Overview
ISO/IEC 29170-2:2015 - "Information technology - Advanced image coding and evaluation - Part 2: Evaluation procedure for nearly lossless coding" standardizes a subjective test procedure to determine whether light (nearly lossless) image coding used in display streams is visually lossless. The procedure is display-technology independent and measures if observers can distinguish a reconstructed (coded) image from an uncompressed reference to a statistically meaningful level using forced-choice psychophysical tests.
Key Topics
- Test protocols: Two forced-choice methods are defined - a non-flickering paired comparison (Annex A) and a more sensitive interleaved-image forced-choice test (Annex B).
- Observer selection & screening: Observers are drawn from general population (experts and non-experts); recommended age range 18–30 years and not exceeding 40. Visual acuity and colour vision checks are required (Snellen 20/20 at 50 cm; Ishihara test). Corrective lenses with multiple focal lengths are disallowed.
- Media selection: Procedures for choosing representative image content appropriate to the target display and use-case are provided (Annex C).
- Viewing conditions: Requirements cover display calibration, lighting, viewing distance, viewing position and viewing time to ensure reproducible subjective testing.
- Test execution: Training sessions, trial structure, retries, block/session definitions, and minimum observer counts (at least 10 passing observers recommended) are specified.
- Evaluation metrics: The procedure uses an Acceptable Quality Level (AQL) and just-noticeable-difference concepts to quantify visually lossless performance.
- Reporting & verification: Test reporting templates and self-test certification guidance are included (Annex D, Annex F).
Applications and Who Uses It
ISO/IEC 29170-2:2015 is intended for:
- Display manufacturers (TV, monitor, mobile panels) validating visually lossless compression on display links.
- Codec and encoder developers working on low-latency, low-complexity compression for display streams.
- System integrators and SoC/graphics engineers evaluating trade-offs between compression, bandwidth, and power.
- Quality assurance and conformance labs performing subjective acceptance testing.
- Standards bodies and researchers comparing coding algorithms under controlled subjective conditions.
Practical uses include validating display stream compression for set-top boxes, mobile device display interfaces, GPU-to-panel links, and any application where compressed streams must be perceptually indistinguishable from originals.
Related Standards
- ISO 3664 (viewing conditions)
- ISO 20462-2 (image evaluation practices)
- ISO/IEC TR 29170-1 (background and guidelines)
Keywords: ISO/IEC 29170-2, visually lossless, nearly lossless coding, display stream compression, forced-choice test, subjective evaluation, AQL, observer screening.