Adjoint filter
In signal processing, the adjoint filter mask formula_1 of a filter mask formula_2 is reversed in time and the elements are complex conjugated. Its name is derived from the fact that the convolution with the adjoint filter is the adjoint operator of the original filter, with respect to the Hilbert space formula_4 of the sequences in which the inner product is the Euclidean norm. The autocorrelation of a signal formula_6 can be written as formula_7.