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)

[darova]

Here is a screenshot from edge function

• I have a current threshold range of [0.1 0.15] for the image.

Also threshold value is a single value (not range)

Answer 1

[Aakash Mehta]

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.

For more details, refer to input arguments section of below link.

https://www.mathworks.com/help/images/ref/edge.html

[darova]

thank you