Add CMYKA Support

[Gibbz]

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What did you do?

Work with CMYK tif images with Alpha (Transparency)

What did you expect to happen?

To work in the same way a RGBA image would.

What actually happened?

Currently fails to load the images

What are your OS, Python and Pillow versions?

• OS: Windows 10
• Python: 3.7
• Pillow: 6.1.0

Attached sample image. Aus_03.zip

[radarhere]

Originally reported in https://github.com/python-pillow/Pillow/issues/3984#issuecomment-513617007.

To understand the scope of what you are interested in, after loading, what would like to do with the images? Convert them to another mode? Save them directly as TIFF again? A different operation?

[Gibbz]

I'm working with a combination of print and screen media, basically what I want to do:

• open a CMYK (no alpha) and convert to CMYKA
• overlay a second CMYKA image (paste operation)
• apply a perspective transform (transform operation)
• save as CMYKA TIFF and also convert to RGBA for saving

Thanks :)

[ioyaeu]

Hello @radarhere, a few days ago I stumbled upon the following keys in a series of tiff files:

('MM', 5, (1,), 1, (8, 8, 8, 8, 8), (1,)) 
('II', 5, (1,), 1, (8, 8, 8, 8, 8), (1,))

Those keys are not referenced in open_info (/PIL/TiffImagePlugin.py). They look very similar to (II, 5, (1,), 1, (8, 8, 8, 8, 8), (0,)): ("CMYK", "CMYKX") but i don't know what is the impact of the extraSamples value. Do you think it would be ok to add those values to the open_info list ?

    (II, 5, (1,), 1, (8, 8, 8, 8, 8), (1,)): ("CMYK", "CMYKX"),
    (MM, 5, (1,), 1, (8, 8, 8, 8, 8), (1,)): ("CMYK", "CMYKX"),

[ioyaeu]

Relating to the sample image provided by @Gibbz it's a similar problem. the key for the sample is : ('II', 5, (1,), 1, (8, 8, 8, 8, 8), (2,)) which is also missing in the open_info. After adding the following keys, pil seems to work as expected.

    (II, 5, (1,), 1, (8, 8, 8, 8, 8), (1,)): ("CMYK", "CMYKX"),
    (MM, 5, (1,), 1, (8, 8, 8, 8, 8), (1,)): ("CMYK", "CMYKX"),
    (II, 5, (1,), 1, (8, 8, 8, 8, 8), (2,)): ("CMYK", "CMYKX"),
    (MM, 5, (1,), 1, (8, 8, 8, 8, 8), (2,)): ("CMYK", "CMYKX"),

Comparing further it seems logical to also add :

    (II, 5, (1,), 1, (8, 8, 8, 8, 8, 8), (1, 0)): ("CMYK", "CMYKXX"),
    (MM, 5, (1,), 1, (8, 8, 8, 8, 8, 8), (1, 0)): ("CMYK", "CMYKXX"),
    (II, 5, (1,), 1, (8, 8, 8, 8, 8, 8), (2, 0)): ("CMYK", "CMYKXX"),
    (MM, 5, (1,), 1, (8, 8, 8, 8, 8, 8), (2, 0)): ("CMYK", "CMYKXX"),

[radarhere]

ExtraSamples describes the state of the alpha - https://www.awaresystems.be/imaging/tiff/tifftags/extrasamples.html. So I would think that the situation from @ioyaeu isn't different from the general request for CMYKA.

[tobkum]

Since I stumbled across the same issue of not being able to open cmyk tiff files with an alpha channel - is supporting those planned in the future?