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AFM Files & Kerning

Mar 19, 2012 9:05 AM

I am on a mac snow leopard working mostly in Illustrator. Others apps InDesign, After Effects, Premiere. Can someone please explain AFM files, how and  when to use them?

 

Please correct or confirm, but my understanding is that AFM information is in the bitmapepd files of older formats, and within opentype, so there really is no need for .AFM files on the mac.

 

If the kerning information is in the font already, then why do you always have to kern ones and periods in most fonts. Optical seems to do a better job than auto, but I often later have to tighten the tracking. Is auto using the AFM infomration in the font, and optical is using the Illustrator engine to calculate new kern pairs.

 
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    Mar 19, 2012 10:36 AM   in reply to Mike Gondek

    AFM (Adobe Font Metric) files contained detailed metrics associated with legacy Type 1 fonts including not only advance widths, but also information such as pair kerning information that would/should be used for layout programs. On the MacOS, most of the AFM information was also included in the bitmap format files that accompanied the actual font outline file. Since the days of Adobe Type Manager and then the built-in Type 1 font renderer in MacOS, the only reason for the bitmap format files was for this font metric information and in fact, you only needed one such bitmap font file per outline file. For Windows, much of AFM information is stored with the .PFM (PostScript Font Metrics) file that accompanies and is installed with the .PFB (PostScript Font Binary) file containing the actual font outlines and some minimal metrics.

     

    TrueType, TrueType OpenType, and OpenType CFF fonts have all font metrics included in the .TTF or .OTF files themselves and as such, do not require any secondary font metrics information.

     

    Whether you kern using the metrics or automatic/optical option, really depends on your tastes and the font itself. The optical option algorithmically creates pair kerning based upon the actaul fit of two glyphs with each other. The techniques are rather sophisticated, but work amazingly well (except when they don't ).

     

              - Dov

     
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    Mar 19, 2012 10:44 AM   in reply to Mike Gondek

    You are correct. Kerning is inside the suitcase for older Mac formats (Mac-version TrueType, and Mac-version PostScript Type 1), and is part of the main file in all the current formats (OpenType and TrueType, OTF/TTF extensions). AFMs are normally seen in conjunction with PostScript fonts.

     

    The only reason I can think of to keep around an .AFM file for a Mac user is if all the following are true:

    - you have an old Mac PostScript Type 1 font

    - there is kerning in the AFM that involves glyphs not encoded in the font which therefore can't be maintained in the suitcase kerning either (requires the font actually have those glyphs, as well as have kerning for them, a rare combination)

    - you might be converting the font to OpenType CFF yourself (which may or may not be allowed by your end-user license agreement), and you want to keep that kerning/

     

    I think that's a pretty isolated corner case. I'm enough of a pack rat that I might keep the kerning, but I can't really recommend it to other people. 

     

    T

     
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    Mar 19, 2012 11:32 AM   in reply to Mike Gondek

    You are correct. They are not needed on Mac OS. The only scenario in which they might be useful is in that font format conversion situation I mentioned above.

     
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    Mar 19, 2012 11:50 AM   in reply to Thomas Phinney

    Confirming Thomas' response as correct!

     

    Note that AdobeSansMM and similar fonts are required substitution fonts used by some Adobe applications. Don't mess with them.

     

              - Dov

     
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    Mar 27, 2012 12:31 AM   in reply to Mike Gondek

    The only factor I would mention, if I may, is that FontAgent PRO (FAP) catches some bad or problem fonts that Font Doctor and FontBook some times miss.  There is a fully functioning demo version of FAP that s good for 30 days.

     

    Just my two cents.

     
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