Split PDF into colour and black/white pages

Here's a variant of un2up, which uses Python with the pyPdf library. Note that you need at least version 1.13 (prior versions did not support scaling). Untested.

#!/usr/bin/env python
import copy, math, sys
from pyPdf import PdfFileWriter, PdfFileReader
input = PdfFileReader(sys.stdin)
output = PdfFileWriter()
for p in [input.getPage(i) for i in range(0,input.getNumPages())]:
    p.scaleBy(math.sqrt(2))
    q = copy.copy(p)
    (w, h) = p.mediaBox.upperRight
    p.mediaBox.upperRight = (w/2, h)
    q.mediaBox.upperLeft = (w/2, h)
    output.addPage(p)
    output.addPage(q)
output.write(sys.stdout)

pdftk is able to cut out a fixed set of pages efficiently. With a bit of scripting glue, this does what I want:

number=$(pdfinfo -- "$file" 2> /dev/null | awk '$1 == "Pages:" {print $2}')
count=$((number / pagesper))
filename=${file%.pdf}

counter=0
while [ "$count" -gt "$counter" ]; do 
  start=$((counter*pagesper + 1));
  end=$((start + pagesper - 1));

  counterstring=$(printf %04d "$counter")
  pdftk "$file" cat "${start}-${end}" output "${filename}_${counterstring}.pdf"

  counter=$((counter + 1))
done

This assumes that you have the number of pages per chunk in $pagesper and the filename of the source PDF in $file.

If you have acroread installed, you can also use

acroread -size a4 -start "$start" -end "$end" -pairs "$file" "${filename}_${counterstring}.ps"

acroread offers the option -toPostScript which may be useful.