three r150 PMREM of env-studio-lq.exr, cubeUV height 1024 maxMip 8
equirect 1024x512 RGBA float32 (converted to float16 afterwards), row 0 = BOTTOM (v=0, lat -90), u=atan2(z,x)/2pi+0.5 in three coords
slice i = three PMREM mip (i-2), i.e. slice 0 = roughness 1, slice 10 = mip 8 (sharpest); three roughness: 1, 0.8, 0.6666666666666667, 0.5333333333333334, 0.4, 0.305, 0.21, 0.15239370284192838, 0.10775862068965518, 0.07619685142096419, 0.05387931034482759
