When the Retina eye sends neural impulses to the brain signalling an image, it spatially encodes (compresses) them to match the optic nerve's limited ability. Compression is quite necessary because there are 100 times more photoreceptor cells compared to the ganglion cells. This is caused by "decorrelation," which is carried out by the "center-surround structures" that are implemented by the ganglion and bipolar cells.