Write round trip for rationals, including nan value

PIL/TiffImagePlugin.py

@@ -497,11 +497,13 @@ class ImageFileDirectory_v2(collections.MutableMapping):
         values = [value] if isinstance(value, basetypes) else value
 
         if tag not in self.tagtype:
-            try:
+            if info.type:
                 self.tagtype[tag] = info.type
-            except KeyError:
+            else:
                 self.tagtype[tag] = 7
-                if all(isinstance(v, int) for v in values):
+                if all(isinstance(v, IFDRational) for v in values):
+                    self.tagtype[tag] = 5
+                elif all(isinstance(v, int) for v in values):
                     if all(v < 2 ** 16 for v in values):
                         self.tagtype[tag] = 3
                     else:

PIL/TiffTags.py

@@ -23,7 +23,7 @@ from collections import namedtuple
 class TagInfo(namedtuple("_TagInfo", "value name type length enum")):
     __slots__ = []
 
-    def __new__(cls, value=None, name="unknown", type=4, length=0, enum=None):
+    def __new__(cls, value=None, name="unknown", type=None, length=0, enum=None):
         return super(TagInfo, cls).__new__(
             cls, value, name, type, length, enum or {})
 

Tests/test_file_tiff_metadata.py

@@ -185,6 +185,20 @@ class TestFileTiffMetadata(PillowTestCase):
         self.assertEqual(im.tag_v2.tagtype[34675], 1)
         self.assertTrue(im.info['icc_profile'])
 
+    def test_exif_div_zero(self):
+        im = hopper()
+        info = TiffImagePlugin.ImageFileDirectory_v2()
+        info[41988] = TiffImagePlugin.IFDRational(0,0)
+
+        out = self.tempfile('temp.tiff')
+        im.save(out, tiffinfo=info, compression='raw')
+
+        reloaded = Image.open(out)
+        self.assertEqual(0, reloaded.tag_v2[41988][0].numerator)
+        self.assertEqual(0, reloaded.tag_v2[41988][0].denominator)
+
+
+
 
 if __name__ == '__main__':
     unittest.main()

Tests/test_tiff_ifdrational.py

@@ -1,7 +1,8 @@
 from __future__ import print_function
 
-from helper import PillowTestCase
+from helper import PillowTestCase, hopper
 
+from PIL import TiffImagePlugin, Image
 from PIL.TiffImagePlugin import IFDRational
 
 from fractions import Fraction
@@ -44,3 +45,17 @@ class Test_IFDRational(PillowTestCase):
         self.assert_(xres and 1)
         self.assert_(xres and yres)
 
+
+    def test_ifd_rational_save(self):
+        for libtiff in (True, False):
+            TiffImagePlugin.WRITE_LIBTIFF = libtiff
+            
+            im = hopper()
+            out = self.tempfile('temp.tiff')
+            res = IFDRational(301,1)
+            im.save(out, dpi=(res,res), compression='raw')
+
+            reloaded = Image.open(out)
+            self.assertEqual(float(IFDRational(301,1)),
+                             float(reloaded.tag_v2[282]))
+