1. Data delivery Adolf Knoll National Library of the Czech Republic

2. Data delivery The goal is to make the data transfer easier under slow speed Internet connection In practice  Decrease of resolution  Decrease of image depth  Compression of data  Delivery of necessary chunks of data of still acceptable quality

3. Slow speed Internet connection At home: 28.8 kbps – 56 kbps At work: 155 Mbps What does it mean?  56 kbps = 7 KB of data transferred per each second  155 Mbps = 19.375 MB transferred per each second  400 simultaneous users = 48.5 KB transferred per each second in average per user !!!

4. Solutions… Higher speed Research networks (Czech backbone 2.5 Gbps) Used for sharing computational resources and storage (grid computing) Thinner files To deliver only shat is necessary  Decrease of resolution  Decrease of image depth  Compression of data  Delivery of necessary chunks of data of still acceptable quality

5. 75 dpi 300 dpi Decrease of resolution WHAT HAPPENS? Computer screen has a fix resolution…

6. Decrease of image depth 24 bit 8 bit4 bit1 bit 2 colours16 colours256 coloursCa. 16.700.000 colours

7. Decrease of image depth 24-bit1-bit4-bit8-bit 1/3 1/241/61

8. 16 million colours 16 colours 256 colours

9. 1 1/24 1/3 1/6 Size reduction through decrease of the colour depth

10. Methods for decrease of image depth onto 1-bit (dithering) If compressed by CCITT Fax Group 3 1694 B 4364 B 3734 B 3682 B Nearest colour Floyd-Steinberg BurkesStucki

12. Delivery of necessary chunks Pre-processing and a set of images of various quality levels  Thumbnail  Preview  Internet  User  Archival Image servers  Dynamic on-the-fly conversion  Delivery from multiresolutional source Controlled by user

13. Compression in general lossless lossy

14. Typical situations Colour Image: PNG vs. JPEG Black-and-White Image: TIFF/G4 vs. JP2 Sound: CDA vs. MP3 Video: ….. Motion pictures are lossy by their nature, as they create illusion of motion through successive display of discrete frames !!! Compression will be explained in more detail in concrete chapters concerning characteristic types of digital data.

15. Compression – working groups Image  JBIG (Joint Bi-level Image Group)  JPEG (Joint Photographic Expert Group) Audiovisual  MPEG Video (Motion Pictures Expert Group)  sound