Fix unexpected error when saving zero dimension images

Tests/test_file_gif.py

@@ -310,6 +310,14 @@ def test_roundtrip_save_all_1(tmp_path: Path) -> None:
         assert reloaded.getpixel((0, 0)) == 255
 
 
+@pytest.mark.parametrize("size", ((0, 1), (1, 0), (0, 0)))
+def test_save_zero(size: tuple[int, int]) -> None:
+    b = BytesIO()
+    im = Image.new("RGB", size)
+    with pytest.raises(SystemError):
+        im.save(b, "GIF")
+
+
 @pytest.mark.parametrize(
     "path, mode",
     (

Tests/test_file_pcx.py

@@ -37,6 +37,14 @@ def test_sanity(tmp_path: Path) -> None:
         im.save(f)
 
 
+@pytest.mark.parametrize("size", ((0, 1), (1, 0), (0, 0)))
+def test_save_zero(size: tuple[int, int]) -> None:
+    b = io.BytesIO()
+    im = Image.new("1", size)
+    with pytest.raises(ValueError):
+        im.save(b, "PCX")
+
+
 def test_p_4_planes() -> None:
     with Image.open("Tests/images/p_4_planes.pcx") as im:
         assert im.getpixel((0, 0)) == 3

Tests/test_file_spider.py

@@ -64,6 +64,14 @@ def test_save(tmp_path: Path) -> None:
         assert im2.format == "SPIDER"
 
 
+@pytest.mark.parametrize("size", ((0, 1), (1, 0), (0, 0)))
+def test_save_zero(size: tuple[int, int]) -> None:
+    b = BytesIO()
+    im = Image.new("1", size)
+    with pytest.raises(SystemError):
+        im.save(b, "SPIDER")
+
+
 def test_tempfile() -> None:
     # Arrange
     im = hopper()

src/PIL/GifImagePlugin.py

@@ -937,7 +937,13 @@ def _get_optimize(im: Image.Image, info: dict[str, Any]) -> list[int] | None:
     :param info: encoderinfo
     :returns: list of indexes of palette entries in use, or None
     """
-    if im.mode in ("P", "L") and info and info.get("optimize"):
+    if (
+        im.mode in ("P", "L")
+        and info
+        and info.get("optimize")
+        and im.width != 0
+        and im.height != 0
+    ):
         # Potentially expensive operation.
 
         # The palette saves 3 bytes per color not used, but palette

src/PIL/PcxImagePlugin.py

@@ -146,6 +146,10 @@ def _open(self) -> None:
 
 
 def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
+    if im.width == 0 or im.height == 0:
+        msg = "Cannot write empty image as PCX"
+        raise ValueError(msg)
+
     try:
         version, bits, planes, rawmode = SAVE[im.mode]
     except KeyError as e:

src/PIL/SpiderImagePlugin.py

@@ -244,7 +244,7 @@ def loadImageSeries(filelist: list[str] | None = None) -> list[Image.Image] | No
 
 def makeSpiderHeader(im: Image.Image) -> list[bytes]:
     nsam, nrow = im.size
-    lenbyt = nsam * 4  # There are labrec records in the header
+    lenbyt = max(1, nsam) * 4  # There are labrec records in the header
     labrec = int(1024 / lenbyt)
     if 1024 % lenbyt != 0:
         labrec += 1