Internet draft Graham Klyne Integralis Ltd. 8 December 1997 Expires: 8 June 1997 Some comments on the TIFF 'application' parameter Status of this memo This document is an Internet-Draft. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as ``work in progress''. To learn the current status of any Internet-Draft, please check the ``1id-abstracts.txt'' listing contained in the Internet-Drafts Shadow Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast). Distribution of this document is unlimited. Abstract This draft attempts to clarify some misunderstandings concerning use of the 'Application' parameter with the MIME type 'image/tiff'. It is not intended to prescribe or proscribe future use of the 'Application' parameter, but simply to indicate the intention behind its introduction. Internet Fax Working Group This is an unofficial discussion document for the IETF Internet Fax Working Group. All comments on this document should be forwarded to the email distribution list at . Klyne [Page 1] Some comments on the TIFF 'application' parameter 8 December 1997 draft-ietf-fax-tiff-application-00.txt Expires: 8 June 1997 1. Discussion The 'Application' parameter of MIME type 'image/tiff' was defined by [1]. Some discussions in the IETF fax working group have been based on a misunderstanding of the meaning of this parameter. It has been assumed by many that this parameter was intended to indicate a minumum set of capabilities, or to otherwise define interoperability between a TIFF file writer and reader. Glenn Parsons (co-author of the document which defines the 'Application' parameter) has it that the intent of the 'Application' parameter was simply to assist a receiver in dispatching a suitable application program to handle display or processing of the image file. In cases where the receiver has only one application available to process a TIFF file, the 'Application' parameter has no use. This means that the application parameter generaly serves to designate a broad range of TIFF image handling capabilities, and is therefore of limited value for fax sender or receiver conformance requirements or capability identification. The following text is excerpted from [1]: There are cases where it may be useful to identify the application applicable to the content of an image/TIFF body. As a result, an optional "application" parameter is defined for image/TIFF to identify the TIFF application of the encoded image data, if it is known. and: There is no default value for application, as the absence of the application parameter indicates that the encoded TIFF image is Baseline TIFF or that it is not necessary to identify the application. It is up to the implementation to determine the application (if necessary) and present the image to the user. and: The ability of implementations to handle all the defined applications of TIFF may not be ubiquitous. As a result, the absence of the application parameter would force implementations to decode and attempt to display the encoded TIFF image data in order to determine if it could actually be viewed. The final extract quoted above seems to contradict the idea that the 'Application' parameter was not intended to provide capability identification. But the intent was to make possible detection of Klyne [Page 2] Some comments on the TIFF 'application' parameter 8 December 1997 draft-ietf-fax-tiff-application-00.txt Expires: 8 June 1997 situations where available applications could not handle a file, without actually having to launch an application. For example, if a new application parameter value is received, and the dispatcher has no knowledge of any application to handle that value, it has an option to immediately display some kind of diagnostic message. 2. Acknowledgements This note is based on part of a conversation led by Steve Zilles, and involving Glenn Parsons, Dan Wing, Ritsuo Shirahama, Dave Crocker, Larry Masinter, Lloyd MacIntyre and Rob Buckley. Thanks in particular to Glenn Parsons for confirming the intention behind the introduction of the "Application" parameter. 3. References [1] "Tag Image File Format (TIFF) - image/TIFF MIME Sub-type Registration", Glenn W. Parsons, Nortel Technology James Rafferty, Human Communications Internet draft: Work in progress, September 1997. 4. Author's addresses Graham Klyne Integralis Ltd Brewery Court 43-45 High Street Theale Reading, RG7 5AH United Kingdom Telephone: +44 118 930 6060 E-mail: GK@ACM.ORG Klyne [Page 3]