Coded-Mask Imaging in Gamma-Ray Astronomy - Separating the Real and Imaginary parts of a Complex subject

The concept of coded mask imaging in theory and in practice is reviewed, with particular emphasis on image reconstruction techniques. The techniques are simple in principle but become more complicated when one takes into account real, `as-built', instruments, as opposed to idealised imaginary ones. Procedures are discussed with particular reference to the instruments of Integral.