Support image reading while ignoring EXIF orientation info (#1091)

* Support image reading while ignoring EXIF orientation info

Add unit test for ignore_orientation flags in imread()

* add documentation for imread

* Add test cases

mmcv/image/io.py

@@ -5,7 +5,8 @@ from pathlib import Path
 
 import cv2
 import numpy as np
-from cv2 import IMREAD_COLOR, IMREAD_GRAYSCALE, IMREAD_UNCHANGED
+from cv2 import (IMREAD_COLOR, IMREAD_GRAYSCALE, IMREAD_IGNORE_ORIENTATION,
+                 IMREAD_UNCHANGED)
 
 from mmcv.utils import check_file_exist, is_str, mkdir_or_exist
 
@@ -30,7 +31,10 @@ supported_backends = ['cv2', 'turbojpeg', 'pillow', 'tifffile']
 imread_flags = {
     'color': IMREAD_COLOR,
     'grayscale': IMREAD_GRAYSCALE,
-    'unchanged': IMREAD_UNCHANGED
+    'unchanged': IMREAD_UNCHANGED,
+    'color_ignore_orientation': IMREAD_IGNORE_ORIENTATION | IMREAD_COLOR,
+    'grayscale_ignore_orientation':
+    IMREAD_IGNORE_ORIENTATION | IMREAD_GRAYSCALE
 }
 
 imread_backend = 'cv2'
@@ -102,7 +106,8 @@ def _pillow2array(img, flag='color', channel_order='bgr'):
             array[:, :, :3] = array[:, :, (2, 1, 0)]  # RGB to BGR
     else:
         # Handle exif orientation tag
-        img = ImageOps.exif_transpose(img)
+        if flag in ['color', 'grayscale']:
+            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':
@@ -117,17 +122,18 @@ def _pillow2array(img, flag='color', channel_order='bgr'):
                 img_rgba = img.convert('RGBA')
                 img = Image.new('RGB', img_rgba.size, (124, 117, 104))
                 img.paste(img_rgba, mask=img_rgba.split()[3])  # 3 is alpha
-        if flag == 'color':
+        if flag in ['color', 'color_ignore_orientation']:
             array = np.array(img)
             if channel_order != 'rgb':
                 array = array[:, :, ::-1]  # RGB to BGR
-        elif flag == 'grayscale':
+        elif flag in ['grayscale', 'grayscale_ignore_orientation']:
             img = img.convert('L')
             array = np.array(img)
         else:
             raise ValueError(
-                'flag must be "color", "grayscale" or "unchanged", '
-                f'but got {flag}')
+                'flag must be "color", "grayscale", "unchanged", '
+                f'"color_ignore_orientation" or "grayscale_ignore_orientation"'
+                f' but got {flag}')
     return array
 
 
@@ -139,8 +145,13 @@ def imread(img_or_path, flag='color', channel_order='bgr', backend=None):
             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` backend does not support `unchanged`.
+            candidates are `color`, `grayscale`, `unchanged`,
+            `color_ignore_orientation` and `grayscale_ignore_orientation`.
+            By default, `cv2` and `pillow` backend would rotate the image
+            according to its EXIF info unless called with `unchanged` or
+            `*_ignore_orientation` flags. `turbojpeg` and `tifffile` backend
+            always ignore image's EXIF info regardless of the flag.
+            The `turbojpeg` backend only supports `color` and `grayscale`.
         channel_order (str): Order of channel, candidates are `bgr` and `rgb`.
         backend (str | None): The image decoding backend type. Options are
             `cv2`, `pillow`, `turbojpeg`, `tifffile`, `None`.

tests/test_image/test_io.py

@@ -184,12 +184,30 @@ class TestIO:
         # 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
+        assert img_cv2_exif.shape == (400, 300, 3)
+        assert img_pil_exif.shape == (400, 300, 3)
         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
+        assert img_cv2_exif_unchanged.shape == (300, 400, 3)
+        assert img_pil_exif_unchanged.shape == (300, 400, 3)
+        img_cv2_color_ignore_exif = mmcv.imread(
+            self.exif_img_path, flag='color_ignore_orientation')
+        img_pil_color_ignore_exif = mmcv.imread(
+            self.exif_img_path,
+            backend='pillow',
+            flag='color_ignore_orientation')
+        assert img_cv2_color_ignore_exif.shape == (300, 400, 3)
+        assert img_pil_color_ignore_exif.shape == (300, 400, 3)
+        img_cv2_grayscale_ignore_exif = mmcv.imread(
+            self.exif_img_path, flag='grayscale_ignore_orientation')
+        img_pil_grayscale_ignore_exif = mmcv.imread(
+            self.exif_img_path,
+            backend='pillow',
+            flag='grayscale_ignore_orientation')
+        assert img_cv2_grayscale_ignore_exif.shape == (300, 400)
+        assert img_pil_grayscale_ignore_exif.shape == (300, 400)
 
     def test_imfrombytes(self):
         # backend cv2, channel order: bgr