dataset.py        

if (self.augment or MIRROR_FOLD_APPLY_TO_VAL) and should_apply_mirror_fold():

            if mosaic:

                car_box = get_car_box_with_fallback(w, h, img)

            else:

                car_box = _mirror_fold_box_for_letterbox((h0, w0), (h, w), ratio, pad)

                if car_box is None:

                    car_box = get_car_box_with_fallback(img.shape[1], img.shape[0], img)

            if car_box is not None:

                img, labels = _apply_mirror_fold_det(img, labels, car_box)