Abstract: To determine the asymmetry of the line spread function in digital imaging systems, two modulation-transfer functions are calculated by differentiation of the edge spread function followed by Fourier transformation. To that end a method is used in which a radiation intensity distribution spatially modulated by a series of equidistant elongated block elements in a test object is incident upon an input screen of a detector which is connected to a digital data processing device for storing detector signal values in memory locations which correspond to picture elements of the input screen.

Abstract: The modulation transfer function of a digital imaging system is measured using a test object comprising a number of slits. The effect of geometrical distortions on the MTF measurement, is minimized by making the dimension of the test object as small as possible with respect to the image detector. The minimum slit spacing d enabling suitable MTF measurement is expressed in the number of pixels N over a dimension L of the image detector: d>8L/N.