Gap Fraction Threshold

Canopy gap fraction is the probability of a ray of light passing through the canopy without encountering foliage or other plant elements.The CI-110 Plant Canopy Analysis software includes several different methods to analyze the Gap Fraction, including the Otsu method, Entropy Crossover method and manual threshold. The Entropy Crossover method is automatic, as the user is not required to input anything.

The choice of appropriate Gap Fraction method is left to the discretion of the user. It is recommended to experiment and use the threshold method that best separates canopy and sky. Most likely, very similar results will be acquired with any method used. The following research involves the comparison of several gap fraction methods:

An Improved Estimate of Leaf Area Index Based on the Histogram Analysis of Hemispherical Photographs

Agricultural and Forest Meteorology, volume 149, pages 920-928, 2009.
Juarez, R., Riberio da Rocha, H., Silva e Figueira, A., Goulden, M., Miller, S.