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Table 3 Convexity defect measures used for ranking

From: SHERPA: an image segmentation and outline feature extraction tool for diatoms and other objects

Absolute measures
CDF "Convexity Defection Factor", depicts the percentaged difference between area resp. perimeter of contour and convex hull [53]
PCAF The "Percent Concave Area Fraction" compares the areas of contour and convex hull [54].
CHMDF For the "Convex Hull Maximum Distance Factor" each convexity defect’s maximum distance between contour and convex hull is calculated. For distances larger than pixelwidth the squares of the distances are summed up to the CHMDF [53].
Relative measures
CDF-Match Ratio of CDF of object and template
PCAF-Match Ratio of PCAF of object and template
Compactness-Match Ratio of heuristic descriptor "compactness" between object and template shape
  1. Absolute measures result from the object and are judged directly by their values, relative measures result from comparing values between object and best matching template.