Merge pull request #5390 from radarhere/gif_missing_background

Use zero if GIF background color index is missing

Author: hugovk

Tests/images/missing_background.gif

@@ -864,3 +864,11 @@ def test_extents():
         assert im.size == (100, 100)
         im.seek(1)
         assert im.size == (150, 150)
+
+
+def test_missing_background():
+    # The Global Color Table Flag isn't set, so there is no background color index,
+    # but the disposal method is "Restore to background color"
+    with Image.open("Tests/images/missing_background.gif") as im:
+        im.seek(1)
+        assert_image_equal_tofile(im, "Tests/images/missing_background_first_frame.gif")

Tests/images/missing_background_first_frame.gif

@@ -270,14 +270,14 @@ def _seek(self, frame):
 
                 Image._decompression_bomb_check(dispose_size)
                 self.dispose = Image.core.fill(
-                    "P", dispose_size, self.info["background"]
+                    "P", dispose_size, self.info.get("background", 0)
                 )
             else:
                 # replace with previous contents
                 if self.im:
                     # only dispose the extent in this frame
                     self.dispose = self._crop(self.im, self.dispose_extent)
-        except (AttributeError, KeyError):
+        except AttributeError:
             pass
 
         if interlace is not None: