DLF Standards. Imaging guides outline. File formats for digital masters

Imaging Guides

V. FILE FORMATS FOR DIGITAL MASTERS

The purpose of this guide is to identify how to contain and formally describe the reproduction qualities of digital masters as defined in another guide in this series. This guide focuses on the features of the containers - the file formats - that affect the performance of the digital master in various uses and that affect the ability of the custodian of the master to ensure that it persists over time as technology changes. Some parts of this discussion may identify technical requirements for product features that need, or may already be the subject of, further research and development, and so may not yet be commercially available in a suitable form.

Attributes associated with performance

Ability of file to open easily on any platform
Encoding byte order
File naming (including rules for extensions)

Scope (size of containers)

Pros and cons of various formats, given their capability to contain:

Detail (max. number of pixels)
Tone (max. number of bits per pixel)
Color (dynamic range of color space associated with format)
Effects of gamma setting
Scanner data (anything related to signal or transformations)
Administrative data (number of file headers)

Image processing (viability to create "deliverable images" from digital masters)

Formats natively optimized for the screen
Formats natively optimized for print
Telescoping ("Russian doll") formats such as FlashPix: pros and cons
Range of support by scanning software
Speed of transmission to and decompression at client
Open versus closed formats
Extent to which software allows reading from formats
Extent to which software allows writing to formats
Note range of support in scanning and image processing software: and whether software is either optimized for or restricted to certain platforms)

Attributes associated with persistence

Archival format for digital photography: myth or reality?
TIFF EP (ISO 12234-2 draft standard)
TIFF IT extensions relevant to preservation?
UPF
Implications of version (e.g., TIFF 6.0 vs. 5.0)

Standards

Criteria to judge "openness"
Who maintains standards
Opportunities for participation in standards development

Color representation

How to calibrate images for a long-term repository rather than to a specified device profile (whether "standard" or not)
Pros and cons of various formats [if not already covered in Scope above: sRGB, ISO RGB, NIF RGB, YCC, and other relevant options
Gamma setting in scanning [if not already covered in Scope above]

Compression

Risks and rewards of various choices (including no compression)
File sizes
Information loss
Speed of decompression
How to avoid proprietary traps

Storage

Choice of media (lifespan, relative risks)
National Media Lab reports (and other recommendations)
Accessibility to data (off-line versus near-line or on-line access)
Automatic error correction and detection viable for all formats?

Documentation

File headers
Essential self-describing characteristics of image to include in header
Advisability of embedding gray step/color patch values
Viability of automating this process
Pros and cons of embedding document names and/or page numbers
Viability of automating the process
Fitting documentation into the workflow
Populating headers during scanning, post-scanning, or both?
Pros and cons of creating documentation outside the file header
Risks of losing information in file headers
Controls that can be used to mitigate potential for loss during migration

References and other resources

This guide should identify:
Recommended means of assessing new formats in relation to performance and persistence
General background materials, such as standards, articles, journals, texts
Ready reference list, including working groups/papers, white papers, journals, listservs, FAQs

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