'Returns the size of row items that would be written to the raw FITS
file, taking into account the possibility of unicode columns being
compactified.
Currently for internal use only.'

@property
def _raw_itemsize(self):

    if _has_unicode_fields(self):
        total_itemsize = 0
        for field in self.dtype.fields.values():
            itemsize = field[0].itemsize
            if (field[0].kind == 'U'):
                itemsize = (itemsize // 4)
            total_itemsize += itemsize
        return total_itemsize
    else:
        return self.itemsize
