Figure 3. Superior performance of optical flow tracking over standard correlation-based approaches.

(a) The deviation of traction magnitude (DTM defined as 0 when error free and −1 in the case of complete underestimation (b) Signal to noise ratio (SNR) is shown for four different displacement algorithms tested as discussed in methods, shown for the surface (2D) bead configuration. Using KLT to reconstruct the displacements yields a better force reconstruction in both magnitude and quality of the traction images, especially for small adhesions. (c) Linear fit to the computation time needed for the displacement analysis as a function of evaluation points within one image. KLT is several orders of magnitude more efficient than correlation-based approaches, also at a large number of evaluation points (beads).