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Access to digital resources: principles

Access to digital resources: distribution

Adding to the catalog

The aim of adding a resource to the BnF catalog is to create a copy of that resource – the “digital” copy – and to attach it to the bibliographical record that already exists in the catalog and describes the paper primary document that has been digitized. This enables digital resources to be accessed directly from the BnF master catalog. Once this process has been completed, the new resource is added to BnF’s digital OAI warehouse (OAI-NUM). The document metadata and identifier then become available to the Gallica search engine, as well as to all partners wishing to reference the document on their own websites (e.g. Europeana).

Creating distribution files

The second stage consists of converting the resource into a format that can be accessed as easily as possible by Internet users.

Since BnF digitizes documents at very high definition, they cannot be accessed via the Internet in their unaltered state for reasons of network speed.

Compression and format conversion: a compromise between readability and size

Digital resources must use the smallest possible file size so as to speed up their transmission over the network, without adversely impacting the way in which they are used by Internet users (viewing, downloading, copying, etc.). A compromise must therefore be found between the document’s readability and the size of the associated file.

The formats available within Gallica have been selected by BnF to be as widely accessible as possible while favoring open or de facto standards: 

  • PNG, JPEG, TIFF and GIF for viewing documents digitized in image format
  • HTML for viewing documents in text format 
  • PDF and TIFF for downloading documents in image format 
  • multilayer PDF and TXT for downloading documents in text format 
  • MP3 for playing and downloading sound recordings

Compression

A process that reduces the size of a computerized file. Compression is very widely used on the Internet, since it lowers the connection speed required by Internet users to access resources. Compression can be carried out with or without loss of information relative to the source file. One compression method consists of removing pixels which are not visible to the naked eye.
(N.B.: compression is just one way of reducing file size. The size of a file can also be reduced by changing its physical dimensions – e.g. in pixels for an image file – or its resolution, i.e. pixel density per centimeter or inch/DPI).

 


Tiling: “cutting up” large digital files for large formats

Oversize documents such as maps, daily newspapers, and images, may also be “tiled”.

This approach involves preparing large digital files by cutting them up into collections of small components or “tiles”.

For example, some of the maps available within Gallica can be accessed using a zoom function: this enables users to view a specific area of a map at a very high level of detail without having to download the entire document.

Tuesday, March 22, 2011

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