Skip tests that require libtiff if it is not installed, fixes #1866

Tests/test_file_libtiff.py

@@ -489,6 +489,21 @@ class TestFileLibTiff(LibTiffTestCase):
         im.save(out, format='TIFF')
         TiffImagePlugin.WRITE_LIBTIFF = False
 
+    def test_page_number_x_0(self):
+        # Issue 973
+        # Test TIFF with tag 297 (Page Number) having value of 0 0.
+        # The first number is the current page number.
+        # The second is the total number of pages, zero means not available.
+        outfile = self.tempfile("temp.tif")
+        # Created by printing a page in Chrome to PDF, then:
+        # /usr/bin/gs -q -sDEVICE=tiffg3 -sOutputFile=total-pages-zero.tif
+        # -dNOPAUSE /tmp/test.pdf -c quit
+        infile = "Tests/images/total-pages-zero.tif"
+        im = Image.open(infile)
+        # Should not divide by zero
+        im.save(outfile)
+
+
 
 if __name__ == '__main__':
     unittest.main()

Tests/test_tiff_ifdrational.py

@@ -45,7 +45,11 @@ class Test_IFDRational(PillowTestCase):
         self.assertTrue(xres and yres)
 
     def test_ifd_rational_save(self):
-        for libtiff in (True, False):
+        methods = (True, False)
+        if 'libtiff_encoder' not in dir(Image.core):
+            methods = (False)
+            
+        for libtiff in methods:
             TiffImagePlugin.WRITE_LIBTIFF = libtiff
 
             im = hopper()