Logan Leonhart said:
Ummm...what´s the difference between linear, bilinear and trilinear filtering?
"Linear" filtering (point sampling) is like what you see in old Software 3D games (DOOM, Duke Nukem), and PSX. Basically the textures aren't filtered in any way at all, the video engine just takes one texel from the applicable texture, that being the 'best fit' for the pixel being shown. This leads to textures being REASONABLE at certain distances, shimmery like nothing else at a distance, and severely blocky up close.
Bilinear filtering takes a broader approach; instead of just taking the one 'best fit' sample, it takes the FOUR nearest samples and blends them together. This results in textures looking pretty decent at range, very good at the right distance, and blurry but still OK up close. Every 3D-accelerated game uses this, and consoles starting with N64 do, too.
There's a technique which can be used to improve speed and quality a little bit called MIP mapping, basically what this does is it stores textures at 1/4, 1/16, etc. the size of the original texture, and uses different quality levels at a distance. The end result of MIP mapping is a decent performance gain in some cases, and a more realistic effect of surfaces having less visible detail at range.
There's a catch to MIP mapping though: used with bilinear filtering, there are VERY noticeable 'bands' between MIP map quality levels... so for a short distance around you, things will be very sharp and hi-Q, but then after a short distance the sharpness will abruptly become blurred.
The answer to this is TRIlinear filtering. Trilinear filtering works exactly the same as bilinear filtering (4 samples per MIP level), BUT to combat the MIP map bands, it takes four samples from TWO adjacent quality levels (so basically 8 samples instead of 4). This results in the error between the MIP levels being spread out very evenly and making the transition from very sharp to very blurry a very smooth one