From 8945875c6ce48fee62d17cea1414938e24808a9f Mon Sep 17 00:00:00 2001
From: Andrew Murray <radarhere@users.noreply.github.com>
Date: Sat, 28 Dec 2024 21:28:44 +1100
Subject: [PATCH] Populate DPI from JFIF cm density

---
 Tests/images/jfif_unit_cm.jpg | Bin 0 -> 391 bytes
 Tests/test_file_jpeg.py       |   4 ++++
 src/PIL/JpegImagePlugin.py    |   3 +++
 3 files changed, 7 insertions(+)
 create mode 100644 Tests/images/jfif_unit_cm.jpg

diff --git a/Tests/images/jfif_unit_cm.jpg b/Tests/images/jfif_unit_cm.jpg
new file mode 100644
index 0000000000000000000000000000000000000000..78b50e60a236bf320a29c433eae2c9afeb759fe9
GIT binary patch
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literal 0
HcmV?d00001

diff --git a/Tests/test_file_jpeg.py b/Tests/test_file_jpeg.py
index 5dd50fd0809..bf0dec4b80e 100644
--- a/Tests/test_file_jpeg.py
+++ b/Tests/test_file_jpeg.py
@@ -181,6 +181,10 @@ def test(xdpi: int, ydpi: int | None = None) -> tuple[int, int] | None:
         assert test(100, 200) == (100, 200)
         assert test(0) is None  # square pixels
 
+    def test_dpi_jfif_cm(self):
+        with Image.open("Tests/images/jfif_unit_cm.jpg") as im:
+            assert im.info["dpi"] == (2.54, 5.08)
+
     @mark_if_feature_version(
         pytest.mark.valgrind_known_error, "libjpeg_turbo", "2.0", reason="Known Failing"
     )
diff --git a/src/PIL/JpegImagePlugin.py b/src/PIL/JpegImagePlugin.py
index 5025f88ea97..457690aac51 100644
--- a/src/PIL/JpegImagePlugin.py
+++ b/src/PIL/JpegImagePlugin.py
@@ -90,6 +90,9 @@ def APP(self: JpegImageFile, marker: int) -> None:
         else:
             if jfif_unit == 1:
                 self.info["dpi"] = jfif_density
+            elif jfif_unit == 2:  # cm
+                # 1 dpcm = 2.54 dpi
+                self.info["dpi"] = tuple(d * 2.54 for d in jfif_density)
             self.info["jfif_unit"] = jfif_unit
             self.info["jfif_density"] = jfif_density
     elif marker == 0xFFE1 and s[:6] == b"Exif\0\0":