Editing TIFF (section)

=== {{anchor|TIFF Extensions}}Part 2: TIFF Extensions ===
Many TIFF readers support tags additional to those in Baseline TIFF, but not every reader supports every extension.<ref>{{cite web |url=http://support.microsoft.com/kb/319196/en-us |title=You cannot preview scanned TIFF file in Windows Picture and Fax Viewer |author=Microsoft |access-date=2011-02-28}}</ref><ref name="wfax-packbits">{{cite web |url=http://support.microsoft.com/kb/329270 |title=You Cannot View TIFF Images Using Windows Picture and Fax Viewer |author=Microsoft |access-date=2011-02-28}}</ref><ref>{{cite web |url=http://suppressingfire.org/~burner/evil-mods-tiff/ |title=Handling Microsoft Office Document Scanning TNEF and TIFFs in Linux |author=Microsoft |access-date=2011-02-28 |url-status=dead |archive-url=https://web.archive.org/web/20130430204808/http://suppressingfire.org/~burner/evil-mods-tiff/ |archive-date=2013-04-30 }}</ref> As a consequence, Baseline TIFF features became the lowest common denominator for TIFF. Baseline TIFF features are extended in TIFF Extensions (defined in the TIFF 6.0 Part 2 specification) but extensions can also be defined in private tags.

The TIFF Extensions are formally known as ''TIFF 6.0, Part 2: TIFF Extensions''. Here are some examples of TIFF extensions defined in TIFF 6.0 specification:<ref name="tiff6" />

====Compression====
* CCITT T.4 bi-level encoding
* CCITT T.6 bi-level encoding
* [[Lempel–Ziv–Welch|LZW]]
* [[JPEG]]

====Image types====
* [[CMYK]] Images
* [[YCbCr]] Images
* HalftoneHints
* Tiled Images
* [[CIE Lab|CIE L*a*b*]] Images

====Image trees====
A baseline TIFF file can contain a sequence of images (IFD). Typically, all the images are related but represent different data, such as the pages of a document. In order to explicitly support multiple views of the ''same'' data, the ''SubIFD'' tag was introduced.<ref name="supplement1">[https://web.archive.org/web/20060114005938/http://partners.adobe.com/public/developer/en/tiff/TIFFPM6.pdf TIFF Specification Supplement 1], Retrieved 2022-06-29</ref> This allows the images to be defined along a [[tree structure]]. Each image can have a sequence of children, each child being itself an image. The typical usage is to provide thumbnails or several versions of an image in different color spaces.

=====Tiles=====
A TIFF image may also be composed of a number of tiles. All tiles in the same image have the same dimensions and may be compressed independently of the entire image, similar to strips (see above). Tiled images are part of TIFF 6.0, Part 2: TIFF Extensions, so the support for tiled images is not required in Baseline TIFF readers.

====Other extensions====
According to TIFF 6.0 specification (Introduction), all TIFF files using proposed TIFF extensions that are not approved by Adobe as part of Baseline TIFF (typically for specialized uses of TIFF that do not fall within the domain of publishing or general graphics or picture interchange) should be either not called TIFF files or should be marked some way so that they will not be confused with mainstream TIFF files.

==== Private tags ====
Developers can apply for a block of "private tags" to enable them to include their own proprietary information inside a TIFF file without causing problems for file interchange. TIFF readers are required to ignore tags that they do not recognize, and a registered developer's private tags are guaranteed not to clash with anyone else's tags or with the standard set of tags defined in the specification. Private tags are numbered in the range 32,768 and higher.

Private tags are reserved for information meaningful only for some organization, or for experiments with a new compression scheme within TIFF. Upon request, the TIFF administrator (currently Adobe) will allocate and register one or more private tags for an organization, to avoid possible conflicts with other organizations. Organizations and developers are discouraged from choosing their own tag numbers arbitrarily, because doing so could cause serious compatibility problems. However, if there is little or no chance that TIFF files will escape a private environment, organizations and developers are encouraged to consider using TIFF tags in the "reusable" 65,000–65,535 range. There is no need to contact Adobe when using numbers in this range.<ref name="tiff6" />