Format of AFP character sets
The InfoPrint Font Collection supplies character sets in these formats:
- 240-pel raster
- 240-pel raster fonts are bounded-box fonts used on 240-pel printers. The resolution of these fonts is 240 dots per inch. All character positioning metrics in these fonts are expressed in whole-pel (fixed-metric) values.
- 300-pel raster
- 300-pel raster fonts are used on printers where the resolution is 300 dots per inch. The character positioning values are expressed in relative metrics and the exact pel count is determined at print time.
- Type 1 outline
- Type 1 outline is the format used with Type Transformer for General Library fonts. This format includes outlines of the various type families, which can be transformed for use by AFP printers in sizes from 1–999 points (AFP outline fonts) or from 1–72 points (raster fonts).
- CID-Keyed outline
- CID-Keyed outline is the format used with Type Transformer for CJK fonts. This format includes outlines of the various type families, which can be transformed for use by AFP printers in sizes from 1–999.9 points (AFP outline fonts) or from 1–72 points (raster fonts).
- AFP outline
- AFP outline is the format by which Print Services Facility (PSF) and other AFP applications can identify Type 1 outline fonts. The Type 1 or CID-Keyed outlines are encapsulated in FOCA wrappers that allow them to be accessed as AFP resources. AFP outlines utilize relative metrics in the same way as 300-pel fonts.
- Fixed metrics
- Fixed-metric fonts have all character positioning metrics expressed in whole-pel values. All 240-pel fonts are fixed-metric fonts. For example, the character increment of the ‘A' in 240-pel Helvetica Latin1 roman medium 10 pt is 22 pels. When 240-pel fonts are created, any fractional pels found are eliminated by rounding up or down to whole-pel values.
- Relative metrics
- Relative metrics were developed for scalable outline fonts where a single metric value could be used
to determine a pel value given a desired resolution and point size. Relative metrics
are based on 1000 units per
em space,which means the fonts are designed for a hypothetical 1000 dpi, 72-point font where each side of the bounding box is 1000 pels. All AFP outlines and 300-dpi fonts contain relative metrics. The exact pel values are determined when the font is used, such as during document formatting or printing. For example, the character increment for A in 300-pel Helvetica Latin1 roman medium is 667 relative units. In the hypothetical 1000 dpi, 72-point font, the A would have a character increment of 667 pels, but at 10 points and 300-dpi resolution, the character increment of the A is 27.8 pels. The fractional pel (.8 in this case) is accumulated by the printer and a whole white pel is inserted when the accumulator = 1. Constantly adjusting the character increments in this way makes sure that the output text is as close to the original outline specification as possible.