Quality Levels of Reproduction Adolf Knoll National Library of the Czech Republic.
-
Upload
natalie-sparks -
Category
Documents
-
view
214 -
download
1
Transcript of Quality Levels of Reproduction Adolf Knoll National Library of the Czech Republic.
Archival image Access image
Facsimile printing or displayPreprocessed set of various
quality level images
Dynamically postprocessedImage on demand
Transition from analogue to digital = first loss of information • Acceptable technical parameters (resolution, colour depth, lossy compression)• Acceptable colour fidelity (ICC profiles, calibration, metadata for still images)
Original
Dig
ital w
orld
Ana
logu
e w
orld
continuousdiscrete
What is necessary and what not?
Visual representation of documents To deliver only the necessary quantity of
information from the whole source Where is the limit between necessary and
unnecessary? It is given by the purpose of communication:
facsimile printing, understanding of text, study of illuminations, general idea what the document is about, structure and character of objects on the digitized page, …?
Typical documents
Illuminated manuscripts Textual manuscripts and old printed books Old periodicals Typewritten documents Modern journals (with colour photographs) Maps Administrative documents and forms Computer generated documents ...
Possible solutions
Decreased colour depth 16.7 mio colours 256 colours or shades of gray (1/3 of volume) 16 colours/shades of gray (1/6) 2 colours (black-and-white images, 1/24)
Decreased resolution (down to the limit when necessary details are still seen)
Combined colour depth with resolution Loss of information (colour or detail)
Lossless Colour
LZW = 11,441 KB PNG = 8,849 KB JP2 = 6,647 KB
BW Fax Group 3 Fax Group 4 = 272 KB Fax Group 4 = 166 KB (JBIG, JBIG2)
JB2 (in DjVu)
Lossy Colour
DCT JPEG = 318 KB Wavelet = better, but
mixed photos with text do not give too much space for improvement
BW JBIG2-based
JB2 = 98 KB JB2 = 32 KB
BEST LOSSY METHODS COMBINED = Mixed Raster Content = DjVu = 55 KB
Compression
How about other originals?
Typewritten text (93 dpi) 2,326 KB BW
GIF = 23 KB Fax Gr. 3 = 20 KB PNG = 17 KB Fax Gr. 4 = 14 KB JB2 DjVu = 8 KB
JPEG = 546 KB DjVu = 10 KB
Illuminated manuscript 225 dpi; 54,654 KB TIFF/LZW = 36,355 PNG = 28,404 JP2 lossless =
22,595
Wavelet = 1,322 (JP2, IW44 in DjVu)
Colour fidelity
ICC profile included Calibration table:
Printed on permanent paper with permanent colours
Scanned with original Stored with the digital
copy
Metadata description of the image stored in a special SGML/XML file
Solutions for archiving
Rely on well established ISO standards : uncompressed TIFF TIFF/Fax Gr. 4 for black-and-white images JPEG
Can rely on other well established formats: GIF (simple graphics and bw) PNG (everything for efficient lossless
compression) PDF for computer generated documents
Solutions for delivery
The archival formats and pre-processed sets of imagesor
More efficient modern solutions: DjVu (for almost everything) MrSID (maps)
Viewing comfort at the user’s side must be solved (integration of plug-ins or ActiveX components into web browsers)
IE has problems with larger JPEG, but DjVu and MrSID very good viewing tools
Netscape Communicator – everything possible, but obsolete in handling
Netscape 6.xx – good plug-in and file association properties, but latest viewing components only as ActiveX (DjVu)
Critical points in modern solutions
Slow encoding and high requirements for computation power at larger images
Many of them depend on expensive software that must be purchased
Viewing problems and integration in web browsers
Good solutions have free browser plug-ins available and free encoding software for home use (smaller images or less functionality); they enable flexible display of very large files (DjVu, MrSID)