MATLAB: How to follow only the black line of an image

Question

I want to follow the black line on this image and get the x,y coordinates of it. However if the black line is not completing an edge of an image (as an extra line extruded as shown) I want to neglect those pixels. I want it to work similar to the concept of line following robot where it checks the next two pixel around it in each direction and maybe decide which pixel's [x,y] values it needs to consider

Answer 1

I = imread('1.png') ;
I1 = rgb2gray(I) ;
[y,x] = find(I1==0) ;

(x,y) are the locations of the black line. Now you have the points in hand. You can do what you want.