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What is DjVu Compression?
DjVu is a computer file format created to hold scanned documents, particularly ones that include text, line drawings, indexed color pictures, and photographs. It uses various methods such as image layer separation of text and background/pictures, progressive loading, arithmetic coding, and lossy compression for bitonal (monochrome) images to compress the files.
People who want to distribute high-resolution documents in the public domain need a lossy compression technique to deliver a high compression rate. These documents are usually read in a web browser. The compression technique employed should have a rapid decoding rate to allow displaying such a high-resolution document in a web browser. DjVu offers a perfect solution for this requirement.
A decoder is built in the form of a plug-in that can be used with any standard web browser. With the aid of this decoder, zooming and panning a file with a picture is a breeze. A user may immediately see the first version of a file, and the file's quality progressively increases as more bits come.
How Effective is DjVu Compression?
DjVu can compress files up to 1000 times. When compared to other compression algorithms, this degree of compression is 5 to 10 times better.
Full-color pages scanned at 300 dpi may be reduced from 30 Mb to 30-50 Kb without sacrificing quality.
Color documents with picture and text compressed using the DjVu method are often 5 to 10 times smaller than JPEG files of comparable quality.
Black-and-white papers compressed using the DjVu method are typically 10 to 20 times smaller than JPEG and 5 times smaller than GIF files.
Similarly, compared to PDF files, files compressed using the DjVu method are roughly 5 times smaller.
Components of DjVu
The document is split into three components in the DjVu compression technique: mask, foreground, and background. The mask component consists of the text and lines in the bi-level form. The background component refers to the pixels that represent the picture and the paper background.
The decoder decodes the three components. The decoder increases the resolution of the background and foreground components back to their original level to generate the final decompressed image based on the mask.
Before the standardization of PDF in 2008, DjVu had been considered the best option due to it being an open file format, whereas PDF was a proprietary software at the time.
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