Description of the Harris operator from Spring 05's version of the assignment page
In this step, you will identify points of interest in the image using the Harris corner detection method. The steps are as follows (see the lecture
slides/readings for more details) For each point in the image, consider a
window of pixels around that point. Compute the
Harris matrix H for that point, defined as
where the summation is over all pixels p in the window. The upside-down Delta operator is the gradient, and Ip is the intensity at pixel p.
The weights 
should
be chosen to be circularly symmetric (for rotation invariance). A common choice
is to use a 3x3 or
5x5 Gaussian mask.
Note that H is a 2x2 matrix.
To find interest points, first compute the
corner strength function
Once you've computed c for every point in the image, choose points where c is
above a threshold. You also want c to be a local maximum in at least a 3x3
neighborhood.