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Willus.com's K2pdfopt
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5 Jan 2019

(Windows, Linux, OSX)

(GUIs; Native Kindle PDF Viewer)

(with videos)








Linux Install

Mac Install
K2pdfopt optimizes PDF/DJVU files for mobile e-readers (e.g. the Kindle) and smartphones. It works well on multi-column PDF/DJVU files and can re-flow text even on scanned PDF files. It can also be used as a general PDF copying/cropping/re-sizing/OCR-ing manipulation tool. It can generate native or bitmapped PDF output, with an optional OCR layer. There are downloads for MS Windows, Mac OSX, and Linux. The MS Windows version has an integrated GUI. K2pdfopt is open source.

Note to MS Word users: Before using k2pdfopt on your PDF file you might want to check my most recommended solution on my PDF Conversion Tips page.

Here's a quick example of what k2pdfopt can do (click on the images below to get the PDF files):

(8.5 x 11 PDF or DJVU file)
   . . . INTO THIS.

(6-inch reader screen)
     . . . OR THIS.

(4-inch smartphone screen)

MS Windows integrated GUI front-end

Unsolicited comments from k2pdfopt users (refresh the page to change the comments):

         "Thank you for all your efforts with k2pdfopt, it's enabling me to make some real use of my "nook Simple Touch" to read technical manuals etc." -- October 16, 2012         

         "The reason why I love your product is that it doesn't destroy math formulas . . . Great software!" -- October 12, 2014         

9 May 2020    A new Mac OSX and Linux GUI called rebook is being developed for k2pdfopt by Pu Wang. It is written in Python and Tcl/Tk. Wang's goal is to mimic the Windows GUI as closely as possible. While adding rebook to my third-party contribution page, I took the time to update that page, particularly the section on KOReader, which I had not looked it in a while. It has evolved into a very polished application for e-ink devices.
14 Mar 2020    I'm still here. The amount of time I can afford to work on k2pdfopt has dwindled, but I still hope to get around to some key bug fixes and updated builds at some point. In the mean time, I do still answer questions on the mobileread forum and I just did a long overdue update to the OCR help page.
3 Aug 2019    My site (willus.com) now offers SSL/https connectivity. Apparently this happened without my being notified, at no charge to me, which is nice. As a result, today I configured my site (and my backup site willus.org) to automatically re-direct http requests to https requests. Enjoy the added security!
5 Jan 2019    K2pdfopt v2.51a for MS Windows released. Fixes a bug displaying PDF file information in the MS Windows GUI. The download page now shows v2.51a. The MS Windows binaries will show v2.51a, but the Linux and OSX binaries will show v2.51 since they are not affected by the bug. See details in the k2pdfopt version history.
4 Jan 2019    K2pdfopt v2.51 released. This fixes an issue in v2.50 where the Tesseract OCR would not run on modern PCs and enhances the accuracy of the Tesseract v4.0.0 OCR. See details in the k2pdfopt version history.
31 Dec 2018    I've posted some k2pdfopt beta Windows builds (link since removed) due to reports of v2.50 Tesseract OCR failing on machines with AVX-capable CPUs (which includes most modern CPUs since Sandybridge). If some people could give me feedback on whether the beta version Tesseract OCR works on their AVX-capable CPU, that would be helpful. If you have time, please try all three versions.
27 Dec 2018    K2pdfopt v2.50 released. The major enhancement in this release is compiling in the Tesseract v4.0.0 library. Most other third-party libraries have also been updated to recent releases. See details in the k2pdfopt version history.
[... more news]

K2pdfopt (Kindle 2 PDF Optimizer) is a stand-alone program which optimizes the format of PDF (or DJVU) files for viewing on small (e.g. 6-inch) mobile reader and smartphone screens such as the Kindle's. The output from k2pdfopt is a new (optimized) PDF file. K2pdfopt is meant for text-based files on a white background which may also have graphics or figures, and it works equally well on native and/or scanned or bitmapped PDF or DJVU files. It is fully automated and can batch-process PDF/DJVU files. K2pdfopt works by converting each page of the PDF/DJVU file to a bitmap and then scanning the bitmap for viewable areas (rectangular regions) and cutting and cropping these regions and assembling them into multiple smaller pages without excess margins so that the viewing region is maximized. Making use of this method, k2pdfopt can re-flow text lines, even on scanned documents (see the Winnie the Pooh example below). You can see another example of how k2pdfopt works on this help page.

