[Fix] Fix `LoadMultiViewImageFromFiles` to be compatible with `DefaultFormatBundle` (#611)

* unravel multi-view img to list

* add unit test

mmdet3d/datasets/pipelines/loading.py

@@ -41,12 +41,15 @@ class LoadMultiViewImageFromFiles(object):
                 - img_norm_cfg (dict): Normalization configuration of images.
         """
         filename = results['img_filename']
+        # img is of shape (h, w, c, num_views)
         img = np.stack(
             [mmcv.imread(name, self.color_type) for name in filename], axis=-1)
         if self.to_float32:
             img = img.astype(np.float32)
         results['filename'] = filename
-        results['img'] = img
+        # unravel to list, see `DefaultFormatBundle` in formating.py
+        # which will transpose each image separately and then stack into array
+        results['img'] = [img[..., i] for i in range(img.shape[-1])]
         results['img_shape'] = img.shape
         results['ori_shape'] = img.shape
         # Set initial values for default meta_keys
@@ -61,8 +64,10 @@ class LoadMultiViewImageFromFiles(object):
 
     def __repr__(self):
         """str: Return a string that describes the module."""
-        return f'{self.__class__.__name__} (to_float32={self.to_float32}, '\
-            f"color_type='{self.color_type}')"
+        repr_str = self.__class__.__name__
+        repr_str += f'(to_float32={self.to_float32}, '
+        repr_str += f"color_type='{self.color_type}')"
+        return repr_str
 
 
 @PIPELINES.register_module()

tests/test_data/test_pipelines/test_loadings/test_load_images_from_multi_views.py

+import numpy as np
+import torch
+from mmcv.parallel import DataContainer
+
+from mmdet3d.datasets.pipelines import (DefaultFormatBundle,
+                                        LoadMultiViewImageFromFiles)
+
+
+def test_load_multi_view_image_from_files():
+    multi_view_img_loader = LoadMultiViewImageFromFiles(to_float32=True)
+
+    num_views = 6
+    filename = 'tests/data/waymo/kitti_format/training/image_0/0000000.png'
+    filenames = [filename for _ in range(num_views)]
+
+    input_dict = dict(img_filename=filenames)
+    results = multi_view_img_loader(input_dict)
+    img = results['img']
+    img0 = img[0]
+    img_norm_cfg = results['img_norm_cfg']
+
+    assert isinstance(img, list)
+    assert len(img) == num_views
+    assert img0.dtype == np.float32
+    assert results['filename'] == filenames
+    assert results['img_shape'] == results['ori_shape'] == \
+        results['pad_shape'] == (1280, 1920, 3, num_views)
+    assert results['scale_factor'] == 1.0
+    assert np.all(img_norm_cfg['mean'] == np.zeros(3, dtype=np.float32))
+    assert np.all(img_norm_cfg['std'] == np.ones(3, dtype=np.float32))
+    assert not img_norm_cfg['to_rgb']
+
+    repr_str = repr(multi_view_img_loader)
+    expected_str = 'LoadMultiViewImageFromFiles(to_float32=True, ' \
+                   "color_type='unchanged')"
+    assert repr_str == expected_str
+
+    # test LoadMultiViewImageFromFiles's compatibility with DefaultFormatBundle
+    # refer to https://github.com/open-mmlab/mmdetection3d/issues/227
+    default_format_bundle = DefaultFormatBundle()
+    results = default_format_bundle(results)
+    img = results['img']
+
+    assert isinstance(img, DataContainer)
+    assert img._data.shape == torch.Size((num_views, 3, 1280, 1920))