PDFlib Text Extraction Toolkit (TET) Manual

7.2 Unicode Preprocessing (Filtering)
TET applies several filters to remove text which is unlikely to be useful. These filters
modify the text before applying any Unicode postprocessing steps. While some filters
are always active, others require the Wordfinder and are therefore active only for
granularity=word or above.
7.2.1 Filters for all Granularities
The following filters can be used with all granularities.
Text in unwieldy font sizes. Very small or very large text can optionally be ignored, e.g.
large characters in the background of the page. The limits can be controlled with the
fontsizerange page option. By default, text in all font sizes will be extracted.
The following page option limits the range of font sizes for extracted text from 10 to
50 points; text in other font sizes will be ignored:
fontsizerange={10 50}
Invisible text. Invisible text (i.e. text with textrendering=3) is extracted by default. Note
that text in PDF may be invisible for various other reasons than the textrendering property,
e.g. the text color is identical to the background color, the text may be obscured by
other objects on the page, etc. The behavior described here relates only to text with
textrendering=3. This PDF technique is commonly used for the results of OCR where the
text sits invisibly »behind« the scanned raster image.
Invisible text can be identified with the textrendering member of the TET_char_info
structure returned by TET_get_char_info( ) (see Table 10.15, page 179), or with the Glyph/
@textrendering attribute in TETML.
Use the following page option if you want to ignore invisible text:
ignoreinvisibletext=true
Completely ignore text with certain font names or font types. In some situations it
may be useful to completely ignore text in one ore more fonts specified by name, e.g. a
symbolic font which does not contribute any meaningful text. As an alternative, the
problematic fonts can also be specified by font type. This is mainly useful for Type 3
fonts which are sometimes used for ornaments. This filter can be controlled via the
remove suboption of the glyphmapping document option.
E.g. ignore all text in Type 3 fonts:
glyphmapping={{fonttype={Type3} remove}}
Ignore all text in the Webdings, Wingdings, Wingdings 2, and Wingdings 3 fonts:
glyphmapping={{fontname=Webdings remove} {fontname=Wingdings* remove}}
The conditions for font name and font type can also be combined, e.g. ignore text in all
Type 3 fonts starting with the letter A:
glyphmapping={{fonttype={Type3} fontname=A* remove}}
94 Chapter 7: Advanced Unicode Handling