caserta@athena.mit.edu (Francesco Caserta) (04/29/91)
Many fax machines have now the Superfine transmission option. I remember to have read in this newsgroup that this kind of trasmission is actually obtained from one of the standard options (std or fine) with a suitable shifting. Can anyone explain better the situation? In particular, is a superfine transmission dependent also of the receiving end? Can two machines, both supporting superfine mode, but of different brand names, perform a superfine transmission? Thank you very much. Francesco Caserta
sl@wimsey.bc.ca (Stuart Lynne) (04/29/91)
In article <1991Apr28.192301.10631@athena.mit.edu> caserta@athena.mit.edu (Francesco Caserta) writes: }Many fax machines have now the Superfine transmission option. I remember }to have read in this newsgroup that this kind of trasmission is actually }obtained from one of the standard options (std or fine) with a suitable }shifting. } }Can anyone explain better the situation? In particular, is a superfine }transmission dependent also of the receiving end? Can two machines, both supporting superfine mode, but of different brand names, perform a }superfine transmission? The only difference between standard and fine is that twice as many raster lines are sent by the originating machine. Specifically a resolution of either 3.85 lines/mm or 7.7 lines/mm. The horizontal resolution is fixed at 1728 pels along a scan line length of 215 mm +/- 1%. (Yes this is the way it's expressed in the T.4 CCITT standard.) One method of doing a "superfine" transmission is to double the number of scan lines again. For example to 15.4 lines/mm. While there are probably a number companies doing this there is another problem. The CCITT T.30 standard specifies a specific set of parameters that each machine must send to each other to determine among other things what resolution the receiver is capable of and the sender wants to send. T.30 does not currently have any parameter that specifies that the sender wants to send "superfine" or the the receiver is capable of "superfine". To circumvent this each manufacturer uses another facility of T.30 called "Non Standard Frames". This allows the fax machine to send additional parameters to the other side. NSF frames that are not understood are just thrown away. This allows manufactures to setup proprietary functionality when there is one of their machines at each end. So what you have is two machines sending NSF frames to each other. If they are from the same manufacturer then they sync up and can do "superfine". But if they are from competing manufacturers then they don't understand and can't. Even if they really have the capability. They just where unable to agree to use the capability. There are proposals being studied by various standards committees (CCITT, TIA TR29 for example) to add the functionality to the standard part of T.30. At that point uptodate machines that implemented "superfine" and the new T.30 (T.30bis?) standard would be able to send and receive in "superfine" mode. These proposals also are looking at alternate resolutions. Roughly speaking the current resolutions are 98x202 and 196x202 with superfine being 392x202. The other suggested resolutions being 392x404 and 300x300. -- Stuart Lynne Computer Signal Corporation, Canada ...!van-bc!sl 604-937-7785 604-937-7718(fax) sl@wimsey.bc.ca
hrs1@cbnewsi.att.com (herman.r.silbiger) (04/30/91)
In article <1991Apr28.192301.10631@athena.mit.edu>, caserta@athena.mit.edu (Francesco Caserta) writes: > Many fax machines have now the Superfine transmission option. I remember > to have read in this newsgroup that this kind of trasmission is actually > obtained from one of the standard options (std or fine) with a suitable > shifting. > > Can anyone explain better the situation? In particular, is a superfine > transmission dependent also of the receiving end? Can two machines, both supporting superfine mode, but of different brand names, perform a > superfine transmission? > > Thank you very much. > > Francesco Caserta The horizontal resolution is specified (at least in Group 3) as number of pels along a scan line of specified length. The scanner has sufficient elements to meet that requirements. The vertical resolution is determined by the number of lines down the page. To go from basic resolution to fine resolution the stepper motor which moves the paper is double stepped. To get superfine it steps 4 times. The only way to get a higher horizontal resolution is by having twice as many elements in the scanner. As far as your second questions is concerned, the answer is probably not. Higresolution is a Non-Standard Facility, and is invoked by a manufacturer dependent code. A machine from another manufacturer would not know what this code meant, unless the code has been shared. This is usually not done, for competetive reasons. Herman Silbiger
hrs1@cbnewsi.att.com (herman.r.silbiger) (04/30/91)
> > These proposals also are looking at alternate resolutions. Roughly speaking the > current resolutions are 98x202 and 196x202 with superfine being 392x202. The other > suggested resolutions being 392x404 and 300x300. > > -- > Stuart Lynne Computer Signal Corporation, Canada > ...!van-bc!sl 604-937-7785 604-937-7718(fax) sl@wimsey.bc.ca Resolutions being considere are the "square" resolutions of 200x200, 300x300, and 400x400 ppi, as well as the doubling resolutions. There is also a proposal to migrate from the old resolutions and make the square resolutions the standard over a number of years. The distortion transmitting from 196 ppi to 200 ppi is not perceptible to the naked eye. Herman Silbiger