 formula_211 is also called the mapping function.The values of formula_213 can be obtained from the values of the 1_D prototype formula_214.The conditions for choosing
the mapping function are
Considering a two dimensional case to compute the size of formula_215, If the 1-D prototype has size formula_216 and the mapping function has size formula_217,then the size of the desired formula_215 will be formula_219

The main advantages of this method are

Methods such as Convolution or implementation using the DFT can be used for the implementation of FIR filters.