Fine structure of an image facsimile synthesized with a Gaussian spot

A TV picture or any other line-scan image facsimile is anisotropic. Its intensity varies continuously along a sweep, and its resolution capability in this direction can be described by a modulation transfer function (MTF). In the orthogonal direction the facsimile's fine structure is discontinuous, and only discrete spatial frequencies can be reproduced. Such a system can be characterized by its MTF in the sweep direction and the ratio of its sweep interval and spot diameter. If the spot has a rotationally symmetric Gaussian intensitydistribution, the fine structure of the facsimile can be described in terms of the Gaussian spot profile. With a compatible relay-lens design, the optimum spot diameter for a CRT-to-film recording system is less than that for a directly viewed display.