Indirect Fourier transform is a solution of ill-posed given by Fourier transform of extremely noisy data (as from biological small-angle scattering) proposed by Glatter.[1]
Transform is computed by linear fit to a family of functions corresponding to constraints on the reasonable solution. If a result of the transform is distance distribution function, it is common to assume that the function is non-negative, and is zero at P(0) = 0 and P(Dmax) ≥ 0, where Dmax is a maximum diameter of the particle. It is approximately true, although it disregards inter-particle effects.
IFT is also performed in order to regularize noisy data.[2]