Representing contrast detection as an eigenvalue problem.

Contrast detection can be formulated as an eigenvalue problem. One of the simplest resulting models has only two parameters. The model is space variant and employs the Hermite functions as eigenfunctions. Computing the response to a sinusoidal acuity grating yields the observer's contrast response. The model itself, however, is developed within an abstract mathematical framework which is general enough to include Fourier analysis as a special case. Consequently, the methods of Fourier analysis are generalized to those of eigenfunction expansion and the spectral theory of linear operators.