Bitmap Fonts

Through the years many bitmap font formats fit with today’s standard of font technology. There are so many, probably no one could know all of them. Let us concentrate on the most common ones.

The probably most common and general bitmap font format is BDF (Bitmap Distribution Format) which Adobe updated in the early 90ies. It consists of human-readable ASCII text, with bitmaps embedded in hex codes. Besides information on the bitmaps, BDF contains all kinds of general information for fonts, e. g. names, metrics and encoding. The size of the bitmap is unlimited, as well as the number of glyphs and their resolution. The encoding of a BDF font can be anything from named glyphs, to Unicode™ indexed glyphs. BDF also supports custom color tables.

Hewlett Packard LaserJet printers need a HP soft font. A soft font is a bitmapped font in black and white only. The maximum size of a glyph bitmap is 256 X 256 pixels. A soft font can contain up to 256 characters, which are not structured by name or Unicode index. It can be downloaded to your printer and used just like any other printer font. Their resolution matches the resolution of the HP LaserJet printer. First it was 300 dpi (dots per inch) and later when the resolution became higher it was 600 dpi. Typically on the Windows platform a soft font is generated by the HP printer driver. The driver converts the desired font and downloads it to the printer. Nevertheless it is possible to create soft fonts with a bitmap font editor program and then download it to the printer.

The bitmap font format used by Microsoft since Windows 3.1 is quite similar to the HP soft font format. It has the extension ‘fon’, is a binary format and supports only black & white bitmaps. Microsoft internally understands fon-files as dynamic link libraries which a developer can link to from a running program. See the meaning of this format for a Windows developer here.
‘fon’-files can not contain two glyphs with the same code. This means no two or more characters can be mapped to one position in an encoding. Glyphnames and Unicode indexes can be written into the file. A maximum of 256 Glyphs may have a size up to 256 X 256 pixels.
On Palm OS (the operating system of Palm PDA’s) the Palm OS font format is used. It has the extension pdb, but this is rather a general format in PalmOS than a specific bitmap font format. Only Black & White glyphs can be stored. No glyph names or Unicode indexes can be added and 256 characters is the minimum capacity of one font.

The last format to look at is the photofont format. As already mentioned they are human readable xml files that contain information on font names, metrics and encoding. The image format which is used to save the glyphs in Photofonts is PNG (Portable Netword Graphics) which like GIF is much smaller than bitmaps. Photofont format supports true color mode (32-bit) and does not drop below that color resolution level. They have the file extension .phf and are not supported by any system. Until now Photofonts are only usable in InternetExplorer and Adobe Photoshop – both applications require a special plug-in.
Photofonts can also contain any coding, glyph name scheme or Unicode index. The .phf format is the latest format in this list and it improves the features of all other bitmap font formats. In means of generalisation it overhauls even the BDF format.

Here is a table showing the features of the specific formats:

Colors

Glyphs
BMP Size

Encoding

BDF
B & W to true color & custom color table
unlimited
unlimited
Names, Codes, Unicode index or nothing
HP Soft Font
Black & White
256
256 x 256

Codes
(not negative or duplicated)
Win.FON
Black & White

256
256 x 256
Names, Unicode index
(both not necessary), codes (not negative or duplicated)
Palm OS
Black & White
256
256 x 256
Codes
(not negative or duplicated)
PhotoFont
B & W to true color
(can only be saved in true color mode)
unlimited
unlimited
Names, Codes, Unicode index or nothing

more ... Many Formats, many Tools