TIFF faxes with non-square pixels look weird

Question

Level 1

1 points

TIFF faxes with non-square pixels look weird

Hi,
first of all I don't know if this is the right section.
I'm using a free FAX service who sends to my e-mail address all the faxes I receive.
However, they look weird (in 10.6 Preview.app or Xee.app and Photoshop, but not in 10.5 or Windows 7) because the vertical and horizontal dpi resolutions are different.
i.e:
1728x1135
v dpi 98dpi
h dpi 204dpi

How can I resize either the vertical or horizontal dpi resolution, so that the pixels will have a square aspect ratio, and the faxes will finally look the way they should be?
Any way to do that via Automator or Applescript, so that I can fix the glitch in one-click solution?

thanks

Ibook 12'' 1.33ghz (10.4) and MBP 15'' 2.2ghz (10.5), Mac OS X (10.4.11)

Posted on Oct 26, 2010 10:29 AM

Reply

Answer 1

greg sahli

Level 7

25,508 points

Oct 26, 2010 2:03 PM in response to flapane

I guess a good free solution would be ImageMagick:
http://www.imagemagick.org/script/binary-releases.php?ImageMagick=hpqqb4rulbe80p n35rj6145na7#macosx
It is a commandline tool with lots of options & switches. Once you figure out the correct command, it will be very easy to do all the files at once.
Or maybe you already have Graphic Converter:
http://mac.softpedia.com/get/Graphics/Graphic-Converter-X.shtml

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Answer 2

flapane Author

Level 1

1 points

Oct 26, 2010 2:07 PM in response to greg sahli

Hi there,
it would be a great idea, as one could embed the imagemagick cli inside Automator.
I'll try in the next days.
Thanks

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Answer 3

PAHU

Level 6

16,711 points

Oct 26, 2010 3:25 PM in response to flapane

The resolutions you are quoting are correct for fax communication.

A typical fax machine has a default (Standard) horizontal resolution of 8 pels/mm, which is roughly 204 pels per inch (or 204dpi). Some faxes are also capable of increasing the horizontal res to 16 pels/mm - roughly 400dpi.

The vertical resolution is measured in lines per mm and there are three supported resolutions;

Standard @ 3.85 l/mm - which is approx 98dpi
Fine @ 7.7 l/mm - which is approx 196dpi
Super Fine @ 15.4 l/mm - which is approx 391dpi

So I suggest you don't look at changing the resolutions of the received fax but at the way your apps are displaying them. You mention 10.5 and Win 7 showing them correctly. For your info, we have our MFD forwarding received faxes to a folder on 10.6 Server and the TIFF looks fine in Preview on 10.6. So I don't know what you look at but I did just want to inform you that the resolutions of the received fax were correct.

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Answer 4

flapane Author

Level 1

1 points

Oct 27, 2010 3:23 AM in response to PAHU

Hi,
thanks for your reply, but honestly I don't know where to look.
The fact that Photoshop displays it "stretched" is consistent with the preview shown in Preview.app (which afaik doesn't have a setting to ignore the aspect ratio of the pixels), because the pixels don't have a square form (vert dpi res is different from the horiz dpi res), so maybe it's just that 10.5 and Win7 are ignoring the vertical dpi and horizontal dpi resolutions.
It's curious to see that your 10.6 Server shows the faxes correctly, by the way.

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Answer 5

flapane Author

Level 1

1 points

Oct 27, 2010 4:20 AM in response to flapane

In the meanwhile, I solved in this way:
imagemagick -> convert foo.tif foo.pdf
Pdf metadata loose the dpi values, so the pixels have a square shape.

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