# Kernel Sizes

You specify the Gaussian kernel size by providing a smoothness value corresponding to the feature size, in pixels, below which you wish to smooth. The relationship between the smoothing value you specify and the size of the resulting Gaussian curve given by the following formula:

where s is the smoothing value and σ is the standard deviation of the resulting curve. The size of the Gaussian kernel itself is then computed using the following formula:

where s is the smoothing value.

Note: You can specify independent values for smoothing in the x- and y-directions, so the kernel might not be square.

Smoothing | Sigma (s) | Kernel Width
--- | --- | ---
1 | .866 | 4
2 | 1.414 | 7
3 | 1.936 | 10
4 | 2.449 | 13
5 | 2.958 | 16

In general, you should start with a smoothing value of 1 or 2 and increase it until you obtain the desired smoothing.