title: How to determine the window size of a Gaussian filter
body: <p>Gaussian smoothing is a common image processing function, and for an introduction of Gaussian filtering, please refer to <a href="http://homepages.inf.ed.ac.uk/rbf/HIPR2/gsmooth.htm" rel="noreferrer">here</a>. As we can see, one parameter: standard derivation will determine the shape of Gaussian function. However, when we perform convolution with Gaussian filtering, another parameter: the window size of Gaussian filter should also be determined at the same time. For example, when we use <code>fspecial</code> function provided by MATLAB, not only the standard derivation but also the window size must be provided. Intuitively, the larger the Gaussian standard derivation is the bigger the Gaussian kernel window should. However, there is no general rule about how to set the right window size. Any ideas? Thanks!</p>