[hylafax-users] Ghostscript commands to convert PDFs

[Steve Underwood <steveu@xxxxxxxxxxx>]

Hi,

The typical recommendation for Ghostscript commands to generate a FAX 
TIFF file from a PDF is something like:

gs -q -r204x98 -dNOPAUSE -dBATCH -dSAFER -sDEVICE=tiffg3 
-sOutputFile=output.tif -f in.pdf

If the PDF is a scalable one this usually works well. If the PDF 
contains a series of bit images of pages the resulting TIFF file has a 
width the same as those images. The TIFF file is then unsendable. If the 
size of the resulting images is forced with:

gs -q -r204x98 -g1728x2156 -dNOPAUSE -dBATCH -dSAFER -sDEVICE=tiffg3 
-sOutputFile=output.tif -f in.pdf

The images will always (at least in every test I tried) be 1728 pixels 
wide, and sendable. However, if the original images were only, say, 850 
pixels wide, the resulting FAX file contains images filling only half 
the width of the page.

Does anyone know a way to coax Ghostscript into always producing the 
kind of result we want for FAXing? It is certainly possible to run 
Ghostscript with the first command, check the sizes of the resulting 
images, and then rescale when the size is wrong. However, rescaling a 
bi-level monochrome image produces dreadful results, so its a pretty 
desperate measure. Most PDFs containing bit images contain gray-scale or 
true colour ones. It seems Ghostscript should be able to dither them 
down to a bi-level image 1728 pixels wide, of reasonable quality, if 
only I could figure out how.

Steve


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