Hi everyone,
Some years ago I tested my Sigma 8mm lens, f3.5. At the time I found several sources online claiming it to be equi-solid angle (-vth), but it didn’t match my personal experiences with the lens, so I tested it. My tests showed it to be equidistant (-vta), i.e. identical to the angular fish eye projection in RADIANCE. So, in my experience, the 8mm Sigma lens is equidistant. Cheers, Claus Claus B. Madsen Assoc. Prof., Ph.D. | Department of Architecture and Media Technology Phone: +45 9940 8788 | E-mail: [email protected]<mailto:[email protected]> Aalborg University | Rendsburggade 14 | 9000 Aalborg | Denmark Employee No.: 107255 | Vat No.: DK29102384 From: "J. Alstan Jakubiec" <[email protected]> Reply-To: High Dynamic Range Imaging <[email protected]> Date: Friday, 27 January 2017 at 11.33 To: "[email protected]" <[email protected]> Subject: Re: [HDRI] Convert equisolidangular to equiangular projection A little followup that is worth noting is that Axel Jacobs measured the Sigma 4.5mm and found it to have an equi-solid angle projection. See his presentation here: https://www.radiance-online.org/community/workshops/2012-copenhagen/Day2/Jacobs/Jacobs-AJ09-HDR_Radiance_WS-2012.pdf Alstan On 1/27/2017 6:26 PM, J. Alstan Jakubiec wrote: Hi Tobias, I just purchased a pair of Sigma 8mm f/3.5's for my work, but I haven't measured them for vignetting and angular verification yet. It is on my to do list :). I will be disappointed if they are equi-solid angular however. Will let you know sometime after the Lunar new year. Alstan On 1/27/2017 6:17 PM, Tobias Porsch wrote: Hi Alstan, I'm not sure if your below description is correct. In my experience it's exactly the opposite. The Sigma f=8mm F/3.5 lens is an equi-solid angle (-vth) and the Sigma f=4.5mm F/2.8 is an equi-distant (-angular) (-vta) lens. Can you please double-check that issue for me? Cheers Tobias Von: J. Alstan Jakubiec [mailto:[email protected]] Gesendet: Donnerstag, 26. Januar 2017 06:58 An: [email protected]<mailto:[email protected]> Betreff: Re: [HDRI] Convert equisolidangular to equiangular projection Hi Zhe, As far as I am aware, the Sigma 8mm f/3.5 is an equi-angular (-vta) lens, and the Sigma 4.5mm f/2.8 is an equi-solid angle (-???) lens. I am having trouble finding a source from Sigma right now, but Cauwerts, Bodart and Deneyer's paper<http://www.tandfonline.com/doi/abs/10.1582/LEUKOS.2012.08.03.002> says so. That said, if you do end up with an equi-solidangle image, I have a python script that converts equi-solid angle to equi-angle for each source jpeg while maintaining the EXIF data. I used this to convert equi-solidangle images from my Canon 8-15mm fisheye lenses. Best, Alstan On 1/26/2017 8:48 AM, Gregory J. Ward wrote: Hi Zhe, You should be able to apply the fisheye_corr.cal file I gave you earlier to correct the distortion and make it an angular fisheye image that pinterp works with. (Why you need pinterp, I am not sure.) The command is as suggested in the fisheye_corr.cal file itself: pcomb -f fisheye_corr.cal -o fisheye.hdr \ | getinfo -a "VIEW= -vta -vh 180 -vv 180" \ > corrected.hdr This will also crop the area outside of 180° to black, assuming that is what you want. It assumes that you have already cropped the image to a minimum square area. You should apply vignetting correction and absolute calibration first. Cheers, -Greg From: Zhe Kong <[email protected]><mailto:[email protected]> Date: January 25, 2017 1:15:49 PM PST Dear list: I am trying to compare HDR images and simulated luminance maps. Since I use SIGMA 8mm 1:3.5 for Canon, I need to convert equisolid-angular to equiangular project. I see very useful information from the post below: https://www.radiance-online.org:447/pipermail/radiance-general/2015-August/011184.html However, I still have some questions need to figure out. 1) pinterp does not include equisolid-angular projection, so a equation needs to be applied to the function. Greg mentioned this simple expression, sin(theta)/theta, but I am still confused. Could anyone offer me the command? 2) The post discussed the steps of processing HDR images. If I get it right, the steps following "adjust exposure" are vignetting correction, adding view information, converting project from equisolidangular to equiangular, then calibrating the image. I use a GOSSEN Starlite 2 to record the luminance value on a grey card for calibration. My question is, should I calibrate the image before or after converting fisheye projection? Any suggestions or explanation would be appreciated. Zhe _______________________________________________ HDRI mailing list [email protected]<mailto:[email protected]> http://www.radiance-online.org/mailman/listinfo/hdri _______________________________________________ HDRI mailing list [email protected]<mailto:[email protected]> http://www.radiance-online.org/mailman/listinfo/hdri _______________________________________________ HDRI mailing list [email protected]<mailto:[email protected]> http://www.radiance-online.org/mailman/listinfo/hdri
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