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3.2 Creating fonts

The previous section described pictorially the usual order in which these programs are used. This section will do the same in words.

Naturally, you may not need to go through all the steps described here. For example, if you are not starting with a scanned image, but already have a bitmap font, then the first step--running Imageto--is irrelevant.

Here is a description of the usual font creation process, starting with a scanned image of a type specimen and ending with fonts which can be used by Ghostscript, TeX, etc.

  1. To see what an image I consists of, run Imageto with the `-strips' option. This produces a bitmap font `Isp' in which each character is simply a constant number of scanlines from the image.

  2. Run Fontconvert (see section 8. Fontconvert) on `Isp' with the `-tfm' option, to produce a TFM file. This is because of the next step:

  3. Run TeX on `imageto/strips.tex', telling TeX to use the font `Isp'. This produces a DVI file which you can print or preview as you usually do with TeX documents. (If you don't know how to do this, you'll have to ask someone knowledgeable at your site, or otherwise investigate.) This will (finally) show you what is in the image.

    An alternative to the above steps is to run Imageto with the `-epsf' option. This outputs an Encapsulated PostScript file with the image given as a simple PostScript bitmap. Then you can use Ghostscript or some other PostScript interpreter to look at the EPS file. This method is simpler, but has the disadvantage of using much more disk space, and needing a PostScript interpreter.

  4. If the original was not scanned in the normal orientation, the image must be rotated 90 degrees in some direction and/or flipped end for end. (Sometimes we have not scanned in the normal orientation because the physical construction of the book we were scanning made it difficult or impossible.) In this case, you must rotate the image to be upright. The program IMGrotate does this, given the `-flip' or `rotate-clockwise' option. Given an image RI, this outputs the upright image I.

  5. Once you have an upright image I, you can use Imageto (see section 6. Imageto) to extract the characters from the image and make a bitmap font `I.dpigf', where dpi is the resolution of the image in pixels per inch. (If the image itself does not contain the resolution, you must specify it on the command line with `-dpi'.) To do this, you must first prepare an IFI file describing the image. See section 6.2 IFI files, for a description of IFI files.

  6. To view the resulting GF file, run Fontconvert to make a TFM file, as above. Then run TeX on `testfont.tex' and use the \table or \sample commands to produce a font table. Next, print or preview the DVI file that TeX outputs, as before. This will probably reveal problems in your IFI file, e.g., that not all the characters are present, or that they are not in the right positions. So you need to iterate until the image is correctly processed.

    `testfont.tex' should have come with your TeX distribution. If for some reason you do not have it, you can use the one distributed in the `data' directory.

  7. Once all the characters have been properly extracted from the image, you have a bitmap font. Unlike the above, the following steps all interact with each other, in the sense that fixing problems found at one stage may imply changes in an earlier stage. As a result, you must expect to iterate them several (billion) times.

    At any rate, given a bitmap font f you then run Charspace (see section 9. Charspace) to add side bearings to f, producing a new bitmap font, say g, and a corresponding TFM file `g.tfm'. To do this, you must prepare a CMI file specifying the side bearings. See section 9.2 CMI files, for a description of CMI files.

  8. To fit outlines to the characters in a bitmap font, run Limn (see section 10. Limn). Given the bitmap font g, it produces the BZR (see section 11.6 BZR files) outline font `g.bzr'. The side bearings in g are carried along.

    Although Limn will (should) always be able to fit some sort of outline to the bitmaps, you can get the best results only by fiddling with the (unfortunately numerous) parameters. See section 10.2 Invoking Limn.

  9. To convert from the BZR file `g.bzr' that Limn outputs to a font format that a typesetting program can use, run BZRto (see section 11. BZRto). While developing a font, we typically convert it to a Metafont program (with the `-metafont' option).

    As you get closer to a finished font, you may want to prepare a CCC file (see section 11.4 CCC files) to tell BZRto how construct composite characters (pre-accented `A's, for example) to complete the font.

  10. Given the font in Metafont form, you can then either make the font at its true size for some device, or make an enlarged version to examine the characters closely. See section 11.1 Metafont and BZRto, for the full details.

    Briefly, to do the former, run Metafont with a mode of whatever device you wish (the mode localfont will get you the most common local device, if Metafont has been installed properly). Then you can use `testfont.tex' to get a font sample, as described above.

    To do the latter, run Metafont with no assignment to mode. This should get you proof mode. You can then use GFtoDVI to get a DVI file with one character per page, showing you the control points Limn chose for the outlines.

  11. Problems can arise at any stage. For example, the character spacing might look wrong; in that case, you should fix the CMI files and rerun Charspace (and all subsequent programs, naturally). Or the outlines might not match the bitmaps very well; then you can change the parameters to Limn, or use XBfe (see section 13. XBfe) to hand-edit the bitmaps so Limn will do a better job. (To eliminate some of tedium of fixing digitization problems in the scanned image, you might want to use the filtering options in Fontconvert before hand-editing; see 8.1.3 Character manipulation options.)

    Inevitably, as one problem gets fixed you notice new ones ...

3.2.1 Font creation example  A real-life example.

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