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Two C, or not two C – that is the question

Gareth Williams

EN_W8_Comp_Blu286_1_rgbIf you are using Zetafax with Windows 8.1, you will be pleased to know that Microsoft has now released a fix for a printing issue which was introduced in that update.

The fix is being rolled out automatically, so you don’t really need to know much more than that.  However I thought I’d take the opportunity to explain the background, for anyone who is interested in understanding a bit more about the fax world.

The worldwide standard for fax is called T.30., and this includes several different resolutions for sending faxes.  Resolutions are usually given in “dots per inch” (or dpi), and the most common two fax resolutions are often described as “200 x 200 dpi” (for fine resolution) and “200 x 100 dpi” (for normal/standard resolution).  However that’s just an approximation, and in reality it’s rather more complicated!

The fax standard specifies the resolution in metric units (pels or lines per millimeter).  The horizontal resolution is really 8 pels/mm, which equates to 203.2 dpi.

Unfortunately, the T.30 committee decided that they would make the vertical resolution a little bit different to the horizontal resolution, just to keep people on their toes.  Nobody seems to know exactly why, though physical factors in the fax hardware played a part.  However the end result was that they set the vertical resolution as 7.7 pels/mm for fine resolution, and 3.85 pels/mm for standard.

So, fine resolution is really 203.2 x 195.58 dpi, or 204 x 196 dpi if we round up.  You can see why we usually refer to it as 200 x 200 dpi instead!

This means that the “dots” on a fax image aren’t quite square.  When the fax standard was agreed that was quite common, and many dot-matrix printers had non-square pixels.  However nowadays it is pretty unusual – most modern printers have square pixels, which is why you usually just see a single figure when referring to a printer resolution (eg 300 dpi).

Windows 8.1 includes quite a few changes to the core printing components.  Unfortunately these weren’t fully tested on printers with non-square pixels, including fax printers like the Zetafax Printer.  The result was that when you used one of these printers the image was squashed by Windows to 25% of the correct size.

We found a way of working around the issue, using advanced settings in the Zetafax Printer to tell Windows that it had square pixels (true 200 x 200 dpi resolution).  This wasn’t ideal as it required a manual configuration step and changed the page size slightly, but allowed Windows 8.1 users to continue sending faxes.

We reported the issue to the nice people at Microsoft, who confirmed the fault and said they would give it top priority.  I’m pleased to say that they’ve done exactly what they promised.  The fix has been published (in record time!), and has been included in the Windows 8.1 January rollup release via the Windows Update Service.  Pretty soon you won’t know the problem ever existed.

If you have Windows 8.1 computers in your company and have already made the settings change for the Zetafax Printer then you don’t need to do anything more.  This will still work after installing the Microsoft fix without any change.

If you haven’t upgraded to Windows 8.1 yet, then you shouldn’t have to do anything either.  Provided you have installed Zetafax 2014 (or the Zetafax 2012 Windows Client Update Pack), and updated Windows 8.1 with the January rollup, then everything will work fine.

If you want more details about the Windows fix please see our technote, or contact your local Zetafax support team.  You can find out more about Zetafax 2014, which includes full support for Windows 8.1, on our website.

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