Confusion matrix.

<p>The matrix is calculated for the = 24 reference pixels of each of = 16 gray value-strata of a hemispherical photograph. Column and row sums show how many pixels were classified by a binarization algorithm (image classified data) and by an operator (reference data) into the categories vegetation (V) and sky (S). The four central cells show how many pixels were classified by an algorithm and the operator in agreement (, ) and in disagreement (, ). The image marginal proportion displays the overall fraction of pixels classified by the algorithm as vegetation () or sky () within the respective stratum. Adapted from Congalton and Green 2009.