Density dependence of the line spread function of radiographic screen-film systems

It has been suggested that the modulation transfer function (MTF) of radiographic screen-film systems may be a function of the density of the test image. This might impair the usefulness of the MTF. Since, in the slit method, the MTF is calculated from the line spread function (LSF), the density dependence of the LSF has been studied in this investigation. A series of slit images, having six different peak densities ranging from about one to three, are made with a sharp and an unsharp screen-film system. At each peak density three LSFs are measured independently. Values of the LSFs at various distances from the centre are plotted as a function of peak density. Results show that the LSFs of the screen-film systems examined are invariant with peak density. It is concluded, therefore, that the MTFs of these systems are also independent of density when they are obtained by the slit method.