character shift in faxing

By gbhall
Jan 16, 2007
  1. Ok here is a REAL weird one. I wrote a system in Visual foxpro which enables users to fax or email from their desktops. A very small proportion of faxes are received with layout exactly as it should be, but with every character and number replaced with the next character UP in the ascii order - so a becomes b and A becomes B etc all through the fax.

    I am trying hard to discover exactly where this is happening, and when I describe how a fax is created you will see why this is not easy.

    First a postscript driver is used to produce a postscript 'print' file on the server. Various postscript drivers have been shown to produce differing results, but the one I have standardised on is IBM 4039 laserprinter plus PS, which has different options under Win98 and WinXP but always seems to produce good results.

    Next that postscript file is translated into a pdf file using public domain software called GhostScript (version 8.54 the latest is in use). This conversion runs on a PC I call the 'fax server' and the files are read and written locally, the postscript files having already been copied there. Visual foxpro actually calls Ghostscript as a command processor with an huge choice of available options. Conversion has been known to occasionally produce blank pages instead of a pdf file for no known reason, but the vast majority of pdfs are fine. They are small, use built-in fonts and are infinitely scaleable without loss of definition.

    Then a commercial package called Relayfax takes over to (in the case of an email) immediately transmit the fax with the pdf file as an attachment. So far, it is possible but unproven that the problem character shift does not happen in this case.

    If the desired output is a fax, then RelayFax uses a built-in converter to generate a TIFF image of the pdf, and that image is what is ultimately faxed, via a telephone modem. It has been noted that on rare occasions adobe pdf reader pops up momentarily, or appears in the task bar without popping up, so the suspicion is that adobe reader DLL's may be involved at some stage.

    Various versions of adobe reader have been tried, and again I have ended up at the latest version, with no apparent change to the resulting outputs.

    Told you it was messy ! But since in 99.5% of cases the whole thing works beautifully, you can see that before throwing all that hard work away, I want to plead for anybody who has ever seen a fax scrambled in that way if there is any idea what might cause it.

    Suggestions are very welcome indeed.
  2. RealBlackStuff

    RealBlackStuff TS Rookie Posts: 6,503

    TIFF files are not that popular, and not all PCs support it.
    Can you change that into another picture-format: first choice EPS, secondly Adobe's PSD, alternatively JPG, GIF or even RAW?
    I must say it's quite a convoluted way, but if it works, hey!
  3. gbhall

    gbhall TechSpot Chancellor Topic Starter Posts: 2,431   +77

    solution found

    in case anybody would like to know the end of the story......

    It was possible, due to unexpected events, (the user selecting printout, but not selecting a printer, immediately choosing fax instead), that the output could be written to a Postscript file by a non-postscript printer driver (results in blank converted pages), or by a different postscript printer driver (probably resulting in the character shift problem).

    now works 100% of time.
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