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Q: Photomatric units

Posted: Mon Oct 06, 2014 10:03 pm
by sebbo
I have a question about which photometric units are used in the dome light and the physical sky ?

we want to have our hdr images physically correct in terms of real world light intensities and now we stuck a little
on which units to calibrate to as we don't really know what is used in maxwell.

also are the the units used in the dome the same as in area lights ?


cheers seb

Re: Q: Photomatric units

Posted: Tue Oct 07, 2014 9:25 pm
by tom
Intensity for skydome is cd/m2 (also called nit). Emitters have different options... Which plugin are you using?

Re: Q: Photomatric units

Posted: Wed Oct 08, 2014 4:56 pm
by sebbo
Maya is the plug in... but what about the dome light when using HDR images ?

Re: Q: Photomatric units

Posted: Wed Oct 08, 2014 10:42 pm
by eric nixon
I calibrate hdr's by setting the approx EV for the camera, then adjusting the gamma/exposure of the hdr. Beware that exr's can go out of range if pushed far enough (the sun spot will become black in the rendered reflections even though it remains white in photoshop) adjusting maxwells hdr sky intensity setting can overcome that problem.

Re: Q: Photomatric units

Posted: Thu Oct 09, 2014 12:30 am
by sebbo
Hey Eric

my goal is to calibrate our HDRIs to real world values... so what im interessted is it the units used in maxwell so that we can adjust the pixel intensitys to it.
We used photomatics defaults but the is a discrapency with the factor of around 1000... so we are trying to understand the whole light unit thing a bit but get somehow confused with too many variables.

Re: Q: Photomatric units

Posted: Fri Oct 10, 2014 1:33 pm
by eric nixon
Well the only unit I would trust is the camera EV, but thats a good starting point. Maxwell sky seems to be out by a factor of seven in a recent test I did!

Re: Q: Photomatric units

Posted: Fri Oct 10, 2014 4:38 pm
by AlexP
Try sky intensity 0.2 and sun 5. Maxwell sky seems to be out of proportions too.