Why does mgetty only send raw G3 fax files, instead of converting
arbitrary image files (like TIFF) on the fly?

>From Chris Lewis:

"As I understand it, in addition to its own formats, TIFF can encapsulate
some number of other formats.  Put another way, TIFF is, at least to some
extent, simply a way of getting magic numbers into other formats so that
TIFF-capable converters can handle multiple formats transparently.

"Yes, you certainly can have TIFF encapsulate a G3, and mgetty wouldn't
have much trouble with that.  However, that leaves you with the question -
what does mgetty do if it's not a G3 that's been encapsulated?  It
would have to convert it.  And then we would encounter situations where
mgetty's conversion speeds couldn't meet the class II FAX transmission
timeouts, and you've wasted telephone time...  Ditto on reception.  Indeed,
there is a real possibility that mgetty would not be able to keep up
if the input or output file was anything other than a G3.

"Approaching this from another viewpoint, we should also remember that
mgetty is a transfer protocol and implementation.  *Not* conversion
software.  mgetty needs to read and write G3s, and that's all.  Leave
conversions to other software."

And from Gert Doering:

"Well, TIFF is a very complex file format, that can support dozens of
different page data encodings, different byte / bit orderings,
multiple pages per file, and so on.  While TIFF is a flexible format,
parsing it is a complex task.

"In contrast, mgetty's "g3" files are raw G3 data. No headers, no
formatting, no need for the transmission code to dig around in the file
to find the actual page data.  One page per file, simplest possible.

"Ignoring TIFF (leaving TIFF conversions to outside software)
simplifies mgetty and sendfax enormously, but doesn't complicate the
user interface much, as long as "faxspool" or similar tools are used
that will hide the internals, that is, how the fax backend expect its
data, from the user. To be precise, leaving out TIFF support
*simplifies* mgetty.  Many Unix programs can read pbm and converting
g3 -> pbm is very easy, while I haven't seen a good *multipage*-Tiff -
to - PBM converter yet."