TIFFOpen
TIFFOpen(3T) TIFFOpen(3T)
NAME
TIFFOpen, TIFFFdOpen, TIFFClientOpen - open a TIFF file for reading or
writing
SYNOPSIS
#include <tiffio.h>
TIFF* TIFFOpen(const char* filename, const char* mode)
TIFF* TIFFFdOpen(const int fd, const char* filename, const char* mode)
typedef tsize_t (*TIFFReadWriteProc)(thandle_t, tdata_t, tsize_t);
typedef toff_t (*TIFFSeekProc)(thandle_t, toff_t, int);
typedef int (*TIFFCloseProc)(thandle_t);
typedef toff_t (*TIFFSizeProc)(thandle_t);
typedef int (*TIFFMapFileProc)(thandle_t, tdata_t*, toff_t*);
typedef void (*TIFFUnmapFileProc)(thandle_t, tdata_t, toff_t);
TIFF* TIFFClientOpen(const char* filename, const char* mode, thandle_t clientdata,
TIFFReadWriteProc readproc, TIFFReadWriteProc writeproc, TIFFSeekProc seekproc,
TIFFCloseProc closeproc, TIFFSizeProc sizeproc, TIFFMapFileProc mapproc,
TIFFUnmapFileProc unmapproc)
DESCRIPTION
TIFFOpen opens a TIFF file whose name is filename and returns a handle
to be used in subsequent calls to routines in libtiff. If the open
operation fails, then zero is returned. The mode parameter specifies
if the file is to be opened for reading (``r''), writing (``w''), or
appending (``a'') and, optionally, whether to override certain default
aspects of library operation (see below). When a file is opened for
appending, existing data will not be touched; instead new data will be
written as additional subfiles. If an existing file is opened for
writing, all previous data is overwritten.
If a file is opened for reading, the first TIFF directory in the file
is automatically read (also see TIFFSetDirectory(3T) for reading direc-
tories other than the first). If a file is opened for writing or
appending, a default directory is automatically created for writing
subsequent data. This directory has all the default values specified
in TIFF Revision 6.0: BitsPerSample=1, ThreshHolding=bilevel art scan,
FillOrder=1 (most significant bit of each data byte is filled first),
Orientation=1 (the 0th row represents the visual top of the image, and
the 0th column represents the visual left hand side), SamplesPer-
Pixel=1, RowsPerStrip=infinity, ResolutionUnit=2 (inches), and Compres-
sion=1 (no compression). To alter these values, or to define values
for additional fields, TIFFSetField(3T) must be used.
TIFFFdOpen is like TIFFOpen except that it opens a TIFF file given an
open file descriptor fd. The file's name and mode must reflect that of
the open descriptor. The object associated with the file descriptor
must support random access.
TIFFClientOpen is like TIFFOpen except that the caller supplies a col-
lection of functions that the library will use to do UNIX-like I/O
operations. The readproc and writeproc are called to read and write
data at the current file position. seekproc is called to change the
current file position a la lseek(2). closeproc is invoked to release
any resources associated with an open file. sizeproc is invoked to
obtain the size in bytes of a file. mapproc and unmapproc are called
to map and unmap a file's contents in memory; c.f. mmap(2) and mun-
map(2). The clientdata parameter is an opaque ``handle'' passed to the
client-specified routines passed as parameters to TIFFClientOpen.
OPTIONS
The open mode parameter can include the following flags in addition to
the ``r'', ``w'', and ``a'' flags. Note however that option flags must
follow the read-write-append specification.
l When creating a new file force information be written with Lit-
tle-Endian byte order (but see below). By default the library
will create new files using the native CPU byte order.
b When creating a new file force information be written with Big-
Endian byte order (but see below). By default the library will
create new files using the native CPU byte order.
L Force image data that is read or written to be treated with bits
filled from Least Significant Bit (LSB) to Most Significant Bit
(MSB). Note that this is the opposite to the way the library
has worked from its inception.
B Force image data that is read or written to be treated with bits
filled from Most Significant Bit (MSB) to Least Significant Bit
(LSB); this is the default.
H Force image data that is read or written to be treated with bits
filled in the same order as the native CPU.
M Enable the use of memory-mapped files for images opened read-
only. If the underlying system does not support memory-mapped
files or if the specific image being opened cannot be memory-
mapped then the library will fallback to using the normal system
interface for reading information. By default the library will
attempt to use memory-mapped files.
m Disable the use of memory-mapped files.
C Enable the use of ``strip chopping'' when reading images that
are comprised of a single strip or tile of uncompressed data.
Strip chopping is a mechanism by which the library will automat-
ically convert the single-strip image to multiple strips, each
of which has about 8 Kilobytes of data. This facility can be
useful in reducing the amount of memory used to read an image
because the library normally reads each strip in its entirety.
Strip chopping does however alter the apparent contents of the
image because when an image is divided into multiple strips it
looks as though the underlying file contains multiple separate
strips. Finally, note that default handling of strip chopping
is a compile-time configuration parameter. The default
behaviour, for backwards compatibility, is to enable strip chop-
ping.
c Disable the use of strip chopping when reading images.
BYTE ORDER
The TIFF specification (all versions) states that compliant readers
must be capable of reading images written in either byte order.
Nonetheless some software that claims to support the reading of TIFF
images is incapable of reading images in anything but the native CPU
byte order on which the software was written. (Especially notorious
are applications written to run on Intel-based machines.) By default
the library will create new files with the native byte-order of the CPU
on which the application is run. This ensures optimal performance and
is portable to any application that conforms to the TIFF specification.
To force the library to use a specific byte-order when creating a new
file the ``b'' and ``l'' option flags may be included in the call to
open a file; for example, ``wb'' or ``wl''.
RETURN VALUES
Upon successful completion TIFFOpen, TIFFFdOpen, and TIFFClientOpen
return a TIFF pointer. Otherwise, NULL is returned.
DIAGNOSTICS
All error messages are directed to the TIFFError(3T) routine. Like-
wise, warning messages are directed to the TIFFWarning(3T) routine.
"%s": Bad mode. The specified mode parameter was not one of ``r''
(read), ``w'' (write), or ``a'' (append).
%s: Cannot open. TIFFOpen() was unable to open the specified filename
for read/writing.
Cannot read TIFF header. An error occurred while attempting to read
the header information.
Error writing TIFF header. An error occurred while writing the default
header information for a new file.
Not a TIFF file, bad magic number %d (0x%x). The magic number in the
header was not (hex) 0x4d4d or (hex) 0x4949.
Not a TIFF file, bad version number %d (0x%x). The version field in
the header was not 42 (decimal).
Cannot append to file that has opposite byte ordering. A file with a
byte ordering opposite to the native byte ordering of the current
machine was opened for appending (``a''). This is a limitation of the
library.
SEE ALSO
libtiff(3T), TIFFClose(3T)
January 9, 1996 TIFFOpen(3T)