As of v1.50, k2pdfopt will also embed OCR text into the PDF so that text can be searched and highlighted, and v1.60 can create output files with the native PDF instructions from the source file (if the source file is PDF). Any kind of PDF/DJVU file (best if it has a primarily white background) can be converted. K2pdfopt works especially well on two-column or multi-column PDF/DJVU files such as IEEE and other technical journal articles (see examples below--it auto-detects two-column regions on the page), but even single-column files will often be significantly improved and much easier to read (see examples). K2pdfopt has the advantage over other PDF converters in that it fully preserves the rendered PDF fonts and graphics from the original file, unlike programs that convert the PDF to an e-book format. Also, because k2pdfopt is completely independent of language or fonts, it will work equally well on documents in any language.

   No install is required and no extra files or packages are necessary to run k2pdfopt (Mac/Linux users please see the mac install notes or linux install notes). Just drag and drop your PDF/DJVU file icon onto the k2pdfopt icon to convert it. You will be prompted for conversion options (as of v1.16). Click Convert All Files (MS Windows GUI) or Press <Enter> to convert the file using the default settings. A new PDF file with _k2opt at the end of the name will be created. The output file is optimized for viewing on Kindles and other mobile readers with 6-inch screens (if the settings are not customized). You can also drop a folder full of PDF/DJVU files onto the k2pdfopt icon to batch process them. You can even drop a folder full of bitmap images to have them converted into a single PDF as if they were pages of a PDF file (page ordering will be alphabetical by file name).

See my k2pdfopt help page for more detailed help.

Note that some older e-readers (e.g. the first-gen kindle) cannot read PDF files. If you have a Kindle 2, it must have the latest firmware that allows it to view native PDF files.

MORE EXAMPLES (click on images to get PDF file)
Example Type Original
Default Conversion
optimized for 6-inch
screen at 167 dpi
Smartphone Conversion
(-odpi 250)
optimized for 4-inch
screen at 250 dpi
Text re-flow
Text re-flow on
scanned pages
(must use -col 4)

    5-10-16    e-okuyucu.com (In Turkish)
    3-18-16    epubor.com (nice tutorial)
    7-10-15    blog.the-ebook-reader.com
    6-14-15    MacWorld.co.uk
    7-22-14    VidaSemPapel.com.br (In Portuguese)
    6-20-14    ghacks.net
    4-11-14    betanews.com
    4-11-14    TrishTech.com
    3-14-14    Dr. Simon Bance
    1-28-13    Intelligent Rumblings
    1-7-13    Net Buffalo (In Japanese)
    12-1-12    blog.trufanov.com (In Russian)
    11-4-12    abstractmodem.com (archived)
    9-20-12    ozgurlukicin.org (in Turkish)
    6-27-12    equiscentrico.com (in Spanish)
    6-26-12    ketabkhan.info (in Persian)
    1-4-12    TechLogon.com
    11-9-11    Świat Czytników (in Polish)
    11-5-11    tivasyk.info (in Ukrainian)
    11-1-11    WMLCloud.com
    10-31-11    linospapa.blogspot.com (in Greek)
    10-27-11    Steve Gibson's Security Now #324
    10-21-11    addictivetips.com
    10-12-11    Paper4Kindle (in Chinese)
    (varies)    mobileread.com forums
    9-7-11    habrahabr.ru (in Russian)
    8-4-11    steepbend.ru (in Russian)
    8-3-11    ssnjara.wordpress.com (in Croatian)
    8-2-11    howtogeek.com (note comments from "willus")
    7-30-11    artiss.co.uk
    7-30-11    ideasfor.info (in Russian)
    7-27-11    guidingtech.com (note comments from "willus")
    7-22-11    blog.rgub.ru (in Russian)
    7-22-11    aldus2006.typepad.fr (in French)
    7-22-11    korben.info (in French)
    7-21-11    lifehacker.ru (in Russian)
    7-20-11    redferret.net
    7-19-11    freewaregenius.com (full review)

See my page on PDF Conversion Tips.

This is my plug for Krzysztof Kowalczyk's Sumatra PDF reader: a small, efficient, yet feature-rich open-source PDF reader that does everything I want. Sumatra also displays several file types other than PDF, including XPS, DJVU, CBZ, CBR, and PS/EPS (PS/EPS requires Ghostscript), EPUB, and MOBI. It is a refreshing alternative to Adobe's bloatware. I highly recommend it.

This page last modified
Saturday, 05-Jan-2019 10:33:11 PST