TIFFFieldWithName() and TIFFFieldWithTag() return a pointer to TIFF field information structure fip by
the tag's field_name or its tag number.
TIFFFindField() searches for the TIFF field information structure fip of a given tag number and a
specific TIFFDataTypedt. With dt== TIFF_ANY the behaviour is the same than for TIFFFieldWithTag().
All three functions return NULL, when the tag is not registered within libtiff (see also DefaultTagAuto-registration ).
Such a TIFFDataType dependent search could be useful when the same tag is defined twice but with
different data types, which is true for rare cases like TIFFTAG_XCLIPPATHUNITS. However, the libtiff
does currently not support multiple definitions of the same tag.
The following routines return status information about TIFF fields.
fip is a field information pointer previously returned by TIFFFindField(), TIFFFieldWithTag(),
TIFFFieldWithName().
TIFFFieldIsAnonymous() returns true (nonzero) if the field, read from file, is unknown to libtiff and an
anonymous field has been auto-registered. Return is zero "0" if field is known to libtiff. See DefaultTagAuto-registration for more information.
TIFFFieldSetGetSize() returns the data size in bytes of the field data type used for libtiff internal
storage. This is also the data size of the parameter to be provided to TIFFSetField() and
TIFFGetField(). Custom TIFF_RATIONAL values can be stored internally either as float or double.
TIFFFieldSetGetSize() would then return "4" or "8", respectively.
TIFFFieldSetGetCountSize() returns size of count parameter of TIFFSetField() and TIFFGetField() and also
if it is required: 0=none, 2= uint16_t, 4= uint32_t. See also description of TIFFFieldReadCount().
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