NISO Metadata for Images in XML

NISO Metadata for Images in XML (MIX) is an XML schema for encoding the technical metadata needed to manage digital still image collections. Developed and maintained by the Library of Congress in partnership with NISO, MIX implements the data dictionary defined in ANSI/NISO Z39.87-2006, providing a standardized format for recording and exchanging the technical characteristics of digital images in preservation and access workflows.

Background

The need for standardized technical metadata for digital images emerged from the digital preservation community in the early 2000s. NISO's Technical Metadata for Digital Still Images Standards Committee developed the Z39.87 data dictionary, first published in 2006. The Library of Congress then created the MIX XML schema to provide a machine-actionable implementation of this data dictionary. MIX Version 1.0 corresponded to the original Z39.87 data dictionary, and MIX Version 2.0 — the current version — refines and extends the schema.

Purpose & Scope

MIX captures the technical characteristics of digital still images that are essential for long-term management and preservation. The schema covers several categories of information:

• Basic digital object information — file format, byte order, compression scheme, file size
• Basic image information — width, height, color space, bits per sample
• Image capture metadata — scanner or camera make and model, capture settings, orientation
• Image assessment metadata — spatial resolution, target data for quality benchmarking
• Change history — processing actions applied to the image, software used, dates of changes
• Color encoding — color profiles, primary chromaticities, white point

MIX is not intended to record descriptive or administrative metadata about the intellectual content of images. Its scope is limited to the technical properties required to render, validate, and preserve image files.

Serializations & Technical Formats

MIX is expressed as a W3C XML Schema (XSD). The current version 2.0 schema is available at https://www.loc.gov/standards/mix/mix.xsd. The MIX namespace is http://www.loc.gov/mix/v20. MIX records are commonly embedded as extension schemas within METS (Metadata Encoding and Transmission Standard) documents, particularly in the <techMD> section for technical metadata.

Governance & Maintenance

MIX is maintained by the Network Development and MARC Standards Office of the Library of Congress on behalf of NISO. Feedback and discussion occur through the MIX Listserv (MIX@LOC.GOV), which is open to subscribers. Changes to the schema are coordinated with the broader NISO standards process to ensure alignment with the Z39.87 data dictionary.

Notable Implementations

MIX is widely used in digital preservation systems, including:

• Library of Congress digital collections
• HathiTrust Digital Library preservation metadata
• JHOVE (JSTOR/Harvard Object Validation Environment), which can extract and validate MIX metadata from image files
• Institutional repository platforms that embed MIX within METS packages
• National and academic library digitization programs worldwide

Related Standards

• METS — Metadata Encoding and Transmission Standard; MIX is commonly embedded within METS packages as technical metadata
• PREMIS — Preservation Metadata: Implementation Strategies; complementary preservation metadata covering provenance, rights, and digital object relationships

Further Reading

• MIX Official Page (Library of Congress)
• ANSI/NISO Z39.87-2006 Data Dictionary
• MIX Schema 2.0 (XSD)
• JHOVE Validation Environment