scanned-books-crop-resize

This is a collection of bash/linux commands useful for editing a scanned book. You start with a scanned double-page-per-side pdf and you come up with a single-page, cropped and reduced in size pdf.

Required

In this procedure I assume that you are familiar with linux command line. If you don't, there are many tutorials out there. You may have to install the following tools:

poppler-utils imagemagick

Procedure

The procedure is the following. We extract images from pdf file, then we crop the right pages and the left pages, we convert images back to pdf files and we join them toghether. Note: to have a good result you must be very careful to scan the pages maintaining the book aligned in the same position, athought cropping may cut out part of text from some pages.

Create a directory to store extracted images

mkdir img

Extract pages from the pdf to image files

pdfimages input.pdf img/page

Now we must separate right pages from left pages so let's create two directories

mkdir right/img

mkdir left/img

We need to define the area to crop. We crop first the right side and then the left. To do so

Open one of the images in img/ with GIMP (or another image program), use rectangular selection tool to select the area you want to become the right page. Write down the position X0,Y0 and the size WIDTH,HEIGHT of the selection.

Now we can use imagemagick convert to crop right pages

for a in img/*.pbm; do convert -crop WIDTHxHEIGHT+X0+Y0 $a right/$a ; done

Remember to replace the values with the ones you wrote down.

We must now repeat the same (defining area and cropping) for the left pages

for a in img/*.pbm; do convert -crop WIDTHxHEIGHT+X0+Y0 $a left/$a ; done

To have pages ordered properly before we join right pages and left pages we rename the pages

rename s/.pbm/b.pbm/ right/img/*

rename s/.pbm/a.pbm/ left/img/*

Copy the right and the left pages in the same directory

mkdir pages; cp left/img/* pages/; cp right/img/* pages/;

convert all the images to pdf

for a in pages/*; do convert $a $a.pdf; done

and join them toghether

pdfunite pages/*.pdf output.pdf

Delete temporary files

Check if your final pdf is OK, then you can remove all the temporary directories created. rm -R right/ left/ img/ pages/

Quality settings

Now we have the final cropped pdf. That will probably a high quality, big file. We can adjust the size of our file:

gs -dNOPAUSE -dBATCH -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=setting -sOutputFile=output-final.pdf output.pdf

replacing "output-final.pdf" with the name you want and "setting" with a desired quality level. Quality level settings are /screen the lowest resolution and lowest file size, but fine for viewing on a screen; /ebook a mid-point in resolution and file size; /printer and /prepress high-quality settings used for printing PDFs.

Notes

Improvements to this procedure are welcome.