We were all trying to figure out what the Extended HDR, the new graphical option in Team Fortress 2, is.

Zips from CS-Nation visited VALVe, and came back with an answer:

Extended HDR uses full floating-point 32 methods for calculating the HDR. Essentially, in the Orange Box titles it allows for better handling of the particle effects and other minor visual improvements. On particles, there is full feather filtering. This is in contrast to the “Full HDR” setting that only partially feathers the particles and creates a rather abrupt cut-off line where the particle effect meets the rest of the world. The feathering allows for smoother visual transitions for particles.

I don’t pretend to know much about this sort of thing, so I won’t even try to offer up a technical comparison between the current HDR method and this new, “extended” method. I’m personally under the impression that only cards equipped with SM3.0 support (and above) will be able to make use of the extended option. FP32 HDR is said to have a much higher contrast ratio for HDR ranges. The higher the floating-point number, the closer the contrast ratio comes to accurately mimicking the ratio of the human eye.

There are more interesting things there, so go read!