ValueError: unknown raw mode for given image mode

[Darkpingouin]

What did you do?

I tried to save a BMP Image

What did you expect to happen?

Have the image saved

What actually happened?

I got a ValueError: unknown raw mode for given image mode error

What are your OS, Python and Pillow versions?

• OS: Ubuntu 22.04 LTS
• Python: 3.10.4
• Pillow: 9.1.1

Here is the link to the stackoverflow post with stuff i tried

from io import BytesIO

from PIL import Image


def get_img_base64(filename):
    # Open Image
    image = Image.open(filename)
    # Saving the format
    format = image.format
    buffered = BytesIO()
    image.save(buffered, format)  # CRASH HERE
    img_str = base64.b64encode(buffered.getvalue())
    return "data:image/" + format + ";base64," + img_str.decode()


get_img_base64("IMG.BMP")

Traceback of the error :

Traceback (most recent call last):
  File "test.py", line XXX, in XXX
    imgBase64 = get_img_base64(path)
  File "test.py", line XXX, in get_img_base64
    image.save(buffered, format)
  File "python3.10/site-packages/PIL/Image.py", line 2264, in save
    self._ensure_mutable()
  File "python3.10/site-packages/PIL/Image.py", line 626, in _ensure_mutable
    self._copy()
  File "python3.10/site-packages/PIL/Image.py", line 619, in _copy
    self.load()
  File "python3.10/site-packages/PIL/ImageFile.py", line 234, in load
    err_code = decoder.decode(b"")[1]
  File "python3.10/site-packages/PIL/BmpImagePlugin.py", line 326, in decode
    self.set_as_raw(bytes(data), ("P", 0, self.args[-1]))
  File "python3.10/site-packages/PIL/ImageFile.py", line 684, in set_as_raw
    d = Image._getdecoder(self.mode, "raw", (rawmode))
  File "python3.10/site-packages/PIL/Image.py", line 435, in _getdecoder
    return decoder(mode, *args + extra)
ValueError: unknown raw mode for given image mode

Link to the image to reproduce

Just doing Image.open('YOURIMAGE').convert('RGB') causes the error

[radarhere]

I've created PR #6384 to resolve this.