A unified formula for light-adapted pupil size.

The size of the pupil has a large effect on visual function, and pupil size depends mainly on the adapting luminance, modulated by other factors. Over the last century, a number of formulas have been proposed to describe this dependence. Here we review seven published formulas and develop a new unified formula that incorporates the effects of luminance, size of the adapting field, age of the observer, and whether one or both eyes are adapted.

Dipole statistics of discrete finite images: two visually motivated representation theorems.

A discrete finite image I is a function assigning colors to a finite, rectangular array of discrete pixels. A dipole is a triple, ((dR, dC), alpha, beta), where dR and dC are vertical and horizontal, integer-valued displacements and alpha and beta are colors. For any such dipole, D(I)((dR, dC), alpha, beta) gives the number of pixel pairs ((r1, c1), (r2, c2)) of I such that I[r1, c1] = alpha, I[r2, c2] = beta and (r2, c2) - (r1, c1) = (dR, dC).

Every discrete, finite image is uniquely determined by its dipole histogram.

A finite image I is a function assigning colors to a finite, rectangular array of discrete pixels. Thus, the information directly encoded by I is purely locational. Such locational information is of little visual use in itself: perception of visual structure requires extraction of relational image information.

Photon noise and constant-volume operators.

In an earlier paper [J. Opt. Soc.

Intensity-dependent spatial summation.

Psychophysical evidence indicates that, in the human retina, the size of the spatial-summation area decreases as illuminance increases. Such a relationship would be beneficial for the detection of spatial contrast in the presence of photon noise. We analyze an image-processing mechanism in which the area of a strictly positive point-spread function varies inversely with local illuminance while its volume remains constant.