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How to digitise slides. Recommendations and working lists for the reproduction of a very special artefact

Checking lists to organise the internal workflow, and to outsource the work

Checking lists help to control whether all the important aspects of a scanning project have been thought of. The following lists are not exhaustive. They concern the collection to be scanned, the physical state of the objects, the scanning instrument, the scanning order, parameters for the evaluation of collection segments etc.

 

  1. Checking lists to prepare and organise the workflow
  1. Check what in the collection has also to be scanned:

1.1. Is contextual information available on the object, which should be scanned as well: e.g. a text that accompanies the slides series? Should it be scanned together with the slide(s)? Should it be scanned at a later moment?

1.2. Are supplementary objects in 3D to be photographed: e.g. the box containing the slides or the lantern it was once sold with?

 

  1. Check the physical state of the object:

2.1 What positive aspects may the scanning have for the artefact: e.g. to rescue of the image on the slide from vanishing (due to acute and heavy disintegration)?

2.2 What negative aspects may the scanning have for the artefact: e.g. damaging the integrity of the object by putting it in the scanner?

2.3 Is the object dirty and should it be cleaned before being scanned? If it needs to be cleaned, will this eventually damage the slide?

2.4 Does it have to be repaired before the scanning? Should it even be restored?

2.5 What is best for the material that has to be scanned: to be handled now? In the near future? Much later? Not at all?

 

  1. Check what has to be scanned how:

3.1 Is the object translucent (thus ideal for reproduction with transmissive light) or opaque (thus better captured with the help of reflective light)? Is the object’s surface heterogeneous (possibly use two digitising methods: one scan perpendicular from above, one photo from a different angle with a different lamp (spot) to show structures in the frame and image), or homogeneous (one digitising method)?

3.2 Is the slide flat or voluminous (three-dimensional)? Can all information desired be retrieved with the scanner or does the object need additional digitisation with a photo camera? If three-dimensional: should this quality be kept in the reproduction?

3.3. Is the slide small enough to be put on the scanner? Will its proportions leave enough space around its edges for an “overscan”?

3.4 Is it movable and will this quality be adequately reproducible by the scanner?

3.5. Is the slide only black and white (no greys)? Does it contain e.g. (simple) drawings and diagrams that ask for a correct reproduction of lines, dots and surfaces?

3.6. Does the slide show variations in grey (grey scale or half-tone images) or is it purely black and white? Does it contain nothing than black text on an otherwise empty (thus 100% transparent) glass?

3.7. Is the slide a positive which may be difficult to reproduce correctly due to aspects such as half-tones, “faded” looking pastel colours, weak / hard contrast? Does it have large transparent and opaque areas which may risk clippings in white and black? (When only two “tones” are registered – white (full light) and black (absence of light) – scanners can have difficulties to reproduce pure black and pure white.) Are these characteristics historical traces which should be preserved / erased in the reproduction?

3.6 Is the slide a black and white negative that will be difficult to scan due to its weak / hard contrast, narrow / wide grey scale, or just monochrome appearance with large black and white areas which may not be correctly reproducible?

3.7 How many “slide sets” (e.g. images of a specific collection, slides produced by the same company) can be created that ask for the same scanning parameters, allow one scanner setting and make the naming of the files easier? This is an essential point for a successful workflow.

 

  1. Check the order of the scanning (workflow):

4.1 Does the scanning have to be done in two or more batches?

4.2. Which part of the collection should be scanned first, which second etc.? Is there any reason to deal with one part first?

4.3 How large is the working space? How many slides can be kept “on location” to scan them all in one “portion” (to keep the setting for slides that are more or less identical in their materiality)? Can they stay there for a while or does the scanning have to be done in a specific time slot as other archive departments need the scanner?

4.4. Does the workstation and digital asset management have enough free memory to receive the scans? For how long will their digital storage space be sufficient?

4.5. Will the workstation be needed for more than just quality checking (once the scanning is done)? Is in-house post production intended? Right away after digitising the slides or later?

4.6. Which staff members will be involved in the whole process besides the operator: e.g. to fetch and bring back the slides (storage department), to clean them (restoration department), to re-name the files (documentation department), ingest them in the media asset management (IT department) etc.

4.7 What would be the fastest / safest / simplest / cheapest way to organise the scanning process: e.g. steps needed for a smooth workflow, analysis of potential critical moments, planning of convenient moments during the next 12 months to do the scanning etc.

