Fourier analysis and nonlinear optical systems.

The modulation transfer function is based on Fourier techniques which imply the validity of the principle of superposition. This is clearly violated in the nonlinear film development process. A pseudotransfer function is defined to represent an artificial linear filter which, if it replaced the actual optical and photographic process, would result in precisely the same image as would be produced by the real system. The significance of such a function in a statistical approach and the results of a typical calculation are presented for purpose of illustration.