Hande exif orientation with `pillow` backend in `imread` (#805)

* Add breaking test

* Handle exif orientation tag

mmcv/image/io.py

@@ -15,7 +15,7 @@ except ImportError:
     TJCS_RGB = TJPF_GRAY = TJPF_BGR = TurboJPEG = None
 
 try:
-    from PIL import Image
+    from PIL import Image, ImageOps
 except ImportError:
     Image = None
 
@@ -92,6 +92,8 @@ def _pillow2array(img, flag='color', channel_order='bgr'):
         if array.ndim >= 3 and array.shape[2] >= 3:  # color image
             array[:, :, :3] = array[:, :, (2, 1, 0)]  # RGB to BGR
     else:
+        # Handle exif orientation tag
+        img = ImageOps.exif_transpose(img)
         # If the image mode is not 'RGB', convert it to 'RGB' first.
         if img.mode != 'RGB':
             if img.mode != 'LA':

tests/test_image/test_io.py

@@ -26,6 +26,7 @@ class TestIO:
         cls.gray_img_dim3_path = osp.join(cls.data_dir, 'grayscale_dim3.jpg')
         cls.gray_alpha_img_path = osp.join(cls.data_dir, 'gray_alpha.png')
         cls.palette_img_path = osp.join(cls.data_dir, 'palette.gif')
+        cls.exif_img_path = osp.join(cls.data_dir, 'color_exif.jpg')
         cls.img = cv2.imread(cls.img_path)
 
     def assert_img_equal(self, img, ref_img, ratio_thr=0.999):
@@ -174,6 +175,16 @@ class TestIO:
 
         mmcv.use_backend('cv2')
 
+        # consistent exif behaviour
+        img_cv2_exif = mmcv.imread(self.exif_img_path)
+        img_pil_exif = mmcv.imread(self.exif_img_path, backend='pillow')
+        assert img_cv2_exif.shape == img_pil_exif.shape
+        img_cv2_exif_unchanged = mmcv.imread(
+            self.exif_img_path, flag='unchanged')
+        img_pil_exif_unchanged = mmcv.imread(
+            self.exif_img_path, backend='pillow', flag='unchanged')
+        assert img_cv2_exif_unchanged.shape == img_pil_exif_unchanged.shape
+
     def test_imfrombytes(self):
         # backend cv2, channel order: bgr
         mmcv.use_backend('cv2')