RE : Pixel to solid angle transformation

Maybe this can help you:

you can use the pcomb program to obtain the solid angle of each pixel of a picture!

for instance this will translate a radiance picture (origin.pic) into a "solid angle" picture (solid_angle.pic) where each pixel has a brightness value that matches the solid angle of the same pixel in the original picture:

pcomb -e 'lo=S(1)' origin.pic >solid_angle.pic