UC Irvine

Constant volume (CV) operators are nonlinear image processing operators in which the area covered by the pointspread function around each point in the input image varies inversely with the light intensity at that point. This operation is designed to make spatial resolution increase with retinal illuminance, but it proves to have unexpected side-effects that mimic other important properties of human spatial vision, including Mach bands and Weber’s law. Mach bands are usually attributed to lateral inhibition in the retina, and when retinal image processing is modeled by a linear operator they imply such inhibition, since they cannot be produced by a nonnegative impulse response. CV operators demonstrate that Mach bands and other high-pass filter effects can be created by purely positive pointspread functions, i.e., without inhibition. This paper shows in addition that if one attempts to combine lateral inhibition with a CV operation, the results are dramatically wrong: the edge response always contains Mach bands that bulge in the wrong direction. Thus within the nonlinear theoretical framework provided by CV operators, lateral inhibition is neither necessary nor sufficient for modeling Mach bands and other high-pass filter properties of spatial vision. © 1989.