TIFF CHANGE INFORMATION
This document describes the changes made to the software between the
previous and current versions (see above). If you don't
find something listed here, then it was not done in this timeframe, or
it was not considered important enough to be mentioned. Please consult
the ChangeLog file in the source package for full change details. The
following information is located here:
MAJOR CHANGES:
BigTIFF support changes:
- The options parameter in the TIFFOpen and TIFFClientOpen funcs has
been extended. When creating new files, you can add option '4' to
specify you want to create a ClassicTIFF file, though that is the
default and the option is not strictly necessary. (As such, old
calling code will continue to function and create ClassicTIFF files.)
Or you can add option '8' to specify you want to create a BigTIFF file
instead. This new option is also reflected in some of the tools we
already upgraded. For instance, you can use the -8 option on tiffcp to
have tiffcp produce BigTIFF files instead of the default ClassicTIFF.
(Whilst on additional option is provided for version selection when
creating new files, no such option is necessary when reading TIFF
files. LibTiff reads ClassicTIFF and BigTIFF both, and the application
does not need to be aware which TIFF version an opened file is.)
- Although the tag count in BigTIFF is 64bit, we restricted the
count in the implementation to a much more reasonable size. This is
necessary in current implementation, because all tag data gets read
automatically in the IFD reading stage, so if there's half a dozen
private tags with multiple gigabytes of data that causes considerable
overhead even if the application level is never interested in these
tags. Our choice to ignore tags with data longer then a certain sanity
value is much needed as things stand. We also recommend to step away
from writing tiles that are 8 kilobyte in their uncompressed form, or
writing single-line strips, in really big files, resulting in mega's
of tiles or strips. It's much more efficient to choose bigger tile or
strip sizes, up to several megabyte if needed, and have a few kilo of
tiles or strips instead.
- Although it's rare, some application code does directly access
file offsets. Some of these are automatically upgraded because they
used the toff_t type, others need to be aware that the datatype
changed and need to start using toff_t or uint64. This impacts access
to tags like the EXIF IFD tag, for example, or the SubIfds tag, or to
StripOffsets or TileOffsets, the return type of functions like
TIFFCurrentDirOffset, and a parameter type to functions like
TIFFSetSubDirectory.
- Although it's rare, some application code does use structures
like TIFFHeader or TIFFDirEntry that used to be an exact binary
representation of TIFF structures. These need to change. The old
TIFFHeader structure is replaced by the new TIFFHeaderClassic,
TIFFHeaderBig, and TIFFHeaderCommon structures that are an exact
binary representation of the ClassicTIFF and BigTIFF header, and of
the part that is common to both. There is no new equivalent for the
old TIFFDirEntry structure (or more precisely, there is still a
TIFFDirEntry structure, but it is changed, moved to library-private
definition, and no longer an exact binary representation of the tag
structure of either TIFF version).
- Sizer functions, like TIFFTileSize or TIFFScanlineSize and the
like, return a tmsize_t value (tmsize_t is defined as int32 on 32bit
machines, and int64 on 64bit machines, and as such it is meant to
represent signed memory sizes). This is because we figure 98% of the
calling code uses the return value as sizes in allocations and the
like. So, any overflow that is theoretically possible with BigTIFF
when LibTiff is running on a 32bit system, is best detected inside the
sizer functions and it is best to return a type that makes sense as a
memory size. If your calling code is the exception and is interested
in actual file size, you best use the newer TIFFTileSize64 or
TIFFScanlineSize64 function that returns an uint64 type.
- These TIFF tags require a 64-bit type as an argument in
libtiff 4.0.0:
- TIFFTAG_FREEBYTECOUNTS
- TIFFTAG_FREEOFFSETS
- TIFFTAG_STRIPBYTECOUNTS
- TIFFTAG_STRIPOFFSETS
- TIFFTAG_TILEBYTECOUNTS
- TIFFTAG_TILEOFFSETS
Other important backward incompatible changes in the public API:
- TIFFRewriteField() renamed into _TIFFRewriteField() and moved out
from the public interface (from tiffio.h to tiffiop.h). Type of its
'count' parameter changed from uint32 to tmsize_t.