 

  1. Check the parameters to be used for (different parts of) the collection:

5.1 What will / should be done with the scans? How should the scanner be programmed to achieve this?

5.2 Do different parts of the slide collection need different scanning parameters? Which could these be?

5.3 In how far will this influence the workflow?

5.4 Will the parameters chosen for capturing support the technical needs of the post production work? Will the scan quality be sufficient for all the applications planned?

5.5 What would be useful for the future users of the scans (archivists, researchers, publishers etc.): e.g. to scan the slide with a rule (to show the dimensions of the slide) and a colour chart (to give colour parameters for orientation), to scan the whole slide (with some space around the edges to recognise the state of the protection paper and the precise form of the frame) and not only the image, to scan the slide from two sides to preserve inscriptions, embossed signs etc.

5.6. What can’t be reproduced with a scanner (e.g. manufacturer’s details on the small edges of the frame) and which slides need another solution (photographing)?

 

  1. Checking list to prepare the scanning area
  1. Is there enough space for the operator to move easily around the scanner without the risk of damaging objects? Are all potential tripping hazards eliminated to avoid accidents?
  2. Is there enough space to set shelves / tables to keep the slides to be scanned separate from those that have been scanned already (to avoid double scanning)? Where can the slides be put to acclimatise properly before being photographed?
  3. If working with control monitors: does the light situation in the working space suit the necessary standards (low / dimmed light of one kind of lamps, no direct light falling on the monitor)?
  4. Are there enough light sources (to be switched on/off) to make the working space bright enough: e.g. to read inscriptions on (wooden) frames, to control the order of the delivered slides etc.?
  5. If mass scanning is needed: is the arrangements of the shelves / tables practical to avoid unnecessary coming and going between them?
  6. If different operators work on the same “batch”: how can be made sure that all concerned parties are informed about what has been done already or has still to be done (communication procedure)?
  7. If the scanning has to be interrupted temporarily: how to make sure that the interruption doesn’t cause problems for the staff members or for the material, e.g. can the operator leave her/his stuff in a box / drawer? Is there a facility and a procedure to protect the not yet scanned slides to avoid bringing them back into (cold) storage?
  8. If additional photographing is needed: where to keep a still-camera and a repro-stand with good light sources easily available but not staying in the way?

 

  1. Checking list to prepare the scanning session
  1. Check the cleanliness: scanning pane, light unit, closing lid and slide should be absolutely clean from dust, particles and finger prints; if not, clean them from dust with “liquid” (compressed) air and from finger prints with a clean kitchen towel (to leave no fuzz) to avoid annoying retouching work.
  2. Check that the scanner is programmed according to the standards set by the archive. Homogeneity in settings will also allow migration to be done later automatically.
  3. Make sure that the scanner is cleaned after each scan as e.g. dust, dirt, loose colour particles, dirty finger prints, hair, fluff etc. will be reproduced in the digital copy as part of the slide.
  4. Check whether the glass pane has scratches. If so, change it to avoid that black marks from the scratches have to be eliminated in post production.
  5. Make sure that working rules given by the archive are respected before, during and after scanning (e.g. that gloves are worn when handling slides).
  6. Make sure by implementing the latest “Profile Connection Space” (PCS) that the colour information is translated correctly between scanner, workstation and other devices.
  7. Make sure to calibrate the scanner (before each scanning session) and the monitors used in the workflow (daily), otherwise the registered brightness, hues and contrast may not be reproduced correctly and may lead to erroneous manual programming. If for instance a digital screen (television) or a beamer is used for quality checks, they have to be calibrated as well. It is important to guarantee that the screen is clean and the monitor the brightest light source in the room.
  8. Don’t forget to adjust the white balance to counterbalance a possible tint of the scanner lamp.
  9. Make sure that workstation, external hard discs and other digital storage means have empty memory capacity to receive the scans during the (whole) working session.

 

Hints by the scanner operator:

These recommendations are taken from different books written by specialists in digital reproduction. They complete advices published in the section “Recommendations and general remarks by the working group of “A Million Pictures”, the persons responsible for “Lucerna” and the Trier “eLaterna Archive”, as well as practitioners who scan and photograph slides.

