HDR

The most impressive aspect of the Shader Model 3.0 tests has got to be the use of HDR lighting effects. Now, there’s been a lot of discussion of late as to what is and what isn’t HDR, so let me go into a little detail on this first. HDR or High Dynamic Range refers to the amount of levels between opposite ends of the light intensity spectrum. Now, in real life the number of levels between totally black and a super-intense white light is almost infinite, but in games we’ve had to make do with as few as 256 steps from black to white. This changed with the 1.3 patch to the Far Cry engine, which implemented the OpenEXR method of HDR using 16-bit floating point calculations.

At the point when the 1.3 Far Cry patch was released ATI hardware only supported Shader Model 2.0 and 24-bit floating point, while nVidia hardware supported Shader Model 3.0 and both 16-bit and 32-bit precision – the upshot of this was that ATI hardware could not produce HDR effects.



This situation was countered when Valve implemented Shader Model 2.0 compatible HDR effects into the Source engine and I have to say that it looked pretty damned good. However, the method of HDR that Valve has gone with doesn’t yield the same amount of levels between dark and light as the Shader Model 3.0 method, so the effects can’t be as complex. Because of this, Futuremark decided to use the latter method of HDR rendering, despite it being far more hardware intensive – after all, the point of a benchmark is to be as hardware intensive as possible.

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