e that although the number of cones equates to 200 megapixels, no one seems quite sure why we need that much resolution. So image processing is just like RF signal processing, except that it has to take into account the idiosyncrasies of the human visual system. Note also that although humans are superficially alike (two arms, two legs, two eyes) we are also intrinsically different in terms of optical performance. Some of us are colour blind, some of us have better resolution. Scientists have solved this by creating an 'ideal observer', a sort of 'model man' against which we can judge artificial optical and image processing systems. The human visual system was first described in detail (in the western world at least) by Johannes Kepler (1571-1630) who codified the fundamental laws of physiological optics. Rene Descartes (1596-1650) verified much of Kepler's work and added some things (like the coordinate system) that have proved indispensable in present-day imaging systems. Isaac Newton (1642-1726) worked on the laws of colour mixture ('the rays to speak properly are not coloured') and did dangerous experiments on himself pushing bodkins (long pins) into his eye. He anticipated the modern understanding of visual colour perception based on the Making Telecoms Work activity of peripheral receptors sensitive to a physical dimension (wavelength). All that stuff with the apple was a bit of a sideshow. In 1801 Thomas Young proposed that the eye contained three classes of receptor each of which responded over a broad spectral range. These ideas were developed by Helmholtz and became the basis of Young-Helmholtz trichromatic theory. This optical wavelength business was all a bit curious and still is. Anders Jonas Angstrom (1814-1874) decided quite sensibly that light should be measured in wavelengths and that given that the radiant energy was coming from the sun, then it would be a good idea to relate the measurements to a hydrogen atom. Thus, an Angstrom was defined as being equivalent to the diameter of a hydrogen atom