Specifying the Kernel Size

You specify the Gaussian kernel size by providing a smoothness value. The smoothness value should correspond to the feature size, in pixels, below which you wish to attenuate features.

The relationship between the smoothing value you specify and the resulting Gaussian curve’s size is given by the following formula:

where s is the smoothing value and s 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, accordingly, the kernel might not be square.

The table below gives the sigma size and kernel width for several smoothing values.

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

Sigma size and kernel width

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