Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!pacific.mps.ohio-state.edu!linac!att!cbnewsj!cbnewsi!hrs1
From: hrs1@cbnewsi.att.com (herman.r.silbiger)
Newsgroups: comp.dcom.fax
Subject: Re: Fine mode in Group III faxes
Summary: time factor in fine mode
Message-ID: <1991Apr10.150039.4714@cbnewsi.att.com>
Date: 10 Apr 91 15:00:39 GMT
References: <10335@pitt.UUCP> <1991Apr9.132236.21891@bilver.uucp>
Organization: AT&T Bell Laboratories
Lines: 22

In article <1991Apr9.132236.21891@bilver.uucp>, dandrews@bilver.uucp (Dave Andrews) writes:
> In article <10335@pitt.UUCP> jonathan@cs.pitt.edu (Jonathan Eunice) writes:
> >sample shown (p. 107) makes Fine look *much better* than Standard.  Do
> >most standalone fax machines support the Fine resolution?  I've
> 
> Fine is supported most everywhere, but it takes twice as much time to
> send a fine page as a standard resolution page.  There are a few of
> us pathological types that use Fine regularly because of the quality
> improvement, but not many.

The use of fine mode does not double transmission time if the machine is using
the optional 2-dimensional coding.  In 2-dimensional coding, the coding is
of a line is dependent on the change from the previous line, with (for T.4) a
maximum window size of 4 lines.  Thus, when you increase resolution, lines get 
to be more alike, and the coding is more efficient.

With the optional T.6 encoding, there is no limit to window size, which is the
principal reason for its increased efficiency.

There are similar gains in efficiency when going from 200x200 ppi to 300x300 ppi.

Herman Silbiger