int TIFFCreateCustomDirectory(TIFF *tif, const TIFFFieldArray *infoarray)¶
int TIFFCreateEXIFDirectory(TIFF *tif)¶
int TIFFCreateGPSDirectory(TIFF *tif)¶
int TIFFWriteCustomDirectory(TIFF *tif, uint64 *pdiroff)¶
int TIFFReadCustomDirectory(TIFF *tif, toff_t diroff, const TIFFFieldArray *infoarray)¶
int TIFFReadEXIFDirectory(TIFF *tif, toff_t diroff)¶
int TIFFReadGPSDirectory(TIFF *tif, toff_t diroff)¶
const TIFFFieldArray *_TIFFGetExifFields(void)¶
const TIFFFieldArray *_TIFFGetGpsFields(void)¶
The following routines create a custom directory and retrieve information about directories in an open TIFF file.
TIFFCreateGPSDirectory() will setup a custom directory or one
of the predefined EXIF or GPS directories and set the context of the
tif to that custom directory for functions
TIFFWriteCustomDirectory() will write the contents of the
current custom directory to the file and return the offset to that
pdiroff. That offset has to be written to the main-IFD:
/* Go back to the first directory, and add the EXIFIFD pointer. */ TIFFSetDirectory(tif, 0); TIFFSetField(tif, TIFFTAG_EXIFIFD, pdiroff);
TIFFReadCustomDirectory() will read the custom directory from the
arbitrary offset into the
infoarray and sets the context of the
tif to that custom directory for functions like
has to be according the layout of the custom directory. For the predefined
EXIF and GPS directories, the relevant
are hidden within the functions
TIFFReadGPSDirectory() The code is very similar to
The offset to the custom directory diroff has to be read from the
relative TIFF tag first.
that until a directory is not written to file AND read back, the query functions won't retrieve the correct information!
that LibTiff does not support custom directory chains (NextIFD pointing to another IFD). NextIFD of custom directories is always set to zero and should be zero when reading.
Unfortunately to create or read custom directories with predefined fields
it is necessary to include the private tif_dir.h. However, for EXIF and
GPS directories, which have a predefined schema within
is not necessary. There are some test programmes that briefly demonstrate
the creation and reading of EXIF, GPS and custom directories.
See test/custom_dir.c and test/custom_dir_EXIF_231.c
Hints and detailed instructions¶
Writing TIFF files with more than one directory (IFD) is not easy because some side effects need to be known.
The main point here is that there can only be one
tif structure in
the main memory for a file, which can only hold the tags of one directory
at a time. It is useless to work with two different tiffOut1, tiffOut2
pointers, because there is only ONE TIFF object (TIFF directory) within
libtiff. If you want to address a second directory in the file,
the tags of the current directory must first be saved in the file,
otherwise they will be lost (overwritten or mixed). Then the
structure in the main memory must be tidied up, otherwise the old tags
will beincluded in the new directory.
This can be done either by creating a new, empty
tif structure or by
reading in an directory previously saved in the file.
A sequence to handle a second (or third) TIFF directory - in this case the GPS IFD - is as follows:
Create TIFF file
Complete the "normal" metadata
Set the tag for the custom directory with a “dummy” value in order to get the tag reserved. The final value will be inserted lateron. This prevents the main directory from being written to the file again at an additional area, leaving the first memory area unused:
TIFFSetField(tiffOut, TIFFTAG_GPSIFD, dir_offset);
Save current TIFF-directory to file. Otherwise, it will be lost. Remember also the number of the current directory:
TIFFWriteDirectory(tiffOut); dirNum = TIFFCurrentDirectory(tiffOut);
Create the second TIFF-directory (e.g. custom directory) and set its fields. The TIFFFieldArray infoarray has to be specified beforehand somewhere in your private include files. An example is given for the EXIF directory in tif_dirinfo.c
TIFFCreateCustomDirectory(tiffOut, infoarray); /* for a real custom directory */ /* or alternatively, use GPS or EXIF with pre-defined TIFFFieldArray IFD field structure */ TIFFCreateGPSDirectory(tiffOut); TIFFSetField(tiffOut, GPSTAG_VERSIONID, gpsVersion); /* set fields of the custom directory */
Write custom directory to file. The offset to that directory in the file is returned in
Reload the first directory (i.e. the original TIFF directory). Apparently, this reads the data back from file.
Set the correct offset value of the custom directory IFD tag and save that changes to file.
TIFFSetField(tiffOut, TIFFTAG_GPSIFD, dir_offset); TIFFWriteDirectory(tiffOut);
1 is returned when the contents are successfully written to the file. Otherwise, 0 is returned if an error was encountered when writing the directory contents.