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g2gp 17-01-2009
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Raster Images#

Edited by Kieron Niven#

Section 1: Introduction to Raster Images#

Section 2: Creating Raster Images#

Section 3: Archiving Raster Images#

Section 3: Archiving Raster Images#

    • 3.1deciding what to archive
      • Selection and retention
      • preservation intervention points / file and data lifecycles (specific to guide, will also be covered generically)
    • 3.2 deciding how to archive
      • archiving strategies (migration (to new format, to 'basic' format), emulation, refreshment)?
      • significant properties
      • file types
    • 3.3 Metadata and Documentation
      • project level
      • file level - We normally require captions to go with images. Sometimes the filenames used are long and descriptive enough to provide a caption, but often this won't be the case and the depositor will need to be approached to get captions. If future users don't know what the image is of then they won't be a lot of use really! As mentioned above, it is important to retain any embedded metadata such as EXIF information. In Paint Shop Pro 'SHIFT+I' displays image information - choose EXIF and tick all boxes to view all embedded metadata. Fortunately, Paint Shop Pro, Photoshop and Image Magick all retain this information when converting files to .tif format.
      • standards specific to #
    • 3.4 Structuring your archive

  • Copyright
    • specific copyright considerations for each guide.

Embedded Meta Data#

The process of embedding meta data within images, such as geo-tagging TIF files or producing EXIF information via a digital cameras, has become common practice. Care must be taken when converting or reproducing source images that this meta data be retained and much of the software we often use to convert JPEG to TIFF for preservation do not appear to preserve the EXIF metadata of the original JPEG (eg Image Magick, IrfanView). A quick test shows that Photoshop will preserve the EXIF tags.

There has been much discussion regarding when EXIF metadata would, or would not, be a significant property of a deposited image. The general consensus has been that there are obviously times (such as the VENUS examples) where EXIF metadata is inherently significant, but that EXIF metadata could be considered valuable whenever it could be seen to be valid and accurate, particularly if it has been created at the point of origin i.e. by camera software rather than later image editing software (which can often remove EXIF tags). If embedded EXIF metadata is seen to be valuable, it should be preserved.

Although it is possible to preserve JPEG EXIF within the TIFF tag structure it is better held in a separate file, avoiding the risk of loss or corruption during later migration and making the metadata more easily accessible. Extraction of EXIF fields is relatively straight forward, with a number of free tools available.

It is suggested that EXIF metadata be extracted and stored in a simple XML structure, with a text file of metadata per image. #image_filename#.meta has been suggested as a standard naming scheme, with these XML files to be stored in a "documentation" folder along side the preserved images. Other embedded metadata, such as IPTC or XMP, might also be extracted into this structure. Adding this functionality to the ADS Toolkit GUI would be beneficial in speed of working and standardisation of procedure. The ability for this to be ingested as a file-level metadata stream by Fedora has also been discussed in CATS meetings.

The issue of the possible impact of the additional files on the charging policy was discussed. The very small size of these files, with respect to the preserved images they accompany was pointed out, and is was generally agreed that these are files created for our benefit in managing the archive (as the metadata could be preserved within the image file itself).

--Jon Bateman, 31-Aug-2006

We need to look at our policy re. RAW files. Probably worth taking these as we can no doubt get viewers for the various types but I still think that we should archive as tiff with the metadata separate.

See also AHDS 'Digital images archiving study' at http://ahds.ac.uk/about/projects/archiving-studies/. Is there anything in this study that is useful to us?

Also worth watching out for Windows Media Photo - Microsoft's rival to the JPG

The InSPECT project (http://www.significantproperties.org.uk) is defining sig props of raster images - will be some useful stuff we can pull out of this report when it is finalised in Spring 2009

New DPC technology watch report on JPEG 2000. Needs a read and linking from this document I reckon: http://www.dpconline.org/docs/reports/dpctw08-01.pdf

The Koninklijke Bibliotheek, National Library of the Netherlands, has published a report on possible alternative file formats for storing master images from mass digitisation projects. Uncompressed TIFFs, the KB’s preferred format so far, take up far too much storage capacity to be a viable storage strategy for the long term. The report is available from the KB website.