When calculating the Intersection Over Union the following explanation is widely used.
(Source: A Survey on Performance Metrics for Object-Detection Algorithms, by Padilla et al. 2020)
The image and name suggest that the denominator (the area of union) is the area of both boxes combined, box a + box b
, when in reality it's not a union but rather a symmetric difference, box a + box b - intersection of box a and box b
.
Why is it called "area of union" and not "area of symmetric difference"?