Internet draft                                            Graham Klyne
<draft-ietf-fax-tiff-application-00.txt>               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,
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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 <ietf-fax@imc.org>.











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: <draft-ietf-fax-tiff-reg-02.txt>
     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]