Editing OpenType (section)

===Collections===

Since at least version 1.4, the OpenType specification had supported "TrueType Collections", a feature of the format that allows multiple fonts to be stored in a single file. Such a format is useful for distributing an entire [[typeface]] (font family) in just one file.

By combining related fonts into a single file, font tables that are identical can be shared, thereby allowing for more efficient storage. Also, individual fonts have a glyph-count limit of 65,535 glyphs, and a Collection file provides a "gap mode" mechanism for overcoming this limit in a single font file. (Each font within the collection still has the 65,535 limit, however.) A TrueType Collection file would typically have a file extension of ".ttc".

However, the specification only described collection files being used in conjunction with glyphs that are represented as TrueType outlines or as bitmaps. The potential existed to provide the same storage and glyph-count benefits to fonts that use CFF-format glyphs (.otf extension). But the specification did not explicitly allow for that.

In 2014, Adobe announced the creation of OpenType Collections (OTCs), a Collection font file that combines fonts that use CFF-format glyphs.<ref>{{cite web|url=https://blogs.adobe.com/CCJKType/2014/01/otc.html |title=Introducing & Building OpenType Collections (OTCs) |website=Blogs.adobe.com |date=2014-01-27 |access-date=2017-01-19}}</ref> This provided significant storage benefits for [[CJK characters|CJK]] fonts that Adobe and Google were jointly developing. For example, the [[Noto fonts]] CJK OTC is ~10 MB smaller than the sum of the four separate OTFs of which it is composed.<ref>{{cite web|url=https://www.google.com/get/noto/help/cjk/ |title=Noto Sans CJK – Google Noto Fonts |website=Google.com |access-date=2017-01-19}}</ref> The use of a Collection also allowed for combining a very large number of glyphs into a single file, as would be needed for a pan-CJK font.<ref>{{cite web|url=https://lwn.net/Articles/613284/ |title=Google and Adobe's pan-CJK open font |website=Lwn.net |access-date=2017-01-19}}</ref>

Explicit support for Collections with CFF-format glyphs was incorporated into the OpenType specification in version 1.8.<ref name=ots-changes /> To reflect this more-inclusive applicability, the term "OpenType Collection" was adopted, superseding "TrueType Collection".