Overview
ISO/IEC 18181-3:2025 - Information technology - JPEG XL image coding system - Part 3: Conformance testing specifies the conformance test methodology for the JPEG XL family (ISO/IEC 18181). This second-edition standard defines test case structure, precision tolerances, and pass/fail criteria for both core conformance (pixel-accuracy tests) and extended conformance (metadata and JPEG‑1 reconstruction). It provides electronic testcases and reference files to validate decoders and to guide encoder interoperability testing. Note: robustness and performance testing are explicitly out of scope.
Key topics and requirements
- Test case package: each test case includes a JSON descriptor (test.json), a JPEG XL codestream (input.jxl), a reference image (reference_image.npy) and an ICC profile (reference.icc). Extended tests may add reference_preview.npy, original.icc and reconstructed.jpeg.
- Reference image format: reference_image.npy uses 32-bit IEEE‑754 floats, little-endian, with shape (num_frames, height, width, num_channels). The ICC file indicates the color space (ISO 15076‑1).
- Image similarity metrics: conformance compares decoded samples to the reference in the ICC color space using peak error and root mean square (RMS) error thresholds per frame/channel. Core conformance allows clamping to [0,1]; extended conformance does not.
- Decoder conformance levels: decoders pass conformance for Main profile Level 5 or Level 10 by successfully decoding all test cases listed in the provided test lists (main_level5.txt, main_level10.txt) in the electronic attachments.
- Encoder conformance: an encoder is deemed conforming if it produces codestreams that are successfully decoded by a conforming decoder; the standard gives a practical test procedure (select images, encode, decode, and repeat across parameters).
- File and metadata checks: extended conformance verifies metadata fields (frame name, duration tolerance 0.0001 s, timecode) and JPEG‑1 bitstream reconstruction when applicable (jbrd box).
Applications and users
- Who uses it: codec implementers, library authors, software vendors, digital archivists, and test labs who need interoperability and pixel‑accuracy validation for JPEG XL decoders/encoders.
- Practical value: assures consistent rendering across implementations; supports archival workflows that require pixel‑faithful or metadata‑preserving recompression; helps QA teams automate conformance test suites using the provided testcases and NPY reference assets.
Related standards
Keywords: ISO/IEC 18181-3:2025, JPEG XL conformance testing, decoder conformance, encoder conformance, NPY reference, ICC profile, image similarity, peak error, RMS error.
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