There's probably some locality you can exploit as well. Given the same surface and close proximity, I imagine the coefficients are nearly identical.
Or store only the rotation of certain typical small set of SH coefficients in two values + index. For an ideal, single material sphere, all the coefficients could be lined up exactly, right?
Or store only the rotation of certain typical small set of SH coefficients in two values + index. For an ideal, single material sphere, all the coefficients could be lined up exactly, right?