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 8-bit Grayscale 300 dpi 150-300 dpi PDF, FLASH
24-bit RGB 300 dpi – 600 dpi
News clipping 1-bit Bi-tonal 300 dpi 150-300 dpi PDF
Manuscript 24-bit RGB 300 dpi 150-300 dpi PDF
Photograph 24-bit RGB 300 dpi < 100 dpi JPEG
Book cover 24-bit RGB 150 dpi < 100 dpi JPEG

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 AVI 64 kbps WMA
Motion video MPEG-1 for VCD
MPEG-2 for DVD
MPEG-4 for streaming video
800 kbps RM, WMV

[1] Requirement of Master Image File

  • 1:1 optical resolution without re-sampling;
  • Uncompressed or lossless compression file format;
  • Unedited;
  • High quality print reproduction;
  • Archival purpose for long term retention;
  • Source for derivatives image file creation;
  • TIFF file format;

[2] Requirement of Derivative Image File

  • General access;
  • Compressed file format to reduce file size for fast download;
  • Acceptable image resolution to be displayed for general research;
  • A variety of file format such as JPEG, PDF, FLASH;
  • Incorporate Metadata e.g. OCR, if necessary;

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