Python Pillow 透明 gif 不起作用

Question

我正在尝试制作以下旋转图标的 gif:

为了尝试实现这一点，我使用 Pillow 库在 Python 中运行以下代码:

from PIL import Image, ImageDraw

images = []

icon = Image.open("cameraIcon.png")

for i in range(0, 360):
    images.append(icon.rotate(i))

images[0].save('loadingIcon.gif', format='GIF', save_all=True, append_images=images[1:], duration=40, loop=0, transparency=0)

但是此代码的输出与我想要的不匹配，我得到以下 gif:

我不知道发生了什么，希望得到任何帮助，谢谢。

Answer 1

这里有两个主要问题。

1. 您没有指定Image.save() 的disposal 参数。此参数控制前一帧相对于背景的布置方式。如果未指定，则前一帧“逗留”到下一帧。添加 disposal=2 应该可以解决该特定问题。
2. 其次，截至撰写本文时，pillow 库存在一个影响透明度的长期问题。在许多情况下，它会导致透明区域被黑色像素取代。 issue 4640 中描述了该问题枕头 Github 存储库的。一位用户在相关 issue 4644 中提供了一种解决方法.只要您不需要支持部分 alpha 透明度，此解决方法就可以正常工作。我发现它会使 alpha 变平并且在那种情况下不起作用。

这是我使用的代码(改编自 issue 4644 中的代码)以防有帮助。您只需使用图像和持续时间调用 save_transparent_gif 函数即可。

# This code adapted from https://github.com/python-pillow/Pillow/issues/4644 to resolve an issue
# described in https://github.com/python-pillow/Pillow/issues/4640
#
# There is a long-standing issue with the Pillow library that messes up GIF transparency by replacing the
# transparent pixels with black pixels (among other issues) when the GIF is saved using PIL.Image.save().
# This code works around the issue and allows us to properly generate transparent GIFs.

from typing import Tuple, List, Union
from collections import defaultdict
from random import randrange
from itertools import chain

from PIL.Image import Image


class TransparentAnimatedGifConverter(object):
    _PALETTE_SLOTSET = set(range(256))

    def __init__(self, img_rgba: Image, alpha_threshold: int = 0):
        self._img_rgba = img_rgba
        self._alpha_threshold = alpha_threshold

    def _process_pixels(self):
        """Set the transparent pixels to the color 0."""
        self._transparent_pixels = set(
            idx for idx, alpha in enumerate(
                self._img_rgba.getchannel(channel='A').getdata())
            if alpha <= self._alpha_threshold)

    def _set_parsed_palette(self):
        """Parse the RGB palette color `tuple`s from the palette."""
        palette = self._img_p.getpalette()
        self._img_p_used_palette_idxs = set(
            idx for pal_idx, idx in enumerate(self._img_p_data)
            if pal_idx not in self._transparent_pixels)
        self._img_p_parsedpalette = dict(
            (idx, tuple(palette[idx * 3:idx * 3 + 3]))
            for idx in self._img_p_used_palette_idxs)

    def _get_similar_color_idx(self):
        """Return a palette index with the closest similar color."""
        old_color = self._img_p_parsedpalette[0]
        dict_distance = defaultdict(list)
        for idx in range(1, 256):
            color_item = self._img_p_parsedpalette[idx]
            if color_item == old_color:
                return idx
            distance = sum((
                abs(old_color[0] - color_item[0]),  # Red
                abs(old_color[1] - color_item[1]),  # Green
                abs(old_color[2] - color_item[2])))  # Blue
            dict_distance[distance].append(idx)
        return dict_distance[sorted(dict_distance)[0]][0]

