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Still images

This page provides specs for digitising still images, including minimum standards and best practice for digital conversion and born digital images.

Minimum standard

Reformatting from Hardcopy

  • Scan 20 x 25 cm (8" x 10") images in uncompressed TIFF format at a resolution of at least 300 PPI
  • Smaller  images (< A4, A5, A6, postcard and 6" x 4") should be scanned at higher resolution of 600PPI
  • The dimensions of the longest side should be no less than 3000 pixels in length
  • Use sRGB colour space (this is the common colour space used in consumer digital scanners and cameras)
  • Save master files in 24 bit per pixel (i.e. 8 bit per R, G & B channels)
  • It is possible to scan 35mm film (slides or negatives) on a flat bed scanner with a film scanning attachment.  Use highest resolutions available to record fine details.  Dedicated film scanners are recommended for this task
  • Files created by digitising black and white negative film may be saved as 8 bit greyscale images

Born Digital

  • Capture digital original photographs (in camera) at a resolution of at least 6 Megapixels
  • When capturing live events, portraits, architecture, etc, in JPEG format on consumer level cameras, use highest quality, largest image settings available on the camera.  Using these settings will give images with pixel dimensions of at least 3000 pixels on the long side
  • If reformatting original materials, use 35mm style digital cameras with quality lenses (preferably non-zoom) on a copy stand. Use highest quality, largest image settings available on the camera.  Using these settings will give images with pixel dimensions of at least 3000 pixels on the long side and allow for cropping if necessary
  • Use sRGB colour space
  • Save master files in 24 bit per pixel (i.e. 8 bit per R, G & B channels)

Best practice

Reformatting from hardcopy

  • Scan 20 x 25 cm (8" x 10") images in uncompressed TIFF format at a resolution of at least 600 PPI
  • Smaller images (<A4, A5, A6, postcard and 6" x 4") should be scanned at higher resolutions
  • The dimensions of the longest side should be no less than 5000 pixels in length
  • Save master files in  24 bit per pixel (i.e. 8 bit per R, G & B channels) for reflective materials (photographs, prints, manuscripts, objects etc)
  • Use Adobe RGB 1998 colour space
  • When scanning 35mm film (slides or negatives), higher resolutions e.g. 3000 PPI are necessary to record fine details.  Dedicated film scanners are recommended for this task
  • Save master files in 48 bit per pixel (i.e. 16 bit per R, G & B channels) for transparency and negative materials
  • Files created by digitising black and white negative film may be saved as 16 bit greyscale images, colour space: Grey Gamma 2.2

Born Digital

newpapers_wperson.jpg

Curator working with film

  • Capture archival-quality digital original photographs at a resolution of at least 10 Megapixels in a lossless format
  • When capturing live events, portraits, architecture, etc, use highest quality, largest image settings available on the camera.  Using these settings will give images with pixel dimensions of at least 5000 pixels on the long side.  Using RAW as the capture format is preferred
  • If reformatting original materials, use 35mm style digital cameras with quality lenses (preferably non-zoom) on a copy stand. Use highest quality, largest image settings available on the camera.  Using these settings will give images with pixel dimensions of at least 5000 pixels on the long side
  • If expertise and resources are available, capture images as RAW files (type will vary according to camera system) and process to produce high bit depth TIFF master files
  • Use Adobe RGB 1998 colour space
  • Save images as uncompressed Tiff files (not RAW format) in high bit depth (48 bit per pixel i.e. 16 bit per R,G &B channels)


The National Library's Image capture standards include a table of digitisation specifications.
JISC Digital Media (formerly TASI) - Advice on Still images includes a set of recommendations for digitisation specifications.


Rationale

Creating an enduring, high-quality digital image at the time of capture is of considerable benefit.  Once the master image file is created it can be stored, accessed, converted, and managed in many different ways.

In general, master files have the following attributes:

  • Maintain the essential features and information of the original
  • Represent the best copy produced by a digitising organisation, with best defined as meeting the objectives of a particular project or program
  • Represent digital content that the organisation intends to maintain and manage for the long term
  • Are created primarily for the production of a range of copies used for specific purposes (e.g. derivatives such as production, web or print media files)
  • Document the image at the time of scanning, not what it may once have looked like if restored to its original condition

Digitisation should be done in a “use-neutral” manner, and should not be geared for any specific output.  A well made master file can be repurposed in a number of ways, each optimised for specific output needs e.g. thumbnails, web, print or publication.

RAW files are useful in capture and working stages and many cameras now offer RAW format as an option. They are relatively small files, which contain maximum image quality information but are proprietary and subject to constant upgrades and versions with limited backward capability.  Professional SLR cameras offer RAW as a capture option but very few offer TIFF because of the large file sizes associated with TIFF format. It is recommended that RAW files are converted to high bit depth (48 bit per pixel) TIFF master files before archival storage.  Skills in image processing and digital workflow programs like Adobe PhotoShop are required when working with high bit depth and RAW file formats.

Modern digital cameras are sophisticated, high resolution devices.  10MP is the benchmark for the lowest resolution sensors currently available.  Images taken with these will provide large files with capacity to produce fine detailed prints at sizes greater than A3.  It is important to note that sensor sizes and resolution are not the only factor to consider - lens quality and operator skills are still key factors in determining true imaging quality.

Best results from scanning 35mm film will come from dedicated film scanners.  These are becoming harder to find, as more image creation is born digital, not reformatted from hardcopy.  Nikon Coolscan 4000 and 5000 models are still available second hand.

When acquiring born digital images from donors, collections managers will often have no control over the quality of the images.  If the image is deemed of value, the best possible copy should be requested to be accepted into the local studies collections as the archival master.

While high bit depth files (48 bit) may be the preferred archival master file format for many types of digital objects (they contain greater colour and tonal information), they are double the size of an equivalent 24-bit file.  Even though storage costs have dramatically decreased in the last few years, these large files will rapidly use hard disk space and are slower to work with on standard home or office computers.  Some non-professional software applications may not be able to display these images.  In general practice, high bit-depth files need only be created for rare or valuable collections or from negative and transparency materials where extended tonal and/or colour is required.

JISC Digital Media - Print size and File size calculator is very useful.