DjVu
| DjVu | |
|---|---|
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| File extension : |
.djvu, .djv
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| MIME type : | image / vnd.djvu |
| Developed by: | AT&T Research |
| Type: | Graphic format |
| Website : | http://www.djvu.org |
DjVu [ deʒaˈvy ] ( spoken in French like Déjà-vu , 'already seen' ) is an open file format for raster graphics , which was designed for storing scanned documents and is intended to be an alternative to PDF .
functionality
The main idea behind DjVu is the separation of the source material into several levels and their different compression:
- The page background and the images it contains are compressed lossy using a wavelet- based algorithm called IW44 . This is roughly equivalent to JPEG 2000 compression.
- The text above is compressed as a binary image using the so-called JB2 algorithm. This is very similar to the JBIG2 algorithm, can work either losslessly or lossy and makes use of recurring patterns such as letters.
Text can also be used directly, i.e. H. not in the form of image data, which enables searching and copying of text passages. In the case of scanned documents, this text is generated using text recognition .
history
The underlying technology was developed at AT&T Laboratories from 1996 ( Yann LeCun , Léon Bottou , Patrick Haffner ) and bought up by LizardTech in March 2000 . With the acquisition of LizardTech in 2003 and its dissolution as an independent company in 2005, ownership passed to Celartem .
software
Celartem has published a reference implementation under the GNU General Public License (GPL), which contains a decoder , but only an incomplete encoder , which in particular does not allow the separation of background and text or the lossy compression of the text layer. The creation of DjVu files from scanned material is therefore currently only possible with commercial software or with Celartem's DjVu Solo 3.1 software. The latter is available free of charge on the website.
For viewing DjVu files, Celartem offers browser plug-ins for Windows , Linux and Mac OS X for free download. In addition, DjVuLibre is an open source implementation maintained by the original developers with a viewer program and browser plug-in for Unix .
Free viewers based on the DjVuLibre library:
- WinDjView & MacDjView - viewer for Windows and Mac OS X
- Evince - Viewer for the Gnome desktop, also for other formats
- Okular , a universal document viewer ( KDE )
- PocketDjVu - viewer for Pocket PC
- Sumatra PDF viewer for Windows
DjVu files can also be opened and extracted with the free image viewer IrfanView , provided the plug-in additional package has been installed. The format has not yet been supported for writing or reading by popular image processing software.
Legal
The algorithms used in the reference implementation and patented by Celartem can continue to be used in open source projects within the meaning of the GPL , without having to fear patent claims from Celartem.
Web links
- DjVu.org (English)
- DjVuLibre project page (English)
- DjVu file extension
- Converter between DjVu and PDF formats