Builds Image Field Directory (IFD)
buildIFD(val, typ, tag, endianness = .Platform$endian)
NULL or a list of 2 members:
-min_content: the minimal IFD content,
-add_content: the additional IFD content if 'val' converted to raw does not fit in 4 bytes.
the value of the IFD
desired IFD type
the desired IFD 'tag'
the desired endian-ness ("big" or "little"). Default is .Platform$endian.
Endianness describes the bytes order of data stored within the files. This parameter may not be modified.
if 'val' if of type "character", 'tag' is automatically set to 2.
if 'val' is of length 0 NULL is returned.