Simulated Human Vision..... Ian Overington

Location: Eastbourne. UK
ianoverington@simulatedvision.co.uk ............ www.simulatedvision.co.uk


A great deal of 2D spatial interaction occurs at the retina before data are transmitted from the eye to the brain via the optic nerve (see Chapter 2.4 & Fig. 2.2 of ‘Computer Vision ...’). Most of this spatial interaction results in a variety of difference signals, meaning that the predominant data which are transmitted onward to the visual cortex relate to relatively sudden spatial or temporal changes of light energy, but as initially softened by the relatively gross blur by the eyes' optics. The main spatial interactions may be grouped as in the following paragraphs. In all that follows it should be noted well that, because of the essentially logarithmic response of the receptors, simple differences are equivalent to ratios of incoming luminance, while simple sums are equivalent to products in terms of incoming luminance!


Local 2D interaction occurs between both individual R & G cones and local groups of R or G cones or (R + G) cones to yield Laplacian-like differencing at a variety of spatial scales and with both achromatic and chromatic properties. Because of the hexagonal packing, the ‘natural’ interaction of a unit weighting of a set of six pixels surrounding the addressed pixel becomes equivalent to what is conventionally accepted as the ‘best’ of the various Laplacian interactions for square matrices - that is, unit weightings of four adjacent pixels and 50% weightings at the four diagonal corners! (see Chapter 3.7 of 'Computer Vision ...').

Spatial Interaction at the Retina.