PDFlib Text Extraction Toolkit (TET) Manual

Fig. 6.6
The font report for a logotype font shows that the font contains wrong Unicode mappings.
A custom code list can correct such mappings.
By convention, code lists use the file name suffix .cl. Code lists can be configured with
the codelist resource. If no code list resource has been specified explicitly, TET will search
for a file named .gl (where is the resource name) in the searchpath
hierarchy (see Section 5.2, »Resource Configuration and File Searching«, page 51 for
details). In other words: if the resource name and the file name (without the .cl suffix)
are identical you don’t have to configure the resource since TET will implicitly do the
equivalent of the following call (where name is an arbitrary resource name):
TET_set_option(tet, "codelist {name name.cl}");
The following sample demonstrates the use of code lists. Consider the mismapped logotype
glyphs in Figure 6.6 where a single glyph of the font actually represents multiple
characters, and all characters together create the company logotype. However, the
glyphs are wrongly mapped to the characters a, b, c, d, and e. In order to fix this you
could create the following code list:
% Unicode mappings for codes in the GlobeLogosOne font
x61 x0054 x0068 x0065 x0020 % The
x62 x0042 x006F % Bo
x63 x0073 x0074 x006F x006E x0020 % ston
x64 x0047 x006C x006F % Glo
x65 x0062 x0065 % be
Then supply the codelist with the following option to TET_open_document( ) (assuming
the code list is available in a file called GlobeLogosOne.cl and can be found via the search
path):
glyphmapping {{fontname=GlobeLogosOne codelist=GlobeLogosOne}}
ToUnicode CMap resources for all font types. PDF supports a data structure called
ToUnicode CMap which can be used to provide Unicode values for the glyphs of a font.
If this data structure is present in a PDF file TET will use it. Alternatively, a ToUnicode
CMap can be supplied in an external file. This is useful when a ToUnicode CMap in the
PDF is incomplete, contains wrong entries, or is missing. A ToUnicode CMap will take
precedence over a code list. However, code lists use an easier format the ToUnicode
CMaps so they are the preferred format.
By convention, CMaps don’t use any file name suffix. ToUnicode CMaps can be configured
with the cmap resource (see Section 5.2, »Resource Configuration and File
Searching«, page 51). The contents of a cmap resource must adhere to the standard CMap
syntax. 1 In order to apply a ToUnicode CMap to all fonts in the Warnock family use the
following option to TET_open_document( ):
1. See partners.adobe.com/public/developer/en/acrobat/5411.ToUnicode.pdf
78 Chapter 6: Text Extraction