Retina and LGN: Early Vision Using Gaussian Filters
This Demonstration shows the retinal/LGN receptive fields of the visual system. Center-on receptive fields consist of a central excitatory spot surrounded by an inhibitory ring (and vice versa for their center-off cousins). These are readily modeled using a difference of Gaussians (DoG) filter . Here, the top image on the left shows the filter, with red representing positive values, blue negative and white 0. The bottom image on the left shows the power spectrum of the filtered image. The image on the right is the result of convolution of an image from , with the filter superimposed for size reference. Use the controls to set the size and polarity of the filter. As you increase the scale past 5, the image switches from Albert Einstein to Marilyn Monroe.
 D. Marr and E. Hildreth, "Theory of Edge Detection," Proceedings of the Royal Society B: Biological Sciences, 207(1167), 1980 pp. 187–217. doi:10.1098/rspb.1980.0020.
 A. Oliva, A. Torralba and P. G. Schyns, "Hybrid Images," ACM Transactions on Graphics: Proceedings of ACM SIGGRAPH 2006, 25(3), 2006 pp. 527–532. doi:10.1145/1141911.1141919.