DCamProf - a new camera profiling tool

[AlterEgo]

But Classic also has no patches for accurate flatfielding and flare estimation.

can't you DIY greyscale patches around the edges of CC Classic yourself by mounting into some frame ?

[torger]

On a different subject, just found this: http://www.liulabs.com/Daylight.htm a D65 simulator that actually seems to work like they should work.

Unfortunately they have no put-in-basket button. I don't know what it costs, but hopefully cheaper than buying an X-Rite Spectralight viewing booth, which also is based on precisely designed filtered halogen lights.

(I'm about to give up on Solux + standard color temperature adjustment filter, the spectrum is not nice enough, and my Solux lamps are too low temperature)

LED-based daylight simulators are the future, but I don't know if there is anything affordable yet. Filtered tungsten seems to be the current best.

[Iliah]

> just found this: http://www.liulabs.com/Daylight.htm a D65 simulator
I saw that, but never checked it out.
Booths are adding a lot of flare.
Not sure the precision of design of the filters is that much needed, or, better to say, is placed where it needs to be. Wide and smooth spectrum light source, like a clear sky or xenon flash, normally is enough to reconstruct spectral transmission of a camera with good accuracy.

> Filtered tungsten seems to be the current best.

That's what I'm saying, too.

[Iliah]

can't you DIY greyscale patches around the edges of CC Classic yourself by mounting into some frame ?

You can, but you need to maintain thickness and use same surface materials. There were times when Gretag were selling N-type paper in sheets. Now you can cut a Kodak grey card or something similar and make a border around Classic.

[torger]

Made some glare testing of matte targets outdoor.

Typical dynamic range loss seems to be 0.14 - 0.2 stops, reducing range from 4.8 towards 4.6 stops. The loss happens in the darkest patches. In worse cases it may rise to 0.3, and if you have very dark colors in the target you may get a small visible difference. In a CC24 with a 0.14 stop difference the visible difference with glare correction (that is linearization) enabled is to my eyes negligible. I can see on the histogram that something happens to the image when I change profile, but it's very hard to see any changes in colors in the image.

Now when I've coded and integrated the linearization, with TPS and all, I will include it in the next release. But the use case seems very narrow to me. Either you have so little glare that it makes no visible difference, or you have so much glare that it's still bad after linearization, and redoing the shot or excluding problematic patches is a better choice. The inbetween case seems to be when there's been say 0.3-0.6 stop loss in dynamic range.

[torger]

On a different subject, just found this: http://www.liulabs.com/Daylight.htm a D65 simulator that actually seems to work like they should work.

Mailed and asked. You can buy a D65 MR-16 lamp from them directly, 299 USD + shipping and handling. I would have preferred $60 or so, but well, they truly have something unique if it performs to spec, and for that price I expect it to.

[torger]

How bad do you think D65 fluorescents are by the way? The best seem to follow the D65 curve quite okay, but with those nasty narrow peaks in there. I don't like fluorescents for that reason, but I don't really know how big a problem those spectral spikes are.

[Alexey.Danilchenko]

Mailed and asked. You can buy a D65 MR-16 lamp from them directly, 299 USD + shipping and handling. I would have preferred $60 or so, but well, they truly have something unique if it performs to spec, and for that price I expect it to.

Interestingly, their patent quoted on the site suggests that this is really just a SPD modifying filter sandwich on top of halogen lamp.

[torger]

Interestingly, their patent quoted on the site suggests that this is really just a SPD modifying filter sandwich on top of halogen lamp.

Yes, the principle has been known for very long time, I haven't read the patent in full so I don't know what's actually new in theirs, but I'm suspecting that the new thing is that the package is small enough so you can just clamp filters directly onto the lamp.

The Spectralight viewing booth use the same technique (but filters are away from the lamps), but liulabs product is the only one I've found where you can buy lamps separate, and 300 bucks is a bargain compared to buying a viewing booth.

The challenge is in designing the filter with a precise response to get a good spectral match. We're paying basically 300 bucks for that filter, I guess the lamp is a standard $3 MR-16.

