Hi Jelle,
If you have access to a Mac, you can download Photosphere to do this for you:
http://www.anyhere.com
Mehlika Inanici has done some work validating the software:
http://faculty.washington.edu/inanici/MI-RESEARCH.html
You can subscribe to the hdri mailing list or look at older postings for more
information.
Cheers,
-Greg
> From: Casper Esmeijer <[email protected]>
> Date: August 18, 2010 6:32:36 AM PDT
>
> Hi Jelle,
>
> There's a lot of information available on this topic. You'll have to go
> through different steps to calibrate your camera, define and convert to the
> right color space and you'll need the same picture with several different
> exposure times to cover the dynamic range sufficiently (depending on what you
> want to use it for). Check out the following:
> - Paul E. Debevec, Jitendra Malik. “Recovering High Dynamic Range Radiance
> Maps from Photographs”, Proceedings of SIGGRAPH 97, Computer Graphics
> Proceedings, Annual Conference Series, pp. 369-378 (August 1997, Los Angeles,
> California). Addison Wesley. Edited by Turner Whitted. ISBN 0-89791-896-7.
> - D. Wueller, H. Gabele,“The Useage of Digital Cameras as Luminance Meters”,
> SPIE – IS&T Electronic Imaging Conference 2007.
> - Karel Fliegel, Josef Havlin, “Imaging photometer with a non-professional
> digital camera”, Proc. SPIE, Volume 7443, 74431Q, 2009.
>
> This doesn't mean the answer is simple though.
>
> good luck, Casper Esmeijer
>
> jelle feringa schreef:
>> Hi,
>>
>> On page 330 of RwR there is a nice .cal formula that let's you mimic a
>> camera exposure to a .hdr file.
>> I'd like to do the inverse, and use my camera as an approximate radiance /
>> lux / candela measuring device.
>> I realize this is pretty approximate, but that will do for now.
>> Actually, it could have some general usefulness; let's say you visited a
>> beautiful building some time ago took some shots and would like to know the
>> approx. lighting levels there.
>> Such a tool would be a nice aid.
>>
>> To go all out on this would be to use the exif data from an image, rather
>> than setting these options manually I suppose.
>> (That would be pretty easy to do actually)
>>
>> However, it seems to me that E is returning an exposure setting ( for use
>> with pfilt -e ? ) rather than a Radiance value ( candela, lux conversion
>> could be handy ).
>> How could I retrieve the approximate radiance value?
>>
>> Thanks in advance,
>>
>> -jelle
>>
>>
>> from __future__ import division
>> import optparse, math, sys
>>
>> parser = optparse.OptionParser()
>> parser.add_option('-e', '--exposure-time', action="store", type=float,
>> help="exposure time")
>> parser.add_option('-s', '--iso', action="store", type=int,
>> help="film speed (iso/asa)")
>> parser.add_option('-f', '--f-stop', action="store", type=float,
>> help="camera f-stop")
>> options, remainder = parser.parse_args()
>>
>> for i in ['exposure_time', 'f_stop', 'iso']:
>> if getattr(options, i) is None:
>> print 'the option %s was not set, but is required' % (i)
>> sys.exit()
>>
>> # honestly stolen from Rendering with Radiance page 330
>> # relationship between Radiance exposure and film exposure
>>
>> K = 179*(math.pi/200)
>> # C allows you to ^ on floats and python does not?
>> E = int( K * options.exposure_time * options.iso / options.f_stop ) ^ 2
>> sys.stdout.write('E -> ' + str(E) + '\n')
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