More GPU Path Tracing, honored guest HDR

Hello,
in my last entry (almost a month ago) I said I was working on implementing HDR to make renders look more... plausible. Here you go. These renders (a few glass spheres with fresnel reflection and caustics) are lit completely by an HDR environment map (quite low resolution), providing realistic direction-based lighting. The floor in the left render is also normal-mapped (but not the right render as I did not find a corresponding normal map texture).

The separation between the ground and the surrounding environment map is still far too sharp, I believe an interpolation-based approach to simulate the gradient effect that occurs when sky and earth blend together at the horizon (if that makes sense) could work. Or perhaps the glass spheres are simply too perfect to be physically plausible and could use some random noise to make them look more familiar.

Each render didn't take very long, but then again the geometry is very simple, the only reason the scene looks so complex is thanks to the environment map.

The two (separated) renders are available in my Gallery as well (but no high-resolution version this time as I forgot to render them and changed the code too much since then).