17
Interest point detection algorithm
for window of size w x w
for each pixel [r,c] in image I
   if I[r,c] is not a border pixel and
      interest_operator(I,r,c,w)  ³  threshold
   then add [(r,c),(r,c)] to set of interest points
procedure interest_operator(I, r, c, w) {
   v1 = intensity variance of  horizontal pixels I[r,c-w]…I[r,c+w]
   v2 = intensity variance of vertical pixels I[r-w,c]…I[r+w,c]
   v3 = intensity variance of diagonal pixels I[r-w,c-w]…I[r+w,c+w]
   v4 = intensity variance of diagonal pixels I[r-w,c+w]…I[r+w,c-w]
   return minimum(v1, v2, v3, v4) }
The second (r,c) is a
placeholder for the
end point of a vector.