Subject: Re: comment on feature-T30-mapping-01.txt

From: Graham Klyne <[email-masked]>
Date: Mon, 28 Jun 1999 09:53:31 +0100

Mori-san,

Thank you for your question.

I think that there are two separate responses that I need to make here.

First, taking your final point:

>My point is only to make a provision that Internet fax machine can send
>MR/MMR/
>B4/A3 with TIFF-S structure LEGALLY and to confirm such application will
cause
>no problem.

It is certainly possible and reasonable to express this capability.  I
suggest the appropriate form would be:

#     (& (color=binary)
#        (image-file-structure=TIFF-S)
#        (image-coding=[MH,MR,MMR])
#        (MRC-mode=0)
#        (| (& (dpi=20320/100) (dpi-xyratio=20320/9779) )
#           (& (dpi=20320/100) (dpi-xyratio=20320/19558) )
#           (& (dpi=200) (dpi-xyratio=200/100) )
#           (& (dpi=200) (dpi-xyratio=1) )
#           (& (dpi=300) (dpi-xyratio=1) ) )
#        (size-x<=2150/254)
#        (Paper-size=[A4,B4,A3,Letter]) )

Secondly, turning to your other questions:

>Now is it possible to say
>
>  (& (image-file-structure=[TIFF-S])
>        (image-coding=[MH,MR,MMR]) )
>
>?
>
>To my understanding, TIFF-S is a SET of attributes such as A4/MH/IFD order
>/LSB first/200*100,200*200dpi and so on... 
>
>So the above capablity means that the receiver side is able to handle only
>TIFF-S file except that the coding scheme is only extentible to MR and MMR.
>And other features of TIFF-S shall be kept.

I think it is important to be clear that the (image-file-structure=TIFF-S)
tag is used to describe ONLY image file structure properties, rather than
capabilities described by other feature tags (image-coding, dpi,
paper-size, etc.)  So it DOES indicate the general file structure as
TIFF-FX, with IFD order, LSB first, etc., but it does not of itself imply
A4, 200*100dpi, MH/MR/MMR, etc.

This is covered in RFC 2531 (fax feature schema):

  A.7 Image file structure
  
     -  Media Feature tag name(s):
  
           image-file-structure
  
[...]
     -  Summary of the media features indicated:
  
           This feature indicates a file structure used for transfer and
           presentation of image data.
  
           It does not indicate image data coding:  that is described by
           separate feature tags (image-coding, etc.).
[...]
     -  Considerations particular to use in individual applications,
        protocols, services, or negotiation mechanisms:

           This tag is intended to provide information about an image file
           structure.  Information about image data coding is provided by
           other tags.

           In the case of TIFF-FX image data, there are a number of image
           file format constraints that are imposed by the various usage
           profiles defined in RFC 2301 [7].  The purpose of the 'image-
           file-structure' feature tag is to capture those file format
           constraints.

           Registration of additional image file structure tags should
           focus similarly on image file structure issues, not raw image
           data compression and coding.  As a guide, an image file
           structure may contain image data coded in a variety of ways,
           and carries information to describe that coding separately from
           MIME content-type labelling, etc.

>In the same manner,
>(&  (image-file-structure=[TIFF-S])
>        (image-coding=[MH,MR,MMR])
>             (Paper-size=[A4,Letter,B4,A3]) )
>
>Is this still valid?

This is valid, but incomplete, for the reasons given above.

(And a small matter:  the expression (image-file-structure=[TIFF-S]) is
equivalent to (image-file-structure=TIFF-S).  [RFC 2533 section 4.2.5.]

>I hope this is valid because I believe some fax machines will still have a
>difficulty 
>to fully support TIFF-F structure but rather easy to suport MR/MMR/B4/A3
>within the range of TIFF-S structure.

It is possible to express what I think you are trying to say here, but the
image coding details must all be expressed separately from the image file
structure constraint.

>What about this?
>(&  (image-file-structure=[TIFF-S,TIFF-F])
>        (image-coding=[MH,MR,MMR])
>             (Paper-size=[A4,Letter,B4,A3]) )
>
>It must be probable that the receiver can handle every file structure
>within TIFF-F.
>So there will be no problem although we accept the first two cases.

Same comment as above.

>Then what about this?
>(&  (image-file-structure=[TIFF-S])
>        (image-coding=[MMR]))
>
>Is this equivalent to saying
>(&  (image-file-structure=[TIFF-S])
>        (image-coding=[MH,MMR]))
>?

These are not equivalent because the tag (image-file-sructure=TIFF-S) does
not say anything about image coding, only file structure.  So the two
expressions differ in the image coding that they permit (MMR vs [MH,MMR]).

(You will then notice that the first case does not conform to the _full_
requirements of RFC 2301 mode TIFF-S, and as such is not a legitimate
description of an Internet fax system, but it _is_ a legitimate media
feature expression.   Note that the feature expression format is designed
to express a very much wider range of combinations of capabilities than
those expressed by (say) Internet fax or T.30 DIS frames in Group 3 fax;
this allows a future path to interoperability with a range of other
Internet protocols.)

>A little debatable. I would like to hear your opinions.
>To my feeling it should be regarded as equivalent.

In summary, I think there is some misunderstanding about the meaning of the
'image-file-structure' feature tag.  But apart from that, I believe it is
possible to express all of the capabilities that you indicate to be
important to express.

I hope you find this helpful.

#g

------------
Graham Klyne
([email-masked])

---

From: Yukikazu Mori <[email-masked]>
Date: Mon, 28 Jun 1999 18:36:10 +0900

Graham,

> possible to express all of the capabilities that you indicate to be

You are right.
My lack of undestanding your point was a root of my confusion.
Now I am clear.

> I hope you find this helpful.

It was very helpful.
Thank you very much.

MORI

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