Canny Edge Detection Threshold Values Meaning

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Chloe O'Mahony - 2023-03-13T15:14:47+00:00
Question: Canny Edge Detection Threshold Values Meaning

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)

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    • Expert Answer

    Profile picture of John Williams John Williams answered . 2025-11-20

    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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