File Compression and Formats 4/22/2019 File Compression and Formats HTML isn’t all… Prof. Sheizaf Rafaeli E-Commerce 4/22/2019 Prof. Sheizaf Rafaeli Prof. Sheizaf Rafaeli

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 See “The Bandwidth Conservation Society”, at: http://www.infohiway.com/faster/index.html 4/22/2019 Prof. Sheizaf Rafaeli

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? 4/22/2019 Prof. Sheizaf Rafaeli

File Format Considerations Considerations: Compression, Efficiency (of compression and decode), Quality, Variety, Resolution, Color, Depth, Transportability, Scalability, Standardization, Encryption 4/22/2019 Prof. Sheizaf Rafaeli

File types on the web: plugins                                                                                                    Source: StatMarket, January 2001 4/22/2019 Prof. Sheizaf Rafaeli

Compression 4/22/2019 Prof. Sheizaf Rafaeli

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 4/22/2019 Prof. Sheizaf Rafaeli

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 4/22/2019 Prof. Sheizaf Rafaeli

Compression utilities WinZip StuffIt Zip, .ZOO, ARJ, ARC, .Z, LHA, HQX, TAR, BinHex, Base64, Uuencode, many more 4/22/2019 Prof. Sheizaf Rafaeli

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? 4/22/2019 Prof. Sheizaf Rafaeli

GIF vs. JPG 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 4/22/2019 Prof. Sheizaf Rafaeli

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 4/22/2019 Prof. Sheizaf Rafaeli

Compressing images Run-length encoding compresses images without losing information. 4/22/2019 Prof. Sheizaf Rafaeli

Lossy vs. Lossless 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. 4/22/2019 Prof. Sheizaf Rafaeli

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 4/22/2019 Prof. Sheizaf Rafaeli

Lossy compression 4/22/2019 Prof. Sheizaf Rafaeli

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 4/22/2019 Prof. Sheizaf Rafaeli

Text format files ASCII .TXT, Microsoft’s .DOC, Wordperfect’s .WP , UNICODE... Rich Text Format (RTF), Postscript, Adobe’s PDF 4/22/2019 Prof. Sheizaf Rafaeli

Audio formats MIDI .WAV, .AU, AIFF Real Audio (streaming) MP3 PLJ 4/22/2019 Prof. Sheizaf Rafaeli

Video formats Sample size, sample rate Frames per second .asf .rm .ra .avi .mpg .qt .vdo .viv .mpeg 4/22/2019 Prof. Sheizaf Rafaeli

Video formats: MPEG MPEG (pronounced EHM-pehg), the Moving Picture Experts Group, develops standards for digital video and digital audio compression. 4/22/2019 Prof. Sheizaf Rafaeli

http://www.mpeg.org/MPEG/ : MPEG Pointers and Resources 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.htm Every File Format in the World http://www.matisse.net/files/formats.html Common Internet File Formats 4/22/2019 Prof. Sheizaf Rafaeli