there's a directx9 open source plugin being made by a couple of programmers called 'helan'. It enables to adjust some more detailled settings than brightness, contrast and gamma, for everything that's rendered using directx.
There's a youtube movie 'bout it.
I haven't heard much of the development but it seems a pretty cool plugin if it gets finished. It enables to alter gloom effects which is pretty much what the filter in the altered gameplay video didn't. So everything becomes darker, but light-source remain light-source. It's like altering images in 16-bit instead of 8-bit.