Overview
ISO/IEC 15938-13:2015 - "Information technology - Multimedia content description interface - Part 13: Compact descriptors for visual search" (CDVS) is an international standard within the MPEG‑7 family that specifies a compact, interoperable image description tool for visual search. The standard defines the binary syntax, semantics, extraction and encoding processes for compact descriptors for visual search (CDVS) to enable robust visual content matching across images (objects, landmarks, printed documents) under changes in viewpoint, scale, occlusion and lighting.
Key topics and technical requirements
The standard is organized into clauses and normative/ informative annexes and specifies the following technical building blocks:
- Binary representation syntax and descriptor semantics (Clause 4) - the format and meaning of CDVS image descriptor components.
- Extraction and encoding process (Clause 5) - end‑to‑end procedure for producing an image descriptor from an input image, including required steps and options.
- Interest point detection - scale‑space construction, detection of scale‑space extrema, coordinate refinement to subpixel precision, duplicate elimination and orientation assignment.
- Local feature selection and description - selection probabilities, local region descriptors computed from cell histograms and local feature descriptor construction.
- Descriptor aggregation and compression - methods to aggregate local descriptors into a compact global descriptor, PCA projection, GMM parameters, quantization and compression strategies for both descriptors and location information.
- Encoding order and descriptor length targets - six average image descriptor lengths are specified: 512, 1024, 2048, 4096, 8192 and 16384 bytes.
- Normative annexes (A–J) - implementation parameters such as PCA matrices, GMM parameters, quantization thresholds and coding model probabilities.
- Informative decoding description (Annex K) - guidance on decoding CDVS image descriptors.
Practical applications
CDVS is designed for applications that require compact, standardised image representations for matching and retrieval, including:
- Mobile visual search and image-based product lookup
- Landmark recognition and location‑based services
- Large‑scale image retrieval and deduplication in cloud/search engines
- Augmented reality (AR) and visual navigation systems
- Document image matching and OCR preprocessing
- Video keyframe indexing and surveillance analytics
Who should use this standard
- Software and hardware implementers building interoperable visual search engines and libraries
- Developers of mobile apps, cloud image search, AR toolkits, and multimedia platforms
- Researchers and system integrators needing a standardized compact image descriptor format
- Standards bodies and product teams requiring conformance to MPEG‑7/CDVS conventions
Related standards
ISO/IEC 15938 (MPEG‑7) Parts 1–12 define broader MPEG‑7 description tools (Systems, Visual, Audio, Profiles, Query Format, etc.). ISO/IEC 15938‑13:2015 complements these by providing the compact visual descriptor specification for interoperable visual search.
Keywords: ISO/IEC 15938-13:2015, CDVS, compact descriptors for visual search, MPEG‑7, image descriptor, visual search, interest point detection, descriptor compression.