 

  1. Arrange the original in the right precise position (parallel to the frame of the pane) to avoid that the reproduction has to be manipulated in post production by correcting its horizontal position (Ang 2006, p. 158; Kraus 1989, p. 68).
  2. Put slides or diapositives side-inverted on the glass pane, which means that inscriptions can be read correctly in the pre-scan (Kraus 1989, p. 68).
  3. Put the slides or diapositives next to the edge where the lamp of the scanner is. This avoids that the light unit has to cross a part of the pane before starting to scan the element (Kraus 1989, p. 68-69).
  4. Put the upper edge of slides or diapositives near to the edge where the scanner’s lamp is “parked” (normally indicated by a zero where the two rulers meet in the corner) to avoid horizontal flip-floppers in post production (Kraus 1989, p. 69).
  5. Don’t clean the pane from dust or particles by breathing upon the glass, because breath contains humidity (Ang 2006, p. 158).
  6. Kraus indicates that for a high-end scan, transparent oil or gel is put on the glass pane of the scanner, then diapositives and negatives are placed on the liquid, which acts as a filler of scratches to make them almost invisible or to prevent that air gets between the pane and material to be digitised (Kraus 1989, p. 159).
  7. Scan half-tone images in colour and turn them later into grey scale images as this way scans using the three RGB colour channels can easier be colour corrected during post production (Kraus 1989, p. 81).
  8. Scanners propose a setting for half-tone images to profit of the whole grey scale. In the half-tone mode only light values are noticed. Kraus states that black text, printed on a transparent slide or photographed on a white background, can be scanned in this modus with lower resolution, because in a grey scale image the edges of e.g. letters are “smoothed” by grey pixels and look sharp (Kraus 1989, p. 74-77, 79, 90).
  9. For high-contrast documents a special setting translates light values into the two tones black and white, thus turns the reproduction into a “bi-tonal” image. The scanning software proposes to choose a so-called “threshold value” on the scanner’s grey scale to determine whether a picture element is dark enough to be depicted as black or clear enough to be shown as white, thus all light values below and at the threshold value become black, the rest white, e.g. a value of 128, which is half way between black 0 and white 255, will turn 50% of the grey values into black and 50% into white. This can change the aspect of the image considerably as even the slightest grey values has disappeared. The question is whether this “thresholding method” is acceptable as it falsifies the reproduction of the original: all potential grey half-tones captured from the digitized object are lost (D’Amato 2000).
  10. When defining in pre-scan the “white point” (the light value taken from the original slide that should be reproduced later as “white”, e.g. the value 220 making all nuances between 220 and 255 pure white), this should be done for each colour channel separately to avoid possible tints. To determine the black point should also not be forgotten. A manual correction of the light values avoids that the slide is eventually scanned too dark or to bright (Kraus 1989, p, 104-105).
  11. Never scan an object too bright, as in the clear parts of the image the information is lost; when scanned with too much density, the dark parts can be brightened in post production and will still contain details which were not visible to the eye before (Kraus 1989, p. 106).
  12. Rescan the object when “white noise” appears in the scan; the scanner may have done a “miscalculation” during the first run (Kraus 1989, p. 168).
  13. Don’t digitise a slide that has just come out of a climatised vault. Considering the recommended conservation conditions for photographic glass plates (by ISO 18934:2011) – 0° to 8° Celsius is seen as excellent (deep freezing is considered for newer ones as excellent but older plates risk “brittleness and detaching of the emulsion”), 8° to 16° is still considered as “good”, 16° to 23° Celsius as “acceptable” – it is obvious that a temperature shock can damage the artefact (Kistenich-Zerfaß 2017, p. 14). As to preservation conditions: relative humidity should not exceed 60% as an environment of more than 60% at a temperature higher than 10 degree Celsius offers “favourable” climate conditions for mould which attacks organic dyes.
  14. A scanner lamp sends intense light through the slide. When scanning without pauses, the glass pane can get warm, but not hot. Nevertheless, strong lightning can harm the slide. Lantern expert Damer Waddington (1995, p. 11) made some experiments with slides in projection. He observed that the darker parts get the “full force of the heat” while the transparent glass lets pass most of the light and “absorbs only a small proportion”. Under the influence of the lantern, light dyes may show craquelé, little particles can fall off, in any case an unevenly heated glass is certainly put under stress. More research is needed to show whether this effect may also be caused by the intense light beam of a scanner.

 

 

  1. What to check when the scanning is done by a professional company

“Heritage institutions can undertake digitization and data conservation themselves, provided they have or can obtain the necessary infrastructure, knowledge, funding and staff. The volumes of media that are to be digitized must be sufficiently large in order to exploit economies of scale that justify such a move and the associated expenditure. Otherwise, it is more cost-effective and reliable to delegate the task to specialist service providers.” (Jarczyk et.al. 2017, p. 24) In their analysis, the Swiss authors of the Memoriav recommendations on scanning film (http://memoriav.ch/recommendations-dafv-en/)  examine carefully the question “In-house or outsourcing?” When working with a professional service provider, it is important to frame the “relevant requirements” in a contract or a written agreement. It should clearly define what the supplier has to do, and should not do. The Swiss cultural heritage institution also recommends strongly to include quality control in the specifications.

