Fix imshow_bbox error when input bboxes is empty (open-mmlab#796)

* update imshow_bbox to handle empty bboxes
* update unittest
* add trimesh into requirements (related to open-mmlab#771)

mmpose/core/visualization/image.py

@@ -50,7 +50,8 @@ def imshow_bboxes(img,
     """
 
     # adapt to mmcv.imshow_bboxes input format
-    bboxes = np.split(bboxes, bboxes.shape[0], axis=0)
+    bboxes = np.split(
+        bboxes, bboxes.shape[0], axis=0) if bboxes.shape[0] > 0 else []
     if not isinstance(colors, list):
         colors = [colors for _ in range(len(bboxes))]
     colors = [mmcv.color_val(c) for c in colors]

requirements/optional.txt

@@ -4,3 +4,4 @@ onnxruntime
 poseval@git+https://github.com/svenkreiss/poseval.git
 pyrender
 smplx>=0.1.28
+trimesh

tests/test_visualization.py

@@ -50,6 +50,14 @@ def test_imshow_bbox():
             show=False,
             out_file=f'{tmpdir}/out.png')
 
+        # test case of empty bboxes
+        _ = imshow_bboxes(
+            img,
+            np.zeros((0, 4), dtype=np.float32),
+            labels=None,
+            colors='red',
+            show=False)
+
 
 def test_effects():
     img = np.zeros((100, 100, 3), dtype=np.uint8)