Method and device for determining a modulation transfer function of a digital imaging system

摘要

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. In the data processing device first values and derived by differentiating detector signal values for picture elements located along a picture line which extends across the series of block elements, and thereafter from positive and negative derivative values there is calculated by Fourier transformation respective two sequences of frequency-consecutive local maxima, from whose envelope the respective two modulation-transfer functions are determined.