All you need to know About the DjVu Format

DjVu Logo The DjVu format was developed as an alternative to the PDF format. It is optimized for scanned documents which contain both pictures and text and in many cases performs better than PDF for this kind of documents considering the file size. Therefore it is frequently used for the distribution of scanned documents on the web. In contrast to PDF it is an open file format which means that it can be used by both open source software and proprietary software without any charge.




Properties of the DjVu Format

The DjVu format uses advanced compression technologies which are about 5 to 10 times better then those of JPEG and Tiff. A scanned page in color (resolution 300 DPI) with a file size of lets say about 25 MB can be easily compressed to only 100 kB (!) using DjVu. All DjVu documents can be equipped with a text-layer to make them searchable. These searchable DjVu documents behave very similar to PDF documents.

The .djvu Extension

The DjVu Format usually used the extension .djvu. If you are wondering how to open .djvu files you can either convert them directly to PDF using our handsome online converter or check our list of DjVu Readers which are available for free on many different operating systems.

Differences between the DjVu and PDF Formats

When it comes to sharing documents on the internet, the Adobe PDF file format, released in 1993, is one of the most popular formats in use. If you are looking for an instruction manual online, there will probably be a PDF version of it. Many press releases, reports, and scientific publications are also released in PDF form. That said; there are alternatives to the PDF, one of which is the DjVu file format. There are many similarities between the two actually though DjVu is less well known by many. While the DjVu format was designed to mimic many characteristis of the Adobe PDF format there also obvious differences between the two file formats. The main difference between DjVu and PDF is that the DjVu format is a raster image format while the PDF format is a scalable vector file format.

One of the key advantages of the DjVu format is simply that it is more effective when it comes to compressing its documents. The idea here is that if you are going to take an existing scanned document, and you save it as both a DjVu file and a PDF file, the DjVu file is going to be significantly smaller than the PDF. Even if the compression is greater with DjVu, this does not mean tat the resulting document will look inferior to a PDF version. Instead, you end up with comparable looking documents of different sizes. The compression technology which is used by DjVu was developed in 1996 at the AT&T Laboratories.

The smaller size of DjVu files is important because it will affect the experience of viewing these files and downloading them onto computers, tablets, and mobile phones. Therefore it is especially popular in regions with limited internet bandwidth. Some people will have high-speed internet so large file sizes will not be an issue for them. However, many people have less than stellar internet speeds so they would benefit from file sizes that are significantly smaller. In real world use, a DjVu file always will tend to load quicker than a similar PDF.

DjVu files with an OCR Layer

While one can think of a DjVu as a loose collection of rasterized images which do not contain any searchable text information the DjVu format implements a work-around to make DjVu files searchable and therefore behave very similar to PDFs. The trick is done by a hidden OCR layer which is an economic way of providing the text information in searchable way. Most DjVu files which are circulating in the web contain such a text layer.

While the DjVu file format has the advantage in terms of size and speed, the PDF file format has the benefit of greater familiarity and a larger number of free and commercial applications being available for creating and editing PDFs. Most operating systems will provide standard solutions for opening PDF files while this is may not be the case for DjVu. Meanwhile there are plugins to view DjVu files for all common web browsers for Windows, Linux und Mac OS X and also desktop applications like the popular tool IrfanView provide plugins for DjVu documents.

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