[hylafax-users] 2D and 1D Compression

[lproxy@comcast.net]

I am not a member of this list, but I believe that this message
is an important one and I hope that the moderator will post it.

A lot of receiving fax machines will accept both 2D and 1D
compression for faxes, and HylaFAX is supposed to be able to
determine the proper scheme to use.  According to the sendfax man
page and other documentation "HylaFAX will by default use the
optimal compression scheme supported by the transmitting modem
and receiving facsimile device." 

However, an examination of the system logs shows that, after
giving HylaFAX a PostScript file to transmit, the compression
occurs *before* any negotiation with the receiving fax machine
and hence *before* the capabilities of the receiving machine can
be determined.  In a lot of cases, the logs show that the
receiving fax can accept 2D but the compression has already been
made by HylaFAX to 1D.

The HylaFAX file that does the compression is ps2fax and the
default setting is to use 1D.

I am using a Class 1 modem and it is capable of both 1D and 2D.

Why does the documentation claim that HylaFAX determines optimal
compression based on the receiving machine when this is clearly
not the case?  If the -2 parameter is not specified in the
sendfax command line, HylaFAX will only produce a 1D compressed
file from the PostScript input.

A good improvement for future versions of HylaFAX should be file
compression that occurs only *after* a negotiation with the
receiving fax machine has determined all relevant capabilities.

Larry Andrew Piet
Detroit, MI
USA

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