Document size proposal - take 3

[Graham Klyne <GK@xxxxxxxxxxxxxx>]

All,

It occurred to me that it might help if I clarified the approach to
document size capability description that I personally prefer...

---begin proposal---
2.1 Document Image Size

   - Media Feature tag name(s): 

     size-x
     size-y
    
   - ASN.1 identifier associated with this feature tag:

     ***New assignments by IANA***

   - Summary of the media features indicated by this feature tag:

     These features indicate the size of a displayed, printed or otherwise
     rendered document image;  they indicate horizontal (size-x) and
     vertical (size-y) dimensions.

     The unit of measure is inches (to be consistent with the measure of
     resolution defined by the feature tag 'dpi').

   - Values appropriate for use with this feature tag:

     Rational (>0)

   - The feature tag is intended primarily for use in the following
     applications, protocols, services, or negotiation mechanisms:

     Print and display applications where different media choices will
     be made depending on the size of the recipient device.

     Where no physical size is known or available, a notional horizontal
     size of (say) 10 inches should be declared, and a known pixel size
     communicated through use of an appropriate resolution value.

     For example, to describe a 640x480 pixel display:

        (& (size-x<=10) (size-y<=4800/640) (dpi=640/10) )

     or

        (& (size-x<=640/64) (size-y<=480/64) (dpi=64) )

     (The value 10 inches is used as it represents a "reasonable" physical
     dimension to match documents for which a physical size is specified.)
---end proposal---

The second example above suggests an alternative approach when physical
dimensions are not available is to select a notional resolution of (say)
100dpi as a reasonable value for a lo-resolution pixel display, and use
that to construct notional dimensions based on known pixel dimensions:

    (& (size-x<=640/100) (size-y<=480/100) (dpi=100) )


To recap, the reason I prefer this approach is that in many cases it
eliminates having to specify different size capabilities corresponding to
different resolutions. This is particularly well illustrated by fax.

#g

------------
Graham Klyne
(GK@xxxxxxx)