Digital Gateway
Washington University Digital Gateway

Digital Imaging Standards

Hardware & Software

DLS has the following scanners available for internal library use. Please contact Digital Library Services if you would like to use one of these scanners

  • Atiz BookDrive DYI
  • Atiz BookDrive Pro
  • two Epson flatbed scanners

The Atiz scanners use BookDrive capture software to scan images and editor software to process images from RAW to TIFF files. Please ask DLS for assistance in using this software.

The Epson scanners use Epson capture software for scanning images

DLS recommends Adobe Photoshop for processing and editing images

Adobe Bridge is recommended for managing images and tracking progress


Image Capture Requirements

  • Capture documents from outside front cover to outside back cover and spine, if possible
  • Images should be kept in original order and files should be named in original, serial order
  • Page images should be captured at one single page per file and two page spreads should be captured as two files
  • Page images should be rotated (if applicable) so images are in proper reading order when opened
  • Folded documents should be unfolded before imaging
  • Oversized documents should be captured with copy stand and digital camera
  • Include a documents' unfolded size when considering image capture method
  • A book cradle should be used to support fragile materials
  • If documents fit easily onto standard flatbed scanner and will not be damaged by being flattened, it is acceptable to use a flatbed scanner
  • If volumes have missing pages, mark these with a missing page target (suggested: 8.5x11in blank white page with "missing page" in minimally 36 pt type)
  • If pages are missing, including missing page files in serial order in event that these are added later

Pixel Dimensions

  • Pixel dimensions of the digitized image are dependent upon the size of the original
  • For most files, at a minimum, images should be captured at 4,000 pixels along the longest side

Color


Color Space

  • RGB is the recommended color space for archival master copies
  • Standardized color reference points should be used to calibrate the imaging device
  • For grayscale: use a Photographic Gray Scale (such as Kodak Gray Scale) to ensure gray values fall within recommended aimpoints. Color bars with white, midpoint, and black aimpoints may also be used.
  • For color: compare with color bars (such as Kodak Color Control Patches) to ensure accurate color reprensentation
  • When measuring aimpoints, measure image area of at least 5x5 pixels
  • See NARA's Technical Guidelines for Digitizing Archival Materials for Electronic Access: Creation of Production Master Files - Raster Images pages 35 and 36 for recommended aimpoints for grayscale and color

Image Color Requirements & Bit Depth

Color

  • Color imaging should be used when color is an important attribute of the document
  • Color imaging should be used in the majority of cases
  • Images should be captured at a minimum of 24-bit-color
  • If possible, to preserve the highest level of detail, 48-bit-color should be used for archival purposes.

Grayscale

  • If color content does not exist or is not deemed significant, the material may be captured in grayscale
  • Images should be captured using 8-bit grayscale
  • If the imaging operator is unsure whether to capture the image in color or grayscale, it is safe to assume that color image capture should be used
  • Operators should contact Digital Library Services if grayscale capture is questionable.

Bitmap

  • Bitmap is rarely desirable
  • Please note that some batch processes may be inhibited when using bitmapped images (for example: batch processing tiffs to jpegs using Photoshop)

Resolution

  • Images should be captured at 600ppi at original size
  • Resolution should be achieved without interpolation, if possible
  • If imaging equipment is unable to capture images at 600ppi, contact Digital Library Services for assistance

File Formats

Master Files

  • Files should be saved in an uncompressed, lossless format - JPEG2000 (.jp2, not .jpf) is the preferred file format
  • When saving files as JPEG2000, ensure that lossless, JP2 compatible, include metadata, and XMP boxes are checked to preserve technical metadata
  • Lossless, LZW compressed TIFFs are acceptable aternate file formats

Access Images

  • Access images may be compressed format, such as JPEG and migrated to a lower resolution for web delivery

File Names

  • Image files should follow file naming convention set for each set of materials
  • File names should be constructed so files can be easily located
  • File names should facilitate management of variant forms of an image (master file, access file, thumbnail file, etc.)
  • File names should never contain spaces and should not limit interoperability, such as using system specific syntax or characters. The only special characters used should be underscores, hyphens, or periods
  • DLS recommends: identifying project code, date of publication, and serial order number in filenames to ensure each filename is unique

Quality Control

  • At minimum, 10% of each batch of digital images should be inspected for compliance with above specifications
  • All images should be in focus
  • Digital image should be accurate representation of the original, including clearly legible text and sharp illustrations

Metadata

A discussion of metadata management is needed before beginning any digital imaging project, the depth of which is outside the scope of this resource. Please consult with Digital Library Services if you have questions about managing your project data.


Minimal recommendations

Be consistent! Agree on authority files (LOC, ULAN, AAT, etc.) or local terms and ensure they are used Ideally metadata should be encoded in XML using DC, VRA, CDWA or another accepted standard. If XML is not an option, Excel spreadsheets should be used


Delivery & Preservation

DLS recommends making image collections available online via ARTstor's Shared Shelf or Omeka. DLS can assist you in developing online collections

For preservation, DLS recommends storing images on a secure file server and ingesting image metadata in Fedora


Sources
Getty Introduction to Imaging - Image Capture
University of Michigan Digital Library Production Services Digital Conversion Unit
LOC - Image Quality Standards by Document Type and Expected Outcome
NARA - Technical Guidelines for Digitizing Archival Materials for Electronic Access

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