Saving animated GIF as WebP raises "Background color" error

[jeevic]

What did you do?

convert a animate gif format to animate webP format

What did you expect to happen?

convert success

What actually happened?

osError happen

Traceback (most recent call last):
  File "/Users/jeevi/Documents/WWW/study/python/pillow_img/img/img.py", line 197, in <module>
    im.save(bts, "webP", save_all=True, quality=75,  optimize=True)
  File "/Users/jeevi/Documents/WWW/study/python/pillow_img/python/lib/python3.7/site-packages/PIL/Image.py", line 2240, in save
    save_handler(self, fp, filename)
  File "/Users/jeevi/Documents/WWW/study/python/pillow_img/python/lib/python3.7/site-packages/PIL/WebPImagePlugin.py", line 227, in _save_all
    % str(background)
OSError: Background color is not an RGBA tuple clamped to (0-255): 255

What are your OS, Python and Pillow versions?

• OS: macos Monterey version 12.2.1
• Python: 3.7.11
• Pillow: 8.4.0

use picture

 file = "./YD_cnt_11_019HNWhSb3SJ.gif"
    t = time.time()
    with Image.open(file) as im:
        print("info:", im.info)
        bts = BytesIO()
        im.save(bts, "webP", save_all=True, quality=75,  optimize=True)
        print("长度:{} \n".format(len(bts.getvalue())))
        with open("YD_cnt_11_019HNWhSb3SJ.gif.webP", "wb") as f:
            f.write(bts.getvalue())
        t2 = time.time()
        cost = int(round(t2 * 1000)) - int(round(t * 1000))
        print("耗时:{}ms\n".format(cost))

print info: {'version': b'GIF89a', 'background': 255, 'duration': 160, 'extension': (b'NETSCAPE2.0', 803), 'loop': 0}

i found load gif the background value is 255 and palette is no

webP plugin code can not support

Pillow/src/PIL/WebPImagePlugin.py

Lines 183 to 194 in 15dc291

	if "background" in encoderinfo:
	background = encoderinfo["background"]
	elif "background" in im.info:
	background = im.info["background"]
	if isinstance(background, int):
	# GifImagePlugin stores a global color table index in
	# info["background"]. So it must be converted to an RGBA value
	palette = im.getpalette()
	if palette:
	r, g, b = palette[background * 3 : (background + 1) * 3]
	background = (r, g, b, 0)

error line

Pillow/src/PIL/WebPImagePlugin.py

Lines 220 to 229 in 15dc291

	if (
	not isinstance(background, (list, tuple))
	or len(background) != 4
	or not all(v >= 0 and v < 256 for v in background)
	):
	raise OSError(
	"Background color is not an RGBA tuple clamped to (0-255): %s"
	% str(background)
	)

imagemagick get background is white

 Rendering intent: Perceptual
  Gamma: 0.454545
  Chromaticity:
    red primary: (0.64,0.33)
    green primary: (0.3,0.6)
    blue primary: (0.15,0.06)
    white point: (0.3127,0.329)
  Matte color: grey74
  Background color: white
  Border color: srgb(223,223,223)
  Transparent color: none
  Interlace: None
  Intensity: Undefined
  Compose: Over
  Page geometry: 440x261+0+0
  Dispose: None
  Delay: 16x100
  Iterations: 0
  Scene: 18 of 19
  Compression: LZW
  Orientation: Undefined
  Properties:
    date:create: 2022-03-18T09:24:11+00:00
    date:modify: 2022-03-18T09:24:02+00:00
    signature: 34c9a1dea7efa1fa2e31c58a9483d118b808f13774f8e2619dcad80c1cec2119
  Artifacts:
    verbose: true
  Tainted: False
  Filesize: 951740B
  Number pixels: 114840
  Pixels per second: 61879P
  User time: 1.830u
  Elapsed time: 0:02.855
  Version: ImageMagick 7.1.0-4 Q16 x86_64 2021-07-18 https://imagemagick.org

use pillow i open gif and save gif is success

i think webP plugin can't compatibility background scene

[radarhere]

I've created PR #6147 to resolve this.