DjVu

Browser Note: The DjVu browser plug-in has been updated for 64-bit browser versions, if you are having problems, download the latest version. You may still have to use a 32-bit browser to view djvu files without downloading them. This is required for some multipage djvu documents on railsandtrails.com.

The DjVu file format creates very small and easy to navigate files for viewing on the web. DjVu separates images into foreground (text and sharp lines) and background (color) information and compresses each part using the most effective algorithm for that part. It uses a wavelet technique originally developed by AT&T Labs that provides faster display than typical bit-mapped images.

To view DjVu images you must first install a free browser plug-in available for Macintosh, Windows and Linux/Unix operating systems from Caminova. Be sure to update your plug-in to the latest version.

DjVu has 4 formats. The scanned or clean formats generate very small files with sharp lines and blurred fill colors. Bitonal format generates small files with sharp black lines and no color. Photo format generates much larger files with sharp colors. You can view the foreground and background layers of DjVu scanned images separately by right clicking on the image and choosing View->Layer. Often readability and printing of text and line drawings can be improved by viewing the B&W layer. To be sure no pertinent information is lost before printing, view the background layer to see what is there.

To print DjVu images always use the DjVu print button (or right click on image and choose File->Print) rather than the browser's print button.You can print the section of the image currently displayed or the entire image.

To copy a portion of the image, right click on it and choose Selection->Select Region and draw a rectangle around the area you want to copy. Then right click and choose Selection->Copy. Then paste the selection into your document (Word, Powerpoint, etc.)

To save DjVu images for viewing, editing and printing off-line, click on the DjVu disk icon or right click and choose File->. You can Save Page As or Save Document As (DjVu). DjVu documents containing multiple pages can be saved as Bundled (one large file with all pages) or Indirect (one file for each page and an index file to order them for viewing).

Windows XP SP2 changes settings in Internet Explorer that block the viewing of saved DjVu files. You can disable the warning by opening the Internet Options window in the Tools menu of Internet Explorer. Click on the Advanced tab, scroll down to the Security section and check "Allow active content to run from files on my computer." and/or "Allow active content from CDs to run on my computer." The latest plug-in (6.1) installs a DjVu viewer, eliminating the need to change IE settings. If you have problems after updating to Internet Explorer 7 try this.

To edit a DjVu image you will first need to convert it to a format your image editor understands.You can access additional options by right-clicking (control-clicking in Mac OS X) on the image. Choose Exporting to File... to save the image in an editable file format common to your operating system (BMP on Windows, PICT on Mac). Once saved in this format you can edit the file with any graphics editor. You can then include the edited image in a research paper, power point presentation, video documentary or website (subject to licensing/copyright limitations)

To copy/paste the full resolution image(or selection), you can use the Select Whole Region or Select Region commands (right click->Selection->). If you want the currently displayed resolution, use the Print Screen key to save a copy of the current screen to the clipboard for pasting into another program. Some DjVu images of text based documents have the text embedded in the file. You can search for, select and copy that text. (use control-c to copy, as the copy command in the edit menu is grayed out.)

To create DjVu images you need a commercial program sold by Celartem Technologies (formerly LizardTech). Document Express Professional is available for Windows OS or Linux.. Celartem Technologies also sells Document Express Enterprise batch processing software to institutions converting large numbers of images.

An older Windows version, DjVu Solo (without OCR), is available free for non-profit use at PlanetDjVu. The original developers of DjVu maintain a website promoting its use at DjVuZone.org. They provide a free web based conversion tool, anytodjvu. An open source creation tool is available for Linux at sourceforge.net/projects/djvu.

Tips on using Document Express/DjVu Solo:

Very small file size for color documents is achieved with Scanned and Clean compression. The document is separated into a foreground (text and sharp lines) and background (background color and photos, drawings without sharp lines). If you sharpen and darken the lines in an image editor first, djvu can better separate the lines and text from the background. Using a higher resolution original, does not substantially increase the file size, but often improves clarity, even at lower viewing resolutions. For example, 600 dpi looks sharper than 300 dpi at 300% enlargement in DjVu with only a small increase in DjVu file size. Enlarging a 300dpi document to 600dpi in a graphics program before encoding in DjVu provides similar quality in DjVu scanned or clean format to a document actually scanned at 600dpi.

Bitonal encodes in black & white only, but more accurately displays line drawings with irregular edges that are not encoded well with Scanned or Clean.

Photo encoding creates much larger file sizes (approximately half the size of a comparable jpg image) but the quality of the image is comparable to the original scan. Photos, documents and color maps with many details may require this encoding. Only the background layer is encoded, but at high resolution. Color maps and drawings with sharply delineated lines may be acceptable using Scanned or Clean and thus save considerable space and download time. The only way to know is to try it. If any important information is in the background layer, you will need to use Photo encoding to keep that information sharp when enlarged.

updated 7/18/08

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