Exceptions when trying to convert BMP to TIFF

[sekrause]

https://stuff.realpath.org/test.bmp is a very simple BMP image (unfortunately GitHub doesn't allow to attach it here).

First exception

When I try to convert it to a TIFF:

with Image.open("test.bmp") as im:
    im.save("test.tiff", format="TIFF")

I get the following exception:

Traceback (most recent call last):
  File "convert.py", line 4, in <module>
    im.save("test.tiff", format="TIFF")
  File "venv\lib\site-packages\PIL\Image.py", line 2300, in save
    save_handler(self, fp, filename)
  File "venv\lib\site-packages\PIL\TiffImagePlugin.py", line 1810, in _save
    e = Image._getencoder(im.mode, "libtiff", a, encoderconfig)
  File "venv\lib\site-packages\PIL\Image.py", line 458, in _getencoder
    return encoder(mode, *args + extra)
TypeError: argument 3 must be str, not int

However when disabling compression it works:

with Image.open("test.bmp") as im:
    im.save("test.tiff", format="TIFF", compression=None)

This seems to be an older issue because I found a StackOverflow question from 2019 mentioning this exact problem: https://stackoverflow.com/q/54181211

Second exception

There also seems to be a regression in 9.1.0 compared to 9.0.1. In 9.0.1 using tiff_lzw compression worked without problems:

with Image.open("test.bmp") as im:
    im.save("test.tiff", format="TIFF", compression="tiff_lzw")

However in 9.1.0 I get the following exception:

Traceback (most recent call last):
  File "convert.py", line 4, in <module>
    im.save("test.tiff", format="TIFF", compression="tiff_lzw")
  File "venv\lib\site-packages\PIL\Image.py", line 2300, in save
    save_handler(self, fp, filename)
  File "venv\lib\site-packages\PIL\TiffImagePlugin.py", line 1810, in _save
    e = Image._getencoder(im.mode, "libtiff", a, encoderconfig)
  File "venv\lib\site-packages\PIL\Image.py", line 458, in _getencoder
    return encoder(mode, *args + extra)
ValueError: Requiring 768 items for Colormap

OS, Python and Pillow versions:

• OS: Windows 10
• Python: 3.9 x64
• Pillow: 9.1.0

[radarhere]

I've created #6231 to fix the first part.

[radarhere]

I've created PR #6232 to fix the second part.