Added USE_RAW_ALPHA (#8602)

Co-authored-by: Andrew Murray <[email protected]>

Author: radarhere

Tests/test_file_bmp.py

@@ -224,3 +224,13 @@ def test_offset() -> None:
     # to exclude the palette size from the pixel data offset
     with Image.open("Tests/images/pal8_offset.bmp") as im:
         assert_image_equal_tofile(im, "Tests/images/bmp/g/pal8.bmp")
+
+
+def test_use_raw_alpha(monkeypatch: pytest.MonkeyPatch) -> None:
+    with Image.open("Tests/images/bmp/g/rgb32.bmp") as im:
+        assert im.info["compression"] == BmpImagePlugin.BmpImageFile.COMPRESSIONS["RAW"]
+        assert im.mode == "RGB"
+
+    monkeypatch.setattr(BmpImagePlugin, "USE_RAW_ALPHA", True)
+    with Image.open("Tests/images/bmp/g/rgb32.bmp") as im:
+        assert im.mode == "RGBA"

src/PIL/BmpImagePlugin.py

@@ -48,6 +48,8 @@
     32: ("RGB", "BGRX"),
 }
 
+USE_RAW_ALPHA = False
+
 
 def _accept(prefix: bytes) -> bool:
     return prefix.startswith(b"BM")
@@ -242,7 +244,9 @@ def _bitmap(self, header: int = 0, offset: int = 0) -> None:
                 msg = "Unsupported BMP bitfields layout"
                 raise OSError(msg)
         elif file_info["compression"] == self.COMPRESSIONS["RAW"]:
-            if file_info["bits"] == 32 and header == 22:  # 32-bit .cur offset
+            if file_info["bits"] == 32 and (
+                header == 22 or USE_RAW_ALPHA  # 32-bit .cur offset
+            ):
                 raw_mode, self._mode = "BGRA", "RGBA"
         elif file_info["compression"] in (
             self.COMPRESSIONS["RLE8"],