Improve support for TGA images in P mode with an RGBA palette

Tests/test_file_tga.py

@@ -88,6 +88,24 @@ def test_palette_depth_16(tmp_path: Path) -> None:
             assert_image_equal_tofile(reloaded.convert("RGBA"), "Tests/images/p_16.png")
 
 
+def test_palette_depth_32(tmp_path: Path) -> None:
+    im = Image.frombytes("L", (1, 2), bytes((0, 1)))
+    data = [255, 0, 0, 255, 0, 0, 255, 0]
+    im.putpalette(data, "RGBA")
+
+    out = tmp_path / "temp.tga"
+    im.save(out)
+
+    with Image.open(out) as reloaded:
+        assert reloaded.palette is not None
+        assert reloaded.palette.mode == "RGBA"
+        assert reloaded.getpalette(None) == data
+
+        reloaded_rgba = reloaded.convert("RGBA")
+    assert reloaded_rgba.getpixel((0, 0)) == (255, 0, 0, 255)
+    assert reloaded_rgba.getpixel((0, 1)) == (0, 0, 255, 0)
+
+
 def test_rgba_16() -> None:
     with Image.open("Tests/images/rgba16.tga") as im:
         assert im.mode == "RGBA"

src/PIL/TgaImagePlugin.py

@@ -134,6 +134,7 @@ def _open(self) -> None:
                 self.palette = ImagePalette.raw(
                     "BGRA", bytes(4 * start) + self.fp.read(4 * size)
                 )
+                self.palette.mode = "RGBA"
             else:
                 msg = "unknown TGA map depth"
                 raise SyntaxError(msg)
@@ -224,8 +225,13 @@ def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
         warnings.warn("id_section has been trimmed to 255 characters")
 
     if colormaptype:
-        palette = im.im.getpalette("RGB", "BGR")
-        colormaplength, colormapentry = len(palette) // 3, 24
+        assert im.palette is not None
+        if im.palette.mode == "RGBA":
+            palette = im.im.getpalette("RGBA", "BGRA")
+            colormaplength, colormapentry = len(palette) // 4, 32
+        else:
+            palette = im.im.getpalette("RGB", "BGR")
+            colormaplength, colormapentry = len(palette) // 3, 24
     else:
         colormaplength, colormapentry = 0, 0