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File Compression and Formats

File Compression and Formats. HTML isn’t all… Prof. Sheizaf Rafaeli E-Commerce. It’s about bandwidth It’s about time / quality tradeoff It’s about multimedia It’s about intellectual property. See: “Multimedia File Formats on the Internet”, at: http://128.151.244.128/multimed/contents.htm

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File Compression and Formats

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  1. File Compression and Formats HTML isn’t all… Prof. Sheizaf Rafaeli E-Commerce Prof. Sheizaf Rafaeli

  2. It’s about bandwidthIt’s about time / quality tradeoffIt’s about multimediaIt’s about intellectual property • See: “Multimedia File Formats on the Internet”, at: http://128.151.244.128/multimed/contents.htm • See “The Bandwidth Conservation Society”, at: http://www.infohiway.com/faster/index.html Prof. Sheizaf Rafaeli

  3. File formats • Over 5000 types • Content: text, data (spreadsheet, database, ppt), graphics, audio, video • Executable programs (client, server sides) • Formulae: MIDI, 3D, VRML • How important are file formats for establishing business clout? Prof. Sheizaf Rafaeli

  4. File Format Considerations • Considerations: Compression, Efficiency (of compression and decode), Quality, Variety, Resolution, Color, Depth, Transportability, Scalability,Standardization, Encryption Prof. Sheizaf Rafaeli

  5. File types on the web: plugins Source: StatMarket, January 2001 Prof. Sheizaf Rafaeli

  6. Compression Prof. Sheizaf Rafaeli

  7. Compression • There are various compression methods. • Some searching for and replace characters with codes. e.g. strings of blanks can be replaced with a code that represents them. • Some replace long sequences of repeating characters with one occurance of the character and a number. • Some compression programs create a dictionary Prof. Sheizaf Rafaeli

  8. Compression • UNCOMPRESSED:How much wood could a woodchuck chuck if a woodchuck could chuck wood. • COMPRESSED:How much 1 2 a 1 3 3 if a 1 3 2 3 1. 1=wood 2=could 3=chuck Prof. Sheizaf Rafaeli

  9. Compression utilities • WinZip • StuffIt • Zip, .ZOO, ARJ, ARC, .Z, LHA, HQX,TAR, BinHex, Base64,Uuencode, many more Prof. Sheizaf Rafaeli

  10. Graphic file formats • BMP • WMF, PCX • TIFF, GIF, JPG, PNG • Which is appropriate for web? Bandwidth, “lossy”, rendering fonts, scalability, economically viable? • Which is more “accurate”? • Which is really necessary? Prof. Sheizaf Rafaeli

  11. GIF (Graphical Interchange Format) Smaller file sizes for graphic images with large areas of solid colors and uncomplicated backgrounds Supports transparency, interlacing, animation “Owned” by Compuserve JPEG (Joint Photographic Experts Group) smaller file sizes for images that have gradual transitions or many fine details such as photographs GIF vs. JPG Prof. Sheizaf Rafaeli

  12. GIFs are lossless but may not be as effificent • Graphics with repeating horizontal elements compress better than graphics with repeating vertical elements in the GIF format.200 bytes or so 600 bytes or so Prof. Sheizaf Rafaeli

  13. Compressing images Run-length encoding compresses images without losing information. Prof. Sheizaf Rafaeli

  14. A leading lossless compression scheme is LZW (Lempel-Ziv-Welch). LZW is used in GIF files, and achieves compression ratios of 50 to 90% Lossy compression does not uncompress to the same quality. The leading lossy compression schemes are JPEG and MP3. Compression ratios between 10:1 and 40:1 are common. Lossy vs. Lossless Prof. Sheizaf Rafaeli

  15. Lossy compression Lossy compression reduces the data density, and is not likely to be noticed by the human eye. But if an image is made too large after compression, the image looks rough. see at: http://www.umich.edu/~cisdept/mba/CIS745/balloon.animation.gif Prof. Sheizaf Rafaeli

  16. Lossy compression Prof. Sheizaf Rafaeli

  17. Animation compression SHIFT the existing pixels or DESCRIBE only the NEW PIXELS from one frame to another see at: http://www.umich.edu/~cisdept/mba/CIS745/beach-ball.animation.gif Prof. Sheizaf Rafaeli

  18. Text format files • ASCII .TXT, Microsoft’s .DOC, Wordperfect’s .WP , UNICODE... • Rich Text Format (RTF), Postscript, Adobe’s PDF Prof. Sheizaf Rafaeli

  19. MIDI .WAV, .AU, AIFF Real Audio (streaming) MP3PLJ Audio formats Prof. Sheizaf Rafaeli

  20. Video formats • Sample size, sample rate • Frames per second • .asf .rm .ra .avi .mpg .qt .vdo .viv .mpeg Prof. Sheizaf Rafaeli

  21. Video formats:MPEG MPEG (pronounced EHM-pehg), the Moving Picture Experts Group, develops standards for digital video and digital audiocompression. Prof. Sheizaf Rafaeli

  22. http://www.ora.com/centers/gff//gff-faq/gff-faq1.htm: Graphic File Formats FAQ • http://www.faqs.org/faqs/jpeg-faq and http://www.faqs.org/faqs/compression-faq/part1/preamble.html : Image compression FAQs • http://www.mpeg.org/MPEG/ : MPEG Pointers and Resources • http://whatis.com/ff.htmEvery File Format in the World • http://www.matisse.net/files/formats.htmlCommon Internet File Formats Prof. Sheizaf Rafaeli

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