So, I want to use one of those sphere type images as an env map. Like here I'm useing the uffizi cathedral one. Thing is I have to prefilter.And to do this I have to convert it to a phi/theta notation and convolute with a function that's defined from 0 to Pi/2 now a) Can I just read in the hdr (or if converted, exr) image, take the x,y values, rescale them to [-1,1] range like it says on the linked page, use the u,v vales to compute theta and phi and use those to orden them? b) the function to convolve with is only affected by theta, it's 2D brdf slice so the phi is kept constant. Now my question is, those sphere do 360 degrees where as my (phong) slice goes from 0-Pi/2. any suggestion how to expand this? edit and a third question, not really related. Has anyone ever use the smits method on HDR images?