Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!van-bc!sl
From: sl@wimsey.bc.ca (Stuart Lynne)
Newsgroups: comp.dcom.fax
Subject: Re: Superfine mode
Message-ID: <1991Apr28.232355.1122@wimsey.bc.ca>
Date: 28 Apr 91 23:23:55 GMT
References: <1991Apr28.192301.10631@athena.mit.edu>
Organization: Wimsey Associates
Lines: 49

In article <1991Apr28.192301.10631@athena.mit.edu> caserta@athena.mit.edu (Francesco Caserta) writes:
}Many fax machines have now the Superfine transmission option. I remember
}to have read in this newsgroup that this kind of trasmission is actually
}obtained from one of the standard options (std or fine) with a suitable
}shifting.
}
}Can anyone explain better the situation? In particular, is a superfine
}transmission dependent also of the receiving end? Can two machines, both supporting superfine mode, but of different brand names, perform a
}superfine transmission?

The only difference between standard and fine is that twice as many raster lines are
sent by the originating machine. Specifically a resolution of either 3.85 lines/mm
or 7.7 lines/mm. The horizontal resolution is fixed at 1728 pels along a scan line
length of 215 mm +/- 1%. (Yes this is the way it's expressed in the T.4 CCITT
standard.)

One method of doing a "superfine" transmission is to double the number of scan lines
again. For example to 15.4 lines/mm.

While there are probably a number companies doing this there is another problem. The
CCITT T.30 standard specifies a specific set of parameters that each machine must
send to each other to determine among other things what resolution the receiver is
capable of and the sender wants to send. T.30 does not currently have any parameter
that specifies that the sender wants to send "superfine" or the the receiver is
capable of "superfine". 

To circumvent this each manufacturer uses another facility of T.30 called "Non
Standard Frames". This allows the fax machine to send additional parameters to the
other side. NSF frames that are not understood are just thrown away. This allows
manufactures to setup proprietary functionality when there is one of their machines
at each end. 

So what you have is two machines sending NSF frames to each other. If they are from
the same manufacturer then they sync up and can do "superfine". But if they are from
competing manufacturers then they don't understand and can't. Even if they really
have the capability. They just where unable to agree to use the capability.

There are proposals being studied by various standards committees (CCITT, TIA TR29
for example) to add the functionality to the standard part of T.30. At that point
uptodate machines that implemented "superfine" and the new T.30 (T.30bis?) standard
would be able to send and receive in "superfine" mode.

These proposals also are looking at alternate resolutions. Roughly speaking the
current resolutions are 98x202 and 196x202 with superfine being 392x202. The other
suggested resolutions being 392x404 and 300x300.

-- 
Stuart Lynne	Computer Signal Corporation, Canada
		...!van-bc!sl 604-937-7785 604-937-7718(fax) sl@wimsey.bc.ca