I'm trying to implement the image based lighting described in the UE4 presentation.

The have a function called IntegrateBRDF() which is supposed to return two values (a, b) that are both somewhere between 0 and 1. In my tests b seems to be in the [0, 0.15] range however.

Has anyone played with this function as well? Do I probably have an implementation error or is it supposed to be like that?