At 19:23 17/02/99 -0600, Richard Shockey wrote:
[...]
>>> To quote from what should have been in the IANA registry.
>>>>>> New Value(s): faxbw, faxcolor
>>>>If the attribute specifies the profile (tiff-profiles-supported) isn't
>>this a better resolution than 'faxbw' and 'faxcolor'? Are you proposing
>>an attribute such as "tiff-applications-supported" which would only
>>include 'faxbw' and 'faxcolor'? The BW vs Color can be determined from
>>the "color-supported" Printer Description attribute and the profiles give
>>even better information.
>>>>Ok ... I see your point ... this would start to nest attributes which looks
>like a rathole.
I think that as soon as one gets beyond the broad capability implied by a
MIME type it may be appropriate to use the 'conneg' expression framework to
capture the dependencies. The level of refinement provided there is
necessary to capture the possible capabilities of a G3 fax recipient, for
example.
On the topic of TIFF profiles, it turns out that each covers a range of
possible capabilities. I am not aware of a clear consensus about whether
declaring a capability to handle (say) TIFF-F means handling the minimum,
maximum or some other part of the functionality of that profile.
Finally, in discussion with Glen Parsons some time ago, it was explained
that the TIFF "application" parameter was intended as an aid to dispatching
an image handler, not to indicate capabilities. See
<draft-ietf-fax-tiff-application-00.txt> (if it's still online -- in case
it's not, I attach a copy).
#g
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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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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 <ietf-fax at 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 at ACM.ORG
Klyne [Page 3]
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Graham Klyne
(GK at ACM.ORG)