Fixed reading uncompressed BLP2 with alpha

Author: radarhere

Tests/test_file_blp.py

@@ -2,7 +2,12 @@
 
 from PIL import BlpImagePlugin, Image
 
-from .helper import assert_image_equal, assert_image_equal_tofile, hopper
+from .helper import (
+    assert_image_equal,
+    assert_image_equal_tofile,
+    assert_image_similar,
+    hopper,
+)
 
 
 def test_load_blp1():
@@ -33,6 +38,13 @@ def test_save(tmp_path):
     with Image.open(f) as reloaded:
         assert_image_equal(im.convert("RGB"), reloaded)
 
+    with Image.open("Tests/images/transparent.png") as im:
+        f = str(tmp_path / "temp.blp")
+        im.convert("P").save(f)
+
+        with Image.open(f) as reloaded:
+            assert_image_similar(im, reloaded, 8)
+
     im = hopper()
     with pytest.raises(ValueError):
         im.save(f)

src/PIL/BlpImagePlugin.py

@@ -406,7 +406,10 @@ def _load(self):
                     except struct.error:
                         break
                     b, g, r, a = palette[offset]
-                    data.extend((r, g, b))
+                    d = (r, g, b)
+                    if self._blp_alpha_depth:
+                        d += (a,)
+                    data.extend(d)
 
             elif self._blp_encoding == Encoding.DXT:
                 if self._blp_alpha_encoding == AlphaEncoding.DXT1: