[asterisk-users] Digium Fax for Asterisk questions

[Lee Howard]

Steve Underwood wrote:
> I wonder how much demand there is for colour FAXing.

It's quite niche.  When it's available people will have their fun with 
it for a few times, and after the novelty quickly wears off they never 
use it again.

I have quietly enabled color receiving support on high-volume fax 
receivers, just to see what kinds of things would come through in color 
without advertising it in any way other than the DIS signal.  The 
incidence of color fax reception was on the order of one in ten thousand 
- and in no cases did any of those faxes have meaningful color content; 
someone had simply pressed the "Send Color" button on their fax machine 
instead of "Send Black".

And, in fact, the data size of a JPEG fax image is so much greater than 
that of a monochrome fax image (especially JBIG) that you just can't 
leave color fax support enabled without seriously introducing some 
significant cost risks (channel usage) even for those 
one-in-ten-thousand cases.

In other words, when people are done with the novelty in color faxing, 
and when people are aware of the actual cost involved with color faxing 
(even "accidental" cases) they will disable it.  Thus, color faxing is 
really only ever used in very deliberate cases - where both the sender 
and the receiver have negotiated ahead of time that such a communication 
is being made.

That said, color faxing *does* have its niche.  For example, real estate 
appraisers will commonly have color photographs in their appraisal 
report, and they will deliberately ensure that the color aspect is not 
reduced to monochrome.  Another good example is that of an advertising 
agency in returning proofs to its customers.  In both of these cases 
e-mail attachment tends to be the dominant and preferred mechanism, but 
color faxing can - in some cases serve as an alternative (where the 
sender and receiver both have capable equipment).

> It actually requires some real 
> work, and is not just a matter of linking to libjpeg. The colour space 
> for a JPEG FAX image is different from the colour space used for most PC 
> and camera JPEG images. That creates some real messiness.

Correct.  libjpeg can be used, but libjpeg natively knows nothing about 
the required ITULAB colorspace... which means that the application would 
need to perform the necessary transforms.  That becomes a lot of work.

> HylaFAX+ has 
> partial support for colour, but I think the colour spaces hassles mean 
> it was never completed (I think it just works in one direction).
>   

Yes, it only supports color receive, and to do so it requires a 
specially-patched version of libjpeg (and libtiff).

I've made a couple efforts to try to drum up enough interest in order to 
get libtiff capable of performing the JPEG colorspace transforms to and 
from ITULAB using a native libjpeg-6b, but so far I've always come up 
short.  And, to complicate matters, finding someone who already knows 
enough about JPEG colorspaces and libjpeg who is available for hire is a 
tall order... which means that you've really got to be dedicated and 
interested in learning it yourself.

However, the aforementioned patches to libjpeg and libtiff already 
*will* allow for conversion to and from ITULAB colorspace.  However, the 
patches are "messy" and will never become accepted upstream.  (Don't 
count on libjpeg ever releasing a new version any time soon, and the 
internal JPEG support in libtiff changed in a way that breaks the way 
that the patches worked.)  So if someone really wanted to they could use 
them to learn from.  They work with HylaFAX+ to receive only because 
when sending the image needs a "tagline" put at the top which I never 
got around to developing for color.

Thanks,

Lee.