Editing TIFF (section)

==== Private tags ====
The TIFF/IT specification preserved the TIFF possibility for developers to utilize private tags. The TIFF/IT specification is very precise regarding how these private tags should be treated - they should be parsed, but ignored.<ref name="tiffitprivatetags">{{cite web|url=http://www.ddap.com/resources/privatetags_faqs.html |title=TIFF/IT Private Tags |author=DDAP Association |year=2002 |access-date=2011-03-03 |url-status=unfit |archive-url=https://web.archive.org/web/20030428202922/http://www.ddap.com/resources/privatetags_faqs.html |archive-date=April 28, 2003 }}</ref>

Private tags in the TIFF/IT-P1 specification were originally intended to provide developers with ways to add specific functionality for specific applications. Private tags can be used by developers (e.g., Scitex) to preserve specific printing values or other functionality. Private tags are typically labelled with tag numbers greater than or equal to 32768.

All private tags must be requested from Adobe (the TIFF administrator) and registered.

In 1992, the DDAP (Digital Distribution of Advertising for Publication, later Digital Directions in Applications for Production) developed their requirement statement for digital ad delivery. This was presented to  ANSI-accredited CGATS (Committee for Graphic Arts Technology Standards) for development of an accredited file format standard for the delivery of digital ads. CGATS reviewed their alternatives for this purpose and TIFF seemed like the ideal candidate, except for the fact that it could not handle certain required functionalities. CGATS asked Aldus (the TIFF administrator) for a block of their own TIFF private tags in order to implement what eventually became TIFF/IT. For example, the ability to identify the sequence of the colors is handled by tag 34017 - the Color Sequence Tag.<ref name="tiffitprivatetags" />

TIFF/IT was created to satisfy the need for a transport-independent method of encoding raster data in the IT8.1,
IT8.2 and IT8.5 standards.