Trilinear filtering

Bilinear sampling fixes magnification but leaves a visible line on the ground where the GPU jumps from one mipmap to the next — a sharp band that crawls as the camera moves. A third linear interpolation, this time across the two nearest mip levels, dissolves that band into a gradient. It costs eight texel fetches per sample instead of four. The technique goes back to Lance Williams' 1983 mipmap paper and became hardware-standard in the late 1990s. It still blurs textures viewed at grazing angles, which is the exact problem anisotropic filtering was built to solve.