The well known shift and similarity theorems for the Fourier transform
generalise to two dimensions but new theorems come into existence in
two dimensions. Simple theorems for rotation and shear distortion are
examples. A theorem is Presented which determines what the Fourier tra
nsform becomes when the function domain is subjected to an affine co-o
rdinate transformation. The full theorem contains a variety of simpler
theorems as special cases. It may prove useful in its general form in
image processing where sequences of affine transformations are applie
d.