus they underexpose the targets not looking at the histograms of raw data (though they do have RawDigger and FastRawViewer).

I'm afraid it is close to impossible to make folks shoot targets properly, so we either ignore the patches where flare is about 10% of raw values and higher, or we issue warnings and refuse calculations unless explicit override is specified, or we try to take flare off (you can see it is mostly additive / bias flare, with some scene-dependent flare non-uniformity); or we do all of the above.
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #409 on: June 03, 2015, 03:56:10 pm »

I just made a little sanity check, I shot a glossy printed paper white+black patch beside eachother, 7.89 stop difference on the Y channel according to the colormunki, and I got 7.28 stop on the G channel with the camera, shot in a dark room. The CCSG has a bit less DR than my baryta paper, about 7.0 stop, so the difference should be smaller there.

So it should be possible to shoot the CCSG target a fair bit better than imaging resource does, I guess they have too much light in the room.

With DCamProf, as the complex command line tool it is, I can live with putting extra requirements on shooting glossy targets.

Concerning target design, for DCamProf's 2.5D LUT making as bright colors for a given chromaticity is the way to go. The CCSG does not have an optimal design in that regard.
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #410 on: June 03, 2015, 05:14:25 pm »

Yes, they could have controlled the light better - and it is of course not about the amount of light per se, but about light missing the target, shielding the lens using proper hoods; cleaning the lenses, closing the viewfinder, etc. But we deal with what we have.

As to the amount of light, here is something to take into account. In studio we need profiles for the light we use for production shots. If it is with flashes, it is the same power as in production shots, or spectrum is different. Same with hot lights. So general additive flare is inevitable in such shots. The larger are the softboxes and the more diffused the light is, the more of the light misses the target and scatters back to the lens. As the actual production shot usually occupies the area larger than the target the flare and glare on the target are not characteristic to the scene. Scene needs different linearization.

SG target is suboptimal, as is CC24 as both are based on pigments that were created for quite a different set of spectral response curves (film), not having deep overlaps (like substantial red channel response to the blue-green range of spectrum) like CFAs do. But those are the only readily available. On top of that, CC24 has nothing useful for flat-fielding, even being matt it is still not quite to the challenge of profiling outside the studio.
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #411 on: June 04, 2015, 02:07:13 am »

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.

what are the chances that this thing will work = http://www.ebay.com/itm/381275256818 ? $50+ so I took a chance.
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #412 on: June 04, 2015, 02:30:00 am »

After having compared CC24 results with results of profiling directly against spectral databases I'm not particularly concerned with the spectral shapes of it. Every color can be varied in infinity in terms of spectral shapes, and it seems to me that the soft shapes the CC24 has (and also the CCSG) is a good design that works as well as one can expect. If you make the spectral shape perfectly match one color it will mismatch another. The next level is to design targets with material of what you're going to shoot, which indeed can be feasible for reproduction. Or use SSF and spectral data, but it's then only performing better for that particular set.

If we're really making a reproduction profile (a use case I'm not so much into, I made DCamProf to make generic profiles primarily), then we shouldn't really try to correct glare in the target shot, right? In that case what's important is that the shooting condition stays exactly the same, so any glare in the target shot is the same glare as when we shoot the artwork or whatever. The profile's LUT will correct the glare, if it's a 3D LUT, and it probably should be for this reason.
« Last Edit: June 04, 2015, 02:44:08 am by torger »
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Alexey.Danilchenko

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Re: DCamProf - a new camera profiling tool
« Reply #413 on: June 04, 2015, 05:56:13 am »

what are the chances that this thing will work = http://www.ebay.com/itm/381275256818 ? $50+ so I took a chance.

Lucky you - I missed out on one local recently...
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #414 on: June 04, 2015, 06:15:03 am »

Experimented more with glare reduction algorithms on the Imaging Resource 5Dmk3 shot of the CCSG. Glare reduction can indeed make significant improvements to the result, but it's still worse compared to the result I get when I simply exclude the dark patches when profiling. So from that result the recommended workflow would be to plot and check for the bad ones, create an exclude list for those and then make a new profile.

There's still a risk that the reference data file is not matching the dark patches very well though which makes the result worse than it otherwise would be. It would be interesting to have a CCSG target and measure it with a spectrometer, and then shoot it with lower amounts of glare.

I'll move on to check closer what glare reduction can do on matte targets on outdoor shots.
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Bart_van_der_Wolf

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Re: DCamProf - a new camera profiling tool
« Reply #415 on: June 04, 2015, 07:44:55 am »

I'll move on to check closer what glare reduction can do on matte targets on outdoor shots.

Hi Anders,

You can shoot glossy targets out-door if you e.g. put them flat on the ground, but shoot them from a 45 degree angle (squaring the target is then done in software, and the resampling (if even needed) can be simple because we need uniform colored patches, not edge and other fine detail).

