I would name this _data_format. _data_type sounds more like float vs integer or array vs curve to me.
_data_format
_data_type
Done.
seedee can serialize any ndarray, not just images. I would make a breaking change to serialize_ndarray.
seedee
serialize_ndarray
You could directly use seedee.COMPRESSION_BITSHUFFLE as the default argument. Checking for None is only necessary for mutable default arguments.
seedee.COMPRESSION_BITSHUFFLE
None