Examples of pair-wise aberrated DH images. Top: simulated WFE maps of aberrated segment pairs on the IrisAO segmented DM. The LS cuts off most of the segments in the outer ring of the segmented pupil. The segment numbering is as indicated in Fig. 6, left. Bottom: DH images from the testbed, with resulting fringes from pair-wise aberrated segments during the PASTIS matrix measurement shown in the top row. The DH extent is from 6–10 λ/D_LS, indicated with the dashed circles, and the images are displayed in the same range as the un-aberrated DH in Fig. 3. The pair (3|4) is made of adjacent segments, which produces low-spatial-frequency fringes in the DH. This leads to an overall decrease in the contrast contribution, as is confirmed by their respective entry in the PASTIS matrix in Fig. 6, with a blue entry right next to the matrix diagonal.