2015.03.17 07:44 "Re: TIFF Durations Hylafax/Dialogic", by Kasra Salehi
Thanks a lot for this info. It's actually helped us quite a lot and give us a lot more info regarding how Hylafax/Dialogic handles the TIFF files.
Have a great week :)
On Tue, Mar 17, 2015 at 12:24 AM, Lee Howard <email@example.com> wrote:
> Hello Kasra,
> If I understand correctly, you're saying that if you have an image that in > G3 MH (1D) that is twice as big as an image in G4 MMR (2D) that the
> transmission time is essentially the same for both (when HylaFAX is not > employing RTFCC, real-time format compression conversion)?
> I would suspect that RTFCC is being performed either by HylaFAX or by the
> Dialogic device.
> With all of the bells-and-whistles built-into HylaFAX (including JBIG), > HylaFAX.org versions will perform RTFCC by "blindly" reformatting -
> preferring JBIG over MMR over MR over MH. If JBIG isn't built-in then it's > just MMR over MR over MH. However, a device such as a Dialogic modem
> certainly has the capability to undo or redo that effort to whatever it > chooses.
> 2D compression is not always better than 1D, however. See slides 17 and > 18 in: http://hylafax.sourceforge.net/docs/cluecon2-presentation.odp
> In modern HylaFAX+ versions it employs "intelligent" RTFCC. That means > that it will convert an MH image to MMR and then compare the two of them.
> If the 2D compression is smaller than the 1D then it will prefer MMR and MR > over MH. If it 1D is smaller then it will prefer MH even over MMR. JBIG
> compression is always preferred with "intelligent" RTFCC because there is > no realistic scenario where it is not tighter.
> The URL you cite is incorrect. JBIG is supported by Class 2.1. I don't
> know why the hylafax.org wiki says otherwise. It may be that the
> hylafax.org versions do not support it (I thought they did, though), but > the Class 2.1 spec does support JBIG, and HylaFAX+ does, too.
> So, yes, JBIG is always going to be the best choice if you can use it. > However, you can't always use it. MMR is typically better than MH, but not
> by a whole lot, and if you're sending dithered images then MMR may not > really be any better than MH (in-fact it could be worse). However, for all
> the work you do it could theoretically be undone by the Dialogic device, so > you'd want to check on the hardware configuration.
> On 03/16/2015 02:28 AM, Kasra Salehi wrote:
I trust all is well.
Hope you don't mind me dropping you a quick email but Rhett and the rest of us have been trying to crack down on conversion methods to speed up our fax transmission times. Are you able to provide me with any specific recommendations for achieving faster durations?
I've personally been testing between Group 3 and Group 4, 2D MMR, 1-D but we can't seem to translate anything into real reductions in duration (even if the TIFF is half the size of our original dithering methods).
I've been skimming the net, particularly the Hylafax forums and I can see there are a few people suggesting JBIG compression with v34.
>> http://www.hylafax.org/content/Handbook:Advanced_ >> Server_Configuration:JPEG_and_JBIG_Faxing#JBIG
Is this worth trying or do you have anything specific you think might help us out? I'm happy to play around with the dithering of the document, removing unique black pixels, less stippling, etc but I'd be keen to know if there is a particular type of TIFF compression that is best suited for faster durations.
I look forward to hearing your thoughts.
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