[sane-devel] Scanning for fax - resolution problem

[m. allan noah]

On Thu, Jan 8, 2009 at 7:27 AM, Frank Millman <frank at chagford.com> 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.
>
> The scanner is detected as a Plustec OpticPro U24. The test page I am trying
> to fax is an A4 pre-printed form, where the printing is light-blue on white,
> and the form is completed in handwriting. Windows has no problem in scanning
> and faxing this form.
>
> Initially I did this -
>
>    scanimage --mode Gray --resolution 200 --format tiff -x 215 -y 297 |
> sendfax -n -m -d 1234567
>
> It worked, but the fax came out on the other side with poor resolution.
>
> Then I tried writing the image to a file, using -
>
>    scanimage --mode Gray --resolution 200 --format tiff -x 215 -y 297 >
> /home/frank/test.tif
>
> The size of the file created is 3.9mb. If I then do the following -
>
>    sendfax -n -m -d 1234567 /home/frank/test.tif
>
> it sends the fax ok, but with the same problem.

same problem because you are sending the same data, pipe or file, you
did not change anything.

>
> I enquired on the hylafax list, and got the following response -
>
> "
> My guess is that the image isn't right for direct FAX (T.30) sending, and
> the ghostscript middle-man is the culprit.
>
> You can see the tiff2fax command executed in syslog if you turn up faxq
> logging, and running it by hand (and with -x) will show you the GS running
> to squash the bad-sized tiff to the right-sized tiff (and then you can
> verify that it's the GS making the right-sized tiff look bad).
> "
>
> I did this, and can confirm that, using the tiff file of 3.9mb as input,
> tiff2fax creates a tiff file with a size of 140kb, with the bad resolution.

I dont think 'resolution' is the word you are looking for here,
perhaps quality? can you describe the problem a bit more?

>
> I also got the following suggestion -
>
> "
> Another option would by to try and get SANE to scan to the right format, I
> think your best bet is to try and get it to match:
>
> Horizontal: RES of 204(pi), 1728 pixels wide *exactly*
> Vertial:    RES of 196(pi), variable length (as long as your receiver
> accepts it,
>                 otherwise around 2150 - 2300 pixels for letter/A4
> "
>
> I tried scanimage with lower resolutions, but that resulted in an image with
> a very dark background, virtually unreadable.
>
> I tried scanimage with --mode LineArt, which worked, but the scan lost a lot
> of detail, so that is not a solution.

but faxes are lineart in the end? i guess the GS gray to lineart
conversion is better than that of the scanner?

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.

allan
-- 
"The truth is an offense, but not a sin"