Re: [hylafax-users] Scanner to fax resolution problem

["Frank Millman" <frank@xxxxxxxxxxxx>]

Lee Howard wrote:
> 
> Frank Millman wrote:
> >     scanimage --mode Gray --resolution 200 --format tiff -x
> 215 -y 297
> > | sendfax -n -m -d 1234567
> 
> Don't use --mode Gray.  You want monochrome output.  
> Hopefully your scanner device can produce monochrome (black and white) 
> instead of grayscale.
> 
> Because faxing is done in monochrome if you supply an image to HylaFAX 
> that is not monochrome then HylaFAX will invoke Ghostscript to render 
> it into monochrome, and Ghostscript will have to "dither" the image.  
> By default Ghostscript does a very poor job of this.
> 
> Because you're using HylaFAX+ you have certain script features 
> available already.  You can improve the dithering behaviors greatly by 
> putting this into
> /var/spool/hylafax/etc/FaxModify:
> 
> DITHERING=libtiff-fs
> 
> However, it is my recommendation to use the scanner to convert to 
> monochrome rather than making HylaFAX do the dithering.
> 

Thanks for this, Lee.

I tried monochrome (--mode=LineArt), but it gives a poor result. Most of the
light-blue lines disappear altogether. Maybe a better scanner would give a
higher quality, I don't know.

I tried your suggestion of 'DITHERING=libtiff-fs', and it made a huge
improvement - I would say that the output was acceptable. However, the time
take to transmit the fax increased from 77 seconds to 180 seconds. According
to the log, the number of bytes transmitted increased from 132977 to 330824.
Is this expected?

I checked the archives and found something that looked promising -

    http://thread.gmane.org/gmane.comp.telephony.fax.hylafax.user/10976

This is the important part -

"
For the best quality faxes, however, I prefer to do all the processing
myself.  To resize your TIFF file, I would recommend the following procedure
that is implemented with the NETPBM tools:

tifftopnm 1.tif |
pnmscale -xsize 1728 -ysize 2291 |
pgmtopbm |
pnmtotiff -g3 -rowsperstrip 2156 > 1cf.tif "

The last line is corrected to 'pnmtotiff -g3:1d -rowsperstrip 2291 >
1cf.tif' in a subsequent post.

I tried this, together with some variants based on the latest version of pbm
tools, and it almost works. If I write the result to a file and view it with
viewfax, it looks correct. If I feed it to sendfax and actually fax it, I
get an image on the other side which consists of the bottom-left 1/3 of the
original document, scaled up to A4 size. According to the log, it transmits
36855 characters.

Do you know the correct incantation to get it to fax the document correctly,
or should I not pursue this approach?

Many thanks

Frank


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