OpenGL also provides a number of filtering methods to compute the texel value. There are separate filters for magnification (many pixel fragment values map to one texel value) and minification (many texel values map to one pixel fragment). The simplest of the filters is point sampling, in which the texel value nearest the texture coordinates is selected. Point sampling seldom gives satisfactory results, so most applications choose some filter which does interpolation. For magnification, OpenGL 1.1 only supports linear interpolation between four texel values. Some vendors have also added support for bicubic filtering in which the a weighted sum of 4x4 array of texels is used (Filter4 is a more appropriate name for it since it is only performing cubic filtering when used as a magnification filter). For minification, OpenGL 1.1 supports various types of mipmapping [51], with the most useful (and computationally expensive) being trilinear mipmapping (4 samples taken from each of the nearest two mipmap levels and then interpolating the two sets of samples). OpenGL does not provide any built-in commands for generating mipmaps, but the GLU provides some simple routines for generating mipmaps using a simple box filter.