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Old 07-07-04, 09:42 PM   #1
ChrisRay
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Join Date: Mar 2003
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Arrow NV40 anisotropic filtering investigation



NV40 Filtering Investigation



Test Setup

Athlon XP 3200+ Barton
2.2 Ghz 400 FSB
Geforce 6800NU (325/850)
2x512 DDR400 (Dual Channel)
Albatron KX18D Pro II (Nvidia Nforce 2 400 Ultra)
Nvidia Forceware 61.45 drivers.




Initial Impression: Owners Nv40 line of graphic cards will be quick to notice that these cards are very configurable in regards to anisotropic filtering and texture filtering, The modes include, High Performance, Performance, Quality, and High Quality, Included into these modes is the ability to turn off trilinear optimizations and anisotropic filtering optimizations. The purpose of this analysis is to help the Nv40 users sort out which modes are usable to them and which are not.

Quick Notes


Bilinear Texture Filtering: Bilinear filtering is a computationally cheap but low quality texture filtering. It approximates the gaps between textures by sampling the color of the four closest (above, below, left and right) texels. All modern 3D accelerated video cards can do bilinear filtering in hardware with no performance hit.


Trilinear Texture Filtering: Trilinear filtering is a high quality bilinear filter which uses the four closest pixels in the second most suitable mip map to produce smoother transitions between mip map levels. Trilinear filtering samples eight pixels and interpolates these before rendering, twice as much as bi-linear does. Trilinear filtering always uses mip mapping. Trilinear filtering eliminates the banding effect that appears between adjacent MIP map levels. Most modern 3D accelerated video cards can do trilinear filtering in hardware with no performance hit. Anisotropic filtering is a different story.


Anisotropic Filtering: Anisotropic filtering is the best but most CPU intensive of the three common texture filtering methods. Trilinear filtering is capable of producing fine visuals, but it only samples from a square area which in some cases is not the ideal way. Anisotropic (meaning `from any direction') samples from more than 8 pixels. The number of sampled pixels and which sampled pixels it uses depends on the viewing angle of the surface relative to your screen. It shines when viewing alphanumeric characters at an angle

Mip Mapping: Mip mapping is a technique where several scaled copies of the same texture are stored in the video card memory to represent the texture at different distances. When the texture is far away a smaller version of the texture (mip map) is used. When the texture is near, a bigger one is used. Mip mapping can be used regardless of filtering method (see below). Mip mapping reduces memory bandwidth requirements since the images are in hardware, but it also offers better quality in the rendered image

Brilinear: Net Slang, This is a method where you use less than trilinear filtering, But more than bilinear filtering, Ideally this causes the GPU to do less work while still providing trilinear Quality


Keeping it Simple: Mipmaps join textures together. The Purpose of Bilinear/Trilinear filtering is to help join these mipmaps together. Trilinear filtering will generally hide these transitions better than Bilinear. When seeing these mip map transistions in motion. You will see rolling textures, also known as "Shimmering". To reduce the amount of texture shimmering trilinear filtering is reccomended. Take note of how the transistion will seem much softer with trilinear enabled. All Shots were taken with 4x Anti Aliasing enabled and 1024x768 resolution.






Image Quality Settings




High Performance: Highly optimised trilinear filtering. This mode is pretty much pure bilinear with texture stage optimizations enabled, With texture optimizations disabled there appears to alot of quasi trilinear filtering occuring.

Note:Turning on anisotropic optimizations makes this mode function as as pure bilinear. With anistropic filtering optimizations off there appears to be alot of quasi trilinear filtering occuring.

Performance: High optimised trilinear filtering. This mode is pretty much pure bilinear with texture stage optimizations enabled, With texture optimizations disabled there appears to alot of quasi trilinear filtering occuring. This mode appears to be less aggressive than High Performance mode.

Note: Turning on anisotropic optimizations makes this mode function as as pure bilinear. With anisotropic filtering optimizations off there appears to be alot of Quasi Trilinear filtering occuring.


Quality: The mode most NV40 users are likely to use. This mode by default employs trilinear optimisations. Also known as as "Brilinear".

Note: By default Brilinear filtering is enabled, You can disable it by using the advanced tab in the control panel and switching trilinear optimizations off. Texture stage optimizations are currently default disabled. You can switch them on or off by using the advanced tab in the control panel.


