Fix IOU assigners when ignore_of_thr > 0 and no pred boxes (#2135)

* Fix IOU assigners when ignore_of_thr > 0 and no pred boxes

* remove extra brakets

* fix test linter

mmdet/core/bbox/assigners/approx_max_iou_assigner.py

@@ -118,8 +118,8 @@ def assign(self,
 
         bboxes = squares[:, :4]
 
-        if (self.ignore_iof_thr > 0) and (gt_bboxes_ignore is not None) and (
-                gt_bboxes_ignore.numel() > 0):
+        if (self.ignore_iof_thr > 0 and gt_bboxes_ignore is not None
+                and gt_bboxes_ignore.numel() > 0 and bboxes.numel() > 0):
             if self.ignore_wrt_candidates:
                 ignore_overlaps = bbox_overlaps(
                     bboxes, gt_bboxes_ignore, mode='iof')

mmdet/core/bbox/assigners/max_iou_assigner.py

@@ -98,8 +98,8 @@ def assign(self, bboxes, gt_bboxes, gt_bboxes_ignore=None, gt_labels=None):
         bboxes = bboxes[:, :4]
         overlaps = bbox_overlaps(gt_bboxes, bboxes)
 
-        if (self.ignore_iof_thr > 0) and (gt_bboxes_ignore is not None) and (
-                gt_bboxes_ignore.numel() > 0):
+        if (self.ignore_iof_thr > 0 and gt_bboxes_ignore is not None
+                and gt_bboxes_ignore.numel() > 0 and bboxes.numel() > 0):
             if self.ignore_wrt_candidates:
                 ignore_overlaps = bbox_overlaps(
                     bboxes, gt_bboxes_ignore, mode='iof')

tests/test_assigner.py

@@ -112,6 +112,42 @@ def test_max_iou_assigner_with_empty_boxes():
     assert assign_result.labels is None
 
 
+def test_max_iou_assigner_with_empty_boxes_and_ignore():
+    """
+    Test corner case where an network might predict no boxes and ignore_iof_thr
+    is on
+    """
+    self = MaxIoUAssigner(
+        pos_iou_thr=0.5,
+        neg_iou_thr=0.5,
+        ignore_iof_thr=0.5,
+    )
+    bboxes = torch.empty((0, 4))
+    gt_bboxes = torch.FloatTensor([
+        [0, 0, 10, 9],
+        [0, 10, 10, 19],
+    ])
+    gt_bboxes_ignore = torch.Tensor([
+        [30, 30, 40, 40],
+    ])
+    gt_labels = torch.LongTensor([2, 3])
+
+    # Test with gt_labels
+    assign_result = self.assign(
+        bboxes,
+        gt_bboxes,
+        gt_labels=gt_labels,
+        gt_bboxes_ignore=gt_bboxes_ignore)
+    assert len(assign_result.gt_inds) == 0
+    assert tuple(assign_result.labels.shape) == (0, )
+
+    # Test without gt_labels
+    assign_result = self.assign(
+        bboxes, gt_bboxes, gt_labels=None, gt_bboxes_ignore=gt_bboxes_ignore)
+    assert len(assign_result.gt_inds) == 0
+    assert assign_result.labels is None
+
+
 def test_max_iou_assigner_with_empty_boxes_and_gt():
     """
     Test corner case where an network might predict no boxes and no gt