From bdc53f6c4d499c918cc8d050ed163b8b9a178fe3 Mon Sep 17 00:00:00 2001
From: Andrew Murray <radarhere@users.noreply.github.com>
Date: Wed, 28 Aug 2024 18:33:43 +1000
Subject: [PATCH] Expand C image to match GIF frame image size

---
 Tests/images/test_extents_transparency.gif | Bin 0 -> 415 bytes
 Tests/test_file_gif.py                     |  37 ++++++++++++++++-----
 src/PIL/GifImagePlugin.py                  |  18 ++++++++++
 3 files changed, 47 insertions(+), 8 deletions(-)
 create mode 100644 Tests/images/test_extents_transparency.gif

diff --git a/Tests/images/test_extents_transparency.gif b/Tests/images/test_extents_transparency.gif
new file mode 100644
index 0000000000000000000000000000000000000000..739c82ad47c73560495e23c4b44bab5e1a88184f
GIT binary patch
literal 415
zcmZ?wbhEHbOkqf2Xk=jc&wv1mKUo+V7#JCJKtdpS29AXcj2to^8x|aF<`CA3Ik92k
z;dTLKuQ?tY7ai@EFwVMjV&mfD{R+-qGM<~3oSdu?yej78rlqH+8zi5a<GFd++1VDw
zukM`Oy!`xphh{EWuPrMsF7}wL6?<yS%FD|G7JJS0+PdoM>WIx*cTa6yeSLkx;VxP4
zZEJ3B&bYiP_Vl*3x3?EOJ~h{S`?|ZkD?Y!vdwTo&`}-T1x#fIzY<PIMLs&cROhkbL
QgF8X*7%><P9q(8J09oF=N&o-=

literal 0
HcmV?d00001

diff --git a/Tests/test_file_gif.py b/Tests/test_file_gif.py
index 8cefdb628..7c332149d 100644
--- a/Tests/test_file_gif.py
+++ b/Tests/test_file_gif.py
@@ -1378,16 +1378,37 @@ def test_lzw_bits() -> None:
         im.load()
 
 
-def test_extents() -> None:
-    with Image.open("Tests/images/test_extents.gif") as im:
-        assert im.size == (100, 100)
+@pytest.mark.parametrize(
+    "test_file, loading_strategy",
+    (
+        ("test_extents.gif", GifImagePlugin.LoadingStrategy.RGB_AFTER_FIRST),
+        (
+            "test_extents.gif",
+            GifImagePlugin.LoadingStrategy.RGB_AFTER_DIFFERENT_PALETTE_ONLY,
+        ),
+        (
+            "test_extents_transparency.gif",
+            GifImagePlugin.LoadingStrategy.RGB_AFTER_FIRST,
+        ),
+    ),
+)
+def test_extents(test_file, loading_strategy) -> None:
+    GifImagePlugin.LOADING_STRATEGY = loading_strategy
+    try:
+        with Image.open("Tests/images/" + test_file) as im:
+            assert im.size == (100, 100)
 
-        # Check that n_frames does not change the size
-        assert im.n_frames == 2
-        assert im.size == (100, 100)
+            # Check that n_frames does not change the size
+            assert im.n_frames == 2
+            assert im.size == (100, 100)
 
-        im.seek(1)
-        assert im.size == (150, 150)
+            im.seek(1)
+            assert im.size == (150, 150)
+
+            im.load()
+            assert im.im.size == (150, 150)
+    finally:
+        GifImagePlugin.LOADING_STRATEGY = GifImagePlugin.LoadingStrategy.RGB_AFTER_FIRST
 
 
 def test_missing_background() -> None:
diff --git a/src/PIL/GifImagePlugin.py b/src/PIL/GifImagePlugin.py
index fa8137fb9..82f58905d 100644
--- a/src/PIL/GifImagePlugin.py
+++ b/src/PIL/GifImagePlugin.py
@@ -438,6 +438,13 @@ class GifImageFile(ImageFile.ImageFile):
                 self.im.putpalette("RGB", *self._frame_palette.getdata())
             else:
                 self._im = None
+        if not self._prev_im and self._im is not None and self.size != self.im.size:
+            expanded_im = Image.core.fill(self.im.mode, self.size)
+            if self._frame_palette:
+                expanded_im.putpalette("RGB", *self._frame_palette.getdata())
+            expanded_im.paste(self.im, (0, 0) + self.im.size)
+
+            self.im = expanded_im
         self._mode = temp_mode
         self._frame_palette = None
 
@@ -455,6 +462,17 @@ class GifImageFile(ImageFile.ImageFile):
             return
         if not self._prev_im:
             return
+        if self.size != self._prev_im.size:
+            if self._frame_transparency is not None:
+                expanded_im = Image.core.fill("RGBA", self.size)
+            else:
+                expanded_im = Image.core.fill("P", self.size)
+                expanded_im.putpalette("RGB", "RGB", self.im.getpalette())
+                expanded_im = expanded_im.convert("RGB")
+            expanded_im.paste(self._prev_im, (0, 0) + self._prev_im.size)
+
+            self._prev_im = expanded_im
+            assert self._prev_im is not None
         if self._frame_transparency is not None:
             self.im.putpalettealpha(self._frame_transparency, 0)
             frame_im = self.im.convert("RGBA")