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Author Topic: DCamProf - a new camera profiling tool  (Read 767335 times)

Alexey.Danilchenko

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Re: DCamProf - a new camera profiling tool
« Reply #440 on: June 05, 2015, 10:55:01 am »

I've seen a research paper when they made a good D65 simulator with just 8 LED channels (if you can solder it's probably a quite easy DIY project), you don't really need 20+ like the high end programmable have. But all products I've found are like 3 or 4 channels which means poor spectral properties.

If anyone know about a LED D65 simulator, please post.
And that research project didn't have spikes anywhere in a8 channel LED spectrum? Do you have the link to the publication?
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #441 on: June 05, 2015, 10:58:59 am »

And that research project didn't have spikes anywhere in a8 channel LED spectrum? Do you have the link to the publication?

Desperately trying to find it again, but I haven't found it :-( I'll post if I find it.
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #442 on: June 05, 2015, 11:04:39 am »

I asked Lee filters about that, they have loads of filters
but you asked about _1_ filter - vs the stack of filters (2-3)...
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Alexey.Danilchenko

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Re: DCamProf - a new camera profiling tool
« Reply #443 on: June 05, 2015, 11:14:55 am »

Desperately trying to find it again, but I haven't found it :-( I'll post if I find it.

I suppose this is the one where the simulator is cited but I cannot find a free version of the cited publication (the payable article can be obtained here)
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #444 on: June 05, 2015, 11:24:12 am »

I suppose this is the one where the simulator is cited but I cannot find a free version of the cited publication (the payable article can be obtained here)
may be to write to that author ( ccdcli@leeds.ac.uk ) and ask for a copy ?
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #445 on: June 05, 2015, 11:36:21 am »

Yes it was that, mixed up with this: http://file.scirp.org/Html/14-7600116_16626.htm
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #446 on: June 05, 2015, 11:48:35 am »

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nertog

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Re: DCamProf - a new camera profiling tool
« Reply #447 on: June 05, 2015, 03:20:50 pm »

*Disclaimer: the product in the link below is the result of a research project I work on...so I am slightly biased.*

Here you go: http://ledmotive.com/

10 LED channels, fully programmable and with spectral feedback. Although the website shows more commercial, general illumination applications, we use the light engines in several scientific studies. Multichannel LED light sources are rarely cheap as the electronics to drive the LEDs and especially the optics to ensure an homogeneous beam profile are quite advanced.

An alternative I use myself in a homemade viewing booth are spotlights with UV-pumped white LEDs. Their spectrum is smooth and continues without the pronounced blue spike of standard white LEDs.

Keep up the good work!
Wim
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #448 on: June 05, 2015, 04:03:02 pm »

Thanks for the interesting link.

Indeed I was suspecting that it may be quite expensive to make a multichannel LED, more than those 300 bucks for a filtered halogen.

Could you provide a link to a UV-pumped white LED? I have never heard of them before.

Surfed a bit, the principle seems to be to have a UV led (producing invisible ultraviolet light) and then put in some phosphors there that absorbs the UV an re-emit at a smoother wider spectrum. This links shows what to expect:
http://www.open-photonics.com/featured-technologies/high-cri-leds

Better than fluorescents it seems, but we can't have D65 I guess?
« Last Edit: June 05, 2015, 04:18:43 pm by torger »
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nertog

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Re: DCamProf - a new camera profiling tool
« Reply #449 on: June 05, 2015, 04:24:55 pm »

http://yujiintl.com/high-cri-led-lighting/?gclid=CM6ut6-v-cUCFTHHtAodoGkAyw

Filtered halogens could be more accurate, but the MR16 halogen replacement I tested offered a much higher illuminance and better beam profile than Solux (not to mention they consumed 10x less power). Their mid-power SMD LEDs are excellent!
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #450 on: June 05, 2015, 04:30:43 pm »

http://yujiintl.com/high-cri-led-lighting/?gclid=CM6ut6-v-cUCFTHHtAodoGkAyw

Filtered halogens could be more accurate, but the MR16 halogen replacement I tested offered a much higher illuminance and better beam profile than Solux (not to mention they consumed 10x less power). Their mid-power SMD LEDs are excellent!

Cool, I had just surfed up that exact site and was about to post a link :). A package for 3 5600K lamps is $125 though, so it's not for free. Cheaper than Liulabs $300 D65 simulator though.

(For the application of camera profiling I think a directional spot is a good thing, easier to get nothing but the target lit to minimize any glare issues.)
« Last Edit: June 05, 2015, 04:49:04 pm by torger »
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nertog

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Re: DCamProf - a new camera profiling tool
« Reply #451 on: June 05, 2015, 04:53:51 pm »

Hmm, I bought a couple of MR16 spots from them about a year ago. Maybe worth asking if they still have them?
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #452 on: June 05, 2015, 05:16:39 pm »

These guys also have this kind of thing, http://high-cri-led.com/high-cri-led/led-lighting/high-cri-mr16.php
their latest product brochure was released today, and it has some 6500K products in it, on the web I find only 5600K max though.
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nertog

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Re: DCamProf - a new camera profiling tool
« Reply #453 on: June 05, 2015, 05:52:50 pm »

Interesting! I will contact them and see if I can get some more info. They seem to use the standard blue pump + phosphors to achieve a high CRI. This means the spectrum most likely has a large blue spike at 450-460nm...not something you's want. Let's see.
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #454 on: June 06, 2015, 10:33:54 am »

Experimented with some outdoor shooting techniques to minimize glare and flare issues.

