Contour sharpness parameters.

Illustration of the measurement of the two different contour sharpness parameters. We used two different parameters to objectively evaluate the contour sharpness: the distance between 25% and 75% of the maximal grey value and the slope defined as the difference between 75% and 25% of the maximal grey value in the contour divided by the distance calculated before. d (Distance) = x(75% of the maximal grey value)–(25% of the maximal grey value) m (Slope) = (75% of maximal grey value– 25% maximal grey value)/d.