.\" $Id: TIFFReadDirectory.3tiff,v 1.4 2016-09-25 20:05:49 bfriesen Exp $
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.\" Copyright (c) 1988-1997 Sam Leffler
.\" Copyright (c) 1991-1997 Silicon Graphics, Inc.
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.if n .po 0
.TH TIFFReadDirectory 3TIFF "October 15, 1995" "libtiff"
.SH NAME
TIFFReadDirectory \- get the contents of the next directory in an open
.SM TIFF
file
.SH SYNOPSIS
.B "#include <tiffio.h>"
.sp
.BI "int TIFFReadDirectory(TIFF *" tif ")"
.SH DESCRIPTION
Read the next directory in the specified file and make it the current
directory. Applications only need to call
.I TIFFReadDirectory
to read multiple subfiles in a single
.SM TIFF
file\(em
the first directory in a file is automatically read when
.IR TIFFOpen
is called.
.SH NOTES
If the library is compiled with 
.SM STRIPCHOP_SUPPORT
enabled, then images that have a single uncompressed strip or tile of data are
automatically treated as if they were made up of multiple strips or tiles of
approximately 8 kilobytes each. This operation is done only in-memory; it does
not alter the contents of the file. However, the construction of the ``chopped
strips'' is visible to the application through the number of strips [tiles]
returned by 
.I TIFFNumberOfStrips
[\c
.IR TIFFNumberOfTiles ].
.SH "RETURN VALUES"
If the next directory was successfully read, 1 is returned. Otherwise, 0 is
returned if an error was encountered, or if there are no more directories to
be read.
.SH DIAGNOSTICS
All error messages are directed to the
.IR TIFFError (3TIFF)
routine.
All warning messages are directed to the
.IR TIFFWarning (3TIFF)
routine.
.PP
\fBSeek error accessing TIFF directory\fP.
An error occurred while positioning to the location of the
directory.
.PP
\fBWrong data type %d for field "%s"\fP.
The tag entry in the directory had an incorrect data type.
For example, an
.I ImageDescription
tag with a
.SM SHORT
data type.
.PP
\fBTIFF directory is missing required "%s" field\fP.
The specified tag is required to be present by the
.SM TIFF
5.0 specification, but is missing.
The directory is (usually) unusable.
.PP
\fB%s: Rational with zero denominator\fP.
A directory tag has a
.SM RATIONAL
value whose denominator is zero.
.PP
\fBIncorrect count %d for field "%s" (%lu, expecting %lu); tag ignored\fP.
The specified tag's count field is bad.
For example, a count other than 1 for a
.I SubFileType
tag.
.PP
\fBCannot handle different per-sample values for field "%s"\fP.
The tag has
.I SamplesPerPixel
values and they are not all the same; e.g.
.IR BitsPerSample .
The library is unable to handle images of this sort.
.PP
\fBCount mismatch for field "%s"; expecting %d, got %d\fP.
The count field in a
tag does not agree with the number expected by the library.
This should never happen, so if it does, the library refuses to
read the directory.
.PP
\fBInvalid TIFF directory; tags are not sorted in ascending order\fP.
The directory tags are not properly sorted as specified
in the
.SM TIFF
5.0 specification.
This error is not fatal.
.PP
\fBIgnoring unknown field with tag %d (0x%x)\fP.
An unknown tag was encountered in the directory;
the library ignores all such tags.
.PP
\fBTIFF directory is missing required "ImageLength" field\fP.
The image violates the specification by not having a necessary field.
There is no way for the library to recover from this error.
.PP
\fBTIFF directory is missing required "PlanarConfig" field\fP.
The image violates the specification by not having a necessary field.
There is no way for the library to recover from this error.
.PP
\fBTIFF directory is missing required "StripOffsets" field\fP.
The image has multiple strips, but is missing the tag that
specifies the file offset to each strip of data.
There is no way for the library to recover from this error.
.PP
\fBTIFF directory is missing required "TileOffsets" field\fP.
The image has multiple tiles, but is missing the tag that
specifies the file offset to each tile of data.
There is no way for the library to recover from this error.
.PP
\fBTIFF directory is missing required "StripByteCounts" field\fP.
The image has multiple strips, but is missing the tag that
specifies the size of each strip of data.
There is no way for the library to recover from this error.
.PP
\fBTIFF directory is missing required "StripByteCounts" field, calculating from imagelength\fP.
The image violates the specification by not having a necessary field.
However, when the image is comprised of only one strip or tile, the
library will estimate the missing value based on the file size.
.PP
\fBBogus "StripByteCounts" field, ignoring and calculating from imagelength\fP.
Certain vendors violate the specification by writing zero for
the StripByteCounts tag when they want to leave the value
unspecified.
If the image has a single strip, the library will estimate
the missing value based on the file size.
.SH "SEE ALSO"
.BR TIFFOpen (3TIFF),
.BR TIFFWriteDirectory (3TIFF),
.BR TIFFSetDirectory (3TIFF),
.BR TIFFSetSubDirectory (3TIFF),
.BR libtiff (3TIFF)
.PP
Libtiff library home page:
.BR http://www.simplesystems.org/libtiff/