Changes in TIFF v3.5.3 — LibTIFF 4.6.0t documentation

# Changes in TIFF v3.5.3

References
Current Version | v3.5.3 (tag %sRelease-v3-5-3)
Previous Version | v3.5.2
Master Download Site | ftp://ftp.onshore.com/pub/libtiff/
Master HTTP Site | http://www.simplesystems.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. The following information is located here:

## Major changes

Please note the most important change: LZW compression has been removed.

Unisys has the patent on LZW compression and have been very active in their enforcement of late, demanding payments of $5000 or more from websites using unlicensed software to create GIF’s. They could well do the same do persons using libtiff to create LZW compressed TIFF images.

From Burn All GIF’s Day:

> The catch is that it appears to be difficult or impossible to get a Unisys license to use LZW in free software that complies with the Open Source Definition

Unfortunately, the removal of LZW compression means that saved image size has grown dramatically. Without a change in the TIFF spec to support another lossless compression format, this is unavoidable.

The library can use zip for lossless compression, but as this is not part of the spec, TIFFs using zip compression may not work with other software.

We will be making a patch available that will contain the LZW compression code for users who have either obtained a license from Unisys or are willing to risk it.

LZW decompression is unchanged.

## Software configuration changes

- Added zip creation to release makefile target

## Library changes

- Added html for `TIFFWriteTile.3t` man page.

- Added some changes to `tif_write.c` to support rewriting existing fixed sized tiles and strips. Code mods disabled by default, only enabled if `REWRITE_HACK` is defined for now.

- Added `TIFFWriteTile.3t` man page.

- Added notes on use of `makefile.vc` in `build.html`, and fixed email subscription address.

- Did some casts cleaning up to reduce compiler warnings in `tif_fax3.c`, from Bruce Cameron—modifications of changes made by Frank (sun cc still complained on cast).

- fixed various VC++ warnings as suggested by Gilles Vollant.

- Modified `TIFFquery.3t` man pages info on `TIFFIsByteSwapped()` to not imply applications are responsible for image data swapping.

- HTML-ized the man pages, added to `html/man`.

- Removed LZW Compression to comply with Unisys patent extortion.

- Corrected one remaining `16 -> 32` bit value in `tif_fax3.c`, From Ivo Penzar.

- Added patch from Ivo Penzar to have `TiffAdvanceDirectory()` handle memory mapped files. Ivo Penzar.

## Contributed software changes

- Fixed apocalypse-inducing y2k bug in `contrib/ras/ras2tiff.c`