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DjVu (pronounced "déjà vu") is a new image compression technology developed since 1996 at AT&T Labs to solve precisely that problem. DjVu allows the distribution on the Internet of very high resolution images of scanned documents, digital documents, and photographs. DjVu allows content developers to scan high-resolution color pages of books, magazines, catalogs, manuals, newspapers,historical or ancient documents, and make them available on the Web.
DjVu typically achieves compression ratios about 5 to 10 times better than existing methods such as JPEG and GIF for color documents, and 3 to 8 times than TIFF for black and white documents.
Scanned pages at 300 DPI in full color can be compressed down to 30 to 100KB files from 25MB.. Black-and-white pages at 300 DPI typically occupy 5 to 30KB when compressed.
This puts the size of high-quality scanned pages within the realm of an average HTML page (which is typically around 50KB).
อ่านเพิ่มเติม http://djvu.org/resources/
Typical DjVu file sizes are as follows:
- bitonal scanned documents: 5 to 30KB per page at 300dpi (3 to 10 times smaller than PDF or TIFF)
- color scanned documents: 30 to 100KB per page at 300dpi (5 to 10 times smaller than JPEG).
- photos: 2 times smaller than JPEG, about the same as JPEG-2000, but the decoder/renderer is progressive and has minimal memory requirements.
- palettized images: 2 times smaller than GIF (up to 10 times if it's mostly text).
- digital (non scanned) documents: between 1 and 3 times smaller than PDF or gzipped PS (depending on the amount of pictures), but rendering, page flipping, zooming, panning are incomparably faster, and the image quality on screen desplays is much better (antialiased text, etc).
http://www.djvuzone.org/djvu/photos/jpgvsdjvu01/index.html
http://djvu.org/resources/jpgvsdjvu/comparison.html
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