When saving RGBA, make use of first transparent palette entry

python-pillow · Nov 30, 2021 · 59b08e4 · 59b08e4
1 parent bd00cd9
commit 59b08e4
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Showing 2 changed files with 17 additions and 1 deletion.
diff --git a/Tests/test_file_gif.py b/Tests/test_file_gif.py
@@ -927,3 +927,13 @@ def test_missing_background():
     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")
+
+
+def test_saving_rgba(tmp_path):
+    out = str(tmp_path / "temp.gif")
+    with Image.open("Tests/images/transparent.png") as im:
+        im.save(out)
+
+    with Image.open(out) as reloaded:
+        reloaded_rgba = reloaded.convert("RGBA")
+        assert reloaded_rgba.load()[0, 0][3] == 0
diff --git a/src/PIL/GifImagePlugin.py b/src/PIL/GifImagePlugin.py
@@ -370,7 +370,13 @@ def _normalize_mode(im, initial_call=False):
             palette_size = 256
             if im.palette:
                 palette_size = len(im.palette.getdata()[1]) // 3
-            return im.convert("P", palette=Image.ADAPTIVE, colors=palette_size)
+            im = im.convert("P", palette=Image.ADAPTIVE, colors=palette_size)
+            if im.palette.mode == "RGBA":
+                for rgba in im.palette.colors.keys():
+                    if rgba[3] == 0:
+                        im.info["transparency"] = im.palette.colors[rgba]
+                        break
+            return im
         else:
             return im.convert("P")
     return im.convert("L")