1. 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

2. 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:
See “The Bandwidth Conservation Society”, at:
4/22/2019
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?
4/22/2019
Prof. Sheizaf Rafaeli

4. 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

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

6. Compression
4/22/2019
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
4/22/2019
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 if a =wood 2=could 3=chuck
4/22/2019
Prof. Sheizaf Rafaeli

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

11. 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

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 bytes or so bytes or so
4/22/2019
Prof. Sheizaf Rafaeli

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

14. 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

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:
4/22/2019
Prof. Sheizaf Rafaeli

16. Lossy compression
4/22/2019
Prof. Sheizaf Rafaeli

17. Animation compression
SHIFT the existing pixels or
DESCRIBE only the NEW PIXELS from one frame to another
see at:
4/22/2019
Prof. Sheizaf Rafaeli

18. 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

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

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

21. 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

22. http://www.mpeg.org/MPEG/ : MPEG Pointers and Resources
Graphic File Formats FAQ
and : Image compression FAQs
: MPEG Pointers and Resources
Every File Format in the World
Common Internet File Formats
4/22/2019
Prof. Sheizaf Rafaeli