[sane-devel] Scanning for fax - resolution problem

Dieter Jurzitza dieter.jurzitza at t-online.de
Sun Jan 11 17:17:19 UTC 2009


Hi Frank,
saw this thread only lately, so here's another suggestion how I do this (apart 
from the fact that I do not use hylafax but sendfax ...)

I scan with 600dpi, but lineart mode, I found that this (somehow) improved the 
results (for me ...) though, theoretically, 204 dpi should be optimum 
(because this is what the fax does.

So I have:
/usr/bin/scanimage --mode Lineart --resolution 600 | \
/usr/bin/pnmtops -width 8.5 -height 11.5 -scale 0.12 - > /tmp/faxfile.ps

the latter is being processed by faxspool from sendfax. Please note that 
the "\" marks a continuation of the line - i. e. there should be no 
linebreak.

Hope this helps,
take care




Dieter

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-----------------------------------------------------------Am Sonntag, 11. 
Januar 2009 15:19:05 schrieb Frank Millman:
> Frank Millman wrote:
> > Hi all
> >
> > I have got a scanner and fax modem working perfectly on Windows. I am
> > trying to move them over to a new Fedora 10 server, using sane
> > (scanimage version
> > 1.0.19) and hylafax+ (version 5.2.8).
> >
> > I am battling with getting a suitable tiff file for faxing.
>
> Thanks to all for the replies. I will save some bandwidth and respond to
> them all here ...
>
> [allan]
>
> > I dont think 'resolution' is the word you are looking for here, perhaps
>
> quality? can you describe the problem a bit more?
>
> A block of solid blue comes out as a patterned block of black and white
> dots. A solid line comes out as a dotted line.
>
> > i think your best bet is to scan at 200 dpi (or 204 if your scanner will
>
> do it), and then pass the file thru something like convert to crop or pad
> it to the right width instead of scaling it.
>
> This agrees with the advice I got from the hylafax list. Unfortunately I
> found myself out of my depth with all the options in ImageMagick. However,
> I did get some other suggestions which seem promising - see below.
>
> [Giuseppe]
>
> > Is your fax really able to transmit grey images?
>
> No, hylafax converts the image to monochrome first. Apparently it uses
> Ghostscript to do this, and this is where the loss in quality comes from.
>
> > I suggest you to scan in black and white and/or to increase dpi.
> > (Increased dpi will probably help when hylafax will convert your image
> > to black and white.)
>
> I tried scanning in black and white (--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.
>
> Increasing dpi did not help, I am afraid.
>
> [Jeremy]
>
> > Have you tried scanning your document using my "bscan" bash script?
>
> Thanks very much for this, Jeremy, it looks interesting. Unfortunately I
> could not get it to run - it complained about not finding
> 'gamma4scanimage'. As I got some promising suggestions from the hylafax
> list I did not pursue it, but I do appreciate your assistance.
>
>
> I got this suggestion from Lee Howard on hylafax -
>
> > 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
>
> I don't understand it, but it works. The downside is that it produces an
> output file that is more than double the size, and therefore take more than
> twice as long to transmit. I am following up one other possibility, but if
> that does not prove worthwhile, I will stick with this suggestion.
>
> I must say that there is a lot more to scanning and faxing than I had
> realised. I am used to using Windows, where you install the driver and it
> just works. Nevertheless, it is good to know that there are so many people
> out there willing to help. I shall persevere until I get it working
> properly.
>
> Many thanks to all.
>
> Frank





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