tiffopen.3t

tiff文件开发库

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.\" Copyright (c) 1991-1997 Silicon Graphics, Inc.
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.if n .po 0
.TH TIFFOpen 3T "January 9, 1996"
.SH NAME
TIFFOpen, TIFFFdOpen, TIFFClientOpen \- open a
.SM TIFF
file for reading or writing
.SH SYNOPSIS
.nf
.B "#include <tiffio.h>"
.B "TIFF* TIFFOpen(const char* filename, const char* mode)"
.sp 5p
.B "TIFF* TIFFFdOpen(const int fd, const char* filename, const char* mode)"
.sp 5p
.B "typedef tsize_t (*TIFFReadWriteProc)(thandle_t, tdata_t, tsize_t);"
.B "typedef toff_t (*TIFFSeekProc)(thandle_t, toff_t, int);"
.B "typedef int (*TIFFCloseProc)(thandle_t);"
.B "typedef toff_t (*TIFFSizeProc)(thandle_t);"
.B "typedef int (*TIFFMapFileProc)(thandle_t, tdata_t*, toff_t*);"
.B "typedef void (*TIFFUnmapFileProc)(thandle_t, tdata_t, toff_t);"
.sp 5p
.B "TIFF* TIFFClientOpen(const char* filename, const char* mode, thandle_t clientdata,"
.B "    TIFFReadWriteProc readproc, TIFFReadWriteProc writeproc, TIFFSeekProc seekproc,"
.B "    TIFFCloseProc closeproc, TIFFSizeProc sizeproc, TIFFMapFileProc mapproc,"
.B "    TIFFUnmapFileProc unmapproc)"
.fi
.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 (3T)
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 (3T)
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.
.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 (3T)
routine.
Likewise, warning messages are directed to the
.IR TIFFWarning (3T)
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 (3T),
.IR TIFFClose (3T)