Hello Tim, Peter, Thank you for your replies.
It seems indeed that the only solution is to include Tesseract in my processing pipeline. I don’t know if it might be useful to future readers, but I noticed that *all* pdf created with PDF24 are subject to this behavior. I guess this might fall into the “obfuscation” approach some software adopt :-( Cheers, Giovanni On 2 Apr 2019, 04:48 +0200, Peter Murray-Rust <[email protected]>, wrote: > I agree with Tim's analysis. > > Many "legacy" fonts (including unfortunately some of those used by LaTeX) > are not mapped onto Unicode. There are two indications (codepoints and > names which can often be used to create a partial mapping. I spent a *lot* > of time doing this manually. For example > > > > > WARN No Unicode mapping for .notdef (89) in font null > > WARN No Unicode mapping for 90 (90) in font null > <<< > The first field is the name , the second the codepoint. In your example the > font (probably) uses codepoints consistently within that particular font, > e.g. 89 is consistently the same character and different from 90. The names > *may* differentiate characters. Here is my (handedited) entry for CMSY > (used by LaTeX for symbols): > > <codePoint unicode="U+00B1" name=".notdef" note="PLUS-MINUS SIGN"/> > > But this will only work for this particularly font. > > If you are only dealing with anglophone alphanumeric from a single > source/font you can probably work out a table. You are welcome to use mine > (mainly from scientific / technical publishing) Beyond that OCR/Tesseract > may help. (I use it a lot). However maths and non-ISO-LATIN is problematic. > For example distinguishing between the many types of dash/minus/underline > depend on having a system trained on these. Relative heights and size are a > major problem > > In general, typesetters and their software are only concerned with the > visual display and frequently use illiteracies (e.g. "=" + backspace + "/" > for "not-equals". Anyone having work typeset in PDF should insist that a > Unicode font is used. Better still avoid PDF. > > > > -- > Peter Murray-Rust > Reader Emeritus in Molecular Informatics > Unilever Centre, Dept. Of Chemistry > University of Cambridge > CB2 1EW, UK > +44-1223-763069
