Re: [hylafax-users] Faxes cut in half

[Lee Howard <faxguy@xxxxxxxxxxxxxxxx>]

SCIN - Danilo Bottino wrote:

>  I've managed to store a few of those badly received tiffs and as far 
> as I can see the conversion looks good. Huh.. now what?


Let me give you a run-down of the image proces - maybe it will help you 
understand what we're after.

You submit some document to the server for transmission.  The server 
then looks at that document and "prepares it" for transmission... 
meaning the server has an "info" file describing the known capabilites 
of the remote device, and so it will then prepare the image according to 
what it anticipates will work best and closest to the request of the 
user.  If the submitted document just happens to be in the proper format 
then the server will not do anything to the image for preparation.

Then the call is placed and the remote device is contacted.  The 
remote's feature support is examined, and if we can communicate the fax 
image that we prepared then protocol moves ahead.  If it is not in an 
acceptable format for the receiver then we hang up, prepare the image 
correctly, and then dial again.  Then faxsend reads-in (to RAM) each 
page of image data as it is needed in the protocol, and the tagline is 
put onto it (again, in RAM).  When dealing with an MMR source document 
this requires us to regenerate the entire page of data.  When dealing 
with MH or MR source documents we can snip and cut-n-paste the scanlines 
into place without modifying the rest of the page.  And then, if 
ModemSoftRTFCC is enabled (and it is by default) faxsend with convert 
the image compression between MH, MR, and MMR (and JBIG where available) 
on-the-fly and then transmit that data to the receiver.

In the transmission process it can be done with or without ECM.  With 
ECM there is a virtual guarantee that the data will be correct before 
the receiver attempts to decode it.  Without ECM there is no guarantee 
at all.

The receiver then does whatever it does, but in the process it will 
decode the image data to print it onto paper.

So hopefully you can see all of the points where the image can get 
fouled up from the point where you have the original document on file 
and submit it to the server and the point where the receiver prints it out.

In your case you have shown me logs that indicate that the session used 
MMR source documents and transmitted MMR (thus no RTFCC employed) and 
that ECM is being used.  Now you're confirming that the source documents 
are fine - at least to your TIFF viewer.  The receiver's fax machine is 
confirming all of the ECM frames as received in good form.  The fact 
that the receiver's print-out is being truncated means that at the point 
of truncation the MMR data it has is corrupted according to its T.6 
(MMR) decoder.  The fact that the corruption occurs inside of the page 
image and not immediately below the tagline indicates that the majority 
of the tagline imaging process is okay.

So, where does that leave us?

The options are these...

1) there still could be an error in the source TIFF image document - 
however, this is unlikely given that you've looked at it okay and that 
it's being further processed by the tagline imaging

2) there could be some flaw in HylaFAX's T.6 decoder or encoder as it 
decodes and then re-encodes the data during the imaging process.  This 
is possible, but if it were the case I think that we'd see many more 
instances of this problem with other people

3) something could be wrong the ECM framing of the image data, but 
again, this would seem unlikely as we aren't getting these reports from 
elsewhere

4) the receiver could have a bug in its MMR decoder  -  I think that 
this is the most likely bet... but it's not guaranteed by any means.

I don't think that there are really any other possibilities.

Next thing to do, I would recommend that you use JobControl to limit 
your faxes to these destinations to MH and MR image data compression... 
no MMR.  So you'll want to put this into your faxq configuration file 
(/var/spool/hylafax/etc/config):

   JobControlCmd:  etc/jobcontrol

Then restart faxq.  And then you'll want to make a file (and mark it 
executable!)  /var/spool/hylafax/etc/jobcontrol with this in it:

   #!/bin/sh
   . etc/setup.cache
   . bin/common-functions
   QFILE=sendq/q$1
   parseQfile
   case "$number" in
       5551212|7772323)
           echo "ModemSoftRTFCC: no"
           echo "DesiredDF: 0";;
   esac
   exit 0


Instead of "5551212" and "7772323" put your destinations' phone 
numbers.  That will limit faxes to be MH to those destinations.  ECM 
will still be used.  So any errors will be limited to one single scanline.

Then send faxes and see how things go.

Lee.


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