Convex hull and related measurements:
The Convex hull is calculated from the perimeter (blob outline) using Melkman's algorithm with slight modification (pre-processing to eliminate initial colinear points).
The maximum caliper diameter is given by the most widely separated pair of (antipodal) points on the convex hull. Using antipodal pairs greatly decreases computation time. The minimum caliper diameter (or width) is calculated from the closest pair of antipodal points. Hormoz Pirzadeh's web page on rotating calipers gave me the information for this.
Antipodal pairs of points are those that admit parallel lines of support (Preparata & Shamos '85, p. 172).