Schematic illustration of the detection method used for displacement measurements in a one-dimensional case. In the upper two panels the wavelet decomposition at a scale j of the reference (top panel) and target image is plotted, with two detected SSP marked with colors and letters. The x-axis of each panel is given in pixels. The result of WZNCC between SSP b and the target image is plotted below in the third panel. Two potential displacements are identified within the bounds (gray area) defined by Eq. (9)and the initial displacement guess obtained from analysis at scale j + 1. To select the correct one and to reduce the chance for erroneous cross-correlation, the group motion of causally connected SSP (in this case SSP a and SSP b) is also included in the cross-correlation analysis, which results in the identification of the displacement Δ_j,b = 12.