Raise ValueError if all sizes are too large for image

Author: radarhere

Tests/test_file_ico.py

@@ -224,6 +224,11 @@ def test_only_save_relevant_sizes(tmp_path: Path) -> None:
         # Assert
         assert reloaded.info["sizes"] == {(16, 16), (24, 24), (32, 32), (48, 48)}
 
+    im = Image.new("1", (1, 1))
+    outfile = tmp_path / "temp.ico"
+    with pytest.raises(ValueError, match="All sizes too large for image"):
+        im.save(outfile, sizes=[(2, 2)])
+
 
 def test_save_append_images(tmp_path: Path) -> None:
     # append_images should be used for scaled down versions of the image

src/PIL/IcoImagePlugin.py

@@ -93,6 +93,9 @@ def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
             frame = provided_im.copy()
             frame.thumbnail(size, Image.Resampling.LANCZOS, reducing_gap=None)
             frames.append(frame)
+    if not frames:
+        msg = "All sizes too large for image"
+        raise ValueError(msg)
     fp.write(o16(len(frames)))  # idCount(2)
     offset = fp.tell() + len(frames) * 16
     for frame in frames: