PDF – How to Split Each PDF Page into Two Pages Using the Command Line

image manipulationpdf

I have a few ebooks scanned from originals. They're formatted so that a single PDF page contains two actual pages: one on the left, and one on the right.

I want to programmatically split each PDF page into two, so the left 50% of PDF page 1 becomes page 1 and its right becomes page 2, and so on for all the pages.

Does anyone know of a command line utility or script that could help with this?

Output from pdfimages -list -f 1 -l 1 file.pdf:

page   num  type   width height color comp bpc  enc interp  object ID x-ppi y-ppi size ratio
--------------------------------------------------------------------------------------------
   1     0 image    1921  1561  rgb     3   8  jpeg   no       643  0   200   200  200K 2.3%
   1     1 stencil     1     1  -       1   1  image  no   [inline]   0.692     2    -    - 
   1     2 stencil     1     1  -       1   1  image  no   [inline]   0.722 0.650    -    - 
   1     3 stencil     1     1  -       1   1  image  no   [inline]       3     3    -    -

Second PDF:

page   num  type   width height color comp bpc  enc interp  object ID x-ppi y-ppi size ratio
--------------------------------------------------------------------------------------------
   1     0 image     456   625  gray    1   8  jpx    yes      251  0    72    72 11.7K 4.2%

Best Answer

This should work it needs pdftk tool ( and ghostscript ).

A simple case:

Step One: Split into individual pages

 pdftk clpdf.pdf burst

this produces files pg_0001.pdf, pg_0002.pdf, ... pg_NNNN.pdf, one for each page. It also produces doc_data.txt which contains page dimensions.

Step Two: Create left and right half pages

  pw=`cat doc_data.txt  | grep PageMediaDimensions | head -1 | awk '{print $2}'`
  ph=`cat doc_data.txt  | grep PageMediaDimensions | head -1 | awk '{print $3}'`
  w2=$(( pw / 2 ))
  w2px=$(( w2*10 ))
  hpx=$((  ph*10 ))
  for f in  pg_[0-9]*.pdf ; do
   lf=left_$f
   rf=right_$f
   gs -o ${lf} -sDEVICE=pdfwrite -g${w2px}x${hpx} -c "<</PageOffset [0 0]>> setpagedevice" -f ${f}
   gs -o ${rf} -sDEVICE=pdfwrite -g${w2px}x${hpx} -c "<</PageOffset [-${w2} 0]>> setpagedevice" -f ${f}
  done

Step Three: Merge left and right in order to produce newfile.pdf containing single page .pdf. 

  ls -1 [lr]*_[0-9]*pdf | sort -n -k3 -t_ > fl
  pdftk `cat fl`  cat output newfile.pdf

A more general case:

  1. The example above assumes all pages are same size. The doc_data.txt file contains size for each split page. If the command

    grep PageMediaDimensions <doc_data.txt | sort | uniq | wc -l

    does not return 1 then the pages have different dimensions and some extra logic is needed in Step Two.

  2. If the split is not exactly 50:50 then a better formula than w2=$(( pw / 2 )), used in the example above, is needed.

This second example shows how to handle this more general case.

Step One: split with pdftk as before

Step Two: Now create three files that contain the width and height of each pages and a default for the fraction of the split the left page will use.

  grep PageMediaDimensions <doc_data.txt | awk '{print $2}'    >   pws.txt
  grep PageMediaDimensions <doc_data.txt | awk '{print $3}'    > phs.txt
  grep PageMediaDimensions <doc_data.txt | awk '{print "0.5"}' > lfrac.txt

the file lfrac.txt can be hand edited if information is available for where to split different pages.

Step Three: Now create left and right split pages, using the different pages sizes and (if edited) different fractional locations for the split. 

#!/bin/bash
exec 3<pws.txt
exec 4<phs.txt
exec 5<lfrac.txt

for f in  pg_[0-9]*.pdf ; do
 read <&3 pwloc
 read <&4 phloc
 read <&5 lfr
 wl=`echo "($lfr)"'*'"$pwloc" | bc -l`;wl=`printf "%0.f" $wl`
 wr=$(( pwloc - wl ))
 lf=left_$f
 rf=right_$f
 hpx=$((  phloc*10 ))
 w2px=$(( wl*10 ))
 gs -o ${lf} -sDEVICE=pdfwrite -g${w2px}x${hpx} -c "<</PageOffset [0 0]>> setpagedevice" -f ${f}
 w2px=$(( wr*10 ))
 gs -o ${rf} -sDEVICE=pdfwrite -g${w2px}x${hpx} -c "<</PageOffset [-${wl} 0]>> setpagedevice" -f ${f}
done

Step Four: This is the same merge step as in the previous, simpler, example. 

  ls -1 [lr]*_[0-9]*pdf | sort -n -k3 -t_ > fl
  pdftk `cat fl`  cat output newfile.pdf
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