Current delta is determined by previous disposal

Author: radarhere

Tests/test_file_gif.py

@@ -737,6 +737,25 @@ def test_dispose2_background_frame(tmp_path: Path) -> None:
         assert im.n_frames == 3
 
 
+def test_dispose2_previous_frame(tmp_path: Path) -> None:
+    out = str(tmp_path / "temp.gif")
+
+    im = Image.new("P", (100, 100))
+    im.info["transparency"] = 0
+    d = ImageDraw.Draw(im)
+    d.rectangle([(0, 0), (100, 50)], 1)
+    im.putpalette((0, 0, 0, 255, 0, 0))
+
+    im2 = Image.new("P", (100, 100))
+    im2.putpalette((0, 0, 0))
+
+    im.save(out, save_all=True, append_images=[im2], disposal=[0, 2])
+
+    with Image.open(out) as im:
+        im.seek(1)
+        assert im.getpixel((0, 0)) == (0, 0, 0, 255)
+
+
 def test_transparency_in_second_frame(tmp_path: Path) -> None:
     out = str(tmp_path / "temp.gif")
     with Image.open("Tests/images/different_transparency.gif") as im:

src/PIL/GifImagePlugin.py

@@ -629,20 +629,16 @@ def _write_multiple_frames(im, fp, palette):
                             "duration"
                         ]
                     continue
-                if encoderinfo.get("disposal") == 2:
+                if im_frames[-1]["encoderinfo"].get("disposal") == 2:
                     if background_im is None:
                         color = im.encoderinfo.get(
                             "transparency", im.info.get("transparency", (0, 0, 0))
                         )
                         background = _get_background(im_frame, color)
                         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_frames[-1]["encoderinfo"].get("disposal") != 2
-                    and im_frame.mode != "1"
-                ):
+                    bbox = _getbbox(background_im, im_frame)[1]
+                elif encoderinfo.get("optimize") and im_frame.mode != "1":
                     if "transparency" not in encoderinfo:
                         try:
                             encoderinfo["transparency"] = (