Figure 5. Asymmetrical image brightness alters intensity-based registration output.

A) Cell-level laser ablation registered using rigid body registration. The bulk of the signal is on the left of the image so registration reduces apparent displacement in that portion relative to the right side of the image. This makes it look like the post-ablation recoil was directionally biased to the right in the PIV analysis. B) As an illustrative example, image intensity was halved in the region bounded by the shaded brackets and rigid body registration was repeated. Now the right side of the image is brighter, so its apparent deformation is minimised at the expense of greater discrepancy on the left. PIV shows leftward bias. C) Intensity-independent landmark-based registration suggests the recoil is symmetrical and largely restricted to the region surrounding the ablation. Vertical red lines indicate the ablated border, scale bars = 20 μm.