A pair of on-center and off-center filters derived from the first absolute central moment - A pair of on-center and off-center filters

Due to the absolute value involved, the first absolute central moment can be divided into two complementary filters: a positive deviation e(p) and a negative deviation e(n). The architectures of e(p) and e(n) and their responses to luminous stimuli recall the separation of the ganglion cells into on-center and off-center cells. Once e(p) and e(n) are computed separately both a first derivative operator and a second derivative operator can be obtained with the same filtering stage. A ridge map similar to the ridge map provided by a GoG filter is obtained by subtracting the negative deviation e(n) from the positive deviation e(p). Instead, the sum of e(p) and e(n) provides the same map which is obtained with a DoG filter.