MATLAB: Purpose of ceil in fspecial

fspecial

These are few lines from a code:
s=3;
M=imread('I.jpg');
I=rgb2gray(M);
%filter
h=fspecial('gaussian',ceil(4*s),s);
I need to know that what is the purpose of ceil in fspecial? What is it going to do?

Best Answer

They wanted to specify s, and the second arg must be an integer. They could have done int32(4*s) or floor(4*s) but for whatever reason they chose ceil. They wanted it to be at least as wide as 4 std dev's with the requirement that it be an integer because it's a window size in pixels. As you can find in the help for ceil(), it rounds up to the next highest integer value.
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