If previous disposal was 2, do not fill identical pixels

Tests/test_file_gif.py

@@ -647,6 +647,9 @@ def test_dispose2_palette(tmp_path: Path) -> None:
             # Center remains red every frame
             assert rgb_img.getpixel((50, 50)) == circle
 
+            # Check that frame transparency wasn't added unnecessarily
+            assert img._frame_transparency is None
+
 
 def test_dispose2_diff(tmp_path: Path) -> None:
     out = str(tmp_path / "temp.gif")

src/PIL/GifImagePlugin.py

@@ -638,7 +638,11 @@ def _write_multiple_frames(im, fp, palette):
                         background_im = Image.new("P", im_frame.size, background)
                         background_im.putpalette(im_frames[0]["im"].palette)
                     delta, bbox = _getbbox(background_im, im_frame)
-                if encoderinfo.get("optimize") and im_frame.mode != "1":
+                if (
+                    encoderinfo.get("optimize")
+                    and im_frames[-1]["encoderinfo"].get("disposal") != 2
+                    and im_frame.mode != "1"
+                ):
                     if "transparency" not in encoderinfo:
                         try:
                             encoderinfo["transparency"] = (