In many image processing applications, geometrical transformations facilitate processing. Examples are image restoration , where one frequently wants to model the degradation process as space-invariant, or the calibration of a measurement device, or a correction in order to remove a relative movement between object and sensor. The a ij , b ij , are usually found by some fitting method. This resampling can be done using different methods. The simplest one is the nearest-neighbour interpolation.
Bilinear interpolation uses a weighted average of the four nearest pixels.
The four unknowns a , b , c , d are determined from the four known nearest neighbours, and then used to obtain g 0 .