Digitising the ACMI Collection: part II
We've been collecting films, footage and moving image art on all kinds of formats since 1946, but the last 12 months has been all about going digital. Digitisation of obsolete and rare formats means our collection items are safe, and it also means they can be accessed from anywhere in the world on our YouTube channel.
Our collection includes most film formats (35mm, 16mm, 8mm and 9.5mm), and an array of tape and disc formats including everything from compact-VHS and laserdisc to DVD. We also maintain the legacy equipment needed to playback the films. We've got ZIP drives, Betamax and U-Matic tape decks and a wide range of film handling equipment.
We’ve currently got a few great tools at our disposal, including a 4K 35mm/16mm film scanner; a high-def scanner for Standard 8, Super 8 and 9.5mm film gauges and analogue to digital conversion; and a time-based corrector for our analogue tape material.
This is what we do with them.
Step 1: repair
Once a title has been prioritised for digitisation, the film must be examined. Where multiple prints exist we select the best one. Our technicians check for scratching, dirt, colour fade and most importantly shrinkage and perforation damage. Where necessary repairs are made by hand to ensure safe transport through the scanner.
Step 2: digitise
We digitise 35mm film at 4K, 16mm at 2K and smaller gauges at high-definition. Digitisation is generally done at 24 frames per second (fps) though with fragile materials this may be reduced to as low as 3 frames per second. So in ideal circumstances a 10 minute film takes 10 minutes to record but in the worst case as long as 80 minutes.
Following the initial scan a separate process is undertaken to capture the audio. In the case of 35mm and 16mm, this is via software extrapolation and transposition from an image of the soundtrack to a .wav file.
In the smaller gauges a separate pass is required to capture the sound from the magnetic track. Typically audio extraction adds another 30 minutes to each digital capture.
Our film scanners allow us to capture an overscan image rather than merely the cropped version to ensure the complete image as well as optical soundtrack is recorded. What has been interesting to discover is that many home movies have additional content recorded between the sprocket holes.
Much of the home movie material we are digitising was recorded at speeds other than 24fps. It's often difficult to determine the exact original speed: be it 15fps, 16fps or 18fps. For this reason we've adopted the following strategy. High resolution preservation masters are stored as overscans at 24fps and we produce access copies as both cropped and overscanned versions at the original presentation speed. Our rationale is that the preservation master allows the widest range of reworking in the future, while ensuring the access versions are as faithful to the intentions of the filmmaker.
Step 3: quality control
Once each digital file is trimmed and named according to our cataloguing convention it must be checked to ensure it is a faithful rendition of the source material and no artefacts have been introduced during the digitisation. Again, this is currently a real-time process – taking the same time as the film’s running time. Investigations are ongoing as to how we can improve this process with computer-based QC tools.
Step 4: cataloguing and access
Once each file is QC’d it is moved to either the preservation or access server location and a digital fingerprint (called a checksum) of each file created.
Our cataloguing team prepare the descriptive data for each title to make them discoverable by users of our online catalogue.
We are excited to be increasing access to our collection but as this brief snapshot demonstrates the path from analogue to digital involves numerous steps and is not something that can be hurried. With 120,000 hours of material in the Collection we have many years of work ahead of us!
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