Question
I am using the Canny edge detection method on an image. I am setting the threshold values myself. I have a grayscale image with pixel values in the range 0 to 255. I have a current threshold range of [0.1 0.15] for the image. My question: what do these two numbers actually mean? (i.e. do they represent a percentage value? so if the pixel value is 15% of 255 it turns it into an edge? This doesnt really make sense as 15% is very low compared to the pixel value that is getting considered an edge in the image)
Expert Answer
John Williams
PhD Expert
Answered Aug 20, 2026
The 'Canny' method uses two thresholds.
For example, if the threshold is [0.1 0.15] then the edge pixels above the upper limit(0.15) are considered and edge pixels below the threshold(0.1) are discarded.
Now, you may have a question "what about the pixels in between upper and lower threshold"?
They are considered only if they are connected to pixels in the upper threshold. Thus we get a clean edge.
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