How does TrueDoc achieve such a high level of compression?
TrueDoc achieves its high level of compression through a combination of tactics. First, TrueDoc usually records only the character shapes in the document. If there is no ‘q’ in the original document, there will be no ‘q’ in the PFR. This is called character subsetting. Also as part of its subsetting tactic, TrueDoc uses sophisticated character recognition to break compound characters (accented characters, fractions, etc.) down into their component parts. (If the characters ó, ô, ö, and õ are in a document, TrueDoc saves the ‘o’ once, and each accent separately.) Second, TrueDoc uses an extremely advanced hinting process to ensure the high quality rendering of characters at low resolutions (below 600 dpi). Hints can take up a lot of room in fonts. Bitstream has developed an extremely compact hinting technology to keep TrueDoc PFRs as small as possible.
