Question
Hi all, i try to detect the edges of my image. I use canny edge detector. Then i tried [c,r]=find(Image==1) to detect the white pixels. I thought in a b/w image the edges would be the white pixels, but this not works quite good. For example the vector with the coordinates is the follwing: I made a grid for every pixel in image using the method that Steves proposed As you can see the first pixel [64,2] is not laying on a white pixel while some other are on whites. Does anyone have any idea why this is happening? Are the edges on a binary image the white pixel or not? If yes then why i get also black pixels coordinates.
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Expert Answer
Neeta Dsouza
PhD Expert
Answered Nov 20, 2025
I suspect you're getting confused with your coordinates. In particular, the names of the variables in your line:
[c, r] = find(...rest does not matter
are very misleading, as c is going to be the rows and r the columns where white pixels are found. Typically, one writes:
[r, c] = find(...rest does not matter.
Also, note that the upper left corner of the image is (1, 1) not (0,0). find returns matrix indices which are 1-based.
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