NVIDIA GeForce 7800 GTX

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HDR Rendering & Performance

NVIDIA put a strong emphasis on the GeForce 7800 GTX's HDR performance during our briefing, so we explored the GTX's capabilities in areas with a couple of applications. To initially investigate the GeForce 7800 GTX's HDR (High Dynamic Range) rendering capabilities, we used the "Rthdribl" "Real-time High Dynamic Range Image-Based Lighting" demo produced by Masaki Kawase. Rthdribl uses DirectX 9.0 high-precision texture formats and PS 2.0 for real-time, true HDR rendering.  The demo features true HDR (High-Dynamic Range) Rendering, Image-Based Lighting, Glare Generation (Afterimage, Bloom, Halo, Ghost, & Star), Automatic Exposure Adjustment, Iris shaped Depth of Field blur, Realistic Motion Blur, Full-Scene Anti-Aliasing, and Fresnel Effects (Specular Reflectance). The Glare, Motion Blur, Fresnel Reflection, and Depth of Field effects are possible, and take on a realistic look, because they are rendered using HDR. Some of the effects used in the Rthdribl demo are extremely taxing; as such only a few of them are just now beginning to be used in games. As faster and more capable graphics hardware is delivered, however, effects such as the ones used in this demo will become increasingly more common.


GeForce 7800 GTX
(~120+ FPS)

GeForce 6800 Ultra
(~70+ FPS)

Radeon X850XT PE
(~115+ FPS)

In terms of image quality, the Rthdribl demo didn't show much of a difference between the three cards we tested. All three of them produced clean images with smooth transitions. Older hardware, such as the GeForce FX Series of cards for example, would show banding in this demo that's not visible with new cards such as the 7800 GTX due to their higher-precision pixel shaders and texture filters. Where we did see a notable difference was performance, however. The GeForce 7800 GTX looped through the Rthdribl demo at a frame rate roughly double that of a GeForce 6800 Ultra. The Radeon X850 XT Platinum Edition lagged the 7800 GTX by only a few frames per second though.

HDR Performance with FarCry v1.31
Realism vs. Performance


FarCry Without HDR

FarCry With HDR

With the latest patch installed, FarCry is one of the few games available that has support built in for HDR rendering, so we did some testing with FarCry as well. We enabled level 8 HDR and ran a couple of tests using our custom demo to see what kind of an impact it had on performance. Please note that anti-aliasing is not supported with HDR enabled, so the tests above were run with AA disabled.

As you can see, enabling HDR rendering had a huge impact on performance. At 1,280 x 1,024, the framerate dropped by almost 50%. The impact was even more dramatic at 1,600 x 1,200. Whether or not the more realistic lighting produced with HDR enabled is worth the performance penalty is ultimately up to you, but we suspect enthusiasts will have to wait for another generation or two of graphics cards to be released, before embracing HDR rendering.  Or, you can just link a pair of GeForce 7800 GTX cards together now in an SLI configuration, and game at playable framerates with HDR enabled.

Tags:  Nvidia, GeForce, GTX, force, GT, 7800, 780, id

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