From 3cb2413066e3d1dabdb26db16c3367d8dd558982 Mon Sep 17 00:00:00 2001
From: Andrew Murray <radarhere@users.noreply.github.com>
Date: Thu, 8 Apr 2021 08:04:20 +1000
Subject: [PATCH] Use zero if background color index is missing

---
 Tests/images/missing_background.gif             | Bin 0 -> 660 bytes
 Tests/images/missing_background_first_frame.gif | Bin 0 -> 950 bytes
 Tests/test_file_gif.py                          |   8 ++++++++
 src/PIL/GifImagePlugin.py                       |   4 ++--
 4 files changed, 10 insertions(+), 2 deletions(-)
 create mode 100644 Tests/images/missing_background.gif
 create mode 100644 Tests/images/missing_background_first_frame.gif

diff --git a/Tests/images/missing_background.gif b/Tests/images/missing_background.gif
new file mode 100644
index 0000000000000000000000000000000000000000..550d68d81010bccaf734489d9352b959881796aa
GIT binary patch
literal 660
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literal 0
HcmV?d00001

diff --git a/Tests/images/missing_background_first_frame.gif b/Tests/images/missing_background_first_frame.gif
new file mode 100644
index 0000000000000000000000000000000000000000..be2c95b99936a1a3feaa0203bde0e322fb4a13dc
GIT binary patch
literal 950
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literal 0
HcmV?d00001

diff --git a/Tests/test_file_gif.py b/Tests/test_file_gif.py
index 52d7f035d..400ef43db 100644
--- a/Tests/test_file_gif.py
+++ b/Tests/test_file_gif.py
@@ -853,3 +853,11 @@ 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")
diff --git a/src/PIL/GifImagePlugin.py b/src/PIL/GifImagePlugin.py
index 139f91ea0..dd83d1763 100644
--- a/src/PIL/GifImagePlugin.py
+++ b/src/PIL/GifImagePlugin.py
@@ -270,14 +270,14 @@ class GifImageFile(ImageFile.ImageFile):
 
                 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: