gistfile1.txt

# convert multipage pdf to single page tiff
gs -q -dNOPAUSE -dBATCH -sDEVICE=tiffg4 -sOutputFile=%04d.tif source.pdf -c qui
# or use -sDEVICE=pgmraw to convert to pgm 

# unpaper, rotate the logical page 90 degrees, each logical page contained two scanned physical pages, so we use --layout double (for input) and --output-pages 2 since we want to split these two pages.

unpaper -v --deskew-scan-deviation 3.0 --border-align top --deskew-scan-range 15 --no-grayfilter --no-blurfilter --no-noisefilter --overwrite --pre-rotate 90 --border-scan-step 4 --layout double --output-pages 2 %04d.pgm.pbm unpaper%04d.pbm

# trim the pages and convert the to single-page pdfs
find . -name 'unpaper*' | xargs -i -n1 -P6 convert -trim +repage {} {}.pdf

# finally reassemble the pdf with ghostcript
gs -sDEVICE=pdfwrite -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf *.pdf

# (optional) convert pqm to pbm
find . -name '*.pgm' | xargs -i -n1 sh -c "pgmtopbm {} > {}.pbm"