High Quality: This mode removes all optimizations from texture filtering. Full Trilinear is employed with no texture stage optimizations. Also Bilinear filtering is performed on all other textures.

Note: All optimizations are unchangable with this mode enabled, You cant enable trilinear optimizations or anistropic optimizations.



Image Quality Investigation





Purpose: The purpose of this investigation is to give the user a better idea of what to expect from Nvidias various anisotropic filtering modes. Included within the comparisons are png shots of Unreal Tournament 2003 with colored mip maps enabled and without colored mip maps. Keep in mind that still screenshots do not always illustrate the difference between bilinear and trilinear anisotropic filtering. These differences can be seen in motion. The purpose of the colored mip maps is to illustrate the transistion that can be seen between each shifting mip map.


8x Anistropic Filtering





High Performance

8x High Performance AF with colored mip maps enabled.

8x High Performance AF with colored mip maps disabled

8x High Performance AF (tril opts off) with colored mip maps enabled

8x High Performance AF (tril opts off) with colored mip maps disabled

8x High Performance AF (AF opts on) with colored mip maps enabled

8x High Performance AF (AF opts on) with colored mip maps disabled


Performance

8x Performance AF with colored mip maps enabled

8x Performance AF with colored mip maps disabled

8x Performance AF (tril opts off) with colored mip maps enabled

8x Performance AF (tril opts off) with colored mip maps disabled

8x Performance AF (AF opts on) with colored mip maps enabled

8x Performance AF (AF opts on) with colored mip maps disabled


Quality

8x Quality AF with colored mip maps enabled

8x Quality AFwith colored mip maps disabled

8x Quality AF (tril opts off) with colored mip maps enabled

8x Quality AF (tril opts off) with colored mip maps disabled

8x Quality AF (tril opts disabled) (AF opts enabled) with colored mip maps enabled

8x Quality AF (tril opts disabled) (AF opts enabled) with colored mip maps disabled


High Quality

8x High Quality with colored mip maps enabled

8x High Quality with colored mip maps disabled




16x Anistropic Filtering





High Performance

16x High Performance AF with colored mip maps enabled

16x High Performance AF with colored mip maps disabled

16x High Performance AF (tril opts off) with colored mip maps enabled

16x High Performance AF (tril opts off) with colored mip maps disabled

16x High Performance AF (AF opts on) with colored mip maps enabled


16x High Performance AF (AF opts on) with colored mip maps disabled


Performance

16x Performance AF with colored mip maps enabled

16x Performance AF with colored mip maps disabled

16x Performance AF (tril opts off) with colored mip maps enabled

16x Performance AF (tril opts off) with colored mip maps enabled

16x Performance AF(AF opts on) with colored mip maps enabled.

16x Performance AF(AF opts on) with colored mip maps disabled.


Quality

16x Quality AF with colored mip maps enabled

16x Quality AF with colored mip maps enabled

16x Quality AF (tril opts off) with colored mip maps enabled

16x Quality AF (tril opts off) with color mip maps disabled

16x Quality AF (tril opts off) (AF opts on) with colored mip maps enabled

16x Quality AF (tril opts off) (AF opts on)with colored mip maps disabled)

High Quality

16x High Quality AF with colored mip maps enabled

16x High Quality AF with colored mip maps disabled



Minor Note: One thing to note is the effect texture stage optimisations have on the filtering. This optimization is not enabled by default. However under many circumstances this optimization can be used without effecting image quality and increasing performance. Under most circumstances I keep it turned off.



Performance Analysis





Performance: To conduct the tests I used the DM Antalus map in unreal tournament 2003. I used fraps and took 3 preset runs through antalus and then divided the results by three to reduce margin of error.








Conclusion



Conclusion: Does anyone remember the Geforce 2 days? There was one setting for anisotropic filtering and thats all we used. Tweaking modern day graphic cards can be a chore. With all the buzz circling the latest trilinear optimizations going on in graphic cards Nvidia has stepped forth and allowed users the ability to disable them. Nvidia currently offers the most tweakability with its image quality settings. Die hard image quality freaks and performance enthusiasts alike will easily be able to find a setting that suits them.
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Nzone
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NVIDIA User Group Members receive free software and/or hardware from NVIDIA from time to time to facilitate the evaluation of NVIDIA products. However, the opinions expressed are solely those of the members

Last edited by ChrisRay; 07-14-04 at 08:22 PM.
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