corrected processing of images in P mode with transparency=0 (#238)

Signed-off-by: Alexander Piskun <[email protected]>

CHANGELOG.md

@@ -1,5 +1,11 @@
 All notable changes to this project will be documented in this file.
 
+## [0.x.x - 2024-0x-xx]
+
+### Fixed
+
+- Processing of the images in `P` mode with `transparency` = 0. #238
+
 ## [0.16.0 - 2024-04-02]
 
 This release contains breaking change for monochrome images.

pillow_heif/misc.py

@@ -282,7 +282,7 @@ def _xmp_from_pillow(img: Image.Image) -> Optional[bytes]:
 def _pil_to_supported_mode(img: Image.Image) -> Image.Image:
     # We support "YCbCr" for encoding in Pillow plugin mode and do not call this function.
     if img.mode == "P":
-        mode = "RGBA" if img.info.get("transparency") else "RGB"
+        mode = "RGBA" if img.info.get("transparency", None) is not None else "RGB"
         img = img.convert(mode=mode)
     elif img.mode == "I":
         img = img.convert(mode="I;16L")

tests/write_test.py

@@ -8,7 +8,7 @@
 import helpers
 import pytest
 from packaging.version import parse as parse_version
-from PIL import Image, ImageSequence
+from PIL import Image, ImageDraw, ImageSequence
 
 import pillow_heif
 
@@ -594,6 +594,22 @@ def test_input_chroma_value():
     assert im.info["chroma"] == 420
 
 
+@pytest.mark.parametrize("save_format", ("HEIF", "AVIF"))
+def test_transparency_parameter(save_format):
+    im = Image.new("P", size=(64, 64))
+    draw = ImageDraw.Draw(im)
+    draw.rectangle(xy=[(0, 0), (32, 32)], fill=255)
+    draw.rectangle(xy=[(32, 32), (64, 64)], fill=255)
+
+    buf_png = BytesIO()
+    im.save(buf_png, format="PNG", transparency=0)
+    im_png = Image.open(buf_png)
+    buf_out = BytesIO()
+    im_png.save(buf_out, format=save_format, quality=-1)
+
+    helpers.assert_image_equal(im_png.convert("RGBA"), Image.open(buf_out))
+
+
 def test_invalid_encoder():
     im_rgb = helpers.gradient_rgba()
     buf = BytesIO()