Introduction

The type of data accompanying digitised materials determines how they can be searched, sorted and displayed. Museums are more capable of managing their collections when they use proper database management technologies and documentation in conjunction with digital imaging projects.

Metadata

The images produced in a digitisation project contain valuable data -or information - about the objects which have been photographed. Metadata may be defined as data about this data. It is important to distinguish three main types of metadata:

• data about the subject content of the image - which tells what the image is about and what interpretive significance it may have.
• data which categorises the image within a system of subject headings - which is needed to locate, retreive and handle the subject content
• data about the technical characteristics of the image - which is needed to determine computer equipment and software requirements for retreival, handling, storage and suitability for use in particular interpretive products.

Metadata includes all cataloguing or indexing information created to arrange, describe and otherwise enhace access to an information object. In other words, meta-data describes your digital images and gives them meaning, context and organisation. It also facilitates access to the content of the image and technical information about it.  

Descriptive metadata (content information) is information about the object captured in the image. If a computerised collections management system is in place, this information may be available, although recent studies have shown that many museum collections management systems still lack this type of information, which must be available if data sharing and public presentation are part of the project plan. CHIN's data dictionaries and other related documents on content standards are schemas that can help a museum determine what type of content meta-data it needs to record, and how to record it.

Describing the object

If you already have a computerised collections management system, you may already have textual information describing the object; digital images will add value to your system. In order to provide good information, you should be aware of structural standards and content standards. The former will define the fields you use to describe an object; these may be predefined by your collections management package. The content standards define or provide guidance for the information you will put in the fields. Data structure standards, such as the CHIN Data Dictionaries, provide guidelines to assist in determining what fields of information you should include in your collections management system. They also describe the format in which to enter the data. If you are creating an image database separate from your collections management system, you will want to ensure that this information is consistent. Generally speaking, you should consider displaying the following fields with your record. The following list, taken from CHIN's Data Dictionary for the humanities, includes the record fields you may wish to display with an image. Think of it as the text accompanying an object in your museum. No doubt you have standard fields of information on every object on display. Remember that people looking at your information online do not necessarily follow physical groupings as they are naturally set out in a museum. Even if your online information is grouped online by theme, artist, style or period, it can normally be viewed in any order a viewer may choose; therefore you must provide as much contextual information as possible.

• Object Name
• Object Type
• Title
• Artist/Maker or
• Manufacturer
• Materials
• Technique
• Dimensions (height, length, width, depth) HT/LE/WI/DP
• Subject
• Date: (CHIN Date of object from; Date of object to; production date; School/Style)
• Cultural Context
• Description
• Artist Birth Date
• Artist Death Date
• Institution
• Copyright Details
• Origin Country
• Origin Province

See further information on metadata and how it should be used to describe the image.

Image standards & guidelines

No published standards or guidelines exist for determining the level of image quality required to create digital images. Most of the existing studies conducted to determine optimum image resolution and image file formats indicate that the higher the image quality, the greater the longevity of the images. Choosing a common process and format when digitising a collection will greatly facilitate subsequent image processing. Only the master images should be used to create subsequent surrogate images.

The image capture process should produce digital images of the highest quality feasible in terms of resolution and colour depth. These are the master or archival images, and should be stored in an offline mode or kept accessible in read-only mode. Ordinarily these master images should be accessed infrequently, kept in the original format and used only to create surrogate images.

From master images and surrogate images, working copies can be produced for a variety of purposes. However it is important to remember that different applications require images of varying quality. Consequently if you require Digital images for visual references in an electronic database, such as the World Wide Web, they need only be low-resolution formats. So a copy of a surrogate image would suffice. Digital images used for high-quality printing, however, will require a substantially higher resolution image. To do this you may need to access the master image. However if this is a common request then you should consider producing surrogate images of a relatively high resolution and use these instead of continually accessing your masters.

To ascertain the quality required for digital imaging, it is first necessary to determine the intended uses for the images. The most common use for digital images is to make them available over the World Wide Web, via a collections management system, as low-quality, thumbnail images. Less common, but increasing in importance, is digital reproduction for printing or CDROMs. These larger or more detailed reproductions require images of higher quality. Specialty uses of images for conservation work, detailed analysis of works of art, etc. require substantially higher quality images.

See further information on preservation and storage standards and guidelines.

See more information in a sample image record in the Getting Started module.

Other institutions with useful metadata resources and advice on descriptive, structural and image standards include: CIMI, The Getty Standards Program, MDA, EdNA

Do you understand:

• What object information you should record and why?
• What image information you should record and why?
• What strategies you need to preserve your images?

Date published: 1 August 2001