Data delivery Adolf Knoll National Library of the Czech Republic

Data delivery

Adolf Knoll

National Library of the Czech Republic

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

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 !!!

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

75 dpi 300 dpi

Decrease of resolution

WHAT HAPPENS?

Computer screen has a fix resolution…

Decrease of image depth24 bit 8 bit 4 bit 1 bit

2 colours16 colours256 coloursCa. 16.700.000 colours

Decrease of image depth

24-bit 1-bit4-bit8-bit

1/3 1/241/61

16 million colours

16 colours

256 colours

1

1/24

1/3

1/6

Size reduction through decreaseof the colour depth

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 Burkes Stucki

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

Compression in general

lossless lossy

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.

Compression – working groups

Image JBIG (Joint Bi-level Image Group) JPEG (Joint Photographic Expert Group)

Audiovisual MPEG Video (Motion Pictures Expert

Group) sound