Convert RGBA palette to RGBA image when saving WebP

python-pillow · Sep 25, 2023 · ad12cae · ad12cae
1 parent 6bbed1a
commit ad12cae
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Showing 2 changed files with 11 additions and 6 deletions.
diff --git a/Tests/test_file_webp.py b/Tests/test_file_webp.py
@@ -234,3 +234,13 @@ def test_duration(self, tmp_path):
 
         with Image.open(out_webp) as reloaded:
             assert reloaded.info["duration"] == 1000
+
+    def test_roundtrip_rgba_palette(self, tmp_path):
+        temp_file = str(tmp_path / "temp.webp")
+        im = Image.new("RGBA", (1, 1)).convert("P")
+        assert im.mode == "P"
+        assert im.palette.mode == "RGBA"
+        im.save(temp_file)
+
+        with Image.open(temp_file) as im:
+            assert im.getpixel((0, 0)) == (0, 0, 0, 0)
diff --git a/src/PIL/WebPImagePlugin.py b/src/PIL/WebPImagePlugin.py
@@ -332,12 +332,7 @@ def _save(im, fp, filename):
     exact = 1 if im.encoderinfo.get("exact") else 0
 
     if im.mode not in _VALID_WEBP_LEGACY_MODES:
-        alpha = (
-            "A" in im.mode
-            or "a" in im.mode
-            or (im.mode == "P" and "transparency" in im.info)
-        )
-        im = im.convert("RGBA" if alpha else "RGB")
+        im = im.convert("RGBA" if im.has_transparency_data() else "RGB")
 
     data = _webp.WebPEncode(
         im.tobytes(),