[hylafax-devel] Re: question about text in your patch

[Dmitry Bely <dbely@mail.ru>]

"Bernd Proissl" <news@proissl.de> writes:

>  this is from your patch:
>  +	     * Method of deleting RTC is not quite correct
>  +	     * since RTC may not present in the TIFF
>  +	     * file (if the TIFF was not Hylafax-generated).
>  
>  What exactly do you mean with "if the TIFF was not Hylafax-generated"?
>  
>  What exactly is a hylafax generated tiff? Is it a tiff generated from
>  ghostscript which was called by hylafax?

Well, the comments possibly should be updated. OK, let's see what happens in
details. (for even more details see faxQueueApp.c++). 

Hylafax can handle Plain text, Postscript and TIFF files the following way:

Postscript (plain text handling is very similar):
   passed through ps2fax, invoking (usually) Ghostscript for
rasterizing. GS in turn uses tiffg3 driver which always ADDS byte-aligned
RTC to the end of the written TIFF file.

TIFF:
   passed through tiff2fax, been checked for G3 format and required
session parameters compatibility. Depending on the TIFF structure it can be 
used "as is" (RTC presence not affected), passed through tiffcp, which
always REMOVES RTC, or passed through tiff2ps | ps2fax, which always ADDS
RTC (see above).

So we cannot predict in general if RTC is present or not in the TIFF file,
which Hylafax is going to transmit, without parsing the file. But,

1) the Postscript/Plain text case is most commonly used, and my patch
handles it correctly,
2) even if we cut some bytes in the end of the file, we just corrupt a
couple of rows. Remote fax machine will encounter a noise on the line, but
syncronization will not be lost (reason of endless RTN).

Of course, there is a one more method to eliminate the problem -- add extra 
tiffcp filter which will always reencode ps2fax/tiff2fax result to remove
RTC. But it will take some extra time on the heavy loaded system. What do
you think?

Hope to hear from you soon,
Dmitry



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