Re: [hylafax-users] Do I need to configure anything special to get 2D-MMR+ECM in Class 1 on CVS?

[Lee Howard <faxguy@xxxxxxxxxxxxxxxx>]

On 2003.10.17 11:34 An Intrepid HylaFax User wrote:

> What I always wondered though, is that transcoding tiff files is
> extremely
> fast on modern machines (sub-second execution times)...  this could be
> done
> "on-the-fly" (even atomically as a file operation just prior to
> reading the
> .tiff files) without breaking anything, no?

Yes, almost correct.

HylaFAX (faxsend) will read the TIFF file in, will remove excessive 
trailing whitespace (pagechop), will remove trailing RTC/EOFB/garbage 
data, and will then (with non-MMR TIFFs) image the tag line.  All of 
this occurs before actually transmitting the data.

libtiff allows us to read a TIFF in as "raw" or to decode (rasterize) 
it as it's read-in.  Currently we only read it in raw and must, 
therefore, use the compression type specified in the TIFF file.  
There's no real point to decoding it as it's read in since we can (and 
do) decode it ourselves with the functions I mention above.  Our 
decoder can decode MH, MR, or MMR... no problem.  The problem is, 
though, that to fax it out we must then re-encode it, and our encoder 
only can encode in 1-D (MH or MR, but only 1-D lines for MR).  We 
*could* use the libtiff encoder by writing it to file and encoding it 
simultaneously and then re-read the file, but that's too much disk 
activity as I see it (think about 100 simultaneous outbound faxes).  So 
our encoder needs to be made capable of encoding 2-D lines before we 
can convert on-the-fly or even image a tagline on MMR faxes.

This enhancement to the encoder would have been done a long time ago by 
me, but although I kind-of know modems and fax protocol, I do not 
really understand TIFF decoding/encoding more than superficially.  This 
is a call to action for all TIFF gurus out there! ;-)

Lee.

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