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	Changes in TIFF v4.0.0

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<font size="+3">T</font>IFF <font size="+2">C</font>HANGE <font size="+2">I</font>NFORMATION

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Current Version: v4.0.0

Previous Version: v3.9.5

Master FTP Site: 

ftp.remotesensing.org, directory pub/libtiff

Master HTTP Site: 

http://download.osgeo.org/libtiff 

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

Changes in the software configuration

Changes in libtiff

Changes in the tools

Changes in the contrib area

<font size="+3">M</font>AJOR 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.

<font size="+3">C</font>HANGES 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).

<font size="+3">C</font>HANGES 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.

<font size="+3">C</font>HANGES IN THE TOOLS:

	
tiffset: add -d and -sd switches to allow operation on

	a particular directory, not just the first.

<font size="+3">C</font>HANGES IN THE CONTRIB AREA:

Last updated $Date: 2011-04-09 21:01:00 $.