Nicolas Alvarez wrote:
> I never understood what anisotropic filtering *is*...

  It's related to texturing with bitmaps.

  Regular trilinear filtering (ie. bilinear filtering + mipmapping +
interpolating between mipmaps) works perfectly when the surface being
rendered is parallel to the viewing plane, that is, the texture pixels
are square when projected on screen.

  A problem happens when the surface being rendered is at a high angle
with respect to the viewing plane: In this case the texture pixels, when
projected onto the screen, are very elongated, far from square. This
presents a problem: Which mipmap level to choose? In one direction a
more detailed mipmap would be required, but in the other direction a
much coarser one. If you choose a mipmap which is too detailed, it will
introduce ugly moire patterns. If you choose a mipmap which is too
coarse, the texture will be unnecessarily blurred.
  Most implementations go for the unnecessarily-coarse solution, which
means that textures at steep angles will usually look quite blurred.
(I suppose the rationale is that blurring doesn't look as bad as
flickering moire patterns.)

  Anisotropic filtering is a technique which solves this problem, at the
cost of extra calculation time required.

Post a reply to this message