Correct for PSX color mapping

[zole]

From the spec:

The Playstations RGB values aren't linear to normal RGB values (as used on PCs). The min/max values are of course the same, but the medium values differ:

Intensity        PC      PSX
 Minimum          0       0
 Medium (circa)   16      8
 Maximum          31      31

Ie. on the PSX, the intensity increases steeply from 0 to 15, and less steeply from 16 to 31.

I'm assuming that PSX developers would design their textures around this (although maybe not all of them!), but it seems absurd to make users go through that step, so I'm not sure how to apply this part of the spec. Maybe sampled texels should be converted from linear to PSX space, lit/dithered/etc., and then converted back to linear.