Dear list,
I would like to both scale down the resolution and crop a circular
fisheye HDR photograph of the skyvault using the following commands to
do so but can't figure why I'm getting slight changes in brightness
values.
The max brightness of the original HDR image is:
==> pextrem -o 11:58:00.hdr | rcalc -e '$1=($3+$4+$5)/3*179'
2.23350842
49393.2719
When I crop the fisheye image horizontally to bound the circular
fisheye view evenly in the x and y dimension with:
==> ra_xyze -r -o -u 11:58:00.hdr | pcompos -o -x 3744 - -936 0 >
11:58:00_crop.hdr
I get a higher max value and the EXPOSURE header disappears from the
file:
==> pextrem -o 11:58:00_crop.hdr | rcalc -e '$1=($3+$4+$5)/3*179'
1.88461284
49702.3333
Then when I scale the image down:
==> pfilt -1 -e 1 -x /4 -y /4 11:58:00_crop.hdr >
11:58:00_crop_scale.hdr
I get a lower value:
==> pextrem -o 11:58:00_crop_scale.hdr | rcalc -e '$1=($3+$4+$5)/
3*179'
4.05328376
48270.3333
If I perform the scaling operation first the EXPOSURE header remains
but the value is still lower:
==> pextrem -o 11:58:00_scale.hdr | rcalc -e '$1=($3+$4+$5)/3*179'
2.59250175
48056.5119
Any thoughts on what I might be doing wrong?
As always, thanks!
Chris
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