1. A method for processing a cosine-related fringe pattern using Fourier transforms, said method comprising the steps of: digitizing a cosine-related fringe pattern by measuring point data at a plurality of points, the data for each point having an intensity value associated with coordinate values, and the intensity distribution of the fringe pattern being defined by the formula: EQU i(x,y)=a(x,y)+b(x,y) cos [.phi.(x,y)] where a(x,y) describes background variation and carries additive disturbances, b(x,y) is related to the local contrast of the pattern and carries the multiplicative disturbances, and .phi.(x,y) is the phase; said formula being rewritten as the formula: EQU i(x,y)=a(x,y)+c(x,y)+c*(x,y) where c(x,y)=1/2b(x,y) exp [j.phi.(x,y)], j=.sqroot.-1 and * denotes the complex conjugate; processing said point data in accordance with said rewritten intensity distribution formula and a Fourier transform operation to produce an amplitude spectrum having a trimodal function of the form: EQU I(u,v)=A(u,v)+C(u,v)+C*(u,v), wherein A(u,v) corresponds to a reference modal function, and C(u,v) and C*(u,v) represents modal functions which are symmetrical about A(u,v); removing processed data corresponding to the A(u,v) portion and one of the C(u,v) and C*(u,v) portions of the trimodal function; performing an inverse Fourier transform operation on the processed data corresponding to the remaining portion of the trimodal function to obtain a value for c(x,y); and calculating the phase .phi.(x,y) for each point by using the formula: ##EQU8## where Re denotes the real part and Im the imaginary part.