Re: [hylafax-users] 11x17 & Resolution

[Lee Howard <faxguy@xxxxxxxxxxxxxxxx>]

On 2003.12.17 13:52 Jayson Henkel wrote:
> Hello everyone,
>
> I have a sample hylafax server setup and receiving faxes nicely. Yay!
> However, I have a few questions:
>
> 1.) Are there any caveats to receiving 11x17 faxes (a technical
> drawing), I have  been able to receive them but their seems to be a
> small border that chops off the edge's of the page.

I would be interested in seeing some of these session logs, if you can 
send them.  So much of faxing is done in A4, letter, and legal sizes 
that I'd love to see something different.  Also the faxinfo output 
against the received TIFF would be lovely.

> Is this the source
> fax causing the problem or some config setting within hylafax?

Fax protocol (T.30) basically supports only three different page 
widths: A4 (215 mm), B4 (255 mm), and A3 (303 mm).  Here's a table from 
'man gs':

       PAPERSIZE    X inches   Y inches   X cm      Y cm
       -----------------------------------------------------
       a3           11.6944    16.5278    29.7039   41.9806
       a4           8.26389    11.6944    20.9903   29.7039
       b4           9.84722    13.9167    25.0119   35.3483

       letter       8.5        11         21.59     27.94
       legal        8.5        14         21.59     35.56
       11x17        11         17         27.94     43.18

Because fax protocol also allows for unlimited page length, the last 
three page sizes there can be "approximated" by using A4 for legal and 
letter and then using A3 for 11x17.  The length won't matter, but on 
"legal" and "letter" faxes there's going to be 1/4" missing 
horizontally.  Likewise, with an "11x17" fax there's going to be nearly 
1/2" missing horizontally.

In other words, the "small border" that's being chopped off is probably 
to be expected, as long as we're talking about an image loss of about 
1/2".  If it's more than that... well, then that will take some 
investigation.  If the 1/2 inch is critical, then you may want to see 
if you can get your senders to scale down to and send with A3 size 
rather than 11x17.

> 2.) For the aforementioned  technical drawing is there settings within
> Hylafax that affect the print quality? There appears to be some
> quality
> differences between a "true" fax and the hylafax rendering. This is
> using "Super-fine" on the source fax and 600x600 dpi (max available)
> on
> the output printer (an HP 5000). Is there any way of improving the
> output quality? Especially for very small text.

HylaFAX CVS HEAD (to be 4.2.0) supports extended resolutions 
(particularly in Class 1 - only in Class 2 if your modem supports it) 
which include ~200x400 dpi (often called superfine), 300x300 dpi, and 
~400x400 dpi (often called hyperfine).  Pre-4.2.0 HylaFAX releases will 
only support normal (~200x100 dpi) and fine (~200x200 dpi); thus you're 
currently losing resolution - probably half the vertical resolution.

As resolution increases so does the risk of encountering some corrupted 
image data.  For this reason ECM (error correction) is recommended with 
extended resolution faxing.  HylaFAX CVS HEAD also fully supports ECM 
in Class 1.  (ECM in Class 2 is already supported if your modem also 
supports it.)

> If it helps I am using 4.1.1-3  (Debian versioning) on Debian Stable.

Judging that the current HylaFAX version is 4.1.8 and 4.1.1 was 
released nearly two years ago, I suspect that it will be a very long 
time after release before 4.2.0 ever makes it to Debian Stable... you 
may want to look into independent upgrade options if these features are 
useful to you.

Lee.

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