Conceptual drawing representing step 1 of the flow diagram in Fig. 2. Left: Generic situation in which a pupil modification near the edge of the pupil is performed, with the opposite-sign pupil modification between the pupil image and with a diametrically symmetric pupil modification (top/bottom). Right: Corresponding dOTF in which all terms involved are located relative to the pupil modification. The part that is reflected about the origin (red) and the conjugated part of the pupil field image (blue) are also shown.