Editing TIFF (section)

=== {{anchor|Baseline TIFF}}Part 1: Baseline TIFF ===
When TIFF was introduced, its extensibility provoked compatibility problems. The flexibility in encoding gave rise to the joke that TIFF stands for ''Thousands of Incompatible File Formats''.<ref name="trauth"/> To avoid these problems, every TIFF reader was required to read ''Baseline TIFF''. Among other things, Baseline TIFF does not include layers, or compressed JPEG or LZW images. Baseline TIFF is formally known as ''TIFF 6.0, Part 1: Baseline TIFF''.

The following is an incomplete list of required Baseline TIFF features:<ref name="tiff6" />

==== Multiple subfiles ====
TIFF readers must be prepared for multiple/multi-page images (subfiles) per TIFF file, although they are not required to actually do anything with images after the first one.

There may be more than one Image File Directory (IFD) in a TIFF file. Each IFD defines a subfile. One use of subfiles is to describe related images, such as the pages of a facsimile document. A Baseline TIFF reader is not required to read any IFD beyond the first one.<ref name="tiff6" />

==== Strips ====
A baseline TIFF image is composed of one or more strips. A strip (or band) is a subsection of the image composed of one or more rows. Each strip may be compressed independently of the entire image, and each begins on a byte boundary. If the image height is not evenly divisible by the number of rows in the strip, the last strip may contain fewer rows. If strip definition tags are omitted, the image is assumed to contain a single strip.

==== Compression ====
Baseline TIFF readers must handle the following three compression schemes:<ref name="tiff6" />
* Zero compression
* [[ITU-T|CCITT]] Group 3 1-Dimensional Modified [[Huffman coding|Huffman]] RLE
* [[PackBits]] compression - a form of [[run-length encoding]]

==== Image types ====
Baseline TIFF image types are: bilevel, grayscale, palette-color, and RGB full-color images.<ref name="tiff6" />

==== Byte order ====
Every TIFF file begins with a two-[[byte]] indicator of [[byte order]]: "<code>II</code>" for little-endian (a.k.a. "Intel byte ordering", {{circa|1980}})<ref name="ReferenceA">David Beecher, author of dozens of image processing engines over the last 30 years. Any TIFF file can be viewed with a HEX editor to confirm this.</ref> or "<code>MM</code>" for big-endian (a.k.a. "Motorola byte ordering", {{circa|1980}})<ref name="ReferenceA"/> byte ordering. The next two-byte word contains the format version number, which has always been 42 for every version of TIFF (e.g., TIFF v5.0 and TIFF v6.0).<ref>{{cite book
 |     author = Aldus/Microsoft
 |      title = TIFF
 |    section = 1) Structure
 |    version = Revision 5.0
 |  publisher = Aldus Corporation and Microsoft Corporation
 |       date = 1988-08-08
 |        url = http://cool-palimpsest.stanford.edu/bytopic/imaging/std/tiff5.html
 | archive-url = https://web.archive.org/web/20081204070129/http://cool-palimpsest.stanford.edu/bytopic/imaging/std/tiff5.html
 |archive-date = 2008-12-04
 | access-date = 2009-06-29
 |      quote = The number 42 was chosen for its deep philosophical significance.
 }}</ref>
All two-byte words, double words, etc., in the TIFF file are assumed to be in the indicated byte order. The TIFF 6.0 specification states that compliant TIFF readers must support both byte orders (<code>II</code> and <code>MM</code>); writers may use either.<ref>{{cite book
 |author      = Adobe Developers Association
 |title       = TIFF
 |section     = Section 7: Additional baseline TIFF Requirements
 |version     = Revision 6.0
 |publisher   = Adobe Systems Incorporated
 |date        = 1992-06-03
 |url         = https://www.adobe.io/content/dam/udp/en/open/standards/tiff/TIFF6.pdf
 |access-date  = 2022-06-29
 |quote       = ‘MM’ and ‘II’ byte order. TIFF readers must be able to handle both byte orders. TIFF writers can do whichever is most convenient or efficient.
 |page        = 26
 |archive-url=https://web.archive.org/web/20210108174645/https://www.adobe.io/content/dam/udp/en/open/standards/tiff/TIFF6.pdf
 |archive-date=8 January 2021 |url-status=dead}}</ref>

==== Other TIFF fields ====
TIFF readers must be prepared to encounter and ignore private fields not described in the TIFF specification. TIFF readers must not refuse to read a TIFF file if optional fields do not exist.<ref name="tiff6" />