Difference between the option 'log' and 'zerocross' of function edge?

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Nina 2014-9-29

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评论： Sarah Agnalt 2016-8-11

Hi,

I use the Matlab function edge and I want to know the differences between the option 'log' and 'zerocross' when I use for 'zerocross' the default filter? (BW=edge(I,'log'); BW=edge(I,'zerocross');)

I think the default filter of the option 'zerocross' is 'log'. Are the results the same or are there differences in the calculation of the edges?

Thanks!

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Answer 1

Anand 2014-9-29

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The 'log' method is a specific type of zero-crossing edge detector, where the image is filtered with the Laplacian of Gaussian filter obtained as follows:

>> fspecial('log')

ans =

0448    0.0468    0.0564    0.0468    0.0448
0468    0.3167    0.7146    0.3167    0.0468
0564    0.7146   -4.9048    0.7146    0.0564
0468    0.3167    0.7146    0.3167    0.0468
0448    0.0468    0.0564    0.0468    0.0448

The syntax for 'zerocross' from the documentation of edge is as follows:

BW = edge(I,'zerocross',THRESH,H)

If you do not provide a zero crossing filter kernel H, the Laplacian of Gaussian kernel is used by default. This is why 'zerocross' and 'log' methods will give the same result if you do not specify a filter kernel.