OpenGL Programming Guide: The Official Guide to Learning OpenGL, Version 4.3, Eighth Edition

Filtering

Texture maps may be linear, square, or rectangular, or even 3D, but after being mapped to a polygon or surface and transformed into screen coordinates, the individual texels of a texture rarely correspond directly to individual pixels of the final screen image. Depending on the transformations used and the texture mapping applied, a single pixel on the screen can correspond to anything from a tiny portion of a single texel (magnification) to a large collection of texels (minification), as shown in Figure 6.14. In either case, it’s unclear exactly which texel values should be used and how they should be averaged or interpolated. Consequently, OpenGL allows you to specify any of several filtering options to determine these calculations. ...