Fig. 3

Panel a depicts the influence of the spline step size on the area of the vessel covered by the orthogonal line segments. The chosen step size of 0.1 (approximately 1.88 steps per pixel or a step size of 18 μm) leads to a complete coverage of the underlying vessel area and is thus an optimal choice for unwarping the vessel, as no image information gets lost. Panel b highlights the influence of the Gaussian smoothing σ on the mean difference maps, which has been experimentally chosen as σ=3. For lower values of σ, noise and artifacts become visible in the mean difference maps, while for larger values, structures become less clear due to overly smoothing the maps