- TIFFMergeFieldInfo() returns non-void result now. It returns 0
if successful and -1 if failed. Though this is now obsoleted function
and should not be used in new programs. Use the new tag extension
scheme instead.
- TIFFFieldWithTag() and TIFFFieldWithName() functions now return
pointer to TIFFField constant object instead of TIFFFieldInfo.
- TIFFReassignTagToIgnore() function and TIFFIgnoreSense enumeration
have been removed. They was unused and never been used properly.
Should be unneeded for high-level applications.
- TIFFTagValue structure removed from the public tiffio.h
to private tif_dir.h and not accessible anymore. It should be unneeded
for high-level applications.
CHANGES IN THE SOFTWARE CONFIGURATION:
- Updated autotools: Autoconf 2.68, Automake 1.11.1, libtool
2.4.
- Enabled support for Automake silent build rules
(--enable-silent-rules or 'make V=0')
- Enabled support for Automake colorized and parallel tests.
- Added detection of 64-bit integer types since libtiff 4.0
requires use of 64-bit signed and unsigned integer types.
- Libtiff now provides a more comprehensive test suite with
over 72 tests, which may be executed on Unix-like systems, or
under Microsoft Windows using MinGW/MSYS or Cygwin.
- --disable-lzma configure option to disable use of liblzma.
- --enable-defer-strile-load configure option to enable
experimental deferred strip/tile offset/size loading. May
cause some extremely sophisticated uses of libtiff to fail.
- --enable-chunky-strip-read configure option to enable
experimental enable reading large strips in chunks in
TIFFReadScanline().
- Now always uses WIN32 native I/O functions for Microsoft
Windows except for under Cygwin.
- Now provides a pkg-config support file (libtiff-4.pc).
CHANGES IN LIBTIFF:
- Patches/fixes made to stable libtiff (v3.9.X) are also
applied to 4.0.0. There are too many to list here. See the
distribution ChangeLog for a detailed change list.
- There is considerable change in some files like
tif_dirread and tif_dirwrite. These changes don't impact
backwards compatibility, they are mostly a clean rewrite that
does allow BigTIFF support as well as somewhat more robust
reading of the unexpected already and will also serve future
API extension but does not impact current API or functionality
in a negative way that you need to know about.
- Although there is still a functional definition for types
like toff_t (file offset), tstrip_t (strip index number), etc,
we recommend against using these in newer code. We have
learned that it is next to impossible to use these
consistently and make real abstraction of the binary format of
these types. Instead, at a certain level we always end up
doing casts anyway, and taking the exact binary format into
account, so these types are nothing but dangerously misleading
and obfuscating. You do not need to update calling code that
uses them, as 99.9% of such code will continue to work. But we
recommend against using them in newer calling code, and we
started replacing them with binary clear types like uint16,
uint32 and such in the library.
- We do use and will continue to use one functional type
that is an exception to the above rule, being tmsize_t. This
is a signed memory size type, i.e. it is int32 on 32bit
machines, or int64 on 64bit machines.
- Optionally support LZMA compression via TIFF tag 34925.
Tiffcp supports compression levels similar to "-c lzma:p1" or
"-c zip:p9 for setting the LZMA compression parameters.
- Optionally defer the load of strip/tile offset and size
tags for optimized scanning of directories. Enabled with the
--enable-defer-strile-load configure option (DEFER_STRILE_LOAD
#define in tif_config.h).
- Optionally enable experimental support for reading big
strips in chunks. Enabled with the --enable-chunky-strip-read
configure option.
CHANGES IN THE TOOLS:
- tiffset: add -d and -sd switches to allow operation on
a particular directory, not just the first.
CHANGES IN THE CONTRIB AREA:
Last updated $Date: 2016-09-25 20:05:47 $.