Computation Order of Filtering

[Shin-ichi Maeda]

Dear CV study group members,

About the computation cost,
I forgot to take into account of the filter size.

In practice, we often use a certain small size of the filter
compared with the original image size, N, to be filtered.
When applying such a sparse filter in spatial domain,
the computation order would be O(N) not O(N^2),
which should be smaller than the computation in frequency domain
as Kourosh mentioned today.

Best,

Shin-ichi