HDR: Speed AND Quality
The new generation of ATI’s graphics processors fully supports high dynamic range display modes, known under the common name HDR.
One HDR mode was already available in RADEON X800 family processors, but game developers didn’t appreciate that feature much. We also described HDR in detail in our review of the NV40 processor which supported the OpenEXR standard with 16-bit floating point color representation developed by Industrial Light & Magic (for details see our article called NVIDIA GeForce 6800 Ultra and GeForce 6800: NV40 Enters the Scene ).
OpenEXR was chosen as a standard widely employed in the cinema industry to create special effects in movies, but PC game developers remained rather indifferent. The 3D shooter Far Cry long remained the only game to support OpenEXR and even this game suffered a tremendous performance hit in the HDR mode. Resolutions above 1024x768 were absolutely unplayable. Moreover, the specifics of the implementation of HDR in NVIDIA’s graphics architecture made it impossible to use full-screen antialiasing in this mode (on the other hand, FSAA would just result in an even bigger performance hit). The later released GeForce 7800 GTX, however, had enough speed to allow using OpenEXR with some comfort, but it still didn’t permit to combine it with FSAA.
ATI Technologies took its previous experience into account when developing the new architecture and the RADEON X1000 acquired widest HDR-related capabilities, with various – and even custom – formats. The RADEON X1000 GPUs also allows you to use HDR along with full-screen antialiasing. This is of course a big step forward since the NVIDIA GeForce 6/7, but do the new GPUs have enough performance to ensure a comfortable speed in the new HDR modes? We’ll only know this after we test them, but at least we know now why the R520 chip, the senior model in ATI’s new GPU series, came out more complex than the NVIDIA G70. The above-described architectural innovations each required its own portion of transistors in the die. As a result, the R520 consists of 320 million transistors – the most complex graphics processor today! – although it has 16 pixel pipelines against the G70’s 24.