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Introduction to the nVidia GeForce 7800GTX Series

Introduction to the nVidia GeForce 7800GTX Series - PCSTATS
Price Check: $/£/€
Abstract: The GeForce 7800GTX chipset has a simple purpose; to catapult nVidia back onto the 'fastest, most expensive videocard' throne.
Filed under: Video Cards Published:  Author: 
External Mfg. Website: Nvidia Jul 06 2005   Mike Dowler  
Home > Reviews > Video Cards > Nvidia GeForce 7800GTX

Polygons and SuperSampling

The polygons making up 3D rendered foliage and fences use transparency (alpha) effects to allow realistic sight lines through them, but this means that the pixels making up the visible edge of a blade of grass or leaf are not always on the edge of their polygon, but rather somewhere inside it next to other pixels which have been made transparent. Multi-sampling AA will not smooth out these pixels, meaning that textures that use transparencies will always appear to be jaggy, even in an otherwise glass-smooth 8xAA sampled scene.

The other common method of Anti-Aliasing, SuperSampling, can solve this problem in a way. SuperSampling renders each entire frame at a higher resolution then blends the colour and shade of areas where there is a large amount of difference between pixels, then re-renders the image at the display resolution. Supersampling does not care whether it is blending pixels at the edges of polygons or in the middle of them. The disadvantage though, is that supersampling incurs a huge performance hit, making it difficult to justify.

nVidia's TRSS and TRMS AA technologies provide a more elegant solution. Transparency Adaptive Multi-sampling performs the same AA operations as conventional multi-sampling does, blending pixels on the edges of polygons. It then goes one step further by examining each polygon for pixels with alpha (transparency) information. If it finds them, it applies AA to the pixels adjacent to the transparent areas too.

As far as we can tell, Transparency adaptive SuperSampling performs simple multi-sampling on most of the image as normal, but applies full supersampling to polygons with alpha pixels in them. This results in higher image quality and a larger performance hit than TRMS.

In all, TRSS and TRMS seem like a sensible upgrade to current AA technologies, enabling better all-around image quality without the performance hit associated with full supersampled AA. Games like Far Cry and Half-Life 2 should benefit considerably from nVidia's new tech.

SLI of the future

The GeForce 7800GTX will be fully SLI compatible, as evidenced by the reference card. The potential of this unholy union should have game fanatics drooling. Apparently, future versions of nVidia's Forceware will also allow SLI with cards from different manufacturers (provided they use the same GPU). With the current drivers, this is possible but not all the time.

Also in store for SLI enthusiasts with future Forceware versions is a new 16xAA mode. The video memory requirements for 16xAA are huge, so it's no surprise that nVidia has chosen to restrict it to SLI. Once we begin to see videocards shipping with 512MB of memory as a standard, 16xAA might move into the mainstream.

Purevideo: not new, but improved

The nVidia PureVideo video capture/playback technology that debuted on the 6xxx line of GPUs is back on the 7800 with some enhancements and a new feature. The new feature is High-Definition Spatial-Temporal De-Interlacing , a mouthful which boils down to better high-definition video playback.

The additional horsepower of the 7800GPU is used to improve other facets of video playback and capture also, which should lead to the new graphics processor being a mean multimedia machine.

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Contents of Article: Nvidia GeForce 7800GTX
 Pg 1.  Introduction to the nVidia GeForce 7800GTX Series
 Pg 2.  Smoke and mirrors = eye candy
 Pg 3.  — Polygons and SuperSampling
 Pg 4.  Power draw and Windows Longhorn

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   10 / 15 / 2019 | 4:57PM
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