algorithm to implement 'fspecial' function for motion blur.

Hello. I found a code to implement 'fspecial' function for motion blur as follows. https://kr.mathworks.com/matlabcentral/fileexchange/16201-toolbox-image?focused=5133070&tab=function The result of the code is same as one of the matlab function 'fspecial('motion',).

It seems that distance from each pixel to the rotated line is used. However, I could understand it only a little. Is there any documentation or figure to understand it?

Thank you for your time.

[John D'Errico]

You should contact the author.