Setup as shown in attached image; cut out the side of a cardboard box, cover it with black cloth, and put the glossy target at the bottom. Then shoot the target at an angle from the side, so all reflections is supposed to come from the blackness of the box. You need perspective correction to make the target scannable, and you also need to use the flat-field correction function to even out the light.

I have also lengthened the lens shade. The standard lens shade is designed to not vignette on the largest aperture, so when you shot at f/8 you can have a considerably longer lens shade and reduce any flare. The viewfinder is made light tight (important!). I'm using a 85mm lens as it has few lens elements which is good concerning flare.

I'm not shooting a real target here, just a glossy printer target which has both black and white patches so I can test dynamic range.

7.89 stops: spectrometer reference measurement
7.28 stops: target shot in a dark room with a tungsten light (note: not same lens used here, possibly a little bit better result can be had)
7.19 stops: outdoor with the shown setup using polarization filter
7.15 stops: outdoor with the shown setup using no polarization filter.
6.7 stops: outdoor as shown but without the cardboard box
6.3 stops: outdoor with the shown setup, being sloppy with the viewfinder

Polarization filter does not seem to make any significant difference in this type of setup, so it's probably best not using it as I think they're not fully spectrally flat.

It seems like it may be possible to shoot semi-glossy targets outdoor and get good results using this type of technique, if you're careful when setting it up. At some point I'll test it in full.
« Last Edit: June 06, 2015, 10:35:46 am by torger »
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ah693973

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Re: DCamProf - a new camera profiling tool
« Reply #455 on: June 06, 2015, 11:04:31 am »

All,

I have followed this discussion from its start and am constantly amazed at what the internet allows a few motivated people to do. I just love these kinds of globehopping collaborative projects.

In reading the latter part of the thread and the problems with flare and glare, a question keeps popping into my head; Why do you need to measure a paper target? Why not take a variable light source like the LEDMOTIVE or a homemade alternative (RGB+ LEDs and a ColorMunki?) point it at the camera and take photos as you vary the light? I guess it would look more like a version of display profiling. On that thought, maybe instead of LEDs it could even use a display for the source?

Andy
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #456 on: June 06, 2015, 11:17:44 am »

There are two ways that are currently in use; one is to use bandpass filters over a halogen or xenon stabilized light; the other is to use a target made of gel filters or an IT8 / HCT (http://hutchcolor.com/) target recorded on a slide film and positioned and spectrally measured right on the lighttable (a more stable variation of the same is to use single filters mounted into slide frames in a multiple shot technique, lighttable or slide projector). Light source must have smooth spectrum, and I have not yet seen LEDs that provide such spectrum.
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #457 on: June 06, 2015, 11:32:29 am »

All,

I have followed this discussion from its start and am constantly amazed at what the internet allows a few motivated people to do. I just love these kinds of globehopping collaborative projects.

In reading the latter part of the thread and the problems with flare and glare, a question keeps popping into my head; Why do you need to measure a paper target? Why not take a variable light source like the LEDMOTIVE or a homemade alternative (RGB+ LEDs and a ColorMunki?) point it at the camera and take photos as you vary the light? I guess it would look more like a version of display profiling. On that thought, maybe instead of LEDs it could even use a display for the source?

It's probably harder and more expensive than we'd like to make a home-made programmable multi-channel LED light-source. I'm all for such a project though, but I'm not the right person to do it.

Targets should present relevant types of spectra. Homemade inkjet printed targets have some limitations discussed earlier, X-rite's targets have better spectra, but I think you can use a inkjet super-saturated target as a complement to X-Rite's matte CC24 for example. If you do copy work, such as copy paintings, making an own target by painting patches with the same colors as used in the work you copy will be a good idea.

The core of the problem is that cameras are not colorimetric devices, their SSF do not match the standard observer CMF, that is they register colors in a significantly different way than humans. This means that to make a profile that works as good as it can, we need to make it for the exact reflectance spectra that will be in the scenes we shoot. Unless we do copy work this is not really possible, and then we instead need to do it for some average spectra, then smooth rounded spectra are much better than spiky spectra as it's more similar to natural colors and works smoother over a wider range of similar colors.

Unfortunately displays are very limited in terms of spectra, it's just a red, green, and blue peak which you can mix. This can recreate tristimulus values that work well for a human, but as the camera sees colors otherwise those spectra will not make up for good profiling colors.

It's the same reason why we're so picky about the artificial light sources. The mismatch between human and camera color response makes spiky spectra unpredictable. If you have photographed in low CRI light sometime you have probably noticed that the colors come out quite different from the camera than the eye saw them, and this is a demonstration of the effect of having different color response. The spikier spectra the more the differences are seen. Therefore we want to do camera profiling with full spectrum lightsources with smooth spectra, using colors with smooth wide reflectance spectra.

Using transmissive targets is interesting though. In Image Engineering's CamSpecs product they use transmissive targets with several narrow bands to measure the camera's SSF. And I think if one is going to make some elaborate DIY project with hardware stuff, I think one should try to look into measuring SSF.
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #458 on: June 06, 2015, 11:52:37 am »

> Using transmissive targets is interesting though
And much simpler than one may think. Bonus - they can be measured as mounted on the light, right before shooting, with a German-made, half-the-PR-price JETI device http://www.jeti.com/cms/index.php/instruments-55/radiometer/specbos-1201 ; and additional focus optics is available if the patches are less than 4mm. This makes cheap gel filters very practical, and allows to virtually eliminate scene flare.
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #459 on: June 06, 2015, 12:20:14 pm »

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