“…To emulate the multiscale Hessian-based Vesselness approach used in phenoVein (Bühler et al, 2015), the MATLAB fibremetric implementation of the Frangi 'Vesselness' filter (Frangi et al, 1998) was used with vein thickness between 4 and 9 pixels, applied over four scales using a Gaussian image pyramid (Burt & Adelson, 1983) to cover the largest veins. We also tested improved Hessian-based enhancement techniques using Multiscale Fractional Anisotropy Tensors (MFAT), in both their eigenvalue-based (MFAT λ ) and probability-based (MFAT p ) form (Alhasson et al, 2019), and the intensity-independent, multiscale phase-congruency enhancement developed by Kovesi (Kovesi, 1999(Kovesi, , 2000, which was previously used to segment fungal (Obara et al, 2012), slime mould (Fricker et al, 2017) and ER networks (Pain et al, 2019). We used the normalised local weighted mean phase angle ('Feature Type') to give intensity-independent enhancement of vein structures, initially calculated over 3-5 scales and six orientations, and then applied to an image pyramid to cover larger scales.…”