Fig. 2

a The image of the 14th row of spots from Fig. 1 b is depicted at the bottom. The intensity profile before (broken line) and after (solid line) shock filter iteration is represented on top of the image. Vertical lines are drawn in red at positions of inflection points. The solid lines indicate border lines for the spot in row 14 and column 6. The broken lines confine its local background area. b The image of the 6th column of spots from Fig. 1 b is shown at the bottom (rotated counter clockwise by 90°). The intensity profile before (broken line) and after (solid line) shock filter iteration is depicted on top of the image. Vertical lines are drawn in red at positions of inflection points. The solid lines indicate border lines for the spot in row 14 and column 6. The broken lines confine its local background area