The Sobel and Scharr first derivative operators are to be used to take the x and y derivatives of an image. Then a small region of interest (ROI) is to be defined to detect corners in.

A 2x2 matrix of sums of the

x

and

y

derivatives is created as follows:

Solving where λ is a column vector of the eigen values and

I

is the identity matrix, gives the eigen values. For the 2x2 matrix of the equation above, the solutions may be written in a closed form:

If

λ

1

,

λ

2

>

t

, where

t

is some threshold, then a corner is considered to be found at that location. This can be very useful for object or shape recognition.