UMDL requires two primary groups of information to mount a collection of images: original and/or retouched .tif or .jpg images, and corresponding metadata. The guidelines listed below are based on the requirements of the software we use to produce our repository, DLXS, a product of the University of Michigan.
In addition to these guidelines, you should also consult the Virtually Missouri Digitization Guidelines.
Images
The following are requirements and recommendations for image filenames.
Requirements
- Filenames must not begin with the letter "x" (upper or lower case).
- Images must have 3 character filename extensions. (e.g. .tif or .jpg)
Recommendations
- The fewest complications will be encountered if filenames conform strictly to the ISO 9660 filenaming standard for CD-ROM (i.e. 8 characters, plus a 3 character extention: example1.tif). Often filenames do not conform to the standard, and that is usually fine, though there are many characters that should be avoided when naming files e.g., "(", ")", "&", and "#".
- Image filenames should be unique within a collection.
- Image filenames should not have mixed case.
- Image filenames should not have spaces.
Image Format
DLXS allows display of growing thumbnail images such as JPEG2000 and sid images. UMDL uses JPEG2000 as the default displayed image. The conversion process requires that the original image be in grayscale, RGB, or CMYK modes.
Metadata
We prefer to use the Dublin Core Metadata Element Set, and, specifically, Virtually Missouri's recommended usage of that set, however, each metadata record we receive must minimally have fields of the following type:
- Image Caption(s) - Describes the specific view depicted in the image file. In many cases many or all of the fields of the record might be considered "caption" fields. It works best to consider only the fields that describe the view depicted in the image.
- Image Filename(s) - The image filename including (master) filename extension (.tif, .jpg).
- Identifier - Unique identification of the record within the collection.
File Format
The metadata file should be in a flattened, non-relational database structure (in a delimited text file, a MS Excel file, a Filemaker Pro file, or XML).
Complex Structured Image Collection
A simple image collection consists of a structure of one image per metadata record. Complex structures consist of multiple images per metadata record (such as front and verso images) which share the same metadata.
The metadata for a complex structured image collection differs slightly from a simple collection. Each metadata record requires two things:
- Field for the front image filename
- Field for the related image filenames, delimited (eg. pages of a book, maps grouped by location, multiple views of the same object)
The metadata record may also include:
- Field for a caption of the front image (the caption may be set to be any field in the record)
- Field for a unique caption for the related secondary images (such as back view, side view, top view, verso, etc)
Examples of structured image collections
Additional information on structured image collections http://dlxs.org/docs/11a/class/image/image-imagestructures.html
