cant find the white pixels

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pasta pontikaki 2019-4-2

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评论： pasta pontikaki 2019-4-4

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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Answer 1

Guillaume 2019-4-2

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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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Guillaume 2019-4-2

An edge does not have a colour. An edge (in a binary image) is the transition from black to white or white to black. Matlab The resulting edge image will have the edges shown in white indeed. Which side of the edge is actually set to white depends on the algorithm you use.

pasta pontikaki 2019-4-4