BUG: Inverse color in CMYK images

[pubpub-zz]

closes #1895

CMYK image without decode requires reverting scale (cf p243,2§ last sentence in PDF 1.7 spec)

[MartinThoma]

pypdf/_page.py:2446: in __getitem__
    len_self = len(self)
pypdf/_page.py:2427: in __len__
    return self.length_function()
pypdf/_reader.py:453: in _get_num_pages
    return self.trailer[TK.ROOT]["/Pages"]["/Count"]  # type: ignore
pypdf/generic/_data_structures.py:309: in __getitem__
    return dict.__getitem__(self, key).get_object()
pypdf/generic/_base.py:306: in get_object
    obj = self.pdf.get_object(self)
pypdf/_reader.py:1329: in get_object
    retval = self._get_object_from_stream(indirect_reference)  # type: ignore
pypdf/_reader.py:1252: in _get_object_from_stream
    obj_stm: EncodedStreamObject = IndirectObject(stmnum, 0, self).get_object()  # type: ignore
pypdf/generic/_base.py:306: in get_object
    obj = self.pdf.get_object(self)
pypdf/_reader.py:1393: in get_object
    retval = self._encryption.decrypt_object(
pypdf/_encryption.py:989: in decrypt_object
    return cf.decrypt_object(obj)
pypdf/_encryption.py:208: in decrypt_object
    obj._data = self.stmCrypt.decrypt(obj._data)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <pypdf._encryption.CryptAES object at 0x7fcf1d3e81f0>
data = b'\xe6\x10$\xb7\xe0\xed\xe1x\r\x10.\x14\xd3+@\xa3\xab_\xa76Mc\xffc/\xc6\x87<\x95\x80\xeb2\xc1Lu8\xb1Q\x15|a\xda\x0c\xb...xdc\x8d\x19M\x95\xfd\xf5d\xde\xf4\x14\x1a3\xa8\xf9@\x8aa\x93\xff4\xf5\xef:M\xa8L\xe7b/\xc4\xe4\x83\x89\xfb\xc5 7d\xf12'

    def decrypt(self, data: bytes) -> bytes:
>       raise DependencyError("PyCryptodome is required for AES algorithm")
E       pypdf.errors.DependencyError: PyCryptodome is required for AES algorithm

pypdf/_encryption.py:150: DependencyError

oO ... did I mess something up with the AES support PR?

[pubpub-zz]

this is a new test file which is encrypted. I've added some code to bypass the test if cryptodome is missing

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (c239073) 93.92% compared to head (bc1a495) 93.93%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1947   +/-   ##
=======================================
  Coverage   93.92%   93.93%           
=======================================
  Files          33       33           
  Lines        6983     6993   +10     
  Branches     1382     1386    +4     
=======================================
+ Hits         6559     6569   +10     
  Misses        273      273           
  Partials      151      151           

Impacted Files	Coverage Δ
pypdf/filters.py	93.57% <100.00%> (+0.15%)	⬆️

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[pubpub-zz]

@MartinThoma
all yours 🙂

[MartinThoma]

Nice!

this is a new test file which is encrypted
I should have looked at the code 😅