Photoreceptor sampling

Spatial and temporal sampling of light by a finite receptor array. In a regular one-dimensional point-sampling model with spacing $d$, frequencies $f$ and $f+k/d$ give identical sinusoidal samples because the phase difference at sample $n$ is $2\pi kn$. Restricting a real signal below the Nyquist frequency $1/(2d)$ removes that basic ambiguity. Real retinal mosaics are irregular, two-dimensional and optically filtered.