Matlab: obtaining the normals of binary image contour points

Context

I have a binary image of a silhouette that I wish to add noise to. The noise should be added only to the contour of the silhouette. I would like the noise to be a vector that is added to each contour point, with the length of the vector being sampled from a Gaussian distribution with zero-mean and a variance of x% of the silhouette height. The direction of the vector should be the normal of the given contour point.

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Question

In Matlab, given a binary image, how do I obtain the normals of the contour points?

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Use bwboundaries to obtain the contour (i.e. the sequence of points which make the contour). Since you have the sequence of points thanks to bwboundaries, we can now define 3 points A,B,C where B is between A and C and we want to find the normal at B which is given by:

N = [Ay - Cy;Cx - Ax]';