Best value for threshold in Canny

Question

I have an image which I want to detect edges on that. I found Canny has been used a lot ( I don\'t know whether I have a better option than that). I have set the values as f

Answer 1

I think this should be taken case by case, if you post some sample images would be useful, but I will try to answer anyways. Here is from Opencv Documents

Canny( detected_edges, detected_edges, lowThreshold, lowThreshold*ratio, kernel_size );
where the arguments are:

detected_edges: Source image, grayscale
detected_edges: Output of the detector (can be the same as the input)
lowThreshold: The value entered by the user moving the Trackbar
highThreshold: Set in the program as three times the lower threshold (following Canny’s recommendation)
kernel_size: We defined it to be 3 (the size of the Sobel kernel to be used internally)

What usually works for me is highThreshold = 255 and lowThreshold = 255/3