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jbig2enc; JBIG2; PDF size optimization; compression; DML; digital signature; JB2; DjVu; pdfsign; DML-CZ; EuDML;; Google; JB2 algorithm
This paper describes several innovative PDF document enhancements and tools that can be used when building a digital library. The main result presented in this paper is the PDF re-compression tool, developed using the jbig2enc encoder called pdfJbIm. This re-compression tool enables the size of the original bitonal PDFs to be, on average, downsized by one third. Some modifications to the jbig2enc encoder that increase the compression ratio even further are also described here. Together with another program, the by Péter Szabó, we have managed to decrease PDF storage size to such an extent that the transmission needs of a digital library were significantly reduced. We report the storage saving results that we have achieved on The Czech Digital Mathematics Library DML-CZ—we have downsized the PDF corpus to 43% of its original size. We also describe pdfsign tool for batch digital signature stamping of PDF documents.
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