Clotilde: Are you sure your low dynamic range pictures are properly exposed from which you construct the HDRI?
Meaning, the fastest shutter speed picture has no saturation (i.e. all white pixels) and your slowest shutter speed picture has some black pixels? You need to make sure this is true else you won't get proper illuminance calculation and also your bright spots (i.e. high luminance) will be under reported. - Alex On Wed, Feb 8, 2017 at 11:10 AM, Clotilde Pierson < [email protected]> wrote: > Dear all, > > > > I am using a Canon EOS 5D Mark II with a Sigma EX DG 8mm f/3.5 fisheye > lens to capture LDR images. I then use hdrgen with the response curves I > defined previously to generate HDR images from these LDR images. I > calibrate the HDR images for the vignetting effect and the distortion > (equisolid to equidistant projection). Finally, I apply a calibration > factor of around 1.39. > > > > When comparing the vertical illuminance and luminance values of the HDR > images with the real measures I took (Minolta LS-110 luminancemeter and > Hagner EC1-X luxmeter), I noticed that the HDR images are underestimating > the illuminance (e.g. 1217lux instead of 1993lux) and the high luminance > values (e.g. 208 cd/m² instead of 402.3cd/m²). I determined the illuminance > value of an HDR with Evalglare –V and the luminance values with ximage in > Radiance. > > > > I also tried only applying default hdrgen (+cropping & header modification > to set the VIEW to vta to use in Evalglare) but I still got big differences > between the HDR-derived and the measured luminance and illuminance values. > > > > Is somebody using the same instruments I am? If yes, do you also happen to > have this issue? Or does anybody have already encounter this problem? > > > > Thank you for your insights ! > > > > Best, > > > > Clotilde > > > > *[image: Test]* > > > > *Clotilde Pierson* > > *FNRS PhD Fellow | Arch. Eng.* > > *Architecture et Climat* > Faculté d’architecture, d’ingénierie architecturale et d’urbanisme (LOCI) > > Université catholique de Louvain (UCL) > Place du Levant, 1 bte L5.05.04 B-1348 - Louvain-la-Neuve (Belgique) > [email protected] > > Tél. 32 (0)10 47 91 52 - Fax 32 (0)10 47 21 50 > http://www.uclouvain.be/architecture-climat.html > > > > > > _______________________________________________ > HDRI mailing list > [email protected] > http://www.radiance-online.org/mailman/listinfo/hdri > > -- Alex Mead (616) 901-2479, UC Berkeley Systems Engineering Ph.D. (expected 2017), www.alex-mead.com www.CEEphotos.com <http://www.ceephotos.com> - web master, creator
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