Hi all! Indeed, the alignment of the cameras was far from perfect, and I had to do some post-processing to correct this, which was done simply by shifting pixels with some reference point. Still it was ok for what I needed (using the hdr as light source), but I wouldn't use the same approach again.
Flare from the sun was quite a problem, especially as I was using a filter behind the fish-eye. I'm still not sure if the filter in front would reduce it, as the less flare would be compensated by the need of a longer exposure... Still, the flare affects the lower end of the dynamic range, so it shouldn't be an issue for the measurement of the LED itself. A note about ND filters, I've had very bad experiences with photography filters, especially at high ND values. It really needs to be an optical filter (I ended up using a combination of filters from Edmund Optics). Also, a very good reference is a thesis by Jessi Stumpfel, from USC (working with Paul Debevec) available here: http://gl.ict.usc.edu/skyprobes/ Hope this helps, Santiago ________________________________________ From: Axel Jacobs [[email protected]] Sent: Monday, February 20, 2012 11:24 AM To: High Dynamic Range Imaging Subject: Re: [HDRI] HDRI capture of LED Lars, if this is a question to me--then yes, I did consider using an ND filter, but no, I can't use one because the lens I'm using is a 4.5mm fisheye lens that doesn't allow the use of filters, AFAIK. Either way--you'd want to expose (much) longer than a full cycle which is only 1/100 sec. This severely limits the range of exposure times available for the HDR sequence. If I remember correctly, Santiago Torres captured sunny skies in his PhD thesis, and he had to use two identical cameras for this, one of which was fitted with an ND filter. Aligning the two must have been a nightmare. Axel On 20 February 2012 11:13, Lars O. Grobe <[email protected]> wrote: > Hi, > > did you consider using a filter to work with higher luminances at still > reasonable shutter speeds? > > Cheers, Lars. > > _______________________________________________ > HDRI mailing list > [email protected] > http://www.radiance-online.org/mailman/listinfo/hdri _______________________________________________ HDRI mailing list [email protected] http://www.radiance-online.org/mailman/listinfo/hdri ____________________________________________________________ Electronic mail messages entering and leaving Arup business systems are scanned for acceptability of content and viruses _______________________________________________ HDRI mailing list [email protected] http://www.radiance-online.org/mailman/listinfo/hdri
