Figure 2. Illustration of Intersection Over Union and 5-Fold Cross-validation.

A, IoU is a metric that signifies the degree of overlap between the area annotated as the ground truth (blue) and the predicted area output by the convolutional neural network (yellow). IoU is calculated by dividing the area of overlap (green) by the area of union. B, In 5-fold cross-validation, the annotation data set is split into 5 segments, of which 4 are used as training sets and the remainder as the validation set. The validation is performed for all 5 validation sets, and the mean value is calculated as the performance metric.