Andrea Zanni, 12/05/2016 19:38:
[1] https://it.wikisource.org/wiki/File:Tarchetti_pdf.png [2] https://commons.wikimedia.org/w/index.php?title=File%3ATarchetti_-_Paolina.p... [3] https://it.wikisource.org/wiki/File:Tarchetti_pdf.png
That was meant to be https://it.wikisource.org/wiki/File:Tarchetti_alex_djvu.png
I don't think this has anything to do with DjVu or PDF, the problem is very clear just by looking at https://archive.org/download/digitami_LO10534041 : the JP2 conversion compressed the images 30 times, the PDF compression 5 more times.
The first step in such cases, as documented in https://en.wikisource.org/wiki/Help:DjVu_files#The_Internet_Archive , is to add/increase the fixed-ppi field. I don't understand what was used in https://catalogd.archive.org/log/487271468
Nemo