Since the glossy surface acts like a mirror, you need to put a sheet of black material perpendicular to the target's surface on the other side, so that only the 'black reflection' is what the camera picks up from the surface, which leaves the patch color itself relatively pure. A glossy target will pick up less ambient light reflections (because of the specular reflecting surface that only mirrors the other side at 45 degrees) than a semi-glossy or diffuse target surface (which picks up a more diffuse image of its surroundings, and thus desaturates/pollutes the colors), even with a black plane on the opposite side of the shooting angle.

These surface reflections (which can be colored from nearby walls or trees) need an additive (or subtractive) neutralization model, where as the optical vignetting and light fall-off needs a multiplicative neutralization model

Cheers,
Bart.
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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 #416 on: June 04, 2015, 08:48:32 am »

You can shoot glossy targets out-door

Really interesting technique, but I doubt that it will work well in practice. Even in an ideal indoor situation there is some residual glare issues, and there can be glare issues in the measurement too, those values 6-7 stops down are hard to get precise. Residual issues will be larger outdoor.

Semi-glossy/glossy targets contribute nothing within the normal range of colors, they only increase risk of measurement error. For super-saturated colors they do contribute a little, but I'm quite sure that the residual error in a good outdoor setup will still be large enough to make the profile perform worse on those colors than a profile based on a matte target.

I'm satisfied with the "indoor controlled light pitch-dark room only" recommendation for semi-glossy targets, and then my results indicate that you don't need glare reduction if you do it as good as possible.

When I get back home I'll continue with tests on matte targets and see what conclusions I make from those. I'm not sure I will come to the same conclusions as Iliah, but camera profiling is an "organic" approximate process so it's natural that we can come to different conclusions on how to relate to measurement issues.

My results so far indicate that glare reduction works only in a narrow window. If glare is small, glare reduction only make things slightly worse or no significant improvement, if glare is large results will improve, but results will improve even more if just excluding the dark (=most glare-affected) patches. It seems like matte targets outdoor can be an in-between case where useful results can be had.

If making a commercial easy-to-use software users expect good results even if sub-optimally used. I've seen some bad reviews of the ColorChecker SG which probably are all glare-related. So I do understand the approach of using glare reduction to do the best of what the software get. With DCamProf I have the luxury to say "sorry, junk in, junk out", so I will only include glare reduction if it can provide significant improvements in important use cases. Actually there's only one on the list as I see it -- shooting matte targets outdoor. I'll report back on results.
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #417 on: June 04, 2015, 09:06:24 am »

Lucky you - I missed out on one local recently...
come on - you have a shiny new monochromator setup now !
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #418 on: June 04, 2015, 10:03:07 am »

> After having compared CC24 results with results of profiling directly against spectral databases I'm not particularly concerned with the spectral shapes of it
In real-world photography the blue-purple shifts as well as red being too orange or too magentish are being a plague. The wrong rendition of reds touches upon yellows and causes problems in skin rendition too. In my experience it is target design issue as well as CAT issue. As I make my own targets, I can see it. One of the practical way to minimize those shifts without making new targets is profiling based on spectral response. Using spectral transforms to the latest possible stage and recording light spectrum in the scene is also one of the things I always considered better suited for profiles for photography.

Semigloss and gloss targets were appearing at the time when profiling libraries were designed with the premises that the wider is the range of colours the more accurate will be the estimation of red, green, and blue chromaticities. That started full force with CC DC, and it turned out not to work well even in studio, so Gretag made a special reference with glossy patches being removed from reference data and ignored in the device data. The other hypothesis, including patches for a LUT-oriented cube, also proved to be wrong. Another trouble is that the large white patch in the middle caused flare on the surrounding patches, and CC DC died giving place to CC SG. From the point of view of profiling, SG differs from Classic only in reflectance. But Classic also has no patches for accurate flatfielding and flare estimation. In all other aspects classic has advantages over SG even in studio. That is why we included flatfielding in RawDigger, to make Classic more usable. I always maintained that the targets need to be matt, and that in studio Classic is more practical than Passport - given one can mount the Classic geometrically flat.

I think diagnostics of flare and glare and eliminating patches with excessive amounts of those is a good working approach. Indeed, GIGO.

Profiling and linearization are different tasks, solved at different stages. I do not rely on profile LUTs for linearization (one of the reasons is that CMMs introduce too much noise and rounding errors when working with small numbers; and may even cause posterization). As to glare, I have photographic ways of reducing it, as well as object-level sampling and processing data accordingly, so in my own work glare is not an issue when it comes to profiles. In any case, flare in the final scene can't be characterized based on the shot of  device-level targets like ColorCheckers being shot for profiling.
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #419 on: June 04, 2015, 10:04:47 am »

what are the chances that this thing will work = http://www.ebay.com/itm/381275256818 ? $50+ so I took a chance.
How could I possibly know the chances? :)
This thing is important:
How do I reset my Spectrolino?

To reset your Spectrolino, hold down the measurement button on the top of the instrument for approximately 10 seconds. During this time you will hear a sequence of four tones, then two tones in rapid succession that are repeated after a pause. Continue holding the measure button until you hear a fifth long tone, indicating that the reset is complete.
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