CORF uses as input the responses of center-on and center-off difference of Gaussians (DoG) operators. It achieves orientation selectivity by combining responses of DoG operators that are aligned in a colinear manner at a given orientation.
Besides orientation selectivity, the CORF operator achieves contrast invariant orientation tuning, cross orientation suppression and response saturation, typical properties of simple cells.
You are kindly invited to use this Matlab script and cite the following article:
George Azzopardi and Nicolai Petkov, "A CORF computational model of a simple cell that relies on LGN input outperforms the Gabor function model", Biological Cybernetics, vol.106(3), pp.177-189, 2012.
Paper [pdf]: http://link.springer.com/content/pdf/10.1007%2Fs00422-012-0486-6.pdf