Builds Image Field Directory (IFD)
buildIFD(val, typ, tag, endianness = .Platform$endian)
the value of the IFD
desired IFD type
the desired IFD 'tag'
the desired endian-ness ("big" or "little"). Default is .Platform$endian. Endianness describes the bytes order of data stored within the files. This parameter may not be modified.
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.
if 'val' if of type "character", 'tag' is automatically set to 2. if 'val' is of length 0 NULL is returned.