I've experimented with Solux lamps and standard color balancing filters, and while you easily get 6500K, the spectra is not remotely close to follow a D65 shape.

Halogen can't do UV, so below 400 you don't get much output. For camera profiling this should not be a problem though.

From my experiments the main reason for getting this type of thing would be to profile glossy targets, and for me there's some added value in repeatability when developing the software. Matte targets can be profiled in free outdoor daylight without too much glare issues.

[torger]

Just released 0.7.2.

Not too large code additions, most of the work since last release has been research and testing. There's some more stuff in the docs.

CAT is now enabled per default for reasons discussed earlier in this thread. If you prefer color constant behavior for non-D50 profiles use the "-C" flag. Previously "-C" meant enabling CAT but now that's inverted. Before 1.0 is released there may be some of these "turbulent" changes.

Linearization is now available as a part of the testchart-ff command. I won't be using it myself much as in my tests my own results gets best if I minimize glare in the first case and then just ignore any residual glare rather than applying an approximate correction.

make-profile can now write .icc and .dcp directly (then you get default settings), useful for quick trial-and-error loops when testing how the look changes with parameters etc...

[AlterEgo]

0.7.2 build for Windows (mingw = dcamprof.exe + libgomp_64-1.dll) : https://app.box.com/s/7jsnnhl7orq1nlptk0w9k9qts107ow1f

[Iliah]

I have measured some FL lights, including the top of the line ones used in booths. It was not something I would use, but here is what you may want to look at - DPR "new Studio Scene" is shot under D55 Kino Flo bank, raw files available here: http://www.dpreview.com/reviews/image-comparison

[Iliah]

Interestingly, their patent quoted on the site suggests that this is really just a SPD modifying filter sandwich on top of halogen lamp.

Quite so.

[AlterEgo]

Interestingly, their patent quoted on the site suggests that this is really just a SPD modifying filter sandwich on top of halogen lamp.

actually it is seen right on the photo of the lamp too...

[Alexey.Danilchenko]

actually it is seen right on the photo of the lamp too...

All you see is light and filter which does not per se lead to any conclusion. Patent reading is quite useful anyway...

[AlterEgo]

All you see is light and filter which does not per se lead to any conclusion. Patent reading is quite useful anyway...

sure, but they also write clearly right below

"1. Incandescent lamp with colored glass filters,
 2. Xenon arc lamp with colored glass filters, and "

w/o boasting anything special about the lamps, I'd assume manufacturing of the lamps themselves  is a way more difficult (and $$$) industrial-wise process than procuring the right set of precut to the shape glass blanks to assemble them in layered filter for a small shop like dr. Liu

[Alexey.Danilchenko]

sure, but they also write clearly right below

"1. Incandescent lamp with colored glass filters,
 2. Xenon arc lamp with colored glass filters, and "

Yes and that gives you loads of useful info

I was not criticising them or anything, just making the point that it is interesting to read how it all works. Evidently its not that interesting for everyone (it was for me

[torger]

It's very surprising that it hasn't come any LED solutions, other than the superduperexpensive.

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.

[AlterEgo]

Yes and that gives you loads of useful info

I was not criticising them or anything, just making the point that it is interesting to read how it all works. Evidently its not that interesting for everyone (it was for me

so practical outcome for torger is - measure his smooth halogen light, download some databases (spectral data) of filters (organic or glass) and find a combo of 2 that will filter closest enough to D65...

[torger]

so practical outcome for torger is - measure his smooth halogen light, download some databases (spectral data) of filters (organic or glass) and find a combo of 2 that will filter closest enough to D65...

I asked Lee filters about that, they have loads of filters, but they didn't manage to come up with a solution that works from their standard products  

Here's a paper showing how to build a D65 simulator based on Lee filters (there is a full text link there on the page):
http://www.degruyter.com/view/j/msr.2011.11.issue-5/v10048-011-0025-y/v10048-011-0025-y.xml

the result is not that good though, about the same as my Solux with an 80B filter