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Font File Organization and Subsetting

Each Type 1 font file is a special Postscript program defining three Postscript-dictionaries:

The main principle in subsetting is to decrypt the font and reorganize it, leaving out charstrings that are not required in the current context. For example, if a document uses only the character 'A' from the font Garamond, then this font may be subsetted preserving the character outline for 'A' only. The resulting file, which will be much smaller than the original file, can then be included verbatim into the Postscript file containing the document. At the same time, optionally, the encoding vector could be redefined to contain only the entry for 'A' at the appropriate location and .notdef otherwise.

A still more consequent subsetting would involve leaving out those subroutines from the Private-dictionary that are not needed by the preserved charstrings. Leaving out some subroutines on the other hand would require to interprete and check all charstrings for the subroutines they require and all preserved charstrings would have to be adapted to the reorganized index. Since the subroutines usually do not consume that much memory this is not considered worth the effort.


next up previous contents index
Next: Functions for Subsetting Up: Font Subsetting Previous: Font Subsetting   Contents   Index
2004-10-04