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