Fix missing EXIF orientation handling

RELEASE.md

@@ -0,0 +1,3 @@
+Release type: patch
+
+Auto-rotate images based on EXIF Orientation tag before applying user transforms, and clear the orientation tag in the output to prevent double-rotation in EXIF-aware viewers.

pelican/plugins/image_process/image_process.py

@@ -22,7 +22,7 @@
 from urllib.request import pathname2url, url2pathname
 
 from bs4 import BeautifulSoup
-from PIL import Image, ImageFilter, UnidentifiedImageError
+from PIL import Image, ImageFilter, ImageOps, UnidentifiedImageError
 
 from pelican import __version__ as pelican_version, signals
 
@@ -102,6 +102,7 @@ def _copy_tags(self, src, dst):
             b"-TagsFromFile",
             src.encode(self.encoding, ExifTool.errors),
             dst.encode(self.encoding, ExifTool.errors),
+            b"-Orientation=1",
         )
         self._send_command(params)
         params = (
@@ -752,6 +753,8 @@ def process_image(image, settings):
         except (UnidentifiedImageError, FileNotFoundError):
             return None
 
+        i = ImageOps.exif_transpose(i)
+
         for step in image[2]:
             if callable(step):
                 i = step(i)

pelican/plugins/image_process/test_image_process.py

@@ -6,7 +6,7 @@
 import warnings
 
 from bs4 import BeautifulSoup
-from PIL import Image, UnidentifiedImageError
+from PIL import Image, ImageChops, ImageStat, UnidentifiedImageError
 import pytest
 
 from pelican.plugins.image_process import (
@@ -47,6 +47,11 @@
     TEST_DATA.joinpath("noexif", f"pelican-bird.{ext}").resolve()
     for ext in SUPPORTED_EXIF_IMAGE_FORMATS
 ]
+EXIF_ORIENTATION_TEST_IMAGES = [
+    TEST_DATA.joinpath("exif", f"pelican-bird-rot90.{ext}").resolve()
+    for ext in SUPPORTED_EXIF_IMAGE_FORMATS
+]
+PIXEL_DIFF_MEAN_THRESHOLD = 2
 TRANSFORM_RESULTS = TEST_DATA.joinpath("results").resolve()
 
 # Register all supported transforms.
@@ -826,6 +831,38 @@ def test_copy_exif_tags_does_not_add_exif_dims_tags(tmp_path, image_path):
     assert "ExifImageHeight" not in actual_tags
 
 
+@pytest.mark.parametrize("image_path", EXIF_ORIENTATION_TEST_IMAGES)
+@pytest.mark.parametrize("copy_tags", [True, False])
+def test_exif_orientation(tmp_path, image_path, copy_tags):
+    original_path = TEST_DATA.joinpath("pelican-bird.png")
+    original = Image.open(original_path)
+
+    settings = get_settings(IMAGE_PROCESS_COPY_EXIF_TAGS=copy_tags)
+
+    transform_params = []
+    image_name = image_path.name
+    destination_path = tmp_path / image_name
+
+    process_image(
+        (str(image_path), str(destination_path), transform_params),
+        settings,
+    )
+
+    result = Image.open(destination_path)
+
+    # The output should be the same size as the original (not the rotated
+    # source), because ImageOps.exif_transpose() should correct the
+    # orientation before saving.
+    assert result.size == original.size
+
+    # Mean per-channel pixel diff must stay under 2. JPEG artifacts
+    # produce values around 1.5, while a wrong orientation (no transpose
+    # applied) would produce values between 8 and ~30 per channel.
+    diff = ImageChops.difference(result.convert("RGB"), original.convert("RGB"))
+    stat = ImageStat.Stat(diff)
+    assert all(m < PIXEL_DIFF_MEAN_THRESHOLD for m in stat.mean)
+
+
 def test_try_open_image():
     for test_image in FILE_FORMAT_TEST_IMAGES:
         assert try_open_image(test_image)