Fix image orientation when generating thumbnail (#5039)

changelog.d/5039.bugfix

+Fix image orientation when generating thumbnails (needs pillow>=4.3.0). Contributed by Pau Rodriguez-Estivill.

synapse/python_dependencies.py

@@ -53,7 +53,7 @@ REQUIREMENTS = [
     "pyasn1-modules>=0.0.7",
     "daemonize>=2.3.1",
     "bcrypt>=3.1.0",
-    "pillow>=3.1.2",
+    "pillow>=4.3.0",
     "sortedcontainers>=1.4.4",
     "psutil>=2.0.0",
     "pymacaroons>=0.13.0",

synapse/rest/media/v1/media_repository.py

@@ -444,6 +444,9 @@ class MediaRepository(object):
             )
             return
 
+        if thumbnailer.transpose_method is not None:
+            m_width, m_height = thumbnailer.transpose()
+
         if t_method == "crop":
             t_byte_source = thumbnailer.crop(t_width, t_height, t_type)
         elif t_method == "scale":
@@ -578,6 +581,12 @@ class MediaRepository(object):
             )
             return
 
+        if thumbnailer.transpose_method is not None:
+            m_width, m_height = yield logcontext.defer_to_thread(
+                self.hs.get_reactor(),
+                thumbnailer.transpose
+            )
+
         # We deduplicate the thumbnail sizes by ignoring the cropped versions if
         # they have the same dimensions of a scaled one.
         thumbnails = {}

synapse/rest/media/v1/thumbnailer.py

@@ -20,6 +20,17 @@ import PIL.Image as Image
 
 logger = logging.getLogger(__name__)
 
+EXIF_ORIENTATION_TAG = 0x0112
+EXIF_TRANSPOSE_MAPPINGS = {
+    2: Image.FLIP_LEFT_RIGHT,
+    3: Image.ROTATE_180,
+    4: Image.FLIP_TOP_BOTTOM,
+    5: Image.TRANSPOSE,
+    6: Image.ROTATE_270,
+    7: Image.TRANSVERSE,
+    8: Image.ROTATE_90
+}
+
 
 class Thumbnailer(object):
 
@@ -31,6 +42,30 @@ class Thumbnailer(object):
     def __init__(self, input_path):
         self.image = Image.open(input_path)
         self.width, self.height = self.image.size
+        self.transpose_method = None
+        try:
+            # We don't use ImageOps.exif_transpose since it crashes with big EXIF
+            image_exif = self.image._getexif()
+            if image_exif is not None:
+                image_orientation = image_exif.get(EXIF_ORIENTATION_TAG)
+                self.transpose_method = EXIF_TRANSPOSE_MAPPINGS.get(image_orientation)
+        except Exception as e:
+            # A lot of parsing errors can happen when parsing EXIF
+            logger.info("Error parsing image EXIF information: %s", e)
+
+    def transpose(self):
+        """Transpose the image using its EXIF Orientation tag
+
+        Returns:
+            Tuple[int, int]: (width, height) containing the new image size in pixels.
+        """
+        if self.transpose_method is not None:
+            self.image = self.image.transpose(self.transpose_method)
+            self.width, self.height = self.image.size
+            self.transpose_method = None
+            # We don't need EXIF any more
+            self.image.info["exif"] = None
+        return self.image.size
 
     def aspect(self, max_width, max_height):
         """Calculate the largest size that preserves aspect ratio which