Vesicle radius and position refinement through radial profile and cross-correlation. (A) Initial segmentation of a vesicle. (B) Radial profile. The blue range is from the membrane center to the outer white halo center. This is defined as the search range for the optimal radius. (C) The second derivative of radial profile was used to define the exact edge of the membrane. (D) Central cross-section in the three-dimensional radial average of the vesicle in its initial position. (E–H) Same as (A–D) after refinement.