True positive (TP); False positive (FP); False negative (FN) pixels for precision and recall calculation. Red regions are the location of blood vessels in the reference image while white regions are the location of blood vessels in the target image. Blood vessel pixels that overlap in both reference and target images are marked as TP (light red). Blood vessel pixels in the target image, but not in the reference image are marked as FP (white). Blood vessel pixels in the reference image, but not the target image are marked as FN (dark red).