______________________________________________________________________ test_alpha[png] ______________________________________________________________________args = (), kwds = {'extension': 'png', 'request': <FixtureRequest for <Function test_alpha[png]>>} @wraps(func) def inner(*args, **kwds): with self._recreate_cm():> return func(*args, **kwds)/usr/lib64/python3.13/contextlib.py:85: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _lib/matplotlib/testing/compare.py:474: in compare_images expected_image = _load_image(expected)lib/matplotlib/testing/compare.py:405: in _load_image img = img.convert("RGB")_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _self = <PIL.PngImagePlugin.PngImageFile image mode=P size=200x100 at 0x7FF8F9401FD0>, mode = 'RGB', matrix = None, dither = None, palette = <Palette.WEB: 0>colors = 256 def convert( self, mode: str | None = None, matrix: tuple[float, ...] | None = None, dither: Dither | None = None, palette: Palette = Palette.WEB, colors: int = 256, ) -> Image: """ Returns a converted copy of this image. For the "P" mode, this method translates pixels through the palette. If mode is omitted, a mode is chosen so that all information in the image and the palette can be represented without a palette. This supports all possible conversions between "L", "RGB" and "CMYK". The ``matrix`` argument only supports "L" and "RGB". When translating a color image to grayscale (mode "L"), the library uses the ITU-R 601-2 luma transform:: L = R * 299/1000 + G * 587/1000 + B * 114/1000 The default method of converting a grayscale ("L") or "RGB" image into a bilevel (mode "1") image uses Floyd-Steinberg dither to approximate the original image luminosity levels. If dither is ``None``, all values larger than 127 are set to 255 (white), all other values to 0 (black). To use other thresholds, use the :py:meth:`~PIL.Image.Image.point` method. When converting from "RGBA" to "P" without a ``matrix`` argument, this passes the operation to :py:meth:`~PIL.Image.Image.quantize`, and ``dither`` and ``palette`` are ignored. When converting from "PA", if an "RGBA" palette is present, the alpha channel from the image will be used instead of the values from the palette. :param mode: The requested mode. See: :ref:`concept-modes`. :param matrix: An optional conversion matrix. If given, this should be 4- or 12-tuple containing floating point values. :param dither: Dithering method, used when converting from mode "RGB" to "P" or from "RGB" or "L" to "1". Available methods are :data:`Dither.NONE` or :data:`Dither.FLOYDSTEINBERG` (default). Note that this is not used when ``matrix`` is supplied. :param palette: Palette to use when converting from mode "RGB" to "P". Available palettes are :data:`Palette.WEB` or :data:`Palette.ADAPTIVE`. :param colors: Number of colors to use for the :data:`Palette.ADAPTIVE` palette. Defaults to 256. :rtype: :py:class:`~PIL.Image.Image` :returns: An :py:class:`~PIL.Image.Image` object. """ if mode in ("BGR;15", "BGR;16", "BGR;24"): deprecate(mode, 12) self.load() has_transparency = "transparency" in self.info if not mode and self.mode == "P": # determine default mode if self.palette: mode = self.palette.mode else: mode = "RGB" if mode == "RGB" and has_transparency: mode = "RGBA" if not mode or (mode == self.mode and not matrix): return self.copy() if matrix: # matrix conversion if mode not in ("L", "RGB"): msg = "illegal conversion" raise ValueError(msg) im = self.im.convert_matrix(mode, matrix) new_im = self._new(im) if has_transparency and self.im.bands == 3: transparency = new_im.info["transparency"] def convert_transparency( m: tuple[float, ...], v: tuple[int, int, int] ) -> int: value = m[0] * v[0] + m[1] * v[1] + m[2] * v[2] + m[3] * 0.5 return max(0, min(255, int(value))) if mode == "L": transparency = convert_transparency(matrix, transparency) elif len(mode) == 3: transparency = tuple( convert_transparency(matrix[i * 4 : i * 4 + 4], transparency) for i in range(0, len(transparency)) ) new_im.info["transparency"] = transparency return new_im if mode == "P" and self.mode == "RGBA": return self.quantize(colors) trns = None delete_trns = False # transparency handling if has_transparency: if (self.mode in ("1", "L", "I", "I;16") and mode in ("LA", "RGBA")) or ( self.mode == "RGB" and mode in ("La", "LA", "RGBa", "RGBA") ): # Use transparent conversion to promote from transparent # color to an alpha channel. new_im = self._new( self.im.convert_transparent(mode, self.info["transparency"]) ) del new_im.info["transparency"] return new_im elif self.mode in ("L", "RGB", "P") and mode in ("L", "RGB", "P"): t = self.info["transparency"] if isinstance(t, bytes): # Dragons. This can't be represented by a single color> warnings.warn( "Palette images with Transparency expressed in bytes should be " "converted to RGBA images" )E UserWarning: Palette images with Transparency expressed in bytes should be converted to RGBA imagesvenv/lib64/python3.13/site-packages/PIL/Image.py:1054: UserWarning
PR summary
@oscargus suggested oxipng in#29816.
I went with the hook suggestion of
-o 4compression (though their normal default is 2), though maybe we want to up it to the max, since it shouldn't happen very often. I did not enable metadata stripping (as suggested) since knowing what version of Matplotlib was used for the plot might be useful. I also didn't add alpha channel optmization, as they say it is technically lossy.PR checklist