Smooth

Smoothing is implemented as simple convolution in which the convolution matrix is a matrix of constant, i.e., every pixel is replaced by the average of its nearest nine neighbors

$\displaystyle \left[\vphantom{ \matrix{ 1 & 1 & 1 \cr
1 & 1 & 1 \cr
1 & 1 & 1 \cr } }\right.$$\displaystyle \matrix{ 1 & 1 & 1 \cr
1 & 1 & 1 \cr
1 & 1 & 1 \cr } $$\displaystyle \left.\vphantom{ \matrix{ 1 & 1 & 1 \cr
1 & 1 & 1 \cr
1 & 1 & 1 \cr } }\right]$$\displaystyle \ceqno$