General reproduction standards in scanning
2.1 Reproduction standards in scanning cultural heritage:
Institutions such as the British Library recommend standards for each type of material (opaque / transparent, printed / typed / photographed, paper / glass, negative / positive): see Julianna Barrera-Gomez, Digitization Guidelines for Photographs and Textual Documents, University of Michigan, July 2012 (http://deepblue.lib.umich.edu/bitstream/handle/2027.42/98757/BHL_digitizationguidelines_20120719.pdf?sequence=1&isAllowed=y). Also the German Research Foundation Deutsche Forschungsgesellschaft (DFG) has published guidelines on Digitisation (“DFG-Praxisregeln ‘Digitalisierung’”) (www.dfg.de/formulare/12_151/12_151_de.pdf).
References from practical experience are given by the The National Film and Sound Archive (NFSA) in 2010 by Shingo Ishikawa and Darren Weinert (https://www.nfsa.gov.au/latest/glass-cinema-slides-3) and by Kathleen Brosseau, Mylène Choquette and Louise Renaud from the Canadian Museum of Civilization Corporation in 2006 (http://museumsassn.bc.ca/wp-content/uploads/2015/01/smcc_numerisation-cmcc_digitization-eng.pdf). They should be considered “just” recommendations (not obligatory) as they are of general nature, not specifically laid down for slides. They may not be adequate for the special conditions of a collection or a particular use of the reproductions.
Each archive may get inspired by external recommendations but should determine its own standards according to the needs of its collection and the demands of the institution; and it should not forget to take into account the consequences of its choice (exchangeability of data, ulterior migration, digital storage space etc.). Self-issued reproduction standard should cover all requirements, from a low resolution purpose (e.g the use in a power-point lecture, the inset for internet-demonstrations on the museum’s online-database or external presentations on websites such as LUCERNA, Flickr and Europeana) to high resolution use (e.g. printing, screening, migration, file “derivatives “). The medium with the highest demand should be the landmark for image resolution and colour depth.
As the National Film and Sound Archive (NFSA) stresses: “Scanner settings will depend on the end product. If a large poster is to be produced from the digital file, the scanning operator needs to know the final poster size in order to calculate the correct output file size. Calculating these requirements involves a simple mathematical formula. To set the largest size that may be printed from the distribution file, divide the pixel size of the image by the printing resolution required, for example: 5004 pixels / 300 ppi = 16.68 inches.” (Ishikawa, Weinert 2010)
There are no commonly agreed on and practised standards for scanning slides yet as there is for film and photography. So for now the basic principle could be: it is always better to reach for a higher digital quality and scale down if needed. Scaling up means addition of mathematically created pixels with a risk of digital artefacts and the “chance” to create a strange looking image.
2.2 Reproduction standards in photographing cultural heritage
As photographing art works in museums is a long-time practice starting in the midst of the 19th century, certain standards have been developed. An interesting experimental project was described by Franziska Frey and her colleagues in Benchmarking Art Images Interchange Cycles. Final Report 2011. The report informs about the ins and outs of photographic reproductions (on paper as “hardcopy” and digital as “softcopy”) as they were used around 2010 in some of the biggest US-institutions. The authors give recommendations but don’t consider them more than an addition to already existing guidelines such as the Guidelines by the Universal Photographic Digital Imaging members (UPDIG) (http://www.updig.org/index.html), the “Digitization Guidelines” by the Federal Agencies Digitization Initiative (http://www.digitizationguidelines.gov/guidelines/FADGI_Still_Image-Tech_Guidelines_2010-08-24.pdf), the standards developed by the International Organization for Standardization (ISO) or Metamorfoze Preservation Imaging Guidelines (https://www.metamorfoze.nl/sites/metamorfoze.nl/files/publicatie_documenten/Metamorfoze_Preservation_Imaging_Guidelines_1.0.pdf) on image quality by a Dutch consortium of museums, archives and libraries. A résumé of the most important recommendations by these institutions can be found in Frey (2011, 127-128), links to the mentioned guidelines in the section “Links to related websites”.