Get coordinates of edges - Image Processing

Lets say image_test is the output binary image (After Roberts Method)

data=corner(image_test);
r_data=data(:,1);
c_data=data(:,2);

min_colm=min(c_data);
idx1=find(c_data==min_colm);
ver1=[r_data(idx1(1)),min_colm]

max_colm=max(c_data);
idx2=find(c_data==max_colm);
ver2=[r_data(idx2(1)),max_colm]

min_row=min(r_data);
idx3=find(r_data==min_row);
ver3=[min_row,c_data(idx3(1))]

max_row=max(r_data);
idx4=find(r_data==max_row);
ver4=[max_row,c_data(idx4(1))]