[Octave-bug-tracker] [bug #46547] image package: canny detector in edge() should use LoG as first step

[Hartmut]

Follow-up Comment #7, bug #46547 (project octave):

Please find attached a new PATCH. It includes the mentioned changes of my last
two posts in a more orderly form.

Please
* test this patch if it improves the situation of this bug report
* has any other side effectcs

I have observed that this patch mostly fixes the original bug report: 
* The resulting edge image is already quite nice if you give the explicit
threshold values (values probably chosen for Matlab) of post 1.
* If you then fine tune the threshold values for Octave, e.g. to threshold =
0.3, then you will get results that are as good in quality as the Matlab
results (but not identical).
* If you dont't give any thresholds manually, then you will get a worse result
(I don't know what Matlab will give you, but probably also a worse result).
But you can already anticipate the correct edge contours and only need to fine
tune the manual threshold values (which is the normal workflow).

The main remaining difference to the Matlab implementation of the Canny edge
detector seems to be the automatic guessing of threshold values, if the user
doesn't give them explicitly. Octave currently guesses those automatic
thresholds values via the mean of the edge strength in the image. I think that
Matlab has some algorithm for this to have a certain percentage of the image
pixels as edges. But as I said before I don't think it's worth to perfectly
mimic this Matlab behavior as well.

(file #35672)
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Additional Item Attachment:

File name: edge_canny_fix-integers-etc.patch Size:2 KB


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