It is best used to compressīlack and white images representing text and simple drawings. Takes advantage of repetitions of nearly identical shapes on the page (such as characters) to efficiently compress text images. Typically half the size as JPEG for the same distortion.ĭjVuBitonal, also known as JB2, is a bitonal image compression that It is best used for encoding photographic images in colors or in shades of gray. The DjVu image compression is based on three technologies:ĭjVuPhoto, also known as IW44, is a wavelet-based continuous-tone imageĬompression technique with progressive decoding/rendering. What is being considered here is not just a document imageĬompression technique, but a whole platform for document delivery.ĭjVu is an image compression technique, a document format, and a software platform for delivering documents images over the Internet that fulfills the above All these requirements call for a very sophisticated but parsimonious control mechanism to handle on-demandĭownloading, pre-fetching, decoding, caching, and progressive rendering of the page images. DjVu decomposes each page into multiple components (text, backgrounds, images, libraries of common shapes.) that may be shared by This can be achieved with a combination of advanced compression, pre-fetching, pre-decoding, caching, and Sequential page flipping, and quick rendering. Efficient browsing requires efficient random page access, fast To individual pages of the document without waiting for the entire document to download. Important, most existing document formats force users to download the entire document first before displaying a chosen page. Special provision must be made to ensure that flipping pages be instantaneous and effortless so as to maintain a good user experience. Pages in a scanned documents have a natural serial The third reason is that digital documents are more than just a collection of individual page images. Of memory and easily causes disk swapping. Another major problem is that a fully decoded 300 dpi color images of a letter-size page occupies 24 MB Have sufficient quality for viewing and printing, but the file size would be 300 KB to 1000 KB at best, which is Typical magazine page scanned in color at 100 dpi in JPEG would typically occupy 100 KB to 200 KB, but the text would be hardly readable: insufficient for screen viewing and totally unacceptable for printing. Not only are the file sizes and download times impractical, the decoding and rendering times are also prohibitive. Resolution, particularly color documents. The second reason is that long-established image compression standards and file formats have proved inadequate for distributing scanned documents at high This problem is slowly going away with theĪppearance of fast and low-cost color scanners with sheet feeders. The first reason is the relatively high cost of scanning anything else but unbound sheets in black and white. Is not only considerably cheaper, but also more faithful to the original document because it preserves its visual aspect.ĭespite the quickly improving speed of network connections and computers, the number of scanned document images accessible on the Web today is relatively Scanning documents, and distributing the resulting images electronically While many such efforts involve the painstaking process of converting paper documents to computer-friendly form, such as SGML based formats, the high cost of such conversions limits their extent. Many libraries and content owners are in the process of digitizing theirĬollections. Is still trapped on paper in the basements of the world's traditional libraries. Although the Internet has given us a worldwide infrastructure on which to build the universal library, much of the world knowledge, history, and literature
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