Read JPEG EXIF YResolution for the vertical DPI

Tests/test_file_jpeg.py

@@ -15,6 +15,7 @@
     ImageFile,
     ImageOps,
     JpegImagePlugin,
+    TiffImagePlugin,
     UnidentifiedImageError,
     features,
 )
@@ -879,6 +880,40 @@ def test_dpi_from_dpcm_exif(self) -> None:
             # Act / Assert
             assert im.info.get("dpi") == (508, 508)
 
+    def test_dpi_from_exif_different_axes(self) -> None:
+        exif = Image.Exif()
+        exif[0x011A] = 300.0  # XResolution
+        exif[0x011B] = 150.0  # YResolution
+        exif[0x0128] = 2  # ResolutionUnit: inches
+        buf = BytesIO()
+        Image.new("RGB", (16, 16)).save(buf, "JPEG", exif=exif)
+
+        # Remove the JFIF APP0 segment, so that DPI must be read from EXIF
+        data = buf.getvalue()
+        assert data[2:4] == b"\xff\xe0"
+        app0_length = int.from_bytes(data[4:6], "big")
+        data = data[:2] + data[4 + app0_length :]
+
+        with Image.open(BytesIO(data)) as im:
+            assert im.info.get("dpi") == (300, 150)
+
+    def test_dpi_from_exif_invalid_y_resolution(self) -> None:
+        exif = Image.Exif()
+        exif[0x011A] = 300.0  # XResolution
+        exif[0x011B] = TiffImagePlugin.IFDRational(0, 0)  # invalid YResolution
+        exif[0x0128] = 2  # ResolutionUnit: inches
+        buf = BytesIO()
+        Image.new("RGB", (16, 16)).save(buf, "JPEG", exif=exif)
+
+        # Remove the JFIF APP0 segment, so that DPI must be read from EXIF
+        data = buf.getvalue()
+        assert data[2:4] == b"\xff\xe0"
+        app0_length = int.from_bytes(data[4:6], "big")
+        data = data[:2] + data[4 + app0_length :]
+
+        with Image.open(BytesIO(data)) as im:
+            assert im.info.get("dpi") == (300, 300)
+
     def test_dpi_exif_zero_division(self) -> None:
         # Arrange
         # This is photoshop-200dpi.jpg with EXIF resolution set to 0/0:

src/PIL/JpegImagePlugin.py

@@ -521,18 +521,30 @@ def _read_dpi_from_exif(self) -> None:
         try:
             exif = self.getexif()
             resolution_unit = exif[0x0128]
-            x_resolution = exif[0x011A]
-            try:
-                dpi = float(x_resolution[0]) / x_resolution[1]
-            except TypeError:
-                dpi = x_resolution
-            if math.isnan(dpi):
-                msg = "DPI is not a number"
-                raise ValueError(msg)
-            if resolution_unit == 3:  # cm
-                # 1 dpcm = 2.54 dpi
-                dpi *= 2.54
-            self.info["dpi"] = dpi, dpi
+
+            def to_dpi(resolution: Any) -> float:
+                try:
+                    dpi = float(resolution[0]) / resolution[1]
+                except TypeError:
+                    dpi = resolution
+                if math.isnan(dpi):
+                    msg = "DPI is not a number"
+                    raise ValueError(msg)
+                if resolution_unit == 3:  # cm
+                    # 1 dpcm = 2.54 dpi
+                    dpi *= 2.54
+                return dpi
+
+            x_dpi = to_dpi(exif[0x011A])
+            y_dpi = x_dpi
+            y_resolution = exif.get(0x011B)
+            if y_resolution is not None:
+                try:
+                    y_dpi = to_dpi(y_resolution)
+                except (TypeError, ValueError, ZeroDivisionError):
+                    # Keep the X resolution if the Y resolution is invalid
+                    pass
+            self.info["dpi"] = x_dpi, y_dpi
         except (
             struct.error,  # truncated EXIF
             KeyError,  # dpi not included