Ebook Conversion

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Revision as of 16:19, 4 January 2012 by Apos (talk | contribs) (→‎From PDF to epub, or reflow)

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.

Test it

If you like to test you should have the following documents on your side:

  1. Best a LaTeX or LyX document in a separate directory with
    • titlepage
    • table of content
    • footnotes
    • pictures and all that other fancy stuff ;)
  2. Convert this document to HTML, RTF, PDF
  3. Test all the conversion programs
  4. Test your reader software, if it can show
    • titlepage
    • table of content
    • footnotes
    • pictures and all that other fancy stuff ;)

If you like, you can use this Lyx-file: File:Lyx whysiwym editor.zip. Be aware you need Lyx for this file to run.

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 most sophisticated 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 briss.

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 corresponding commands)
  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.
  2. reader software
    1. I did not find any software, that satisfied me
    2. There is mainly one that can handle PDFs: a fork of fbreader, it's called fbreader-bw and you will find it, when you search the http://www.mobileread.com forum.
    3. Just for note: coolreader can not (!) display PDF files.

Do it with Imagemagick: 

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

A word on djvu an rescanning of PDF

DJVU is a very good format for keeping your scanned documents. It is NOT a good format for reading text on an e-Ink device. It has the same disadvantages as PDF.

There are a lot of converters out there. Mainly

  • pdf2djvu (contained in any linux distribution)
  • djvudigital, which uses ghostscript. Because there are licence issues, you have to compile it by yourself, which isn't very much fun.

If you are interested, please read the corresponding webpage or the onlinemanuals ;)

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, ...)

Elyxer

I am using elyxer to convert my LaTeX files. I have to admit, that I am working - exclusively (!) - with LyX. 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 PDF to epub, reflow and rescanning of PDF

Generally: no good idea, but possible. Why? The reason is simple: PDF has almost no met information about the document structure any more. So all tools more or less have to guess - of course a very clever guess - about the document structure, what is a heading, what is text, which kind of heading do we have, 2 or more column pages. What should I say: I leave it and read my PDf-Files - if they are too big for my screen - in landscape format. Any 10 device is capable to turn the pages 90° to the left or right so you can read the pages.

It doesn't matter, how you generate your epub out of an PDF or use a reflow software - either standalone or integrated in your reader: the more complex your PDF document is, the more disappointing the result will be. So better don't waste your time. There might be a time when these converters are that smart, that they can produce acceptable results out of complex documents, but my approach would be, to buy an appropriate format (like HTML or EPUB) before I run into this trouble!

For those, who like to try it out:

From HTML to epub or mobi

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

HTML is - from my point of view - the best starting point for conversion. As described above it can easily be created using LaTeX or even other word processors. 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.

My prerequisites for a conversion tool

  • should be opensource
  • crossplatform (Windows, Linux, Mac, ...)
  • commandline batch processing

So here are the candidates:

  1. The free tool kindlegen from amazon.
  2. The shareware Jutoh, but for demonstration purposes you can test it.

Kindlegen

Is crossplattform and does a very good job. I hav nothing to complain. It produces files in the "*.mobi"-format.

The only problem I have:

  • the "table of content" goes away!

Jutoh

This is not free software. But it is a full featured Editor for ebook generation.

Advantages:

  • Support of almost any ebook format
  • Fully WHYSIWYG editor

But I don't need the latter, because I want to edit my documents with the processor of my choice.

Disadvantages:

  • Project based. So you first have to import a document via GUI in a project file.
  • This is a GUI-tool, no commandline tool. But it has a batch mode.
  • Generation of the "table of content" will not allays succeed with my LaTeX documents.

PocketBook Pro

A description of the device I already made in this thread (in language german) at mobileread) and here more actual. A Youtube video you can find here.

Fbreader software

Tried the fbreader180. The features are really good, but the integration with the PocketBook 912 Pro is disappointing:

  • No TTS
  • No Notes

So I stay with the stock, but a little buggy fbreader and will wait until it becomes more mature.

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