From a682ceaf47abbe28dc70c6bd4aab06f8f3f4ac90 Mon Sep 17 00:00:00 2001
From: Andrew Murray <radarhere@users.noreply.github.com>
Date: Thu, 13 Jul 2023 15:20:44 +1000
Subject: [PATCH] Do not use transparency if it has been removed when
 normalizing mode

---
 Tests/test_file_gif.py    | 15 +++++++++++++++
 src/PIL/GifImagePlugin.py |  6 +-----
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/Tests/test_file_gif.py b/Tests/test_file_gif.py
index f4a17264f..b1c9f731f 100644
--- a/Tests/test_file_gif.py
+++ b/Tests/test_file_gif.py
@@ -1086,6 +1086,21 @@ def test_transparent_optimize(tmp_path):
         assert reloaded.info["transparency"] == reloaded.getpixel((252, 0))
 
 
+def test_removed_transparency(tmp_path):
+    out = str(tmp_path / "temp.gif")
+    im = Image.new("RGB", (256, 1))
+
+    for x in range(256):
+        im.putpixel((x, 0), (x, 0, 0))
+
+    im.info["transparency"] = (255, 255, 255)
+    with pytest.warns(UserWarning):
+        im.save(out)
+
+    with Image.open(out) as reloaded:
+        assert "transparency" not in reloaded.info
+
+
 def test_rgb_transparency(tmp_path):
     out = str(tmp_path / "temp.gif")
 
diff --git a/src/PIL/GifImagePlugin.py b/src/PIL/GifImagePlugin.py
index cf2993e38..255643de6 100644
--- a/src/PIL/GifImagePlugin.py
+++ b/src/PIL/GifImagePlugin.py
@@ -683,11 +683,7 @@ def get_interlace(im):
 def _write_local_header(fp, im, offset, flags):
     transparent_color_exists = False
     try:
-        if "transparency" in im.encoderinfo:
-            transparency = im.encoderinfo["transparency"]
-        else:
-            transparency = im.info["transparency"]
-        transparency = int(transparency)
+        transparency = int(im.encoderinfo["transparency"])
     except (KeyError, ValueError):
         pass
     else: