support pathlib in imageio (#208)

* support pathlib in imageio

* support pathlib in imageio

* add Path type for the annotation.
Co-authored-by: xurui4 <xurui4@sensetime.com>

mmcv/image/io.py

 # Copyright (c) Open-MMLab. All rights reserved.
 import os.path as osp
+from pathlib import Path
 
 import cv2
 import numpy as np
@@ -61,9 +62,9 @@ def imread(img_or_path, flag='color', channel_order='bgr'):
     """Read an image.
 
     Args:
-        img_or_path (ndarray or str): Either a numpy array or image path.
-            If it is a numpy array (loaded image), then it will be returned
-            as is.
+        img_or_path (ndarray or str or Path): Either a numpy array or str or
+            pathlib.Path. If it is a numpy array (loaded image), then
+            it will be returned as is.
         flag (str): Flags specifying the color type of a loaded image,
             candidates are `color`, `grayscale` and `unchanged`.
             Note that the `turbojpeg` backened does not support `unchanged`.
@@ -72,6 +73,9 @@ def imread(img_or_path, flag='color', channel_order='bgr'):
     Returns:
         ndarray: Loaded image array.
     """
+    if isinstance(img_or_path, Path):
+        img_or_path = str(img_or_path)
+
     if isinstance(img_or_path, np.ndarray):
         return img_or_path
     elif is_str(img_or_path):
@@ -91,7 +95,8 @@ def imread(img_or_path, flag='color', channel_order='bgr'):
                 cv2.cvtColor(img, cv2.COLOR_BGR2RGB, img)
             return img
     else:
-        raise TypeError('"img" must be a numpy array or a filename')
+        raise TypeError('"img" must be a numpy array or a str or '
+                        'a pathlib.Path object')
 
 
 def imfrombytes(content, flag='color', channel_order='bgr'):

tests/test_image.py

@@ -2,6 +2,7 @@
 import os
 import os.path as osp
 import tempfile
+from pathlib import Path
 
 import cv2
 import numpy as np
@@ -17,8 +18,10 @@ class TestImage(object):
     def setup_class(cls):
         # the test img resolution is 400x300
         cls.img_path = osp.join(osp.dirname(__file__), 'data/color.jpg')
+        cls.img_path_obj = Path(cls.img_path)
         cls.gray_img_path = osp.join(
             osp.dirname(__file__), 'data/grayscale.jpg')
+        cls.gray_img_path_obj = Path(cls.gray_img_path)
         cls.img = cv2.imread(cls.img_path)
         cls.mean = np.float32(np.array([123.675, 116.28, 103.53]))
         cls.std = np.float32(np.array([58.395, 57.12, 57.375]))
@@ -47,6 +50,18 @@ class TestImage(object):
         assert img_cv2_unchanged.shape == (300, 400)
         img_cv2_unchanged = mmcv.imread(img_cv2_unchanged)
         assert_array_equal(img_cv2_unchanged, mmcv.imread(img_cv2_unchanged))
+
+        img_cv2_color_bgr = mmcv.imread(self.img_path_obj)
+        assert img_cv2_color_bgr.shape == (300, 400, 3)
+        img_cv2_color_rgb = mmcv.imread(self.img_path_obj, channel_order='rgb')
+        assert img_cv2_color_rgb.shape == (300, 400, 3)
+        assert_array_equal(img_cv2_color_rgb[:, :, ::-1], img_cv2_color_bgr)
+        img_cv2_grayscale1 = mmcv.imread(self.img_path_obj, 'grayscale')
+        assert img_cv2_grayscale1.shape == (300, 400)
+        img_cv2_grayscale2 = mmcv.imread(self.gray_img_path_obj)
+        assert img_cv2_grayscale2.shape == (300, 400, 3)
+        img_cv2_unchanged = mmcv.imread(self.gray_img_path_obj, 'unchanged')
+        assert img_cv2_unchanged.shape == (300, 400)
         with pytest.raises(TypeError):
             mmcv.imread(1)