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             CHAPTER 5                                                                             Text



  5.5.4 Type 3 Fonts

             Type 3 fonts differ from the other fonts supported by PDF. A Type 3 font dictio-
             nary defines the font; font dictionaries for other fonts simply contain information
             about the font and refer to a separate font program for the actual glyph descrip-
             tions. In Type 3 fonts, glyphs are defined by streams of PDF graphics operators.
             These streams are associated with character names. A separate encoding entry
             maps character codes to the appropriate character names for the glyphs.

             Type 3 fonts are more flexible than Type 1 fonts because the glyph descriptions
             may contain arbitrary PDF graphics operators. However, Type 3 fonts have no
             hinting mechanism for improving output at small sizes or low resolutions. A Type
             3 font dictionary contains the entries listed in Table 5.9.

                                 TABLE 5.9 Entries in a Type 3 font dictionary
KEY               TYPE             VALUE

Type              name             (Required) The type of PDF object that this dictionary describes; must be
                                   Font for a font dictionary.

Subtype           name             (Required) The type of font; must be Type3 for a Type 3 font.

Name              name             (Required in PDF 1.0; optional otherwise) See Table 5.8 on page 413.

FontBBox          rectangle        (Required) A rectangle (see Section 3.8.4, “Rectangles”) expressed in the
                                   glyph coordinate system, specifying the font bounding box. This is the small-
                                   est rectangle enclosing the shape that would result if all of the glyphs of the
                                   font were placed with their origins coincident and then filled.
                                   If all four elements of the rectangle are zero, no assumptions are made based
                                   on the font bounding box. If any element is nonzero, it is essential that the
                                   font bounding box be accurate. If any glyph’s marks fall outside this bounding
                                   box, incorrect behavior may result.

FontMatrix        array            (Required) An array of six numbers specifying the font matrix, mapping
                                   glyph space to text space (see Section 5.1.3, “Glyph Positioning and
                                   Metrics”). A common practice is to define glyphs in terms of a 1000-unit
                                   glyph coordinate system, in which case the font matrix is
                                   [ 0.001 0 0 0.001 0 0 ].

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