文件说明：
canny.m ------- canny边缘检测函数， function e = canny(Im,sigma,fsize,lowThresh,highThresh)
参数为：
% Im ------- the input gray image.
% sigam ------- the gaussian filter's standard deviation.
% fsize ------- the gaussian filter's size,i.e,[fsize,fsize].
% lowThresh ------- input lower thresh value.
% highThresh ------- input high thresh value.
% e ------- output edge image which is a binary image.
cannytest.m ------- 利用canny函数对lena图形进行边缘检测。
