BLP1 files are not handled

[Meithal]

What did you do?

I tried to open a BLP1 file

What did you expect to happen?

I expected to see the image

What actually happened?

I saw a black square

What are your OS, Python and Pillow versions?

• OS: Windows10 x64
• Python: 3.7
• Pillow: 7.2

You first need a blp1 picture, I think it is a proprietary format so i'm not sure I can put one here
To easily get one go on https://www.epicwar.com, download a map then open it with a MPQ viewer, every map has a thumbnail in the blp1 format.

from PIL import Image
with Image.open("file.blp") as pil:
    convert = pil.convert('RGB')
    convert.show()
    convert.save((work_folder / name).with_suffix('.jpg'))