 

It is necessary to make sure that the following deliverables are agreed on by the service provider:

  1. uncompressed (“raw”) data (e.g. RAW- and eventually TIFF-files) as “preservation file” and a “proxy” e.g. JPEG-files to serve as “access file”; other files can always be produced from the raw scan;
  2. a colour depth of 48-bit (3 x 16-bit per colour channel) suitable for TIFF; JPEG has only 24-bit (3 x 8-bit) which is not enough for post production;
  3. information on the scanner that will be used and its potential in resolution, colour depth and density range;
  4. confirmation that the scanning will be done by the company in-house and under no circumstances will be outsourced;
  5. confirmation to get test results with slides selected for their high / low contrast, high / low luminosity, missing / good sharpness, strong / pale colours, nuances in details, different forms (sharp edges, circles) etc. (NB: the results should be assessed by more than one staff member).
  6. confirmation that no (automatic) image correction software will be used without preliminary agreement by the archive to suppress scratches and dirt, enhance luminosity and sharpness or counterbalance colour. (Correction software can limit the potential of the “raw scan”. Besides, all these “flaws” can be treated in post production.)
  7. if no fixed price per batch is settled: delivery of a price list for all proposed services to make costs transparent (JPEG-files are standard, but TIFF-files may cost more, the carriers may be expensive).
  8. information about the carrier (external hard disk, CD-Rom, USB-stick, memory card, “cloud” transfer services etc.) that will be used to deliver the scans; the naming of the files by the company is another point to be agreed on.
  9. information about the time the scanning will take, and about factors (holidays etc.) that can disturb the planning;
  10. name and contact data of the person(s) responsible for the scanning;
  11. covenant to provide regular news on the course of the scanning (in case of mass scanning);
  12. written agreement with the price and scanning parameters, the planned schedule, the quantity of slides that the company can deal with during a given period of time and the intervals in which to bring new slides, receive scans and get back scanned material;
  13. confirmation that the company has an insurance (in case slides are damaged and have to be restored).

 

The authors of the Memoriav recommendations propose similar requirements: “If you are working together with a service provider, they must be prepared to provide you with details of their equipment and explain and discuss the signal paths and procedures they use, and this should form part of a work contract. It should also be possible to view their facilities – the details on their website will not usually be sufficient.” (Jarczyk et.al. 2017, p. 30)

 

  1. The series “Guides to Quality in Visual Resource Imaging”

The Guides were written by experts on behalf of the Digital Library Federation and other institutions. Although they date from the year 2000 for the reproduction of photographic images, they give valuable advice which can be also used for slides. The idea behind the series is to disseminate information in order to avoid the ‘reinvention of the wheel’: “Museums, archives, and libraries worldwide are converting visual resources into digital data, and in each case managers of those conversion programs face the same series of decisions about how to create the best possible image quality.”  (https://www.oclc.org/research/publications/library/visguides/#background)

 

Linda Serenson Colet (2000) wrote the first guide titled “Planning an Imagining Project”. It contains helpful hints on how to start the digitisation project and what has to take care of when points come up such as “whether the image is being created for a use-specific project or a use-neutral archive”, “whether the project can be done within one’s institution, outsourced to a vendor, or accomplished through a hybrid approach” or “how the digital initiative can support the activities of specific departments and projects within the institution”. It is interesting to check their control lists which go far beyond the short one we have set up for the digitisation of slides.

 

Colet also gives some general recommendations to guarantee a higher efficiency:

“[…]

  1. Set up a physical workspace that is conducive to the safety of the originals and the workers. Digital capture operators should have comfortable work setups when doing repetitive tasks.
  2. Balance quality controls with production targets for an efficient workflow.
  3. Chase the bottlenecks in the production flow: as one is removed, another may arise.
  4. Keep administrative tasks (storing metadata) to a minimum. Unless a dedicated staff member in the studio is assigned to do this in the assembly line, this task should be done outside the studio.
  5. Consider ways to continue the workflow outside of the studio (storing the master image, disseminating the derivatives, and creating an enterprise-wide solution for archiving and accessing). An institution that is not set up for the massive organization that is required once the digital file leaves the studio, may have to secure outside services for this purpose.
  6. Organize work in batches (i.e., by size and by like medium) for maximum efficiency.”

(https://www.oclc.org/research/publications/library/visguides/visguide1.html)