Difference of Gaussian vs LoG

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RuiQi 2016-4-9

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/278120-difference-of-gaussian-vs-log

编辑： RuiQi 2016-4-9

Hello

I am trying to approximate the log using the dog but i am not getting the right results. The notes here mention that it can be approximated by setting the sigma as shown below. I did a surf plot of the log and dog i constructed but they were not close. Also, the log generated by fspecial does not sum up to zero.

sigma = 5;
sigma1 = sigma/sqrt(2);
sigma2 = sigma*sqrt(2);
LoG = fspecial('log', 2*floor(3*sigma)+1, sigma);
% Generate LoG
DoG1 = fspecial('gaussian', 2*floor(3*sigma1)+1, sigma1);
DoG2 = fspecial('gaussian', 2*floor(3*sigma2)+1, sigma2);
DoG = DoG1 - DoG2;