Hi Greg,
the image is 5000x5000 pixels.
The sun is 225 pixels for the original and the corrected for the 5°
position. I also tested other positions - the results are in the table
below.
angle [°] Pix-Sun-org Pix-Sun-corr Pixel-Ratio solid angle vta
solid angle equi-dist. Solid-Angle-Ratio
5 225 225 1.00 2.654E-07 3.20E-07 0.83
15 204 204 1.00 2.915E-07 3.20E-07 0.91
25 189 187 1.01 3.157E-07 3.20E-07 0.99
45 167 159 1.05 3.548E-07 3.20E-07 1.11
75 151 138 1.09 3.902E-07 3.20E-07 1.22
According to this, the ratio of the "sun" pixels change after 25°, which
is the angle when the solid-angle for vta gets larger than the
solid-angle of the equi-solid-angle projection.
In the table the column two and three are the amount of pixels for the
sun for the two images, column 4 is a ratio for those two, the last
column is the ratio of the two solid angles.
FYI, these are the scripts for producing the files:
for i in 5 15 25 45 75; do gensky -ang $i 0 +s >sk_$i.rad; oconv -f
sk_$i.rad >sk_$i.oct; rpict -vp 0 0 0 -vd 0 0 1 -vu 0 -1 0 -vta -vv 180
-vh 180 -x 5000 -y 5000 -dc 0 -dj 0 -ps 0 sk_$i.oct >sk_$i.hdr & done
for i in 5 15 25 45 75; do pcomb -f
/usr/local/radiance/lib/fisheye_corr.cal -o sk_$i.hdr | getinfo2 -a
"VIEW= -vta -vh 180 -vv 180" >sk_$i"corr.hdr"; done
The solid angles I calculated with pcomb (and checked also with
evalglare). The amount of pixels I calculated with pvalue -H -h -o -b
image.hdr |awk '{if ($3>1) print $0}'|wc -l and checked also with
evalglare.
cheers
Jan
On 27/06/17 18:13, Gregory J. Ward wrote:
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] <mailto:[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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