.\" $Id: TIFFOpen.3tiff,v 1.2 2005-07-01 12:36:22 dron Exp $

.\"

.\" Copyright (c) 1988-1997 Sam Leffler

.\" Copyright (c) 1991-1997 Silicon Graphics, Inc.

.\"

.\" Permission to use, copy, modify, distribute, and sell this software and 

.\" its documentation for any purpose is hereby granted without fee, provided

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.\" WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.  

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.\" IN NO EVENT SHALL SAM LEFFLER OR SILICON GRAPHICS BE LIABLE FOR

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.\" OF THIS SOFTWARE.

.\"

.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>"</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)