Ebook Conversion

A word before we start

When I bought an eBook-Reader last chrismas (2011), an PocketBook Pro 912 with an open sourced linux operating system and firmware and an e-Ink Display. By the way:

• this article is based on the prerequisites of a reader with an e-Ink display
• this article uses Linux (ubuntu 11.10) and a lot of bash shell scripting, so be prepared

You might be able to adjust some things for other devices, but this is mainly intended for working with devices with e-Ink displays, and mainly the ones of a 10 size!

I didn't know, how much work it will cost myself to dive deep into the theme. The e-Ink-technology was what kept my interest. What I didn't know: this technology also needs a special way of reading your documents. It is not possible to simply throw a PDF to your device being sacrificed.

Years ago, when a began dealing with LaTeX - my preferred text processing method - I already had been aware of the problem, that the information about the semantics of the given text, or the "metainformations" is low, if not exists at all any more. In technical term one would say, the entropy of a PDF-document is - compared to HTML, SGML, or XML, or even LaTeX - very low. This is, why PDF is only a media for printing but not a document format used by computer programs, thereby viewed on a screen or an e-reader.

Concrete:

• you cannot alter the font size
• a program cannot guess the text flow
• on a reader with e-ink display, it might be impossible to read the document, because the fonts are to small

That's why you might want to convert your documents.

How do you like to do this?

• unattended
• batch-like
• automatically
• repeatedly
• with open source software ;)

Let's have a look at the general workflow.

The process

Reading plain PDF

There are mainly 3 points of interest, when it comes to read an PDF on an e-Ink device:

1. Keep all metainformation - like the table of content - after conversion
2. Cut as much of unnecessary space (title, white borders, ...)
3. Batch processing

Cropping the pages is the solution

I had different approaches to cut the pages my PDFs, from the commercial acrobat writer, over imagemagick and other "crop"-tools. After all, and keeping the 3 points from above in mind the only tool I can recommend is [1].

Download and extract it somewhere. Written in java, and so that you can use it as any other program, you should write a little wrapper an put in in your path (e.g. ~/bin, /usr/local/bin, /usr/bin):

#!/bin/bash
version="0.0.13"
cd "$(pwd)"
java -jar /local/share/pdfr/briss-${version}/briss-${version}.jar "${@}"

This way prepared, I wrote a batch conversion program. The main problem when writing a conversion script is, that many ebook titles contain chars like "[" or "&". This is something the bash does not like at all! Speaking shortly: I know this script has a lot of duplicate code in it. But believe me when I say: I tried more than once to change this.

The script (assumed you name it crop_with_briss.sh) mainly does the following:

• General: all found PDF's are cropped and prefixed with "_cropped.pdf" (this is the default way briss works in batch mode "-s")
• crop_with_briss.s myPDF.pdf: The given PDF will be automatically cropped to myPDF_cropped.pdf
• crop_with_briss.s -l : Scan for all PDF-files in the local directory. Files which are formerly cropped (a file with the name *_cropped.pdf" exists, will not be cropped again!
• crop_with_briss.s -lf : Scan for all PDF-files in the local directory. All (!!!) PDF's are cropped again.
• crop_with_briss.s -r : Same as -l, but the script recurses into all (!) subdirectories.
• crop_with_briss.s -rf : Same as -lf, but the script recurses into all (!) subdirectories.

So, here we go:

#!/bin/bash
which briss > /dev/null || echo "Briss must be installed to run this script."
which briss > /dev/null || exit 0

[ "${1}" == "" ] && echo "Please specify -l (local path only) or -r (recursive) as parameter." && exit 1
MODE=""
FORCE="false"
[ "${1}" == "-r" ]  && MODE="recursive"
[ "${1}" == "-rf" ] && MODE="recursive"
[ "${1}" == "-rf" ] && FORCE="true"
[ "${1}" == "-l" ]  && MODE="local"
[ "${1}" == "-lf" ] && MODE="local"
[ "${1}" == "-lf" ] && FORCE="true"
file ${1} | grep -v grep | grep "PDF document" && MODE="single"

if [ "${MODE}" == "single" ]
then
	cd $(pwd)
	briss -s "${1}"
	exit 1

fi

	
if [ "${MODE}" == "recursive" ]
then

if [ "${FORCE}" == "true" ]
then	
# First scan the local dir, then recursive
find '.' -name "*.pdf" | grep -v "cropped" | awk '{print $0}' | sed -e 's/^\.\///g' | sed -e 's/\.pdf$//g' | sed -e 's/(/\\(/g' | sed -e 's/)/\\)/g' | sed -e "s/'/\\\'/g" | sed -e 's/\[/\\[/g' | sed -e 's/\]/\\]/g' | sed -e 's/\&/\\&/g' | sed -e 's/\ /\\ /g' | awk '{system("briss -s " $0 ".pdf");}'
exit 1

else
find '.' -name "*.pdf" | grep -v "cropped" | awk '{print $0}' | sed -e 's/^\.\///g' | sed -e 's/\.pdf$//g' | sed -e 's/(/\\(/g' | sed -e 's/)/\\)/g' | sed -e "s/'/\\\'/g" | sed -e 's/\[/\\[/g' | sed -e 's/\]/\\]/g' | sed -e 's/\&/\\&/g' | sed -e 's/\ /\\ /g' | awk '{system("\[ -f " $0 "_cropped.pdf \] \|\| briss -s " $0 ".pdf");}'
exit 1

