int TIFFFieldWriteCount(const TIFFField* fip)
TIFFFieldWriteCount returns the number of values to be written into the specified TIFF field; that is, the number of arguments that should be supplied to TIFFSetField. For most field types this is a small positive integer, typically 1 or 2, but there are some special values:
TIFF_VARIABLE indicates that a variable number of values is possible; then, a uint16_t count argument and a pointer data argument must be supplied to TIFFSetField.
TIFF_VARIABLE2 is the same as TIFF_VARIABLE except that the count argument must have type uint32_t. (On most modern machines, this makes no practical difference, and the count argument can simply be an int in either case.)
TIFF_SPP indicates that the number of arguments must be equal to the image's number of samples per pixel.
fip is a field information pointer previously returned by TIFFFindField, TIFFFieldWithTag, or TIFFFieldWithName.
For most field types, TIFFFieldWriteCount returns the same value as TIFFFieldReadCount, but there are some exceptions.
TIFFFieldWriteCount returns an integer.
Libtiff library home page: http://www.simplesystems.org/libtiff/