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 | 1-bit | Bi-tonal | 300 dpi | 150-300 dpi | |
| Newspaper | 24-bit | RGB | 300 dpi | 300 dpi | TIF, HOCR |
| Periodicals | 24-bit | RGB | 300 – 600 dpi | 300 dpi | |
| 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.
