Save all MODES as all SAVE formats

[CTimmerman]

Fixes #2663
Fixes #9428

Changes proposed in this pull request:

• Save all MODES as all SAVE formats.
• Accept extensions in format for unnamed file object saving of mode L in BW etc.
• Document name feature of file pointer if user still prefers to not use the format parameter for nameless file objects.
• Convert between all MODES.

[CTimmerman]

I don't know why only amazon-2-amd64 failed to load the jpeg2k plugin, but that might relate to #9432.

Also, mode CMYK fails to save in Jpeg2k plugin, but only on the Ubuntu test machines, so on sys.platform "linux" i also convert CMYK to RGBA when saving JPEG2000.

[radarhere]

I don't know why only amazon-2-amd64 failed to load the jpeg2k plugin

It would be because OpenJPEG is not installed - https://github.com/python-pillow/Pillow/actions/runs/22418319033/job/64909670542?pr=9447#step:6:694

External libraries are not always installed by users in the real world either, and tests should accommodate this by avoiding checking that functionality with something like

Pillow/Tests/test_image.py

Line 191 in e96c5a5

if ext == ".jp2" and not features.check_codec("jpg_2000"):

or

Pillow/Tests/test_image.py

Line 861 in e96c5a5

@skip_unless_feature("webp")

[CTimmerman]

Thanks for the touch up. I assume since the modebase uses the same color space as the mode, it doesn't need the dither argument? checks implementation Nope, that only returns L or RGB so should get dithered as well.

[CTimmerman]

That one fail is a pipeline glitch.

[CTimmerman]

I see the struct error for PCX with a zero size is 'H' format requires 0 <= number <= 65535 which is confusing as the size was zero, so i'll restore the ValueError code.

[CTimmerman]

save_all still needs work.

Update: Fixed.

[CTimmerman]

The LAB to RGBA code in Image.py appears to be redundant, and the missing handler case should break. Updating code.

[CTimmerman]

Image.MODES is a superset of the ones tested in Tests\test_image_convert.py
Modes to test: 13: ('1', 'L', 'LA', 'P', 'PA', 'I', 'F', 'RGB', 'RGBA', 'RGBX', 'CMYK', 'YCbCr', 'HSV')
Modes there are: 20: ['1', 'CMYK', 'F', 'HSV', 'I', 'I;16', 'I;16B', 'I;16L', 'I;16N', 'L', 'LA', 'La', 'LAB', 'P', 'PA', 'RGB', 'RGBA', 'RGBa', 'RGBX', 'YCbCr']

The 7 differences are:

>>> set(['1', 'CMYK', 'F', 'HSV', 'I', 'I;16', 'I;16B', 'I;16L', 'I;16N', 'L', 'LA', 'La', 'LAB', 'P', 'PA', 'RGB', 'RGBA', 'RGBa', 'RGBX', 'YCbCr']) - set(('1', 'L', 'LA', 'P', 'PA', 'I', 'F', 'RGB', 'RGBA', 'RGBX', 'CMYK', 'YCbCr', 'HSV')) {'I;16', 'I;16N', 'LAB', 'I;16B', 'RGBa', 'I;16L', 'La'}

All work now.