pdfsandwich generates "sandwich" OCR pdf files, i.e. pdf files which contain only images (but no editable text) will be processed by optical character recognition (OCR) and the text will be added to each page invisibly "behind" the images.
pdfsandwich is a command line tool which is supposed to be useful to OCR scanned books or journals. It is able to recognize the page layout even for multicolumn text.
Essentially, pdfsandwich is a wrapper script which calls the following binaries: convert, unpaper, tesseract, gs, and hocr2pdf (if tesseract < 3.03). It is known to run on Unix systems and has been tested on Linux and MacOS X. It supports parallel processing on multiprocessor systems.
In contrast to most competing sandwich programs, it performs preprocessing of the scanned images, such as de-skewing or removal of dark edges etc.
For further information please read the manual: http://www.tobias-elze.de/pdfsandwich/index.html
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