Standards

Digitisation standards provide guidelines on resolution, colour space and bit depth for the production of a master image file [1] and a derivative image file [2] below. To deposit the digital images for a long term retention, CUHK Library digital collections adhere to the following requirements according to different sources of material. However, depending on the specific objectives of digital collections, adopting a higher resolution and special formats are desirable for some materials.

Printed Materials

Source Master image file format Derivative image file format
Bit depth Colour space Resolution Resolution Format
Book 24-bit RGB 400 – 600 dpi 200 dpi JPG
News clipping/Periodicals 1-bit Bi-tonal 300 dpi 150-300 dpi PDF
Manuscript 24-bit RGB 400 – 600 dpi 200 dpi JPG
Photograph 24-bit RGB 600 dpi 200 dpi JPG
Book cover 24-bit RGB 150 dpi < 100 dpi JPG

Thumbnail may be created for the purpose of quick preview of original image. The thumbnail images would use 256 colour and 15-30 dpi resolution.

Multimedia Materials

Source Master image file format Derivative image file format
Format Bit rate Format
Audio MP3 128 kbps MP3
Motion Video MP4 800 kbps MP4

[1] Requirement of Master Image File

  • Format: TIFF image (uncompressed image)
  • Colour: 24-bit RGB colour
  • Resolution: 300 dpi
  • Version: Tiff, version 5.0

Remarks:

  • 1:1 optical resolution without re-sampling; cropping the original book scanned images; single-page tiff
  • High quality print reproduction
  • Archival purpose for long term retention
  • Source for derivatives image file creation

[2] Requirement of Derivative Image File

  • Format: JPEG, PDF file
  • Colour: 24-bit RGB colour
  • Resolution: 300 dpi

Remarks:

  • Directly converted from the master file
  • General access
  • Compressed file format to reduce file size for fast download
  • Acceptable image resolution to be displayed for general research
  • Incorporate Metadata e.g. OCR, if necessary;

Disclaimer
The contents of this page neither serve as tender requirement nor digital guidelines addressing all technical issues.  Should you need further information and guideline, please contact us at digitization@lib.cuhk.edu.hk.