Why plus 1 when calculating the box_area ?

[wujiyang]

In the file : dface/core/utils.py.IoU
box_area = (box[2] - box[0] + 1) * (box[3] - box[1] + 1)
area = (boxes[:, 2] - boxes[:, 0] + 1) * (boxes[:, 3] - boxes[:, 1] + 1)

Is there any tircks has been used when calculating the box_area ? why plus 1 ?

for example,the box[1, 1, 2, 2], the area should be 1, not (2-1+1) * (2-1+1) = 4 ?

[kuaikuaikim]

The count of pixel