Hi Jan, What is the resolution of your image, and how many pixels does the sun cover? Could this be simply due to quantization error? The function moves pixels around, not changing their magnitude, and the accuracy can never be better than +/- 1/(number of pixels in sun).
Cheers, -Greg > From: Jan Wienold <[email protected]> > Date: June 27, 2017 7:06:03 AM PDT > Hi all, > > I'm a bit puzzled by the result of applying fisheye_corr.cal to an fish-eye > image. > > I have a simple example: > I created a fish-eye image with a sun at 5 degree altitude and kept the sky > black (just the sun). Let's assume now this image is equi-solid-angle and we > want to transfer it to a equi-distant (-vta). > For this I applied pcomb -f fisheye_corr.cal -o fisheye.hdr > corrected.hdr. > > In the next step I counted the amount of pixels for the sun in the two > images. They are exactly the same! What has changed is only the position in > the image. Neither the size of the sun nor the luminance has changed. > But: The difference between the solid angles of a pixel at 85° from the > center between equi-solid-angle and equi-distant projection is around 20%! > (in my example the solid angle per pixel for a 5000x5000 image at 85° is: > 3.2e-7sr vs 2.58e-7sr) > I would have expected also a change in size, accounting for the difference in > solid angles per pixel for the different projection methods, the luminance of > course should be the same. > Am I doing sth. wrong? > thx for the help. > > Jan
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