Canny Edge detector threshold values gives different result

Question

I am trying to find contour of a image, before that I am applying Canny\'s edge detector. It\'s giving different result for different images.For one image it\'s giving perf

Answer 1

In laymen terms, edge detection needs a threshold to tell what difference/change should be counted as edge. For details read here.

So, the edges depend on the the content of image ie the level of brightness/darkness/contrast. I suggest you to simply find the mean of whole gray image and take threshold as follows:

min_threshold = 0.66 * mean

max_threshold = 1.33 * mean

I have tested it and it gives impressive result. You can use median instead of mean, with almost same result. Another alternative is to first equalize the image and then try threshold of your choice/experimental.

But again again strongly recommend to try mean method. In case of any query, write here.

Happy Coding :)