cant find the white pixels

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.