text: .\" $Id: TIFFOpen.3tiff,v 1.2 2005/07/01 12:36:22 dron Exp $
  .\"
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  .\" Copyright (c) 1991-1997 Silicon Graphics, Inc.
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  .if n .po 0
  .TH TIFFOpen 3TIFF "July 1, 2005" "libtiff"
  .SH NAME
  TIFFOpen, TIFFFdOpen, TIFFClientOpen \- open a
  .SM TIFF
  file for reading or writing
  .SH SYNOPSIS
  .B "#include <tiffio.h>"
  .sp
  .BI "TIFF* TIFFOpen(const char *" filename ", const char *" mode ")"
  .br
  .BI "TIFF* TIFFFdOpen(const int " fd ", const char *" filename ", const char *" mode ")"
  .sp
  .B "typedef tsize_t (*TIFFReadWriteProc)(thandle_t, tdata_t, tsize_t);"
  .br
  .B "typedef toff_t (*TIFFSeekProc)(thandle_t, toff_t, int);"
  .br
  .B "typedef int (*TIFFCloseProc)(thandle_t);"
  .br
  .B "typedef toff_t (*TIFFSizeProc)(thandle_t);"
  .br
  .B "typedef int (*TIFFMapFileProc)(thandle_t, tdata_t*, toff_t*);"
  .br
  .B "typedef void (*TIFFUnmapFileProc)(thandle_t, tdata_t, toff_t);"
  .sp
  .BI "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 ")"
  .SH DESCRIPTION
  .IR TIFFOpen
  opens a
  .SM TIFF
  file whose name is
  .I filename
  and returns a handle to be used in subsequent calls to routines in
  .IR libtiff .
  If the open operation fails, then zero is returned.
  The
  .I 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.
  .PP
  If a file is opened for reading, the first
  .SM TIFF
  directory in the file is automatically read
  (also see
  .IR TIFFSetDirectory (3TIFF)
  for reading directories 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
  .SM TIFF
  Revision 6.0:
  .IR BitsPerSample =1,
  .IR ThreshHolding "=bilevel art scan,"
  .IR FillOrder =1
  (most significant bit of each data byte is filled first),
  .IR Orientation =1
  (the 0th row represents the visual top of the image, and the 0th
  column represents the visual left hand side),
  .IR SamplesPerPixel =1,
  .IR RowsPerStrip =infinity,
  .IR ResolutionUnit =2
  (inches), and
  .IR Compression =1
  (no compression).
  To alter these values, or to define values for additional fields,
  .IR TIFFSetField (3TIFF)
  must be used.
  .PP
  .IR TIFFFdOpen
  is like
  .IR TIFFOpen
  except that it opens a
  .SM TIFF
  file given an open file descriptor
  .IR fd .
  The file's name and mode must reflect that of the open descriptor.
  The object associated with the file descriptor
  .BR "must support random access" .
  .PP
  .IR TIFFClientOpen
  is like
  .IR TIFFOpen
  except that the caller supplies a collection of functions that the
  library will use to do \s-1UNIX\s+1-like I/O operations. 
  The
  .I readproc
  and
  .I writeproc
  are called to read and write data at the current file position.
  .I seekproc
  is called to change the current file position a la
  .IR lseek (2).
  .I closeproc
  is invoked to release any resources associated with an open file.
  .I sizeproc
  is invoked to obtain the size in bytes of a file.
  .I mapproc
  and
  .I unmapproc
  are called to map and unmap a file's contents in memory; c.f.
  .IR mmap (2)
  and
  .IR munmap (2).
  The
  .I clientdata
  parameter is an opaque ``handle'' passed to the client-specified
  routines passed as parameters to
  .IR TIFFClientOpen .
  .SH 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.
  .TP
  .B l
  When creating a new file force information be written with
  Little-Endian byte order (but see below).
  By default the library will create new files using the native
  .SM CPU
  byte order.
  .TP
  .B 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
  .SM CPU
  byte order.
  .TP
  .B L
  Force image data that is read or written to be treated with
  bits filled from Least Significant Bit (\s-1LSB\s+1) to
  Most Significant Bit (\s-1MSB\s+1).
  Note that this is the opposite to the way the library has
  worked from its inception.
  .TP
  .B B
  Force image data that is read or written to be treated with
  bits filled from Most Significant Bit (\s-1MSB\s+1) to
  Least Significant Bit (\s-1LSB\s+1); this is the default.
  .TP
  .B H
  Force image data that is read or written to be treated with
  bits filled in the same order as the native 
  .SM CPU.
  .TP
  .B 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.
  .TP
  .B m
  Disable the use of memory-mapped files.
  .TP
  .B 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 automatically
  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 chopping.
  .TP
  .B c
  Disable the use of strip chopping when reading images.
  .TP
  .B h
  Read TIFF header only, do not load the first image directory. That could be
  useful in case of the broken first directory. We can open the file and proceed
  to the other directories.
  .SH "BYTE ORDER"
  The 
  .SM TIFF
  specification (\fBall versions\fP) states that compliant readers
  .IR "must be capable of reading images written in either byte order" .
  Nonetheless some software that claims to support the reading of
  .SM TIFF
  images is incapable of reading images in anything but the native
  .SM 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 
  .SM 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''.
  .SH "RETURN VALUES"
  Upon successful completion 
  .IR TIFFOpen ,
  .IR TIFFFdOpen ,
  and
  .IR TIFFClientOpen
  return a 
  .SM TIFF
  pointer.
  Otherwise, NULL is returned.
  .SH DIAGNOSTICS
  All error messages are directed to the
  .IR TIFFError (3TIFF)
  routine.
  Likewise, warning messages are directed to the
  .IR TIFFWarning (3TIFF)
  routine.
  .PP
  \fB"%s": Bad mode\fP.
  The specified
  .I mode
  parameter was not one of ``r'' (read), ``w'' (write), or ``a'' (append).
  .PP
  .BR "%s: Cannot open" .
  .IR TIFFOpen ()
  was unable to open the specified filename for read/writing.
  .PP
  .BR "Cannot read TIFF header" .
  An error occurred while attempting to read the header information.
  .PP
  .BR "Error writing TIFF header" .
  An error occurred while writing the default header information
  for a new file.
  .PP
  .BR "Not a TIFF file, bad magic number %d (0x%x)" .
  The magic number in the header was not (hex)
  0x4d4d or (hex) 0x4949.
  .PP
  .BR "Not a TIFF file, bad version number %d (0x%x)" .
  The version field in the header was not 42 (decimal).
  .PP
  .BR "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.
  .SH "SEE ALSO"
  .IR libtiff (3TIFF),
  .IR TIFFClose (3TIFF)
  