    def _remap_palette_idx_zero(self):
        """Since the first color is used in the palette, remap it."""
        free_slots = self._PALETTE_SLOTSET - self._img_p_used_palette_idxs
        new_idx = free_slots.pop() if free_slots else \
            self._get_similar_color_idx()
        self._img_p_used_palette_idxs.add(new_idx)
        self._palette_replaces['idx_from'].append(0)
        self._palette_replaces['idx_to'].append(new_idx)
        self._img_p_parsedpalette[new_idx] = self._img_p_parsedpalette[0]
        del(self._img_p_parsedpalette[0])

    def _get_unused_color(self) -> tuple:
        """ Return a color for the palette that does not collide with any other already in the palette."""
        used_colors = set(self._img_p_parsedpalette.values())
        while True:
            new_color = (randrange(256), randrange(256), randrange(256))
            if new_color not in used_colors:
                return new_color

    def _process_palette(self):
        """Adjust palette to have the zeroth color set as transparent. Basically, get another palette
        index for the zeroth color."""
        self._set_parsed_palette()
        if 0 in self._img_p_used_palette_idxs:
            self._remap_palette_idx_zero()
        self._img_p_parsedpalette[0] = self._get_unused_color()

    def _adjust_pixels(self):
        """Convert the pixels into their new values."""
        if self._palette_replaces['idx_from']:
            trans_table = bytearray.maketrans(
                bytes(self._palette_replaces['idx_from']),
                bytes(self._palette_replaces['idx_to']))
            self._img_p_data = self._img_p_data.translate(trans_table)
        for idx_pixel in self._transparent_pixels:
            self._img_p_data[idx_pixel] = 0
        self._img_p.frombytes(data=bytes(self._img_p_data))

    def _adjust_palette(self):
        """Modify the palette in the new `Image`."""
        unused_color = self._get_unused_color()
        final_palette = chain.from_iterable(
            self._img_p_parsedpalette.get(x, unused_color) for x in range(256))
        self._img_p.putpalette(data=final_palette)

    def process(self) -> Image:
        """Return the processed mode `P` `Image`."""
        self._img_p = self._img_rgba.convert(mode='P')
        self._img_p_data = bytearray(self._img_p.tobytes())
        self._palette_replaces = dict(idx_from=list(), idx_to=list())
        self._process_pixels()
        self._process_palette()
        self._adjust_pixels()
        self._adjust_palette()
        self._img_p.info['transparency'] = 0
        self._img_p.info['background'] = 0
        return self._img_p


def _create_animated_gif(images: List[Image], durations: Union[int, List[int]]) -> Tuple[Image, dict]:
    """If the image is a GIF, create an its thumbnail here."""
    save_kwargs = dict()
    new_images: List[Image] = []

    for frame in images:
        thumbnail = frame.copy()  # type: Image
        thumbnail_rgba = thumbnail.convert(mode='RGBA')
        thumbnail_rgba.thumbnail(size=frame.size, reducing_gap=3.0)
        converter = TransparentAnimatedGifConverter(img_rgba=thumbnail_rgba)
        thumbnail_p = converter.process()  # type: Image
        new_images.append(thumbnail_p)

    output_image = new_images[0]
    save_kwargs.update(
        format='GIF',
        save_all=True,
        optimize=False,
        append_images=new_images[1:],
        duration=durations,
        disposal=2,  # Other disposals don't work
        loop=0)
    return output_image, save_kwargs


def save_transparent_gif(images: List[Image], durations: Union[int, List[int]], save_file):
    """Creates a transparent GIF, adjusting to avoid transparency issues that are present in the PIL library

    Note that this does NOT work for partial alpha. The partial alpha gets discarded and replaced by solid colors.

    Parameters:
        images: a list of PIL Image objects that compose the GIF frames
        durations: an int or List[int] that describes the animation durations for the frames of this GIF
        save_file: A filename (string), pathlib.Path object or file object. (This parameter corresponds
                   and is passed to the PIL.Image.save() method.)
    Returns:
        Image - The PIL Image object (after first saving the image to the specified target)
    """
    root_frame, save_args = _create_animated_gif(images, durations)
    root_frame.save(save_file, **save_args)