Texture Filtering Quality & Analysis
Here's some sample filtering outputs from SS:SE...
Aggressive - No Anisotropic Filtering
Aggressive - 8X Anisotropic Filtering
Balanced - No Anisotropic Filtering
| Application - No Anisotropic Filtering | |
Application - 8X Anisotropic Filtering
The colour texture filtering images here tell us quite a lot about the filtering that's being used here.
The first thing to note its that 'Application' is the one that appears to be doing 'True' Trilinear filtering. Also, we can see that its filter kernel is very similar to that of GeForce4, with the curved mip-map boundary. With 8x AF enabled we can see that the curved boundary remains, and the mip-map transitions are pushed quite far back, as we would expect.
When we look at the 'Balanced' mode we notice that the Trilinear filtering has become a lot 'looser' - where we would expect Trilinear filtering to always be blending mip-map levels we can see that large portions of the mip-map levels consist of only one unblended colour, which means it's only sampling from one mip-map level. Also, where the filtering kernel starts out as curved without AF applied, it has flattened out with 8x, and the mip-map transitions are pushed a little forward in comparison to the 'Application' mode.
The Agressive mode takes what was seen with Balanced even further. The Trilinear blending transitions are so small its tantamount to Bilinear filtering. Again, with 8x AF allied there is a straight line at the first mip-map transition, as opposed to curved, and the mip-maps are pushed further forward again.
Let's take another look at the filtering methods used with "samX"'s Anisotropic Filtering Test application. We'll take samples from all the available AF levels, and the 'Application' setting is on the left, the 'Balanced' in the center column, and 'Aggressive' on the right.
1x (None) Anisotropic Filtering
2x Anisotropic Filtering
4x Anisotropic Filtering
8x Anisotropic Filtering
These images from the filtering test output highlight what we saw under the SS:SE screenshots. Under 'Application' mode we see that the GeForce FX's filtering is behaving very much as it did with GeForce4. Under The Balanced and Aggressive modes we can see that as the degree of filtering increases the filtering kernel is much squarer. With these modes less is actually being filtered with high LOD mip map levels - with the 'Aggressive' mode there is only a tiny fraction of different filtering different between 4x and 8x. Bearing in mind that the most notable area of filtering is between the first and second mip-map levels, there may not appear to be too much difference between 2x and 4x Aggressive modes during gameplay.
Looking at the difference between the 1x Balanced and Application modes we can clearly see that the Balanced mode is not accurately Trilinear filtering. Something to bear in mind is that 'Balanced' is the default setting, and all the games testing was done in this mode, which is not a fully accurate Trilinear Filtering mode.
