Original Shepp–Logan phantom (Shepp & Logan, 1974). The grey scale has been adjusted to make the features in the ellipse discernible. In this way the background (pixel value = 0.0) and the ellipse contour (pixel value = 2.0) are saturated. The dotted line shows the position of the line profiles in Figs. 6 and 7. The dashed square delimits the area used for the histograms shown in the same figures.