UKOLN AHDS QA Toolkit: Raster Images


This one of the first components of the QA Toolkit. It is currently a beta version. We would welcome feedback before its release. Please send any comments to M.Guy AT

This self assessment QA sheet will eventually be part of the QA Focus Toolkit and is based on the Raster Images briefing paper. This module provides a checklist for development of good practices when choosing an image format.

What are Raster Images?

Raster images refer to digital graphics that accurately represent a photograph, cartoon or drawing. They are often described as bitmapped images. Common raster-based formats include JPEG, GIF and PNG.

1. Ownership of Standard
The standard is owned by an acknowledged open standards body (e.g. PNG)?
The standard is owned by a company (e.g QuickTime) (i.e. a proprietary standard)
2. Openness of Proprietary Format
If the standard is proprietary:
The format is covered by patents that limit its usage (e.g. GIF)
The format is open and is not covered by existing patents (e.g. PNG)
3. Which option best describes the format in use:
Popular as a result of its ubiquity on a single platform (e.g. BMP on MS Windows)?
Common on all platforms with a suitable web browser and editing tools.
4. Fitness for Purpose
When digitising photographs, cartoons, other images, is the format:
Ideal for the purpose envisaged?
Appropriate for the purpose envisaged?
Not particularly appropriate for the purpose envisaged?
5. When digitising photographs, does the format offer a sufficient bit-depth to realistically represent the image?
No (dithered or inaccurate colours)
6. Compression
What compression is used?
Lossless compression used?
Lossy compression used?
7. Storing backups for preservation purposes
The image has been saved as:
A high-quality preservation copy and a lower-quality distribution copy
A high-quality preservation copy that is also distributed on the Internet
A low-quality preservation copy that is also distributed on the Internet
8. Internet delivery
When creating thumbnail images for Internet pages, does the format create a recognisable image in:
0 - 5 kilobytes
6 - 10 kilobytes
10 - 15 kilobytes
16 - 20 kilobytes
21+ kilobytes
9. Migration
If it becomes necessary to migrate to an alternative format will it be:
Easy to migrate to alternative formats without loosing information (e.g. lossless format)?
Difficult to migrate to alternative formats without loosing information (e.g. lossy format such as JPEG)?
10. Conversion
When migrating image data from one format to another for the purpose of distribution, the following procedure has been used:
Conversion from 'lossy' format to 'lossless' format (e.g. JPG to GIF)
Conversion from 'lossless' preservation format to 'lossy' format (e.g. TIFF to JPG)

Note that QA Focus does not keep a record of the answers submitted.