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 ).
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.
Thank you for your replies. I am cleaning up a font library for an agency manually correcting some problems and using font doctor so am looking for as much information as possible to make the font cleanup a good one.
There are plenty of Type 1 fonts they have, especially from one of my favorite studios Sudtipos. How do I load/utilize the AFM files on a mac? I thought the AFM infomration was in the bitmapped FFIL font for Type 1, so that the AFM were not needed, can you clarify in regards to type 1?
I am considering trashing the type 1 version when a .otf verison exists, so the font library does not have 2 versions. Opinions?
Font doctor is wanting to do some potentially bad things to some of the system fonts. EG: AdobeSanMM & Adobe Sans MM are seen as not a connected pair of printer and screen font, even though they are next to each other. Font Doctor asks to disable. I am saying no to be safe. I may possibly be able to say yes if they are loaded elsewhere, but have decided to leave the Acrobat required fonts untouched. Anyone else use Font Doctor and experience this and have advice?
Thanks Thomas. Will backup a copy of AFM files, incase they are ever needed for opentype versions(cross platform poweproint presentations, and stopping the zero K when putting type 1 on a pc server some to mind).
If anyone else has anything else to share when cleaning up font libraries, please chime in. Font doctor wants to remove AdobeSanMM even though Adobe Sans MM is right next to it. For now am saying no as I don't wnat Acorbat to stop working, but seems besides that font doctor is a very helpful product even better than my old friend FontDA mover.