Alex Brollo, 13/05/2016 11:06:
Simply, from a practital point iof view, my suggestion is: don't try to get a good djvu from IA pdf, use instead _jp2.zip images (after conversion to jpg the images are very good), and the result will be much better - almost as good as images into IA viewer, that uses the same images.
In my experience, when there are problems, usually the JP2 images are either too little compressed or too compressed. This has precise reasons and no trivial solution: http://www.digitizationguidelines.gov/still-image/documents/JP2LossyCompress...
Nemo