From 8a9bd2cdcdd7fc9ecd89fa79323463f4d24f53b8 Mon Sep 17 00:00:00 2001
From: Marcus Brinkmann <m.brinkmann@semantics.de>
Date: Thu, 19 Jan 2017 17:24:28 +0100
Subject: [PATCH] Default to inch-interpretation for missing ResolutionUnit in
 TiffImagePlugin.

---
 PIL/TiffImagePlugin.py  |  6 +++++-
 Tests/test_file_tiff.py | 18 ++++++++++++++++++
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/PIL/TiffImagePlugin.py b/PIL/TiffImagePlugin.py
index e5009d0f1..505025bb8 100644
--- a/PIL/TiffImagePlugin.py
+++ b/PIL/TiffImagePlugin.py
@@ -1163,11 +1163,15 @@ class TiffImageFile(ImageFile.ImageFile):
         yres = self.tag_v2.get(Y_RESOLUTION, 1)
 
         if xres and yres:
-            resunit = self.tag_v2.get(RESOLUTION_UNIT, 1)
+            resunit = self.tag_v2.get(RESOLUTION_UNIT)
             if resunit == 2:  # dots per inch
                 self.info["dpi"] = xres, yres
             elif resunit == 3:  # dots per centimeter. convert to dpi
                 self.info["dpi"] = xres * 2.54, yres * 2.54
+            elif resunit == None: # used to default to 1, but now 2)
+                self.info["dpi"] = xres, yres
+                # For backward compatibility, we also preserve the old behavior.
+                self.info["resolution"] = xres, yres
             else:  # No absolute unit of measurement
                 self.info["resolution"] = xres, yres
 
diff --git a/Tests/test_file_tiff.py b/Tests/test_file_tiff.py
index bf19947a1..1fe3ad45e 100644
--- a/Tests/test_file_tiff.py
+++ b/Tests/test_file_tiff.py
@@ -93,6 +93,24 @@ class TestFileTiff(PillowTestCase):
 
         self.assertEqual(im.info['dpi'], (72., 72.))
 
+    def test_xyres_fallback_tiff(self):
+        from PIL.TiffImagePlugin import X_RESOLUTION, Y_RESOLUTION, RESOLUTION_UNIT
+        filename = "Tests/images/compression.tif"
+        im = Image.open(filename)
+
+        # v2 api
+        self.assertIsInstance(im.tag_v2[X_RESOLUTION],
+                              TiffImagePlugin.IFDRational)
+        self.assertIsInstance(im.tag_v2[Y_RESOLUTION],
+                              TiffImagePlugin.IFDRational)
+        self.assertRaises(KeyError,
+                          lambda: im.tag_v2[RESOLUTION_UNIT])
+
+        # Legacy.
+        self.assertEqual(im.info['resolution'], (100., 100.))
+        # Fallback "inch".
+        self.assertEqual(im.info['dpi'], (100., 100.))
+
     def test_int_resolution(self):
         from PIL.TiffImagePlugin import X_RESOLUTION, Y_RESOLUTION
         filename = "Tests/images/pil168.tif"