int TIFFFieldReadCount(const TIFFField* fip)
TIFFFieldReadCount returns the number of values available to be read from the specified TIFF field; that is, the number of arguments that should be supplied to TIFFGetField. 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 count argument and a pointer data argument must be supplied to TIFFGetField.
TIFF_VARIABLE2 is the same as TIFF_VARIABLE except that the count argument must have type uint32.
TIFF_SPP indicates that the number of arguments is equal to the image's number of samples per pixel.
fip is a field information pointer previously returned by TIFFFindField, TIFFFieldWithTag, or TIFFFieldWithName.
TIFFFieldReadCount returns an integer.
Libtiff library home page: http://www.simplesystems.org/libtiff/