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

[Lee Howard <faxguy@xxxxxxxxxxxxxxxx>]

Frank Millman wrote:
> 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've not met a scanner that didn't do what I needed to scan 
appropriately for faxing.  Sometimes it took a bit to get the settings 
right.  Make sure you're scanning at 200 dpi and monochrome.  Then try 
adjusting the "contrast" and "brightness" settings.  You'll eventually 
find a happy setting.

> 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?
>   

Yes, because the image is dithered.  All of the colors get turned into 
patterns of dots.  And the more black-to-white-to-black transitions that 
there are the less-effective the data compression will be (with MH, MR, 
and MMR... JBIG may handle it okay still).

> 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?

I don't have any meaningful experience with which to offer assistance 
with pnm other than to warn you that it gets complicated.  Again, I 
think that your time would be better-spent in learning how to better-use 
your scanner for faxing.

Thanks,

Lee.


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