 This makes their impulse response always absolutely summable and thus FIR filters are always stable.formula_9 is the multidimensional input signal and formula_10 is the multidimensional output signal.For a formula_11 dimensional spatial domain, the output formula_12 can be represented as

formula_13

The above difference equation can be represented in the Z-domain as follows

formula_14,

where formula_15 and formula_16 are the Z-transform of formula_17, and formula_18 respectively.