k2pdfopt: optimizes PDFs for viewing on e-readers

[sanon]

That looks nice... There are so many command line options but one has to practically know how to use them. And for GUI-people this is obviously much harder... Thanks again.

Off topic: In GUI I can't select PW3. It automatically changes to Kindle Voyage. Is this normal?

[willus]

Originally Posted by sanon

Off topic: In GUI I can't select PW3. It automatically changes to Kindle Voyage. Is this normal?

Yes, because they have the exact same resolution. They are equivalent (in terms of how k2pdfopt sees them).

[roger64]

Hi

Is there a way to produce a fixed-size djvu file -say 9×12cm with some margins- using k2pdfopt starting from an EPUB file?

This online site can do it -without fixed size.

If not, what would be missing?

[willus]

Originally Posted by roger64

Hi

Is there a way to produce a fixed-size djvu file -say 9×12cm with some margins- using k2pdfopt starting from an EPUB file?

This online site can do it -without fixed size.

If not, what would be missing?

Definitely not k2pdfopt. It neither reads epub files nor writes djvu files. This question probably belongs in the epub forum. Maybe calibre can do this?

[roger64]

@willus

Thanks for your reply. As far as I know, Calibre converts from djvu format but not to djvu format.

I had expected k2pdfopt to have some DJVU capabilities, misunderstanding this excerpt (from the first page presentation)

Or drop a folder full of PDF/DJVU files onto the k2pdfopt icon to batch process.

[willus]

Originally Posted by roger64

@willus

Thanks for your reply. As far as I know, Calibre converts from djvu format but not to djvu format.

I had expected k2pdfopt to have some DJVU capabilities, misunderstanding this excerpt (from the first page presentation)

Sorry--I can see the confusion after looking back at my web page. It's not entirely obvious, but k2pdfopt can only read djvu files, not write them. It can only write PDF files (and, more recently, png or jpeg files). My guess would be that the best solution would be to use one of the tools in the software forum to convert (or print) the ePub to a PDF file (not sure which of them have this capability, but presumably one or more does), and then I'm sure there are tools to convert PDF to djvu.

So why the focus on djvu? Why not just convert the epub to a PDF if you want to be able to add margins to it?

[roger64]

I have been converting for some years now (5?) Epub to 9×12 PDF using the Prince PDF plugin published here by Jellby. (a more recent Sigil version of it made by Doitsu exists).

djvu seems quite an interesting format and I am looking for a similar capability as it seems that it could -potentially and ideally- produce even smaller files (at the same quality level).

Up to now, I found that the online site convertio produces directly nice documents in djvu format from epub but it does not seem to offer any choice for dimensions. (it produces standard A4 files). They offer a "conversion API" choice but I failed to spot any dimension choice there -maybe I missed something.

Other sites pretending to convert Epub to djvu do much worse. Sobolsoft uses a two step process, converting first to a temporary PDF and them converting to djvu.

I could already do the same, for example using Jellby's plugin and then the excellent opensource pdf2djvu software. But the output djvu file exceeds the PDF size which defeats my initial purpose...

The STDU viewer is said to be able to view (among many other formats) Epub files but I failed to do so with every single Epub I used.

[willus]

This would have been good information to put in your first post so that people did not waste time recommending things you had already tried.

I don't recommend the djvu format for converting your epubs into fixed page format unless your epubs are mostly images. With text-based epubs, converting to djvu creates a bitmap for each page, whereas converting to PDF should store the text from the epub directly as text strings (as convertio does) without the need for bitmaps. This results in a very small PDF file size when converting large, mostly text epubs unless those epubs have a lot of different fonts that get embedded into the PDF. This is probably why the pdf2djvu utility ends up creating a larger djvu file than the original PDF file. There is also the added benefit that the text in the PDF file will render perfectly (with smooth edges) at any magnification, whereas the text in the djvu bitmapped pages will not.

The djvu format is optimized for archiving scanned documents, not for converting epubs.

[loviedovie]

Hi

Can k2pdfopt optimize pdfs without changing the files? I download pdfs from archive.org but you know those files are pain in the neck to browse on mobile devices, they are the pdf viewer killer. I am wondering if I can use this app to just optimize them without chaning orientation, order, page set up etc.Basically I want to keep the pdfs as is and just optimize thme such that they are much easier to read on my mobile devices.

I have many pdfs from archive.org so I do not want to go back and try to download djvu files becasue they seems to be abit nice to browse but not many readers support djvu also.


thanks

[willus]

Originally Posted by loviedovie

Can k2pdfopt optimize pdfs without changing the files? ...

Yes. The files from archive.org are viewer killers because they use JPEG-2000 compression (JPX encoding), which is very efficient, but more resource intensive for viewers to render. You can convert those PDFs to faster-rendering .png or .jpg with this command:

k2pdfopt -mode copy -odpi 300 sourcefile.pdf

You can adjust the output DPI to suit your preference. The above command does "Flate" (.png) compression. If you prefer .jpg compression, you can add, for example, -jpeg 90 (90 specifying the quality level, 1 - 100). I've attached an example source and conversion using .png compression. You'll notice the converted file is much larger (5x) than the source file. This is the price you pay for the faster viewing.

Also, by default k2pdfopt tries to optimize contrast and changes the gamma factor of the text to make it darker on e-books. If you want to disable this "tinkering" with the source file, add these options: -cmax -1 -g 1

If you want to see what encoding is being used in a PDF file, you can use the -i option (or the INFO button or 'i' or CTRL-D in the MS Windows GUI):

k2pdfopt -i sourcefile.pdf

[loviedovie]

willus

That is great news. I will give it a try. Thanks for your help.

[loviedovie]

wilus

I think that this will work for me. Is there a way to disable "exit" conformation when the command line is done?

thanks

[willus]

Originally Posted by loviedovie

... Is there a way to disable "exit" conformation when the command line is done?

Yes: Use the -x option. Use -ui- to disable user menu prompting also.

[loviedovie]

wıllus

How about optimizing for the fıle size without giving up much quality? I like that I can make archive.org pdfs usable again but there could be instances where I would like to go the other way.

thanks

[willus]

Originally Posted by loviedovie

wıllus

How about optimizing for the fıle size without giving up much quality? I like that I can make archive.org pdfs usable again but there could be instances where I would like to go the other way.

thanks

At present, k2pdfopt does not have JPEG-2000 encoding capability. Even if it did, I gather from what I've researched so far that the encoding process is not entirely trivial and has many tuneable parameters. If you want to see how to get smaller output file sizes from bitmapped k2pdfopt output (jpeg or png), then see the file size help page.