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djvu size advantage and creation
#1  roger64 06-22-2017, 08:01 AM
Hi

This is a request for information about djvu size advantage and creation.

I read that many organizations use djvu for the storage of electronic documents because of its size saving features. I did a few tries to check it. As I am a Linux user, I used the handy pdf2djvu conversion tool with a 300 dpi resolution. I got the following results:
- a 7.2 MB pdf became a 13.3 MB djvu. It contains 99.8% text and one cover image.
- a 26.5 KB pdf black and white image (300 dpi) became a 37.6 KB djvu.
- a 2.8 MB pdf colour image (600 dpi) produced by my scan printer became a 176 KB djvu image (300 dpi)

Out of the third test, these tries do not seem very enticing as far as size saving is concerned. So, for the time being, it seems it does not make much sense to use pdf to produce djvu save for some rare use cases.

I also like to convert EPUB to customized pdf (in 9×12 cm format). I do not know how to it directly with djvu. There is one online tool that makes it cleanly.(https://convertio.co/). However there seems to be no way to tell it beforehand what the dimensions of the output (width, height, margins) should be like we can do with the Prince PDF plugin. Hopefully one day, a new Sigil plugin may appear to go directly from epub to djvu format.

I am not aware of any other easy way to produce djvu and get some of its size saving advantage (over pdf). But, probably I am missing something?
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#2  DaleDe 06-22-2017, 09:39 PM
There are two kinds of PDF's. One is an image (with or without some search text) and the second is pure text which is likely the kind you are testing with. Typically DJVU shines with an set of images that look like text. DJVU looks at the images and breaks them up into reusable graphics items that look for all intents and purposes like a set of fonts and then just references these as needed. This is typically better compression than an image would be, also the latest PDF is now using a better (JP2000) compression than it did formerly.

Dale
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#3  roger64 06-23-2017, 03:54 AM
@Dalede

Thanks for your clarification. Looking from the wonderful Alice in Wonderland that you can download from here where the text is searchable even when the content is a set of images, one can only be amazed by the extraordinary size advantage of this format. (3.3 MB for 114 pages filled with text and images)

The only question is how to manage to repeat such a feat. It does not seem very easy to duplicate without many command lines and/or custom scripts.
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#4  DaleDe 06-23-2017, 12:16 PM
Quote roger64
@Dalede

Thanks for your clarification. Looking from the wonderful Alice in Wonderland that you can download from here where the text is searchable even when the content is a set of images, one can only be amazed by the extraordinary size advantage of this format. (3.3 MB for 114 pages filled with text and images)

The only question is how to manage to repeat such a feat. It does not seem very easy to duplicate without many command lines and/or custom scripts.
You might want to start with our DJVU@Wiki » wiki page.

Dale
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