13.3.5.3.1 Arithmetic Mean

The arithmetic mean simply takes an average of the pixels in the kernel. Each element in the filter is equal to $1$ divided by the total number of elements in the filter. Thus the 3x3 arithmetic mean filter is:

$$\left[ \begin{array}{r r r} \frac{1}{9} & \frac{1}{9} & \fra... ...rac{1}{9} & \frac{1}{9} & \frac{1}{9} \\ \end{array} \right]$$