fi

fi

if [ "${MODE}" == "local" ]
then

if [ "${FORCE}" == "true" ]
then
ls -b *.pdf | grep -v "cropped" | awk '{print $0}' | sed -e 's/\.pdf$//g' | sed -e 's/(/\\(/g' | sed -e 's/)/\\)/g' | sed -e "s/'/\\\'/g" | sed -e 's/\[/\\[/g' | sed -e 's/\]/\\]/g' | sed -e 's/\&/\\&/g' | sed -e 's/\ /\\ /g' | awk '{system("briss -s " $0 ".pdf");}'
exit 1

else
ls -b *.pdf | grep -v "cropped" | awk '{print $0}' | sed -e 's/\.pdf$//g' | sed -e 's/(/\\(/g' | sed -e 's/)/\\)/g' | sed -e "s/'/\\\'/g" | sed -e 's/\[/\\[/g' | sed -e 's/\]/\\]/g' | sed -e 's/\&/\\&/g' | sed -e 's/\ /\\ /g' | awk '{system("\[ -f " $0 "_cropped.pdf \] \|\| briss -s " $0 ".pdf");}'
exit 1

fi

fi

Contrast enhancement

Briss is doing a very good job cropping the documents. But e-Ink devices normally only can show 16 gray scale "colors". So it would be handy to convert a document to grayscale and thereby enhance the contrast ;)

The solutions:

1. convert the PDF with imagemagick ("convert" or "mogrify" are the correspondig comands)
2. use a reader software with the capability of enhance the gamma or contrast of the content

The problems:

1. imagemagick
   1. does not preserve the metacontent of our PDF (table of content)
   2. the document is not searchable any more, or a TTS is not working any more
   3. the document becomes significantly bigger
   4. the result on my Pocketbook 912 is not what I expected, when it comes to quality and contrast enhancement. The PDf's seam to be not that crispy, clear.

convert -density 600 -contrast -gamma 0.1 -colorspace GRAY input.pdf output.pdf

1. reader software
   1. I did not find any software, that satisfied me
   2. There is mainly one: a fork of fbreader, it's called fbreader-bw and you will find it, when you search the http://www.mobileread.com forum.

From LaTeX to PDF or HTML

My LaTeX-documents can easily be altered to produce appropriate output for an e-Ink device.

But generating a PDF will be only suitable for a certain e-Ink device (when it comes to the font size). By the way: there is no direct possibility to create a ebub or mobi document from LaTex (as far as I know at the moment).

So my preferred output format is HTML! There is nothing more to say about.

• The table of content is preserved
• No problems with font-sizing
• Easy conversion to other ebook formats (epub, mobi, ...)

I am using [2] to convert my LaTeX files. I have to admit, that I am working - exclusively (!) - with [3]. So everything here (elyxer, scripts) is only suitable, if you are working with lyx. You can alter the scripts for usage with plain latex, there should not be any problem.

The next script converts all lyx-files, either locally ( -l ) or recursively ( -r ):

#!/bin/bash
[ ! -f /usr/bin/elyxer.py ] && echo "Elyxer must be installed to run this script." && exit 0

[ "${1}" == "" ] && echo "Please specify -l (local path only) or -r (recursive) as parameter." && exit 1

if [ "${1}" == "-r" ]
then
	for myfile in "$(find '.' -name "*.lyx" | awk '{print $0}' | sed -e 's/ /\\ /g' | sed -e 's/.lyx//g')"
	do 
        	echo "${myfile}" | awk '{system("elyxer.py " $0 ".lyx > " $0 ".html");}'
	done
fi

if [ "${1}" == "-l" ]
then
	for myfile in "$(ls *.lyx | awk '{print $0}' | sed -e 's/ /\\ /g' | sed -e 's/.lyx//g')"
	do 
        	echo "${myfile}" | awk '{system("elyxer.py " $0 ".lyx > " $0 ".html");}'
	done
fi

The same script for producing PDF-files using pdflatex ( lyx --export pdf2 ). You can easily adopt this:

#!/bin/bash

[ "${1}" == "" ] && echo "Please specify -l (local path only) or -r (recursive) as parameter." && exit 1

if [ "${1}" == "-r" ]
then
	for myfile in "$(find '.' -name "*.lyx" | awk '{print $0}' | sed -e 's/ /\\ /g')"
	do 
        	echo "${myfile}" | awk '{system("lyx --export pdf2 -f " $0);}'
	done
fi

if [ "${1}" == "-l" ]
then
	for myfile in "$(ls *.lyx | awk '{print $0}' | sed -e 's/ /\\ /g')"
	do 
        	echo "${myfile}" | awk '{system("lyx --export pdf2 -f " $0);}'
	done
fi

From HTML to epub

One of the most sophisticated formats when it comes to eBooks is epub.

There are a lot of tools out there converting from e.g. HTML. But almost none is capable of keeping the "table of content". And this is - when it comes to ereading - one of the most important part.