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Help - Djvu
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This section outlines the following:
Basic Facts About DjVu
Q:
What is DjVu?
A:
DjVu is an image compression technology specifically designed for scanned document pages such as books, magazines,catalogs, newspaper articles, technical publications, ancient and historical documents.
Q:
How can I view DjVu documents?
A:
You need to download the free DjVu plug-in for Netscape Navigator (3.0 and above) or Microsoft Internet Explorer (3.0 and above).from the AT&T DjVu web site http://www.djvu.com/.
Q:
How should I pronounce DjVu?
A:
DjVu is pronounced like the French "déjà vu" (deh zha vu), which literaly means "already seen". DjVu can bring to cyberspace all the documents that are "déjà vu" in the real world. The DjVu technology is anything but "déjà vu".
Questions About DjVu Plug-in
Q:
How big is the plug-in?
A:
The distribution for Win95/98/NT is 580KB. The plug-in can be downloaded and installed with a few mouse-clicks in a few minutes.
Q:
For what platforms is the plug-in available?
A:As of July 1998, the plug-in is available on Win95, Win98, WinNT, Linux/x86, Solaris2.x, Irix6.x, and MacOS8/ppc. It will be available soon on other Unix platforms (Linux/Alpha, HPUX,...).
Q: How big is a DjVu file?
A:
A DjVu file for a typical magazine page at 300 DPI in colour is generally between 40KB and 70KB. A Black and White page at 300 DPI is generally 15 to 40KB.
Q:
What happens when I install the DjVu plug-in for Windows?
A:
The plug-in installation software copies a file called npdjvu.dll in the "plugin" folder of your browser. In the same folder, it also copies a "djvu" folder which contains various help files.
Q:
What is the recommended configuration to view DjVu images under Windows?
A:
A Pentium 90Mhz or faster, 16MB of RAM, a graphic card with 2MB of RAM configured for 800x600 resolution with at least 65536 colours (16 bits).
Q:
What graphic setting is recommended?
A:
800x600 resolution or better, with 65536 colours (16 bits) or more. This requires a graphic card with at least 2MB of RAM. The DjVu plug-in will work with 256 colours (8 bits), but it won't look nice, although the plug-in "dithers" the images to make them look as good as possible.
DjVu in Use
Q.
The images look too dark or too light?
A:
All our images are scanned to a pre-determined contrast range, consequently certain reports will differ in contrast. You can compensate for this by adjust the contrast preference on the DjVu preferences palette.
Q.
How can I quickly navigate through a document
A:
If you find the contents page of the report - generally page 2 or 3 you can calculate which DjVu page correspondes to the printed page - in most cases add 2 to the printed page reference and this will give you the corresponding DjVu page
Technical Issues
Q.
Where can I find technical information on DjVu?
A:
Technical papers are available in DjVu format.
Q:
How much better than GIF or JPEG is DjVu?
A:
For colour pages at 300 dpi that contain text and pictures, DjVu files are generally 5 to 8 times smaller than GIF or JPEG for a similar level of subjective quality. For colour pictures that do not contain text DjVu is better than JPEG, but not enough to justify switching, except for very large images.
Q:
How is DjVu different from PDF?
A:
PDF is primarily designed for documents that are produced electronically, while DjVu is primarily designed for scanned documents. PDF can be used to compress scanned documents, but it uses standard compression algorithms such as, JPEG and CCITT G4 produces files that are 4 to 10 times larger than with DjVu. DjVu can also be used for electronically produced documents, but it restricts the resolution of those documents.
Q:
How can DjVu display these very large images without filling up the memory of my computer?
A:
The DjVu plug-in uses a unique on-the-fly decompression technology that allows to keep the images compressed in the memory of the computer and to decompress only the piece that is being displayed on the screen.
Q:
Does DjVu perform a "lossy" compression or "lossless" compression?
A:
DjVu performs a "lossy" compression. A "lossy" compression means that after compression, the reconstructed image may be different from the original image. Like JPEG and most image compression algorithms, DjVu allows the loss of some high frequency information to achieve high compression rates. Unlike JPEG, this is not done at the expense of document readability.
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