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Sharky Extreme : December 3, 2008





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MATROX G400's 3D capabilities are feature complete in comparison with current accelerators. There is, however, widespread variation in the implementation of mip-mapping and trilinear filtering among different accelerators. Screen captures of 'Quake3 Test' show up differences among G400, TNT2 and Savage4. Although not shown here, these differences are present in Unreal as well.

Below is a thumbnail of a scene from 'Quake3 Test Ver 1.06' which was originally captured at 1024x768x32, using 32-bit textures set to maximum quality. The boxed region is then shown at actual size as rendered on the G400, TNT2 and Savage4, comparing Trilinear and Bilinear modes for each.


Thumbnail of scenario in Quake3 Test
Actual resolution: 1024x768x32

G400 employs 'per pixel mip-mapping' which gives rise to horizontal 'mip-banding' as shown below. 'Mip-banding' is a set of artifacts that occur when there is an abrupt transition from one mip-map level to another. Trilinear filtering is a technique to remove 'mip-banding' artifacts introduced by mip-mapping. With trilinear filter switched on, 'mip-banding' is effectively removed.


Trilinear filter - G400

Bilinear filter - G400

TNT2 uses 'trilinear dithering' which actually introduces dithering artifacts. In addition, the 'mip-band' is sloped, resembling 'per triangle mip-mapping'. Compared to 'per pixel mip-mapping', 'per triangle mip-mapping' requires less computation and is therefore easier to implement. However, the results are not quite as visually appealing as 'per-pixel mip-mapping'.


'Trilinear dithering' - TNT2
OpenGL quality set at maximum

Bilinear filter - TNT2

Savage4 produces a horizontal 'mip-band' that is characteristic of 'per pixel mip-mapping'. Of the three, Savage4's mip-map implementation has the least 'blurring'. Notice the clearly defined tiles at the far end of the narrow path.


Trilinear filter - Savage4

Bilinear filter - Savage4

On to the benchmarks.





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