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]
*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
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