DJVU, DjVu image files (.djvu)
The DJVU Raster image file format
DJVU is a compressed image format which was developed by LizardTech. This file format was primarily designed to store different kinds of scanned documents; especially documents that contain a combination of text, pictures, indexed color images, and line drawings. These features make it an appropriate open source alternative to Adobe's PDF. The DJVU format allows the distribution of high resolution images through the internet. DJVU viewers, appropriate browser plugins, as well as DJVU encoders and decoders are easily available for the operating systems Windows and Mac.
Technical details of DJVU files
DjVu was developed at the AT&T labs by Yann LeCun, Leon Bottou, Patrick Haffner and Paul G. Howard around the early 1990's and early 2000's. Due to its smaller file size and ease of converting large volumes of text into DJVU format, and due to its open file format, it is considered superior to the PDF format. Files with the DJVU extensions can be separated into three different kinds of images - background, foreground, and a mask image with a higher resolution. Background and foreground images are typically compressed using the compression algorithm IW44 and the mask mage using JB2. Thus, the file size is reduced significantly.